Sequential desilication–isomorphous substitution route to prepare mesostructured silica nanoparticles loaded with ZnO and their photocatalytic activity

• ZnO/MSN catalyst was prepared by a simple electrochemical and impregnation method.
• Sequential desilication–isomorphous substitution occurred during impregnation.
• The Si–O–Zn bond formed was the active species that enhanced the catalytic activity.
• Increasing the ZnO loading increased the electron–hole pair recombination rate.

A simple electrochemical method followed by impregnation was employed to prepare a coral-like zinc oxide catalyst loaded on mesostructured silica nanoparticles (ZnO/MSN). The introduction of zinc species onto a silica framework was found to form an interaction between the host and support material. XRD analysis suggested the presence of zinc on the internal pore walls of MSN. FE-SEM and TEM analyses displayed nanorods, nanoparticles and coral-like shapes of ZnO, MSN and ZnO/MSN, respectively. 29Si NMR and FTIR results showed that desilication occurred in the silica framework of the MSN accompanied by isomorphous substitution of Zn2+ cations to form an active species Zn–O–Si bond. The photocatalytic activity of the ZnO/MSN was tested by decolorizing methyl orange (MO). It was found that increasing the ZnO loading led to a higher recombination rate of photoinduced electron–hole pairs, which resulted in decreased photocatalytic activity. The highest decolorization rate was obtained using 1 g L−1 of 5 wt% ZnO/MSN with an optimum dosage of 3.06 × 10−2 mM MO after 8 h contact time at pH 2 under UV irradiation. A kinetic study demonstrated that the photocatalytic reaction followed the pseudo first-order model. The photocatalyst was still stable after five cycling runs with a small amount of Zn was leached (<3.0%).

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