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1

Structure and dynamics of water adsorbed on the lignite surface: Molecular dynamics simulation

You Xiaofang, He Meng, Cao Xiaoqiang, Lyu Xianjun, Li Lin

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 1

10--20

EN

The effects of oxygen-containing functional groups on the structure and dynamic properties of water molecules near a lignite surface were investigated through molecular dynamics (MD) simulations. Because of its complex composition and structure, a graphite surface containing hydroxyl, carboxyl, and carbonyl groups was used to represent the lignite surface model. According to X-ray photoelectron spectroscopic (XPS) results, the composing proportion of hydroxyl, carbonyl and carboxyl is 21:13:6. The density profiles of oxygen and hydrogen atoms indicate that the brown coal surface characteristics influence the structural and dynamic properties of water molecules. The interfacial water is much more ordered than bulk water. The results of the radial distribution functions, mean square displacements, and local self-diffusion coefficients for the water molecules in the vicinity of three oxygen-containing functional groups confirmed that carboxyl groups are the preferential adsorption sites.

2

Molecular simulation study on hydration of low-rank coal particles and formation of hydration film

Xia Yangchao, Yang Zili, Xing Yaowen, Gui Xiahui

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 2

586--596

EN

Water molecules in low-rank coal (LRC) significantly influence its upgrading and utilization. To investigate the hydration of LRC particles and the formation of a hydration film, molecular simulation techniques were innovatively used, including molecular dynamics (MD) simulations and density functional theory (DFT) calculations. The adsorption of water molecules on LRC and various oxygen-containing groups was analyzed. The results show that water molecules adsorb close to the LRC surface and form a large overlapping layer at the LRC/water interface. The radial distribution functions (RDFs) show that the adsorption affinity of water molecules on oxygen-containing sites is stronger than that on carbon-containing sites, and the RDF peaks indicate the existence of a hydration film. Moreover, the differences in adsorption between various oxygen-containing groups depend on both the number of hydrogen bonds and the adsorption distances. The calculated binding energies indicate that the adsorption capacity follows the order carboxyl > phenolic hydroxyl > alcoholic hydroxyl > ether linkage > carbonyl. Experimental results show that a high sorption rate exists between water vapor and LRC samples at the beginning of sorption, which verified the simulation results.

3

Kropla wody. Esej

Wrembel H.

Ekologia i Technika

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2007

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R. 15, nr 5

179-190

PL

W pracy przedstawiono właściwości fizyczne wody, rozważono możliwość powstania jej na Ziemi, pokazano właściwości różnych odmian izotopowych wody, omówiono znaczenie jakości wody pitnej dla zdrowia ludzkiego.

EN

The aim of this work is to show some physical properties of water, Its occurrence on the Earth and diferennces in the behaviour of different isotopic water molecules. The irnportance on the health problerns of the quality of drinking water, is shown.

4

LOcal Rovibrational Instability in a water Molecule

Konarski J., Mańkowski M.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 11

1615-1623

EN

Using the stability matrix method, the occurrence of locally unstable states in the water molecule has been shown. Detailed analysis of this problem reveals a dependence of the state stability on the rotational quantum numbers Jand k, as well as on the rotation about the z axis perpendicular to the molecular plane, i.e. on the rotation at which the Coriolis coupling reaches a maximum.

5

Struktura ciekłej wody. Cz.1. Modele struktury wody

Dutkiewicz E., Jakubowska A.

Wiadomości Chemiczne

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1998

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[Z] 52, 11-12

773--786

EN

Without doubt, water is the most studied system in chemistry. Despite this fact, water is still far from being satisfactorily described on the molecular level and continues to fascinate new generations of chemists. This situation reflects the difficulty of providing a structural description that accounts for the dynamic behaviour of the H-bonding ability of water, i.e., the ability of water molecules to from different structures. The aim of this work was to present different models describing: 1) a water molecule; 2) hydrogen-bond networks; 3) the water structure. The first model of a water molecule was created by Bjerrum. Various modifications of this model were proposed later. Water models proposed by Ben-Naim and Stillinger (BNS model) and Stillinger-Rahman (ST2 model)are typical ones among the four-point charge models. The model proposed by Rowlinson is a modified four-point charge model. Matsuoka-Clementi-Yoshimine's model is a three-point charge model of the water molecule. Jorgensen's model is also described in this work. Besides these rigid models of a water molecule, flexible models have also been introduced. Typical ones are the central force (CF) model and its modifications proposed by Bopp-Jancsó-Heinzinger (BJH). We present also different models describing hydrogen-bond networks: model based on polygons, bond percolation models and lattice models (square water, simplified square water, brick water). Models describing the water structure may be divided into two main classes: mixture models (a fluid composed of molecular clusters of various sizes) and continuum models. Continuum models are not sufficient to explain the unusual behaviour of H2O and D2O. Water can also appear to be a macroscopic, space-filling gel-like network. This structural picture of water combines ideas of continuum models with ideas of mixture models.