Removal of Cr (VI) from aqueous solution using MCM-41.

Mesoporous molecular sieves (MCM-41) was successfully synthesized using hydrothermal synthesis and characterized by X-ray diffraction and nitrogen adsorption-desorption. Characterization results show that synthesized MCM-41 is a good adsorption material of good crystallinity, large surface area (1,040m²/g) and uniform diameter (centered at 2.8 nm). Removal of Cr (VI) from aqueous solution using MCM-41 was carried out by UV-Vis spectrophotometry. The different parameters affecting the adsorption efficiency were investigated and obtained their optimal values (pH 4, temperature 35°C, initial Cr (VI) concentration < 10 mg/L, adsorption time 2 h, adsorbent concentration of 10mg/L). It is very useful and important to dealwith Cr (VI) fromaqueous solution. The adsorption isotherm was also investigated. It is found that the adsorption isotherm follows the Langmuir model better. What's more, b of 76.71 mg^-1 and q of 904 mg/g were calculated from Langmuir linear fitting. The adsorption reaction is spontaneous and endothermic as ΔG⁰ < 0 and ΔH⁰ > 0. Finally, we studied the adsorption kinetics and find that the adsorption of Cr (VI) ions onto MCM-41 is more suitable for pseudo-second-order kinetics. q_e and k₂ were calculated. The detailed kinetic mechanism is that film diffusion is its mainly controlling step, but intra-particle diffusion is a considerable contribution to adsorption mechanism, which must be meaningful to accelerate adsorption rate. [ABSTRACT FROM AUTHOR]