Biologically Synthesised Silver Nanoparticles as Photocatalysts for Removal of Synthetic Textile Dyes

Abstract

The textile industry is a major water consumer and a major producer of hazardous wastewater, contributing significantly to environmental degradation. Synthetic textile dyes such as reactive red and methylene blue are persistent environmental pollutants owing to their toxicity, chemical stability, and resistance to biodegradation, posing significant ecological and public health concerns. They impart intense colouration to water bodies, inhibit photosynthesis, disrupt aquatic ecosystems, and pose serious health hazards to humans. Nanotechnology-based treatments have demonstrated remarkable efficiency in degrading pollutants due to the high reactivity and surface area of nanoparticles. The present study explores the biosynthesis of silver nanoparticles (AgNPs) using Escherichia coli and their application in the photocatalytic degradation of synthetic textile dyes, reactive red and methylene blue. The formation of nanoparticles was confirmed through UV-Vis spectroscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy, revealing spherical morphology, nanoscale dimensions (17.1–83.2 nm), and biomolecule-assisted stabilisation. Dye degradation experiments were conducted using varying volumes of AgNPs (0.5–5 mL) over 24 hours, with an initial 7-hour exposure to natural sunlight followed by incubation at 37 °C. Results demonstrated time- and dose-dependent decolourisation, with noticeable fading after 7 hours, particularly at higher nanoparticle concentrations. After 24 hours, the maximum degradation efficiencies were 19.04% for reactive red and 19.17% for methylene blue. Control samples showed negligible change, confirming the catalytic role of AgNPs. These findings highlight the potential of green-synthesised AgNPs as eco-friendly photocatalysts for mitigating persistent dye pollution in textile wastewater.