Photocatalytic degradation of methylene blue using natural ilmenite upgraded via HCl leaching: Modelling and optimization

The photocatalytic activity of a natural ilmenite has been improved by leaching with HCl solution. The natural and the upgraded ilmenites were characterized using X-ray fluorescence (XRF) and scanning electron microscopy (SEM). Upon leaching of the natural ilmenite with HCl solution, the proportion of TiO2 increased from 48.86 % wt. to 57.81% wt.; while that of Fe2O3 decreased from 39.09 % wt. to 29.16 % wt. The photocatalytic activity of the natural and the upgraded ilmenites was investigated by studying the kinetics of photocatalytic degradation of methylene blue dye (MB) under visible light irradiation. Photocatalytic degradation of MB follows pseudo-first order approximation of the Langmuir-Hinshelwood kinetic model. The upgraded ilmenite exhibits higher photocatalytic activity (with kapp value of 0.023 min-1) than the natural ilmenite (with kapp value of 0.011 min-1) under similar experimental conditions. Response surface methodology (RSM) based central composite design (CCD) was used to design experiments and analyze the experimental data for photocatalytic degradation of MB using the upgraded ilmenite as the photocatalyst under visible light irradiation. A quadratic model equation was developed for photocatalytic degradation of MB using the upgraded ilmenite. The developed model equation was validated by comparing the predicted and experimental results under the predicted optimum conditions. At the optimum process conditions (pH of 3.00, MB initial concentration of 10 mg/L, and photocatalyst dosage of 0.29 g/L), the upgraded ilmenite could decolorize 82.4 % of MB within 60 minutes of visible light irradiation. The obtained results indicate that HCl leaching can be used to enhance the photocatalytic activity of natural ilmenites