Tailoring the oxidation state of cobalt through halide functionality in sol-gel silica

The functionality or oxidation state of cobalt within a silica matrix can be tailored through the use of cationic surfactants and their halide counter ions during the sol-gel synthesis. Simply by adding surfactant we could significantly increase the amount of cobalt existing as Co3O4 within the silica from 44% to 77%, without varying the cobalt precursor concentration. However, once the surfactant to cobalt ratio exceeded 1, further addition resulted in an inhibitory mechanism whereby the altered pyrolysis of the surfactant decreased Co3O4 production. These findings have significant implications for the production of cobalt/silica composites where maximizing the functional Co3O4 phase remains the goal for a broad range of catalytic, sensing and materials applications

Visible-light activation of Ti02 photocatalysts: advances in theory and experiments

The remarkable achievement by Fujishima and Honda (1972) in the photo-electrochemical water splitting\ud results in the extensive use of TiO2 nanomaterials for environmental purification and energy\ud storage/conversion applications. Though there are many advantages for the TiO2 compared to other\ud semiconductor photocatalysts, its band gap of 3.2 eV restrains application to the UV-region of the electromagnetic\ud spectrum ( \ud ≤\ud 387.5 nm). As a result, development of visible-light active titanium dioxide\ud is one of the key challenges in the field of semiconductor photocatalysis. In this review, advances in\ud the strategies for the visible light activation, origin of visible-light activity, and electronic structure of\ud various visible-light active TiO2 photocatalysts are discussed in detail. It has also been shown that if\ud appropriate models are used, the theoretical insights can successfully be employed to develop novel\ud catalysts to enhance the photocatalytic performance in the visible region. Recent developments in theory\ud and experiments in visible-light induced water splitting, degradation of environmental pollutants,\ud water and air purification and antibacterial applications are also reviewed. Various strategies to identify\ud appropriate dopants for improved visible-light absorption and electron–hole separation to enhance the\ud photocatalytic activity are discussed in detail, and a number of recommendations are also presented