Activation of chlorine by photocatalysts under near-UV-visible-light irradiation for 2-methylisoborneol degradation

Novel advanced oxidation processes to activate chlorine by g-C3N4 under visible light irradiation at 420 nm (Vis/g-C3N4/chlorine, VgC) and TiO2 under near-UV irradiation at 365 nm (nUV/TiO2/chlorine, UTC) for the 2-methylisoborneol (2-MIB) degradation are proposed in this study. Fig. 1a shows the 2-MIB degradation by the Vis/chlorine, Vis/g-C3N4 and VgC processes for 15 minutes in the presence of 1.0 g/L g-C3N4 and 2.0 mg/L free chlorine at pH 7.0. A control test showed that no 2-MIB was degraded in the dark/g-C3N4/chlorine process. In the Vis/chlorine and Vis/g-C3N4 processes, about 15% and 10% of 2-MIB were degraded, respectively. While the degradation of 2-MIB in the VgC process reaches about 70%. The 2-MIB degradation in the three processes follows pseudo-first order kinetic, and its degradation rate constant by the VgC process is 6.86 x 10-2 min-1 , which is about 14 and 6 times higher than those by the Vis/g-C3N4 and Vis/chlorine processes, respectively. Fig. 1b shows the 2-MIB degradation by the nUV/chlorine, nUV/TiO2 and UTC processes for 3 minutes in the presence of 0.05 g/L TiO2 and 2.0 mg/L free chlorine at pH 6.0. A control test showed that no 2-MIB was degraded in the dark/TiO2/chlorine process. In the nUV/chlorine and nUV/TiO2 processes, about 15% and 80% of 2-MIB were degraded, respectively. While the degradation of 2-MIB in the UTC process reaches about 99% in 1.5 min. The 2-MIB degradation in the three processes also follows pseudo-first order degradation kinetic, and its degradation rate constant by the UTC process is 2.605 min-1 , which is 4.6 and 64 times higher than that by the nUV/TiO and nUV/chlorine processes, respectively. The enhanced 2-MIB degradation in the VgC and UTC processes is mainly due to production of larger quantities of stronger reactive radical species, for example, HO radical and RCS by the activation of chlorine by electrons and O2- radical generated from TiO2 and UV light at 365 nm and g-C3N4 and visible light at 450 nm.