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      Confined pyrolysis of metal–organic frameworks to N-doped hierarchical carbon for non-radical dominated advanced oxidation processes

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          Abstract

          The possible degradation and synergistic mechanism for non-radical dominated advanced oxidation processes.

          Abstract

          Development of metal–organic framework (MOF) derived carbon materials toward advanced oxidation processes (AOPs) is essential for environment-friendly catalysts. In this work, a confined pyrolysis strategy to prepare N-doped hierarchical carbon (NDHC) catalysts for non-radical advanced oxidation processes is proposed. After simply pyrolyzing phenolic resin (PR) coated zeolite imidazole framework (ZIF) particles, NDHC with favorable structural and compositional properties is obtained. To present the catalytic performance of resultant NDHC, bisphenol A (BPA) is selected as the target contaminant. The results show that 98% of BPA (20 ppm) was removed by NDHC in 5 min, which is superior to many other peroxymonosulfate (PMS) catalysts. Based on electron paramagnetic resonance (EPR) analysis and scavenger experiments, a singlet oxygen-dominated non-radical mechanism is confirmed in the degradation process. In addition, the influencing factors including solution pH, catalyst/PMS dosage, BPA concentration, reaction temperature, and anion/organic matter are also investigated. This confined pyrolysis strategy endows MOF derived carbon materials wide application prospects in environmental remediation.

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          Most cited references59

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          Metal-organic framework materials as catalysts.

          A critical review of the emerging field of MOF-based catalysis is presented. Discussed are examples of: (a) opportunistic catalysis with metal nodes, (b) designed catalysis with framework nodes, (c) catalysis by homogeneous catalysts incorporated as framework struts, (d) catalysis by MOF-encapsulated molecular species, (e) catalysis by metal-free organic struts or cavity modifiers, and (f) catalysis by MOF-encapsulated clusters (66 references).
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            Radical generation by the interaction of transition metals with common oxidants.

            Nine transition metals were tested for the activation of three oxidants and the generation of inorganic radical species such as sulfate, peroxymonosulfate, and hydroxyl radicals. From the 27 combinations, 14 M/Ox couples demonstrated significant reactivity toward transforming a model organic substrate such as 2,4-dichlorophenol and are further discussed here. It was found that Co(II) and Ru(III) are the best metal catalysts for the activation of peroxymonosulfate. As expected on the basis of the Fenton reagent, Fe(III) and Fe(II) were the most efficient transition metals for the activation of hydrogen peroxide. Finally, Ag(I) showed the best results toward activating persulfate. Quenching studies with specific alcohols (tert-butyl alcohol and ethanol) were also performed to identify the primary radical species formed from the reactive M/Ox interactions. The determination of these transient species allowed us to postulate the rate-determining step of the redox reactions taking place when a metal is coupled with an oxidant in aqueous solution. It was found that when Co(II), Ru(III), and Fe(II) interact with peroxymonosulfate, freely diffusible sulfate radicals are the primary species formed. The same was proven for the interaction of Ag(I) with persulfate, but in this case caged or bound to the metal sulfate radicals might be formed as well. The conjunction of Ce(III), Mn(II), and Ni(II) with peroxymonosulfate showed also to generate caged or bound to the metal sulfate radicals. A combination of sulfate and hydroxyl radicals was formed from the conjunction of V(III) with peroxymonosulfate and from Fe(II) with persulfate. Finally, the conjunction of Fe(III), Fe(II), and Ru(III) with hydrogen peroxide led primarily to the generation of hydroxyl radicals. It is also suggested here that the redox behavior of a particular metal in solution cannot be predicted based exclusively on its size and charge. Additional phenomena such as metal hydrolysis as well as complexation with other counterions present in solution might affect the thermodynamics of the overall process and are further discussed here.
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              The active site of methanol synthesis over Cu/ZnO/Al2O3 industrial catalysts.

              One of the main stumbling blocks in developing rational design strategies for heterogeneous catalysis is that the complexity of the catalysts impairs efforts to characterize their active sites. We show how to identify the crucial atomic structure motif for the industrial Cu/ZnO/Al(2)O(3) methanol synthesis catalyst by using a combination of experimental evidence from bulk, surface-sensitive, and imaging methods collected on real high-performance catalytic systems in combination with density functional theory calculations. The active site consists of Cu steps decorated with Zn atoms, all stabilized by a series of well-defined bulk defects and surface species that need to be present jointly for the system to work.
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                Author and article information

                Contributors
                Journal
                JMCAET
                Journal of Materials Chemistry A
                J. Mater. Chem. A
                Royal Society of Chemistry (RSC)
                2050-7488
                2050-7496
                May 21 2019
                2019
                : 7
                : 20
                : 12547-12555
                Affiliations
                [1 ]Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse
                [2 ]School of Environmental and Biological Engineering
                [3 ]Nanjing University of Science and Technology
                [4 ]Nanjing 210094
                [5 ]People's Republic of China
                Article
                10.1039/C9TA02931A
                a58d4e7a-28e4-4ac8-aceb-e84bf03e8234
                © 2019

                http://rsc.li/journals-terms-of-use

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