Accelerated Synergistic Photo-Fenton/Photocatalysis Reactions at Aqueous Interfaces

Photocatalysis and photo-Fenton oxidation are promising advanced oxidation technologies for water treatment. Nevertheless, their relatively slow kinetics largely limited their practical applications. Herein, we performed synergistic photocatalysis and photo-Fenton reactions in water microdroplets for the degradation of organic dyes. The efficiency of the microdroplet-based photoreactions was significantly improved with a degradation rate of 98.96% in microdroplets, while it was only 38.14% in the bulk solution. The enhanced degradation efficiency was due to the synergistic effect of the photocatalysis and photo-Fenton reactions in the microdroplets. First, the enrichment of both the dye (rhodamine B) and the catalyst (g-C₃N₄ nanosheets) at the aqueous interfaces enlarged the local surface concentration, playing a role in the reaction acceleration. Second, the spontaneously generated hydrogen peroxide (17.13 μM) at the aqueous interfaces triggered the photo-Fenton cycle and thus largely promoted the charge separation of g-C₃N₄ as well as the effective utilization of the photogenerated electrons and holes, leading to a significantly improved degradation efficiency of organic dyes. Further, we quantified the reaction kinetics of individual microdroplets in a real-time manner. The reaction constant in 10 μm microdroplets was 4.86 × 10^-3 s^-1, which was 22 times higher than that in the bulk phase (0.22 × 10^-3 s^-1). This study provided a better understanding of accelerated photoreactions at aqueous interfaces and a strategy for addressing the low efficiency of organic dye degradation.