Synthesis of TiO2/polyaniline photocatalytic nanocomposite and its effects on degradation of metronidazole in aqueous solutions under UV and visible light radiation

TiO2/polyaniline (TiO2/Pani) nanocomposite was prepared by in situ polymerization of aniline on TiO2 nanoparticle structures. Fourier transform infrared, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, diffuse reflectance spectroscopy, and thermogravimetric analysis techniques were utilized to characterize the composition and structure of the nano composite and its components. All these techniques showed that TiO2/Pani nanocomposite was formed successfully and thus can activate by exposure to UV and visible light. The photocatalytic activity of the synthetic nanocomposite on degradation of metronidazole (MNZ) molecules in aqueous solution was investigated under UV and visible light radiation as a function of time, MNZ concentration, catalyst dose and stability, and solution pH during several steps of the degradation process. The optimal condition for maximum MNZ degradation efficiency was obtained to be 98% and 96%, respectively, with 1 g L–1 of TiO2/Pani nanocomposite, 10 mg L–1 of MNZ, and pH 7.0 after 120 min of exposure to UV and visible light. Kinetic studies, chemical oxygen demand, total organic carbon, average oxidation state, reusability test, and predicted degradation mechanism of the optimal condition were investigated in the present study. The photocatalytic activity of TiO2/Pani nanocomposite under UV and visible light radiation was higher than TiO2 nanoparticles. The velocity constants for MNZ degradation by TiO2/Pani nanocomposite under UV and visible light radiations were 387 × 10–4 and 286 × 10–4 min–1, respectively, which were approximately 1.63 and almost 95 fold over TiO2. It was also confirmed that hydroxyl (•OH) and superoxide anion (•O2−) radicals, respectively, played central roles in MNZ degradation. Finally, the mechanism of increase in the photocatalytic activity was discussed. The improvement of photocatalytic activity under UV and visible light radiation was related to the remarkable absorption of UV and visible light and the reduction of recombination of the charge carriers.