Incorporative Effect of Pt and Na2CO3 on TiO2‑Photocatalyzed Degradation of Phenol in Water

2016-10-27T00:00:00Z (GMT) by Xianqiang Xiong Xiao Zhang Yiming Xu
Carbonate anions are often present in aqueous solution, but their effect on the semiconductor-photocatalyzed reaction has been rarely studied. In this work, we report a positive effect of Na2CO3 on the TiO2-photocatalyzed degradation of phenol, 2,4-dichlorophenol, and H2O2 in an aerated aqueous suspension at initial pH 8.0. The rate of phenol degradation, upon the addition of 2.0 mM Na2CO3, 0.52 wt% Pt, and 2.0 mM Na2CO3 plus 0.52 wt % Pt, was increased by 1.78, 3.38, and 6.63 times, respectively. Such positive effect of carbonate was also observed from a TiO2 and Pt/TiO2 film electrode for the photoelectrochemical oxidation of phenol, but not water. However, the rates of phenol degradation over TiO2 and Pt/TiO2 became decreased as carbonate concentration exceeded 5.0 and 2.0 mM, respectively. It is proposed that CO3•– radicals are formed mainly from the hole oxidation of dicarbonate adsorbed on TiO2, followed by phenol degradation. At a high concentration, the CO3•– radicals would recombine to a peroxocarbonate that easily decomposes into CO2 and O2. The carbonate-mediated hole transfer from TiO2 to phenol would incorporate with the Pt-mediated electron transfer from TiO2 to O2, consequently resulting in a great improvement in the efficiency of charge separation for the reactions at interface.