Nitrogen-doped char as a catalyst for wet oxidation of phenol-contaminated water


Catalytic wet oxidation (CWO) of aqueous effluents rich in organic compounds is a very promising technology for the treatment of liquid wastes from biomass conversion processes. CWO reactions occur through the formation of free radical species, produced in the presence of an oxidant, which act on organic contaminates in the effluent. Although the reaction is well known, there exists a lack of affordable catalysts to conduct this process at the lower temperatures and pressures in novel bioenergy processes. This study assessed the catalytic effect of nitrogen-doped chars as such an option. Phenol in aqueous solution was used as a model waste effluent. Treatment was conducted at moderate temperatures (190 to 260 °C), oxygen partial pressure of 1 MPa, and reaction times of 15, 30, and 45 min in stainless steel and glass-lined tube reactors. High pressure liquid chromatography (HPLC) analyses of the products quantified phenol and by-product concentrations used in the calculation of reaction activation energy. The char catalyst was studied by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) in order to gain insight into its structure and surface composition. The results indicate that nitrogen-doped char catalysts accelerate the oxidation of phenol by decreasing its reaction activation energy from 82.2 kJ/mol (non-catalyzed) to 40.4 kJ/mol (catalyzed). An analysis from first principles using density functional theory (DFT) was conducted to ascertain which N functional group has the most significant impact on free radical formation in the presence of oxygen. Among all the N functional groups studied, the dipyridinic functional groups showed the most promising characteristics to facilitate the formation of hydroxyl free radicals.

Graphical abstract

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10
Fig. 11
Fig. 12
Fig. 13
Fig. 14
Fig. 15


  1. 1.

    Adib F, Bagreev A, Bandosz TJ (2000) Adsorption/oxidation of hydrogen sulfide on nitrogen-containing activated carbons. Langmuir 16(4):1980–1986.

    Article  Google Scholar 

  2. 2.

    Agency for Toxic Substances and Disease Registry (ATSDR) (2018). Toxicological profile: phenol, (>), Accessed 26, February 2019.

  3. 3.

    Ashourirad B, Sekizkardes AK, Altarawneh S, El-Kaderi HM (2015) Exceptional gas adsorption properties by nitrogen-doped porous carbons derived from benzimidazole-linked polymers. Chem Mater 27(4):1349–1358.

    Article  Google Scholar 

  4. 4.

    Ayiania M, Carbajal-Gamarra FM, Garcia-Perez T, Frear C, Suliman W, Garcia-Perez M (2019) Production and characterization of H2S and PO43− carbonaceous adsorbents from anaerobic digested fibers. Biomass Bioenergy 120:339–349.

    Article  Google Scholar 

  5. 5.

    Ayiania M, Smith M, Hensley AJR, Scudiero L, McEwen JS, Garcia-Perez M (2020) Deconvoluting the XPS spectra for nitrogen-doped chars: an analysis from first principles. Carbon 162:528–544.

    Article  Google Scholar 

  6. 6.

    Bhargava SK, Tardio J, Prasad J, Fo K, Akolekar DB, Grocott SC (2006) Wet oxidation and catalytic wet oxidation. Ind Eng Chem Res 45(4):1221–1258.

    Article  Google Scholar 

  7. 7.

    Blume R, Rosenthal D, Tessonnier J-P, Li H, Knop-Gericke A, Schlögl R (2015) Characterizing graphitic carbon with X-ray photoelectron spectroscopy: a step-by-step approach. ChemCatChem 7(18):2871–2881.

    Article  Google Scholar 

  8. 8.

    Chen H, Sun F, Wang J, Li W, Qiao W, Ling L, Long D (2013) Nitrogen doping effects on the physical and chemical properties of mesoporous carbons. J Phys Chem C 117(16):8318–8328.

    Article  Google Scholar 

  9. 9.

    Denis PA, Iribarne F (2013) Comparative study of defect reactivity in graphene. J Phys Chem C 117(37):19048–19055.

    Article  Google Scholar 

  10. 10.

    Devlin HR, Harris IJ (1984) Mechanism of the oxidation of aqueous phenol with dissolved oxygen. Ind Eng Chem Fundam 23(4):387–392.

    Article  Google Scholar 

  11. 11.

    Ding D, Yang S, Qian X, Chen L, Cai T (2020) Nitrogen-doping positively whilst sulfur-doping negatively affect the catalytic activity of biochar for the degradation of organic contaminant. Appl Catal B: Environ 263(1):118348.

