Transition metal (TM) doped semiconductor materials are extensively employed for light harvesting and photocatalytic applications to increase the light absorption and charge mobility. The position and site occupancy of the dopant dictate the physical properties of these materials, particularly the recombination kinetics. Therefore, this work focuses on the parameters affecting dopant diffusion from the bulk to the surface, resulting in the spatial tailoring of dopant position for select applications. In this work, highly doped TiO2:Ni2+ (15 mol %) nanoparticles are synthesized via sol-gel chemistry. The drying and annealing of the aged sol are shown to affect the segregation of NiO onto the surface of TiO2 and resulting optical properties. The diffusion of the dopant onto the surface of TiO2 was observed to be a moisture driven phenomenon, which is studied using time resolved UV-Vis, Raman, and FTIR spectroscopy measurements. Furthermore, the effect of annealing rate on dopant segregation and crystallization is investigated by XRD and TGA/DSC studies. Preliminary XRD results show that rapid annealing of the TiO2:Ni powders form a doped anatase phase while slow annealing resulted in the formation of segregated anatase and NiO phases. Similar trend of dopant segregation was observed with other first row TM doped TiO2 powders upon slow annealing. The evolving local environment is probed via x-ray absorption spectroscopy (XAS) and High-Resolution TEM to elucidate the difference in the dopant local environment with photocatalytic performance. This ability to incorporate higher dopant concentrations while engineering the dopant position in nanostructures will assist in the development of improved optoelectrical properties and photoconversion efficiencies in solar cells, photocatalytic devices, etc.

Engineering the position of transition metal dopant in solid hosts for enhanced photocatalytic properties

256th National Meeting (2018)

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