Trapping waste metal ions in a hydrogel/coal powder composite for boosting sewage purification via solar-driven interfacial water evaporation with long-term durability

The improper disposal of effluents contaminated with waste metal ions poses significant threats to clean water resources. Recently, solar-driven interfacial water evaporation has gained increasing interests for sustainable water purification, nevertheless, the presence of various hydrated metal ions from industrial effluents makes it challenging for conventional distillers to achieve efficient purification performances. Herein, a waste metal ion trapping strategy based on a novel solar vapor generator (SVG) toward highly efficient solar-driven sewage purification with prolonged durability is reported. This SVG is constructed based on a polyion complex (PIC) hydrogel/coal powder composite (PCC), where the PIC skeleton provides metal ion entrapment capabilities, and the low-cost coal powders act as solar absorbents. PCC enables improved solar-driven sewage purification from two aspects: first, the entrapped multivalent ions help to activate the water molecules inside PCC and lower water evaporation enthalpy, leading to enlarged evaporation rate; second, the strong interactions between the multivalent metal ions and polyelectrolyte chains aid in stabilizing their porous structure and maintaining continuous water transport capabilities. The resultant PCC-based SVG demonstrated high evaporation rate up to 3.6 kg · m−2 · h−1 in simulated industrial sewage under one sun illumination, as well as stable and efficient clean water generation in actual coal washery wastewater even for three weeks. We envision that the rational design of SVG with ions trapping capabilities and cost-effective solar absorbers should broaden the practical applications of SVG for harsh wastewater treatment.