    Article  Google Scholar 

  12. 12.

    Djeffal L, Abderrahmane S, Benzina M, Fourmentin M, Siffert S, Fourmentin S (2014) Efficient degradation of phenol using natural clay as heterogeneous Fenton-like catalyst. Environ Sci Pollut Res 21(5):3331–3338.

  13. 13.

    Duan W, Meng F, Cui H, Lin Y, Wang G, Wu J (2018) Ecotoxicity of phenol and cresols to aquatic organisms: a review. Ecotoxicol Environ Saf 157(2018):441–456

    Article  Google Scholar 

  14. 14.

    Eisenhauer HR (1964) Oxidation of phenolic wastes. Water Pollution Control Federation 36(9):1116–1128.

    Article  Google Scholar 

  15. 15.

    Eisenhauer HR (1971) Increased rate and efficiency of phenolic waste ozonization. Water Pollution Control Federation 43(2):200–208

    Google Scholar 

  16. 16.

    Estrade-Szwarckopf H (2004) XPS photoemission in carbonaceous materials: a ‘defect’ peak beside the graphitic asymmetric peak. Carbon 42(8-9):1713–1721.

    Article  Google Scholar 

  17. 17.

    Figueiredo JL, Pereira MFR (2006) Carbon as catalyst. In: Carbon Materials for Catalysis. John Wiley & Sons Inc., Hoboken, New Jersey, USA, pp 177–217

    Google Scholar 

  18. 18.

    Grant TM, King CJ (1990) Mechanism of Irreversible Adsorption of Phenolic Compounds by Activated Carbons. Ind Eng Chem Res 29(2):264–271.

  19. 19.

    Goran JM, Phan ENH, Favela CA, Stevenson KJ (2015) H2O2 Detection at Carbon Nanotubes and Nitrogen-Doped Carbon Nanotubes: Oxidation, Reduction, or Disproportionation? Anal Chem 87(12):5989–5996.

  20. 20.

    He S, Bijl A, Barana PK, Lefferts L, Kersten SRA, Brem G (2020) Recycling strategy for bioaqueous phase via catalytic wet air oxidation to biobased acetic acid solution. ACS Sustain Chem Eng 8(39):14694–14699.

    Article  Google Scholar 

  21. 21.

    Imamura S (1999) Catalytic and noncatalytic wet oxidation. Ind Eng Chem Res 38(5):1743–1753.

    Article  Google Scholar 

  22. 22.

    Joubert D (1999) From ultrasoft pseudopotentials to the projector augmented-wave method. Phys Rev B: Condens Matter Mater Phys 59(3):1758–1775.

    Article  Google Scholar 

  23. 23.

    Kapteijn F, Moulijn JA, Matzner S, Boehm HP (1999) Development of nitrogen functionality in model chars during gasification in CO2 and O2. Carbon 37(7):1143–1150.

    Article  Google Scholar 

  24. 24.

    Kolaczkowski ST, Beltran FJ, McLurgh DB, Rivas FJ (2002) Wet air oxidation of phenol. Process Saf Environ Prot 75(4):257–265.

    Article  Google Scholar 

  25. 25.

    Kolaczkowski ST, Plucinski P, Beltran FJ, Rivas FJ, McLurgh DB (1999) Wet air oxidation: a review of process technologies and aspects in reactor design. Chem Eng J 73(2):143–160.

    Article  Google Scholar 

  26. 26.

    Krasheninnikov, A. V, and Nieminen, R. M. (2011). Attractive interaction between transition-metal atom impurities and vacancies in graphene: a first-principles study, Theor Chem Accounts 129(3-5), 625-630. DOI:

  27. 27.

    Kresse G, Furthmüller J (1996) Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys Rev B: Condens Matter Mater Phys 54(16):11169–11186.

  28. 28.

    Kulkarni SJ, Kaware JP (2013) Review on research for removal of phenol from wastewater. International Journal of Scientific and Research Publications 3(4):1–5

    Google Scholar 

  29. 29.

    Levec J (1992) Catalytic oxidation of toxic organics in aqueous solution. Appl Catal 63:345–357.

    Article  Google Scholar 

  30. 30.

    Liotta LF, Gruttadauria M, Di Carlo G, Perrini G, Librando V (2009) Heterogeneous catalytic degradation of phenolic substrates: catalyst activity. J Hazard Mater.

  31. 31.

