Application of Mn/MCM-41 as an adsorbent to remove methyl blue from aqueous solution

• Mn/MCM-41 was prepared and used as a novel adsorbent to remove methyl blue.
• Mn modification increased active sites on MCM-41 for removing methyl blue.
• Mn/MCM-41 exhibited highly adsorption capacity of methyl blue.
• The electrostatic interaction is the main mechanism of adsorption of methyl blue.
• Methyl blue adsorption on Mn/MCM-41 was endothermic and spontaneous.

In this study, the application of Mn loaded MCM-41 (Mn/MCM-41) was reported as a novel adsorbent for methyl blue (MB) from aqueous solution. The mesoporous structure of Mn/MCM-41 was confirmed by XRD technique. Surface area, pore size and wall thickness were calculated from BET equation and BJH method using nitrogen sorption technique. FT-IR studies showed that Mn were loaded on the hexagonal mesoporous structures of MCM-41. It is found that the MCM-41 structure retained after loading of Mn but its surface area and pore diameter decreased due to pore blockage. Adsorption of MB from aqueous solution was investigated by Mn/MCM-41 with changing Mn content, adsorbent dosage, initial MB concentration, contact time, pH and the temperature. Under the chosen condition (25 °C, 0.02 g adsorbent dosage, 6.32 pH, 50 mg L−1 MB, 1 wt.% Mn), a high MB adsorption capacity (45.38 mg g−1) was achieved by Mn/MCM-41 process at 120 min, 8.6 times higher than MCM-41. The electrostatic interaction was considered to be the main mechanism for the dye adsorption. The experimental data fitted well to Freundlich and Dubinin–Radushkevich isotherms. The adsorption of MB on Mn/MCM-41 followed pseudo-second-order kinetics. Thermodynamic parameters suggested that the adsorption process is endothermic and spontaneous.

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