Green-synthesized zeolite Y-supported zero-valent iron nanocomposite for enhanced adsorptive reduction of hexavalent chromium from aqueous solutions

Abstract

Hexavalent chromium (Cr(VI)), a major pollutant in tannery wastewater, poses significant environmental and health risks. Zeolite Y possesses a high cation-exchange capacity but low affinity for Cr(VI), which predominantly exists in anionic forms in aqueous solutions. This study aimed to modify zeolite Y with zero-valent iron nanoparticles (nZVI) to enhance its capacity to adsorb Cr(VI). The zeolite Y/nZVI composite was synthesized using green tea extract. nZVI effectively reduces Cr(VI) to less toxic Cr(III), which precipitates as Cr(OH)₃. The composite was characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), particle size analysis (PSA), and pH point-zero charge analysis. The highest Cr(VI) adsorption capacity was achieved under acidic conditions (pH = 1), elevated temperature (343 K), an initial Cr(VI) concentration of 30 ppm, and a contact time of 45 min. The adsorption data were well fitted to the Langmuir isotherm and pseudo-second-order kinetic models. The thermodynamic analysis indicated that the adsorption process was endothermic and spontaneous at higher temperatures. The modification of zeolite Y with zeolite Y/nZVI enhanced the adsorption capacity from 0.9 mg g⁻¹ to 7.1 mg g⁻¹.