Nanoparticles are fine particles having diameter in the range of 1 nanometer to 100 nanometer . Metal nanoparticles are very special because of their surface porperties ,they are simply very large molecules .The synthesis and stabilization of large structurally -well-defined metal clusters requires the presence of surface bound moieties that are now referred as”LIGANDS” as opposed to “ADSORBATES”.We can consider metal nanoparticle as ATOMIC CLUSTER . Nanoparticles have fascinating optical and electronic properties so they have wide applications in fields like nanoelectronics and heterogeneous catalysis .Metal nanoparticles synthesis has problem of instability of particles due to themodynamic , electronic repulsion and many other factors causing FORMATION OF AGGLOMERATES OF METAL IONS. Metal nanoparticles are widely used in catalysis and electrocatalysis. Metal nanoparticles can lower time of reaction ,decrease cost of catalyst and improve effectiveness and efficiency of catalytic process. There are two main challenges in this area of catalysis ,the first is developement methods for stabilizing nanoclusters by eliminating aggregation without blocking most of active sites on cluster surfaces or otherwise reducing catalytic efficiency , the second key challenge involves controlling cluster size ,size distribution and perhaps even particle shape. Metal nanoparticles synthesis is carried on support called as” TEMPLETE” on which metal clusters get adsorbed . Today scientist are engaged in finding out new eco friendly green materials which may be served as templetes to get rid of costly synthetic templetes such as “DENDRIMERS “.Dendrimers are 3 DIAMENSIONAL STRUCTURES . nanoparticles synthesis using dendrimers involves mixing of metal ion and dendrimer and subsequent reduction of metal ion (shown in figure below , borohydride ion is used as reducing agent)
GREEN TEMPLETES FOR NANOPARTICLES SYNTHESIS :
Green materials i.e biomaterials which are biodegradable prove beneficial source for application in nanoparticles synthesis at industrial level . From the stone age to the scientific era of today man is emulating the nature for finding solutions to many problems . “TEMPLETE ” for synthesis should possess porous structure and active sites for binding metal ions cluster . The structure and properties of metal nanoparticles are found to be particularly useful when these materials have regular or patterned structure.Living organisms show an amazing hierarchical arrangement of their organic and inorganic components .Unique pattern from nanoscale to macroscopic scales can be seen in wood , cork , bone , ivory , sea shells ,etc .
CELLULOSE AND BOVINE BONE AS TEMPLETE FOR NANOPARTICLES SYNTHESIS :
CELLULOSE IS NATURAL CARBOHYDRATE RICH IN OXYGEN CONTAINING ANHYDROGLUCOSE UNITS LINKED BY HYDROGEN BOND.NATURAL CELLULOSE FIBERS HAVE A POROUS STRUCTURE ,COMPOSED OF 10-30 nm MICROFIBERS WIDELY CONNECTED IN ALL 3-D .THIS FIBROUS MORPHOLGY CAN PROVIDE A UNIQUE SCENARIO FOR PARTICLE SYNTHESIS , ALLOWING IMPROVED ACCESS OF MOLECULES INCORPORATED TO NANOPOROUS FILMS .THIS UNIQUE ARCHITECTURE ALLOWS FOR SIZE AND SPACE DISTRIBUTION CONTROL OF NANOPARTICLES BY ADJUSTING PARAMETERS SUCH AS CONCENTRATION OF METAL IONS AND REDUCTION TIME.THESE NANPOROUS STRUCTURES ALONG WITH HIGH DENSITY OF OXYGEN IN THE CELLULOSE FIBERS COMBINE TO CREATE HIGHLY EFFECTIVE NANO REACTORS. NANOPORES ARE ESSENTIAL FOR CONTROLLED DIFFUSION OF METAL IONS AND REDUCING AGENTS AND OXYGEN AND HYDROXYL GROUPS DO HELP IN STABILIZATION OF RESULTING METAL NANOPARTICLES.
BONE IS A BIOMATERIAL COMPOSED MAINLY OF CALCIUM PHOSPHATE ALONG WITH DIFFERENT ANIONS SUCH AS FLUORIDE,CHLORIDE,HYDROXYL,ETC. HYDROXYAPATITE CAN BE FOUND MAINLY IN BONES AND TEETH WHICH HAS REGULAR HEXAGONAL CRYSTAL STRUCTURE AND PREDICTABLE SPACING GROUPS. BIOLOGICAL APATITES POSSESS STRUCTURAL IMPERFECTIONS DUE TO INCORPORATION OF SODIUM,POTASSIUM,MAGNESIUM,CHLORIDE AND FLUORIDE IONS.
BOVINE BONES ARE COMPOSED MAINLY OF HYDROXYAPATITE ALONG WITH COLLAGEN AND PROTEIN IN LESS EXTENT. POROUS STRUCTURE OF BOVINE BONE CAN BE USED AS NANO REACTOR FOR CONTROLLED SYNTHESIS OF PARTICLES WITH DEFINED STRUCTURES. HIGH DENSITY OF ELECTRO NEGATIVE LINKAGES DUE TO HYDROXYL IONS INSIDE CREVICES OF BONES MAY CONTROL DIFFUSIONAL GROWTH AND FORCE NEWLY FORMED NANOPARTICLES TO AGGREGATE ALONG THE EDGES OF HEXAGONAL SURFACE OF THE BONE. THE RENOWNED APPLICATION OF BOVINE BONE FOR SYNTHESIS OF PLATINUM(Pt) AND SILVER (Ag) NANOPARTICLES IS APPRECIABLE. FOR PLATINUM PARTICLES REDUCTION OF SALT PLATIUM (IV)CHLORIDE WITH SODIUM BOROHYDRIDE AND IN CASE OF SILVER PARTICLES REDUCTION OF SILVER NITRATE WITH SODIUM BOROHYDRIDE IS DONE ON BONE SURFACE . THE USE OF NATURAL RENEWABLE, ABUNDANT AND LOW COST MATERIAL SUCH AS BONE FOR CONTROLLED SYNTHESIS OF METAL NANOPARTICLES AT ROOM TEMPERATURE AND USE OF WATER AS SOLVENT OPEN AN INTERESTING AREA FOR CHEMICAL SYNTHESIS WITH GREEN AND SUSTAINABLE APPROACH.