Dye Degradation from Aqueous Solution by Green Synthesised Silver Nanoparticles (AgNPs) from Smooth Pigweed (Amaranthus hybridus): Kinetics and Thermodynamics Studies.

Abstract

Background: The textile industry, predominantly the dye industry, represents the world's major contributor to water pollution. The waste from such industries makes the water bodies coloured, detrimental to terrestrial and aquatic environments. Objectives: This study investigated and reported Malachite green adsorption from aqueous solution using silver nanoparticles (AgNPs). Methodology: AgNPs were prepared via an eco-friendly approach and characterised by Fourier transform Infrared spectroscopy (FTIR), X-ray diffractometry (XRD), UV-visible spectrophotometer and Scanning electron microscopy (SEM). Adsorption study was investigated under different conditions such as, pH, adsorbent dosage, contact time, temperature and initial concentration of dye to determine the optimal conditions and the maximum adsorption capacities. Results: XRD revealed the crystalline nature of the AgNP. However, the SEM micrograph of the AgNPs showed a spherical shape with a non-uniform granular shape attributed to the bio-mediated process. Whereas, FTIR spectra of AgNPs exhibited 3407, 2956, 2834, 2725, 1660, 1358 and 1096 cm^-1, representing free OH molecules, stretching C-H modes, stretching alkenes C=O bonds, carbonyl group stretching C-OH band, stretching C-O alcohols and ethers, respectively. The kinetic study of malachite green onto silver nanoparticle adsorbents showed that the adsorption kinetics followed both the pseudo-first-order and pseudo-second-order rate. Conclusion: The AgNPs can be effective adsorbents for removing dyes from aqueous solutions. Recommendation: The study suggests implementing eco-friendly practices in the textile dyeing process to reduce water pollution, targeting the adoption of biodegradable materials and sustainable dyes. It further suggests conducting further research on optimising adsorption conditions using silver nanoparticles to improve pollutant removal efficiency from wastewater in the textile industry.