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<?xml version="1.0"?>

<!DOCTYPE TEI.2 SYSTEM "base.dtd">




<title>Mechanism of action of photoirradiated TiO2 in oxidising organic pollutants in water</title></titleStmt>

<publicationStmt><distributor>BASE and Oxford Text Archive</distributor>


<availability><p>The British Academic Spoken English (BASE) corpus was developed at the

Universities of Warwick and Reading, under the directorship of Hilary Nesi

(Centre for English Language Teacher Education, Warwick) and Paul Thompson

(Department of Applied Linguistics, Reading), with funding from BALEAP,

EURALEX, the British Academy and the Arts and Humanities Research Board. The

original recordings are held at the Universities of Warwick and Reading, and

at the Oxford Text Archive and may be consulted by bona fide researchers

upon written application to any of the holding bodies.

The BASE corpus is freely available to researchers who agree to the

following conditions:</p>

<p>1. The recordings and transcriptions should not be modified in any


<p>2. The recordings and transcriptions should be used for research purposes

only; they should not be reproduced in teaching materials</p>

<p>3. The recordings and transcriptions should not be reproduced in full for

a wider audience/readership, although researchers are free to quote short

passages of text (up to 200 running words from any given speech event)</p>

<p>4. The corpus developers should be informed of all presentations or

publications arising from analysis of the corpus</p><p>

Researchers should acknowledge their use of the corpus using the following

form of words:

The recordings and transcriptions used in this study come from the British

Academic Spoken English (BASE) corpus, which was developed at the

Universities of Warwick and Reading under the directorship of Hilary Nesi

(Warwick) and Paul Thompson (Reading). Corpus development was assisted by

funding from the Universities of Warwick and Reading, BALEAP, EURALEX, the

British Academy and the Arts and Humanities Research Board. </p></availability>




<recording dur="00:53:40" n="8966">


<respStmt><name>BASE team</name>



<langUsage><language id="en">English</language>



<person id="nm0693" role="main speaker" n="n" sex="m"><p>nm0693, main speaker, non-student, male</p></person>

<person id="sm0694" role="participant" n="s" sex="m"><p>sm0694, participant, student, male</p></person>

<person id="sf0695" role="participant" n="s" sex="f"><p>sf0695, participant, student, female</p></person>

<personGrp id="ss" role="audience" size="s"><p>ss, audience, small group </p></personGrp>

<personGrp id="sl" role="all" size="s"><p>sl, all, small group</p></personGrp>

<personGrp role="speakers" size="5"><p>number of speakers: 5</p></personGrp>





<item n="speechevent">Lecture</item>

<item n="acaddept">Chemistry</item>

<item n="acaddiv">ps</item>

<item n="partlevel">UG3</item>

<item n="module">"UV Spectroscopy, Photochem and Rad Chem"</item>




<u who="nm0693"> i guess in the last three lectures what we've been looking at has been has been the generality <pause dur="0.2"/> of photochemical processes <pause dur="0.5"/> and today <pause dur="0.6"/> i want to continue with the notion of <pause dur="0.2"/> specific problems and looking <pause dur="0.3"/> looking at them in some depth as illustrating <pause dur="0.4"/> # the sorts of things that # <pause dur="0.2"/> you can do with photochemistry <pause dur="0.4"/> now last week we were looking at the splitting of water <pause dur="0.6"/> with <pause dur="0.5"/> sunlight <pause dur="0.5"/> and we recognized that water <pause dur="0.4"/> doesn't draw <pause dur="0.5"/> sunlight at all <pause dur="0.4"/> but if you put it in with the right catalyst <pause dur="0.5"/> and the catalyst we <pause dur="0.6"/> talked about very much was this ruthenium catalyst <pause dur="0.4"/> then <pause dur="0.2"/> provided you had a cocatalyst there as well <pause dur="0.6"/> then you had the <pause dur="0.2"/> possibility of the ruthenium complex <pause dur="0.3"/> splitting the water <pause dur="0.3"/> into hydrogen and oxygen <pause dur="0.5"/> and this could be done <pause dur="0.5"/> but there were drawbacks and that the drawbacks you remember were that # particularly <pause dur="0.5"/> # the catalyst didn't go on for ever <pause dur="0.6"/> the yields were rather low <pause dur="0.3"/> and you had to have a sacrificial donor in the system <pause dur="0.3"/> now if you were going to do that <pause dur="0.3"/> well you might

as well say we'll go to biomass <pause dur="0.4"/> but it looks as though photoelectrochemistry <pause dur="0.3"/> where you actually generated an electric current from such a system <pause dur="0.4"/> was a much better bet and work is still going on with that <pause dur="0.6"/> now what i'd like to talk about today is something <pause dur="0.3"/> # <pause dur="0.6"/><kinesic desc="puts on transparency" iterated="n"/> which is <pause dur="0.2"/> related but different <pause dur="0.4"/> and that is the <pause dur="0.3"/> use of irradiated # <pause dur="0.2"/> catalyst that absorbs the U-V components of sunlight <pause dur="0.5"/> to destroy organic pollutants <pause dur="0.6"/> and # that will be the subject of today <pause dur="2.2"/><kinesic desc="changes transparency" iterated="y" dur="16"/> and the <trunc>f</trunc> the first <pause dur="0.3"/> question is <pause dur="0.5"/> # why should one <pause dur="0.4"/> # choose titanium dioxide <pause dur="0.2"/> as a <pause dur="0.4"/> a a thing to do this <pause dur="0.6"/> # <pause dur="0.3"/> there are various other things that one could have maybe thought about <pause dur="0.5"/> but # i'll <pause dur="0.4"/> put down <pause dur="0.3"/> # <pause dur="0.3"/> almost a kind of summary of the lecture <pause dur="0.3"/> # before i <trunc>begi</trunc> <pause dur="0.2"/> # before i've given it <pause dur="0.3"/> and that is that # <pause dur="1.4"/> it's <pause dur="0.3"/> very cheap and it's readily available <pause dur="0.5"/> T-I-O-two as i said before is used as a # the whitener <pause dur="0.3"/> in <pause dur="0.3"/> emulsion paints <pause dur="0.5"/> # for getting a white finish <pause dur="0.3"/> on any gloss paints as well <pause dur="0.4"/> it's also environmentally harmless there's # <pause dur="0.3"/> there's

sacks of titanium <pause dur="0.3"/> all around the world <pause dur="0.4"/> and nobody suffers from it <pause dur="0.8"/> we know <trunc>f</trunc> # that it's got a very good <pause dur="0.4"/> turnover number <pause dur="0.2"/> in other words you can irradiate it again and again and again and again and again and <pause dur="0.4"/> it will still function <pause dur="1.2"/> # it turns out to be efficient for a wide range of pollutants and i'll illustrate that in the lecture <pause dur="1.0"/> # <pause dur="0.2"/> another advantage is you can attach it to supports rather readily <pause dur="0.3"/> in other words <pause dur="0.4"/> # if you take T-I-O-two which is a # a white <pause dur="0.3"/> powder a bit like talcum powder <pause dur="0.3"/> and you stood it up in water <pause dur="0.4"/> or even sonicate it with <trunc>s</trunc> with a <trunc>s</trunc> with a sonicator you know sound wave emitter <pause dur="0.4"/> # <pause dur="0.4"/> you get a suspension <pause dur="0.6"/> if you lay the suspension onto glass and allow it to evaporate <pause dur="1.0"/> the T-I-O-two powder sticks to the glass <pause dur="0.6"/> really very fiercely and it's really quite hard to get off <pause dur="0.4"/> particularly if after you've layered it you you heat it <pause dur="0.5"/> maybe to # <pause dur="0.3"/> a hundred degrees or so for a <pause dur="0.6"/> twenty-four hours <pause dur="0.3"/> it becomes even more firmly attached to glass <pause dur="0.4"/> and it means that # you've got a stable <pause dur="0.2"/> thin

layer <pause dur="0.5"/> # which will be <trunc>c</trunc> <pause dur="0.2"/> really quite a useful advantage <pause dur="1.0"/> you might have <trunc>p</trunc> <pause dur="0.4"/> predicted at the outset from what we said last week from the # <pause dur="1.2"/> the other lecture <pause dur="0.2"/> where we talked about T-I-O-two <pause dur="0.2"/> it's got rather a large band gap <pause dur="0.8"/> # <pause dur="0.2"/> under solar irradiation there isn't a lot of U-V <pause dur="0.5"/> but <pause dur="0.3"/> there is some <pause dur="0.5"/> so that there's a reasonable chance that you'll get something out of it <pause dur="0.2"/> but clearly <pause dur="0.2"/> if you could activate it <pause dur="0.4"/> by # <pause dur="0.5"/> putting in maybe a <trunc>t</trunc> an inorganic ion strip in the lattice to move the action spectrum towards the visible <pause dur="0.4"/> then you could probably <pause dur="0.4"/> increase its # <pause dur="0.3"/> its efficiency <pause dur="0.5"/> # as i've as i've <kinesic desc="indicates point on transparency" iterated="n"/> indicated there <pause dur="0.4"/> so <pause dur="0.3"/> those are the # <pause dur="0.3"/> those are the main features and i shall spend quite a bit of time <pause dur="0.3"/> # <pause dur="0.2"/> underlining those notes # throughout the lecture <pause dur="0.8"/> okay have you have you <pause dur="0.3"/> got have you got all that </u><pause dur="0.5"/> <u who="sm0694" trans="pause"> not yet </u><pause dur="0.3"/> <u who="nm0693" trans="pause"> not yet okay i'll <trunc>hol</trunc> i'll hold for on a sec <pause dur="0.5"/> while you # <pause dur="0.3"/> try and get it down </u><gap reason="break in recording" extent="uncertain"/> <u who="nm0693" trans="pause"> right <pause dur="0.6"/> what i'd like to do next is <trunc>t</trunc> for us to sort of think about what a T-I-O-two particle <kinesic desc="changes transparency" iterated="y" dur="3"/> titanium dioxide particle is like <pause dur="0.5"/> and we have

here <pause dur="0.4"/> a <pause dur="0.3"/> very <pause dur="0.2"/> # <pause dur="0.2"/> schematic view of what it's like <pause dur="0.5"/> so it's irregular <pause dur="0.2"/> it's roughly roughly kind of spherical <pause dur="0.6"/> and <pause dur="0.5"/> essentially <pause dur="0.4"/> the two points to <pause dur="0.6"/> note <pause dur="0.4"/> are these <pause dur="0.5"/> you've got within the crystal <kinesic desc="indicates point on transparency" iterated="n"/> because it's a semiconductor <pause dur="0.5"/> you've got a valence band and a conduction band <pause dur="0.5"/> got these two energy levels <pause dur="0.7"/><kinesic desc="indicates point on transparency" iterated="n"/> but they're really bands where i've just drawn them as lines for the to simplify things <pause dur="0.7"/> and when you <pause dur="0.4"/> optically pump the thing by shining light on it <pause dur="0.3"/> you push an electron <pause dur="0.3"/> out of the valence band <pause dur="0.3"/> into the conduction band just as <pause dur="0.2"/> just as i talked about last week <pause dur="0.8"/> and <pause dur="0.4"/> the <pause dur="0.4"/> a <trunc>l</trunc> hole <pause dur="0.6"/><kinesic desc="indicates point on transparency" iterated="n"/> here this H-plus <pause dur="0.6"/> or the absent electron <pause dur="0.5"/> this will migrate from within the crystal to the surface <pause dur="0.3"/> so you've got to imagine this in three dimensions of course <pause dur="0.3"/> # so you can imagine to get to the surface <pause dur="0.2"/> and you've got <kinesic desc="indicates point on transparency" iterated="n"/> holes dotted around the surface as i've indicated there <pause dur="0.6"/> the electrons <pause dur="0.3"/> also <pause dur="0.4"/> migrate to the surface <pause dur="1.2"/> they also of course stand a good chance of # recombining <pause dur="0.6"/> and if you didn't have <pause dur="0.2"/> anything else in the system <pause dur="0.4"/> they would recombine <pause dur="0.3"/> and

