COMPUTATIONAL AND EXPERIMENTAL STUDIES OF CO₂ PHOTOREDUCTION ON TITANIA

My research focuses on the conversion of carbon dioxide (CO₂) to useful organic compounds like methane using light energy and water. It has become evident in recent times that economic means of CO₂ (i.e. carbon) management and alternate energy sources are required by our society in order to maintain a high standard of living without detrimental consequences to the environment. Solar photoconversion of CO₂ to produce fuels has the potential to not only be a mechanism to store intermittent solar energy but also recycle CO₂ while decreasing the use of fossil fuels.  The science of CO₂ activation at metal oxide surfaces also has implications for future human space exploration and the abiotic origins of life. My research comprises of computational and experimental components. The computational studies aim at understanding the intermediates and energetics of various reactions involved in the photoconversion of CO₂ in greater detail. Knowledge of these intermediate steps will enable us to design materials that catalyze this photoconversion process. The experimental studies aim at synthesis, characterization and testing of rare earth doped titania catalysts. These catalysts have been shown to perform well in other photoreactions. Our modeling results have shown that carbonate radicals can form at titania TiO₂ surfaces during the course of the photoreaction. This is the first computational study that has identified carbonate radicals on irradiated titania surfaces. Our preliminary photoconversion experiments have shown that lanthanum doped TiO₂ converts CO₂ to methane (CH₄) under UV-B radiation.

 The processes involved in CO₂ photoreduction are as shown in the figure to the left.:  A semiconductor like TiO₂, under band gap irradiation, produces electron hole pairs. A majority of these charge carriers recombine on a very fast time scale. The remainder can be utilized to do useful work, in this case, the conversion of  light energy into chemical energy. The holes can react with water, oxidizing it and producing oxygen. The electrons react with CO₂ producing CH₄ in a series of reactions. Our computational and experimental studies aim at understanding the various reactions that happen during CO₂ photoconversion to CH₄.