Photodegradation mechanisms of phenol in the photocatalytic process

Investigating the photodegradation pathways of phenol, as well as the efficiency of photocatalysis by commercial TiO2 is the main task in this present work. Commercial TiO2 particles with the following characteristics: 96 % anatase, 4 % rutile, and 400 nm particles size were used as catalyst source. The photocatalytic process was carried out by mixing 100 ppm of phenol solution and 0.9 g/L of TiO2 particles with magnetic stirrer under UV-C light with 210 nm wavelength. UV-Vis spectrophotometer and COD measurement were used to evaluate the efficiency of photocatalysis. On the other hand, the formed intermediate products during phenol photodegradation were identified by LC-MS, UV-Vis spectrophotometer, and photoluminescence techniques. The results indicated that phenol was removed completely after 24 h of UV-C irradiation. The absorbance peak of phenol slightly decreased during the first 16 h. However, the peak dramatically reduced and disappeared at 24 h of irradiation. This degradation mechanism also occurred similarly to the COD value. There were two phases in photocatalysis of phenol. In phase-I, phenol was decomposed to hydroxylated compounds such as catechol, benzoquinone, and complexes with two benzene rings. In the mineralization phase, hydroxylated compounds were mineralized strongly by hydroxyl radicals, hydrogen radicals, and UV energy to form short-chain organic compounds such as formic acid, glycerol, and oxalic acid. Finally, hydrocarbon chains were broken easily and removed in the forms of carbon dioxide and water.