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So welcome back to the lecture series on application of nanotechnology in agriculture.So in the previous class I was talking to you about manganese cluster, so I showed youthe scheme of the photosynthesis and I told you that you now there are 2 photosystem forsystem A for system B and both the photosystem receives light and both the photosystem ejectsout electron and while ejecting out electron for system A as well as for system B getsoxidized because you are giving an electron.This electron passes through a cascade of proteins which are sitting in photosyntheticassembly or in the chloroplast and if you look at that nano architecture of chloroplastthis is very interesting, this something like this thylakoid membrane and these are allconnected structure and these are the kind of inspiration for the next generation nanotechnology,something like this and whatever reactions I am showing here are all happening at onedot out here.The dots I am doing now, this is where these kind of reactions are happening and the dimensionswhat we are talking about if a cell is of 30 micron, this we are talking about somethinglike want 1 to 2 micron the whole structures automatically these are nano machines, thesesmall ones are those small, small nano machines where all these reactions re happening.So the electron then cascade through these different proteins standing at different reductionpotential if you look on your left hand side further highlighting it, now through thiscascade of oxidation reduction finally for system A out here which was oxidised got reducedand brought back to the ground state, but still for system B is an excited state.So for system B gets back to its ground state because of electron which is donated by themanganese cluster which strips the water it photo catalytically kind of trap the watermolecule to break it down.Now in nature if you look at it all the processes which nature has been following are energyintensive processes of photo catalysis.Photo catalysis is such a powerful technique if it is successful then when these kind ofdesalination and if recollect all these could really change the way we are progressing.So now talking about photo catalysis here, this emulating manganese cluster.This is a dream the day mankind will be emulating the manganese cluster, this will be the Dday for energy and environment and possibly from this day on mankind will learn one ofthe cheapest or cheap on the right word say one of the most elegant ways by which naturedoes its own catalysis.Now where we are currently, the lot of research happening on understanding the manganese clusterat atomic level it will trying to crystalize this whole assembly.But nano world currently is using one of the molecule which they are using which triodesinspiration from here is titanium oxide, we have talked about this titanium oxide, todayI will talk little bit more about titanium oxide.TiO2, so titanium oxide is a photo catalyst and if I go back in the historical perspectiveof titanium oxide then Fujishima that 2 guys Fujishima and Honda in 1972 demonstrated thatthe first one to demonstrate that titanium oxide which is semiconductor TiO2 semiconductorcould split water into hydrogen and oxygen in a photo electrochemical cell or in a yeahphoto electrochemical cell.And if you essentially this work has triggered the development of semiconductor based photocatalysis for a wide range of environmental and energy application.So if you look at it, so semiconductor which whenever we talk about semiconductor we talkabout electronics right and this is what I was trying to highlight in last few lecturesif you guys go back if you see this, this was what was I was trying to highlight multifunction,so it has electronics applications titanium oxide.It has to be used for water purification and maybe it can be used for waste management,use for energy.So this is when I say a material should have multifunctionality this is exactly what Imeant, that this is how multifunctionality of material could be decided.Now if I look at titanium oxide how it does and what are the challenges which have beenmade.So I gave you this example of visible light doing this water splitting.And this is all visible light of the spectrum, now titanium oxide has a band gap of approximately3.2 will come to tha.So one of the aspects what titanium oxide what I wish to highlight is that titaniumoxide in nature remains in 3 polymorphs.It has a anatase, retile and broukite phases, anatase form so these are called the polymorphsof titanium oxide anatase, retile, and broukite.And all 3 polymorphs can be readily synthesized in laboratory and typically the metastableanatase and broukite will transform to the thermodynamically stable retile upon calcinationat temperature exceeding 600 degree centigrade.So you realise that much of these when you are synthesizing they all go for a prettyhigh-temperature, similarly if you look at it in all the 3 form titanium is existingin Ti4+ form, so the valence