Synthesis and immobilization of BiVO4/graphene oxide composites on 3D/2D structured supports for the solar-LED photocatalytic oxidation of cytostatic drugs in polluted water

Abstract

Bismuth vanadate and its composites with graphene oxide (BiVO4/GO) were synthetized by a hydrothermal method, varying the GO content (0.5–5.0 wt%) and the basification agent (NaOH, urea or none, as reference sample). All materials were exhaustively characterized by complementary techniques and their activity was assessed for the degradation of both methotrexate (MTX) and 5-fluorouracil (5-FU) cytostatic drugs in aqueous solution under solar-LED irradiation. The addition of urea and GO in the synthesis favors the degradation of both pollutants. This enhanced activity is due to the formation of BiVO4 and Bi2O2CO3 phases changing the symmetry of the VO43– tetrahedra and the establishment of a heterojunction or rich-electron regions, which facilitate the mobility of photogenerated charges towards graphenic layers. The most efficient photocatalyst was the composite containing urea and 1.0 wt% GO (BiVO4-U/1GO), which achieved total degradation of MTX in 240 min and 5-FU in 480 min. The immobilization of BiVO4-U/1GO was optimized, with the best results obtained through dip-coating on 3D-Raschig rings (BR). In contrast, filtration proved to be more appropriate for 2-D α-Al2O3 membranes, as it enabled a homogenous distribution of higher amount of immobilized photocatalyst on the membrane. This resulted in higher photoactivity (39.7 ×10–6 min–1 mg–1) compared to dip-coated membranes and BR supports (21.0 ×10–6 and 23.3 ×10–6 min–1 mg–1, respectively). Reutilization experiments with coated BRs demonstrated that the immobilized photocatalyst had a good stability and reusability for the MTX degradation in recirculation mode. Finally, the MTX by-products formed during the reaction and the degradation pathway were elucidated