RETURN TO ISSUEPREVCorrespondence/Rebut...Correspondence/RebuttalNEXT

Comment on “Activation of Persulfate by Graphitized Nanodiamonds for Removal of Organic Compounds”

View Author Information
Department of Chemical Engineering, Curtin University, GPO Box U1987, WA 6845, Australia
School of Engineering, Edith Cowan University, 270 Joondalup Drive, Joondalup, Perth, WA 6027, Australia
*(H.S.) Phone: +61 8 6304 5067; e-mail: [email protected]
*(S.W.) Phone: +61 8 9266 3776; e-mail: : [email protected]
Cite this: Environ. Sci. Technol. 2017, 51, 9, 5351–5352
Publication Date (Web):April 14, 2017
https://doi.org/10.1021/acs.est.7b00399
Copyright © 2017 American Chemical Society
Article Views
1909
Altmetric
-
Citations
LEARN ABOUT THESE METRICS
PDF (214 KB)

Since the discovery of graphene, (1) carbon nanotubes, (2) and nanodiamonds (3) as peroxymonosulfate (PMS)/persulfate (PS) activators for aqueous-phase oxidation by our group, immense research interests have been aroused in environmental remediation with the state-of-the-art carbocatalysis. Recently, Lee et al. (4) reported an article entitled Activation of Persulfates by Graphitized Nanodiamonds for Removal of Organic Compounds, in which the authors utilized graphitized nanodiamonds (G-NDs) as carbocatalysts for persulfate activation. Despite a similar material preparation and experimental design to our previous study, (5) the authors proposed a nonradical-dominated mechanism (unfortunately our original reports (6, 7) on nonradical reactions of carbons were not cited). Since the mechanism on carbon-catalyzed persulfate activation remains controversial, we would like to raise some neglected points in Lee et al. study.

1 The Role of Reactive Radicals

ARTICLE SECTIONS
Jump To

The authors utilized radical scavengers to screen the effects of SO4•– and OH on phenol oxidation and believed that the radicals presented a marginal effect. However, there are several tricky points in the experimental design in Lee’s study. First, a very low dosage of radical quenching agents (200 times of PS) were applied into the G-ND/PS system, which dramatically slowed down the complete phenol oxidation from 10 (control experiment) to 30 min for both methanol and dimethyl sulfoxide. The differences in reaction rates measured in the absence versus presence of radical quenching agents would have been more appropriately illustrated by including a plot (bar chart) comparing the measured rate constants. The G-ND/PS system in Lee’s study is intrinsically distinct from the exclusively nonradical-based systems of CuO/PS (8) and CNT/PS (9) that alcohols hardly affected the catalytic performance. Moreover, ultrahigh loading of the oxidant (1 mM PS) was applied, which was almost 100 times of the target organic compound (0.01 mM phenol), whereas complete phenol mineralization only requires 0.14 mM PS. Thus, despite that the radical pathway was terminated by the quenching agents, phenol could still be oxidized via the nonradical pathway in the presence of excessive PS. The radical quenching tests in Lee’s study cannot rule out the crucial role of free radicals in phenol oxidation.
Besides, Lee and co-workers employed in situ electron paramagnetic resonance (EPR) to capture the free radicals during the PS activation. Strangely, the EPR spectra presented in Lee’s Supporting Information did not present any signal in G-ND/PS and then Lee et al. claimed that no measurable radicals were produced in the nonradical process. However, the EPR response in Lee’s experiment is conflicting with the recently reported nonradical-based systems investigated by Lee’s group for carbon nanotubes (CNTs)/PS (9) and Pd–Al2O3/PMS, (10) in which 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) would be directly oxidized by the nonradical processes to exhibit strong characteristic peaks of 5,5-dimethylpyrrolidone-2-(oxy)-(1) (DMPOX). In terms of carbon-catalyzed systems from other studies, both sulfate radicals (DMPO–SO4) and hydroxyl radicals (DMPO–OH) were obviously revealed in quinone/PS, (11) graphene/PS, (12) nanodiamond/PS, (5) CNTs/PS, (13, 14) and biochar/PS. (15) Therefore, the EPR tests in Lee’s study need to be reconsidered.

