Study of catalytic reduction and photodegradation of methylene blue by heterogeneous catalyst

The photocatalytic degradation of methylene blue is investigated in aqueous solution containing CoS/nanoAl-MCM-41 photocatalyst under visible light. The catalyst is characterized by X-ray diffraction (XRD), UV–vis diffused reflectance spectra (UV–vis DRS) and transmission electron microscopy (TEM) techniques. The effect of CoS, nanoAl-MCM-41 support and different wt% of CoS over the support on the photocatalytic degradation and influence of parameters such as CoS loading, catalyst amount, pH and initial concentration of methylene blue on degradation are evaluated. Hypsochromic effects (i.e. blue shifts of spectral bands) resulting from N-demethylation of the dimethylamino group in methylene blue occurs in presence of CoS/nanoAl-MCM-41 under ambient condition. Meanwhile, the bleaching of methylene blue MB, by sulfide ion, in an aqueous solution is studied in the presence nanoAl-MCM-41 catalyst. In the presence of sulfide ions, MB is bleached to its colorless leuco (LMB) and MBH2+ forms. In an acidified solution (pH < 2) the bleaching process generates LMB and by changing pH between 2.0 and 7.0 bleaching of MB dye to MBH2+ form is observed. Using nanoAl-MCM-41 with encapsulated CoS nanoparticles only causes demethylation of MB in aqueous solution.

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► Synthesis AlMCM-41 as support.
► Demethylation of MB by catalyst.
► Reduction of MB by S2−.