Synthesis and characterization of Ni-MCM-41 for methyl blue adsorption

• Ni-MCM-41 was reported as a novel adsorbent for the removal of methyl blue effectively.
• Electrostatic interactions and π-complexation might be the possible mechanisms of adsorption.
• Monolayer adsorption of methyl blue on homogeneous distributed adsorption sites in Ni-MCM-41 was suggested.
• The adsorption underwent three processes and attained the final equilibrium.

Adsorbents from Ni functionalized MCM-41 (Ni-MCM-41) were prepared for methyl blue (MB) removal from aqueous solution. The mesoporous structure of Ni-MCM-41 is confirmed by XRD technique. Surface area, pore size and wall thickness are calculated from BET equation and BJH method by nitrogen sorption technique. FT-IR studies show that Ni has been loaded on the hexagonal mesoporous structure of MCM-41. It is found that the MCM-41 structure remains unaltered after the loading of Ni, but its surface area and pore diameter decrease due to pore blockage. The effects of Ni content, adsorbent dosage, initial MB concentration, contact time, pH and temperature on adsorption were investigated. The results indicate that a much higher MB adsorption capacity is achieved by Ni-MCM-41 than MCM-41, and the optimum conditions are identified as: the MB initial concentration of 50 mg/L, 0.02 g Ni-MCM-41 with Ni content of 1 wt. % at 25 °C and pH value of 6.32. Adsorption of MB on Ni-MCM-41 can be well described by pseudo-second-order kinetics and intra-diffusion model, and equilibrium data is well fitted by Langmuir model. Thermodynamic parameters suggest that the adsorption process is endothermic and spontaneous. The possible adsorption mechanisms might be electrostatic interactions between sulfonic acid groups of MB and the positive Si–O–Ni+ of Ni-MCM-41, and π-complexation mechanism resulting from the interaction between aromatic cycles of MB and Ni functionality of Ni-MCM-41 might also be plausible.

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