SYNTHESIS AND CHARACTERIZATION OF METAL-SEMICONDUCTOR AND METAL-OXIDE POROUS MATERIALS
Porous materials are of scientific and technological importance as they possess unique ability to interact with atoms, ions and molecules not only on their surface but throughout their large interior network. Aerogels are high surface area and low density porous materials obtained via supercritical drying of wet gels synthesized using traditional sol-gel chemistry. Aerogels consist of nanoparticle building blocks connected to form an open highly porous network. Aerogels have been utilized in wide variety of applications such as cosmic dust collection, thermal and acoustic insulation, as electrodes in batteries and capacitors, storage of nuclear waste, heterogeneous catalysis, and bio-sensing. In this dissertation, two distinct types of aerogels, metal-semiconductor and metal-oxide are presented. The porous unsupported metal-semiconductor (CdS–Ag and CdS-Au) luminescent aerogels were synthesized using a nanoparticle condensation strategy. It was observed that the amount of metal (Ag, Au) added significantly affected the rate of surface oxidation of thiol and the gelation kinetics. Also, the concentration of metal added had a huge impact on the strength, microstructure and porosity of the resultant metal-semiconductor aerogels. Such solid state CdS–Ag and CdS-Au aerogels could have a significant impact in several areas of materials science including future photonic devices and optical switches. For metal-oxide aerogels, the focus of our research was to investigate divalent transition metal ion precursors to synthesize pure and composite metal oxide materials using an epoxide addition method. Two different types of metal oxide (cobalt oxide and nickel oxide) aerogels were synthesized using the epoxide addition method. The effect of addition of single-walled carbon nanotubes (SWNT) and alumina as supports to cobalt oxide aerogels and nickel oxide aerogels respectively, are discussed. Successful synthesis of pure a Co-aerogel and Co-SWCNT composite aerogel was done. The presence of the SWCNT in the Co-aerogel induced the aerogel to have a ribbon-like morphology, which was clearly observed by SEM. This change in internal structure of the Co-SWCNT aerogel also resulted in the aerogel becoming less aggregated upon annealing. In addition, monolithic NiO/Al aerogels were successfully synthesized using epoxide addition method. The structure and morphology of the NiO/Al aerogels was found to depend on the metal ratio used to form the gel. The nickel (II) oxide materials exhibited high surface areas and porosities, making them attractive catalyst materials. In chapter 4, preliminary work using significantly different materials than the previous sections was presented. However, in keeping with the theme, the utility of semiconductor nanoparticles in sensing applications such as the detection of latent fingerprints and heme-proteins are discussed.