Interface dependent electron shunting in graphene-integrated intimately coupled photocatalytic biodegradation

Intimately coupled photocatalytic biodegradation (ICPB) has been recently developed as an efficient wastewater treatment technique, particularly for removing persistent organic pollutants. However, photocatalyst/biofilm interaction in terms of photoelectron transfer and its effect on the overall performance of ICPB has not been explored. To investigate these points, interface-engineered composites of bismuth vanadate and reduced graphene oxide with low degree (BiVO₄/rGO-LC) and high degree of their contact (BiVO₄/rGO-HC) were fabricated and applied for ICPB. As a result, the composites displayed interface-dependent optical, structural and charge carrier separation properties. The photoelectrochemical measurements confirmed the presence of photoelectron shunting between photocatalyst and biofilm, while the current density was higher (smaller Nyquist arc) for BiVO₄/rGO-HC than BiVO₄/rGO-LC and BiVO₄ in ICPB protocol, confirming the crucial role of intimate interfacial contact for photoelectron shunting from BiVO₄ to biofilm. Consequently, the presence of graphene and its interfacial quality dictated the photoelectron shunting between photocatalyst and biofilm, enhancing photoelectron-holes separation and achieving superior degradation rate of tetracycline hydrochloride for BiVO₄/rGO-HC (0.035 h^-1) compared to BiVO₄/rGO-LC (0.0128 h^-1) and BiVO₄ (0.011 h^-1) in ICPB protocol. The electrical energy per order required for removal of tetracycline hydrochloride in the ICPB protocol exhibited the lowest value for BiVO₄/rGO-HC among the tested materials and treatment protocols. These results highlight the importance of photoelectron shunting in enhancing efficiency of ICPB by engineering graphene at the interface of photocatalyst and biofilm. This unveiled mechanism may serve as an excellent potential in designing energy-efficient ICPB systems targeting wastewater matrices.