A bifunctional polyacrylamide-alginate-TiO2 hydrogel solar evaporator for integrated high-efficiency desalination and photocatalytic degradation

Integrating interfacial solar steam generation with photocatalytic degradation technology holds significant prospects for practical applications in simultaneous clean water collection and organic pollutant degradation. However, existing photothermal-photocatalytic bifunctional evaporators still suffer from performance deficiencies such as limited light absorption, insufficient evaporation rate and degradation efficiency, leading to the partial contaminant residual in complex wastewater. Herein, we propose a surface functionalization-bicrosslinking strategy to develop a novel photothermal-photocatalytic bifunctional hydrogel solar evaporator. The strategy involves surface functionalization of TiO₂ nanoparticles to form core-shell structured bifunctional TiO₂@C nanoparticles by dopamine-modified thermal treatment, followed by composting with polyacrylamide/sodium alginate (PAM/SA) to achieve microporous double-network hydrogel. The resultant TiO₂@C/PAM/SA hydrogel composites exhibit efficient sunlight absorption of up to 99.87 %, a remarkable evaporation rate of 2.97 kg m⁻² h⁻¹ with an outstanding photothermal efficiency of 92.13 %, as well as high photodegradation efficiency of 84.37 % under one sun irradiation. We further integrate such hydrogel composites into the fabrication of photothermal-photocatalytic bifunctional evaporators, which demonstrate efficient purification and photocatalytic efficacy in various water samples, including low-to-high concentrated brines and heavy metal ion/organic pollutant-containing wastewater. Such a strategy of designing high-performance photothermal-photocatalytic hydrogels opens a new avenue to coherent solar desalination and organic pollutant degradation for complicated seawater/wastewater systems.