RETURN TO ISSUEPREVCorrespondence/Rebut...Correspondence/RebuttalNEXT

Response to Comment on “Electrolytic Manipulation of Persulfate Reactivity by Iron Electrodes for TCE Degradation in Groundwater”

View Author Information
State Key Lab of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, P. R. China
*Phone: (+86)-027-67848629; fax: (+86)-027-67883456; e-mail: [email protected]
Cite this: Environ. Sci. Technol. 2014, 48, 8, 4632–4633
Publication Date (Web):March 28, 2014
https://doi.org/10.1021/es501323n
Copyright © 2014 American Chemical Society
Article Views
806
Altmetric
-
Citations
LEARN ABOUT THESE METRICS
PDF (202 KB)

We appreciate the concerns that Zou et al. (1) raised on our paper (2) regarding the relative contribution of •OH and SO4•– to TCE degradation in persulfate/iron electrodes system. The authors doubted our conclusion that •OH played a more significant role than SO4•– on TCE degradation. They argued that SO4•– is the dominant radical for the oxidation of organic contaminants by Fe2+ activated persulfate. (1) We will address their doubt from the results reported in literature and obtained in our study. The authors cited references to support their argument. One important reference cited by the authors is reported by Anipsitakis and Dionysiou. (3) However, Anipsitakis and Dionysiou concluded that “sulfate and hydroxyl radicals are formed at almost equal proportions” according to tert-butyl-alcohol (TBA) and ethanol scavenging results. (3) In a previous study conducted by Zou et al., (4) the contributions of •OH and SO4•– in Fe2+/peroxymonosulfate system reflected by the differences of rate constants with additions of TBA and methanol (Figure 5 (4)) were about 85 and 9%, respectively. In another important study from Watts’ group, (5) use of isopropanol and TBA demonstrated that approximately 86% of the oxidation activity in iron(II)-ethylenediaminetetraacetic acid (EDTA) was attributable to •OH activity. Literature reporting the relative contribution of •OH and SO4•– to contaminants degradation in Fe2+/persulfate system are limited, (2-5) whereas all the results available agree with our conclusion. (2)

To further support the more significant role of •OH than SO4•– in our paper, (2) additional experiments were conducted using higher scavenger concentrations. Three scavengers were added independently. Thirty mM TBA was spiked into the solution (0.10 mM TCE) to quench •OH but leave SO4•– active. The concentrations of methanol were set at higher than 1 M that could scavenge both •OH and SO4•–. Ethanol was also added for comparison due to its higher reactivity with SO4•– than methanol. (1) As shown in Figure 1, 30 mM TBA significantly inhibited TCE degradation, decreasing the pseudo first-order rate constant from 0.315 ± 0.007 min–1 without scavengers to 0.112 ± 0.009 min–1. This reduction was attributable to the quenched •OH. In the presence of 1 and 5 M methanol, TCE degradation was almost completely ceased, suggesting the quench of both •OH and SO4. The rate constant dropped to 0.009 ± 0.002 min–1 (1 M methanol). Similar inhibition was observed with the addition of 1 M ethanol. There are two methods for calculating the relative contribution of •OH and SO4•–. One is based on the difference in transformation percentage, (3) and the other derives from the difference in rate constants. (5) Consistent results are obtained if the reaction follows pseudo zero-order kinetics. Otherwise, contributions calculated from the difference in transformation percentage are time-dependent, and SO4•–contribution would approach 100% by prolonging the time. As the pseudo first-order rate constant integrates the participation of radicals, calculation derived from rate constant difference is more appropriate. The relative contributions of •OH and SO4•– were thus calculated to be 64.4 and 32.7%, respectively. This experimental result further supports the conclusion reported in our paper. (2)

Figure 1

Figure 1. Effect of radical scavengers on TCE degradation in persulfate/iron electrode. The reaction conditions are based on 5 mM initial Na2S2O8 concentration, 0.10 mM TCE, +50 mA on the iron anode, initial pH of 5.6 and 410 mL solution in a 520 mL closed reactor. The curves refer to the fittings by pseudo first-order kinetics for the data points in the same color. The data points for 5 M methanol and 1 M ethanol can not fitted by pseudo first-order kinetics.

Another concern that Zou et al. (1) raised is the origin of •OH. We agree that oxidation of H2O by SO4•– under neutral and acidic conditions can not produce the observed levels of •OH because of the extremely low rate constant. As our paper is focused on the manipulation of persulfate reactivity by iron electrodes, (2) an extended discussion on the mechanism of •OH generation was not included. However, it would be interesting to elucidate the mechanism because it is still unknown regardless of the awareness of its significant contribution. (2, 3, 5) A possible pathway is that persulfate oxidizes H2O to form H2O2, (3) and then Fe2+ activates H2O2 producing •OH through Fenton reactions.

Author Information

ARTICLE SECTIONS
Jump To

  • Corresponding Author
    • Songhu Yuan - State Key Lab of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, P. R. China Email: [email protected]
  • Author
    • Peng Liao - State Key Lab of Biogeology and Environmental Geology, China University of Geosciences, 388 Lumo Road, Wuhan, 430074, P. R. China
  • Notes
    The authors declare no competing financial interest.

