Identification of produced powerful radicals involved in the mineralization of bisphenol A using a novel UV-Na₂S₂O₈/H₂O₂-Fe(II,III) two-stage oxidation process

A two-stage oxidation (UV-Na₂S₂O₈/H₂O₂-Fe(II,III)) process was applied to mineralize bisphenol A (BPA) at pH_i (initial pH) 7. We take advantage of the high oxidation potential of sulfate radicals and use persulfate as the 1st-stage oxidant to oxidize BPA to less complex compounds (stoichiometric ratio: [S₂O₈^2-]₀/[BPA]₀ = 1). Afterwards, the traditional photo-Fenton process was used to mineralize those compounds to CO₂. To the best of our knowledge, this is the first attempt to utilize the two processes in conjunction for the complete degradation of BPA. During the 2nd-stage reaction, other oxidants (H₂O₂ and Iron alone) were also employed to observe the extent of enhancement of photo-Fenton. Further, qualitative identification of both hydroxyl and sulfate radicals was performed to evaluate their dominance under different conditions. The BPA degradation in this UV/persulfate process formulated a pseudo-first-order kinetic model well, with a rate constant of approximately 0.038 min^-1 (25 °C), 0.057 min^-1 (35 °C), and 0.087 min^-1 (50 °C), respectively. The much lower activation energy (ΔE = 26 kJ mol^-1) was further calculated to clarify that the thermal-effect of an illuminated system differs from single heat-assisted systems described in other research. Final total organic carbon (TOC) removal levels of BPA by the use of such two-stage oxidation processes were 25-34%, 25%, and 87-91% for additional Fe(II,III) activation, H₂O₂ promotion, and Fe(II,III)/H₂O₂ promotions, respectively.