Loading

Mega May PDF Sale - NOW ON! 25% Off Digital Certs & Diplomas Ends in : : :

Claim My Discount!

Module 1: Overview of Nanotechnology

Study Reminders
Support
Text Version

Set your study reminders

We will email you at these times to remind you to study.
  • Monday

    -

    7am

    +

    Tuesday

    -

    7am

    +

    Wednesday

    -

    7am

    +

    Thursday

    -

    7am

    +

    Friday

    -

    7am

    +

    Saturday

    -

    7am

    +

    Sunday

    -

    7am

    +

Welcome back to the course on nanotechnology applications in agriculture.So in this module exclusively we will be talking about the nanomaterial synthesis, nanomaterialclassification and the characterization tools which are being employed.So, as you are already aware, in the previous class we talked about the classification ofnanomaterials and in that just to have a brief recap about what we talked about.We talk about the shape and geometry based on which the nanoparticles are being classified,we talked about the chemical nature based on which they have been classified.(Refer slide time: 00:58)And we talked about nano cages, nano crystals, nano belts.(Refer slide time: 01:03)Nano fibre, nanoparticles, nanotubes, nano wires, quantum dots and nano composites.(Refer slide time: 01:11)And I gave exclusive examples highlighting how each one of these could be helpful andone thing which I missed out in many of these structures, are exceptionally helpful in developingnext generation of biosensors for agricultural applications.Because when we talk about precision farming, where we are talking about based on the soilassay, how precisely we have to apply the fertilizer in order to ensure a sustainablegrowth of the ecosystem.Then we need to test, we need to have small sensors or micro sensors which would be usedor utilised to detect the different contaminants in the soil.So one of the areas where tremendous amount of a stress has been put in precision farmingis developing nano based sensors for agricultural applications.So the next classification route what you have discuss was the chemical nature wherewe talked about the organic, inorganic and carbon based.And in the organic we talked about dendrimers, micelles, liposomes, ferritin and most ofthem are biodegradable and non-toxic and most of them have hollow pores and they could beused as nano capsules to delivery any kind of active ingredient or any kind of agrochemicalsat a specific site, not only that much of these organic nano capsules could be tailormadeto open up or close according to the electromagnetic radiation or any other form of radiation likeheat or some other source of energy.Similarly in the same line we have the inorganic nanomaterial which are mostly the aluminium,cadmium, cobalt, copper, silver, gold, iron, zinc, lead.So most of these metal-based are also used to deliver different forms of pesticides orthey could even at times could replace the pesticides in order to reduce the requirementsof pesticides.So we have talked about these different forms of inorganic ones.We talked about the metal sulphide, rare earth and metal oxide based once and then we talkedabout the carbon based on where we highlighted about fullerenes, grapheme, carbon nanotubes,carbon nano fibres, carbon dots, activated carbon, nano diamonds and all these kind ofother structures.So today what we will do we will pick up this part where we talk about broadly about thesynthesis of nanomaterials.Let us start the synthesis of nanomaterials in terms of the synthesis when we talk aboutthere are 3 broad classification of synthesis either it will be a physical synthesis orit will be a chemical synthesis or it will be a biological synthesis.Now there may be time where we may be using 2 different techniques may be we will be usingphysical and chemical physicochemical method of synthesis or chemicobiological methodsof synthesis or biophysical methods of synthesis.So or maybe we may use all the 3 physical, chemical, biological route of synthesis, asmore and more nano technology is advancing these watertight compartments of synthesisof nanomaterial is slowly kind of you know the gap or the clear cut demarcation is slowlygetting removed.They are almost now merging, but what is interesting to note here is that all these synthesis fallunder 2 different approach.(Refer slide time: 06:02)Whether it is a top down approach or it is a bottom up approach.So when we talk about a top-down approach so basic classification they could be classifiedinto 2 groups start different methods of synthesis of nanomaterials.So either it will be a top down approach or it will be a bottom up approach, when we talkabout a top-down approach, so essentially what we are talking about is we take a bulkmaterial, something like this, this is a bulk material which is filled with atoms whichare constituting the bulk material, now this bulk material has exposed surface area likethis, this is the exposed surface area you could see, now what we do is we take thisbulk materials and we break it down into say powder, so what we are getting is somethinglike this, it could be uniform or you can categorise them, then you can fine tune them,you can filter them something like this depending on how precise or how precision filters youare having.And based on that something like this, so depending on how finer you go, you decidethe size of the nanomaterial, say for example if each of the circle represents a singleatom, then we are talk about a single atom out here, we talk about 2 atoms, we talk about3 atom, 4 and 5.So now if you look at it the amount of surface which are available is for that particularvolume is this much.So if you realize as you are increasing the number of atoms your per unit surface to volumeratio is decreasing and if you are reducing the number of atoms your third unit surfaceto volume ratio is increasing.So the reactivity of so if you look at it as we go down with the size the reactivityis increasing in this order and the exposed surface area out here on the other side isdecreasing like this.So it is surface to volume, where out here it is the reactivity which is increasing.So this is a top-down approach where we take a bulk material, grind it by different techniquesand bring it to the atomic resolution.Whereas