Sustainable recovery of silver from X-ray film processing effluents using a novel thiourea derivative-grafted XAD-7 resin and its application in nano silver particle synthesis

The efficient reovery of silver from industrial waste is crucial for resource sustainability and environmental protection. In this study, a novel adsorbent, 4,4’-(((oxalylbis(azanediyl))bis(carbonothioyl))bis(azanediyl))bis(3-hydroxy naphthalene-1-sulphonic acid)-impregnated Amberlite A×D7(TUD@AXD7), was synthesised and characterised using SEM, BET, FTIR, ¹H NMR, ¹³C NMR, and GC-MS. The material exhibited a substantial surface area of 238.54 m²/g, contributing to its impressive Ag(I) adsorption capacity of 345.5 mg/g at pH 5.0. Adsorption equilibrium was best described by the Langmuir isotherm model (R² > 0.99), indicating monolayer adsorption. Kinetic analysis revealed that the process followed a pseudo-second-order model (k₂ = 0.0011 g mg⁻¹ min⁻¹), suggesting a chemisorption mechanism. The thermodynamic evaluation confirmed that adsorption was both spontaneous and endothermic, with ΔG° = −13.36 kJ/mol, ΔH° = 1120.1 kJ/mol, and ΔS° = 48.574 J/mol·K. The highest adsorption efficiency was achieved under optimised conditions, including pH 5.0, a contact time of 30 minutes, and an adsorbent dose of 80 mg at ambient temperature. The adsorbed silver was desorbed as AgNO₃ and subsequently utilised for the green synthesis of silver nanoparticles (AgNPs) using trisodium citrate as a reducing agent. The synthesised AgNPs were thoroughly characterised to assess their morphology, composition, and structural properties. Additionally, the TUD compound exhibited promising antioxidant (H₂O₂ scavenging) and antifungal activity, broadening its potential applications. The adsorbent demonstrated excellent stability and reusability over multiple adsorption-desorption cycles without significant efficiency loss. These findings highlight TUD@AXD7 as a cost-effective and sustainable material for silver recovery and contribute to the field of environmental science and materials chemistry by providing a novel method for silver recovery and its applications in nanotechnology and environmental remediation.