Photocatalytic degradation of azo dyes assisted by biosynthesized AgNPs loaded in physically cross-linked PVA/CS hydrogel nanocomposites

Abstract

Silver nanoparticles (AgNPs) are extensively utilized in industrial applications due to their unique physicochemical and antimicrobial properties. However, the development of eco-friendly and scalable synthesis methods remains a challenge. This study introduced a novel AgNP-embedded Polyvinyl Alcohol/Chitosan (PVA/CS) hydrogel with enhanced photocatalytic and antibacterial properties, synthesized via a green, plant-mediated approach. AgNPs were biosynthesized using Asparagus officinalis (AO) extract, where phytochemicals from the AO stem acted as reducing agents, leading to the formation of spherical AgNPs (around 80 nm). The synthesized nanocomposite exhibited a porous structure, excellent water absorption capacity (swelling ratio: 236.29 %), and superior mechanical properties compared to the pristine hydrogel. The photocatalytic efficiency of the hydrogel was evaluated for the degradation of dye pollutants, specifically Methylene blue (MB) and Congo red (CR). After 210 min of direct sunlight exposure, the bio-fabricated hydrogel nanocomposite achieved degradation efficiencies of 72 %, follow pseudo-first-order with a rate constant of k = 0.00591 min⁻¹ (MB) and 71 % with k = 0.00927 min⁻¹ (CR). This study advances prior research on AgNP-based hydrogels by integrating a sonication-assisted green synthesized AgNPs, which enhances their stability, dispersibility, and interaction with the hydrogel matrix. Unlike conventional AgNP-based hydrogels that rely on chemical synthesis and UV-assisted photocatalysis, this study presents an eco-friendly and energy-efficient approach that operates effectively under natural sunlight. Furthermore, the optimization of synthesis conditions ensures improved photocatalytic efficiency, addressing limitations in previous studies related to particle aggregation and reduced stability. These findings contribute to the advancement of biodegradable and reusable AgNP-based hydrogels for potential applications in wastewater treatment and environmental remediation.