Preferential Sorption of Tannins at Aluminum Oxide Affects the Electron Exchange Capacities of Dissolved and Sorbed Humic Acid Fractions

Abstract

Natural organic matter and humic substances (HS) in soils and sediments participate in numerous biogeochemical processes. Sorption to redoxinert aluminum oxide (Al 2 O 3 ) was recently found to affect the redox properties of HS both in sorbed and dissolved state. With this study, we aim to decipher the molecular basis for these observations by applying Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS) and mediated electrochemical analysis to Elliott soil, Pahokee peat, and Suwannee river humic acid (HA) samples before and after sorption to polar Al 2 O 3 and a nonpolar sorbent (DAX-8 resin). The FT-ICRMS data provided evidence of preferential sorption of specific HA fractions, primarily tannin-like compounds, to Al 2 O 3 . These oxygen-rich compounds bear a high density of redox-active functional groups, and their adsorption leads to a depletion of electron exchange capacity in dissolved HAs and enrichment of HAs adsorbed at Al 2 O 3 . Sorption of HAs to DAX-8 was less selective and caused only slight changes in electron exchange capacities of dissolved and sorbed HA fractions. By combining FT-ICRMS and electrochemical approaches, our findings suggest that a selective sorption of oxygen-rich compounds in HA fractions to mineral oxides is a decisive factor for the different redox properties of dissolved and sorbed HA fractions.

Photochemical Behavior of Microbial Extracellular Polymeric Substances in the Aquatic Environment

“…As salts were excluded in the pretreatments, the formulas that contained carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) were interpreted in this work. Data calculations are described in the Supporting Information, S5, and the chemical rules for the formula generations followed the previously provided instructions …”

“…Data calculations are described in the Supporting Information, S5, and the chemical rules for the formula generations followed the previously provided instructions. 27 Tetracycline Degradation and Transformation Products. A total of 40 mg/L of tetracycline (TC) was prepared along with the M-EPS solution mentioned above.…”

Linkage Between Dissolved Organic Matter Transformation, Bacterial Carbon Production, and Diversity in a Shallow Oligotrophic Aquifer: Results From Flow-Through Sediment Microcosm Experiments

“…The group of oxygenated aliphatics included a large complement of carbohydrates, aromatic and aliphatic methyl esters and methyl ethers, peptides, and carboxyl-rich alicyclic matter (Supplementary Figure S3). After 1 week of operation of the microcosms, DOM-5x that has passed the active sediments showed a selective depletion in aromatic methyl esters and -ethers by ~35% ( Supplementary Figure S1C), in line with a known preferential sorption of aromatic compounds (Chefetz and Xing, 2009;Young et al, 2018;Subdiaga et al, 2020). After 171 days of experiment, the long-term supply of DOM-5x has led to an altered dynamic equilibrium, with increased proportions of aromatic and olefinic molecules as well as aliphatic methyl esters, compared with the DOM from t0 ( Supplementary Figures S1A,B).…”

Interfacial Molecular Fractionation on Ferrihydrite Reduces the Photochemical Reactivity of Dissolved Organic Matter

“…As expected, the EDC of DOM decreased after adsorption, and the reduction percentage was higher at the higher Fe/C ratio (Figure c), suggesting that DOM fractions with high EDC were preferentially sequestered by ferrihydrite. A reduction in the EDC of DOM induced by adsorption on aluminum oxide was also observed in a recent study . Both light absorption properties and electron transfer characteristics have been considered to affect the photochemical behavior of DOM directly or indirectly; , we therefore speculate that the adsorption of DOM on ferrihydrite might regulate the photochemical behavior of DOM.…”

“…A reduction in the EDC of DOM induced by adsorption on aluminum oxide was also observed in a recent study. 57 Both light absorption properties and electron transfer characteristics have been considered to affect the photochemical behavior of DOM directly or indirectly; 58,59 we therefore speculate that the adsorption of DOM on ferrihydrite might regulate the photochemical behavior of DOM.…”