Investigation of the roles of lignin in biomass-based hydrogel for efficient desalination

The shortage of freshwater has become a global challenge, and solar-driven interfacial evaporation for desalination is a promising way to alleviate the crisis. To develop highly efficient and environmentally friendly photothermal evaporator, the hydroxyethyl cellulose (HEC)/alkaline lignin (AL)/graphene oxide (GO) hydrogels (CLGs) with remarkable evaporative performance were successfully fabricated by a facile sol-gel method using biomass residues. The influence of AL content on the physicochemical properties of the evaporator was investigated. The increasing content of AL improves the mechanical properties, saturated water content and crosslink density of the hydrogels. The designed materials exhibit outstanding thermal insulation capacity (the thermal conductivity of less than 0.05 Wm(-1)K(-1)) and high light absorption capacity of more than 97%. The solar evaporation efficiency and water evaporation rate of the HEC/64 wt % of AL/GO hydrogels (CLG4) achieve 92.1% and 2.55 kgm(-2)h(-1) under 1 sun, respectively. The salt resistance test results reveal that the evaporation rate of the CLG4 can still reach 2.44 kgm(-2)h(-1) in 3.5 wt % NaCl solution. The solar evaporation rate of the CLG4 can maintain in the range of 2.45-2.59 kgm(-2)h(-1) in five cycles. This low-cost lignin-based photothermal evaporator offers a sustainable strategy for desalination.