Tunable all-in-one bimodal porous membrane of ultrahigh molecular weight polyethylene for solar driven interfacial evaporation

• A tunable all-in-one bimodal porous membrane of UHMWPE with interconnected porous network was fabricated. • Polydopamine (PDA) was allowed to enter the porous membrane and deposit on the surface of the pore walls. • The bimodal porous structure exhibits a solar absorptance nearly 96% and photothermal conversion efficiency about 96.3%. • Bimodal porous structure provided a large internal surface area for functionalization. Solar driven interfacial evaporation is a promising technology to produce freshwater by clean energy source. Rational design of the porous structure of photothermal membranes for efficient energy conversion and vapor generation in long-term use is a key challenge. Herein, tunable all-in-one bimodal porous membrane of ultrahigh molecular weight polyethylene with interconnected porous network is first designed, which can effectively regulate porous structure by thermal-induced phase separation and NaCl-templet leaching. Carboxylated carbon nanotubes are evenly dispersed and embedded in the pore walls, efficiently absorbing solar energy and converting it into heat, exhibiting a satisfactory solar absorptance nearly 96% and photothermal conversion efficiency about 96.3%. Particularly, polydopamine is allowed to enter the porous membrane and deposit on the surface of the pore walls for water transport and water activation by flowing deposition, achieving water evaporation rate of 1.53 kg m -2 h -1 at ∼97.6% energy efficiency under 1 sun illumination. The membrane with lightweight, high porosity and abundant porous structure is able to stably desalinate in both 3.5 wt% and 10 wt% saline due to quick water exchange that suppresses salt crystallization during evaporation. This bimodal porous structure design is generic and can be expanded to other photothermal systems for advanced solar-thermal applications.