on the other hand if you follow back bottom up approach what you do here is youare already having small moieties like this in the form of salt, in the form of gels andwhatsoever.Now using you are having the atoms and the molecules at your disposal, you either someform of self-assembly either it maybe template-based or natural self-assembly or template wasteself-assembly or chemical self-assembly grammatical routes what you can follow here by virtueof which you are creating specific structures say you create structure like this, what youtalked about nano ribbons or you create structure like this.What we talked about cubes, like ribbon like structure, you can create particles like this,you can have different kind of dimension, different kind of shapes like this.So this is the other approach where from a small components you can find them the wayyou do it is you can find these particles you are allowing them to react while you arereacting, you add some kind of agents in between which will give them something some kind ofa capping agent what we call about which will give them some form of assistance to self-assemblein a certain way.So depending on the type of capping agent which is used in a very small concentrationas compared to the amount of nanoparticle, there is in a very very small concentration,but they help to separate out the particles in a way that suppose it is there is onceto introduced the capping agent out here, they will help toseparate out these particles in a certain way and it may be possible, you may receivesomething like this, something like this depending on what kind of capping agent you are using.And as a matter of fact based on the capping agent in a synthesis where all the parametersare kept constant just by addition of different kind of capping agent we can vary the geometryof the particle very extensively, fairly extensively you can change the whole geometry of the particlebecause the catching agent is just like not only it separates out the atom, it createsa finite distance between the atoms and it create a certain kind of unique bond dynamicsbetween the atoms.So this is essentially a bottom up approach of synthesis of nanoparticles, so where youreach here which is or here same way or you reach like this out here you reach out here,so these are the 2 broad ways and under these 2 broad with the top down and bottom up approachwhat you are having are the broad classification nanoparticle synthesis which is your physicalmethods, chemical methods and biological methods.(Refer slide time: 15:24)So when we talked about physical methods, so what we are essentially talk about is weare creating mechanical pressure or high energy radiationor thermal energy or electrical energy.These are the different routes we are following or these are the different forces which areemploying and what they essentially do these different forces, they causes material abrasion,one aspect they may cause melting, evaporation because of this physical forces or they mayhave been cause condensation.And this is how we generate nano structures, so what you are getting is in this physicaltechnique is most, I want to see completely but mostly employed for if you look back tothe previous slide we talked about mostly employed for top down approach.But that is not the complete fact, there may be a situation they could be used these physicalforces could be used for this kind of self-assembly process also in the assistant self-assembly.But mostly if you look at it the kind of physical forces we are talking about here are mechanical,pressure, high energy radiation, thermal energy, electrical energy.All could be used for both.So all these forces, so in other word when the physical forces are used for bottom upapproach in that case that will cause this may cause in that situation self-assemblyalso.When we are talking about bottom up approach, self-assembly leading to the formation ofnanostructure.So this is where we are talking about bottom up approach and this is where we are talkabout these kind of things happen in top down approach.So now what are the different physical tools which are, so this is how the process workseither there will be mechanical pressure, there will be high energy radiation or therewill be thermal energy or their electric energy or even this even could use magnetic field.It is possible that you can use magnetic field or the part of energy could be utilized toeither self-assemble for bringing about some of these top down approach.Now what are the different physical techniques, so this is the whole basis how it happens.(Refer slide time: 20:18)Now let us talk about the techniques the physical techniques which available.So one of the technique major technique is high energy ball milling, high energyball milling.So when you talk about highly ball milling so this is basically say for example supposeyou have 2 balls like this and we are moving at different directions.So this is where you are allowing your material, you know to grind you can control the speedof this.So this is a material something like this, you can control the speed of these spares,you can control the size, you can control the contact area between them.So you can do lot of manipulation but this is something like an energy ball milling,will talk later about the pictures of this how they really work let us enumerate at thistime what are the different techniques which are being used.Next in the line is pulse vapour deposition, we will talk later about the detail of thistechnique pulse vapour deposition.To one point you will realise in most of these physical techniques they are pretty cost intensivetechnique, the third one is laser pyrolysis, they are pyrolizing something using laserenergy, then you have flash, spray pyrolysis followed by electro spring, then you havemelt mixing.So at that is point we are just enumerating all the different techniques which are availablefor physical mode of generating nanomaterials and then we will talk individual about thesetechniques, what they signify and how these could be used and what are the cost involvedin it and what are the different kind of nanomaterials which may require this kind of pretty abrasiveand pretty cost intensive techniques, and all of them are fairly cost intensive technique.