Gao Zhengyang, Ding Yi, Yang Weijie, Han Wentao
The Department of Power Engineering, North China Electric Power University, Baoding, 071003, China.
J Mol Model. 2017 Jan;23(1):27. doi: 10.1007/s00894-016-3194-7. Epub 2017 Jan 7.
High moisture content is a main characteristic of low-rank coal, such as lignite. Numerous oxygen containing functional groups in lignite make it represent some special properties, and these functional groups affect the adsorption mechanisms of water molecules on lignite surface. This study reports some typical water · · · lignite conformations, along with a detailed analysis of the geometry, electrostatic potential distribution, reduced density gradient of interaction, and interaction energy decomposition. The results show that water molecules tend to aggregate around functional groups, and hydrogen bonds play a dominant role in the interaction. The adsorption energy of water cluster on lignite surface is larger than that of isolated water molecule, a good linear relationship between the interaction distance and adsorption energy of layers has been found. Since water is a polar molecule, the local minima and maxima of electrostatic potential in conformations increase along with more water adsorbing on lignite surface. Reduced density gradient analysis shows that H-bonds, van der Waals interaction, and a little steric make up the interaction between water cluster and lignite molecule. In these studied conformations which mainly are H-bond complexes, electrostatic and exchange repulsion play a dominant role, whereas polarization and dispersion make relatively small contribution to the interaction. Attractive and repulsive interaction both affect the stability of water · · · lignite conformations.
高含水量是低阶煤（如褐煤）的一个主要特征。褐煤中大量的含氧官能团使其具有一些特殊性质，并且这些官能团影响水分子在褐煤表面的吸附机制。本研究报道了一些典型的水···褐煤构象，并对其几何结构、静电势分布、相互作用的约化密度梯度以及相互作用能分解进行了详细分析。结果表明，水分子倾向于在官能团周围聚集，并且氢键在相互作用中起主导作用。水簇在褐煤表面的吸附能大于孤立水分子的吸附能，已发现层间相互作用距离与吸附能之间存在良好的线性关系。由于水是极性分子，随着更多的水吸附在褐煤表面，构象中静电势的局部最小值和最大值会增加。约化密度梯度分析表明，氢键、范德华相互作用以及少量的空间位阻构成了水簇与褐煤分子之间的相互作用。在这些主要为氢键复合物的研究构象中，静电和交换排斥起主导作用，而极化和色散对相互作用的贡献相对较小。吸引和排斥相互作用都影响水···褐煤构象的稳定性。
