Response surface methodology approach for optimization of the removal of chromium(VI) by NH2-MCM-41

• Removal of Cr(VI) by amine-functionalized MCM-41(NH2-MCM-41).
• Response surface methodology for optimizing the operating parameters.
• The adsorbent was characterized by FTIR, XRD and EDS.
• The maximum adsorption capacity was found to be 38.55 mg/g.

A central composite design (CCD) combined with response surface methodology (RSM) was employed for maximizing chromium (Cr(VI)) removal from aqueous solution by using amine-functionalized MCM-41 (NH2-MCM-41). Four independent variables namely initial pH, metal ion concentration, temperature and adsorbent dosage were investigated. Analysis of variance (ANOVA) of the quadratic model suggested that the predicted values were in good agreement with experimental data. Maximum removal was attained as 98.70% at initial pH 3.5, Cr(VI) concentration of 10 mg/L, temperature 40 °C with an adsorbent dosage of 5 g/L. The synthesized adsorbent was characterized by Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS). The kinetics were evaluated by pseudo-first-order and pseudo-second-order models, pseudo-second-order model was found to describe the process better with a higher correlation. The adsorption data conformed well to Langmuir and Freundlich isotherms. Thermodynamic analysis revealed that the adsorption process was spontaneous and endothermic. The results from adsorption–desorption cycles showed that NH2-MCM-41 held good desorption and reusability.