Study of C.I. Acid Orange 7 removal in contaminated water by photo oxidation processes

C.I. Acid Orange 7 (AO7) commonly used as a textile dye and could be degraded by UV/ZnO,
UV/H2O2 and UV/H2O2/Fe (III) (photofenton) processes. In the photocatalytic degradation of
dye by UV/ZnO process, effect of some parameters such as UV irradiation time, presence of
ZnO and UV irradiation, pH, concentrations of ZnO, dye, H2O2 and ethanol was examined and
first order reaction rate constant was calculated equal to 2.39×10-2 min-1 at experimental
condition. The semi-log plot of dye concentration versus time was linear, suggesting first order
reaction. Efficiency of photodegradation process in the absence of ZnO photocatalyst and UV
light was small. Increasing the UV irradiation time increased AO7 removal. Ethanol had
inhibitory effect on this process. Maximum AO7 removal was seen at neutral pH area. In the
UV/H2O2 process, effect of some parameters such as presence of H2O2 and UV irradiation,
amount of H2O2, effect of pH and addition of bicarbonate on the efficiency of dye removal
were examined. Absence of each of UV irradiation or H2O2 decreased AO7 removal efficiency
near to zero. Increasing H2O2 concentration increased dye removal to some extent but at
higher H2O2 concentrations, dye removal efficiency did not increase. Increasing pH to value
about 9 increased the AO7 removal efficiency and increasing bicarbonate anion concentration
decreased it. Rate constant of AO7 removal by this process was calculated to be equal to
4.221×10-1 min-1 at experimental condition. Also, the order of UV/ H2O2/Fe (III) > UV/ H2O2 >
UV/Fe (III) > H2O2/Fe (III), was seen for AO7 removal efficiency of these processes.
Increasing Fe (III) and oxalate concentration increased dye removal efficiency.