Water-soluble volatile organic compounds (VOCs) are among the most difficult-to-treat species during wastewater treatment. The current purification and removal of high-concentration VOCs still rely on the energy-consuming distillation and high-pressure driven reverse osmosis technology. There is an urgent need for an advanced technology that can effectively remove high-concentration VOCs from water. Here, we report a metal–organic framework (MOF)/polyaniline (PANI) nanofiber array composite photothermal membrane for removal of high-concentration VOCs from water via molecular sieving during a solar-driven evaporation process. The modified zeolitic imidazole framework-8 (ZIF-8) layer grown on a PANI nanofiber array acts as a molecular sieving layer to evaporate water but intercept VOCs. The composite membrane exhibits high VOCs rejection and a high-water evaporation rate for water containing different concentrations of VOCs. When treating water containing VOCs with a concentration of up to 400 mg L–1, the VOCs rejection rate is up to 99% and the water evaporation rate is 1.0 kg m–2 h–1 under 1 sun irradiation (1 kW m–2). Our work effectively combines the molecular sieve effect with a solar-driven evaporation process, which provides an effective strategy for the treatment of water containing VOCs.
In recent years, conductive membranes have attracted significant attention and have been extensively studied for their unique antifouling mechanisms and regenerative properties. The current strategy primarily focuses on enhancing the conductivity of membranes. Yet, the resulting antifouling performance enhancement is limited due to lack of capacitance-tuning. Herein, we constructed hierarchicalnanostructure membrane carbon nanotubes−polyaniline−graphene quantum dots (CNT-PANI-GQDs), first demonstrating a capacitance-tuning strategy for enhancing the membrane's antifouling performance. PANI covers the CNTs' surface and cross-links them, forming a conductive 3D structure polymer substrate. GQDs assisted with PANI are used for tuning the membrane capacitance. The CNT-PANI-GQDs had the highest capacitance among all the membranes and exhibited the highest water flux, the best antifouling performance, and mechanical stability. Cross-flow filtration experiments were conducted with the organic model foulants. After treating a 100 ppm bovine serum albumin (BSA) solution with a voltage of −2.5 V and running continuously for one h, the CNTs-PANI-GQDs membrane maintained a normalized flux of over 97%. Electrochemical measurement and Derjaguin−Landau−Verwey−Overbeek (DLVO) analysis revealed that PANI and GQDs simultaneously enhance the pseudocapacitance and double-layer capacitance, and the hierarchical nanostructure membrane possesses excellent charge transfer ability and a large electrochemically active surface area. Increased capacitance leads to greater accumulation of surface charges and enhances the electrostatic repulsion against impurities. This work may offer valuable references to guide the design of electric antifouling membranes to favor water purification applications.
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