Photocatalytic degradation of 4-tert-octylphenol in water and the effect of peroxydisulfate as additives

Photocatalytic degradation of 4-(tert-octyl)phenol (4-OP) has been investigated by recirculating the aqueous solution through a packed bed reactor with TiO2. The first-order rate constant k for the degradation of 4-OP was evaluated to be 5.40 × 10−3 min−1 and an activation energy of 18.6 kJ mol−1 was obtained. The rate constant k was not dependent of the flowrate but a decrease in total organic carbon (TOC) became smaller as the flowrate increased. Under the illumination for 6 h at the flowrate of 28.5 ml min−1, 83.2% of 4-OP was degraded but 60.7% of the initial TOC was remained. Measurements of LC/MS using electrospray ionization revealed the formation of byproducts having molecular weights of 136, 178, 192, 220 and 222. Possible candidates for these byproducts were proposed. The degradation rate of 4-OP was remarkably accelerated by addition of K2S2O8: 4-OP was completely disappeared under irradiation of 4 or 2 h, respectively, in the presence of 4 × 10−3 or 2 × 10−2 mol dm−3 K2S2O8. In the latter case, the TOC decreased to 34.6% by continuing the irradiation even after 4-OP was disappeared. In the presence of S2O82−, 4-OP was degraded without TiO2, which is attributable to the reaction by SO4− radicals. We demonstrated that the UV/TiO2/S2O82− system was more appropriate than the UV/S2O82− for decontamination of 4-OP in water.