Enhancing dichromate transport and reduction via electric fields induced by photocatalysis

Mass transport is a fundamental yet often overlooked factor in influencing adsorption and photocatalytic reaction kinetics. This study examines the role of mass transport using the model system of monoclinic bismuth vanadate (BiVO₄) films and potassium dichromate (K₂Cr₂O₇) in a representative photocatalytic reaction. We show that diffusion-driven delivery of K₂Cr₂O₇ to the BiVO₄ surface increases adsorption capacity but decreases the adsorption rate constant. Notably, during the model photocatalytic reduction, long-range electric fields were observed around the illuminated BiVO₄ films, a phenomenon also confirmed in a separate reaction system using TiO₂ as the photocatalyst. These electric fields, distinct from the localized fields formed within heterojunctions, enhance dichromate transport by more than three orders of magnitude. This enhanced transport ensures a continuous supply of reactant to the photocatalyst, significantly improving reaction efficiency without additional energy input. These findings introduce a new strategy for optimizing photocatalytic processes, offering broad insights for advancing sustainable chemical engineering applications.