2 Evolution of Singlet Oxygen

ARTICLE SECTIONS
Jump To

Lee et al. determined that no noticeable singlet oxygen (1O2) was generated in G-ND/PS and that it was not accounted for phenol oxidation. However, the addition of l-histidine and azide ions obviously inhibited the oxidation with much lower rate constants (roughly estimated from the original data by pseudo-first-order kinetics). In contrast, the quenching experiments implied that singlet oxygen was produced and partially contributed to the organic removal. We further performed EPR tests and confirmed that singlet oxygen was indeed captured by 2,2,6,6-tetramethyl-4-piperidinol (TMP) with an increased intensity with the reaction proceeded (data not shown here due to page limit).

3 Reaction Pathways and Intrinsic Active Sites

ARTICLE SECTIONS
Jump To

In Lee’s study, a nonradical mechanism was proposed in which phenol and PS were simultaneously bonded with the G-ND surface to facilitate the electron transfer from the organic (electron donor) to the oxidant (electron acceptor). Ahn et al. previously revealed a similar nonradical process that Pd nanoparticles (Pd–Al2O3) worked as an electron-tunnel for oxidative degradation, and PMS could rarely be activated without organic pollutants. (10) However, a high PS decomposition efficiency was still achieved on G-NDs and CNTs without the presence of phenol, implying that G-NDs served as a catalyst rather than ’just an electronic bridge for persulfate activation. Lee et al. also did not provide reasonable explanations for the results that graphene and carbon nanotubes, with highly graphitic frameworks and superior electronconductivity, exhibited inferior catalytic activities than G-NDs, which is not supportive for their mechanism of “electron-transfer mediator”. We suggest that the charge conductivity of the carbon materials was not the key factor for PS-driven oxidation and G-NDs might not simply engage as a mediator for electron-transfer. PS activation with carbocatalysis may still rely on certain active sites, possibly the structure defects (dangling bonds, vacancies, and edging sites) formed during the high-temperature annealing.
Lastly, we would like to provide clarification regarding some incorrect conclusions about our earlier paper (5) that were reported in Lee’s paper. Lee et al. stated our previous study of PS/G-ND was a hydroxyl radical-based system, which is definetely not the case. In our study, (5) we clearly illustrated that the G-ND/PS system was not effective for degradation of benzoic acid and nitrobenzene, the hydroxyl radical probes, suggesting that SO4•– was still the dominating radicals accounting for organic oxidation. The excess ethanol (500–2000 times of PS) drastically slowed down the oxidation, which implied the crucial contribution of the radical-induced oxidation. Moreover, we proposed that the low EPR intensity of DMPO–SO4 and remaining oxidation potential under exccesive radical scavengers were due to the formation of surface-confined sulfate radicals, (5) which was similar to Wang’s study (16) using nitrogen-doped graphene as a PS activator. However, we still believe that the partial water oxidation on carbon surface may be experienced which has be witnessed by the in situ EPR detection and predicted by the theoretical calculations. (17) Additionally, Lee et al. also omitted an important factor that the carbon structures (onion-like carbon (1) and sp2/sp3 nanohybrid (5)) in these two studies are intrinsically different, not to mention that the original materials are from two distinct sources with completely different size, surface chemistry, and crystalinity.

Author Information

ARTICLE SECTIONS
Jump To

  • Corresponding Authors
  • Author
    • Xiaoguang Duan - Department of Chemical Engineering, Curtin University, GPO Box U1987, WA 6845, Australia
  • Notes
    The authors declare no competing financial interest.

References

ARTICLE SECTIONS
Jump To

This article references 17 other publications.

