| Perfluorooctanoic acid (PFOA) is a kind of persistent organic pollutants (POPs) with large distributions, bioaccumulation and varieties biological toxicity, which makes the traditional biological method and physical-chemical process show slightly degradation efficiency and mineralization rate for PFOA. Hence, high-efficiency technology is eagerly needed to deal with PFOA. A synergetic system of dielectric barrier discharge plasma over water (DBDow) combined with Fe3O4@SiO2@BiOBr (FSB) was developed to investigate the decomposition performance and mechanisms of perfluorooctanoic acid (PFOA) by making full use of UV&visible light and H2O2 produced in DBD process. The main conclusions of this paper are listed as follows:(1) FSB catalyst was synthesized by a modified percipication method. Characterization results show that the diameter of FSB is about 2-3 μm. The actual loading amout of BiOBr is approximately 30%wt%. The light absorption intensity was enhanced when covered by BiOBr. HRTEM of BiOBr shows two set of different clear lattice fringes, indication indicating its high crystallinity. The clear lattice fringes with interplane were found with the d spacing of 0.35 nm and 0.28 nm, corresponding to the (101) and (110) plane of BiOBr, respectively. The energy gap of BiOBr is 2.73 eV, which makes it responsed not only in UV light but also in visible light region.(2) DBDow synergism with FSB catalyst is a efficient way for PFOA degradation. Defluorinations with different catalysts followed the order of FSB> BiOBr≈Fe3O4> P25. PFOA and TOC removal were enhanced from 73.5% to 92.9% and 28.9% to 62.5% as FSB was introduced into DBD system, respectively. Defluorination of PFOA increased from 21% to 32.8% while energy efficiency of defluorination improved from 46.39 mg·kW-1h-1 to 72.47 mg·kW-1h-1.(3) The defluorination rate of PFOA with FSB kept over 28% after 4th run. The results of cyclic voltammetry curve reveals that FSB catalyst is generally stable based on the fact the curve almost coincide with 10 times cyclic voltammetry sweep, indicating that FSB has good stability in acidic condition. The catalytic mechanism might be ascribed to two reasons. One is photocatalytic effect. The other one is Fenton-like reaction.(4) In DBDow-FSB synergetic system, the concentration of H2O2 is greatly improved when FSB was added into the system. Tertiary butanol and citric acid show inhibiting effect on the defluorination of PFOA, and the inhibiting effect ehhanced with the increase of tertiary butanol concentration. ·OH is the main active group in the combined system and h+ takes subsidiary function. The degradation mechanism of DBDow and FSB synergistic system could ascribed to:①Firstly, photo-generated h+ captured the e" of PFOA to generate C7F15COO·radical, but C7F15COO· radical is quite stable and is easily decompose to C7F15·, and then, C7F15·react with O2 directly or oxidation by OH to form C6F13COOH. ② The-CF2-COOH bond and C-C bond of PFOA molecule were attacked by OH, resulting in the broken of-COOH bond and generation of C7F15·, which could react with O2 directly or oxidation by OH to C6F13COOH. ③ ·OH would replace two F atom of PFOA melecule to produce C6F13C(OH)2COOH, then generate C6F13COCOOH via molecular dehydration, finally, C6F13COCOOH was oxidized by OH to generate C6F13COOH. |
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