Sustainable synthesis of Ag/UiO-66 composites using recycled silver for efficient adsorption of methylene blue and crystal violet.

Authors

Hazem Ibrahem, Hassanien Gomaa, Ahmed A Gahlan, Adham M Nagiub

Published in

Scientific reports. Volume 16. Issue 1. Aug 11, 2026. Epub Aug 11, 2026.

Abstract

Synthetic dyes are persistent and toxic water pollutants that require efficient removal technologies, and metal-organic frameworks (MOFs) have emerged as promising adsorbents for this purpose. In this work, a defect-engineered zirconium-based UiO-66 framework was synthesized by an HCl-modulated solvothermal route. UiO-66 was then functionalized with silver nanoparticles through a post-synthetic impregnation-reduction method to form an Ag/UiO-66 composite for the removal of the cationic dyes methylene blue (MB) and crystal violet (CV). The silver was recovered from electrical contact waste, thereby adding a resource-recovery dimension to the synthesis. Powder X-ray diffraction, XPS, FTIR, SEM, and TEM supported the incorporation of metallic Ag⁰ nanoparticles (about 3.3 nm; 3.11 wt%), uniformly dispersed on the crystals, with full preservation of the UiO-66 framework. Silver loading decreased the BET surface area from 870 to 642 m² g^-1, indicating partial pore occupation. Nevertheless, Ag/UiO-66 exhibited higher Langmuir capacities than pristine UiO-66, reaching 113.49 and 46.72 mg g^-1 for MB and CV, respectively, compared with 104.98 and 43.72 mg g^-1 for the pristine framework. Removal efficiencies above 98% were achieved at neutral pH, with equilibrium attained within 45 min. The adsorption was favored above the point of zero charge (pH_pzc = 5.88) through electrostatic attraction, followed the pseudo-second-order kinetic model, and was best described by the Langmuir isotherm (R² > 0.98), indicating monolayer adsorption. Thermodynamic analysis indicated a spontaneous, exothermic process, with ΔH° values ranging from - 4.91 to - 9.31 kJ mol^-1. The combined isotherm, kinetic, and spectroscopic results indicated that the uptake occurs through both physical and chemical interactions, including electrostatic attraction, π-π stacking, hydrogen bonding, and binding at the silver and defect sites. The composite retained over 90% removal after five adsorption-desorption cycles and removed 95.3% of MB and 93.6% of CV from Nile River water. These results demonstrate that silver recovered from electronic waste can be used to prepare effective, reusable Ag/UiO-66 adsorbents for the removal of cationic dyes.

PMID:
42575927
Bibliographic data and abstract were imported from PubMed on 11 Aug 2026.

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