In 22]. Therefore, pH of solution is one of

In this study, the
determined pHpzc value of used -Al2O3 was 8.6. The
effect of initial solution pH (3, 8, and 10) was investigated on the degradation
of PCP in SOP and COP. Fig.2 represents the effects of pH on PCP degradation in
COP and SOP. As can be seen, after 15 min and in pH 10, 83 and 100% of PCP was
removed in SOP and COP, respectively. These findings
indicate that oxidation of PCP in both processes under the selected condition
was increased by increasing pH and reaction time. Also, at different pH
points, the PCP removal in COP was overall higher than SOP. Furthermore, the
results confirmed the influence of pH on drastic changes in color of the PCP
solution during ozonation. So, the solution color changed from yellow to orange
at pH 3, to brownish orange at pH of 8, and to dark brown at pH of 10 (Fig.3).

In heterogeneous catalytic
ozonation, surface properties including pHpzc and the density of the
hydroxyl groups on catalyst’s surface have an important function in the ozonation
process. Surface of metal oxides would absorb water molecules due to their unsaturated
electrons which cause the formation of hydroxyl groups on the surface. Solution
pH is one of the most important factors affecting the surface properties of
metal oxides including -Al2O3. The surface hydroxyl groups
showed different charge properties at different solution pH 21,
22. Therefore, pH of solution is one of main effective
factors in metal oxides such as -Al2O3 and ozone decomposition. Fei
et al. 23 studied the influence of -Al2O3 surface properties on
catalyzed ozonation of 2,4,6-trichloroanisole (TCA). They found that the
solution pH was more effective on the rate of catalytic ozonation of TCA in the
presence of -Al2O3. As when solution pH is
closed to pHpzc of the -Al2O3, the oxides revealed the
maximum effect on ozone. Therefore, zero charge surface of -Al2O3 was more active than electropositive
or electronegative surface in catalytic ozonation of TCA. Hence, based on the
results of our study, according to the pHpzc of alumina (8.6) and
due to the economic problems caused by the increasing pH, the more experiments
were carried out at pH of 8. Also, the effects of different pH (3, 8, and 10)
resulted in drastic changes in the color of PCP solution during ozonation that
is consistent with the result of Hong et al. 19. In their study and within the first 7 min of ozonation,
color of PCP solution was shifted from yellow to red due to the production of
ketones and kinone compounds, and then within 45 min, the color intensity of
the solution was gradually reduced. They also assessed the change in color of
the solution by changes in the optical absorption spectrum and indicated that
optical spectra and changes in its absorption is quite different at various pH
points during ozonation caused by generation of byproducts and balance of
organic acids at different pHs.

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Chloride anion was another
experimental reaction product. The release of Cl? was dissimilar in different pHs (3, 8, and 10). The maximum of Cl? concentration was obtained at pH 10, which amounted to 66 mg/L after
complete degradation of PCP (C0 = 200 mg/L) at 15 min of ozonation (Fig.
4).