Polypyrrole@melamine Sponge-Based Solar Evaporator with Detachable Salt Collection for Solar Desalination and Salt Harvesting

Solar interfacial evaporation is considered a sustainable strategy for seawater desalination and wastewater treatment, yet salt fouling on evaporator surfaces remains a critical challenge that limits long-term performance. Continuous salt harvesting is therefore essential to sustain purified water production while enabling simultaneous salt collection. Here, we design an evaporator (PPy@MS-Filter paper, PMF) that achieves the spatial decoupling of water evaporation and salt crystallization by integrating a photothermal evaporation zone with a detachable salt-collection zone. The in situ polymerization of polypyrrole on a melamine sponge (PPy@MS) was designed for efficient water evaporation, and a superhydrophilic filter paper was wrapped around its upper edge to facilitate salt collection. Owing to the synergistic effects of a strong wettability-induced capillary pressure gradient and an evaporation-induced temperature gradient established between PPy@MS and filter paper, directional liquid and ion transport occurs from the central evaporation zone toward the peripheral filter paper, thereby enabling edge-preferential salt crystallization without compromising the photothermal efficiency of the evaporation interface. Consequently, this PMF evaporator maintains stable evaporation at 3.34 kg m^–2 h^–1 in 20 wt % brine, together with up to 314 g m^–2 h^–1 salt collection rate under 1 kW m^–3. The replaceable filter paper enables prolonged operation for over 80 h while sustaining efficient salt harvesting. This modular strategy effectively mitigates salt fouling and advances solar desalination toward integrated freshwater production and salt resource utilization.