Photoreactivity of metal-organic frameworks in the decolorization of methylene blue in aqueous solution

• The photocatalytic decolorization of methylene blue dye in aqueous solution was studied.
• Isostructural MIL-100(M) (M = Al, Fe, V and Cr) materials were used as photocatalysts.
• Reactivity of isostructural MIL-100(M) materials depends on the type of metal ions.
• Isoreticular UiO-66-R (H, NH2 and NO2) materials were used as photocatalysts.
• Reactivity of isoreticular UiO-66-R materials depends on the functional groups in organic ligands.

The effect of metal ions and functional groups in organic ligands on the photocatalytic properties of metal-carboxylates, such as isostructural MIL-100(M) (M = Al, Fe, V, and Cr), isoreticular UiO-66-R (R = H, NH2, and NO2), MIL-47(V), and MIL-125(Ti), was investigated using the decolorization of methylene blue in aqueous solution at pH 7.0 and 20 °C under UV radiation. The metal-carboxylates were characterized by diffuse reflectance UV/vis measurements. The determination of the band gap (Eg) on the basis of DR-UV/vis measurements showed that Eg values correlate with ionic covalent parameters, i.e., the strength of the interaction between metal and oxygen in the “M+n-O2− pair. According to DR-UV/vis spectroscopic and catalytic investigations, the reactivity of metal-carboxylates correlated with the band-gap value (Eg), which could be adjusted by varying the nature of the metal ions in SBUs or functional groups in the organic ligands.

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