A novel method for synthesis of nano-γ-Al2O3: study of adsorption behavior of chromium, nickel, cadmium and lead ions

Nano-γ-Al₂O₃ adsorbent was synthesized by the novel sol–gel method. The adsorbent was characterized by transmission electron microscope, Fourier transform infrared and X-ray powder diffraction. The effects of several variables such as, adsorbent weight, pH and contact time on adsorption of chromium (Cr⁶⁺), nickel (Ni²⁺), cadmium (Cd²⁺) and lead (Pb²⁺) ions were studied in batch experiments. The results showed that the synthesized nano-γ-Al₂O₃ had a good capacity to adsorb Cr and Pb. The kinetic data were described with pseudo-first- and pseudo-second-order models. Three isotherm models, namely Freundlich, Langmuir and Tempkin, were used for analysis of equilibrium data, and results showed that Langmuir and Freundlich models were suitable for describing the equilibrium data of Cr⁶⁺, Cd²⁺, Ni^2
+ and Pb²⁺. Using Langmuir isotherm, the maximum sorption capacities of Cr⁶⁺, Pb²⁺, Cd²⁺ and Ni²⁺ were estimated to be 13.3, 6, 1.1 and 0.33 (mg/g) at 25 ° C, respectively. The sorption capacity did not change remarkably after reuse of sorbent for sorption–desorption cycle. The selectivity order of Cr⁶⁺, Pb²⁺, Cd²⁺ and Ni²⁺ sorption onto the adsorbent was Cr⁶⁺> Pb²⁺> Cd²⁺> Ni²⁺.