Low-cost synthesis of metal oxide nanoparticles and their application in adsorption of commercial dye and heavy metal ion in aqueous solution

Metal oxide nanoparticles such as ZnO and SnO2 with specific surface areas of 15.75 and 24.48 m2/g respectively were successfully synthesized by precipitation method and then employed as adsorbents for removal of Malachite Green Oxalate (MGO) and hexavalent Chromium (Cr) from aqueous solution. The nanoparticles were characterized by XRD, SEM, TEM, SAED, FT-IR and BET surface area analysis. The adsorption of MGO and Cr was achieved under different adsorbate concentration, contact time, adsorbent dosage, pH and temperature conditions. Adsorption equilibrium was studied with Langmuir and Freundlich isotherm models. Equilibrium data were best fitted with the Langmuir and Freundlich isotherm models. Kinetic studies indicated that the adsorption process follows second order kinetics and particle diffusion mechanisms are operative. Thermodynamic parameters were studied in detail to know the nature and mechanism of adsorption. The spent adsorbents were regenerated with CH3COOH or NaOH solutions and regenerated adsorbents showed very good adsorption efficiencies. All the above results demonstrated that metal oxide nanoparticles could be used as a possible alternative low-cost adsorbent for the efficient removal of dyes and heavy metals from aqueous solution.