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Effect of oxalate and pH on photodegradation of pentachlorophenol in heterogeneous irradiated maghemite System

Paper ID Volume ID Publish Year Pages File Format Full-Text
25934 43920 2016 9 PDF Available
Title
Effect of oxalate and pH on photodegradation of pentachlorophenol in heterogeneous irradiated maghemite System
Abstract

•PCP can be effectively photodegraded in UV/maghemite/oxalic acid system at different pH.•At low pH, the dominant mechanism is OH attack with a higher content of H2O2 and the formation of small molecules intermediates.•At high pH, the dominant mechanism is direct photolysis with a much less H2O2.•The capacity of γ-Fe2O3 to adsorb oxalic acid was consistent with its ability to photodegrade PCP and to form H2O2.

Photochemical degradation in the system of iron oxides and oxalic acid (OX) is the important reaction for detoxification of organic pollutants in natural environments, including surface soils, surface water, and even aerosols, and it was more effective at low pH according to previous studies. However, in this study, the photodegradation of pentachlorophenol (PCP) proceeded rapidly at different pH conditions in the system with maghemite and OX under UV light illumination. It was observed that the removal of PCP was 77.7% ± 0.90%, 79.9% ± 0.80% and 74.3% ± 1.50% at initial pH of 3.5, 5.0 and 7.0, respectively. To explore the degradation mechanism, the interaction of OX and maghemite were systematically studied as a function of pH. The presence of OX of 1.2 mM effectively decreased the iso-electric point (iep) of the maghemite from 5.6 to 1.8. The maximum adsorption amount of maghemite adsorbing OX increased with increasing pH value from 208 mmol kg−1 at pH = 3.5 to 293 mmol kg−1 at pH = 9.0. However, PCP (0.0375 mM) inhibited the adsorption of oxalic acid at pH = 3.5 and pH = 5.0 but promoted it at pH = 7.0 and pH = 9.0. When the initial content of OX was 1.2 mM, the highly active compounds of Fe(C2O4)33− as Fe(III) and Fe(C2O4)22− as Fe(II) were the dominant species at different pH. The formation of H2O2 also relied on the value of pH and the concentration range of H2O2 during PCP degradation was 0–1.67 mg L−1, 0–1.16 mg L−1 and 0–0.16 mg L−1at initial pH of 3.5, 5.0 and 7.0, respectively. The low pH conditions favored the iron cycling, the H2O2 generation and the broken of aromatic ring of PCP, so as to enhance the degradation rates of PCP. At the high pH conditions, due to the slowdown of the iron cycling and the decreased amount of H2O2 formation, the direct photolysis was responsible for the enhanced degradation of PCP. The foundation of high photochemical efficiencies of OX and maghemite for PCP degradation at large-scale pH conditions improves the photochemical mechanisms of OX-iron oxide system and is of important for understanding the transformation of organic pollutants in light environments.

Keywords
Iron oxides; PCP; Oxalic acid; Degradation mechanism; pH condition
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Effect of oxalate and pH on photodegradation of pentachlorophenol in heterogeneous irradiated maghemite System
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 328, 1 September 2016, Pages 198–206
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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Any Questions? feel free to contact us