Acta Chim. Sinica ›› 2017, Vol. 75 ›› Issue (6): 617-620.DOI: 10.6023/A17030082 Previous Articles     Next Articles

Special Issue: 铁环境化学



刘瑾a, 杨建军b,d, 曾希柏b, Wang Jianc, Donald Sparksd   

  1. a 中国农业科学院农业资源与农业区划研究所 北京 100081;
    b 中国农业科学院农业环境与可持续发展研究所 北京 100081;
    c 萨斯卡切温大学加拿大光源 加拿大萨斯卡切温省萨斯卡通市创新大道44号 S7N 2V3;
    d 特拉华大学 特拉华环境研究所 美国特拉华州纽瓦克市科学街221号 19711
  • 投稿日期:2017-03-01 发布日期:2017-04-12
  • 通讯作者: 杨建军, Wang Jian;
  • 基金资助:


Fe(III)-induced Sequestration of Citric Acid on Kaolinite Surface Probed by STXM-NEXAFS Spectroscopy

Liu Jinaa, Yang Jianjunb,d, Zeng Xibaib, Wang Jianc, Donald Sparksd   

  1. a Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081;
    b Institute of Environmental and Sustainable Development in Agriculture, Chinese Academy of Agricultural Science, Beijing 100081;
    c Canadian Light Source Inc., University of Saskatchewan, Saskatoon, Canada, S7N 2V3;
    d Delaware Environmental Institute, University of Delaware, Newark 19711, USA
  • Received:2017-03-01 Published:2017-04-12
  • Contact: 10.6023/A17030082;
  • Supported by:

    Project supported by the Innovation Funds of the Chinese Academy of Agricultural Science for Overseas Elite Youth Program, and National Natural Science Foundation of China (Nos. 41601313, U1632134).

Organic carbon (OC) stability in tropical soils is strongly affected by the mutual interactions of OC, kaolinite and the Fe(Ⅲ) cation. Low molecular weight organic acids (LMWOAs) represent the most biodegradable constituent of OC in soils. Therefore, investigating retention mechanisms of LMWOAs in kaolinite-Fe(Ⅲ)-LMWOAs systems are of significant importance in understanding the sequestration and cycling of OC in tropical soils. However, retention mechanisms of LMWOAs in the kaolinite-Fe(Ⅲ)-LMWOAs system remains unclear, and there is a lack of direct evidence at the molecular level. In this study, citric acid (CA) was chosen as a model compound for LMWOAs and a sorption sample was collected after batch experiment using kaolinite, Fe(Ⅲ), and CA as reagents at pH 3.5 and at an initial Fe/CA molar ratio of 2.0. Synchrotron-based scanning transmission X-ray microspectroscopy (STXM) was applied to characterize the distribution of carbon (C), iron (Fe) and silicon (Si), representing CA, Fe(Ⅲ) cation/Fe hydroxides and kaolinite respectively, at the submicron scale in the sorption sample. After that, the hot spots of C and Fe were selected and further probed by STXM coupled with Near-edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy at the C and Si K-edge and the Fe L3-edge, respectively, to reveal the molecular structures of C, Si and Fe. Our results indicated the similar correlation of C-Fe (R2=0.965) to C-Si (R2=0.960) in the sorption sample, which implied a close relationship between CA and Fe hydroxides as well as kaolinite. We also found two Fe species as ferrihydrite and kaolinite-Fe(Ⅲ)-citrate complex coexisted in the Fe-enriched hot spots probed by STXM coupled with Fe L3-edge NEXAFS spectroscopy. These results provide direct evidence of the contribution of CA retention through ferrihydrite-induced adsorption/coprecipitation and ternary complexation of CA and kaolinite via an Fe bridge in the investigated ternary system. This study will enhance our understanding of the stability of CA and the sequestration and cycling of LMWOAs in tropical soils.

Key words: soil carbon sequestration, multivalent cation, STXM, NEXAFS, ferrihydrite