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Open AccessArticle

Investigation of Catalytic Ozonation of Recalcitrant Organic Chemicals in Aqueous Solution over Various ZSM-5 Zeolites

1
State Key Laboratory of Petroleum Pollution Control, China University of Petroleum, Beijing 102249, China
2
Hawaii Natural Energy Institute, University of Hawaii at Manoa, Honolulu, HI 96822, USA
3
Department of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa, Honolulu, HI 96822, USA
4
College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, China
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Catalysts 2018, 8(4), 128; https://doi.org/10.3390/catal8040128
Received: 31 January 2018 / Revised: 9 March 2018 / Accepted: 20 March 2018 / Published: 22 March 2018
Catalytic ozonation processes (COPs) are an emerging technology for wastewater treatments. NaZSM-5 zeolites in three different SiO2/Al2O3 ratios (31, 45, and 120) and their metallic oxides loaded samples were compared for COP of nitrobenzene solution. NaZSM-5(120) showed high total organic carbon (TOC) removals (70.2–74.0%) by adsorption relative to NaZSM-5(45) (0.4–0.6%) at various initial pH conditions. NaZSM-5(31) was obtained by NaOH treatment of NaZSM-5(45) and displayed 20.9–23.8% of TOC removals by adsorption. In COPs, the different ZSM-5 zeolites exhibited various TOC removals and different reaction pathways. COP-NaZSM-5(120) showed high TOC removals compared to COP-NaZSM-5(45) and COP-NaZSM-5(31). The repeated uses of zeolites in COPs were performed to understand the reaction pathways and contribution of adsorption versus ozonation (i.e., catalytic oxidation and/or direct ozonation). Both adsorption and direct ozonation in COP-NaZSM-5(120) contributed TOC removal for the first use, whereas direct ozonation and •OH mediated oxidation dominated the process for eight repeated uses. Direct ozonation and •OH-mediated oxidation controlled the COP-NaZSM-5(45) process for the first and eight repeated uses. Adsorption and direct ozonation governed the COP-NaZSM-5(31) process for the first use, whereas the direct ozonation dominated it for eight repeated uses. In COPs, NaZSM-5(120) and NaZSM-5(45) showed the catalytic activity, whereas NaZSM-5(31) displayed negligible catalytic activity. The high catalytic activity of NaZSM-5(120) may be due to more Si-O bonds on zeolite surfaces. The results revealed that loading of Mg oxide on ZSM-5 zeolites can increase catalytic activity in COPs. These results show the application potential of ZSM-5 zeolites in ozonation of recalcitrant chemical wastewaters. View Full-Text
Keywords: ozonation; ZSM-5 zeolites; SiO2/Al2O3 ratios; nitrobenzene; adsorption ozonation; ZSM-5 zeolites; SiO2/Al2O3 ratios; nitrobenzene; adsorption
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Wang, Y.; Ma, W.; Yoza, B.A.; Xu, Y.; Li, Q.X.; Chen, C.; Wang, Q.; Gao, Y.; Guo, S.; Zhan, Y. Investigation of Catalytic Ozonation of Recalcitrant Organic Chemicals in Aqueous Solution over Various ZSM-5 Zeolites. Catalysts 2018, 8, 128.

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