CuO synthesized by solvothermal method as a high capacity adsorbent for hexavalent chromium

The ability of copper oxide synthesized by three different methods (solvothermal, precipitation method, and precursor calcination) for the adsorption of hexavalent chromium (Cr(VI)) ions from aqueous solutions was investigated, highlighting adsorption capacity dependence on specific synthesis conditions. Copper oxide nanoparticles with monoclinic phase and high specific surface areas (around 120 m(2) g(-1)) were successfully synthesized by solvothermal and precipitation method. Studies on Cr(VI) adsorption capacity of the synthesized materials were conducted at different temperatures, pH, time, and initial Cr(VI) solution concentration. The results revealed a key role of acetate groups bound to CuO surface in Cr(VI) adsorption. These groups were preserved during solvothermal synthesis, while they were partially volatilized by the precipitation method and completely eliminated with precursor calcination. Thermodynamic analysis of the adsorption data confirmed a physisorption behavior, which is consistent with the proposed complexing role of acetate groups. The correlation coefficient for each isotherm-model (Langmuir, Freundlich and Temkin) showed that the equilibrium adsorption behavior of Cr(VI) is adjusted to the Langmuir model with a maximum adsorption capacity of 245 mg g(-1) at 25 degrees C. (C) 2016 Published by Elsevier B.V.