Lignin hydrogel-based solar-driven evaporator for cost-effective and highly efficient water purification

Solar-driven interfacial evaporation is an emerging water treatment technology for fresh water generation. However, poor thermal localization performance and rapid salt accumulation of the designed evaporator are the two factors, restricting the practical application. Here, a cost-effective lignin-based hydrogel with three dimensional meso/micro-porous structures is prepared by a facile and scalable crosslinking-polymerization strategy. Benefiting from numerous hydrophilic hydroxyls in lignin as well as 3D hierarchical porous structure, the designed hydrogel exhibits sufficient water supplement, effective water activation, as well as fantastic anti-salt accumulation performance. Our lignin hydrogel-based evaporator achieves a high and stable evaporation rate of 2.25 kg·m−2·h−1 for 24 h continuous operation without salt crystallizing and blocking, and shows a good stability in a wide range of pH value from 1 to 14. In addition, heavy metal ions, including Cu2+, CrO42−, Co2+ are efficiently removed from polluted water by electrostatic interaction with excess hydroxyl groups in the lignin hydrogel. Therefore, lignin hydrogel-based evaporator offers a cost-effective and long-term anti salt blocking strategy for solar-driven water purification.