<trunc>nothi</trunc> not very much would happen <pause dur="0.6"/> but # <pause dur="0.4"/> what happens is that you're able to fix the charge separation <pause dur="0.5"/> because <pause dur="0.2"/> essentially it's in water <pause dur="0.9"/> and the water <pause dur="0.5"/> is being purged with oxygen <pause dur="0.4"/> or <pause dur="0.8"/> even less extreme if you've got some air in in the water and we would normally have some air there <pause dur="0.3"/> and certainly if you were talking about <pause dur="0.3"/> # <pause dur="0.5"/> river water lake water something like that <pause dur="0.5"/> # <pause dur="0.3"/> then <pause dur="0.5"/> there will be there would be oxygen present from the air <pause dur="0.2"/> at about you know twenty twenty per cent of the # <pause dur="0.3"/> dissolved gases would would be oxygen <pause dur="0.4"/> so the oxygen <pause dur="1.1"/> in the solution <pause dur="0.5"/> will migrate around of course it will collide with the particles <pause dur="0.4"/> and it will trap the electron <pause dur="1.2"/> and make it O-two-minus the so-called superoxide ion <pause dur="0.9"/> and if it's trapped as this <pause dur="0.4"/> then the electron is no longer mobile because it's become O-two-minus <pause dur="1.1"/> the other thing that happens <pause dur="0.4"/> is that the H-plus <pause dur="0.9"/> is a very powerful oxidizing agent <pause dur="1.6"/> and it will oxidize water <pause dur="0.8"/> to <pause dur="0.9"/> O-H radicals <pause dur="0.4"/> so <pause dur="0.4"/> quite quickly <kinesic desc="indicates point on transparency" iterated="n"/> all of these H-pluses <pause dur="0.8"/> will <pause dur="0.3"/> react with the water <pause dur="0.7"/> on the

surface of the particle <pause dur="0.4"/> and they will be converted to O-H <pause dur="0.8"/> so you've got O-H which is an oxidizing agent upon the surface <pause dur="0.6"/> and you've got O-two-minus <pause dur="1.0"/> which is <pause dur="0.5"/> also <pause dur="0.5"/> an oxidizing agent it's not as powerful as O-H but it's still <pause dur="0.8"/> certainly not a reducing agent <pause dur="0.7"/> # <pause dur="1.0"/> the other thing that can happen <pause dur="0.4"/> is that the O-H <pause dur="0.3"/> is absorbed going to move that into a solution <pause dur="0.2"/> so you've got the absorbed O-H becoming a solution O-H <pause dur="0.5"/> the O-two-minus is absorbed and with that become <pause dur="0.5"/> an O-two-minus in solution <pause dur="0.6"/> so all <pause dur="0.3"/> of the <pause dur="0.5"/> species produced by further excitation end up <pause dur="0.4"/> either by being oxidizing agents absorbed on the surface <pause dur="0.4"/> or they become oxidizing agents out in solution <pause dur="0.6"/> and this is the <pause dur="0.2"/> this is the basis of the <pause dur="0.2"/> the photoreactivity <pause dur="0.4"/> <trunc>o</trunc> of T-I-O-two <pause dur="0.4"/> you're generating all these oxidizing species <pause dur="1.6"/> now before <pause dur="0.3"/> going any further into T-I-O-two and # <pause dur="0.7"/> # its various merits <pause dur="0.3"/> i will # <pause dur="0.3"/> briefly <pause dur="0.5"/> # cast an eye over one or two competitor type systems that you might have thought about <pause dur="0.7"/> and these have all been tried <pause dur="0.5"/> # as

you can imagine <pause dur="0.7"/> # this is quite a complicated # transparency you may not be able to <pause dur="0.2"/> draw all of this but i'll just <pause dur="0.4"/> highlight <pause dur="0.2"/> what's important <pause dur="0.7"/><kinesic desc="changes transparency" iterated="y" dur="3"/> so <pause dur="0.3"/> what have i got down here <pause dur="0.8"/> well this is quite a <pause dur="0.3"/> a complex picture <pause dur="0.5"/> # <pause dur="0.3"/> the point here is that # <pause dur="0.4"/> you can look at a whole series of other semiconductors <pause dur="0.4"/> and all of the all of these that are quite well known <pause dur="0.4"/> because they've all been used <pause dur="0.4"/> # in photoelectrochemical cells so the technology has already been explored <pause dur="0.3"/> for these things <pause dur="0.6"/> and what i've got here <pause dur="0.2"/> are the band gaps <pause dur="0.6"/> the band gaps <pause dur="0.3"/> # <pause dur="1.2"/> the distance between the <pause dur="0.3"/> valence band and the conduction band <pause dur="0.5"/> the T-I-O-two <pause dur="0.3"/> is about three-point-two electron volts <pause dur="0.5"/> as you go to some of <kinesic desc="indicates point on transparency" iterated="n"/> these ones then it's getting less one-point-seven one-point-four <pause dur="0.3"/> # <pause dur="0.2"/> two-point-four <pause dur="0.2"/><kinesic desc="indicates point on transparency" iterated="n"/> these are coloured of course because the band gap is now in the visible <pause dur="0.3"/> and these things are either orange or yellow <pause dur="0.3"/> # or whatever <pause dur="0.6"/> # zinc sulphide white 'cause you've got really really quite a big band gap there <pause dur="0.3"/> and strontium titanate is very similar to this <pause dur="0.4"/> W-O-three <pause dur="0.2"/> is probably just about on the

edge of the <trunc>o</trunc> of the on the edge of the visible so it will have a faint maybe a probably a <pause dur="0.3"/> a a a a slight colour <pause dur="0.8"/> you know slightly coloured yellow <pause dur="0.6"/> # <pause dur="0.6"/> the point is that # <pause dur="0.3"/> the the band gaps for these are very attractive <pause dur="0.4"/><kinesic desc="indicates point on transparency" iterated="n"/> but unfortunately <pause dur="0.6"/> # <pause dur="0.4"/> the <pause dur="0.7"/> flip side of having a narrow band gap which would be very sensitive to visible light which is a good thing <pause dur="0.4"/> is that you don't actually get enough <pause dur="0.3"/> in the way of potential <pause dur="0.2"/> to <pause dur="0.3"/> # <pause dur="0.4"/> oxidize the water through to O-H <pause dur="0.3"/> you've got if you want to get O-H radicals <pause dur="0.2"/> you've got to get past this <unclear>well</unclear> this potential <kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="0.2"/> as we run across the bottom <pause dur="0.6"/> so in a sense <pause dur="0.3"/> # <pause dur="0.4"/> there's a whole all all <kinesic desc="indicates point on transparency" iterated="n"/> of these ones are going to fail <kinesic desc="indicates point on transparency" iterated="n"/> this might just just about creep in <pause dur="0.6"/> # <pause dur="0.4"/> but <pause dur="0.2"/> the ones that are going to win on energy are those <kinesic desc="indicates point on transparency" iterated="n"/> those three there <pause dur="0.5"/> # <pause dur="0.3"/> these <pause dur="0.3"/><kinesic desc="indicates point on transparency" iterated="n"/> which might have seemed attractive <pause dur="0.7"/> simply don't win on potential <pause dur="0.2"/> you've got to get the oxidizing potential <pause dur="1.3"/> to get the oxidation to O-H <pause dur="0.5"/> but you've <pause dur="0.3"/> also got to try and match the band gap as best you can to what's <pause dur="0.3"/> in <pause dur="0.2"/> sunlight if you're going to use

sunlight <pause dur="0.6"/> now if you decide you're not going to use sunlight at all <pause dur="0.3"/> but you're going to use fluorescent tubes <pause dur="0.3"/> you stand a much better chance because <kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="0.3"/> you can make tubes emitting U-V <pause dur="0.3"/> with a a a a high level of efficiency <pause dur="0.4"/> so <pause dur="0.5"/> the way <pause dur="0.2"/> thinking has gone is to move away from <pause dur="0.6"/> # using sunlight <pause dur="0.7"/> # <pause dur="0.5"/> not completely away by the way but <pause dur="0.4"/> more towards using <trunc>U</trunc> <trunc>U</trunc> U-V tubes <pause dur="0.3"/> so the idea would be if you had <pause dur="0.4"/> # <pause dur="0.2"/> a <pause dur="0.3"/> a factory <pause dur="0.5"/> emitting some polluted water say polluted with low levels of <pause dur="0.5"/> really <pause dur="0.2"/> poisonous materials <pause dur="0.4"/> but <pause dur="0.5"/> down at say a micromolar <pause dur="0.5"/> if you passed that <pause dur="0.6"/> effluent past a bank of U-V tubes all switched on <pause dur="1.2"/> and <pause dur="0.4"/> if you had the T-I-O-two present in the system in some form <pause dur="0.6"/> it wouldn't be a suspension obviously 'cause it would be washed away <pause dur="0.2"/> but if you can immobilize the T-I-O-two <pause dur="0.5"/> on <pause dur="0.3"/> sheets <pause dur="0.4"/> or rods or fibres <pause dur="0.4"/> then you would destroy <pause dur="0.5"/> the <pause dur="0.2"/><kinesic desc="indicates point on transparency" iterated="n"/> polluting organic <pause dur="0.5"/> and you stand a reasonable chance of cleaning up <pause dur="0.4"/> because <pause dur="0.5"/> i can <trunc>s</trunc> <pause dur="0.2"/> i can tell you sort of in anticipation <pause dur="0.4"/> <kinesic desc="indicates point on transparency" iterated="n"/> this is a remarkably

efficient system it works really quite well <pause dur="0.3"/> and much better than you'd ever believe <pause dur="0.2"/> from the outset <pause dur="0.5"/> okay <pause dur="0.2"/> so <pause dur="0.4"/> the the <trunc>messa</trunc> the message from that slide really is that # <pause dur="0.2"/> you got to get <kinesic desc="indicates point on transparency" iterated="n"/> past this point here to get O-H radicals <pause dur="0.4"/> and <kinesic desc="indicates point on transparency" iterated="n"/> those three work quite well <kinesic desc="indicates point on transparency" iterated="n"/> this is another possibility <pause dur="0.3"/> and <kinesic desc="indicates point on transparency" iterated="n"/> those don't really <trunc>s</trunc> <pause dur="0.2"/> you know stand much of a chance <pause dur="0.8"/> okay <pause dur="1.1"/> right so i'll take that off now hoping that you've got the the the basic message <kinesic desc="changes transparency" iterated="y" dur="14"/> without copying everything down furiously <pause dur="0.5"/> # <pause dur="0.4"/> what i'd like to do next is # <pause dur="0.3"/> perhaps show you <pause dur="0.3"/> how some of these # <pause dur="0.2"/> semiconductors compare with each other <pause dur="0.3"/> so you can just see <pause dur="0.3"/> <trunc>whi</trunc> you know which really are the good ones and and the not so good ones <pause dur="0.4"/> and what i've got here <pause dur="0.6"/> is a slide <pause dur="0.6"/> and this is where we're looking at # <pause dur="0.6"/> pentachlorophenol <pause dur="1.1"/> now this is <pause dur="0.4"/> all the chlorophenols are quite good things to look at because <pause dur="0.4"/> many <pause dur="0.5"/> of the <pause dur="0.4"/> pollutants that # <pause dur="0.9"/> # <trunc>eman</trunc> emanate from <pause dur="0.2"/> # <pause dur="0.6"/> waste sites and dumps and the like <pause dur="0.7"/> they've been partly converted by bacteria <pause dur="0.4"/> from

