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Hydrogen peroxide (H 2 O 2) has attracted considerable interest due to its status as an eco-friendly oxidant and a sustainable energy carrier. This review summarizes current advancements in various photocatalysts, including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), titanium dioxide (TiO 2), ionic carbon nitride, quantum dots (QDs), coordination polymer (CP), and heterojunction materials, applied for H 2 O 2 production in several types of two-phase systems, composed of benzyl alcohol (BA), toluene or octanol organic phase and water phase. Such two-phase media enables spontaneous separation of the produced reduction product (H 2 O 2) from oxidation product, benzaldehyde (BAL) or octanal and photocatalysts suppressing H 2 O 2 decomposition. The goal of the present review is to provide more fresh perspective on the future developments in the field of sustainable H 2 O 2 production in two-phase system. [Display omitted] • Two-phase systems with organic and water phases were used in H 2 O 2 photo-synthesis. • The biphasic system inhibits H 2 O 2 decomposition via separating H 2 O 2 from catalysts. • Different methods of hydrophobic modification on diverse materials were summarized. • Autocatalysis of benzyl alcohol/benzaldehyde shows little impact on this system. [ABSTRACT FROM AUTHOR]

Photocatalytic synthesis of hydrogen peroxide (H 2 O 2) coupled with benzyl alcohol (BA) oxidation reaction is preferred based on the economic consideration. Herein, we developed a hydrophobic TiO 2 material (DNOPA-TiO 2), co-modified with 2,3-dihydroxynaphthalene (2,3-DN) and octadecylphosphonic acid (OPA), which enables H 2 O 2 synthesis under visible-light-irradiation in a two-phase system consisting of BA and water. This system allows the separation of generated H 2 O 2 in the aqueous phase from benzaldehyde (BAL), the product of BA oxidation, present in the organic phase. The hydrophobic DN2OPA2-TiO 2 exhibited higher and more stable H 2 O 2 production (3522 μmol L−1) over an 8-hour reaction under visible light (λ > 450 nm). The addition of 2,3-DN facilitates visible light harvesting and donates electrons to TiO 2 through the formation of charge-transfer complexes, which promotes the O 2 reduction reaction (ORR) and improves H 2 O 2 production. Moreover, the remarkable stability of DN2OPA2-TiO 2 is originated from the hydrophobic nature of the catalysts thanks to OPA modification. This modification allows TiO 2 to exist in the organic phase with better dispersion, inhibiting the decomposition of H 2 O 2 resulting from direct contact between produced H 2 O 2 and TiO 2. [Display omitted] • DN/OPA-TiO 2 is used for photocatalytic H 2 O 2 production in a two-phase system. • 2,3-DN enhances visible light absorption by forming charge-transfer complexes. • OPA imparts TiO 2 hydrophobic and inhibits the decomposition of produced H 2 O 2. • DN2OPA2-TiO 2 exhibits higher visible-light activity (3522 μmol L−1, λ > 450 nm). [ABSTRACT FROM AUTHOR]

Recently, the combination of photocatalytic reduction and oxidation reactions has attracted great attention, especially for the photocatalytic synthesis of hydrogen peroxide (H 2 O 2) integrated with benzyl alcohol (BA) oxidation reaction. The plasmonic Au nanoparticles (NPs) driven by surface plasmon resonance (SPR) excitation can be efficiently applied for photocatalysis. In this study, the effect of a hydrophobic Au-deposited TiO 2 material (OPA-Au/TiO 2) modified with octadecylphosphonic acid (OPA) on the photosynthesis H 2 O 2 performance in a two-phase system, comprising water and BA phases, is investigated. The SPR effect of plasmonic Au NPs facilitates the generation of substantial photoexcited hot electrons, which transfer to the conductive band of TiO 2. Moreover, OPA-Au/TiO 2 present in the BA phase, exhibits dramatically enhanced activity (567 μmol g−1 h−1) under λ > 420 nm irradiation owing to the separation from produced H 2 O 2 in the aqueous phase, which efficiently suppresses the H 2 O 2 decomposition. [Display omitted] • OPA-modified Au/TiO 2 is effective for biphasic photocatalytic H 2 O 2 production. • Au with surface plasmon resonance provides rich hot electrons for TiO 2. • OPA imparts TiO 2 hydrophobic and inhibits the decomposition of produced H 2 O 2. • OPA-Au/TiO 2 exhibits enhanced visible-light activity (567 μmol g−1 L−1, λ > 420 nm). [ABSTRACT FROM AUTHOR]