  1. 1
    Sun, H. Q.; Liu, S. Z.; Zhou, G. L.; Ang, H. M.; Tade, M. O.; Wang, S. B. Reduced graphene oxide for catalytic oxidation of aqueous organic pollutants ACS Appl. Mater. Interfaces 2012, 4, 5466 5471 DOI: 10.1021/am301372d
  2. 2
    Sun, H. Q.; Kwan, C.; Suvorova, A.; Ang, H. M.; Tade, M. O.; Wang, S. B. Catalytic oxidation of organic pollutants on pristine and surface nitrogen-modified carbon nanotubes with sulfate radicals Appl. Catal., B 2014, 154, 134 141 DOI: 10.1016/j.apcatb.2014.02.012
  3. 3
    Duan, X. G.; Ao, Z. M.; Li, D. G.; Sun, H. Q.; Zhou, L.; Suvorova, A.; Saunders, M.; Wang, G. X.; Wang, S. B. Surface-tailored nanodiamonds as excellent metal-free catalysts for organic oxidation Carbon 2016, 103, 404 411 DOI: 10.1016/j.carbon.2016.03.034
  4. 4
    Lee, H.; Kim, H.; Weon, S.; Choi, W.; Hwang, Y. S.; Seo, J.; Lee, C.; Kim, J. H. Activation of persulfates by graphitized nanodiamonds for removal of organic compounds Environ. Sci. Technol. 2016, 50, 10134 10142 DOI: 10.1021/acs.est.6b02079
  5. 5
    Duan, X. G.; Su, C.; Zhou, L.; Sun, H. Q.; Suvorova, A.; Odedairo, T.; Zhu, Z. H.; Shao, Z. P.; Wang, S. B. Surface controlled generation of reactive radicals from persulfate by carbocatalysis on nanodiamonds Appl. Catal., B 2016, 194, 7 15 DOI: 10.1016/j.apcatb.2016.04.043
  6. 6
    Duan, X. G.; Sun, H. Q.; Wang, Y. X.; Kang, J.; Wang, S. B. N-doping-induced nonradical reaction on single-walled carbon nanotubes for catalytic phenol oxidation ACS Catal. 2015, 5, 553 559 DOI: 10.1021/cs5017613
  7. 7
    Duan, X. G.; Ao, Z. M.; Zhou, L.; Sun, H. Q.; Wang, G. X.; Wang, S. B. Occurrence of radical and nonradical pathways from carbocatalysts for aqueous and nonaqueous catalytic oxidation Appl. Catal., B 2016, 188, 98 105 DOI: 10.1016/j.apcatb.2016.01.059
  8. 8
    Zhang, T.; Chen, Y.; Wang, Y.; Le Roux, J.; Yang, Y.; Croué, J. P. Efficient peroxydisulfate activation process not relying on sulfate radical generation for water pollutant degradation Environ. Sci. Technol. 2014, 48, 5868 5875 DOI: 10.1021/es501218f
  9. 9
    Lee, H.; Lee, H. J.; Jeong, J.; Lee, J.; Park, N. B.; Lee, C. Activation of persulfates by carbon nanotubes: Oxidation of organic compounds by nonradical mechanism Chem. Eng. J. 2015, 266, 28 33 DOI: 10.1016/j.cej.2014.12.065
  10. 10
    Ahn, Y. Y.; Yun, E. T.; Seo, J. W.; Lee, C.; Kim, S. H.; Kim, J. H.; Lee, J. Activation of peroxymonosulfate by surface-loaded noble metal nanoparticles for oxidative degradation of organic compounds Environ. Sci. Technol. 2016, 50, 10187 10197 DOI: 10.1021/acs.est.6b02841
  11. 11
    Fang, G. D.; Gao, J.; Dionysiou, D. D.; Liu, C.; Zhou, D. M. Activation of persulfate by quinones: free radical reactions and implication for the degradation of PCBs Environ. Sci. Technol. 2013, 47, 4605 4611 DOI: 10.1021/es400262n
  12. 12
    Duan, X. G.; Sun, H. Q.; Kang, J.; Wang, Y. X.; Indrawirawan, S.; Wang, S. B. Insights into heterogeneous catalysis of persulfate activation on dimensional-structured nanocarbons ACS Catal. 2015, 5, 4629 4636 DOI: 10.1021/acscatal.5b00774
  13. 13
    Zhang, X. L.; Feng, M. B.; Qu, R. J.; Liu, H.; Wang, L. S.; Wang, Z. Y. Catalytic degradation of diethyl phthalate in aqueous solution by persulfate activated with nano-scaled magnetic CuFe2O4/MWCNTs Chem. Eng. J. 2016, 301, 1 11 DOI: 10.1016/j.cej.2016.04.096
  14. 14
    Feng, M. B.; Qu, R. J.; Zhang, X. L.; Sun, P.; Sui, Y. X.; Wang, L. S.; Wang, Z. Y. Degradation of flumequine in aqueous solution by persulfate activated with common methods and polyhydroquinone-coated magnetite/multi-walled carbon nanotubes catalysts Water Res. 2015, 85, 1 10 DOI: 10.1016/j.watres.2015.08.011
  15. 15
    Fang, G. D.; Liu, C.; Gao, J.; Dionysiou, D. D.; Zhou, D. M. Manipulation of persistent free radicals in biochar to activate persulfate for contaminant degradation Environ. Sci. Technol. 2015, 49, 5645 5653 DOI: 10.1021/es5061512
  16. 16
    Wang, X. B.; Qin, Y. L.; Zhu, L. H.; Tang, H. Q. Nitrogen-doped reduced graphene oxide as a bifunctional material for removing bisphenols: Synergistic effect between adsorption and catalysis Environ. Sci. Technol. 2015, 49, 6855 6864 DOI: 10.1021/acs.est.5b01059
  17. 17
    Duan, X. G.; Ao, Z. M.; Sun, H. Q.; Zhou, L.; Wang, G. X.; Wang, S. B. Insights into N-doping in single-walled carbon nanotubes for enhanced activation of superoxides: A mechanistic study Chem. Commun. 2015, 51, 15249 15252 DOI: 10.1039/C5CC05101K

