Dual role of gas–water microbubbles as interfacial reactors and optically active scatterers for photochemical synthesis of hydrogen peroxide

Gas–water microbubbles are introduced as dual‑function photochemical reactors that couple interfacial catalysis with optically driven light scattering to enhance hydrogen peroxide production. In a transparent microbubble reactor containing suspended graphitic carbon nitride (g‑C3N4), microbubbles provide a highly reactive gas–water interface that promotes radical pathways, while simultaneously acting as optically active inclusions that scatter and redistribute ultraviolet light around the photocatalyst, increasing the effective optical path length and local photon flux. Systematic variation of gas composition, microbubble residence time, g‑C3N4 loading, and irradiation period reveals that oxygen microbubbles and an optimal catalyst mass of 100 mg (1.0 g L⁻¹) maximize hydrogen peroxide yield, whereas prolonged irradiation leads to net decomposition. Under optimized conditions, the integration of microbubbles and g‑C3N4 results in approximately two‑order‑of‑magnitude enhancement in hydrogen peroxide concentration compared to bubble‑only controls after 60 s of exposure. A wireless bipolar electrochemical–electrochemiluminescence sensor enables in situ, spatially resolved quantification of interfacial hydrogen peroxide, directly correlating production with bubble stability and bubble-induced light-scattering efficiency. The observation of measurable hydrogen peroxide generation even with nitrogen microbubbles in degassed water highlights the intrinsic reactivity of the gas–water boundary driven by interfacial electric fields and charge‑transfer processes. These findings establish gas–water microbubbles as robust, optically active interfacial reactors for scalable and energy‑efficient photocatalytic synthesis of hydrogen peroxide.