Turning Humidity Into Function: Heterojunction Interfaces for Dual‐Mode Removal of Nonpolar Vapors

ABSTRACT A core–shell heterojunction photocatalyst, MIL–88B(Fe)@Fe 3 (PO 4 ) 2 , is directly synthesized on an oxidized iron wire that serves as both an iron source and a structural scaffold. The resulting wire‐grown hetero‐catalytic adsorbent (MIL@FeP@wire) exhibits efficient generation of superoxide (•O 2 − ) and hydroxyl (•OH) radicals under light irradiation. Its gas‐phase removal performance is evaluated using cyclohexane (C 6 H 12 ) as a representative nonpolar volatile organic compound (VOC). MIL@FeP@wire demonstrates combined dual‐mode cyclohexane removal across 10%–90% relative humidity (RH), whereas single‐component materials display an adsorption‐ or catalysis‐dominated behavior. Notably, this work elucidates how ambient humidity mediates VOC‐adsorbent interactions by distinctly regulating adsorption and photocatalytic degradation pathways. Dynamic vapor sorption and hydrophobic interaction chromatography show that water vapor forms a hydration layer on MIL@FeP@wire, enhancing interfacial affinity for nonpolar cyclohexane and promoting adsorption. Concurrently, electron spin resonance confirms humidity‐enhanced •OH generation, which accelerates photocatalytic oxidation. This pathway‐resolved analysis, which distinguishes adsorption and photodegradation contributions, identifies water vapor as a functional mediator that regulates adsorption and catalytic degradation through hydration‐induced interfacial effects in air purification.