Kuan, C-C, Chang, S-Y and Schroeder, SLM orcid.org/0000-0002-4232-5378 (2015) Fenton-Like Oxidation of 4−Chlorophenol: Homogeneous or Heterogeneous? Industrial & Engineering Chemistry Research, 54 (33). pp. 8122-8129. ISSN 0888-5885
Abstract
Heterogeneous Fenton-like catalysts have received considerable research attention because they could potentially be attractive for oxidative removal of organic contaminants from tertiary wastewater. However, process design is still hampered by insufficient understanding of the chemical pathways involved, and especially whether oxidation activity stems from heterogeneous surface chemistry or minute concentrations of dissolved metal ions in the homogeneous phase. Using inductively coupled plasma-optical emission spectroscopy (ICP-OES) in combination with pH monitoring and ultraviolet–visible spectroscopy (UV–vis) we have monitored the degradation of 4-chlorophenol (4-CP) over two Fenton-like heterogeneous systems, namely FeOx supported on TiO2 and CuFe2O4. We show conclusively that these systems proceed predominantly through a homogeneous route via dissolved metal ions from the solid phase catalysts. Control experiments with homogeneous Fe3+ or Cu2+ systems reveal that even minute concentrations (μM/subppm) of dissolved metal ions leached from the solid phases account for the observed 4-CP degradation rates in the heterogeneous systems. ICP-OES revealed that metal leaching was time-dependent and variable because of pH variations associated with changing acid release rates. Buffering solutions at pH 7.4 suppressed metal leaching (and hence 4-CP degradation) in the FeOx/TiO2 system, but not in others. For example, pH buffering did not entirely suppress metal leaching from CuFe2O4, for which 4-CP degradation was retained through small concentrations of Fe and Cu ions in solution. Our results highlight the importance of careful monitoring of metal content in the aqueous phase, certainly with analytical sensitivity below ppm concentrations of the dissolved metals, and also the crucial influence of time-dependent pH variations on the reaction process. Recyclability of catalysts, pH buffering of solutions or monitoring of metal content in the solid phase by less sensitive analytical methods, for example, chemical analysis, gravimetry, X-ray fluorescence, or energy dispersive X-ray analysis in electron microscopes, cannot exclude the homogeneous Fenton route in the presence of solid catalysts.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | This document is the Accepted Manuscript version of a Published Work that appeared in final form in Industrial and engineering chemistry research, copyright © American Chemical Society 2015 after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.iecr.5b02378 |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemical & Process Engineering (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 28 Aug 2015 09:47 |
Last Modified: | 27 Oct 2020 15:10 |
Published Version: | http://dx.doi.org/10.1021/acs.iecr.5b02378 |
Status: | Published |
Publisher: | American Chemical Society |
Identification Number: | 10.1021/acs.iecr.5b02378 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:89223 |