Architecting Janus hydrogel evaporator with polydopamine-TiO₂ photocatalyst for high-efficient solar desalination and purification

Solar-powered water distillation is one of the effective and promising ways of water purification. However, new high-efficiency evaporators are especially needed to reduce the energy requirement and improve water yields under natural sunlight. In this study, a Janus structured hydrogel with an interpenetrating double network was formed by polyvinyl alcohol and natural polysaccharide to speed up solar water purification. Due to its unique pore structure, water molecules can quickly escape from the surface of Janus hydrogel by molecular dynamics simulations. The Janus evaporator worked stably and the evaporation rate was achieved to 3.53 kg·m⁻²·h⁻¹ under 1 sun illumination, which was attributed to the outstanding water transport capacity and thermal localization capacity. Meanwhile, the Janus-based solar evaporator exhibited excellent durability in wide acid–base range (pH 1–13) and salinity range (0–350‰), and long term (30 days). The daily yield of the Janus hydrogel reached 24.5 kg·m⁻²·h⁻¹ in outdoor tests. The Janus evaporator enables efficient desalination and purification of other unconventional water sources, and can degrade more than 95% of organic dyes (trypan blue and Congo red) as a result of the synergistic effect of Polydopamine (PDA) /TiO₂ nanoparticles. This Janus structured hydrogel evaporator opens up potential applications in desalination and wastewater treatment.