Photothermal Hydrogel with Enhanced Heavy Metal Ion Adsorption Capacity for Soil Remediation

Solar-driven interfacial evaporation presents a promising, sustainable route for desalination and wastewater treatment. However, simultaneously removing heavy metal contaminants from water and soil during the evaporation process remains a significant challenge. Here, we designed a hybrid hydrogel that integrates solar evaporation with the removal of heavy metals. The hydrogel was synthesized by embedding carbon nanotubes (CNTs) into a sodium alginate/polyacrylamide (SA/PAM) polymer network, enabling the efficient removal of heavy metal ions from wastewater and soil. The key to its function lies in the abundant -COO^- groups from SA, which offer specific chelation sites for heavy metal ions, enabling effective immobilization through ion exchange and coordination. Under 1 kW m^-2 irradiation, the hydrogel achieved an evaporation rate of 1.96 kg m^-2 h^-1 while simultaneously adsorbing heavy metal ions, with enhanced capacities of 112.40 mg g^-1 for Cd²⁺ and 117.80 mg g^-1 for Cu²⁺. More importantly, the hydrogel demonstrated effective remediation of contaminated soil, reducing the Cu²⁺ concentration to below the agricultural soil risk-screening threshold. This work demonstrates an integrated strategy for simultaneous water purification and soil remediation achieved by combining photothermal conversion and selective adsorption within a single material platform.