Polydopamine modified ZIF-L/sodium alginate composites as the highly efficient photothermal membrane for solar steam generation

Interfacial solar steam generation (ISSG) technology is considered to be one of the most promising approaches to alleviating the global shortage of clean water due to its high solar thermal conversion efficiency. However, achieving stable evaporation in high salinity solutions and preventing the occurrence of salt deposition phenomena remains a challenge. Here, an efficient and stable photothermal membrane-based evaporator has been developed, which consists of polydopamine (PDA) modified leaf-like zeolitic imidazolate framework (ZIF-L) implanted in sodium alginate (SA) membrane supported on a melamine sponge (S-ZIF-L/PDA sponge), providing more advantages for boosting the photothermal conversion performance and preventing salt deposition. This S-ZIF-L/PDA sponge displays an excellent light absorption (>95 %), and remarkable evaporation rate of 1.66 kg·m−2·h−1 with a solar-thermal efficiency of 91.06 % under 1.0 sun (1 kW·m−2) illumination. Benefiting from the super hydrophilic feature of the melamine sponge and the rejection properties of the SA membrane structure, the obtained sponge effectively prevents salt and contaminants from depositing on the surface. Particularly, the S-ZIF-L/PDA sponge achieves an evaporation efficiency of 86.17 % in 20 wt% NaCl solution, along with excellent resistance to salt deposition and marvelous stability in cycling tests. The salt ion concentration of the obtained fresh water is much lower than the World Health Organization (WHO) drinking water standard, and the organic removal rate exceeds 99 %. This work provides a competitive solution for high-salinity desalination and wastewater treatment.