Removal of Cr(VI) from aqueous solution using Fe-modified activated carbon prepared from luffa sponge: kinetic, thermodynamic, and isotherm studies

In this study, the removal of Cr(VI) from aqueous solution using Fe-modified activated carbon (AC-Fe) was investigated. AC-Fe before and after Cr(VI) adsorption was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller surface area. The effects of various parameters were investigated by batch experiments, such as contact time, temperature, pH, adsorbent dose, and initial Cr(VI). The results showed that the modification method greatly improves the adsorption property. The surface area of the activated carbon was relatively high (834.006m(2)), and the Fe-AC structure was found to be a well-developed array of microvoids and mesopores. FTIR revealed that the abundance of O-H, N-H, C-O, metal-oxygen, and metal-hydroxyl functional groups on the surface of the Fe-AC may play an important role for the adsorption of Cr(VI). The optimum pH was 1 with maximum removal efficiency of 98.71%. The batch equilibrium data fitted well to the Langmuir isotherm (R-2=0.9960) at 308K, which indicated monolayer adsorption. Kinetic data were best fitted with the pseudo-second-order kinetic model, which was considered as the rate-limiting factor. The negative G values confirmed the spontaneity of the adsorption process. Positive H and S values indicated endothermic and irreversible adsorption.