Persistent free radicals in carbon-based materials on transformation of refractory organic contaminants (ROCs) in water: A critical review

Yaxin Qin, Guiying Li, Yanpeng Gao, Lizhi Zhang, Yong Sik Ok, Taicheng An

Research output: Contribution to journalReview articlepeer-review

261 Citations (Scopus)


With the increased concentrations and kinds of refractory organic contaminants (ROCs) in aquatic environments, many previous reviews systematically summarized the applications of carbon-based materials in the adsorption and catalytic degradation of ROCs for their economically viable and environmentally friendly behavior. Interestingly, recent studies indicated that carbon-based materials in natural environment can also mediate the transformation of ROCs directly or indirectly due to their abundant persistent free radicals (PFRs). Understanding the formation mechanisms of PFRs in carbo-based materials and their interactions with ROCs is essential to develop their further applications in environment remediation. However, there is no comprehensive review so far about the direct and indirect removal of ROCs mediated by PFRs in amorphous, porous and crystalline carbon-based materials. The review aims to evaluate the formation mechanisms of PFRs in carbon-based materials synthesized through pyrolysis and hydrothermal carbonization processes. The influence of synthesis conditions (temperature and time) and carbon sources on the types as well as the concentrations of PFRs in carbon-based materials are also discussed. In particular, the effects of metals on the concentrations and types of PFRs in carbon-based materials are highlighted because they are considered as the catalysts for the formation of PFRs. The formation mechanisms of reactive species and the further transformation mechanisms of ROCs are briefly summarized, and the surface properties of carbon-based materials including surface area, types and number of functional groups, etc. are found to be the key parameters controlling their activities. However, due to diversity and complexity of carbon-based materials, the exact relationships between the activities of carbon-based materials and PFRs are still uncertain. Finally, the existing problems and current challenges for the ROCs transformation with carbon-based materials are also pointed out.

Original languageEnglish
Pages (from-to)130-143
Number of pages14
JournalWater Research
Publication statusPublished - 2018 Jun 15

Bibliographical note

Funding Information:
This work was financially supported by the National Natural Science Foundation of China ( 41425015 , 41573086 and 41373102 ). Appendix A

Publisher Copyright:
© 2018 Elsevier Ltd


  • Black carbon
  • Carbon-based materials
  • Hydrochar
  • Persistent free radicals
  • Pollution control mechanism
  • Refractory organic contaminants

ASJC Scopus subject areas

  • Ecological Modelling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution


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