Strong chromate-adsorbent based on pyrrolic nitrogen structure: An experimental and theoretical study on the adsorption mechanism

Young Jin Ko, Keunsu Choi, Soonjae Lee, Kyung Won Jung, Seokwon Hong, Hiroshi Mizuseki, Jae Woo Choi, Wook Seong Lee

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)

Abstract

Chromate is considered a toxic contaminant in various water sources because it poses a risk to animal and human health. To meet the stringent limits for chromium in water and wastewater, pyrrolic nitrogen structure was investigated as a chromate adsorbent for aqueous solutions, employing a polypyrrole coating on carbon black. The characteristics of the adsorbent were analyzed by high-resolution transmission electron microscopy, energy-filtered transmission electron microscopy, and X-ray photoelectron spectroscopy. Chromate was adsorbed as both Cr(III) and Cr(VI). The chromate adsorption capacity increased (from 50.84 to 174.81 mg/g) with increasing amounts of pyrrole monomers (from 50 to 86%) in the adsorbent. The adsorption capacity was well-correlated with the pyrrolic nitrogen content (from 2.06 to 6.57 at%) in the adsorbent, rather than other types of nitrogen. The optimized adsorption capacity (174.81 mg/g in the equilibrium batch experiment and 211.10 mg/g at an initial pH of 3) was far superior to those of conventional adsorbents. We investigated the mechanism behind this powerful chromate adsorption on pyrrolic nitrogen via physical/chemical analyses of the pH-dependent adsorption behavior, supported by first-principles calculation based on density functional theory. We found that Cr(III) and Cr(VI) adsorption followed different reaction paths. Cr(III) adsorption occurred in two sequential steps: 1) A Jones oxidation reaction (JOR)-like reaction of Cr(VI) with pyrrolic N that generates Cr(III), and 2) Cr(III) adsorption on the deprotonated pyrrolic N through Cr(III)–N covalent bonding. Cr(VI) adsorption followed an alternative path: hydrogen-bonding to the deprotonation-free pyrrolic N sites. The pH-dependent fractional deprotonation of the pyrrolic N sites by the JOR-like reaction in the presence of chromate played an important role in the adsorption.

Original languageEnglish
Pages (from-to)287-296
Number of pages10
JournalWater Research
Volume145
DOIs
Publication statusPublished - 2018 Nov 15

Bibliographical note

Funding Information:
This work was supported by the institutional program grant (2E28210) from the Korea Institute of Science and Technology. This work was supported by the institutional program grant (2E28120) from the Korea Institute of Science and Technology and the Korea Ministry of Environment as a “Global Top Project” (Project No.: 2016002190003). This study was also partly supported by the computational resources of the inter-university cooperative research program of Institute for Materials Research, Tohoku University (Proposal No. 17S0007), Japan. The authors are grateful to M. K. Cho (at the Advanced Analysis Center, KIST) for comments regarding the TEM characterization.

Funding Information:
This work was supported by the institutional program grant ( 2E28210 ) from the Korea Institute of Science and Technology . This work was supported by the institutional program grant ( 2E28120 ) from the Korea Institute of Science and Technology and the Korea Ministry of Environment as a “ Global Top Project ” (Project No.: 2016002190003 ). This study was also partly supported by the computational resources of the inter-university cooperative research program of Institute for Materials Research, Tohoku University (Proposal No. 17S0007 ), Japan. The authors are grateful to M. K. Cho (at the Advanced Analysis Center, KIST) for comments regarding the TEM characterization.

Publisher Copyright:
© 2018 Elsevier Ltd

Keywords

  • Chromate adsorption
  • First-principles calculation
  • Jones oxidation
  • Polarization screening
  • Pyrrolic nitrogen

ASJC Scopus subject areas

  • Water Science and Technology
  • Ecological Modelling
  • Pollution
  • Waste Management and Disposal
  • Environmental Engineering
  • Civil and Structural Engineering

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