Engineering a carbon dot-decorated fluorescent nanoplatform to promote heavy metal reutilization and photothermal evaporation with antibacterial activity

Solar steam generation is an efficient way to address global freshwater shortages. Heavy metals in wastewater pose serious environmental challenges and result in significant resource wastage. Developing an evaporator that integrates efficient water evaporation function, heavy metal (such as Fe) detection capability, and removal technology, with the aim of upgrading potentially discarded heavy metals into valuable materials, is undoubtedly an important technological challenge that urgently needs to be overcome. Herein, we report a fluorescent hydrogel grafted with lignin-based carbon dots (N-CDs) for Fe(III) ion recognition, self-assembled within a 3D tannic acid-based hydrogel network. The quantum yield of N-CDs is 5.9 % (λ_ex = 300 nm, λ_em = 342 nm). The fluorescent hydrogel exhibited excellent sensitivity for Fe(III) ion detection within the range of 0 to 200 µM, with a detection limit of 5.4 × 10^-4 M. Adsorption experiments confirmed that the hydrogel exhibited a high Fe(III) ion extraction capacity of over 239.2 mg g⁻¹ at room temperature. Subsequently, the exhausted waste material was converted into a material suitable for solar steam generation. The upcycled hydrogel evaporators exhibited outstanding evaporation rates of 2.62 kg m^-2h⁻¹ under one sun irradiation and displayed superior antibacterial efficacy. These findings not only provide a strategy for controlling heavy metal ions but also offer a pathway to recycle hazardous waste for wastewater treatment.