References

ARTICLE SECTIONS
Jump To

This article references 5 other publications.

  1. 1
    Zou, J.; Ma, J.; Zhang, J. Q. Comment on “Electrolytic manipulation of persulfate reactivity by iron electrodes for TCE degradation in groundwater Environ. Sci. Technol. 2014,  DOI: 10.1021/es501061n
  2. 2
    Yuan, S.; Liao, P.; Alshawabkeh, A. N. Electrolytic manipulation of persulfate reactivity by iron electrodes for TCE degradation in groundwater Environ. Sci. Technol. 2014, 48, 656 663
  3. 3
    Anipsitakis, G. P.; Dionysiou, D. D. Radical generation by the interaction of transition metals with common oxidants Environ. Sci. Technol. 2004, 38 (17) 3705 3712
  4. 4
    Zou, J.; Ma, J.; Chen, L. W.; Li, X. C.; Guan, Y. H.; Xie, P. C.; Pan, C. Rapid acceleration of ferrous iron/peroxymonosulfate oxidation of organic pollutants by promoting Fe(III)/Fe(II) cycle with hydroxylamine Environ. Sci. Technol. 2013, 47, 11685 11691
  5. 5
    Ahmad, M.; Teel, A. L.; Furman, O. S.; Reed, J. I.; Watts, R. J. Oxidative and reductive pathways in iron-ethylenediaminetetraacetic acid-activated persulfate systems J. Envion. Eng. ASCE 2012, 138, 411 418

Cited By


This article is cited by 4 publications.

  1. Ghulam Abbas Ashraf, Raqiqa Tur Rasool, Jing Chen, Lianjie Li, Muhammad Hassan, Jazib Ali, Lanting Zhang, Hai Guo. Novel LaCr substituted Mhexaferrite photocatalyst for decontamination of organic pollutants by peroxymonosulfate activation. Journal of Molecular Liquids 2022, 345 , 117840. https://doi.org/10.1016/j.molliq.2021.117840
  2. Tatianna Marshall, Erica Pensini. Vitamin B12 and Magnesium: a Healthy Combo for the Degradation of Trichloroethylene. Water, Air, & Soil Pollution 2021, 232 (8) https://doi.org/10.1007/s11270-021-05295-w
  3. Guangzhou Qu, Rongjie Chu, Hui Wang, Tiecheng Wang, Zengqiang Zhang, Hong Qiang, Dongli Liang, Shibin Hu. Simultaneous removal of chromium(VI) and tetracycline hydrochloride from simulated wastewater by nanoscale zero-valent iron/copper–activated persulfate. Environmental Science and Pollution Research 2020, 27 (32) , 40826-40836. https://doi.org/10.1007/s11356-020-10120-8
  4. Wen-Da Oh, Zhili Dong, Teik-Thye Lim. Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects. Applied Catalysis B: Environmental 2016, 194 , 169-201. https://doi.org/10.1016/j.apcatb.2016.04.003
  • Figure 1

    Figure 1. Effect of radical scavengers on TCE degradation in persulfate/iron electrode. The reaction conditions are based on 5 mM initial Na2S2O8 concentration, 0.10 mM TCE, +50 mA on the iron anode, initial pH of 5.6 and 410 mL solution in a 520 mL closed reactor. The curves refer to the fittings by pseudo first-order kinetics for the data points in the same color. The data points for 5 M methanol and 1 M ethanol can not fitted by pseudo first-order kinetics.

  • References

    ARTICLE SECTIONS
    Jump To

    This article references 5 other publications.

    1. 1
      Zou, J.; Ma, J.; Zhang, J. Q. Comment on “Electrolytic manipulation of persulfate reactivity by iron electrodes for TCE degradation in groundwater Environ. Sci. Technol. 2014,  DOI: 10.1021/es501061n
    2. 2
      Yuan, S.; Liao, P.; Alshawabkeh, A. N. Electrolytic manipulation of persulfate reactivity by iron electrodes for TCE degradation in groundwater Environ. Sci. Technol. 2014, 48, 656 663
    3. 3
      Anipsitakis, G. P.; Dionysiou, D. D. Radical generation by the interaction of transition metals with common oxidants Environ. Sci. Technol. 2004, 38 (17) 3705 3712
    4. 4
      Zou, J.; Ma, J.; Chen, L. W.; Li, X. C.; Guan, Y. H.; Xie, P. C.; Pan, C. Rapid acceleration of ferrous iron/peroxymonosulfate oxidation of organic pollutants by promoting Fe(III)/Fe(II) cycle with hydroxylamine Environ. Sci. Technol. 2013, 47, 11685 11691
    5. 5
      Ahmad, M.; Teel, A. L.; Furman, O. S.; Reed, J. I.; Watts, R. J. Oxidative and reductive pathways in iron-ethylenediaminetetraacetic acid-activated persulfate systems J. Envion. Eng. ASCE 2012, 138, 411 418