    Liu C, Chen L, Ding D, Cai T (2019) From rice straw to magnetically recoverable nitrogen doped biochar: efficient activation of peroxymonosulfate for the degradation of metolachlor. Appl Catal B Environ 254:312–320.

    Article  Google Scholar 

  32. 32.

    Luo W, Wang B, Heron CG, Allen MJ, Morre J, Maier CS, Stickle WF, Ji X (2014) Pyrolysis of cellulose under ammonia leads to nitrogen-doped nanoporous carbon generated through methane formation. Nano Lett 14(4):2225–2229.

    Article  Google Scholar 

  33. 33.

    Marsh H, Rodriguez-Reinoso F (2006) Activated Carbon. Elsevier, London, UK

    Book  Google Scholar 

  34. 34.

    Miguelez JRP, Bernal JL, Sanz EN, de la Ossa EM (1997) Kinetics of wet air oxidation of phenol. Chem Eng J 67:115–121

    Article  Google Scholar 

  35. 35.

    Monkhorst HJ, Pack JD (1976) Special points for Brillouin-zone integrations. Phys Rev B 13(12):5188–5192.

    MathSciNet  Article  Google Scholar 

  36. 36.

    Mood SH, Ayiania M, Jefferson-Milan Y, Garcia-Perez M (2020) Nitrogen doped char from anaerobically digested fiber for phosphate removal in aqueous solutions. Chemosphere:240.

  37. 37.

    Muley PD, Henkel C, Abdollahi KK, Marculescu C, Boldor D (2016) A critical comparison of pyrolysis of cellulose, lignin, and pine sawdust using an induction heating reactor. Energy Convers Manag 117:273–280

    Article  Google Scholar 

  38. 38.

    Nandi M, Okada K, Dutta A, Bhaumik A, Maruyama J, Derks D, Uyama H (2012) Unprecedented CO2 uptake over highly porous N-doped activated carbon monoliths prepared by physical activation. Chem Commun 48(83):10283–10285.

    Article  Google Scholar 

  39. 39.

    Panisko E, Wietsma T, Lemmon T, Albrecht K, Howe D (2015) Characterization of the aqueous fractions from hydrotreatment and hydrothermal liquefaction of lignocellulosic feedstocks. Biomass Bioenergy 74:162–171

    Article  Google Scholar 

  40. 40.

    Perdew JP, Burke K, Ernzerhof M (1996) Generalized gradient approximation made simple. Phys Rev Lett 77(18):3865–3868.

  41. 41.

    Pruden BB, Le H (1976) Wet air oxidation of soluble components in waste water. Can J Chem Eng 54(4):319–325

    Article  Google Scholar 

  42. 42.

    Rivas FJ, Kolaczkowski ST, Beltran FJ, McLurgh DB (1999) Hydrogen peroxide promoted wet air oxidation of phenol: influence of operating conditions and homogeneous metal catalysts. J Chem Technol Biotechnol 74(5):390–398.<390::AID-JCTB64>3.0.CO;2-G

    Article  Google Scholar 

  43. 43.

    Rivas FJ, Kolaczkowski ST, Beltrán FJ, McLurgh DB (1998) Development of a model for the wet air oxidation of phenol based on a free radical mechanism. Chem Eng Sci 53(14):2575–2586.

    Article  Google Scholar 

  44. 44.

    Rocha RP, Soares OSGP, Gonçalves AG, Órfão JJM, Pereira MFR, Figueiredo JL (2017) Different methodologies for synthesis of nitrogen doped carbon nanotubes and their use in catalytic wet air oxidation. Appl Catal A Gen 548:62–70.

    Article  Google Scholar 

  45. 45.

    Rodrı́guez-Ramos I, Oliviero L, Bachiller-Baeza B, Duprez D, Barbier J, Guerrero-Ruiz A (2002) Catalytic wet air oxidation of phenol and acrylic acid over Ru/C and Ru-CeO2/C catalysts. Appl Catal B Environ 25(4):267–275.

    Article  Google Scholar 

  46. 46.

    Santiago M, Stüber F, Fortuny A, Fabregat A, Font J (2005) Modified activated carbons for catalytic wet air oxidation of phenol. Carbon 43(10):2134–2145.

    Article  Google Scholar 

  47. 47.

    Smith M, Scudiero L, Espinal J, McEwen JS, Garcia-Perez M (2016) Improving the deconvolution and interpretation of XPS spectra from chars by ab initio calculations. Carbon 110:155–171.

    Article  Google Scholar 

  48. 48.

