One-step eco-friendly synthesis of Ag nanoparticles on bentonite-g-C₃N₄ for the reduction of hazardous organic pollutants in industrial wastewater.

Abstract

Silver nanoparticles (Ag NPs) supported on natural materials have garnered significant attention due to their wide applicability across various research fields. This study presents an eco-friendly, scalable, and one-step approach to synthesizing high-purity Ag NPs supported by bentonite-graphitic carbon nitride (Bt-g-C₃N₄) nanocomposites via thermal reduction. The successful integration of Ag NPs into the Bt-g-C₃N₄ matrix was confirmed through several characterization techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDX). XRF analysis identified the clay as beidellite-rich (Si/Al molar ratio less than 2), while EDX spectra and XRD patterns confirmed the presence of Ag NPs, with characteristic peaks at 38.04^° and 44.24^°. SEM and TEM images showed uniform Ag NP distribution with an average particle size of 4.75 nm and a spherical morphology. Acid-activated bentonite preserved its layered structure and exhibited a significant surface area increase, reaching 113.77 m²/g after hydrochloric acid treatment, thereby enhancing its capacity for supporting nanoparticle-based catalysts. The synthesized nanocomposites demonstrated exceptional catalytic performance, achieving reduction efficiencies of approximately 99 % for various organic pollutants, including nitrophenols (within 7 min for 4-nitrophenol), cationic dyes (within 12 min for Rhodamine B), and anionic dyes (within 5 min for methyl orange), using sodium borohydride (NaBH₄) as the reducing agent. The reduction followed first-order kinetics, with activity factors (k′) calculated as 134 s⁻¹.g⁻¹, 260 s⁻¹.g⁻¹, and 92 s⁻¹.g⁻¹ for 4-NP, MO, and RhB, respectively. Furthermore, the Ag NPs/Bt-g-C₃N₄ nanocomposites exhibited remarkable recyclability, maintaining high catalytic efficiency across multiple cycles.