SYNTHESIS OF NANOHYBRIDS, NANODOTS AND CORE-SHELL NANOMATERIALS AND THEIR APPLICATIONS

The research embodied in the present thesis entitled “SYNTHESIS OF NANOHYBRIDS, NANODOTS AND CORE-SHELL NANOMATERIALS AND THEIR APPLICATIONS” deals with the synthesis and characterization of core-shell nanoparticles and various nanohybrid systems and their various applications.Chapter 1 is the general introduction and it provides the comprehensive literature survey on nanomaterials including metal nanoparticles/nanoclusters, coreshell nanoparticles, nanohybrid gels with carbon-based nanomaterials and noble metal nanoparticles/nanoclusters. This chapter highlights structural and morphological features of nanohybrid gels and their different applications. This chapter also consists of different classes of carbon-based nanohybrid gels, their synthetic procedure and various applications. Chapter 2 describes the reagents used and experimental procedures, carried out to perform the entire work embodied in this thesis. Chapter 3 describes the synthesis of Ag@Au core-shell nanoparticles by using a fluorescent dipeptide β-Ala-Trp in water medium and at a room temperature without using any external reducing and stabilising agents. The shell thickness of Au can also vary from 1:1 to 1:2 by changing the Au (III) precursor keeping the other conditions same. The optical property of the core-shell nanoparticles varies with the shell thickness. Interestingly, these core-shell nanoparticles exhibit good catalytic activity for the reduction of nitrophenols to aminophenols and nitroanilines to aminoanilines. A series of nitrophenol and nitroaniline compounds have been taken as substrates for reduction. Moreover, this core–shell nanoparticle displays remarkable difference in catalytic property for reduction of nitro group with variation of shell thickness. This catalyst (Ag@Au core-shell nanoparticle) can also be recycled for several times indicating its reusability.Chapter 4 describes the synthesis of graphene oxide (GO)-based hydrogels by using vitamin B2/B12 and vitamin C (ascorbic acid) in water (at neutral pH value). These gel-based soft materials have been used to synthesize various metal nanoparticles, including Au, Ag, and Pd nanoparticles, as well as nanoparticle-containing reduced graphene oxide (RGO)-based nanohybrid systems. This result indicates that GO-based gels can be used as versatile reactors for the synthesis of different nanomaterials and hybrid systems on the nanoscale. Moreover, the RGO-based nanohybrid hydrogel with Pd nanoparticles was used as an efficient catalyst for C-C bond-formation reactions with good yields and showed high recyclability in Suzuki–Miyaura coupling reactions. Chapter 5 provides a vivid description the preparation of trihybrid gel by incorporating graphene oxide (GO) and in situ synthesized gold nanoparticles (AuNPs) into the pyrene conjugated single amino acid-based native gel matrix. The morphology of this system indicates the presence of three distinctly different nanostructures: nanofibers, nanosheets, and nanoparticles. Rheological studies reveal that stiffness of the gel increases with the inclusion of GO into the native gel and stiffness of this hybrid gel is increased further due to the incorporation of gold nanoparticles into the GO containing hybrid hydrogel in a trihybrid system. Moreover, catalytic property of AuNPs can be tuned from only AuNPs containing hybrid gel to trihybrid gel. The catalytic efficiency of this trihybrid system is enhanced relative to that of AuNPs in a dihybrid system. Chapter 6 describes the in situ preparation of gel based various nanohybrid systems by using sunlight. A naturally occurring amino acid L-phenylalanine derivative has formed a hydrogel with graphene oxide (GO)/reduced graphene oxide (rGO) at physiological pH and this hydrogel has been used in presence of silver ions and diffuse sunlight to form initially a tri-nanohybrid system consisting of six atom silver nanoclusters, nanosheets and nanofibers. Interestingly, a time-dependent morphological transformation occurs in this nanohybrid system to form one tri-nanohybrid to another tri-nanohybrid with the appearance of a novel, nanoscopic intermediate, tetrananohybrid system consisting of four distinctly different nanomaterials (nanofibers, nanosheets, nanosphere and nanoparticles). UV-Vis and fluorescence spectroscopic analyses, transmission electron microscopic, X-ray photo electron spectroscopic and MALDI-TOF mass spectral analyses with time have been applied to characterize these morphological transformations in gel based nanohybrids. Interestingly, one of thesenanohybrid systems (silver nanoparticles containing rGO based hydrogel) show catalytic property in reducing nitroarenes to aminoarenes and the catalytic efficiency is modulated by changing the size of silver nanoparticles with time in diffuse sunlight. The mechanism for different catalytic activities for different hybrids with varying size of silver nanoparticles has also been deciphered. Chapter 7 describes a new strategy of making peptide functionalized carbon nanodots and these carbon nanodots were used as a template for making of ruthenium nanodots from a ruthenium salt in the presence of a reducing agent, sodium borohydride in water medium. These functionalized carbon nanodots exhibit a blue emission with a high quantum yield (69.8%). Various techniques including UV-Vis, fluorescence, FTIR, X-ray photo electronic (XPS), Raman and X-ray diffraction and transmission electron microscopic (TEM) analyses have been used to characterize carbon nanodots and hybrid nanodots. Moreover, this nanohybrid acts as a potential catalyst for the reduction of organic azides to the corresponding amines in aqueous medium with high yield, good chemoselectivity and remarkable reuability. Each chapter (chapter 3 to 7) begins with a short ‘Introduction’ followed by ‘Experimental Section’, ‘Results and Discussion’ and ‘Conclusion’. For Convenience,Research was carried out under the supervision of Prof. A. Banerjee of the Biological Chemistry division under SBS [School of Biological Sciences]Research was conducted under CSIR fellowshi