Dual-structured PTFE/PI-PI/PANI composite membranes for photothermal membrane distillation with excellent photothermal conversion and open pathways for water vapor transport.

Photothermal membrane distillation (PMD) achieves localized temperature increase by absorbing and converting light energy to drive evaporation and phase change processes. It is expected to solve the challenges of low energy conversion efficiency and fouling of traditional membrane distillation (MD). A dual-structured photothermal composite membrane was constructed by oxidatively polymerizing photothermal functional materials on an electrospinning substrate membrane. The superhydrophobic Polytetrafluoroethylene/Polyimide (PTFE/PI) substrate membranes offer a spacious pore structure and excellent mechanical properties with low mass transfer resistance and low heat loss. The presence of the densely connected region of the Polyaniline (PANI) in the photothermal layer accelerates the local photothermal conversion. The porous structure formed by interconnecting fibers loaded with PANI is conducive to the repeated refraction of light beams and thus enhances the absorption of light energy. Under 1 kW·m−2 light intensity, the permeate flux of the PTFE/PI-PI/PANI membrane is stable at 1.44 ± 0.02 L·m−2·h−1 within 480 h PMD. With the outstanding salt rejection performance of 99.99 % and high photothermal conversion efficiency of 90.3 %, the photothermal membrane can be applied in areas where fresh water and fuel resources are scarce but solar energy resources are abundant. [Display omitted] • The superhydrophobic layer prevents membrane wetting for durable PMD operation. • The hydrophilic photothermal layer mitigates the temperature polarization effect. • The dual heating mode of composite membrane boots the mass transfer driving force. • The overall porous structure expands efficient water vapor transmission channels. [ABSTRACT FROM AUTHOR]