Biochar-based interfacial evaporation materials derived from lignosulfonate for efficient desalination

The solar-driven interfacial evaporation has attracted great attention for the purpose of alleviating freshwater shortage. Lignosulfonate (LS), a main byproduct of sulfite pulping processes, is an abundant natural resource but has not been reasonably utilized. To mitigate the above problems, biochar-based interfacial evaporators derived from LS for solar steam generation were studied in this paper. First, LS was used as a raw material for fabricating carbon materials by carbonization to construct LS-derived carbon (CLS). Meanwhile, LS-derived porous carbon (PCLS) in the presence of CaCO₃ as the activator was also prepared. Next, the two biochar powders, as solar absorbers, were crosslinked with polyvinyl alcohol to prepare the interfacial evaporation materials (PVA@PCLS and PVA@CLS). The open porous structure facilitated the capillary effect and water transport to the evaporator surface. It was also found that the light absorption of the materials could reach more than 97% in the 250–2500 nm range. Moreover, the water evaporation rate and the solar-to-vapor conversion efficiency of PVA@PCLS and PVA@CLS were 2.33, 1.82 kg m⁻² h⁻¹, and 83.7%, 69.3% respectively under 1 sun (1 kW m⁻²) irradiation. The solar-to-vapor conversion efficiency of PVA@PCLS was much increased after the carbonization of LS. In addition, the material cost of PVA@PCLS is only $38.3/kg due to the low price of LS. Therefore, this work provides an economic and efficient strategy for solar-driven desalination and a possible way for the high-value utilization of lignin.