Characterization of coconut shell-based activated carbon and its application in the removal of Zn(Ⅱ) from its aqueous solution by adsorption

摘要

Adsorption kinetics and loading capacity of Zn(Ⅱ) onto a coconut shell-based activated carbon (AC) was investigated at different solution concentrations, pH values, and temperatures. Characterization of the AC was performed by using scanning electron microscopy, N_2 adsorption and desorption isotherms, pore size distribution, surface area determination, determination of point of zero charge (pH_(PZC)), and Boehm titration. The equilibrium studies showed that the Zn(Ⅱ) adsorption onto the AC increases from 1.98 to 4.24 mg/g by increasing the initial Zn(Ⅱ) concentration from 23 to 148 mg/L. The kinetic experiments revealed that the initial adsorption rate of Zn(Ⅱ) is rapid and decreased afterwards. The adsorption rate significantly increased with raising the temperature from 25 to 45 ℃. The activation energy for the adsorption of Zn(Ⅱ) ions onto the AC was 54.23 kJ/mol. Both of the adsorption kinetics and loading capacity decreased with increasing the acidity of solution. The results of Boehm titrations, determination of pH_(PZC), and the time course of the system pH during the sorption process showed that the adsorption of Zn(Ⅱ) ions onto the AC takes place through cation-exchange mechanism with acidic surface functional groups. The results of linear and nonlinear regression methods showed that the equilibrium data among different two- and three-parameter isotherm models closely obey from a three-parameter isotherm model, namely Koble-Corrigan. The results of linear regression method revealed that the kinetic data among different kinetic models closely obey from Elovich model. The rate-limiting step in the adsorption of Zn(Ⅱ) onto the AC was assessed through the Webber and Morris plots.