is 4+ atoms and are coordinated to 6 oxygen atom 4, 5, 6 andoxygen atoms are sitting this.So essentially what we have is TiO6, it is an octahedral geometry it follows whereasanatase is made up of converters sharing octahedral which forms 001 planes.You do not have to go to the plains and it gets the tetragonal structure and titaniumoxide is typically is an n type semiconductor and this n type semiconductor due to its oxygendeficiency, locks in deficiency gives hit a entire features and it is a band gap of(()) (10:11) of 3.2 electron volt, for anatase it is, for anatase and for retile it is 3and 3.24 broukite.So it is around they can 3 to 3.2 electron volt, all the 3 polymers are standing at thatand all of them are as I mention all of them are n type semiconductors and Tio2 is mostwidely used investigated photo catalyse due to its photo toxicity, low cost, low toxicityand good chemical and thermal stability.So this is another aspect which I was highlighting Tio2 for photo catalysis.So these are the features which are important.It is pretty high photo activity one aspect, the second aspect it is pretty low cost, soin another word it is economical you have something easily manufacturable, it has lowtoxicity, so handle able and good thermal and chemical stability.These are the 4 features which made this a very popular material for all sorts of photocatalysis and water splitting and water purification.In the last few decades there have been several exciting breakthroughs with respect to titaniumdioxide, the major advance was in 1972 which I mentioned when Fujishima and Honda reportedthe photo electrochemical splitting of water using titanium oxide anode and a platinumcounter cathode.So basically Fujishima and Honda story was something like this where you have this anodeand you have cathode.So what essential you had titanium dioxide electrochemical cell has titanium dioxideas anode and platinum as cathode.This is your anode, this is your cathode, so followed by that titanium dioxide photoelectrolysis was first used for remediation of environmental pollution.So see look at it for the same material in 1976 by Frank and Bard.This was another major breakthrough, so water splitting is one of the aspect titanium dioxidedoes.The second thing is pollution remediation, so basically titanium oxides photo catalysiswas utilised for remediation of environmental pollution in 1977.So if you look at they are not very old 1977 by 2 guys called Frank and Bard, they reportedthat the reduction of cyanide Cn- in water, Frank and Bard so water+Cn-, so this Cn- isgetting reduced in the presence of this whole things happening.Tio2 and TiO2 is getting activated by flight, so that lead to a dramatic increase in theresearch in this area because of the potential for water and air purification through utilisationof free solar energy.So your major source of solar energy is free, other significant breakthrough included Wangin 1997 who reported that titanium oxide surfaces with excellent anti fogging and self-cleaningabilities.So this was another breakthrough, so when we talk about the again I will highlight thisaspect multifunctional, sustainable green material multifunctional.This is the word which is very important for you guys to understand that this is wherethe future lies something which has multiple application.So similarly when we talk about the next breakthrough, the next breakthrough was 1997 where thiswas shown potential water and air purification followed by Wang Etal who showed that titaniumoxide surface has anti fogging.So it means you can use it in the car anti fogging properties, self-cleaning abilities,next thing what it has an attributed to the super hydrophilicproperties of photo excited TiO2 surfaces.So titanium oxide when it is photo excited thatis super hydrophilic.Now photo excited TiO2 surfaces and use of nano titanium dioxide is an efficient dyesensitized solar cell.In 1991 there was another report and this came from Grätzel he is in Switzerland.Grätzel cell whose name this is the dye sensitized cell call Grätzel cells or this is reportedby Grätzel and O’ Regan that TiO2 is because when light is falling it is generating anelectron and this electron could be now incorporated into a dye sensitized solar cell, will talkabout this will get more about dye-sensitized solarcell and what these are.So these are the areas where lot of research is happening all over the world.So if you look at it same titanium dioxide it is being usedfor photo electrochemical cell to split water, so technically we can use this for hydrogenenergy, this could be used as semiconductor material of course there are issues whichwill come very soon whilewewill talk about mechanism of action for pollution remediation, for Grätzel celland for anti-fogging and self-cleaning.So the same material having multiple function, this is where the future lies, this is wheremuch of these work are happening.So inthe next class wewill talk about brief mechanism of titanium dioxide and how it execute this process, thankyou.