Insight into crystal-structure dependent charge separation and photo-redox catalysis: A combined experimental and theoretical study on Bi(IO3)(3) and BiOIO3

Solar-driven conversion for CO2 reduction and oxygen activation reactions show huge potentials for energetic and environmental applications. However, the influence of crystal structure of a photocatalyst on its photocatalytic performance has been seldom investigated so far. Herein, to probe the relationship between crystal structure and photocatalytic properties, two bismuth iodates, the centrosymmetric (CS) monoclinic Bi(IO3)(3) and noncentrosymmetric (NCS) orthorhombic BiOIO3 are employed as the models. The photocatalytic reduction and oxidation capabilities of Bi(IO3)(3) and BiOIO3 were surveyed by monitoring the CO2 reduction and oxygen activation reactions. The results revealed that BiOIO3 shows far superior photocatalytic activity than Bi(IO3)(3), which can more efficiently convert CO2 into CO and produce larger amounts of .O-2(-) and OH. The experimental characterizations and DFT calculations co-uncovered that much more efficient charge separation and migration occur in BiOIO3 in compared to Bi(IO3)(3), which are responsible for the obviously higher photoactivity of BiOIO3. This is mainly due to that the NCS crystal structure of BiOIO3 that gives rise to a large macroscopic polarization, facilitating the separation of photogenerated electron-hole pairs. The microscopic first hyperpolarizability for BiOIO3 was calculated to be 2.56 X 10(-30) esu for the dominant component at the static limit and 15.73 x 10(-30) esu at the wavelength 409.1 nm, which well verifies the strong polarization of BiOIO3. This study may furnish the perspective into designing high-performance photocatalytic materials on the basis of crystal structure engineering.