Synergetic Degradation of Rhodamine B at a Porous ZnWO₄ Film Electrode by Combined Electro-Oxidation and Photocatalysis

Synergetic degradation of rhodamine B (RhB) was investigated by combining electro-oxidation and photocatalysis using porous ZnWO₄ film at various bias potentials. The applied bias potential below 0.8 V enhanced the photocatalytic degradation of RhB by promoting the separation and transfer of photogenerated holes and electrons. At the potential between 0.8 and 1.0 V, the degradation of RhB was further enhanced, which is induced by direct electro-oxidation and photocatalysis. At the potential greater than 1.3 V, indirect electro-oxidation of RhB occurred with the largest synergetic effect. The synergetic effect can also increase the mineralization degree of the RhB. On the basis of the X-ray photoelectron spectra (XPS) analysis of the surface of the electrode after electrochemical reaction, the electropolymerization occurred which blocked the electrode and slowed the electro-oxidation of RhB. Active species generated via the photocatalytic process can activate the passivated electrode and promote the electro-oxidation of RhB. The O₂ electrochemically generated at the anode promoted the photocatalysis by capturing the photogenerated electrons and may induce the formation of H₂O₂. Thus, more active species could be formed through new reactive routines in the photoelectrocatalytic (PEC) process. RhB degradation was mainly through decomposition of the conjugated chromophore structure with slight occurrence of de-ethylation. The stability of the electrode in the PEC process was confirmed based on the XPS and Raman analysis.