Synergistic volatiles removal via diffusion inhibition and catalysis degradation by photothermal-photocatalytic hydrogel distillation membranes for sustainable water purification.

Photothermal membrane distillation (PMD) faces critical challenges in volatile organic compounds (VOCs) penetration due to their inherent volatility. Herein, we propose a hierarchically engineered photothermal-photocatalytic hydrogel (PPH) membrane with dual defense barriers, integrating an alginate (Alg) hydrogel layer as a kinetic diffusion suppressor and a BiOBr/carbon nanotube layer as a photocatalytic promoter on a hydrophobic substrate. This design enables simultaneous stable water production (2.93 kg m⁻² h⁻¹) and nearly complete VOCs removal (100%) under one-solar irradiation. PPH membrane maintains a high VOCs removal under fluctuating irradiances, temperatures, VOCs concentrations and types. Crucially, the Alg hydrogel creates selective VOCs diffusion barriers via hydrogen-bond dominated interactions, with Alg-aniline interactions (22.68 kcal/mol) stronger than Alg-water (12.29 kcal/mol), and differential mass transfer kinetics (aniline: 0.35 × 10⁻⁵ cm²/s, 7.8-fold lower than water), establishing a molecular gating mechanism for VOCs transport suppression. The photocatalytic layer synergistically degrades residual VOCs via photogenerated radicals, ensuring VOCs complete removal. Furthermore, outdoor experiment and practical validation using challenging hypersaline waters demonstrates a durable photothermal water purification capacity, highlighting feasibility for treating petrochemical wastewater and marine oil spill scenarios. This work provides a new design principle for hydrogel-based membranes, offering providing an engineered solution for sustainable water reclamation from volatile-contaminated sources.