something like <pause dur="0.4"/> # polychlorobiphenyls <pause dur="1.1"/> into chlorophenols <pause dur="0.7"/> and so the chlorophenols tend to be the water soluble form which gets leached into the aquifers or the <pause dur="0.4"/> water table <pause dur="0.2"/> and get into rivers <pause dur="0.5"/> so <pause dur="0.4"/> the chlorophenols have been looked at very closely <pause dur="0.4"/> because they are really ideal model compounds to work with <pause dur="0.4"/> and here we've got pentachlorophenol <pause dur="0.6"/> # <pause dur="0.6"/> and it's a concentration of about <pause dur="0.2"/> i suppose <pause dur="0.5"/> four <pause dur="0.2"/> times ten-to-the-minus-five mole per litre <pause dur="0.4"/> this has been irradiated various <pause dur="0.4"/> semiconductors <pause dur="0.3"/> are present <pause dur="0.4"/> and you can see <pause dur="0.2"/> T-I-O-two is here <pause dur="0.5"/><kinesic desc="indicates point on transparency" iterated="n"/> Z-N-O <kinesic desc="indicates point on transparency" iterated="n"/> is there <pause dur="0.5"/><kinesic desc="indicates point on transparency" iterated="n"/> this is cadmium sulphide <pause dur="0.4"/> and then up here <kinesic desc="indicates point on transparency" iterated="n"/> you've got W-O-three <pause dur="0.4"/> and tin oxide <pause dur="0.3"/> and you can see that by far the best two <pause dur="0.4"/> are the T-I-O-two and the Z-N-O <pause dur="0.5"/> which the previous slide <pause dur="0.3"/> would have would have led you to believe <pause dur="0.3"/> so the previous slide was a kind of theoretical prediction if you like the rationalization <pause dur="0.4"/> this is the experimental result <pause dur="0.4"/> # i suppose the thing is that # <pause dur="0.5"/> # C-D-S is rather better than we might have thought it was <pause dur="0.3"/> but it's still nothing like as good <pause dur="0.3"/> as T-I-O-two <pause dur="0.2"/>

or zinc oxide <pause dur="0.7"/> so # <pause dur="0.2"/> that's # <pause dur="0.3"/> a a a <trunc>n</trunc> a nice sort of comparator experiment <pause dur="0.3"/> on pentachlorophenol <pause dur="1.9"/><kinesic desc="changes transparency" iterated="y" dur="25"/> the next question is i suppose what actually happens <pause dur="0.4"/> when <pause dur="0.3"/> the # <pause dur="0.5"/> the light falls on the <pause dur="0.3"/> particle what are the subsequent reactions <pause dur="0.3"/> after <pause dur="0.3"/> what i've described so i'll # <pause dur="1.6"/> i'll show you <pause dur="0.2"/> # that as on on the next slide this is quite a complicated one <pause dur="0.4"/> and i'll follow it up with one or two rather easier ones <pause dur="0.4"/> so here we go <pause dur="0.7"/> # <pause dur="0.2"/> and i'll take you through it <pause dur="0.4"/> fairly slowly <pause dur="1.0"/> okay <pause dur="0.5"/> can you actually read <kinesic desc="indicates transparency" iterated="n"/> read those on there <pause dur="0.4"/> yeah i'll i'll call them out anyway <pause dur="0.3"/> so we start off on with T-I-O-two with light <pause dur="0.3"/> we get the whole <pause dur="0.2"/> we get the electron <pause dur="0.5"/> so i said before the electron picks up O-two <pause dur="0.3"/> to give O-two-minus <pause dur="0.5"/> # <pause dur="0.3"/> it's not very well <pause dur="0.5"/> done as a as a minus but it ought to be a minus dot really 'cause it's a free radical <pause dur="0.5"/><kinesic desc="indicates point on transparency" iterated="n"/> this is a O-two-minus-dot <pause dur="0.3"/> an O-two-minus-dot can go on <pause dur="0.4"/> # it can react two of these react together to give you <kinesic desc="indicates point on transparency" iterated="n"/> these <pause dur="0.2"/> it gives you H-O-two <pause dur="0.6"/> you've got it can react with protons and it's

slightly acidic to give you H-O-two radicals <pause dur="0.4"/> and H-O-two itself <pause dur="0.3"/> is is # <pause dur="0.3"/> a weak oxidant it can attack organics <pause dur="0.4"/> in the absence of the organics <pause dur="0.2"/> # <pause dur="0.2"/> the thing will go on it will form oxygen and hydrogen peroxide <pause dur="0.5"/> # <pause dur="0.2"/> it can pick up electrons <pause dur="0.2"/> to give this <pause dur="0.3"/><kinesic desc="indicates point on transparency" iterated="n"/> <gap reason="inaudible" extent="1 sec"/> that's E-minus of the proton is equivalent of H atom <pause dur="0.6"/> and H atom will react with H-O-two to give you H-two-O-two <pause dur="0.5"/> and then <pause dur="0.2"/> further electrons will give you <pause dur="0.2"/> O-H radicals <pause dur="0.5"/> and then you've got further reactions here <kinesic desc="indicates point on transparency" iterated="n"/> so you end up by making some more O-H radicals <pause dur="0.5"/> if the thing is not intercepted <pause dur="0.4"/> by an organic <pause dur="0.6"/> so that's the # <pause dur="0.6"/> that's what's happening to the electron it's being converted ultimately <pause dur="0.3"/> in a number of steps <pause dur="0.2"/> through to <pause dur="0.2"/> hydroxyl radicals <pause dur="0.3"/> # <pause dur="0.8"/> unless the thing gets picked up beforehand <pause dur="1.0"/> this side <pause dur="0.2"/><kinesic desc="indicates point on transparency" iterated="n"/> you've got H-plus <pause dur="0.7"/> and the H-plus surface gets on to the surface <pause dur="0.3"/> it <trunc>ma</trunc> it <gap reason="inaudible" extent="1 sec"/> the contribution system gets to the surface <pause dur="0.5"/> oxidizes the water to O-H radicals <pause dur="0.4"/> the O-H radical sticks <pause dur="0.3"/> # on the surface <pause dur="0.2"/> near to a titanium <pause dur="0.6"/> # what's going to happen then <pause dur="0.4"/> well basically if you've got

# in the system <pause dur="0.5"/> # <pause dur="1.4"/> an organic which we can denote R <pause dur="0.4"/> or a <trunc>f</trunc> organic radical <pause dur="0.7"/> or just set it on carbon or another organic radical which is basically a <pause dur="0.3"/> a semi-oxidized alcohol <pause dur="0.6"/> # all of these things <pause dur="0.3"/> react with # <kinesic desc="indicates point on transparency" iterated="n"/> all of those things which have come from <kinesic desc="indicates point on transparency" iterated="n"/> here you see all most of these will spill down over into <kinesic desc="indicates point on transparency" iterated="n"/> there now <pause dur="0.3"/> and you get oxidized species <pause dur="0.9"/> so ultimately <pause dur="0.5"/> after many many steps <pause dur="0.4"/> and if you think about it if you've got something like pentachloro<pause dur="0.3"/>phenol or even a thing like say phenol itself <pause dur="0.4"/> to get phenol through to carbon dioxide <pause dur="0.5"/> you've got many many electrons needed you need to take many electrons out of phenol <pause dur="0.5"/> to get it <pause dur="0.4"/> to a point <pause dur="0.3"/> where the phenol molecule <pause dur="0.4"/> is often being converted right through to C-O-two <pause dur="0.6"/> the process of converting these organics <pause dur="0.2"/> right through <pause dur="0.3"/> to either C-O-two <pause dur="0.5"/> or <pause dur="0.3"/> if you've got a chloryl organic to chloride anion <pause dur="0.3"/> which is harmless <pause dur="0.5"/> # both of these are <trunc>p</trunc> are pretty harmless <pause dur="0.4"/> # compared with the start material <pause dur="0.5"/> then it's called mineralization <pause dur="0.4"/> because <pause dur="0.3"/> carbonic

acid and H-shell are mineral acids <pause dur="0.3"/> so the whole process is called mineralization <pause dur="0.4"/> or if you like <pause dur="0.3"/> photomineralization <pause dur="0.7"/> so this this is a <trunc>f</trunc> a a <trunc>f</trunc> <pause dur="0.4"/> a fairly fairly complete mechanism <pause dur="0.6"/> # <pause dur="0.2"/> it's told you what's happening to all these oxygen radicals <pause dur="0.3"/> it hasn't said very much of what what's happening <pause dur="0.4"/> # <kinesic desc="indicates point on transparency" iterated="n"/> <gap reason="inaudible" extent="1 sec"/> department there <pause dur="0.2"/> all you can <pause dur="0.3"/> # # <pause dur="0.2"/> all this says at the moment is that these <trunc>c</trunc> these carbon centres <pause dur="0.4"/> are either organic <pause dur="0.5"/> # <pause dur="0.3"/> or an organic radical <pause dur="0.3"/> or a hydroxylated organic radical <pause dur="0.2"/> all of these <kinesic desc="indicates point on transparency" iterated="n"/> three will all of these will get oxidized <pause dur="0.4"/> in in the process <pause dur="0.4"/> so that's a <trunc>k</trunc> a kind of total scheme <pause dur="0.8"/> so it's an elaboration of my particle picture <pause dur="0.2"/> i've now got a lot more reactions there <pause dur="1.4"/> okay <pause dur="1.0"/> have you have you got that <pause dur="2.0"/> well <pause dur="0.8"/> now just in slightly more detail <pause dur="0.4"/> # i want to try and explain <pause dur="0.7"/> the kind of <pause dur="0.4"/> reactions that go on <pause dur="0.6"/> when any organic system is being oxidized <pause dur="0.3"/> so <trunc>thi</trunc> <trunc>thi</trunc> what i've got next is not just peculiar to this system <pause dur="0.5"/> this is <pause dur="0.2"/> a generality <pause dur="0.4"/> for the oxidization of all <kinesic desc="changes transparency" iterated="y" dur="7"/> organics <pause dur="0.3"/> including polymers as it happens <pause dur="0.6"/> so <pause dur="0.4"/>

here we go <pause dur="1.6"/> well the one i've got <pause dur="0.2"/> i've put it down # <pause dur="0.2"/> it's actually for the <pause dur="0.4"/> oxidation using hydrogen peroxide <pause dur="0.5"/> # you can use that instead of T-I-O-two <pause dur="0.5"/> # <pause dur="0.5"/> but it's not as good because you use it up <pause dur="0.8"/> but the chemistry is exactly the same <pause dur="0.7"/> if you irradiate hydrogen peroxide with pentachlorophenol you destroy it <pause dur="0.7"/> # <pause dur="0.9"/> but of course you destroy the H-two-O-two as well <pause dur="0.3"/> the T-I-O-two <pause dur="0.3"/> you constantly regenerate the T-I-O-two it goes on and on and on <pause dur="0.4"/> # <pause dur="0.2"/> going through all these steps <pause dur="0.3"/> but the the key point is this <pause dur="0.6"/> right so <pause dur="0.4"/> we start with off <pause dur="0.5"/> with an organic <pause dur="0.4"/> and we'll call the organic molecule <pause dur="0.4"/> whatever it you know it can be anything you like phenol benzene <pause dur="0.5"/> # ethanol <pause dur="0.6"/> a dye stuff <pause dur="0.6"/> we'll call it H-R-H <pause dur="0.3"/> that's two hydrogens bonded to <pause dur="0.8"/> quite a complex network of carbons <pause dur="0.3"/> but we'll just call it H-R-H <pause dur="1.2"/> you've got the O-H radical formed <pause dur="0.4"/><kinesic desc="indicates point on transparency" iterated="n"/> i've got it formed from H-two-O-two there but of course it's formed as we've already said from T-I-O-two under photolysis <pause dur="1.2"/> so the O-H radical is <kinesic desc="indicates point on transparency" iterated="n"/> formed here <pause dur="0.6"/> and it attacks the H-R-H <pause dur="0.5"/> it pulls a

