Improving solar desalination in high-salinity brine through zwitterionic salt containing hydrogels

By tightly locked zwitterionic salts in CNF-based hydrogel network, the hydrogel exhibit excellent evaporation rates in high salinity brines due to the anti-polyelectrolyte effect. Recently, solar vapor generation (SVG) has emerged as a cost-effective and environmentally friendly approach for sea water desalination aimed at producing clean water. However, salt accumulation inside and on the hydrogel will lower the evaporation performance and impact the durability of evaporators. Herein, small molecule zwitterionic salts are incorporated into CNF (carboxylated cellulose nanofiber)/hPEI (polyethyleneimine) hydrogel network containing loaded reduced graphene oxide. Benefiting from distinctive anti-polyelectrolyte properties, the hydrogel containing phosphocholine chloride calcium salt exhibits evaporation rates of 3.26 and 3.13 kg m -2 h −1 in 3.5 wt% and 10 wt% brines, which are approximately 30 % and 25 % higher than that in pure water under one sun irradiation. It indicates that the introduction of phosphocholine chloride calcium salt (PCCa) results in the anisotropic lamellar porous structure of the gel with higher porosity (91.83 %), faster water transport capacity (0.45 g s −1 ), lower equivalent enthalpy (1221.05 J g −1 ) and high salt flux (59.16g m -2 h −1 in 3.5 wt% brine, 57 % higher than that of gel without PCCa). Outdoor experiments revealed that the evaporator achieves an average evaporation rate of 2.47 kg m -2 h −1 even under less than 1 kW m −2 solar intensity, producing 12.35 kg m −2 clean water in 5 h. The remarkable performance of the SVG and the fundamental design principles may supply insights for the development of next-generation practical desalination systems.