UV photodegradation of azo dye Diacryl Red X-GRL

The direct UV photodegradation of Diacryl Red X-GRL was studied in an immersion photochemical reactor equipped with monochromatic UV source of 253.7 nm. Different process parameters that may influence the UV photodegradation were studied. These parameters included temperature, pH, radiation flow rate of UV lamp, carrier gas flow rate, initial concentration of dye, concentration of t-BuOH, and the concentration of dissolved oxygen. Four possible photodegradation pathways of dye in the presence of dissolved oxygen were assumed to be as follows: homolysis of excited dye to radicals; electron transfer of excited dye to form radical dye cation; decomposition by superoxide radical anion; and decomposition by singlet oxygen. Based on photodegradation pathways the photodegradation rate equation was derived, and the overall quantum yield of photodegradation was determined using Line Source Spherical Emission Model (LSSE Model), which describes the radiation flow rate absorbed by the solution in the photodegradation process. The overall quantum yield is enhanced enormously from 0.46 × 10−3 in the absence of dissolved oxygen to 7.35 × 10−3 in the presence of 1.21 × 10−3 M dissolved oxygen. However, the temperature had negative effect on the overall quantum yield, which varied from 8.54 × 10−3 at 288 K to 5.53 × 10−3 at 308 K. Finally, by using non-linear regression analysis, the overall quantum yield was correlated to be a function of temperature and dissolved oxygen in a modified Arrhenius equation with activation energy of 11.3 kJ mol−1.