The photocatalytic dehalogenation of chlorophenols and bromophenols by cobalt doped nano TiO2

• Co doped TiO2 nanoparticle was used as photocatalyst for halophenols degradation.
• It is the first time to compare the degradation rate between CPs and BPs on TiO2/Co.
• The degradation of both CPs and BPs obeys the pseudo-first-order kinetics.
• BPs are easier to be photodegradated than CPs by TiO2/Co nano catalyst.
• The degradation of 2,4,6-TCP and 2,4,6-TBP occurs via the dehalogenation pathway.

Cobalt doped TiO2 nanoparticle prepared by ultrasonic-assisted hydrothermal method was used as the photocatalyst in the degradation of chlorophenols (CPs) and bromophenols (BPs). The doping content of cobalt in this catalyst was optimized as 0.5 wt%. The degradation rates of 2,4,6-trichlorophenol (2,4,6-TCP), 2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP), 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4,6-tribromophenol (2,4,6-TBP), 2,4-dibromophenol (2,4-DBP), 2,6-dibromophenol (2,6-DBP), 2-bromophenol (2-BP) and 4-bromophenol (4-BP) were estimated based on the quantitative determination of the degradation products. It was found that the degradation of CPs and BPs underwent dehalogenation process with pseudo-first-order kinetics. Moreover, the photodegradation kinetics was compared between CPs and BPs. The degradation rate of BPs was more quickly than CPs due to the difference in bond energy of carbon–halogen, and the degradation rates of BPs and CPs were mainly dependent on the number and the position of substituting halogen atom respectively. In addition, 2,4,6-TCP and 2,4,6-TBP can be effectively degraded by more than 95.1% and 93.5%, respectively, within 240 and 30 min. Tri-substituted phenols were firstly photodegraded to corresponding di-substituted ones, then to mono-substituted ones, and finally to phenol by TiO2/Co nano catalyst, although there were some differences in selectivity, rate and yield in the dehalogenation pathway of 2,4,6-TCP and 2,4,6-TBP.

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