Fabrication, characterization and adsorption investigation of Nano zinc oxide–sodium alginate beads for effective removal of chromium (VI) from aqueous solution

Zinc oxide nanoparticles (ZnO-NPs) were prepared by modified wet chemical method while alginate-zinc oxide (Alg-ZnO) composite was synthesized by the interaction between the prepared zinc oxide nanoparticles and calcium alginate. The solid adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-Vis spectroscopy. Adsorption isotherms of chromium ions were investigated onto the prepared solid adsorbents with varying the initial concentration of Cr(VI) under different application conditions such as pH, contact time, adsorbent dosage, and temperature. Adsorption of Cr(VI) was investigated by different isotherm models like Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models. Maximum adsorption capacities (31.09 and 34.63 mg/g) were achieved by ZnO-NPs and Alg-ZnO, respectively at 25 ℃. The results of isotherm models indicate the perfect applicability of Langmuir and Dubinin-Radushkevich models, revealing the dominance of monolayer and the physisorption of chromium ions onto the studied adsorbents.