Polyzwitterionic hydrogel using waste biomass as solar absorbent for efficient evaporation in high salinity brine

Solar-driven interfacial vapor generation (SVG) is a promising strategy for brine purification. However, the effective combination of functional evaporator backbones and solar absorbers for SVG enhancement remains challenging in high-salinity brines (≥ 10 wt%). Herein, a biomass-based polyzwitterionic hydrogel (PZH) was developed to improve the SVG performances in 10 wt% brine. Zwitterions with specific anti-polyelectrolyte effects served as backbones for accelerating H₂O transportation, with fewer salt deposits and macropore channels. The biomass of straw prepared at a pyrolysis temperature at 600 ℃ was the most effective solar absorber. The synthesis of So600-PZH-8mm yielded the optimal solar evaporator with a low evaporation enthalpy of 877.79 J·g⁻¹, a remarkable solar-to-vapor energy efficiency of 87.1%, and a high evaporation rate of 3.57 kg·m⁻²·h⁻¹ under 1 sun irradiation and a relative humidity of 30%. Multi-cycle evaporation tests further verified the high quality of the steam water, high salt resistance, reliability, and durability of So600-PZH-8mm in practical applications. Furthermore, density functional theory (DFT) calculations of the binding energies of charged groups and ions verified the anti-polyelectrolyte effect and swelling behavior of the PZHs. Overall, this study demonstrated the effectiveness of waste biomass as solar absorber for high-efficiency solar adsorption and water activation, which opens a new perspective to inspire the up-conversion of waste biomass in more valuable and meaningful ways.