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

Bismuth vanadate and its composites with graphene oxide (BiVO 4 /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/or GO in the synthesis favors the degradation of both pollutants. This enhanced activity is due to the formation of BiVO 4 and Bi 2 O 2 CO 3 phases changing the symmetry of the VO 4 3– 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 (BiVO 4 -U/1GO), which achieved total degradation of MTX in 240 min and 5-FU in 480 min. The immobilization of BiVO 4 -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-Al 2 O 3 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. • BiVO 4 materials were prepared hydrothermally by changing the basification agent • Graphene oxide was also added to enhance the properties and activity of BiVO 4 • Raschig rings and Al 2 O 3 membranes were selected as photocatalyst supports • Al 2 O 3 membranes prepared by filtration was the best BiVO 4 /GO support