Enhancing photocatalytic degradation of methyl orange by crystallinity transformation of titanium dioxide: A kinetic study

This work aimed to enhance the photocatalytic degradation of methyl orange (MO) by crystallinity transformation of titanium dioxide (TiO2 ). In addition, the kinetic degradation of MO was determined. To transform its crystallinity, TiO2 was synthesized using a sol-gel method and calcined at between 200°C to 600°C. Calcination at a temperature of 250°C resulted in TiO2 that showed the best performance, corresponding to MO removal of 87% ± 7%. MO removal by TiO2 calcined between 250°C to 400°C was higher than for commercial TiO2 powder (Sigma-aldrich) (62% ± 4%). TiO2 with a small crystallite size and high anatase fraction enhanced the photocatalytic degradation of MO, while the specific surface area and surface roughness seemed to play a minor role. The photocatalytic degradation of MO was NaCl-independent, while the photocatalytic activity increased with decreased pH. Reused TiO2 showed similar photocatalytic degradation of MO compared with pristine TiO2 , at 84 ± 2%. The oxidation kinetics of TiO2 calcined at 250°C were fitted to the Langmuir-Hinshelwood model (R2 = 0.9134). The kr and Ks values were 0.027 mg L-1 min-1 and 0.621 L/mg, respectively. Crystallinity transformation was a major factor in the enhancement of photocatalytic degradation of MO. PRACTITIONER POINTS: Photocatalytic activity of TiO2 depends on calcination temperature, pH, and a number of UVC lamps. TiO2 with a small crystallite size and high anatase fraction enhanced the photocatalytic degradation of MO.