Rational Design of Advanced Three-Dimensional Flexible Hydrogels for Photocatalytic Water Remediation Integrated via Energy Storage and Resource Recovery

Abstract

The synthesis of multifunctional and sustainable materials with ability to remediate the environment along with generating energy using renewable sources presents a great challenge for water treatment systems in future. Herein, a novel three-dimensional (3D) flexible hydrogel system based on sodium alginate, InFeO₃, polypyrrole (PPy) and black phosphorus (BP) is described, which serves as a multifunctional system for photo-catalytic degradation of contaminants, photo-energy storage and resource recovery. The structural, morphological, optical and electrochemical analyses indicated that the photocatalytic components are successfully incorporated in the hydrogel structure and an interlinked charge transfer network is formed. Upon exposure to light, photogenerated electron-hole pairs are formed in InFeO₃ and the conductive PPy network acts as a trap for photogenerated electrons allowing energy storage and sustaining photocatalysis such that even after the light source has been turned off. Using sulfamethoxazole (SMX) as a model emerging contaminant, 98% degradation was observed within 60 min of exposure to visible light and the degradation of contaminants in dark after only 10 min of illumination. At the same time, the hydrogel provided in situ generation of H₂O₂ of concentration 357 μM. Apart from pollutant degradation, the multifunctional system was able to produce ammonia via an efficient photocatalytic reaction, up to a concentration of 279 μM, indicating the possibility of sustainable resource recovery. Due to its superior flexibility and mechanical strength, the hydrogel can be easily incorporated into the complicated water treatment systems without the risk of structural damage. This study proposes a self-sufficient photocatalytic hydrogel capable of degrading pollutants, storing photo energy, producing hydrogen peroxide, and ammonia all in one place.