Cited By


This article is cited by 12 publications.

  1. Wei Ren, Gang Nie, Peng Zhou, Hui Zhang, Xiaoguang Duan, Shaobin Wang. The Intrinsic Nature of Persulfate Activation and N-Doping in Carbocatalysis. Environmental Science & Technology 2020, 54 (10) , 6438-6447. https://doi.org/10.1021/acs.est.0c01161
  2. Xiaoguang Duan, Wenjie Tian, Huayang Zhang, Hongqi Sun, Zhimin Ao, Zongping Shao, Shaobin Wang. sp2/sp3 Framework from Diamond Nanocrystals: A Key Bridge of Carbonaceous Structure to Carbocatalysis. ACS Catalysis 2019, 9 (8) , 7494-7519. https://doi.org/10.1021/acscatal.9b01565
  3. Xiaoguang Duan, Hongqi Sun, Shaobin Wang. Metal-Free Carbocatalysis in Advanced Oxidation Reactions. Accounts of Chemical Research 2018, 51 (3) , 678-687. https://doi.org/10.1021/acs.accounts.7b00535
  4. Peidong Hu, Hanrui Su, Zhenyu Chen, Chunyang Yu, Qilin Li, Baoxue Zhou, Pedro J. J. Alvarez, and Mingce Long . Selective Degradation of Organic Pollutants Using an Efficient Metal-Free Catalyst Derived from Carbonized Polypyrrole via Peroxymonosulfate Activation. Environmental Science & Technology 2017, 51 (19) , 11288-11296. https://doi.org/10.1021/acs.est.7b03014
  5. Hongshin Lee, Changha Lee, and Jae-Hong Kim . Response to Comment on “Activation of Persulfate by Graphitized Nanodiamonds for Removal of Organic Compounds”. Environmental Science & Technology 2017, 51 (9) , 5353-5354. https://doi.org/10.1021/acs.est.7b01642
  6. Hak-Hyeon Kim, Donghyun Lee, Jaemin Choi, Hongshin Lee, Jiwon Seo, Taewan Kim, Ki-Myeong Lee, Anh Le-Tuan Pham, Changha Lee. Nickel–Nickel oxide nanocomposite as a magnetically separable persulfate activator for the nonradical oxidation of organic contaminants. Journal of Hazardous Materials 2020, 388 , 121767. https://doi.org/10.1016/j.jhazmat.2019.121767
  7. Yangke Long, Yixuan Huang, Huiyi Wu, Xiaowen Shi, Ling Xiao. Peroxymonosulfate activation for pollutants degradation by Fe-N-codoped carbonaceous catalyst: Structure-dependent performance and mechanism insight. Chemical Engineering Journal 2019, 369 , 542-552. https://doi.org/10.1016/j.cej.2019.03.097
  8. Xin Cheng, Hongguang Guo, Yongli Zhang, Gregory V. Korshin, Bo Yang. Insights into the mechanism of nonradical reactions of persulfate activated by carbon nanotubes: Activation performance and structure-function relationship. Water Research 2019, 157 , 406-414. https://doi.org/10.1016/j.watres.2019.03.096
  9. Brenna C. Hodges, Ezra L. Cates, Jae-Hong Kim. Challenges and prospects of advanced oxidation water treatment processes using catalytic nanomaterials. Nature Nanotechnology 2018, 13 (8) , 642-650. https://doi.org/10.1038/s41565-018-0216-x
  10. Xiaoguang Duan, Hongqi Sun, Zongping Shao, Shaobin Wang. Nonradical reactions in environmental remediation processes: Uncertainty and challenges. Applied Catalysis B: Environmental 2018, 224 , 973-982. https://doi.org/10.1016/j.apcatb.2017.11.051
  11. Penghui Shao, Jiayu Tian, Feng Yang, Xiaoguang Duan, Shanshan Gao, Wenxin Shi, Xubiao Luo, Fuyi Cui, Shenglian Luo, Shaobin Wang. Identification and Regulation of Active Sites on Nanodiamonds: Establishing a Highly Efficient Catalytic System for Oxidation of Organic Contaminants. Advanced Functional Materials 2018, 28 (13) , 1705295. https://doi.org/10.1002/adfm.201705295
  12. Qingxia Zhao, Qiming Mao, Yaoyu Zhou, Jianhong Wei, Xiaocheng Liu, Junying Yang, Lin Luo, Jiachao Zhang, Hong Chen, Hongbo Chen, Lin Tang. Metal-free carbon materials-catalyzed sulfate radical-based advanced oxidation processes: A review on heterogeneous catalysts and applications. Chemosphere 2017, 189 , 224-238. https://doi.org/10.1016/j.chemosphere.2017.09.042
  • This publication has no figures.
  • References

