Light-trapping Janus nanofibrous membranes with surface-confined PDA for photothermal membrane distillation

A Janus nanofibrous membrane was fabricated via sequential electrospinning. • Fiber light trapping enhanced solar absorption for photothermal conversion. • PDA deposition was optimized to balance mass transfer and photothermal heating. • The membrane achieved 1.97 L m −2  h −1 flux and >99.99% salt rejection. • Stable PMD performance was maintained during 70 h continuous operation. Solar-driven photothermal membrane distillation (PMD) is a promising approach for sustainable desalination, but its practical application is still limited by temperature polarization, membrane wetting, and the trade-off between photothermal conversion and vapor transport. Herein, a polydopamine (PDA)@Janus nanofibrous membrane with asymmetric hydrophilic/hydrophobic architecture was developed by sequential electrospinning and in situ oxidative polymerization of dopamine. The membrane consisted of a hydrophobic polydimethylsiloxane (PDMS)@polystyrene (PS)/thermoplastic polyurethane (TPU) support layer and a hydrophilic poly(m-phenylene isophthalamide) (PMIA)/polyamic acid (PAA) functional layer, with PDA nanoparticles uniformly deposited on the hydrophilic fiber surfaces to construct a fiber-based light-trapping photothermal architecture. The interconnected nanofibrous network promoted multiple light reflections, while the surface-confined PDA coating enhanced light absorption within the measured UV-visible range without substantially blocking the interconnected vapor transport pathways. By systematically regulating dopamine concentration and polymerization time, the PDA deposition morphology, surface wettability, pore structure, mechanical properties, and photothermal performance were effectively optimized. The optimized PDA@Janus-2.0-12 membrane exhibited a water contact angle of 49.21 ± 2.6°, a tensile strength of 7.70 ± 0.6 MPa, and a stable photothermal response under simulated solar irradiation. Under 1.0 kW m −2 solar irradiation with 35 g L −1 NaCl feed, the membrane achieved a permeate flux of 1.97 ± 0.05 L m −2  h −1 with a salt rejection of >99.99%, while maintaining an average photothermal conversion efficiency of 88.67%. The membrane also maintained stable desalination performance during 70 h of continuous PMD operation. Furthermore, the membrane retained a flux of 1.58 ± 0.04 L m −2  h −1 even at a NaCl concentration of 150 g L −1 , demonstrating excellent tolerance to highly saline feeds. These results demonstrate that the synergistic combination of fiber-based light trapping, PDA interfacial photothermal conversion, and asymmetric Janus architecture effectively balances solar energy utilization, vapor transport, and long-term structural stability, providing a promising strategy for solar-driven desalination of high-salinity NaCl brines; further evaluation toward practical complex high-salinity wastewater will be required in future work. Download: Download high-res image (398KB) Download: Download full-size image