Enhancement of photocatalytic activity of TiO2 film electrode by in situ photoelectro-generating active chlorine

The photoelectrocatalytic activity of TiO2 film electrodes in the degradation of nitrite ion was greatly enhanced in the presence of chlorine ion. The influences of NaCl concentration and initial pH value on the degradation rate of NO−2 and active chlorine production were studied. The results show that the decay rate of NO−2 and the accumulation rate of active chlorine increase with increasing NaCl concentration. At pH < 8, both the decay of NO−2 and active chlorine formation rates are enhanced with increasing NaCl concentration, while at pH > 10, they are suppressed. In addition, contrast to conventionally accepted view, in which an advantage of anatase over the rutile modification of TiO2 is in terms of photoactivity, it is found that a thermal oxidation rutile TiO2 electrode is more suitable for both photcgenerating active chlorine and degrading NO−2 in the presence of Cl−. The correlative mechanism was also discussed in detail. Specific adsorption of Cl− on the electrode causes its energy band edges to move towards positive value and also lower the photocurrent, thus less OH· radicals are produced. However, more active species of CI· that have longer lifetime are available to take part in the oxidation of NO−2, thus improving its degradation rate.