All-Natural Photothermal Hydrogel for Efficient Desalination and Heavy Metal Enrichment

Solar-driven interfacial evaporation technology presents a promising approach for large-scale, sustainable water resource utilization, with significant potential in seawater desalination and wastewater treatment. However, the simultaneous removal of waterborne pollutants during solar interfacial evaporation remains a significant challenge. This study introduces an all-natural photothermal hydrogel composed of chitosan, cellulose nanofibers, and carbonized spent bleaching earth (C@SBE) for efficient seawater desalination and heavy metal remediation. The hydrogel performance was enhanced by optimizing its three-dimensional porous structure and incorporating C@SBE to improve photothermal conversion efficiency and adsorption capacity. Under one-sun irradiation, the hydrogel achieved an impressive evaporation rate of 2.17 kg m^-2 h^-1 with an evaporation efficiency of 90.8%, exhibiting excellent salt resistance and long-term operational stability. Furthermore, the hydrogel demonstrated a maximum Cu²⁺ adsorption capacity of 145.3 mg/g, with adsorption kinetics following the pseudo-second-order model and isotherms aligning with the Langmuir model. The adsorption mechanism involved synergistic effects of chitosan amino chelation, C@SBE electrostatic interactions, and ion exchange. Soil remediation experiments further revealed that the hydrogel effectively reduced Cu²⁺ concentrations in contaminated soil from 500 to 45.6 mg/kg under one-sun irradiation, while simultaneously promoting healthy wheat seed growth. This study highlights a green, efficient, and sustainable multifunctional photothermal hydrogel, offering a novel technological platform and theoretical foundation for solar-driven water purification and environmental remediation.