Reducing Heat Conduction Enhances the Photothermal Efficiency of Upcycled Adsorbents

Abstract Solar steam generation is an efficient way to address global freshwater shortages. However, water evaporation suffers from either inefficient heat conduction or relies on expensive materials and complex equipment. Herein, a porous hydrogel (AC‐H) with molecular meshes, micron channels, and internal gaps is fabricated and used for metal ion adsorption. AC‐H exhibits excellent uptake ability and can attain the levels required by industrial water safety standards. Subsequently, the exhausted AC‐H hydrogel is vulcanized in situ (AC‐MS) and upcycled for solar steam generation resulting in ≈1.41 kg m⁻² h⁻¹ evaporation rate under one sun irradition, which reduces costs and converts the waste into a resource. Furthermore, a heat management strategy is developed where a cold surface of specific area is introduced between the AC‐MSx and bulk water to adsorb the heat loss. When the cold area is increased, the energy in the bulk water can be extracted by the coldsurface. which enhances the water evaporation rate. Significantly, the theoretical simulations are in good agreement with the experimental results. Therefore, this research provides a novel strategy to upcycle exhausted materials for photothermal technologies and reduces the heat conduction during solar‐to‐thermal evaporation.