hydrogen off <pause dur="0.6"/> to give us water so the O-H becomes water <pause dur="0.5"/> the H-R-H <kinesic desc="indicates point on transparency" iterated="n"/> comes through here <pause dur="0.2"/> and becomes R-H-dot <pause dur="0.4"/> so there's our organic radical <pause dur="0.8"/> the organic radical <pause dur="0.4"/> if you didn't have any oxygen in the system <pause dur="0.5"/> it would almost certainly dimerize <pause dur="0.3"/> to give you a polymeric product <pause dur="0.4"/> and you do actually get some <pause dur="0.2"/> if you have a look at these phenols you do get some # <pause dur="1.6"/> polyphenols in the system you can get dimers from trimers of phenol <pause dur="0.3"/> as a side product <pause dur="0.2"/> but they tend to be fairly minor <pause dur="1.2"/> normally of course <pause dur="0.2"/> you make a point of having oxygen there you make sure the system is has got air <pause dur="0.5"/> absorbed in it <pause dur="0.4"/> or if you're a bit worried about that you can blow air through it <pause dur="0.5"/> and if you want to be really definite you can blow some oxygen through it because what we tend to do in the laboratory <pause dur="0.3"/> is not really <pause dur="0.5"/> a viable proposition for <pause dur="0.2"/> an industrial plant <pause dur="0.2"/> mind you could do it but it would make it more expensive you don't need to really <pause dur="0.7"/> R-H <pause dur="0.5"/> will will react with oxygen <pause dur="0.5"/> to give <pause dur="0.3"/> a peroxide radical <pause dur="0.3"/> that's an organic

peroxide radical <pause dur="0.4"/> and it's got # <pause dur="0.5"/> normally it's written as R-O-two-dot <pause dur="0.4"/> but because we've written this as R-H-dot we'll just put the oxygen on and call it R-H-O-two-dot <pause dur="0.4"/> so this is <pause dur="0.4"/> this is a <kinesic desc="indicates point on transparency" iterated="n"/> peroxyl <pause dur="0.2"/> radical R-O-two-dot <pause dur="0.7"/> now the R-O-two-dot can do all sorts of things <pause dur="0.4"/> # <pause dur="0.6"/> and there's a there's a variety of things that it can do there <pause dur="0.4"/> # <pause dur="1.2"/> it can reverse <pause dur="0.6"/> that is not <pause dur="0.3"/> particularly important i will say <pause dur="0.7"/> # <pause dur="0.2"/> but what it <pause dur="0.7"/> can also do <pause dur="0.4"/> and this is the important one <pause dur="0.5"/> it can attack another R-H-R-H <pause dur="0.2"/> which i've written <kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="0.5"/> by pulling off a <trunc>hy</trunc> a hydrogen <pause dur="0.5"/> and we end up by getting <kinesic desc="indicates point on transparency" iterated="n"/> R-H-O-two-H there <pause dur="0.8"/> and we go back <pause dur="0.5"/> to <kinesic desc="indicates point on transparency" iterated="n"/> R-H here <pause dur="0.2"/> so basically you've got little a little chain reaction going along <kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="0.3"/> where you're constantly diverting H-R-H through to the <pause dur="0.3"/><kinesic desc="indicates point on transparency" iterated="n"/> this hydroperoxide <pause dur="0.6"/> so you convert it through to the hydroperoxide <pause dur="0.5"/> and then you've got some other steps <kinesic desc="indicates point on transparency" iterated="n"/> up here <pause dur="0.4"/> # <pause dur="0.6"/> you've got various <trunc>si</trunc> scissions this is to actually cleave to give an R-O radical <pause dur="0.5"/> # <pause dur="0.2"/> you can go up to R-H-plus <pause dur="0.3"/> you can go round to O-two-minus <pause dur="0.3"/>

and get back to H-two-O-two <pause dur="0.5"/> but i would say the important the really important steps here <pause dur="0.3"/> what the first one is the abstraction by O-H to take you through to <kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="0.5"/> the next important step is the picking up of oxygen to go through to <kinesic desc="indicates point on transparency" iterated="n"/> there <pause dur="0.4"/> the next step is to go round <kinesic desc="indicates point on transparency" iterated="n"/> this way <pause dur="0.3"/> to give you <pause dur="0.6"/> a hydroperoxide <pause dur="0.2"/> so you've now taken your organic <pause dur="0.4"/> which started out like <kinesic desc="indicates point on transparency" iterated="n"/> this <pause dur="0.3"/> through to <kinesic desc="indicates point on transparency" iterated="n"/> there <pause dur="0.5"/> but of course it doesn't stop there <pause dur="0.3"/> because what then happens is <pause dur="0.3"/> the the whole thing starts all over again <pause dur="0.2"/> this time you would write <kinesic desc="indicates point on transparency" iterated="n"/> R-H-O-two-H in here <pause dur="0.3"/> and again you would pull off another hydrogen atom <pause dur="0.3"/> and you'd take it to one higher state of oxidation <pause dur="0.3"/> so it goes round and round and round and round <pause dur="0.2"/> and every time it goes round <pause dur="0.2"/> you strip one hydrogen out <pause dur="0.3"/> and you put an O-H on <pause dur="0.3"/> so <pause dur="0.3"/> you know you in the end you end up with if you like <pause dur="0.2"/> if you imagine a carbon with four hydroxy groups around it <pause dur="0.3"/> that's all that really is C-O-two and some protons so <pause dur="0.3"/> # <pause dur="0.2"/> you are really you're really taking the through through the

thing through <pause dur="0.4"/> from <pause dur="0.2"/> a fully reduced form with carbons with lots of hydrogens <pause dur="0.3"/> through to a very highly oxygenated form <pause dur="0.2"/> that finally becomes C-O-two <pause dur="0.6"/> so <pause dur="0.2"/> that is the # <pause dur="0.2"/> that's the sequence <pause dur="0.2"/> of reactions <pause dur="0.4"/> in in the H-two-O-two U-V process <pause dur="0.3"/> it's exactly the same <pause dur="0.4"/> if you have the T-I-O-two there as well <pause dur="0.3"/> if i wrote T-I-O-two for H-nu <pause dur="0.6"/> it's <trunc>ju</trunc> it's exactly it's just the same sort of thing <pause dur="1.0"/> in fact people working on these systems there are three favourite things to work on one's T-I-O-two <pause dur="0.4"/> one's H-two-O-two and the third one's ozone <pause dur="0.3"/> 'cause if you irradiate ozone <pause dur="0.3"/> you get <pause dur="0.2"/> O-two molecule <pause dur="0.6"/> and an oxygen atom <pause dur="0.4"/> and the oxygen atom inserts into water <pause dur="0.3"/> it's extremely reactive <pause dur="0.3"/> and gives you two O-H radicals <pause dur="0.2"/> so <pause dur="0.2"/> the whole thing is centred on making O-H radicals <pause dur="0.5"/> O-H radicals are the great purifying radicals <kinesic desc="changes transparency" iterated="y" dur="20"/> in this life <pause dur="1.8"/> now this system has been looked at very very extensively <pause dur="1.3"/> # with all manner of pollutants <pause dur="0.5"/> and i'll give you a <trunc>t</trunc> a a another slide now <pause dur="0.2"/> with about a million compounds on <pause dur="0.2"/> and you're not to <pause dur="0.2"/> try and write

all these down <pause dur="0.5"/> but you could just maybe write down well well one or two examples <pause dur="0.4"/> so # <pause dur="0.3"/> here we go <pause dur="0.6"/> so these are <pause dur="0.3"/> photomineralization of organic pollutants <pause dur="0.3"/> sensitized by T-I-O-two <pause dur="0.3"/> examples of compound studied <pause dur="0.6"/> and the very simplest compound methane pentane dodecane <pause dur="0.4"/> they go <pause dur="0.3"/> hologenated hologenated alkanes <pause dur="0.4"/> tetrachloroethane <pause dur="0.3"/> dibromoethane so for all these rather <pause dur="0.2"/> dangerous solvents you know which at one time were very beloved of the dry cleaning industry <pause dur="0.3"/> # <pause dur="0.2"/> can be degraded using the T-I-O-two system <pause dur="0.7"/> alcohols <pause dur="0.2"/> absolutely no problem <pause dur="0.6"/> acids the next stage up from alcohols no problem <pause dur="0.4"/> alkenes <pause dur="0.6"/> straight away <pause dur="1.2"/> chloroalkenes again dry cleaning solvents <pause dur="0.4"/> they can be destroyed <pause dur="0.5"/> and the dreaded aromatics like benzene <pause dur="0.6"/> they can be destroyed <pause dur="0.5"/> halogens <pause dur="0.7"/> well here we've got dichlorophenol dichlorophenol <pause dur="0.3"/> these are all the <trunc>de</trunc> degraded products <pause dur="0.3"/> from things like polychloro<pause dur="0.3"/>biphenyls <pause dur="0.3"/> they're also degraded products from dioxins the <pause dur="0.2"/> famous # <pause dur="0.2"/> Seveso disaster in Italy <pause dur="0.5"/> where <pause dur="0.2"/> # <pause dur="0.6"/> a whole <pause dur="0.5"/> area # was heavily contaminated

a lot of people <pause dur="0.5"/> # died <pause dur="0.3"/> from ingesting # the these toxic materials <pause dur="0.9"/> the straightforward phenols are vulnerable <pause dur="0.9"/> carboxylic acids <pause dur="0.5"/> polymers are not they're not quite so easy to do with polymers but they you can <pause dur="0.4"/> degrade polymers with T-I-O-two <pause dur="0.5"/> # 'cause these aren't water soluble <pause dur="0.2"/> so it's it's not it's not straightforward <pause dur="0.2"/> you have to grind them into a powder or do something to them <pause dur="0.3"/> to <pause dur="0.5"/> # <pause dur="0.5"/> expose them properly to the T-I-O-two but T-I-O-two will will will remove them <pause dur="0.5"/> whole series of # surfactants <pause dur="0.7"/> # <pause dur="0.5"/> all manner of surfactants of course get out into the <pause dur="0.9"/> aqueous systems into rivers <pause dur="0.2"/> streams and lakes <pause dur="0.5"/> # <pause dur="0.5"/> they're used very extensively in industry and also domestically <pause dur="0.5"/> and they're really quite <trunc>di</trunc> difficult things to get rid of <pause dur="0.5"/> # <pause dur="0.5"/> but T-I-O-two <pause dur="0.2"/> will <pause dur="0.3"/> # attack them all <pause dur="0.4"/> then you get down to herbicides <pause dur="0.4"/> # <pause dur="0.4"/> simazine and <pause dur="0.2"/> things like that <pause dur="0.7"/> the pesticides like D-D-T parathion and lindane <pause dur="0.4"/> and then also dye stuffs they're quite important because a lot of factories <pause dur="0.5"/> that use dye stuffs <pause dur="0.4"/> they're only allowed

to discharge at very very low levels so they have to process their effluent themselves <pause dur="0.4"/> otherwise they're <pause dur="0.2"/> subject to heavy fines <pause dur="0.5"/> and they're always looking for they normally do this by some sort of chemical means <pause dur="0.3"/> but if you get down to very low levels <pause dur="0.4"/> then you can use T-I-O-two <pause dur="0.2"/> to finish off the <pause dur="0.3"/> to finish off the job <pause dur="0.5"/> so a vast array of compounds <pause dur="0.3"/> and they all go <pause dur="0.3"/> through this organic radical route <pause dur="0.4"/> # by going to giving you # <pause dur="0.2"/> O-H attack it to give a carbon radical <pause dur="0.2"/> which picks up oxygen to give a peroxy radical <pause dur="0.4"/> and you get a hydroperoxide <pause dur="0.3"/> and then that <pause dur="0.2"/> in turn is <kinesic desc="changes transparency" iterated="y" dur="18"/> destroyed further <pause dur="0.5"/> so that's the kind of thing that # <pause dur="0.3"/> that goes on <pause dur="1.5"/> # <pause dur="7.9"/> this is <pause dur="0.6"/> # # <pause dur="0.3"/> not as not as important a slide but i'll i'll i'll just # show you the the type of thing that people <pause dur="0.3"/> study here <pause dur="0.6"/> # <pause dur="0.9"/> there are two ways of going at this really one is to try and analyse the pollutant disappearance <pause dur="0.5"/> # which you can do by monitoring the pollutant level by G-C-M-S or something like that <pause dur="0.4"/> the other is to look at C-O-two evolution <pause dur="0.5"/> and

