Video 1: Stoichiometric Defect and Chemosynthesis
Welcome back to the course on nanotechnology and its role in agriculture, so the previousclass we started with iron pyrite and we talked about the different role of iron pyrite forlast 100 years or little more than 100 years and if you recollect.So, we talked about the ubiquitousness of iron pyrite, so it is kind of available mostof the places and it has been used for or in the attempts are being made to use it asa photovoltaic material and in India it has been largely used during 1970s, 75, 78 toreclaim sodic soil or other alkaline soil because once it is gets into the soil in bulkamount it make the soil pH like lower, so from an alkaline soil you can bring in downto a neutral pH by adding iron pyrite.And it has been observed in such soil it has been let to a more nitrogen absorption bythe crops, especially by the rice crops.Whereas when it has been used directly into normal soil it has actually made soil acidic.So, I have to really handle for any kind of for reclamation it has to be handled withextreme care, apart from it, it has been observed that these kinds of a material have somethingcalled stoichiometric defect what is the stoichiometric defect is that is where we ended in last class.So, this is where we are going to talk about a stoichiometric defect, so whenever we talkabout FeS2 the assumption or understanding is that there is 1 atom of Fe, and 2 atomsof sulfur.Now in real life that is brought what happens what essentially happens is out of say 10million molecules of FeS2.The surface durably molecules which or maybe slightly into the core there will be moleculewhich does not balanced it out like all the time the ratio 1:2 of iron to sulfur is notmaintained.There are molecules which may not have 1 sulfur maybe instead of FeS2 in the cluster theywill be some FeS.So likewise, it has been observed that the final ratio what it turns out be 2-X and thisX could be 0.5, 0.2 or it could be 0.1 whatever you know that is the material.The point is not that every iron atom has bonded to 2 sulfur.There will be iron atom which maybe divide of it and these kinds of defects are calledstoichiometric defect.And stoichiometric defect plays a critical role in the surface property of these molecules.And this is what is very very critical for you to understand that iron pyrite comes withset of stoichiometric defects and that is why lot of it is application in electronicskind of got hampered because of it.But there is a positive sight to it and will come later into that what is the positivesight of having stoichiometric defect.And stoichiometric defect cold be utilized for multitude of applications in agriculture,organic waste disposal and maybe even in water purification thismay come pretty handy especially when you have to remove organic residues.But at this stage just understand the fundamental concept of stoichiometric defect.And this is stoichiometric defect could be exploited at the nano level at a much easieror with lot of more ease.Now previous class I talked about the presence of iron pyrite in the hydrothermal vents.So, hydrothermal vents, so as of now talk while talking about hydrothermal vent if weunderstand there are 2 ways life has formed.The original understanding was that life has evolved on the floor of earth in the oceanfrom the water and the process which has govern much of it is sun.The energy the major source of energy sun and living system in the form of plants havetrap solar energy in the form of photosynthesis, photo means light and synthesis of food usinglight energy synthesis of food or in other words synthesis of glucose molecule.So, solar energy driven synthesis of food by the plants or carbohydratesand these carbohydrates are the plants are consumed by herbivores, herbivores consumedby carnivores or omnivores and then again, they become part of the organic matter andthe simple cycle continued what we call as food chain.Now the first the only thing which is known about formation of life in terms of survivalof life in terms of photosynthesis.But the storyline changed some I would say 30, 40 years back almost 4 decades back nowduring 19 late 70s it was observed deep inside the ocean fairly deep in different Atlanticand Pacific rims as these diverse were going down almost close to the float or sea floor.They observe something which they observe lot of smoke coming out from deep inside theocean and this is where there is absolutely no sunlight.And around these smokers they name this is smokers are white and black smokers, aroundthese smoking chimneys in and around it was filled with something strange life forms.And these were growing, these were bubbling all over the place very very strange lifeforms another question which absolutely boggled a scientist is what is the source of energy,energy source.Because all our textbooks up to that point was relying on the fact that sun is the onlysource of energy.But then this is a very different situation here there is no sun, no sun rays really canpenetrate through this yet this place is filled with life.So, who is giving energy to them and it look this whole area is rich in different kindof transition metal, metal sulfides.And the one which is in such amount is pyrite, so this pyrite the source of energy or isit playing a critical role.So stoichiometric defect the first fact I gave you.The second fact what I am holding out here after telling you is the metal sulfides inhydrothermal vents, we will pull all these threads together soon.So, the third in the same line I am going to put across is.If you look at the cell membrane all of we have seen the cell membrane any cell membraneplant cell membrane, animal cell membrane we will observe something very interesting.If these are the lipid bi-layers which is forming the cell membranethen you will see lot of proteins which are present there like this, several proteins.So just to give your idea, so this is what you are looking at, this is a cell and thebox is the one which I am amplifying out here.And this is the bilipid membrane here is the magnification of bilipid membrane with polarhead groupsand polar head groups are here also in both inside and outside.And with a hydrophobic tail and here you are having these areas of membrane protein whichare setting there.There could be channels, there could be pore and series of them are there especially inthe chloroplast, mitochondria.And they in their membrane which are also lipid bilayer membrane, there are lot of ironsulfur clusters.As if and these iron sulfur cluster are involved in electron transfer whether it is mitochondria,whether it is in chloroplast or it is mitochondria.Now if you look at it, it seems like life has evolved around iron and sulfur.In the strangest places if you look at its hydrothermal vent which is one of the strangestplaces where life has evolved.And there was a name which was given to the life form which evolves there which is notdependent on light.So, independent of light there is no light and these kind of life forms which evolvethere is called the process is called chemo-synthesis or the energy called life form to surviveis derive from some kind of a chemical, some kind of a breaking of the chemical.
