Changing the reaction pathway in TiO2 photocatalytic dehalogenation of halogenated aromatic pollutants by surface hydroxyl regulation

Understanding the photocatalytic reductive dehalogenation mechanism of halogenated aromatic pollutants is of great research value. However, the proton source in the photocatalytic dehalogenation process of representative halogenated aromatic pollutants by TiO2 is not clear. In this study, the TiO2 surface was modified by hydro-chloric acid, sodium hydroxide, and sodium fluoride to obtain TiO2 samples with different hydroxyl groups. It was found that the hydroxyl groups on the surface of TiO2 affects the sequence of proton and electron transfer in dehalogenation. The abundance of hydroxyl groups on the surface of TiO2 can accelerate the reductive deha-logenation process of representative halogenated aromatic pollutants. The kinetic solvent isotope effect was used to study the proton-coupled electron transfer process in the reaction. It shows that the enriching of protons on TiO2 bridging oxygen (bridging hydroxyl groups) is conducive to the rapid step of protonation of the reactant, and subsequent proton and electron transfer. On the contrary, the bridging hydroxyl groups can be removed by reacting with strongly basic sodium hydroxide and sodium ions can occupy the bridging oxygen. The substitution of bridging oxygen by fluorine ions can also lead to the destruction of bridge hydroxyl groups. Significantly, the absence of bridging hydroxyl groups on titanium dioxide will lead to the dehalogenation of representative halogenated aromatic pollutants initiated by electron transfer. This study is helpful to understand dehalogena-tion reaction paths catalyzed by TiO2.

Automated summary

Understanding the photocatalytic reductive dehalogenation mechanism of halogenated aromatic pollutants is important for research. This study investigates the proton source in the photocatalytic dehalogenation process using modified TiO2 samples with different hydroxyl groups. The results show that the abundance of hydroxyl groups on the TiO2 surface affects the proton and electron transfer, and increases the efficiency of the dehalogenation process. The study also reveals that the enrichment of protons on bridging oxygen facilitates the rapid protonation and subsequent proton and electron transfer.