# <pause dur="0.2"/> here are we well beyond looking at C-O-two <pause dur="0.2"/> # evolution <pause dur="0.5"/> and we are measuring <pause dur="0.3"/> pollutants at various concentrations in milligrams per <pause dur="0.4"/> per <pause dur="0.9"/> cubic decimetre <pause dur="0.5"/> and <pause dur="0.4"/> # <pause dur="0.3"/> as you can imagine <pause dur="0.5"/> as you begin to increase the concentration of course <pause dur="0.4"/> you'd expect the thing to plateau out <pause dur="0.4"/> because <pause dur="0.6"/> as you raise the concentration <pause dur="0.5"/> you're beginning to saturate the surface of the <pause dur="0.2"/> T-I-O-two particle <pause dur="0.3"/> with the thing you're trying to destroy <pause dur="0.3"/> and so if you go to # <pause dur="0.5"/> # to <pause dur="0.3"/> to levels more than <pause dur="0.5"/> # <kinesic desc="indicates point on transparency" iterated="n"/> around here <pause dur="1.5"/> then <pause dur="0.4"/> you're not going to have such an efficient process <pause dur="0.2"/> simply because <pause dur="0.3"/> you've reached <pause dur="0.3"/> a kind of a <pause dur="0.3"/> saturation of the level it's very much a kind of <pause dur="0.2"/> Langmuir type kinetics # whether you <pause dur="0.4"/> can remember <pause dur="0.3"/> i think i talked about Langmuir kinetics even in first year to you <pause dur="0.5"/> but # <pause dur="0.9"/> Langmuir's idea was that <pause dur="0.3"/> every every surface of a catalyst <pause dur="0.2"/> has a certain number of sites <pause dur="0.9"/> and when the sites were filled <pause dur="0.7"/> then you've got no more catalytic action <pause dur="0.2"/> and you could double treble <pause dur="0.5"/> multiply this concentration by a ten or a

hundred <pause dur="0.3"/> you'd get no more joy <pause dur="0.3"/> in the way of them <pause dur="0.2"/> producing C-O-two <pause dur="0.4"/> or in this case or whatever it was <pause dur="0.3"/> because you've <trunc>s</trunc> <pause dur="0.2"/> saturated the catalyst <pause dur="0.3"/> you can see the saturation coming in here <pause dur="0.3"/> so this illustrates that the <pause dur="0.3"/> the Langmuir <pause dur="0.3"/> type of idea <pause dur="0.4"/> is valid for T-I-O-two <pause dur="0.5"/> a lot of people have done done very detailed surface kinetic study of these systems for a number of things <pause dur="0.3"/> a number of different pollutants <pause dur="0.2"/> and they find all the time <pause dur="0.3"/> the sort of behaviour <pause dur="0.2"/><kinesic desc="indicates point on transparency" iterated="n"/> i've illustrated here <pause dur="0.4"/> you you plateau out <pause dur="0.7"/> now this doesn't matter too much because <pause dur="0.3"/> industrially <pause dur="0.3"/> the sorts of things you're trying to remove <pause dur="0.3"/> like the chlorophenyls and dioxins and things <pause dur="0.3"/> surfactants <pause dur="0.2"/> are actually at very very low levels <pause dur="0.6"/> they're very harmful <pause dur="0.7"/> but they are at very very <trunc>le</trunc> very low levels and so <pause dur="0.6"/> the problem <pause dur="0.5"/> is one <pause dur="0.3"/> that you can reasonably attack <pause dur="0.4"/> because you <pause dur="0.3"/> do not normally have <pause dur="0.3"/> for the pollutant levels <pause dur="0.2"/> sort of <pause dur="0.3"/> you know <pause dur="0.5"/> at <kinesic desc="indicates point on transparency" iterated="n"/> this end you tend to be more towards <kinesic desc="indicates point on transparency" iterated="n"/> that end <pause dur="0.3"/> so the <trunc>t</trunc> the the thing is in your sights <pause dur="0.3"/> you can <pause dur="0.4"/> # <pause dur="0.3"/><kinesic desc="changes transparency" iterated="y" dur="29"/> stand a

reasonable chance <trunc>o</trunc> of getting a a conversion <pause dur="0.5"/> to <pause dur="0.6"/> # <pause dur="0.3"/> free up the system <pause dur="1.9"/> the <pause dur="0.7"/> question of <pause dur="0.6"/> how <pause dur="0.7"/> good a catalyst <pause dur="0.2"/> <trunc>i</trunc> the the T-I-O-two is <pause dur="0.3"/> of course <pause dur="0.7"/> # also revolves around <pause dur="1.0"/> does it <pause dur="0.7"/> wear out <pause dur="0.9"/> do you <pause dur="0.7"/> come up against having to replace it quite frequently <pause dur="0.2"/> how often does it turn over <pause dur="0.5"/> and this is a a a <trunc>n</trunc> a nice little slide here i think <pause dur="0.4"/> # <pause dur="0.4"/> it's only # <pause dur="1.3"/> ten <pause dur="0.3"/> cycles but what what have we got here <pause dur="0.4"/> well we've actually got four-chlorophenol <pause dur="0.5"/> which is again a very typical type of # thing to be looking at <pause dur="0.3"/> and we got one portion of T-I-O-two <pause dur="0.2"/> only one portion <pause dur="0.6"/> we start off <pause dur="0.3"/> # <kinesic desc="indicates point on transparency" iterated="n"/> at <pause dur="0.3"/> this concentration here of about # <pause dur="0.2"/> three times ten-to-minus-#-<pause dur="0.8"/>#-<pause dur="0.2"/>six <gap reason="inaudible" extent="1 sec"/> micromolar <pause dur="0.5"/> you shine the light on <pause dur="0.5"/> and you see the level <pause dur="0.4"/> falls away rapidly and as the <trunc>f</trunc> four-chlorophenol is is being destroyed <pause dur="1.2"/> then what you do <pause dur="0.4"/> is # <pause dur="1.8"/> inject <pause dur="0.4"/> into the system <pause dur="0.6"/> # <pause dur="0.4"/> a fresh <pause dur="0.2"/> quantity <pause dur="0.5"/> syringe the four-chlorophenol <pause dur="0.4"/> away it goes <pause dur="0.3"/> you inject <trunc>f</trunc> a fresh amount away it goes <pause dur="0.3"/> so you're you're acid we use in a catalyst to completely destroy <pause dur="0.4"/> or very nearly destroy your four-chlorophenol <pause dur="0.3"/>

then you if you use some fresh four-chlorophenol <pause dur="0.4"/> and <pause dur="0.2"/> you see it goes on and on and on although i think they did they had ten goes at it and then they probably got bored <pause dur="0.2"/> # <pause dur="0.3"/> after that 'cause they got up to twelve-hundred minutes <pause dur="0.6"/> # which is i suppose # <pause dur="0.2"/> quite a long time <pause dur="0.4"/> and probably the graduate student who <pause dur="0.3"/> # was doing this just got tired and wanted to go home <pause dur="0.3"/> so that # it <trunc>w</trunc> it wasn't taken any <shift feature="voice" new="laugh"/>further <shift feature="voice" new="normal"/> <pause dur="0.4"/> but <pause dur="0.2"/> i think you get the you get the picture <pause dur="0.3"/> the thing is very <pause dur="0.5"/> # adaptable it's very recyclable <pause dur="0.7"/> it takes a long time to exhaust it <pause dur="0.8"/> i <pause dur="0.7"/> i i can add a sort of footnote to that even even when it begins after many many many cycles maybe hundreds to become exhausted <pause dur="1.0"/> you can actually reactivate it you can you can # take it <pause dur="0.3"/> wash it <pause dur="0.4"/> # <pause dur="0.6"/> and heat it to quite a high temperature <pause dur="0.2"/> let it cool down <pause dur="0.2"/> it starts off <pause dur="0.4"/> all over again <pause dur="0.3"/> so you <trunc>i</trunc> it is really renewable <pause dur="0.3"/> so it it's really kind of # <pause dur="0.5"/><kinesic desc="changes transparency" iterated="y" dur="21"/> # almost hypnotically successful you know people <pause dur="0.3"/> # really become very enthusiastic about it <pause dur="0.3"/> <trunc>a</trunc> as a way of # <pause dur="0.7"/> # <pause dur="1.4"/> trying to degrade <pause dur="0.9"/> noxious organics <pause dur="0.8"/> # <pause dur="1.1"/>

how do you sort of set up things like this how do you get it to work these these are some of the practical points now and then i <trunc>n</trunc> i <trunc>g</trunc> moving away from theory <pause dur="0.4"/> there are there are there are <trunc>s</trunc> various ways of doing it <pause dur="0.5"/> # <pause dur="0.4"/> what you can do <pause dur="0.3"/> where we've got we've got # <pause dur="0.2"/> two two set ups and these are two flow reactors <pause dur="0.7"/> flow reactors are probably much better in a way because they model what you want to do <pause dur="0.3"/> in treating industrial effluent <pause dur="0.4"/> much better than batch reactors <pause dur="0.4"/> now you you don't just sort of have to take # <pause dur="0.5"/> a batch of water <pause dur="0.4"/> purify it <pause dur="0.6"/> and then take another batch and purify it you want to be able to purify <pause dur="0.2"/> a constant stream <pause dur="0.2"/> as it comes from some site or other <pause dur="0.5"/> so what have we actually got here <pause dur="0.6"/> well <pause dur="0.2"/> # you've got <pause dur="0.3"/> # in <kinesic desc="indicates point on transparency" iterated="n"/> this one <pause dur="0.5"/> you you're flowing your material <pause dur="0.4"/> # <pause dur="0.6"/> well you you've got you start <trunc>o</trunc> to start off with you've got <pause dur="0.7"/> your fluorescent tube <pause dur="0.3"/> okay just like an ordinary ordinary fluorescent tube <pause dur="0.8"/> and then <pause dur="0.4"/> coaxially <pause dur="0.5"/> positioned to this you've got an outer glass jacket <pause dur="0.7"/> and you flow your solution through <kinesic desc="indicates point on transparency" iterated="n"/>