    ARTICLE SECTIONS
    Jump To

    This article references 17 other publications.

    1. 1
      Sun, H. Q.; Liu, S. Z.; Zhou, G. L.; Ang, H. M.; Tade, M. O.; Wang, S. B. Reduced graphene oxide for catalytic oxidation of aqueous organic pollutants ACS Appl. Mater. Interfaces 2012, 4, 5466 5471 DOI: 10.1021/am301372d
    2. 2
      Sun, H. Q.; Kwan, C.; Suvorova, A.; Ang, H. M.; Tade, M. O.; Wang, S. B. Catalytic oxidation of organic pollutants on pristine and surface nitrogen-modified carbon nanotubes with sulfate radicals Appl. Catal., B 2014, 154, 134 141 DOI: 10.1016/j.apcatb.2014.02.012
    3. 3
      Duan, X. G.; Ao, Z. M.; Li, D. G.; Sun, H. Q.; Zhou, L.; Suvorova, A.; Saunders, M.; Wang, G. X.; Wang, S. B. Surface-tailored nanodiamonds as excellent metal-free catalysts for organic oxidation Carbon 2016, 103, 404 411 DOI: 10.1016/j.carbon.2016.03.034
    4. 4
      Lee, H.; Kim, H.; Weon, S.; Choi, W.; Hwang, Y. S.; Seo, J.; Lee, C.; Kim, J. H. Activation of persulfates by graphitized nanodiamonds for removal of organic compounds Environ. Sci. Technol. 2016, 50, 10134 10142 DOI: 10.1021/acs.est.6b02079
    5. 5
      Duan, X. G.; Su, C.; Zhou, L.; Sun, H. Q.; Suvorova, A.; Odedairo, T.; Zhu, Z. H.; Shao, Z. P.; Wang, S. B. Surface controlled generation of reactive radicals from persulfate by carbocatalysis on nanodiamonds Appl. Catal., B 2016, 194, 7 15 DOI: 10.1016/j.apcatb.2016.04.043
    6. 6
      Duan, X. G.; Sun, H. Q.; Wang, Y. X.; Kang, J.; Wang, S. B. N-doping-induced nonradical reaction on single-walled carbon nanotubes for catalytic phenol oxidation ACS Catal. 2015, 5, 553 559 DOI: 10.1021/cs5017613
    7. 7
      Duan, X. G.; Ao, Z. M.; Zhou, L.; Sun, H. Q.; Wang, G. X.; Wang, S. B. Occurrence of radical and nonradical pathways from carbocatalysts for aqueous and nonaqueous catalytic oxidation Appl. Catal., B 2016, 188, 98 105 DOI: 10.1016/j.apcatb.2016.01.059
    8. 8
      Zhang, T.; Chen, Y.; Wang, Y.; Le Roux, J.; Yang, Y.; Croué, J. P. Efficient peroxydisulfate activation process not relying on sulfate radical generation for water pollutant degradation Environ. Sci. Technol. 2014, 48, 5868 5875 DOI: 10.1021/es501218f
    9. 9
      Lee, H.; Lee, H. J.; Jeong, J.; Lee, J.; Park, N. B.; Lee, C. Activation of persulfates by carbon nanotubes: Oxidation of organic compounds by nonradical mechanism Chem. Eng. J. 2015, 266, 28 33 DOI: 10.1016/j.cej.2014.12.065
