Spectroscopic Characteristics and Speciation Distribution of Fe(III) Binding to Molecular Weight-Dependent Standard Pahokee Peat Fulvic Acid

Yaqin Zhang, Chang Liu, Yuxia Li, Liuting Song, Jie Yang, Rui Zuo, Jian Li, Yanguo Teng and Jinsheng Wang
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Yaqin Zhang: College of Water Sciences, Beijing Normal University, Beijing 100875, China
Chang Liu: College of Water Sciences, Beijing Normal University, Beijing 100875, China
Yuxia Li: College of Water Sciences, Beijing Normal University, Beijing 100875, China
Liuting Song: College of Water Sciences, Beijing Normal University, Beijing 100875, China
Jie Yang: College of Water Sciences, Beijing Normal University, Beijing 100875, China
Rui Zuo: College of Water Sciences, Beijing Normal University, Beijing 100875, China
Jian Li: College of Water Sciences, Beijing Normal University, Beijing 100875, China
Yanguo Teng: College of Water Sciences, Beijing Normal University, Beijing 100875, China
Jinsheng Wang: College of Water Sciences, Beijing Normal University, Beijing 100875, China

IJERPH, 2022, vol. 19, issue 13, 1-18

Abstract: Peat-derived organic matter, as powerful chelators, is of great significance for the transport of Fe to the ocean and the enhancement of dissolved Fe. However, the iron binding capacity of molecular weight (MW)-fractionated dissolved organic matter is variable, due to its structure and composition heterogeneity. In this work, we used the standard Pahokee Peat fulvic acid (PPFA) as an example, and investigated the spectroscopy properties and Fe(III) binding ability of PPFA and different molecular weight fractions by UV–Vis absorbance and fluorescence spectroscopy and the Donnan Membrane Technique (DMT). The results showed binding sites for Fe(III) at the 263 nm and >320 nm regions in differential absorbance spectra. Upon increasing the iron concentration to 18.00 μmol·L −1 , the critical binding capacity was exceeded, which resulted in a decrease in absorbance. Fe(III) was found to prefer to bind to humic-like components, and ultraviolet humic-like fluorophores displayed stronger binding strength. High molecular weight PPFA fractions (>10 kDa) possessed more aromatic and hydrophobic components, displayed a higher degree of humification, and exhibited higher metal binding potential. Furthermore, the speciation analysis and stability constant ( c K) were calculated using Donnan membrane equilibrium. The correlation between c K values and PPFA spectral properties demonstrated that aromaticity, hydrophobicity, molecular weight and humification degree were crucial indices of PPFA–Fe(III) affinity. Significantly, the humification degree, represented by HIX, showed the strongest correlation (r = 0.929, p = 0.003), which could be used to estimate the binding strength. This study provides further understanding of the complexation mechanism of iron and DOM in the peat environment and identifies the considerable effect of molecular weight.

Keywords: Pahokee Peat fulvic acid; dissolved organic matter; iron; complexation; ultraviolet–visible; fluorescence; Donnan Membrane Technique (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2022
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