    Soares OSGP, Rocha RP, Gonçalves AG, Figueiredo JL, Órfão JJM, Pereira MFR (2016) Highly active N-doped carbon nanotubes prepared by an easy ball milling method for advanced oxidation processes. Appl Catal B Environ 192:296–303.

    Article  Google Scholar 

  49. 49.

    Stüber F, Font J, Fortuny A, Bengoa C, Eftaxias A, Fabregat A (2005) Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater. Top Catal 33(1–4):3–50.

    Article  Google Scholar 

  50. 50.

    Sun F, Gao J, Yang Y, Zhu Y, Wang L, Pi X, Liu X, Qu Z, Wu S, Qin Y (2016) One-step ammonia activation of Zhundong coal generating nitrogen-doped microporous carbon for gas adsorption and energy storage. Carbon 109:747–754.

    Article  Google Scholar 

  51. 51.

    Sun Z, Zhao L, Liu C, Zhen Y, Ma J (2019) Catalytic Ozonation of Ketoprofen with in Situ N-Doped Carbon: A Novel Synergetic Mechanism of Hydroxyl Radical Oxidation and an Intra-Electron-Transfer Nonradical Reaction. Environ Sci Technol 53(17):10342–10351.

    Article  Google Scholar 

  52. 52.

    Tanksale A, Beltramini JN, Lu GQM (2010, January) A review of catalytic hydrogen production processes from biomass. Renew Sust Energ Rev.

  53. 53.

    Villegas LGC, Mashhadi N, Chen M, Mukherjee D, Taylor KE, Biswas N (2016) A short review of techniques for phenol removal from wastewater. Curr Pollut Rep 2(3):157–167.

    Article  Google Scholar 

  54. 54.

    Wilson AN, Dutta A, Black BA, Mukarakate C, Magrini K, Schaidle JA, Michener W, Beckham G, Nimlos MR (2019) Valorization of aqueous waste streams from thermochemical biorefineries. Green Chem 21(15):4217–4230.

    Article  Google Scholar 

  55. 55.

    Wan Z, Sun Y, Tsang DCW, Khan E, Yip ACK, Ng YH et al (2020) Customised fabrication of nitrogen-doped biochar for environmental and energy applications. Chem Eng J. Elsevier B.V.

  56. 56.

    Yang Y, Tan M, Garcia A, Zhang Z, Lin J, Wan S et al (2020) Controlling the Oxidation State of Fe-Based Catalysts through Nitrogen Doping toward the Hydrodeoxygenation of m-Cresol. ACS Catal 10(14):7884–7893.

    Article  Google Scholar 

  57. 57.

    Zhang M, Gao B, Varnoosfaderani S, Hebard A, Yao Y, Inyang M (2013) Preparation and characterization of a novel magnetic biochar for arsenic removal. Bioresour Technol 130:457–462.

    Article  Google Scholar 

Download references


Special thanks to Jonathan Lomber of WSU Analytical Chemistry Service Center for his assistance in support of this work, Yaime Jefferson for her analytical support, Katie Johnson of the NARA Summer Intern in the Garcia-Perez Laboratory, and Roberto Esquivel for the graphic support. This research used resources from the Center for Institutional Research Computing at Washington State University. PNNL is a multiprogram national laboratory operated for the US DOE by Battelle.


The study was supported by the Sun Grant subproject, Grant No. 128467-G004003. J.-S.M and A.G. were supported by the National Science Foundation under Contract No. CBET-1703052. This work was partially funded by the Joint Center for Deployment and Research in Earth Abundant Materials (JCDREAM) in Washington State.

Author information



Corresponding author

Correspondence to Manuel Garcia-Perez.

Additional information

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


• Available treatment of phenol-contaminated water is reviewed, and active carbons are proposed as an inexpensive and robust solution to the shortcomings of existing catalysts.

• Nitrogen-doped char, produced from cellulose, is a sustainable and affordable catalyst for adsorption and removal of phenol from water.

• Pyridinic groups comprise the highest percentage of functional groups in N-doped char.

• Density functional theory analysis confirms that in the presence of oxygen, pyridinic groups favorably produce activated oxygen species which are key to catalytic oxidation of phenol in water.

Supplementary Information


(DOCX 560 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Tews, I., Garcia, A., Ayiania, M. et al. Nitrogen-doped char as a catalyst for wet oxidation of phenol-contaminated water. Biomass Conv. Bioref. (2021).

Download citation


  • Nitrogen-doped chars
  • Phenol oxidation
  • Oxidation kinetics