Video 2: Synthesizing Nano-Pyrites
So, clue number 1 what I gave you is stoichiometric defect 1.Second the life form in the hydrothermal vents tune and this part is filled with they appearto what you observed here as I told you is nano FeS2 or nano pyrite.And the third thing is most of our current date cells have lot of this iron sulfur clusterswhich are involved in short- and long-range electron transport.Now the remark we are making looks like iron sulfur complexes or iron sulfur compoundsplays a critical role in our day today life.Now getting in spite by this during 2010, 2011 we attempted a very simple experimentsand that is what we are going to share now.So natural pyrite comes the bulk natural pyrites comes with the contaminants of lot of differentother atoms because it has profound binding with the sulfur atoms and you will see cadmium,arsenic and all these kinds of impurities.So, what we did we synthesize nano pyrites.So, how we synthesize as I told you there were 3 things which you would follow, we willtalk about the synthesis, we will talk about characterization and in that process, we willfigure out what is the shape and the dynamics of the molecule.So, we synthesize nano pyrite by a simple way may its poly sulfur and will I will giveyou the references in 1 tube we made a lot of poly sulfur molecule, poly sulfur meansS2, S4, S6 likewise.It is a mixture which is called polysulfide, made a lot of polysulfides in 1 vessel andin the other vessel we have iron salt to react and this reaction happen in an inert environmentwhere we allow poly sulfide to react with iron salt.And this is one of the process of bottom up approachof synthesizing FeS2 nanoparticles and in an inert environment organized environmentthis reaction happens.The reason to have an organized environment is otherwise iron will get oxidized to Fe3state.So, when we talk about FeS2 or FeS these are the moieties where iron is in oxidation stateof +2.Otherwise if you in any iron compounds the floor of earth they all are oxidized to Fe2to Fe3 in the presence of oxygen.And what we call as which relates to the formation of rusting.So, here we are having certain iron on the rust of earth or in the earth floor whichremain which maintain their oxidation state in 2.And same here most of the iron sulfur cluster or all iron sulfur clusters iron is in anoxidation state of +2, they are in the ferrous state.Same out here iron is in oxidation state of +2 with it is hydro thermal vent.Now we I will provide the detail layout of how we made the iron sulfide.So, but this is the overall synthesis of iron sulfide by end bottom of approach where ina small round bottom flask you created an organized environment, you created and –oxygenenvironment and at moderately low temperature of around 40 degree centigrade to 80 degreecentigrade you synthesize iron sulfide.Next what we try, we thought that could this agent be used as a seed stimulant becauseif iron sulfur has been involved in the evolution of all the survival of life could it do somevery interesting stuff to the seeds, it is a very out of box and just let us give ita shot.So, what we did is instead of because this was clear that you cannot really apply thisto the field because it may lead to acidity and all sorts of other problem.But seed treatment if you recollect in the very beginning when you started of yes seedtreatment or seed pretreatment agent.So, this is where we are starting to do a seed pretreatment.So, what you do you take a vessel you have all your seeds here and you put water andthen and on that you add a finite amount of FeS2 nano FeS2, nano FeS2 does not dissolvein water.So, what its forms is an aqueous suspension, so what will you see is if you really sonicatedit a whole lot you will see suspensions sizes may even go for the smaller but there willbe suspensions all over the place.And to start off with some of our initial experiments where with chick pea, spinach,rice to see what is the effect of nano FeS2 as a seed treatment agent.So, we will continue the story from here what we observe and what is the research whichhave undergone since we say 2011 till 2018 when I am delivering this course on differentcrops are effect of a nanomaterial as a seed priming or as a seed treatment agent, thank you.
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