Experimental and modelling studies on CeO2-based photocatalysts/catalysts

CeO2 has excellent catalytic and photocatalytic characteristics owing to its ready redox and semiconducting properties. CeO2 nanoparticles of different morphologies exhibit characteristic properties because the specific, exposed, low-index surfaces vary in crystallographic and electronic structures. The present work reports an investigation of the physical, chemical, and electronic properties of CeO2. Integration of (1) the precipitation and hydrothermal growth of CeO2 nanoparticles of octahedral, rod-like, and cubic morphologies with (2) density functional theory (DFT) simulations has elucidated the morphology-controlled growth mechanism. Consideration of the defects on the surfaces of the different morphologies indicates that the oxygen vacancy concentrations associated with the exposed surfaces are responsible for the morphology-dependent photocatalytic properties. By normalising the surface areas, the photocatalytic performances of the (100), (110), and (111) planes can be quantified. Since hydrogen production by methanol dissociation is a promising approach to replace fossil fuels, DFT simulations of methanol adsorption on defect-free surfaces of CeO2 were done in order to examine the catalytic properties. It was found that methanol is always dissociated spontaneously by the (100) plane while dissociation on the (110) plane is site-selective and no spontaneous dissociation occurs on the (111) plane. The factor dominating the performances was determined to be the degree of undercoordination of atoms on the three low-index planes. The potential for hydrogen production by water splitting was explored by DFT simulations of doping by all ten 3d transition metals (TM). Although the potential for water splitting is low owing to the unfavorable position of the CeO2 valence band relative to the oxygen oxidation potential, the simulations showed that substitutional solubility is favored over interstitial solubility and that doping can introduce mid-gap states, which can reduce the photo-excitation energy and thus increase the photocatalytic efficiency