PPy nanotubes-enabled in-situ heating nanofibrous composite membrane for solar-driven membrane distillation

Solar-driven membrane distillation is an emerging desalination technology with low energy consumption and efficient vapor collection, but the low vapor flux and limited efficiency hinders its practical application. Here, we demonstrated an innovative photothermal composite membrane by depositing polypyrrole nanotubes (PPy NTs) as functional coating layer onto an electrospun poly (vinylidene fluoride) (PVDF) nanofibrous support layer via vacuum filtration stabilized by adhesive polydimethylsiloxane (PDMS). According to the proportional relationship between the fibrous materials diameter and the pore size, the large-scale surface gaps between adjacent nanofibrous could be replaced by smaller pores from the PPy NTs layer on the PVDF substrate. The PDMS with low surface energy was used as an adhesive to in-situ solder the loose PPy NTs together as well as to enhance the adhesion between the PPy layer and the PVDF substrate to form an integrated and robust dual-layer composite membrane with superhydrophobicity, high porosity and controllable pore size. By exploring the optimal match of PPy loading and PDMS concentration, the solar-to-thermal performance and structural stability could be significantly improved. With 1 sun irradiation, the selected composite membrane thus showed a high-water vapor flux of 1.3 kg/(m2·h) and a photothermal conversion efficiency of 81.6%, specially, the membranes maintained stable permeate conductivity during the 10 h solar-driven DCMD seawater desalination test. These results indicated that the photothermal dual-layer superhydrophobic composite membranes has promising potential for desalination with the help of sustainable energy sources such as sunlight.