here <pause dur="0.4"/> up there <pause dur="0.2"/><kinesic desc="indicates point on transparency" iterated="n"/> and out the top <pause dur="0.4"/> and all the way through here <kinesic desc="indicates point on transparency" iterated="n"/> these sort of things <pause dur="0.4"/> are <pause dur="0.3"/> a glass mesh <pause dur="0.3"/> or they could be glass helices <pause dur="0.3"/> they're all coated with T-I-O-two <pause dur="0.3"/> it's very easy to coat the glass with that <pause dur="0.5"/> # <pause dur="0.5"/> you know we sort of do it all the time <pause dur="0.4"/> # <pause dur="1.8"/> and <pause dur="0.7"/> as the stuff flows up the fluorescent light is on <pause dur="0.2"/> the U-V is coming <kinesic desc="indicates point on transparency" iterated="n"/> this way <pause dur="0.2"/> it hits the helices <pause dur="0.3"/> where the T-I-O-two is layered <pause dur="0.3"/> with a thin layer <pause dur="0.6"/> the T-I-O-two becomes activated by the light <pause dur="0.3"/> you get the degradation occurring <pause dur="0.2"/> so you pass in <pause dur="0.2"/> the chlorophenol or whatever it is at the bottom <pause dur="0.3"/> and at the top <pause dur="0.4"/> you get C-O-two and chloride <pause dur="0.5"/> and that's one way of doing it <pause dur="0.4"/> # another way of doing it <pause dur="0.4"/> is in fact to <pause dur="0.3"/> # <pause dur="0.2"/> it would simply spiral <pause dur="0.5"/> the <unclear>ethene</unclear> <pause dur="0.2"/> round the fluorescent tube <pause dur="0.4"/> and the inside of the <pause dur="0.4"/> glass tube <pause dur="0.5"/> is coated with the T-I-O-two <pause dur="0.7"/> if you have a very thin layer <pause dur="0.3"/> that's okay the light the light will get through <pause dur="0.4"/> a very very thick layer of T-I-O-two <pause dur="0.5"/> so # you can you can do it this way so these these are two kind of flow systems that you can <pause dur="0.3"/> you can operate <pause dur="0.7"/> so

that's a <kinesic desc="changes transparency" iterated="y" dur="22"/> that's a kind of a <pause dur="0.7"/> just just a technical point but i mean you know you might wonder <pause dur="0.3"/> how you're going to set about doing these things <pause dur="1.6"/> # <pause dur="0.8"/> if you want to <pause dur="0.2"/> do a # a batch reaction <pause dur="0.3"/> well you can do it <pause dur="0.4"/> # <pause dur="0.5"/> i guess the first time you ever <pause dur="0.2"/> study these things you tend to do them in batch <pause dur="0.4"/> so but you this would be <trunc>n</trunc> of not much <pause dur="0.4"/> help <pause dur="0.3"/> in # <pause dur="0.4"/> trying to # establish a kind of industrial process <pause dur="0.5"/> but essentially here <pause dur="0.4"/> you <pause dur="0.5"/> # <pause dur="0.3"/> have got # <pause dur="1.6"/> # <pause dur="4.3"/> yeah you've got all your tubes <pause dur="0.8"/><kinesic desc="indicates point on transparency" iterated="n"/> in here you've got a bank of tubes maybe six or eight in in each of those you you sort of bring them together <pause dur="0.5"/> # <pause dur="0.2"/> in a core <kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="0.4"/> B <pause dur="0.6"/> is <pause dur="0.2"/> where you've actually got your # reaction where there's your sample <pause dur="0.5"/> # and you're passing through some oxygen continuously <pause dur="0.5"/> # through through the top <pause dur="0.3"/> through through this # <pause dur="0.2"/><kinesic desc="indicates point on transparency" iterated="n"/> this cylinder here <pause dur="0.7"/> and # <pause dur="2.9"/> it bubbles round and uses the pumping system to pump it around <pause dur="0.7"/> so <pause dur="0.6"/> and you've also got the stirrer <unclear>wheel</unclear> <pause dur="0.5"/> okay so that that would be a typical batch thing <pause dur="0.8"/> # i've got a system here that # <pause dur="0.2"/> i run from time to time which is slightly different

from that i blow the oxygen up <pause dur="0.9"/> the bottom of the tube <pause dur="0.2"/> and at the sort of bottom of the vessel <pause dur="0.2"/> through a glass sinter <pause dur="0.3"/> and as oxygen goes through <pause dur="0.3"/> the oxygen pressure <pause dur="0.5"/> # keeps the <pause dur="0.2"/> aqueous solution above the sinter <pause dur="0.3"/> and the sinter <gap reason="inaudible" extent="1 sec"/> the oxygen into thousands and thousands of tiny streams <pause dur="0.4"/> and so you get a very very good sparging <pause dur="0.3"/> of the oxygen as it goes up through the solution very good # <pause dur="0.4"/> # <pause dur="0.5"/> # use uses <event desc="takes off transparency" iterated="n"/> of the oxygen because you you've broken it down into tiny bubbles <pause dur="0.3"/> you get maximum <pause dur="0.3"/> bubble exposure <pause dur="0.4"/> to to the solution <pause dur="0.9"/> # <pause dur="1.7"/> another way of # <pause dur="0.4"/> # i've got another another slide here <pause dur="0.5"/> # <pause dur="0.9"/> if you're looking at # <pause dur="0.2"/> i mentioned before when you were trying to analyse what was going on <pause dur="0.6"/> you can <pause dur="0.5"/> with <pause dur="0.4"/> # <pause dur="2.2"/> pentachlorophenol you can <pause dur="0.3"/> analyse it by G-C-M-S <pause dur="0.4"/> but much easier is to look at C-O-two evolution <pause dur="0.7"/> and also <pause dur="0.7"/> quite easy is to have a sensor electrode for chloride <pause dur="0.4"/> and again in the studies we do here <pause dur="0.5"/> we use a chloride unselective electrode <pause dur="0.4"/> which simply <trunc>d</trunc> <pause dur="0.2"/> measures chloride as it's

developed <pause dur="0.3"/> as the organic chloride breaks down to chloride <pause dur="0.4"/> you can follow the chloride <pause dur="0.3"/> electrochemically <pause dur="0.2"/> you might remember in the first year i think there was a experiment <pause dur="0.3"/> where you hydrolyse T-butyl chloride <pause dur="0.3"/> and you measure the chloride evolution <pause dur="0.6"/> <trunc>fro</trunc> from the hydrolysis <pause dur="0.4"/> by <pause dur="0.2"/> looking at the conductivity do you remember this experiment from your <pause dur="0.3"/> your misspent youths <pause dur="0.5"/> well anyway <pause dur="0.3"/> # that used to be in the first year even if it's <pause dur="0.2"/> isn't isn't now <pause dur="0.5"/> it's quite easy to have a a little sensor electrode <pause dur="0.4"/> which is sensitive to chloride you have this dipping in <pause dur="0.3"/> and you simply measure the chloride that's produced <pause dur="0.5"/> if you're looking at dye stuff degradation it's much easier <pause dur="0.4"/><kinesic desc="puts on transparency" iterated="n"/> so this is if you've got a a a <trunc>ni</trunc> a nice big chromoform <pause dur="0.2"/> on your molecule <pause dur="0.3"/> and here <pause dur="0.2"/> this is metheylene blue <pause dur="0.3"/> which is a good model for quite a few dyes as quite a few dyes have got a structure similar to metheylene blue <pause dur="0.5"/> and metheylene blue <pause dur="0.2"/> absorbs # well it's blue of course it absorbs in the red <pause dur="0.5"/> a bit of a bit like a sort of <gap reason="inaudible" extent="1 sec"/>

solution <pause dur="0.4"/> and you start off by having <pause dur="0.4"/> an absorption band A <kinesic desc="indicates point on transparency" iterated="n"/> there <pause dur="0.2"/> and as you irradiate at various times <pause dur="0.3"/> the thing <kinesic desc="indicates point on transparency" iterated="n"/> falls away <pause dur="0.2"/> like so <pause dur="0.2"/> so you end up with that as your baseline <pause dur="0.5"/> and you you <trunc>s</trunc> you your baseline's rather high 'cause you've got T-I-O-two <pause dur="0.5"/> buzzing around giving you a quite a bit of a background <pause dur="0.5"/> and if you measure the <pause dur="0.2"/> peak maximum <kinesic desc="indicates point on transparency" iterated="n"/> there the plot of the absorbence versus time <pause dur="0.6"/> normalize it to the baseline <pause dur="0.4"/> you get that sort of thing occurring <pause dur="0.2"/> and you can see that # with this metheylene blue <pause dur="0.3"/> that's <pause dur="0.2"/> ten micromolar roughly <pause dur="0.5"/> # <pause dur="0.3"/> you only need to expose <pause dur="0.4"/> # for <pause dur="0.2"/> five minutes and it's totally destroyed <pause dur="0.7"/> # <pause dur="0.5"/> i've seen this done as a demonstration <pause dur="0.4"/> it's quite effective starts off with deep blue <pause dur="0.3"/> ends up <pause dur="0.2"/> water white <pause dur="0.4"/> so it's really quite a good # <pause dur="0.4"/> quite a good demonstration type experiment <pause dur="0.4"/><event desc="takes off transparency" iterated="n"/> and here we're actually <pause dur="0.3"/> we've got a a a project running at the moment <pause dur="0.3"/> with one of the M-chem students who's going to be looking at other dyes <pause dur="0.5"/> # <pause dur="0.6"/> being destroyed by by this type of system <pause dur="0.9"/> # <pause dur="1.1"/> one or two <pause dur="0.2"/>

other small <pause dur="0.4"/> # kinetic points <pause dur="0.3"/> # <pause dur="0.4"/> that # are <trunc>p</trunc> are probably worth making <pause dur="1.6"/> i mentioned before <pause dur="0.2"/> that if you vary the concentration <pause dur="0.9"/> of the <pause dur="1.1"/> molecule you're attacking your substrate <pause dur="0.6"/> then <pause dur="0.3"/> it follows Langmuir type kinetics in other words to begin with <pause dur="0.2"/> if you double the amount of organic <pause dur="0.3"/> you double the rate of degradation <pause dur="0.3"/> but quite soon <pause dur="0.2"/> it turns over to a plateau <pause dur="0.3"/> because you're saturating the surface <pause dur="0.7"/> of the particles <pause dur="0.4"/> with the organic you're wanting to destroy <pause dur="0.3"/> and that <unclear>any</unclear> more isn't isn't <trunc>mu</trunc> really much <pause dur="0.3"/> much use <pause dur="0.6"/> the other thing you can do is to look at the dependence on the light intensity <pause dur="0.4"/> and you might say well if i go from a hundred watt bulb to a two-hundred watt bulb to a four-hundred watt bulb to a kilowatt bulb <pause dur="0.4"/> am i gaining <pause dur="0.8"/> or <pause dur="0.5"/> is it worth the extra energy input <pause dur="0.4"/> there's been quite a bit of work on that <pause dur="0.3"/> and again we've done some work here on it as well <pause dur="0.2"/> this is not our results but our results are very similar <pause dur="0.4"/><kinesic desc="puts on transparency" iterated="n"/> this is actually degrading isopropanol <pause dur="0.7"/> # <pause dur="0.6"/> okay <pause dur="0.2"/> and you're destroying

