Mesoporous silica derived from agricultural residue as a sustainable platform for silver ion detection and recovery from electronic waste via UV-vis spectrophotometry

This investigation presents a green nanotechnology approach for the fabrication of a cost-effective sensor by immobilizing N-(2-((2-hydroxynaphthalen-1-yl)methyleneamino)-2-methylpropyl)-2,2,2-trifluoroacetamidehiourea-containing ( HMT ) ligand moieties onto mesoporous silica extracted from rice husk waste (RHS), yielding HMT@RHS nanocomposite that integrates waste valorization with precision metal-ion detection. Comprehensive physicochemical characterization confirmed the preservation of the disordered silica architecture (characterized by an amorphous X-ray diffraction (XRD) halo at 2θ ≈ 21.50°) and a well-developed mesoporous network. Ultraviolet-visible spectroscopic analysis elucidated that Ag + coordination to surface-anchored ligand active sites occurs upon metal chelation. Operating under optimized parameters (20 mg adsorbent, pH 5.5, ambient temperature), the HMT@RHS composite achieved a limit of detection (LOD) of 11.11 ppb for Ag+ with an equilibration time of 3 min and exceptional tolerance to various potential interfering metal cations at concentrations up to 100 ppm. The platform demonstrated robust operational stability, retaining high sensing capacity over eight successive adsorption-desorption cycles with a thiourea-HCl regeneration buffer, and high activity after 12 months of ambient-temperature storage under sealed conditions. Practical validation encompassed quantitative silver speciation in industrial circuit board leachates (recovery yields 92.3-96.7%, RSD ≤ 2.9%) and successful silver extraction from e-waste matrices with an overall recovery efficiency of 94.2%, confirming the composite’s utility in both environmental diagnostics and precious metal valorization. These outcomes establish HMT@RHS as a scalable, economically viable, and environmentally conscious alternative to conventional instrumental techniques for on-site Ag + monitoring and the sustainable recovery of Ag+ from mineral-depleting waste streams.