Synthesis, characterization, and photocatalytic activity of silver and zinc co-doped TiO₂ nanoparticle for photodegradation of methyl orange dye in aqueous solution

Abstract

In this study, TiO 2 nanocrystals, 1 mol% Ag-doped TiO 2 , and 1 mol% Ag and 0.6 mol% Zn co-doped TiO 2 powders were synthesized by the sol–gel route. Their photocatalytic activities on methyl orange dye under visible irradiation were investigated. The powders were characterized by X-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), Brunauer–Emmett–Teller (BET), and Fourier transform infrared spectroscopy (FTIR). The XRD results revealed the presence of a rutile phase with an average crystallite size of 9 and 11 nm. The UV–vis spectra showed a red-shift towards a longer wavelength with the corresponding decrease in band gap from 2.9 to 2.5 eV. The BET surface areas of the nanoparticles ranged from 4.7 to 11.8 m 2 g −1 with an average pore size between 18.9 and 56.6 nm. The Ag-doped TiO 2 has the largest surface area of 11.8 m 2 g −1 , whereas the Ag–Zn co-doped TiO 2 was found to have the highest pore size and volume. The absorption bands at 750–500 cm −1 were attributed to the –O–Ti–O– bond in the TiO 2 lattice. The photocatalytic efficiency was highest at an optimum pH of 4.1 for Ag–Zn co-doped TiO 2 . The results confirmed that Ag-doped and Ag–Zn co-doped TiO 2 were more effective than pure TiO 2 . The kinetic data were fitted into a pseudo first-order equation using a Langmuir–Hinshelwood kinetic model.