    10. 10
      Ahn, Y. Y.; Yun, E. T.; Seo, J. W.; Lee, C.; Kim, S. H.; Kim, J. H.; Lee, J. Activation of peroxymonosulfate by surface-loaded noble metal nanoparticles for oxidative degradation of organic compounds Environ. Sci. Technol. 2016, 50, 10187 10197 DOI: 10.1021/acs.est.6b02841
    11. 11
      Fang, G. D.; Gao, J.; Dionysiou, D. D.; Liu, C.; Zhou, D. M. Activation of persulfate by quinones: free radical reactions and implication for the degradation of PCBs Environ. Sci. Technol. 2013, 47, 4605 4611 DOI: 10.1021/es400262n
    12. 12
      Duan, X. G.; Sun, H. Q.; Kang, J.; Wang, Y. X.; Indrawirawan, S.; Wang, S. B. Insights into heterogeneous catalysis of persulfate activation on dimensional-structured nanocarbons ACS Catal. 2015, 5, 4629 4636 DOI: 10.1021/acscatal.5b00774
    13. 13
      Zhang, X. L.; Feng, M. B.; Qu, R. J.; Liu, H.; Wang, L. S.; Wang, Z. Y. Catalytic degradation of diethyl phthalate in aqueous solution by persulfate activated with nano-scaled magnetic CuFe2O4/MWCNTs Chem. Eng. J. 2016, 301, 1 11 DOI: 10.1016/j.cej.2016.04.096
    14. 14
      Feng, M. B.; Qu, R. J.; Zhang, X. L.; Sun, P.; Sui, Y. X.; Wang, L. S.; Wang, Z. Y. Degradation of flumequine in aqueous solution by persulfate activated with common methods and polyhydroquinone-coated magnetite/multi-walled carbon nanotubes catalysts Water Res. 2015, 85, 1 10 DOI: 10.1016/j.watres.2015.08.011
    15. 15
      Fang, G. D.; Liu, C.; Gao, J.; Dionysiou, D. D.; Zhou, D. M. Manipulation of persistent free radicals in biochar to activate persulfate for contaminant degradation Environ. Sci. Technol. 2015, 49, 5645 5653 DOI: 10.1021/es5061512
    16. 16
      Wang, X. B.; Qin, Y. L.; Zhu, L. H.; Tang, H. Q. Nitrogen-doped reduced graphene oxide as a bifunctional material for removing bisphenols: Synergistic effect between adsorption and catalysis Environ. Sci. Technol. 2015, 49, 6855 6864 DOI: 10.1021/acs.est.5b01059
    17. 17
      Duan, X. G.; Ao, Z. M.; Sun, H. Q.; Zhou, L.; Wang, G. X.; Wang, S. B. Insights into N-doping in single-walled carbon nanotubes for enhanced activation of superoxides: A mechanistic study Chem. Commun. 2015, 51, 15249 15252 DOI: 10.1039/C5CC05101K