Microscopic mechanism about the selective adsorption of Cr(VI) from salt solution on O-rich and N-rich biochars

Nan Zhao, Chuanfang Zhao, Daniel C.W. Tsang, Kunyuan Liu, Ling Zhu, Weihua Zhang, Jing Zhang, Yetao Tang, Rongliang Qiu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

18 Citations (Scopus)


The adsorption of Cr(VI) on biochars can be suppressed by coexisting anions, but the roles of O-containing functional groups and in particular N-containing functional groups are unclear. In this study, we combined spectroscopic and molecular simulation approaches to investigate the selective adsorption of Cr(VI) on the O-rich (PB, UB1) and N-rich (UB3, UB5) biochars under strong competition of anions. The elemental analysis and pyrolysis-gas chromatography/mass spectrometry indicated that the structures of PB and UB1 were similar, and so were the UB3 and UB5. Quantification of functional groups showed that for UB1, 75.3% of Cr(VI) removal was attributed to O-containing groups, while 53.3–72.7% of that was mediated by N-containing groups in UB3 and UB5. X-ray photoelectron spectra and density functional theory calculations confirmed that for O-rich biochars, surface complexation and strong H-bonds between carboxyl/hydroxyl and HCrO4 improved Cr(VI) removal in the presence of anions, while for N-rich biochars, Cr(VI) adsorption was depressed by coexisting anions in the order of Cl>NO3 >SO42– because of the weaker H-bond between protonated amino groups and HCrO4. This study presents a novel approach for quantitative, molecular-level evaluation of the roles of biochar functional groups in the Cr(VI) removal from complex environmental systems.

Original languageEnglish
Article number124162
JournalJournal of Hazardous Materials
Publication statusPublished - 15 Feb 2021


  • Complexation modelling
  • Engineered biochars
  • Hydrogen bond
  • Nitrogen/oxygen functionality
  • Selective removal

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution
  • Health, Toxicology and Mutagenesis

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