Structural rearrangement of mesostructured silica nanoparticles incorporated with ZnO catalyst and its photoactivity: Effect of alkaline aqueous electrolyte concentration

Published Date

1 March 2015, Vol.330:10–19, doi:10.1016/j.apsusc.2014.12.192

Title 

Structural rearrangement of mesostructured silica nanoparticles incorporated with ZnO catalyst and its photoactivity: Effect of alkaline aqueous electrolyte concentration

• Author 

• N.W.C. Jusoh ^a
• A.A. Jalil ^a,b,,
• S. Triwahyono ^c
• A.H. Karim ^c
• N.F. Salleh ^a
• N.H.R. Annuar ^c
• N.F. Jaafar ^c
• M.L. Firmansyah ^c
• R.R. Mukti ^d
• M.W. Ali ^a,b

• aDepartment of Chemical Engineering, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
• bInstitute of Hydrogen Economy, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
• cDepartment of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
• dDivision of Inorganic and Physical Chemistry, Faculty of Mathematics and Natural Science, Institut Teknologi Bandung, Jl Ganesha No 10, Bandung 40132, Indonesia

Received 2 September 2014. Revised 12 November 2014. Accepted 30 December 2014. Available online 5 January 2015.

Highlights

• •
  Hierarchical-like structure of MSN was formed in alkaline aqueous electrolyte.
• •
  Desilication generated abundant silanol groups and oxygen vacancies.
• •
  Zn²⁺ inserted to external –OH groups of the MSN to form Si–O–Zn bonds.
• •
  Oxygen vacancies trapped electrons to enhance electron–hole pair separation.
• •
  Hydroxyl radical generated from three main sources greatly influenced photoactivity.

Abstract

ZnO-incorporated mesostructured silica nanoparticles (MSN) catalysts (ZM) were prepared by the introduction of Zn ions into the framework of MSN via a simple electrochemical system in the presence of various concentrations of NH₄OH aqueous solution. The physicochemical properties of the catalysts were studied by XRD, ²⁹Si MAS NMR, nitrogen adsorption–desorption, FE-SEM, TEM, FTIR, and photoluminescence spectroscopy. Characterization results demonstrated that the alkaline aqueous electrolyte simply generated abundant silanol groups on the surface of the catalysts as a consequence of desilication to form the hierarchical-like structure of the MSN. Subsequent restructuring of the silica network by the creation of oxygen vacancies and formation of Si–O–Zn during the electrolysis, as well as formation of new Si–O–Si bonds during calcination seemed to be the main factors that enhanced the catalytic performance of photodecolorization of methyl orange. A ZM prepared in the presence of 1.0 M NH₄OH (ZM-1.0) was determined to be the most effective catalyst. The catalyst displays a higher first-order kinetics rate of 3.87 × 10⁻¹ h⁻¹ than unsupported ZnO (1.13 × 10⁻¹ h⁻¹) that prepared under the same conditions in the absence of MSN. The experiment on effect of scavengers showed that hydroxyl radicals generated from the three main sources; reduced O₂ at the conduction band, decomposed water at the valence band and irradiated H₂O₂ in the solution, are key factors that influenced the reaction. It is also noted that the recycled ZM-1.0 catalyst maintained its activity up to five runs without serious catalyst deactivation.

Graphical abstract

Keywords

• Structural rearrangement
• Alkaline electrolyte
• Mesostructured silica nanoparticles
• Zinc oxide
• Photodecolorization

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  Corresponding author at: Department of Chemical Engineering, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia. Tel.: +60 7 5535581; fax: +60 7 5588166.
  
  

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