Spectroscopic investigations and density functional theory calculations reveal differences in retention mechanisms of lead and copper on chemically-modified phytolith-rich biochars
Journal
Chemosphere
Journal Volume
301
Journal Volume
301
Start Page
134590
ISSN
00456535
Date Issued
2022-08
Author(s)
Li, Jianhong
Zheng, Lirong
Chen, Dongliang
Wu, Zhipeng
Sun, Chenghua
Bolan, Nanthi
Zhao, Hongting
Peng, An-an
Fang, Zheng
Zhou, Rongfu
Liu, Guobin
Bhatnagar, Amit
Qiu, Yong
Wang, Hailong
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.
Subjects
Binding sites
Modification
Potentially toxic elements
Silicon-rich biochar
Synchrotron radiation
Other Subjects
Absorption spectroscopy; Amides; Ammonia; Binding sites; Carbon; Copper; Copper compounds; Density functional theory; Lead compounds; Silicon; Synchrotrons; X ray absorption; X ray absorption near edge structure spectroscopy; X ray photoelectron spectroscopy; Binding-sites; Biochar; Carboxylic group; Coconut coir fibers; Density-functional theory calculations; Modification; Potentially toxic elements; Retention mechanism; Silicon rich; Silicon-rich biochar; Synchrotron radiation; ammonia; charcoal; copper; hydrogen peroxide; lead; carbon; charcoal; lead; biochar; phytolith; retention; spectroscopy; toxic substance; Article; binding site; chemical analysis; chemical modification; coconut; density functional theory; desorption; energy dispersive X ray spectroscopy; fluorescence intensity; immobilization; scanning electron microscopy; spectroscopy; synchrotron radiation; synergistic effect; wavelet transform; X ray fluorescence; X ray photoemission spectroscopy; chemistry; density functional theory; soil pollutant; Carbon; Charcoal; Cocos; Copper; Density Functional Theory; Lead; Photoelectron Spectroscopy; Soil Pollutants
Publisher
Elsevier Ltd
Type
journal article