The oxidation efficiency of H2O2/O3 catalyzed by titanium dioxide (TiO2) for acetic acid (HAc) degradation

a probe compound for hydroxyl radical in ozonation

was investigated

with a focus on the effect of TiO2 crystal phase. The results indicated that the addition of TiO2 showed negative effect on the oxidation efficiency when the initial pH was at 7.0 and 10.0

and among all crystal phases of TiO2 anatase had the biggest negative effect. However

when the initial pH was at 3.0

rutile could significantly improve the oxidation efficiency of the H2O2/O3 system

and anatase had negligible effect. The mechanism study showed that there existed a good correlation between degradation rate of HAc and concentration of H2O2 (or its decomposition rate). Both anatase and rutile could accelerate decomposition of H2O2 at initial pH of 7.0 and 10.0

and faster was for the former than the latter. Too high decomposition rate of H2O2 could reduce removal rate of HAc at the two pH

because the conjugate base HO2- of H2O2 generated could react with ozone to effectively produce hydroxyl radicals (·OH). At initial pH 3.0

the oxidation efficiency of H2O2/O3 system was very low due to the difficulty of H2O2 deprotonation

so the concentration of H2O2 had almost no change. Addition of TiO2 could markedly accelerate the decomposition rate of H2O2

including deprotonation step

and anatase made H2O2 decomposition finish in 5 min and too fast

leading to have no effect on the oxidation efficiency. However

rutile had no such high decomposition rate for H2O2 and could generate HO2- -similar species which could react with ozone to produce hydroxyl radicals (·OH) to degrade acetic acid. The batch test carried out also gave a similar result. Therefore

it can be concluded that suitable initiator and its concentration may play an important role in ozone-based advanced oxidation process

and that too high concentration of initiator might lead to rapid consumption of oxidants. The amounts of superoxide ion radical (·O2-) in H2O2/O3

anatase TiO2/H2O2/O3 and rutile TiO2/H2O2/O3 systems were determined by capturing method of Nitro Blue Tetrazolium Chloride (NBT)

the order was as follows: H2O2/O3< rutile TiO2/H2O2/O3< anatase TiO2/H2O2/O3

which was in accord with the results of the results of HAc degradation.