Janus-interface engineering enhances hydrogel integrated with ZIF-8@Co9S8 composite featuring concave pyramid patterns for efficient solar-driven water purification
Water scarcity and the increasing demand for clean water have driven the development of efficient solar desalination technologies. Interfacial solar steam generation (ISSG) is promising, yet its practical deployment is hindered by insufficient light harvesting and salt crystallization on photothermal surfaces. Here, we report a Janus hydrogel evaporator in which tubular Co9S8 nanocrystals are uniformly embedded in a polyvinyl alcohol (PVA) matrix with a concave pyramid pattern, creating a broadband light-trapping architecture (200–2500 nm) with 96% solar absorption. The top surface is further coated with hydrophobic zeolitic imidazolate framework-8 (ZIF-8), while the bottom retains intrinsic hydrogel hydrophilicity, establishing asymmetric wettability that sustains rapid water supply yet suppresses salt deposition. Under one-sun illumination (1 kW m−2), the Janus evaporator achieves an evaporation rate of 2.69 kg m−2 h−1 and a solar-to-vapor efficiency of 98.15%. Continuous operation in 3.5 wt% brine shows stable performance for 11 h without observable salt crystallization. This work offers an effective, durable pathway toward high-performance solar desalination and wastewater purification.