Advanced Oxidation Technologies Based On Activation Of Peroxymonosulfate By Transition Metal Oxides For Degradation Of Organic Pollutants

Sulfate radical (SO4-) based advanced oxidation technologies (AOTs) have a good application prospect in the field of wastewater treatment due to the stronger oxidizing ability of sulfate radicals (standard potential2.5-3.1V) than hydroxyl radicals (2.2-2.7V), the high mineralization rate, the persistent nature of the precursors (persulfate and peroxymonosulfate (PMS)) compared to H2O2, the high oxidant utilization, wide operating pH range, and its strong endurability to inorganic salts such as carbonate and chloride in practical aqueous enviornment. The key of SO4-based AOTs is to develop highly efficient activation ways and catalysts of persulfate and PMS. The generally used activation ways include physical methods such as light, heating and microwave irradiation and chemical methods by using transition metal ions as activators. Compared to disadvantages of high energy consuming by using physical activation ways, chemical activation can be achieved under ambient conditions and thus has great attention in the activation of persulfate and PMS. Among the two oxidants, PMS has an unsymmetric structure for only one H is replaced by SO3and can be more easily activated by versatile transition metal ions. Among these transition metal ions, Co(Ⅱ) is the most effective catalyst of PMS activation for the production of sulfate radicals. Due to the toxicity of Co(Ⅱ) ion, heterogeneous immobilized cobalt catalysts were developed. However, many of them show high cobalt-leaching and low catalytic stability. Thus, to develop highly catalytic activity and highly stable heterogeneous catalysts for the activation of PMS is a currently hot research spot in the field of environmental catalysis. The aim of this dissertation is to develop heterogeneous catalysts including Co3O4-Bi2O3nanocomposites, CuFe2O4nanoparticles and CuFeO2microparticles to improve the activation ability and the oxidant efficiency of PMS for removal of toxic organic pollutants. The major contents are described as follows:(1) An innovative method involving the couple of reverse co-precipitation method and post-calcination for preparing Co3O4-Bi2O3nanocomposite oxides were developed and the prepred Co3O4-Bi2O3nanocomposite oxides as heterogenous catalysts of PMS for the degradation of several organic pollutants were investigated. It was found there was a strong interaction between Bi and Co components in the nanocomposite, which was found to enhance surface hydroxyl oxygen content and in favor of the formation of Co(Ⅱ)-OH complexes. Co3O4-Bi2O3nanocomposite oxides showed stronger catalytic activity for the heterogeneous activation of PMS and the degradation of organic pollutanst than CO3O4. With the addition0.05g L-1catalysts of and0.5mmol L-1PMS, the Co3O4-Bi2O3nanocomposite oxides produced fast and full degradation of methylene blue (MB,20μmol L-1) with the apparent rate constant of0.36min-1, being8.6folds of that (0.042min-1) over nano-Co3O4. The cobalt leaching to43μg L-1was observed for0.05g L-1Co3O4-Bi2O3nanocomposite oxides, being much less than that (158μg L-1) from Co3O4in the acidic aqueous solutuion (pH3.2-3.4). Due to the excellent chemical stability, Co3O4-Bi2O3nanocomposite oxides show favorable catalytic performance during three successive cycles.(2) A sol-gel method was developed to prepare CuFe2O4nanoparticles and an innovative adcanced oxidation system of CuFe2O4/PMS was constructed. CuFe2O4nanoparticles is a cobalt-free catalyst for the activation of PMS, thus, the cobalt leaching can be avoided. It was found the added tetrabromobisphenol A (TBBPA,10mg L-1) was almost completely removed (with a removal of99%) in30min by using0.1g L CuFe2O4and0.2mmol L-1PMS. With higher addition of PMS (1.5mmol L-1), the degradation yielded a TOC removal of56%and a TBBPA debromination ratio of67%. Radical quenching tests proved that SO4-radicals were the main reactive species. XPS characterization results of the fresh and used CuFe2O4indicated the highly catalytic activity could be attributed to a catalytic mechanism involving both Cu(Ⅱ) and Fe(Ⅲ) in CuFe2O4.Based on the HPLC and LC-MS analysis of the degradation intermediates in the CuFe2O4/PMS system, a detail mechanism for SO4-induced TBBPA degradation was proposed.(3) To further improve the catalytic ability of Cu-Fe compounds, Cu+-bearing CuFeO2microparticles were synthesized and characterized as a new activator of PMS for degradation of organic pollutants. It was found CuFeO2exhibited much higher catalytic activity towards degradation of TBBPA in the presence of PMS in comparison with Fe2O3, Cu2O and CuFe2O4as catalysts. The addition of CuFeO2microparticles (0.5g L-1) induced a TBBPA degradation removal of100%in30min in the presence of0.2mmol L-1PMS, higher than that (25%and66%in30min) by using Fe2O3and Cu2O particles as catalysts under the similar conditions. Furthermore, CuFeO2nanoparticles showed better performances in the TBBPA degradation, TOC removal and debromination than CuFe2O4nanoparticles. By adding1.5mmol L-1PMS,62%TOC removal and74%debromination of TBBPA were observed in the case of0.5g L-1CuFe2O4nanoparticles in60min, which were increased to75%(TOC removal) and81%(debromination ratio) in the case of0.5g L-1CuFeO2nanoparticles. Moreover, CuFeO2microparticles also exihibited excellent catalytic stability and easy recyclability, thus, the method based on the catalytic activation of PMS by CuFeO2microparticles has promising potentials in the application in the field of pollution control as a green oxidation process.Finally, on the basis of the above research results, new possible application and the related investigation of the three innovative catalysts are prospected. The introduction of visible light, the construction of Fenton-like system and phenolic compounds modified Fenton-like system is anticipated to further enhance catalytic activity of these catalysts and extend their application in the field of environmental catalysis.