Optimized preparation of alginate/nanocellulose/polypyrrole composite hydrogel via in-situ polymerization for high-efficiency solar desalination and wastewater purification

In the field of solar steam generation, hydrogels with interfacial evaporation configurations stand as a promising candidate for solar evaporators. Hydrogel-based photothermal materials provide excellent hydration channels for supplying water to an evaporative layer due to their porous structure and hydrophilic nature. This work proposed a facile and in-situ fabrication of sodium alginate hydrogel incorporated with cellulose nanocrystals and polypyrrole as an effective photothermal material. A robust and systematic statistical tool for the design of experiment (DOE) called Taguchi's method was employed to optimize processing conditions to achieve a maximum output. The optimized hydrogel composite demonstrated excellent evaporation rates of 1.47 kg m^-2h^-1 under 1 sun and 2.81 kg m^-2h^-1 under 2 sun along with the evaporation efficiency of 91.3% under 1 sun. Integrating polypyrrole and cellulose nanocrystals into the composite hydrogel has improved its light absorption, integrity, and hydrophilicity. Additionally, the optimized hydrogel revealed excellent removal of salts, hardness, dyes, and heavy metals contaminants.