Investigation of zwitterionic wood evaporator for efficient salt-resistant desalination and water purification

As an environmentally friendly approach to desalination and water purification, solar interfacial evaporation contributes significantly to mitigating global water shortages. However, technical challenges still exist in achieving multipurpose, high evaporation rates, low cost and durability. Herein, we proposed a novel solar evaporator, the zwitterionic wood evaporator, which exhibited high efficiency and energy-saving characteristics while enabling effective desalination of NaCl high-salinity solution. This paper proposed the use of zwitterionic hydrogel as a new platform for solar-driven brine purification under extreme salinity conditions. Zwitterionic hydrogel is a high-water-content polymer network, whose molecular structure simultaneously contains positively charged (-N(CH 3 ) 2 + ) and negatively charged (-SO 3 - ) functional groups. By leveraging the anti-polyelectrolyte property of zwitterionic hydrogels, zwitterionic wood evaporator effectively inhibits the migration of salt ions via its monovalent charge characteristics, while also demonstrating excellent water activation capability. Moreover, this molecular structure promotes the formation of a zwitterionic polymer network and intermediate water, which in turn enhances the evaporation process. By optimizing water evaporation performance, zwitterionic hydrogels contribute to the long-term stability and salt tolerance of zwitterionic wood evaporator by preventing salt crystals accumulation and maintaining structural integrity. Under 1 kW m⁻ 2 solar radiation intensity, the zwitterionic wood evaporator achieved 2.673 kg m⁻ 2 h⁻ 1 evaporation rate in 15 wt% NaCl solution, with 85.29 % energy efficiency. It operated continuously for 12 days (9 hours/day) without obvious salt crystals accumulation. The zwitterionic wood evaporator design and salt crystallization suppression strategy proposed in this study provide a low-cost, sustainable solution for off-grid desalination and zero liquid discharge.