(480i) Photothermal Membranes for an Environmentally Sustainable and Resilient Clean Water Supply

Current desalination techniques, such as the reverse osmosis membrane process, heavily rely on a large-scale infrastructure with high capital costs. Their operation also requires multiple pretreatment steps to handle highly saline feed water. Furthermore, in developing countries, rural areas, or disaster areas, where electricity and the infrastructure are lacking or damaged, conventional desalination is not an option. To tackle this problem, we have developed novel membranes that utilize photothermal effects (sunlight-to-heat conversion in nanostructures), achieving fouling-resistant and energy-efficient water treatment. In the best case, the non-solar energy input is nearly zero. This talk will focus on our recent work on new photothermal membranes for membrane distillation (called photothermal membrane distillation, PMD). We developed a chemically and mechanically stable polydopamine (PDA)-coated polyvinylidene fluoride (PVDF) membrane that can be synthesized via a simple and scalable process. Using a direct contact membrane distillation (DCMD) system under 0.75 kW/m² solar irradiation, the membrane showed the best energy efficiency among existing photothermal MD membranes (45%) and the highest water flux (0.49 kg/m²·h), with high salt rejection (> 99.9%). This performance was facilitated by its high light absorption over a broad light spectrum and the outstanding photothermal conversion properties of PDA coatings. Subsequently, the membrane structures were further thermally engineered to improve the solar-energy to collected-water efficiency and also to utilize two even more environmentally-sustainable materials, optically tuned PDA particles and bacterial nanocellulose (BNC). The PMD system presented here offers a new future for decentralized desalination that supports the resilient global community.