Microwave-Assisted in the Preparation of Nitrogen-Doped TiO2 for the Removal of Organic Dyes: Effect of pH and Catalyst Loading

Abstract

The unmodified TiO₂  was modified using a microwave technique to produce a visible light active nitrogen (N) doped TiO₂. The modified photocatalyst was prepared by mechanical mixing of unmodified TiO₂ with various amount of urea_. It was observed that the N doped TiO₂ at 800 Watt of microwave power irradiation at 3:7 (urea: TiO₂) ratios were defined as the optimum condition for modified photocatalyst.  N doped TiO₂ then was characterized using X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and UV-Vis diffuse reflectance spectra (UV-Vis/DRS) analyses. The XPS and PL proved the successful nitrogen doped into the TiO₂. XPS present of two peaks with binding energy 404.8 and 400.2 eV that indicates the formation of chemical interaction N with titania forming N doped TiO_2. In addition, UV-Vis/DRS confirmed the doped of TiO₂ by decreasing the bandgap energy value from 3.02 eV to 2.9 eV. The photocatalytic activity study of N doped TiO₂ were carried out by irradiating 25 mL of 30, 10 and 5 mg L^-1 of anionic Reactive Red 4 (RR4), cationic Methyl Violet (MV) and cationic Janus Green dyes (JG) in the presence of normal and visible light with the rate of decolourization was estimated from aliquot concentration spectrophotometrically.The irradiation of N doped TiO₂ was conducted using two parameters namely effect of loading and the effect of pH. It can be observed that 0.03g of catalyst loading gives optimum photocatalytic degradation for both anionic and cationic dyes. Effect of pH was conducted based on the optimum loading and conclude that pH 4 and 8 was the optimum pH for anionic and cationic dyes respectively.