Comparison of hydroxyl radical yields between photo- and electro-catalyzed water treatments

In this study, we investigate the production of hydroxyl radicals in photo- and electro-catalytic systems. A model compound, 4-hydroxybenzoic acid (4-HBA), served as a trapping (scavenger) reagent for the determination of hydroxyl radical (OH) concentrations in both systems. Experiments were conducted by controlling different operation parameters (i.e., reaction time, electrolyte, applied voltage, power, and solution pH) to understand their respective impact on OH production. The results show that a number of similar characteristics exist between the photo- and electro-catalytic systems, including the electrolytes Na2SO4 and NaNO3, which are both suitable for photo- and electro-catalysis and increase the applied energy, proportionally enhancing the OH yields. These alkaline conditions are beneficial for generating OH in either the photo- and electro-catalytic system. Notably, electrolyte Na2CO3 is a strong scavenger of OH, which induces the failure of the catalytic system. In summary, the electro-catalytic system demonstrates better OH production rates than those of the photo-catalyst system under the same applied energy and with respect to the catalyst surface area.