Tailoring the metal introduction sequence onto mesostructured silica nanoparticles framework: Effect on physicochemical properties and photoactivity

• Introduction sequence effect of CuO and ZnO onto MSN support was investigated.
• Addition of second metal improved the photocatalytic activity.
• Metal introduction sequence altered the silica arrangement.
• Metal-silica arrangement influenced the photoactivity of catalyst.
• Formation of SiOZn, oxygen vacancies and pore volume led to higher photoactivity.

Cu with variable weight loading (1–5 wt%) was introduced to 5 wt% Zn mixed mesostructured silica nanoparticles (MSN) via an electrochemical method to synthesize CuO–ZnO/MSN (C-ZM) catalysts. The physicochemical properties of the catalysts were characterized by XRD, FTIR, XPS, N2 adsorption–desorption, ESR, and cyclic voltammetry. 3 wt% Cu and 5 wt% Zn were also introduced alternately to MSN (3C-ZM and Z-3CM) to study the metal introduction sequence effect on the properties and catalytic activity. The characterization data showed that an altered arrangement of the silica network was observed with a different structure, particularly in the numbers of SiOSi, SiOZn, and SiOCu bonds as well as oxygen vacancies. The catalytic activity regarding the photodecolorization of methyl orange (MO) was in the following order: 3C-ZM > 5C-ZM > Z-3CM > 1C-ZM. The higher numbers of SiOZn, oxygen vacancies, and the higher pore volume of the 3C-ZM catalyst seemeed to be the main factors behind its higher photoactivity compared to the other catalysts. Further optimization by response surface methodology (RSM) with a central composite design (CCD) model was performed for the decolorization of MO. RSM demonstrated that the experimental value (99.89%) was reasonably close to the predicted value (99.99%) with only 0.1% error for MO decolorization at pH 3.5 using 1.6 g L−1 catalyst with 4 wt% Cu loading.

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