Spectroscopic investigations and density functional theory calculations reveal differences in retention mechanisms of lead and copper on chemically-modified phytolith-rich biochars

Jianhong Li; Shan-Li Wang; Lirong Zheng; Dongliang Chen; Zhipeng Wu; Chenghua Sun; Nanthi Bolan; Hongting Zhao; An-An Peng; Zheng Fang; Rongfu Zhou; Guobin Liu; Amit Bhatnagar; Yong Qiu; Hailong Wang

doi:10.1016/j.chemosphere.2022.134590

Spectroscopic investigations and density functional theory calculations reveal differences in retention mechanisms of lead and copper on chemically-modified phytolith-rich biochars

Chemosphere. 2022 Aug:301:134590. doi: 10.1016/j.chemosphere.2022.134590. Epub 2022 Apr 12.

Authors

Jianhong Li¹, Shan-Li Wang², Lirong Zheng³, Dongliang Chen³, Zhipeng Wu⁴, Chenghua Sun⁵, Nanthi Bolan⁶, Hongting Zhao⁷, An-An Peng⁷, Zheng Fang⁷, Rongfu Zhou⁷, Guobin Liu⁸, Amit Bhatnagar⁹, Yong Qiu¹⁰, Hailong Wang¹¹

Affiliations

¹ College of Oceanology and Food Science, Quanzhou Normal University, Quanzhou, Fujian, 362000, China; Biochar Engineering Technology Research Center of Guangdong Province, School of Environmental and Chemical Engineering, Foshan University, Foshan, Guangdong, 528000, China.
² Department of Agricultural Chemistry, National Taiwan University, Taipei, 10617, Taiwan, ROC.
³ Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China.
⁴ College of Tropical Crops, Hainan University, Haikou, Hainan, 570228, China.
⁵ Department of Chemistry and Biotechnology, Center for Translational Atomaterials, Swinburne University of Technology, Hawthorn, VIC, 3122, Australia.
⁶ School of Agriculture and Environment, The University of Western Australia, Perth, WA, 6001, Australia; The UWA Institute of Agriculture, The University of Western Australia, Perth, WA, 6001, Australia.
⁷ Biochar Engineering Technology Research Center of Guangdong Province, School of Environmental and Chemical Engineering, Foshan University, Foshan, Guangdong, 528000, China.
⁸ The 41st Institute of Sixth Academy of China Aerospace Science & Industry Corp, Hohhot, Inner Mongolia, 010010, China.
⁹ Department of Separation Science, LUT School of Engineering Science, LUT University, Sammonkatu 12, FI-50130, Mikkeli, Finland.
¹⁰ College of Oceanology and Food Science, Quanzhou Normal University, Quanzhou, Fujian, 362000, China. Electronic address: qiuyong@qztc.edu.cn.
¹¹ Biochar Engineering Technology Research Center of Guangdong Province, School of Environmental and Chemical Engineering, Foshan University, Foshan, Guangdong, 528000, China; Key Laboratory of Soil Contamination Bioremediation of Zhejiang Province, Zhejiang A&F University, Hangzhou, Zhejiang, 311300, China. Electronic address: hailong.wang@fosu.edu.cn.

PMID: 35427661
DOI: 10.1016/j.chemosphere.2022.134590

Abstract

A better understanding of different retention mechanisms of potentially toxic elements (PTEs) by biochars during the remediation of contaminated sites is critically needed. In this study, different spectroscopic techniques including synchrotron-based micro-X-ray fluorescence (μ-XRF), X-ray absorption fine structure (XAFS), and near-edge XAFS spectroscopy (NEXAFS), were used to investigate the spatial distributions and retention mechanisms of lead (Pb) and copper (Cu) on phytolith-rich coconut-fiber biochar (CFB), and ammonia, nitric acid and hydrogen peroxide modified CFB (MCFB) (i.e., ACFB, NCFB and HCFB). The μ-XRF analyses indicated that sorption sites on ACFB and NCFB were more efficient compared to those on CFB and HCFB to bind Pb/Cu. XAFS analyses revealed that the percentage of Pb species as Pb(C₂H₃O₂)₂ increased from 22.2% (Pb-loaded CFBs) to 47.4% and 41.9% on Pb-loaded NCFBs and HCFBs, while the percentage of Cu(OH)₂ and Cu(C₂H₃O₂)₂ increased from 5.8% to 32.8% (Cu-loaded CFBs) to 41.5% and 43.4% (Cu-loaded NCFBs), and 27.1% and 35.1% (Cu-loaded HCFBs), respectively. Due to their similar atomic structures of Pb/Cu, Pb(C₂H₃O₂)₂/Pb-loaded montmorillonite and Cu(C₂H₃O₂)₂/Cu(OH)₂ were identified as the predominant Pb/Cu species observed in Pb- and Cu-loaded MCFBs. The NEXAFS analyses of carbon confirmed that increasing amounts of carboxylic groups were formed on HCFB and NCFB by oxidizing carbon-containing functional groups, which could provide additional active binding sites for Pb/Cu retention. Results from the X-ray photoelectron spectroscopy analyses of nitrogen showed that azido-groups of ACFB played major roles in Pb/Cu retention, while amide-groups and pyridine-groups of NCFB primarily participated in Pb/Cu retention. Overall, density functional theory calculations suggested that silicate and the synergistic effect of hydroxyl and carboxylic-groups on MCFBs were highly efficient in Pb retention, while azido-groups and/or carboxylic-groups played major roles in Cu retention. These results provide novel insights into the PTE retention mechanisms of MCFBs.

Keywords: Binding sites; Modification; Potentially toxic elements; Silicon-rich biochar; Synchrotron radiation.

MeSH terms

Carbon
Charcoal / chemistry
Cocos / chemistry
Copper* / chemistry
Density Functional Theory
Lead
Photoelectron Spectroscopy
Soil Pollutants* / analysis

Substances

Soil Pollutants
biochar
Charcoal
Lead
Carbon
Copper