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.