isopropanol <pause dur="0.3"/> using <trunc>T-I</trunc> # well <pause dur="0.4"/> it says rutile that's one of the forms of T-I-O-two <pause dur="0.3"/> and you can see <pause dur="0.2"/> you what you what what's been plotted here <pause dur="0.3"/> is the log <pause dur="0.2"/> of the rate of the acetone formation you can measure acetone quite easily <pause dur="0.4"/> by again by G-C <pause dur="0.6"/> # <pause dur="0.2"/> and <kinesic desc="indicates point on transparency" iterated="n"/> here is the log of the light intensity <pause dur="0.8"/> and <pause dur="0.3"/> if you've got if you remember <unclear>that's really</unclear> if you remember from your again your again from your first year kinetics <pause dur="0.3"/> lectures that # <pause dur="0.6"/> if you've # <pause dur="2.4"/> got <pause dur="0.5"/> a dependence <pause dur="0.6"/> which <pause dur="0.2"/> is <pause dur="1.4"/><event desc="moves board" iterated="n"/> <gap reason="inaudible" extent="1 sec"/> like this and you've got <pause dur="0.6"/><kinesic desc="writes on board" iterated="y" dur="10"/> R <pause dur="0.9"/> is equal to K <pause dur="0.6"/> times some sort of thing like concentration if i call it I for light intensity <pause dur="0.4"/> and you've got that power <pause dur="0.4"/> A <pause dur="0.4"/> okay <pause dur="0.2"/> then what you can do is take logs <kinesic desc="writes on board" iterated="y" dur="11"/> say log-<pause dur="0.2"/>R <pause dur="0.6"/> is equal to K <pause dur="1.5"/> log-K sorry <pause dur="0.8"/> plus A-<pause dur="0.5"/>log-<pause dur="0.6"/>I <pause dur="0.4"/> okay that's taking logs <pause dur="0.5"/> that's actually <trunc>f</trunc> you know first year type work <pause dur="0.5"/> and <pause dur="0.9"/> to find out what A is <pause dur="0.4"/> what is the <unclear>value</unclear> is it depending <trunc>t</trunc> on the light intensity of the first power <pause dur="0.2"/> the second power <pause dur="0.9"/> no power at all it does it not depend on the amount of light you put in <pause dur="0.4"/> then you can

find that out by plotting <pause dur="0.2"/> the log of the rate of the reaction <pause dur="0.3"/> photomineralization in this case <pause dur="0.4"/> versus the log <pause dur="0.8"/> of the light intensity <pause dur="0.4"/> okay <pause dur="0.3"/> so that that that is # <pause dur="0.4"/><kinesic desc="writes on board" iterated="n"/><kinesic desc="indicates point on board" iterated="n"/> first year revisited <pause dur="0.4"/> and you ought to keep you you <trunc>rev</trunc> revisiting first year chemistry <pause dur="0.2"/> for as long as you do chemistry because all the fundamentals come out there <pause dur="0.3"/> you can see here <pause dur="0.3"/> that this <kinesic desc="indicates point on transparency" iterated="n"/> this line <pause dur="0.3"/> going up here <pause dur="0.2"/> is is is a good nice forty-five degrees it's a forty-five degree line <pause dur="0.5"/> it means the thing <pause dur="0.2"/> is strictly first order <pause dur="0.2"/> the slope is one-point-nought <pause dur="0.3"/> and so to begin with <pause dur="0.8"/> the <pause dur="0.2"/> and if you double the light intensity <pause dur="0.4"/> you double the rate <pause dur="0.7"/> but <pause dur="0.2"/> when you get past a certain point <pause dur="1.0"/> you find that the slope <pause dur="0.4"/> falls exactly <pause dur="0.4"/> to half <pause dur="0.2"/> it falls from one-point-nought to nought-point-five <pause dur="0.6"/> so it seems that we can go to very high light intensities <pause dur="1.6"/> that at the <pause dur="0.4"/> rate of evolution <pause dur="0.6"/> of your product <pause dur="0.4"/> is no longer first order in the light <pause dur="0.4"/> it becomes half order in the light <pause dur="0.3"/> so if you double the light <pause dur="0.5"/> you only increase the intensity by one-point-four <pause dur="0.9"/> #

that's an interesting observation <pause dur="0.5"/> # <pause dur="0.4"/> and you might think well i can understand easily why it is if you increase the <pause dur="0.7"/> organic <pause dur="0.4"/> concentration <pause dur="0.3"/> you saturate the surface <pause dur="0.7"/> but <pause dur="0.6"/> surely <pause dur="1.7"/> the more light you put on the system surely all the time <pause dur="0.2"/> the more efficient the process would be 'cause you're getting more excited states <pause dur="0.4"/> which would give you more O-H radicals <pause dur="0.6"/> et cetera et cetera <pause dur="0.8"/> has anyone got any idea why it is that it falls away <pause dur="0.2"/> as you get to very high light intensities <pause dur="0.3"/> any thoughts on that <pause dur="2.4"/> imagine you've got a particle <pause dur="0.4"/> tiny particle <pause dur="0.2"/> it's being irradiated with light <pause dur="0.3"/> and you go on increasing the light more and more and more these are logs here <pause dur="0.2"/> you know <kinesic desc="indicates point on transparency" iterated="n"/> this is a <pause dur="0.3"/> # enormous <trunc>dis</trunc> you're going through <pause dur="0.5"/> between <pause dur="0.4"/> thirteen and eighteen that's five orders of magnitude <pause dur="0.3"/> on the light intensity <pause dur="0.2"/> a hundred-thousand times this is a very detailed study <pause dur="0.6"/> when you go to extremely high light intensities <pause dur="0.3"/> what do you think happens to the <pause dur="0.6"/> whole electron pairs formed in the <pause dur="0.3"/> particle <pause dur="0.5"/> any ideas <pause dur="4.1"/>

well you've got a plus and a minus <pause dur="0.7"/> they're going to move to the surface to <trunc>s</trunc> to <pause dur="0.2"/> localize this plus and minus <pause dur="0.3"/> but what happens when the concentration of the pluses and the minuses on the surface <pause dur="0.6"/> becomes extremely large <pause dur="0.5"/> what will they do to each other </u><pause dur="0.4"/> <u who="sf0695" trans="pause"> they destroy each other </u><pause dur="0.3"/> <u who="nm0693" trans="pause"> they yeah they they mutually destroy each other <pause dur="0.5"/> if you get to growing high light intensities <pause dur="0.3"/> you get to the point <pause dur="0.4"/> where <pause dur="0.2"/> the positive centres <pause dur="0.3"/> and the negative centres although they want to react with the water <pause dur="0.3"/> they want to react with the oxygen <pause dur="0.3"/> they're in such a high concentration now <pause dur="0.8"/> there's quite a good chance they'll actually kill each other off <pause dur="0.3"/> and so you actually begin to lose out <pause dur="0.9"/> once you've gone beyond a certain light intensity the benefits of going to even higher light intensities and i mean <pause dur="0.3"/> enormously powerful lamps <pause dur="0.6"/> tend to be lost <pause dur="0.7"/> so <pause dur="0.2"/> that that again that's an a a a an environmental point well worth <pause dur="0.4"/> kind of taking a note of <pause dur="0.9"/><kinesic desc="changes transparency" iterated="y" dur="23"/> okay <pause dur="0.7"/> # <pause dur="2.6"/> i can # <pause dur="0.7"/> maybe # <pause dur="0.7"/> finish off with a a few more advanced experiments

that have been done <pause dur="0.5"/> and # <pause dur="0.9"/> i'll just look at the <trunc>kinetic</trunc> i've <trunc>ju</trunc> <pause dur="0.2"/> talked about the kinetics several times i'll maybe underline that now by <pause dur="0.3"/> putting up <pause dur="0.7"/> the normal rate of degradation <pause dur="0.8"/> okay so <pause dur="0.5"/> this is for any system now <pause dur="0.4"/> # using a <trunc>semi</trunc> any semiconductor <pause dur="0.4"/> under illumination <pause dur="0.5"/> and what i've got there <pause dur="0.3"/> is the rate of degradation <pause dur="0.7"/> we've got you see got a Langmuir term <kinesic desc="indicates point on transparency" iterated="n"/> here for oxygen <pause dur="0.4"/> and what this what it is what this implies is <pause dur="0.3"/> that <pause dur="0.8"/> if you keep increasing the oxygen <pause dur="0.3"/> you gain benefit <pause dur="0.2"/> but eventually you're going to saturate the surface with oxygen <pause dur="0.6"/><kinesic desc="indicates point on transparency" iterated="n"/> this is the organic chlorophenol <pause dur="0.9"/> you can <pause dur="0.4"/> go on <pause dur="0.2"/> adding chlorophenol but eventually <pause dur="0.7"/> when it when it becomes very high <pause dur="1.4"/> # <pause dur="0.4"/><kinesic desc="indicates point on transparency" iterated="n"/> that term there <pause dur="0.2"/> one plus <pause dur="0.2"/> you know on the right here <pause dur="0.2"/> if C-P is very very high <pause dur="0.3"/> the one is almost negligible <pause dur="0.3"/> and that will then cancel with the thing above <pause dur="0.2"/> and so then it becomes zero order in the chlorophenol in other words it's reached a plateau <pause dur="0.4"/> same with the oxygen <pause dur="0.4"/> so <pause dur="0.3"/> you can you can <pause dur="0.4"/> oxygen is a good thing <pause dur="0.3"/> and

chlorophenol's a good thing <pause dur="0.3"/> but you can have too much of both <pause dur="0.2"/> okay that's the that's the message there <pause dur="0.7"/> and then <pause dur="0.2"/> # <pause dur="1.0"/> you've also well <pause dur="0.6"/> if you've # <pause dur="1.2"/> yeah i think <pause dur="0.2"/> i'll i'll probably skip that i mean # # <pause dur="0.4"/> i think i <trunc>mi</trunc> i might skip <pause dur="0.2"/> the next bit i think i'll leave it at that <pause dur="0.5"/> with just this warning <pause dur="0.4"/><kinesic desc="reveals covered part of transparency" iterated="n"/> # <pause dur="0.2"/> i've talked about the light intensity before <pause dur="0.4"/> # it's gamma-I-A-to-the-power-M <pause dur="0.4"/> and M is one-point-nought <pause dur="0.9"/> low light intensities <pause dur="0.9"/> and it's nought-point-five <pause dur="0.5"/> at high light <pause dur="0.2"/> high light intensities <pause dur="0.3"/><event desc="takes off transparency" iterated="n"/> okay <pause dur="0.5"/> so <pause dur="0.3"/> i think that's <trunc>m</trunc> kind of summarizes what i what i said before <pause dur="1.1"/> in trying to go on and look at <pause dur="0.8"/> # other <pause dur="0.3"/> detailed <pause dur="0.3"/> aspects <pause dur="0.2"/> of the process <pause dur="0.5"/> one of the questions is this <pause dur="2.0"/> does all the <pause dur="0.5"/> reaction take place at the surface <pause dur="0.3"/> of the particle <pause dur="0.9"/> or <pause dur="0.4"/> do some of the O-H radicals escape into solution <pause dur="1.5"/> and some of the superoxide ions escape into solution as well <pause dur="1.2"/> and do we have a solution process <pause dur="1.0"/> as well as a surface process <pause dur="0.8"/> and the question <pause dur="0.2"/> # is is <pause dur="0.3"/> here again quite an <trunc>in</trunc> quite an <trunc>instru</trunc> <pause dur="0.3"/> important one mechanistically <pause dur="0.3"/> is it <pause dur="0.2"/> the

whole thing <pause dur="0.3"/> surface limited <pause dur="0.4"/> or is we've got a surface process <pause dur="0.7"/> and <pause dur="0.2"/> a degradation solution <pause dur="0.5"/> so <pause dur="0.6"/> we began to think was there a way of probing this in some detail <pause dur="0.5"/><kinesic desc="puts on transparency" iterated="n"/> and what i've got here <pause dur="0.7"/> is <pause dur="0.2"/> an experiment <pause dur="0.4"/> # <pause dur="0.7"/> which has only been i've only done about two or three years ago <pause dur="0.6"/> and this is <pause dur="0.2"/> # one where you've got # <pause dur="1.8"/><kinesic desc="indicates point on transparency" iterated="n"/> this glass slide here <pause dur="0.2"/> with a very thick coating of T-I-O-two <pause dur="0.7"/> okay <pause dur="1.3"/> inside <pause dur="0.3"/><kinesic desc="indicates point on transparency" iterated="n"/> this little bath <pause dur="1.8"/> you've got a <gap reason="inaudible" extent="1 sec"/> dish <pause dur="0.5"/> you've got solution of chlorophenol <pause dur="0.4"/> so the chlorophenol <pause dur="0.4"/> is in <kinesic desc="indicates point on transparency" iterated="n"/> there <pause dur="1.6"/><kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="0.2"/> you've got a microelectrode <pause dur="0.5"/> and if i say the word microelectrode you ought to think of the <trunc>w</trunc> the two words <gap reason="name" extent="2 words"/> 'cause he's the chap who makes all the microelectrodes here he's one of <pause dur="0.5"/> probably the U-K's leading expert on microelectrodes <pause dur="0.5"/> and this this electrode <pause dur="0.4"/><kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="1.1"/> is as low as five microns in diameter <pause dur="0.3"/> five microns <pause dur="0.3"/> i think the one we used was about twenty-five microns <pause dur="0.4"/> but he's <pause dur="0.2"/> improved them quite a bit since then <pause dur="0.3"/> this is simply the reference electrode saturated calomel electrode in the

