3.2. Effect of pH on the RB181 decolorization
The pH effect was particularly studied through experiments
with the pH range 2–7. The lower pH values are better than the
higher ones in our experiments. The most likely reason for this
observation is the fast decomposition of hydroxyl radicals and
hydrogen peroxide at high pH and fast reaction of radicals at low
pH value [13]. Fig. 4 shows the decolorization of RB181 for different
initial values of pH.
Furthermore, the deactivation of OH is more important when
the pH of solution is high. The reaction of OH with HO2
is
approximately 100 times faster than its reaction with H2O2. Also
in alkaline medium, the H2O2 becomes highly unstable and
self-decomposition of H2O2 occurs, which is strongly dependent
on pH [4,23]. So our study did not include of basic pH studies.
Experimental data are shown in Table 1. It was also concluded
from Table 2 that RB181 removal by UV/H2O2 oxidation was
an efficient method by the comparison of various removal
efficiencies, pH and operation times with similar studies in the
literature.