Volume 14 Issue 1 - May 21, 2010 PDF
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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
Yi–Fong Huang1, Yao-Hui Huang1,2*
1 Department of Chemical Engineering, National Cheng Kung University, Tainan City 701, Taiwan
2 Sustainable Environment Research Center, National Cheng Kung University, Tainan City 701, Taiwan
 
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This study mainly proposed two novel technologies for efficient Bisphenol A (BPA) decontaminantion, and investigated the behavior of dominant radicals and intermediates involved in these BPA degradation processes.

Firstly, we took advantage of the high oxidation–reduction potential of hydroxyl and sulfite radicals transformed from peroxymonosulfate (PMS) (stoichiometric ratio: [PMS]0/[BPA]0 = 2) as the oxidants to oxidize BPA to less complex intermediates. Fig.1(a and b) and Fig.1(c and d) show that The •OH spectrum and SO4• spectrum are simultaneously identified from the intensity ratio of each characteristic peak as 1:2:2:1 and 1:1:1, respectively. The expected radicals were used to mineralize those compounds very efficient (TOC removal ~40% at 1 h). Further, qualitative identification of both hydroxyl and (bi)sulfate radicals was performed to evaluate their dominance under different conditions.
Fig. 2 The pH variations of reaction solutions including the 1st-stage oxidations and the 2nd-stage oxidations (from t = 50min, pH< 4) (a); BPA degradation during various two-stage oxidations (b) and the sulfate ions generation during various two-stage oxidations (c). The 1st-stage shows the presence of Na2S2O8 (a); UV+Na2S2O8 (b–g); the 2nd-stage is the additional additives of Fe2+ (c); Fe3+ (d); H2O2 (e); Fe2+ +H2O2 (f) and Fe3+ +H2O2 (g). The comparative background experiment for the single photodegradation of BPA with no reagent (h). [BPA]i = 0.05mM, [SPS]i = 0.05mM, [Fe(II,III)]i = 0.045mM, and [H2O2]i = 0.1579mM. Reaction temperature= 25 ℃.
Fig. 1 EPR spetra of SPS (pHi < 4) (a), alkali + SPS (pHi > 10) (b), photon + SPS (pHi <4) (c), and alkali + photon + SPS (pHi > 10) (d). Each trial of 0.05mMSPS solution (acidic or alkaline) was, or was not, photo-activated within 1–2 min of illumination, and was thus detected by EPR with the participation of BPA to identify the expected SO4• and •OH produced. Center field = 3483G, sweep width = 100 G, microwave frequency = 9.8 GHz, and power setting = 400Wand operating temperature = 25 ◦C.

Secondly, a two–stage oxidation (UV–Na2S2O8/H2O2–Fe(II,III)) process was applied to mineralize BPA at pHi (initial pH) = 7 based on the concept for improving the common drawbacks of Fenton’s family (i.e. Fenton, Fered–Fenton and Photo–Fenton processes). Fig. 2 shows the comparative study (pH, [BPA]/[BPA]0, and sulfate generation) of the two-stage oxidation process including extra Fe(II,III) activation, H2O2 promotion, and Fe(II,III)/H2O2 promotions. Consequently, high mineralization performances can be found in Table 1. We take advantage of the high oxidation potential of sulfate radicals and use persulfate (stoichiometric ratio: [S2O82–]0/[BPA]0 = 1) as the 1st–stage oxidant to oxidize BPA to less complex intermediates. Afterwards, photo–Fenton process was used to mineralize those intermediates to CO2 (TOC removal was increased 40% to 91%). To the best of our knowledge, this is the first attempt to utilize the two processes in conjunction for the complete degradation of BPA. This is also the first attempt to evidence that the dominant behavior of radicals in a (bi)sulfite process is very different from that in a persulfate process. Additionally, the utilization of extremely small amounts of activator and oxidant for the complete degradation of BPA was achieved.
Table 1 Comparison of TOC removals between various 2nd-step complex oxidation processes
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