Emulsion of Benzene and Water Phases by an Amphiphilic Hematite/Carbon Nitride Photocatalyst for Phenol Synthesis

Abstract

Photocatalytic hydroxylation of benzene in water using H₂O₂ as the oxidant is a green approach toward phenol synthesis. However, the immiscibility of benzene in water results in poor photocatalytic performance and a low efficiency of H₂O₂ utilization. To enhance drastically the affinity between the aqueous and nonaqueous phases, an amphiphilic heterojunction (Fe₂O₃/crystalline carbon nitride (CCN)) has been synthesized by intimately immobilizing hematite (Fe₂O₃) nanoparticles on a CCN surface for the photocatalytic hydroxylation of benzene to phenol. The unique amphiphilicity of Fe₂O₃/CCN allows the formation and stabilization of homogeneous emulsions in a benzene/water mixture to increase the effective oil/water interface area for more efficient mass transport. Moreover, the well-established type II heterojunction between Fe₂O₃ and CCN facilitates the fast separation and transfer of photoelectrons from CCN to Fe₂O₃ for the photo-Fenton activation of H₂O₂ with high utilization efficiency. We recorded a maximum phenol conversion of 31.6% by using a stoichiometric amount of H₂O₂ (10 mmol) on the photocatalytic hydroxylation of benzene. The apparent quantum yield of phenol production at λ = 420 nm was determined to be 47.1%. This amphiphilic photocatalyst approach would be useful for realizing other advanced oxidation reactions involving immiscible components.