3D Multifunctional Hydrogel for Wastewater Valorization through Photocatalytic Antibiotic Degradation, Green Energy Recovery, and Post-Treatment Applications

Abstract

Water pollution and green energy limitation are two interrelated problems at a global level; thus, effective strategies should be adopted for both. In this regard, multifunctional photocatalytic urea-In₂S₃ 3D hydrogels have been prepared using environmentally friendly hydrogel matrices based on pectin to effectively treat polluted water, recover nutrients, and reuse the products in agriculture. The synthesized beads were characterized by techniques including XRD, SEM, FESEM, FTIR, PL, and UV-Vis DRS, revealing the formation of crystalline In₂S₃ nanoparticles in the hydrogel matrix and their uniform distribution as well as increased absorbance in the visible region. The photocatalytic properties of these hydrogel beads were found to be superior, leading to the complete removal of the antibiotic sulfamethoxazole (SMX) from polluted water of the river Koel by almost 95% in only 20 minutes through visible light. Radicals such as •O₂⁻ and •OH were identified to be responsible for the degradation process. Besides degrading SMX, the produced H₂O₂ was 299 μM in 60min, demonstrating efficient charge separation and ROS production. Post-treatment, the used hydrogels along with the treated water were repurposed in a small-scale aquaponics system wherein sunlight led to nitrogen fixation by transforming atmospheric nitrogen (N₂) into biologically useful ammonium ions (NH₄⁺) through photocatalysis, while an effective release of encapsulated urea. Over the course of seven days, the NH₄⁺ion concentration progressively increased to approximately 2100 μM, indicating a continuous process of nitrogen fixation. The proposed system offers a scalable and environmentally sustainable strategy for wastewater valorization, green-energy recovery, and advancing next-generation eco-friendly water treatment and agricultural applications