Triple-Phase Photocatalytic H₂O₂ Production on a Janus Fiber Membrane with Asymmetric Hydrophobicity

Photocatalytic O₂ reduction is an intriguing approach to producing H₂O₂, but its efficiency is often hindered by the limited solubility and mass transfer of O₂ in the aqueous phase. Here, we design and fabricate a two-layered (2L) Janus fiber membrane photocatalyst with asymmetric hydrophobicity for efficient photocatalytic H₂O₂ production. The top layer of the membrane consists of superhydrophobic polytetrafluoroethylene (PTFE) fibers with a dispersed modified carbon nitride (mCN) photocatalyst. Amphiphilic Nafion (Naf) ionomer is sprayed onto this layer to modulate the microenvironment and achieve moderate hydrophobicity. In contrast, the bottom layer consists of bare PTFE fibers with high hydrophobicity. The elaborate structural configuration and asymmetric hydrophobicity feature of the optimized membrane photocatalyst (designated as 2L-mCN/F-Naf; F, PTFE) allow most mCN to be exposed with gas-liquid-solid triple-phase interfaces and enable rapid mass transfer of gaseous O₂ within the hierarchical membrane, thus increasing the local O₂ concentration near the mCN photocatalyst. As a result, the optimized 2L-mCN/F-Naf membrane photocatalyst shows remarkable photocatalytic H₂O₂ production activity, achieving a rate of 5.38 mmol g⁻¹ h⁻¹ under visible light irradiation.