Photocatalytic microreactors for water purification: Selective control of oxidation pathways

This paper analyzes the different reaction pathways that play major roles in the process of photocatalytic degradation, and presents a novel microfluidic photoelectrocatalytic reactor for selective control of them. This is accomplished by applying positive or negative bias potential to the photocatalytic reaction chamber and to select either the hole-driven or electron-driven oxidation pathway. The experimental results show that the negative bias exhibits higher performance in degrading the model chemical of methylene blue. Such selective control brings several important benefits. It provides another degree of freedom for photocatalysis, and enables detailed kinetic study on the reaction mechanisms. And, the bias eliminates the electron/hole recombination, which is one of the fundamental limits in conventional photocatalytic systems. In additional, the experiment shows that the bias produces a synergetic effect of electrocatalysis and photocatalysis and significantly enhances the degradation efficiency. The photoelectrocatalytic microreactor shows high stability and may be scaled up for high-performance water purification.