Study on composite photocatalyst for artificial photosynthesis system

Abstract

To achieve sustainable utilization of solar energy, development of efficient photocatalyst for water oxidation, the driving force of reductive solar fuel formation, is highly required. Herein, bismuth vanadate (BiVO4) based composite photocatalysts are developed and verified their enhanced photocatalytic activity for water oxidation. First of all, sulfur doped graphitic carbon nitride (SCN) is introduced with BiVO4 by using one-pot impregnated co-precipitation method. FT-IR and XPS analyses demonstrate that the surface of SCN is oxidized during impregnation and the oxidized surface becomes the synthetic site for BiVO4 composition. The composites with BiVO4 and SCN shows twofold higher oxygen evolution rate than that of pristine BiVO4. The mechanism behind this is the enhanced charge carrier lifetime which is lengthened up to 4 times compared to BiVO4 due to the facilitated charge separation through composite. Secondly, the dual phase structure of monoclinic scheelite (BVO-M) and tetragonal zircon-type BiVO4 (BVO-T) moieties with graphitic carbon nitride (g-C3N4) is developed. V K-edge and Bi L3-edge XANES and EXAFS spectra demonstrate that the BVO-T structures form a bridge between BVO-M and g-C3N4 structures so that it acts as an electron mediator to accelerate charge transfer, in agreement with the zeta-potential analysis and the band structure revealed by UV-vis spectroscopy and UPS. Furthermore, a Z-scheme photocatalyst is exhibited to show a 3-fold longer charge carrier lifetime than BVO-M, thereby enabling the greater than three-fold enhancement in photocatalytic water oxidation activity. Additionally, isotope 18O-labelling experiments reveal that evolved oxygen molecules result from water through photocatalytic water oxidation. Finally, BiVO4 composite photocatalyst with sub-nanoscale cobalt oxide which is produced through lithiation-delithiation process is established. The tetragonal BiVO4 and cobalt oxide composite shows 6-fold higher water oxidation catalytic activity. BiVO4 based composite photocatalysts present the potential to achieve photocatalytic water oxidation which is essential to establish sustainable artificial photosynthesis system.