usual way <pause dur="0.4"/> you always have to have a reference electrode <pause dur="0.5"/> the light comes from a lamp <kinesic desc="indicates point on transparency" iterated="n"/> here <pause dur="0.3"/> going through <pause dur="0.3"/> a <pause dur="0.7"/> bank of lenses <pause dur="0.7"/> and bounced off a mirror <pause dur="0.5"/> to arrive there <pause dur="0.2"/> so <kinesic desc="indicates point on transparency" iterated="n"/> <unclear>collect at</unclear> a highly focused <pause dur="0.3"/> spot of light there <pause dur="0.3"/> on the T-I-O-two film <pause dur="0.5"/> and <pause dur="0.2"/> the experiment consisted <pause dur="0.3"/> of looping this microelectrode <pause dur="1.0"/> nearer and further away <pause dur="0.3"/> from the T-I-O-two <pause dur="0.4"/> and the question was <pause dur="0.2"/> would you get <pause dur="0.2"/> a bigger chloride ion development <pause dur="0.4"/> very close <pause dur="0.8"/> or would you get any further away <pause dur="0.2"/> and could you model it <pause dur="0.4"/> with a computer <pause dur="0.5"/> so this is # <pause dur="0.2"/> a <pause dur="0.3"/> # a probe <pause dur="0.4"/> this is a probe type experiment <pause dur="0.2"/> these are becoming really <pause dur="0.4"/> very important # <pause dur="0.3"/> all manner of probe apparatuses have been <pause dur="0.5"/><kinesic desc="changes transparency" iterated="y" dur="16"/> # <pause dur="0.9"/> designed and perfected in in recent years <pause dur="0.3"/> and people are now able to look at almost atomic resolution <pause dur="0.5"/> with some kind of probe <pause dur="0.2"/> with this electrochemical probe rather than optical probe <pause dur="0.7"/> and this is the this is just the result of the experiment <pause dur="0.6"/> # <pause dur="0.6"/> when <pause dur="0.2"/> <trunc>i</trunc> if you turn the light on here <pause dur="0.8"/><kinesic desc="indicates point on transparency" iterated="n"/> you watch <kinesic desc="indicates point on transparency" iterated="n"/> the voltage <pause dur="0.3"/> develop here and the voltage <pause dur="0.3"/>

records <pause dur="0.5"/> the <pause dur="0.2"/> amount of chloride that's developed <pause dur="0.7"/> okay <pause dur="0.4"/> and you could see at ten microns <pause dur="0.5"/> you turn the light on <pause dur="0.2"/> very quickly you get chloride developing <pause dur="1.6"/> and then <pause dur="0.2"/> gradually you <trunc>e</trunc> you're exhausting the chlorophenol it tapers off <pause dur="0.4"/> you turn the light off <pause dur="0.7"/> and the chloride ion <pause dur="0.2"/> dissipates <pause dur="0.2"/> and moves through the solution <pause dur="0.3"/> so clearly mass transport's quite important the chloride ion <pause dur="0.4"/> # <pause dur="0.2"/> moves away from the electrode tip <pause dur="0.3"/> very soon after you turn the light off <pause dur="0.2"/> that's at ten microns <pause dur="0.3"/> between the tip <pause dur="0.7"/> and the T-I-O-two so imagine <pause dur="0.3"/><kinesic desc="writes on board" iterated="y" dur="8"/> there's the tip <pause dur="0.5"/> of the electrode <pause dur="0.3"/> here is the T-I-O-two here <pause dur="0.6"/> and you're measuring chloride <pause dur="0.4"/> being produced <pause dur="0.5"/> in that region <pause dur="1.0"/> if you move the tip <pause dur="0.2"/> eighty microns away <pause dur="0.6"/> then the development is much much much smaller <pause dur="0.6"/> and what this tells us is <pause dur="0.3"/> that virtually all of the action <pause dur="0.5"/> is taking place <pause dur="0.4"/> very close to the surface <pause dur="0.9"/> and we can model <pause dur="0.2"/> these curves <pause dur="0.6"/> very precisely <pause dur="1.8"/> on the basis of purely a surface process <pause dur="0.6"/> you don't need <pause dur="0.2"/> to invoke <pause dur="1.0"/> a reaction occurring in solution <pause dur="0.2"/> and

always in chemistry <pause dur="0.6"/> and in science in general <pause dur="0.3"/> if you've got two possible explanations <pause dur="0.6"/> one is simple <pause dur="0.6"/> and one is more complicated <pause dur="1.2"/> and the simple one is actually <pause dur="0.2"/> works <pause dur="0.3"/> slightly better than the complicated one <pause dur="0.5"/> then you always say the simple one is right <pause dur="0.4"/> and that's called the principle of Occam's Razor <pause dur="0.8"/><event desc="takes off transparency" iterated="n"/> # <pause dur="0.4"/> after William of Occam <pause dur="0.4"/> who was from Northumberland <pause dur="1.0"/> okay <pause dur="0.3"/> # <pause dur="0.3"/> i think the <pause dur="0.5"/> i've got about two minutes to go so i will # <pause dur="0.8"/> # <pause dur="1.2"/> try and # <pause dur="3.3"/> summarize things just # i haven't got a slide to summarize this up <pause dur="0.3"/> but essentially <pause dur="0.6"/> there's a lot of interest in this area because of the environmental possibilities of converting <pause dur="1.9"/> very toxic organics <pause dur="0.3"/> at low concentrations in the aquatic environment <pause dur="0.3"/> to harmless substances <pause dur="0.3"/> by shining <pause dur="0.2"/> U-V light on them <pause dur="0.5"/> in the presence of various catalysts <pause dur="0.5"/> and what i've talked about today is T-I-O-two <pause dur="0.7"/> # it's the one that probably on which most work has been done <pause dur="0.7"/> but you can also <pause dur="0.7"/> <trunc>l</trunc> use hydrogen peroxide <pause dur="0.7"/> as a as a <pause dur="0.2"/> that's not a catalyst <pause dur="0.2"/> but it gives you the O-H

radicals it will degrade the organics very well <pause dur="0.6"/> you can also use ozone <pause dur="0.9"/> all three of these systems <pause dur="0.2"/> are called in the water industry <pause dur="0.4"/> advanced <pause dur="0.2"/> oxidation processes <pause dur="0.3"/> or A-O-Ps <pause dur="0.5"/> so # <pause dur="0.4"/> if you <pause dur="0.2"/> get a if you get go to a job interview at Severn Trent <pause dur="0.4"/><kinesic desc="writes on board" iterated="y" dur="15"/> and they say what do you know about purifying water <pause dur="0.3"/> you can say i know about advanced <pause dur="1.0"/> oxidation <pause dur="2.0"/> processes <pause dur="2.3"/> or A-<pause dur="0.5"/>O-<pause dur="1.6"/>Ps <pause dur="1.9"/> and all of these fall # fall into that group <pause dur="1.2"/> a lot of work going on <pause dur="0.6"/> and the work is interesting not merely from the point of view of the end product that is that # one is trying to perfect systems <pause dur="0.4"/> people are using light pipes <pause dur="0.3"/> to transmit the light <pause dur="0.4"/> they are using # <pause dur="0.5"/> glass wool <pause dur="0.9"/> # there are <pause dur="0.4"/> hospital tiles that are being tried out in America <pause dur="0.4"/> where you take the <trunc>ho</trunc> you take the tile <pause dur="0.9"/> and you coat it with a very thin coating of T-I-O-two <pause dur="1.9"/> and this tile <pause dur="0.5"/> will absorb enough moisture from the air to give a kind of thin monolayer or <pause dur="0.2"/> a few layers of water on the tile <pause dur="0.8"/> and if there is a bacterium floating around <pause dur="0.4"/> in

the hospital and it alights on the tile <pause dur="1.0"/> then believe it or not <pause dur="0.5"/> the <pause dur="0.4"/> action of the fluorescent tubes <pause dur="0.5"/> in the room <pause dur="0.6"/> on <pause dur="0.6"/> the tile surface <pause dur="0.8"/> is to degrade the bacterium <pause dur="0.3"/> the bacteria <pause dur="0.2"/> are actually killed <pause dur="0.6"/> by <pause dur="1.0"/> their location <pause dur="0.5"/> on the surface of the semiconductor <pause dur="0.3"/> because it's able to produce O-H radicals in the thin monolayer <pause dur="0.3"/> which then attack the bacteria <pause dur="0.4"/> so <pause dur="0.2"/> these tiles are are are are have been patented they're now being produced and they're being tried out in hospitals in the States <pause dur="0.4"/> you know <pause dur="0.3"/> the so they're self <pause dur="0.5"/> it's a kind of self-cleaning tile <pause dur="0.3"/> or self-sterilizing tile <pause dur="0.3"/> obviously if somebody <pause dur="0.5"/> puts a muddy <pause dur="0.3"/> muddy hand on the wall that's not going to <pause dur="0.5"/> influence things very much but <pause dur="0.4"/> it's the bacteria <pause dur="0.2"/> that you're interested in you want to <trunc>sterili</trunc> keep the hospital sterile <pause dur="0.3"/> these tiles are <trunc>s</trunc> autosterilizing <pause dur="0.4"/> and also in the States <pause dur="0.4"/> there are patents taken out on light pipes made of <pause dur="0.3"/> # very thin glass fibres <pause dur="0.3"/> coated with T-I-O-two <pause dur="0.2"/> and you can <pause dur="0.4"/> have these in a in the form of i think if you

can imagine a mop <pause dur="0.5"/> # <pause dur="0.2"/> with with a handle and a whole series of # <pause dur="0.5"/> # <pause dur="0.3"/> fibres at the end of it that you normally use for mopping <pause dur="0.3"/> well if you imagine those are glass fibres <pause dur="0.2"/> you could immerse that into a tank of # <pause dur="0.5"/> of toxic water <pause dur="0.6"/> and just rely on sunlight actually <pause dur="0.3"/> and you actually autoclean the water <pause dur="0.2"/> using a system like that so <pause dur="0.3"/> there are a lot there's a there's a lot of technology being developed <pause dur="0.6"/> it hasn't really hit the market place in a big way yet <pause dur="0.4"/> but i think watch this space five years down the line and you'll be very surprised <pause dur="0.8"/> okay <pause dur="0.2"/> has anyone got any questions anything <pause dur="0.5"/> that # <pause dur="0.6"/> that they <pause dur="0.3"/> didn't understand or would like me to go through again any points <pause dur="1.6"/> no okay well we'll <pause dur="0.4"/> we'll wrap it up there <pause dur="0.3"/> and i think # <pause dur="0.4"/> we'll i think tomorrow we got to start looking at the effects of # <pause dur="0.7"/> alpha rays beta particles on substances <pause dur="0.5"/> okay