Malachite Green Degradation by Photocatalysis: Kinetics and Mechanism Using Sol–Gel Synthesized Nano-Titania

In order to remove hazardous cationic dyes such as malachite green (MG) in an environmentally compatible, efficient, and cost-effective manner, this study used hydrolysis of titanium tetra-isopropoxide to create photooxidizer nanocrystalline titanium dioxide (TiO 2 ) nanoparticles of both the rutile and anatase phases. The catalysts were characterized by N 2 adsorption (Brunauer–Emmett–Teller), Fourier-transform infrared absorption spectrophotometer, X-ray diffraction, point of zero charge, UV–vis diffuse reflectance spectra, and scanning electron microscopy examination. Additionally, the photocatalytic activity of the synthesized catalyst was performed by examining the various experimental parameters such as initial MG concentration (30–60 ppm), catalyst dosage (0.2–0.35 g), irradiation time (0–60 min), and pH (4–10) under 8 W UV-218 nm irradiation for 1 h in an aqueous medium. Also, the Mere/interactive effects of benzaldehyde and NaCl salt (0–120 g/L) concentration were interpreted during degradation. The obtained results showed that the removal of MG for anatase and rutile was 97% and 57% in 1 h, respectively. When 1 g/L TiO 2 was added to solution mixtures containing 50 mg/L of MG, 98% of the MG was removed. The percentage of MG dye removal enhanced with an increase in pH, duration of radiation exposure, and anatase dosage. However, photocatalytic removal rate decreased with increasing initial MG concentration. In addition, increasing the salt concentration of the medium diminished the MG degradation. Presence of benzaldehyde also decreased the MG removal which indicated that one of the products was benzaldehyde. The adsorption equilibrium constant and the rate constant were recorded as 1.05 L/mg and 2.7 ppm/min, respectively, according to the Langmuir–Hinshelwood kinetic model.