物理化学学报 >> 2009, Vol. 25 >> Issue (10): 2034-2038.doi: 10.3866/PKU.WHXB20090911

研究论文 上一篇    下一篇

As(V)在TiO2表面的吸附机理

张美一, 何广智, 丁程程, 陈灏, 潘纲   

  1. 中国科学院生态环境研究中心, 环境水质学国家重点实验室, 北京 100085
  • 收稿日期:2009-04-13 修回日期:2009-06-04 发布日期:2009-09-29
  • 通讯作者: 潘纲 E-mail:gpan@rcees.ac.cn

Mechanism of Arsenate (V) Adsorption on TiO2 Surfaces

ZHANG Mei-Yi, HE Guang-Zhi, DING Cheng-Cheng, CHEN Hao, PAN Gang   

  1. State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China
  • Received:2009-04-13 Revised:2009-06-04 Published:2009-09-29
  • Contact: PAN Gang E-mail:gpan@rcees.ac.cn

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摘要：

用延展X射线吸收精细结构(EXAFS)光谱和密度泛函理论(DFT)研究了As(V)-TiO2体系的吸附机理. 离子强度变化对As(V)-TiO2体系吸附无显著影响, 表明吸附后形成了内层络合物. EXAFS结果表明, As(V)原子主要通过—AsO4上的O原子结合到TiO2表面上, 平均As-O原子间距(R)在吸附前后无明显变化, 保持在(0.169±0.001) nm. As-Ti层的EXAFS分析结果与DFT计算的吸附构型的As-Ti原子间距对照表明, 体系存在两种主要亚稳平衡吸附(MEA)结构, 即对应于R1=(0.321±0.002) nm 的双角(DC)强吸附构型和R2=(0.360±0.002) nm的单角(SC)弱吸附构型. 而且随着吸附量由9.79 mg·g-1增加至28.0 mg·g-1, 吸附样品中双角构型配位数与单角构型配位数的比值(CN1/CN2)从3.3降低到1.6, 说明双角亚稳平衡吸附结构在低覆盖度时占优势, 而在高表面覆盖度时单角亚稳平衡吸附结构占优势, 即在表面覆盖度较大时, As(V)在TiO2表面上倾向于形成单角构型.

关键词: TiO2, As(V), 吸附, 延展X射线吸收精细结构, 密度泛函理论, 微观吸附构型

Abstract:

Adsorption of arsenate on TiO2 surfaces was investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) calculation. The adsorption process was independent of ion strength, indicating the formation of inner-sphere complexes of arsenate on TiO2 surfaces. EXAFS analysis showed that the —AsO4 tetrahedral geometry remained relatively rigid before and after adsorption with an As-O distance (R) of (0.169±0.001) nm. When —AsO4 approached TiO2 surfaces, the As—O—Ti bond formed through the O atoms in —AsO4 clusters. Furthermore, based on the combined results from EXAFS and DFT, As(V) in the “equilibrium”adsorption samples was in at least two metastable equilibrium adsorption (MEA) states: double corner (DC) linkage mode (R1=(0.321±0.002) nm, stronger adsorption) and single corner (SC) linkage mode (R2=(0.360±0.002) nm, weak adsorption). The proportion of coordination number between DC and SC MEA states (CN1/CN2) decreased from 3.3 to 1.6 as the surface coverage increased from 9.79 to 28.0 mg·g-1. This result indicated that at low surface loading arsenate was adsorbed in more stable DC MEA state, but As(V) tended to be adsorbed in SC MEA state as surface coverage increased.

Key words: TiO2, As(V), Adsorption, Extended X-ray absorption fine structure, Density functional theory, Microscopic adsorption mode