物理化学学报 >> 2010, Vol. 26 >> Issue (06): 1541-1551.doi: 10.3866/PKU.WHXB20100515

结构化学 上一篇    下一篇

氟置换高岭石层间羟基的能量最小化模拟

牛继南, 强颖怀, 王志辉   

  1. 中国矿业大学材料科学与工程学院, 江苏 徐州 221116
  • 收稿日期:2009-11-23 修回日期:2010-01-13 发布日期:2010-05-28
  • 通讯作者: 强颖怀 E-mail:yhqiang@cumt.edu.cn

Energy Minimization Modeling of Fluorine Substitution for Interlayer Hydroxyl in Kaolinite

NIU Ji-Nan, QIANG Ying-Huai, WANG Zhi-Hui   

  1. School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, Jiangsu Province, P. R. China
  • Received:2009-11-23 Revised:2010-01-13 Published:2010-05-28
  • Contact: QIANG Ying-Huai E-mail:yhqiang@cumt.edu.cn

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摘要：

为了进一步澄清高岭石中结构无序的成因以及氢键对它们的影响程度, 利用补充了氟参数的CLAYFF力场, 对层间羟基不同分数的氟置换进行了能量最小化模拟. 结果发现: 四面体底氧起皱的原因是四、八片层不匹配引起的Al—O(连接氧)键拉伸以及维持四面体自身外形的需要; 四面体旋转的原因与Newnham的解释类似. 八面体上下三原子对旋转是由于: (1) 四、八面体层的不匹配, 具体地说是连接氧/内部羟基氧与八面体铝之间的O—Al—O键角(θ1)和Al—O—Al键角(θ2), 层间羟基氧与八面体铝之间的O—Al—O键角(θ4)和Al—O—Al键角(θ5)的增大, 以及八面体共棱O—Al—O键角(θ3)的减小; (2) 铝硅斥力引起的θ1、θ2变小和θ3变大; (3) (1)和(2)中所有键角变化引起的结构调整; (4) 高岭石特殊的网状结构共同引起的. 八面体O-O共享棱的缩短和铝更靠近层间羟基氧同样也是(1)-(4)作用的结果; θ1、θ2、θ4和θ5增大和θ3减小还引起了八面体展平. 层间氢键对四面体底氧起皱、八面体展平和八面体上下三原子对旋转起阻碍作用, 而对四面体旋转起促进作用. 此外, 当氟对层间羟基的置换摩尔分数较低时(xF=0-0.7), 高岭石层间距并不明显随氟的增加而增加, 这说明了高岭石的水合过程可能并不需要氟化铵的加入.

关键词: 高岭石, 氟置换, 结构无序, 水合

Abstract:

We investigated the causes of distortions and the influence of hydrogen bonding on these distortions in kaolinite. We used CLAYFF supplemented with fluorine potential parameters for the energy minimization modeling of different molar fractions of fluorine substitution for interlayer hydroxyls. Results show that the reasons for tetrahedral basal oxygen corrugation are Al—O (connected oxygen) bond stretching because of the misfit between tetrahedral and octahedral sheets and the requirement of the tetrahedron to maintain its shape. The reason for tetrahedral rotation is similar to Newnham's explanation. The counter-rotation of the upper and lower triads in the octahedron results from: (1) the misfit between tetrahedral and octahedral sheets, specifically the increase in the O—Al—O angle (θ1) and the Al—O—Al angle (θ2) between connected oxygens/inner hydroxyl oxygens and Al, the O—Al—O angle (θ4) and the Al—O—Al angle (θ5) between the interlayer hydroxyl oxygens and Al, and a decrease in the octahedral co-edge O—Al—Oangle(θ3); (2) the decrease in θ1, θ2 and the increase in θ3 because of the repulsion between Al and Si; (3) restructuring caused by the bond angles in (1) and (2); (4) the special network structure of kaolinite. In addition, the shortening of the octahedral O-O co-edge and the approach of Al to the interlayer hydroxyl oxygen also result from effects (1)-(4). Octahedral flattening results from an increase in θ1, θ2, θ4 and θ5 and from a decrease in θ3. The interlayer hydrogen bonds inhibit tetrahedral basal oxygen corrugation, octahedral flattening and the counter-rotation of the upper and lower triads in the octahedron, but it has an opposite role during tetrahedral rotation. Furthermore, when the fluorine content is low (xF=0-0.7), an increase in the interlayer distance is not obvious with an increase in fluorine content and this confirms that ammoniumfluoride may not be necessarily involved in the hydration of kaolinite.

Key words: Kaolinite, Fluorine substitution, Structure distortion, Hydration