XPS and two-dimensional FTIR correlation analysis on the binding characteristics of humic acid onto kaolinite surface

Hongfeng Chen; Qi Li; Mingxia Wang; Daobin Ji; Wenfeng Tan

doi:10.1016/j.scitotenv.2020.138154

XPS and two-dimensional FTIR correlation analysis on the binding characteristics of humic acid onto kaolinite surface

Sci Total Environ. 2020 Jul 1:724:138154. doi: 10.1016/j.scitotenv.2020.138154. Epub 2020 Mar 23.

Authors

Hongfeng Chen¹, Qi Li², Mingxia Wang², Daobin Ji³, Wenfeng Tan⁴

Affiliations

¹ College of Hydraulic & Environmental Engineering, China Three Gorges University, Yichang 443002, PR China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.
² Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China.
³ College of Hydraulic & Environmental Engineering, China Three Gorges University, Yichang 443002, PR China.
⁴ Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, PR China. Electronic address: tanwf@mail.hzau.edu.cn.

PMID: 32272401
DOI: 10.1016/j.scitotenv.2020.138154

Abstract

The stabilization and preservation of soil organic matter have been attributed to the strong reactive sites of mineral surfaces that cause physical isolation and chemical stabilization due to the organic-mineral interface. However, much of the micro-scale knowledge about interactions between organic ligands and minerals largely remains at the qualitative level, and neglects the heterogeneity of functional groups of organic matter. Here, we report the use of molecular-scale technologies of two-dimensional FTIR Correlation Spectroscopy (2D-FTIR-CoS) and X-ray Photoelectron Spectroscopy (XPS) to directly measure the binding processes of humic acid (JGHA) groups onto kaolinite surface. The spectroscopy results showed that the carboxylate groups, aliphatic OH and aromatic structure participate in the binding of JGHA on kaolinite surface. The carboxylic and phenolic hydroxyl interact with kaolinite surface through the interfacial COAl/Si bonds. Kaolinite prefers to adsorb C-groups at pH 4.0 and O-groups at pH 8.0. The interaction of COO^- group at 1566 cm^-1 of JGHA leads to the formation of inner-sphere complex first and then outer-sphere complex with increasing contact time. The interaction of COOH group at 1261 cm^-1 with the AlOH²⁺ of kaolinite was could be ascribed to ligand exchange and/or electrostatic attraction, whose contribution was evaluated to be 13.90%, 7.65% and 0% at pH 4.0, 6.0 and 8.0, respectively. These results of molecular binding provide quantitative mechanistic insights into organic-mineral interactions and expound the effect of functional groups of HA on binding mechanisms, and thus bring important clues for better understanding the mobility and transformation of land‑carbon including mineral-bound carbon.

Keywords: 2D-FTIR-CoS; Binding mechanism; Humic acid; Kaolinite; XPS.