Serendipitous Assembly of Mixed Phase BiVO4 on B-Doped g-C3N4: An Appropriate p-n Heterojunction for Photocatalytic O2 evolution and Cr(VI) reduction.

Type II p-n heterojunction B-doped g-C3N4/BiVO4 moieties have been fabricated by depositing n-type BiVO4 on the surface of p-type 1 wt % B-doped g-C3N4 for the first time. The materials were characterized by PXRD, XPS, UV-vis DRS, IR, PL, and Raman analysis. The photocatalytic activities of as synthesized samples were studied toward reduction of Cr(VI) and water splitting reaction to generate oxygen. The results reveal that Type II p-n heterojunction considerably enhance the photocatalytic activity as compared to neat n-type BiVO4 and p-type B-doped g-C3N4. 50% BiVO4/B-doped g-C3N4 heterostructure exhibited the best photocatalytic activity, which is 7.9-fold higher than that of BiVO4 and followed by a pseudo first order kinetics with apparent first order rate constant of 0.063 min-1. Again the heterojunction is able to produce 4.2 times higher oxygen evolution value as related to pristine BiVO4. The superior photocatalytic activity is attributed to higher visible light utilization and lower recombination of electron-hole pairs by creating a p-n junction. PXRD and HRTEM data suggest the formation of mixed phase monoclinic and tetragonal BiVO4 thereby creating a heterojunction for the improvement of the photocatalytic performances. The formation of mixed-phase BiVO4 is attributed to the high temperature calcination as well as surface energy of B-doped g-C3N4. The oxygen vacancy in the system is confirmed through XPS and Raman analysis. Moreover, the excellent photocurrent response by the designed photocatalyst at lower overpotential and decrease in carrier recombination as compared to bulk one, studied from LSV and electrochemical impedance spectroscopy, validate the unique photocatalytic activity of the catalyst. The formation of the p-n heterojunction is confirmed from a Mott-Schottky analysis. The work shed new light on the assembly of the p-n heterojunction, showing excellent photocatalytic properties in a simple way.