Dual-Emulsifier Coated Photocatalyst for H2O2 Synthesis in Emulsion via Water Oxidation.

Photocatalysis provides a sustainable approach for on-site production of H2O2, yet single-phase systems generally display unsatisfactory efficiency and low concentration of H2O2 due to rapid reverse reactions and dissociation of H2O2. Multiphase systems are developed to yield aqueous H2O2 via oxygen reduction by employing hydrophobic photocatalysts, however, the low solubility of oxygen and the possible dissociation of generated H2O2 result in a limited improvement in catalytic performances. Herein, a lauric acid (LA)‒n-dodecyltrimethoxysilane (DTMS) dual-emulsifier coated Pd/TiO2 (LD-Pd/TiO2) is constructed for the synthesis of H2O2 in a water-nonane system via water oxidation with quintozene as an insoluble hydrogen acceptor in water. While DTMS in the composite coating quenches the decomposition of H2O2, LA facilitates the enrichment of quintozene near the Pd/TiO2 for a rapid consumption of hydrogen atoms. The LD-Pd/TiO2 leads to a remarkable H2O2 concentration of 133 mM with decent stability and a high quantum efficiency (6.5% at 365 nm). Additionally, the system can be demulsified gently after reaction, obtaining aqueous H2O2 solution and oil phase with hydrogenated products for simple separation and collection.