Improved photocatalytic and photoelectrochemical performance of monoclinic bismuth vanadate by surface defect states (Bi1-xVO4)

Due to visible light absorption and photochemical stability, Bismuth vanadate (BiVO4), recognized to be a promising photoanodes for designing high efficiency semiconductor photoelectrochemical (PEC) devices. To improve the photocatalytic and PEC performance of BiVO4, the porous monoclinic BiVO4 with surface bismuth vacancy (Bi1-xVO4 (s-m)) was obtained after the calcination of tetrahedron bismuth vanadate (BiVO4 (s-t)). The photocatalytic experiments showed that despite the relatively lower adsorption capacity of Bi1-xVO4 (s-m) as compared with BiVO4 (s-t), its photocatalytic activity for the photodegradation of tetracyclines (TCs) was 15-fold greater. A four-layer thin films of BiVO4 were deposited by spin coating with intermediate annealing treatment between layers and final calcination at 450 °C in air to shed light on carrier transport in Bi1-x VO4 (s-m). The PEC results indicated that BiVO4 (s-t) showed poor charge carrier mobility, while the Bi1-x VO4 (s-m) showed great improvement by transformation of the tetrahedron BiVO4 (s-t) into monoclinic phase, creation of new surface defect states and formation of a porous structure in Bi1-xVO4 (s-m). Furthermore, Bi1-xVO4 (s-m) showed enhanced and stable photocurrent density of 1.2 mA/cm2 at 1.0 V vs. Ag/AgCl which was achieved under visible light illumination using 0.1 M Na2SO4 aqueous solution. The porous Bi1-xVO4 (s-m) showed the band gap narrowing of 0.08 eV, valence band up-shifting of 0.150 eV and 100 mV cathodic shift in onset potential relative to BiVO4 (s-t). This enhancement is assigned to the longer electron lifetime of Bi1-xVO4 (s-m), 10-fold compared to that of BiVO4 (s-t), resulting in a minimized electron-hole pairs recombination.