Hydrophobic and visible-light responsive TiO₂ as an efficient photocatalyst for promoting hydrogen peroxide production in a two-phase system

Photocatalytic synthesis of hydrogen peroxide (H2O2) coupled with benzyl alcohol (BA) oxidation reaction is preferred based on the economic consideration. Herein, we developed a hydrophobic TiO2 material (DNOPA-TiO2), co-modified with 2,3-dihydroxynaphthalene (2,3-DN) and octadecylphosphonic acid (OPA), which enables H2O2 synthesis under visible-light-irradiation in a two-phase system consisting of BA and water. This system allows the separation of generated H2O2 in the aqueous phase from benzaldehyde (BAL), the product of BA oxidation, present in the organic phase. The hydrophobic DN2OPA2-TiO2 exhibited higher and more stable H2O2 production (3522 mu mol L-1) over an 8-hour reaction under visible light (lambda > 450 nm). The addition of 2,3-DN facilitates visible light harvesting and donates electrons to TiO2 through the formation of charge-transfer complexes, which promotes the O-2 reduction reaction (ORR) and improves H2O2 production. Moreover, the remarkable stability of DN2OPA2-TiO2 is originated from the hydrophobic nature of the catalysts thanks to OPA modification. This modification allows TiO2 to exist in the organic phase with better dispersion, inhibiting the decomposition of H2O2 resulting from direct contact between produced H2O2 and TiO2.