4.7 Article

O, N-doped porous biochar by air oxidation for enhancing heavy metal removal: The role of O, N functional groups

Journal

CHEMOSPHERE
Volume 293, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.chemosphere.2022.133622

Keywords

Porous biochar; Air oxidation; Oxygen and nitrogen doping; Heavy metal removal; Green method; Adsorption mechanism

Funding

  1. Hanoi University of Civil Engineering, Vietnam [10-2021/KHXD-TD]
  2. Ministry of Science and Technology, Taiwan [109-2223-E-002-002-MY3]
  3. National Taiwan University (NTU) Research Center for Future Earth from the Featured Areas Research Center Program by the Ministry of Education (MOE) in Taiwan

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In this study, oxygen- and nitrogen-doped porous oxidized biochar was fabricated through a simple and green oxidation method. The improved surface functionality and porosity resulted in increased heavy metal removal efficiency. The chemical mechanism was mainly governed by monolayer adsorption of Cu(II) onto a homogeneous surface of the doped biochar.
Oxygen-and nitrogen-doped porous oxidized biochar (O,N-doped OBC) was fabricated in this study. Biochar (BC) can be enriched in surface functional groups (O and N) and the porosity can be improved by a simple, convenient and green procedure. BC was oxidized at 200 degrees C in an air atmosphere with quality control via oxidation time changes. As the oxidation time increased, the O and N contents and porosity of the materials improved. After 1.5 h of oxidation, the O and N contents of O,N-doped OBC-1.5 were 54.4% and 3.9%, higher than those of BC, which were 33.4% and 1.8%, respectively. The specific surface area and pore volume of O,N-doped OBC-1.5 were 88.5 m(2) g(-1) and 0.07 cm(3) g(-1), respectively, which were greater than those of BC. The improved surface functionality and porosity resulted in an increased heavy metal removal efficiency. As a result, the maximum adsorption capacity of Cu(II) by O,N-doped OBC was 23.32 mg L-1, which was twofold higher than that of pristine BC. Additionally, for a multiple ion solution, O,N-doped OBC-1.5 showed a greater adsorption behavior toward Cu(II) than Zn(II) and Ni(II). In a batch experiment, the concentration of Cu(II) decreased 92.3% after 90 min. In a filtration experiment, the O,N-doped OBC-based filter achieved a Cu(II) removal capacity of 12.90 mg g(-1) and breakthrough time after 250 min. Importantly, the chemical mechanism was mainly governed by monolayer adsorption of Cu(II) onto a homogeneous surface of O,N-doped OBC-1.5. Surface complexation and electrostatic attraction were considered to be the chemical mechanisms governing the adsorption process.

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