水溶液中NaF缔合行为的分子动力学研究
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摘要
氟是自然界中广泛存在、与人体健康密切相关的元素,其在溶液中物种类型对评价地下水中氟的迁移转化和处理含氟废水具有重要的作用.该文运用经典分子动力学,采用伞形采样方法计算了25℃NaF水溶液中Na~+-F~-离子对的平均力势,以此判断NaF的缔合类型和计算其缔合常数.结果显示NaF溶液中同时存在直接接触型离子对(CIP)、溶剂共享型离子对(SSHIP)和溶剂分隔型离子对(SSIP)3种缔合类型,其中CIP和SSHIP是溶液中最稳定存在的2种类型.但是就相对含量而言,NaF溶液的缔合类型以SSHIP和SSIP为主,CIP只占4.2%.计算得到NaF的缔合反应平衡常数为2.271,与实验结果吻合较好. NaF浓度对Na~+-F~-的径向分布函数和配位数有很大影响,但是对各缔合类型的相对含量影响不大.
Fluoride is an element closely related to the health of organisms. Sodium fluoride is the most common fluoride salt in nature. The study of its speciation in solution plays an important role in evaluating the migration and conversion of fluorine in groundwater and the treatment of fluorine-containing wastewater. In this paper, using classical molecular dynamics, the potential of mean force(PMF) of Na~+-F~- ions pair was calculated by Umbrella Sampling. The association type and association constant at 25 ℃ were determined with the calculated PMF. The results show that there are three association types of CIP, SSHIP and SSIP in NaF solution, among which CIP and SSHIP are the two most stable types. However, in terms of relative content, the association type of sodium fluoride solution is mainly SSHIP and SSIP, and CIP only accounts for 4.2%. The calculated equilibrium constant of NaF is 2.271, which is in good agreement with the experimental results. The NaF concentration has a great influence on the radial distribution function and coordination number of Na~+-F~- , but a little effect on the relative content.
Fluoride is an element closely related to the health of organisms. Sodium fluoride is the most common fluoride salt in nature. The study of its speciation in solution plays an important role in evaluating the migration and conversion of fluorine in groundwater and the treatment of fluorine-containing wastewater. In this paper, using classical molecular dynamics, the potential of mean force(PMF) of Na~+-F~- ions pair was calculated by Umbrella Sampling. The association type and association constant at 25 ℃ were determined with the calculated PMF. The results show that there are three association types of CIP, SSHIP and SSIP in NaF solution, among which CIP and SSHIP are the two most stable types. However, in terms of relative content, the association type of sodium fluoride solution is mainly SSHIP and SSIP, and CIP only accounts for 4.2%. The calculated equilibrium constant of NaF is 2.271, which is in good agreement with the experimental results. The NaF concentration has a great influence on the radial distribution function and coordination number of Na~+-F~- , but a little effect on the relative content.
引文
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[24]Timko J,Bucher D,Kuyucak S.Dissociation of NaCl in water from ab initio molecular dynamics simulations[J].J Chem Phys,2010,132(11):114 510-114 517.DOI:10.1063/1.3360310.
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[27]Zhang Q,Zhang R,Zhao Y,et al.Pairing preferences of the model mono-valence mono-atomic ions investigated by molecular simulation[J].J Chem Phys,2014,140(18):184 504-184 512.DOI:10.1063/1.4874255.
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[29]Berendsen H J,Grigera J R,Straatsma T P.The missing term in effective pair potentials[J].J Phys Chem,1987,91(24):6 269-6 271.DOI:10.1021/j100308a038.
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[31]Lukyanova E V,Zotov A V.Determination of the NaF(aq)association constant for the NaF-NaCl-H2OSystem at 25-75℃by means of potentiometry[J].Russ J Phys Chem A,2017,91(4):672-677.DOI:10.1134/S0036024417040148.
[32]Fuoss R M.Conductimetric determination of thermodynamic pairing constants for symmetrical electrolytes[J].P Natl Acad Sci USA,1980,77(1):34-38.DOI:10.1073/pnas.77.1.34.
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[34]代倩.氯化物盐水溶液微观结构特征的动力学模拟[D].长沙:湖南大学,2015.Dai Q.Theoretical study the structural characteristics of hydration of Chloride brine solution[D].Changsha:Hunan University,2015.
[35]Wang L J,Zhang W,Yang B,et al.Solubility measurements in Na-F-CO3-HCO3-H2O system at(308.15and 323.15)K and development of a Pitzer-based equilibrium model for the Na-F-Cl-SO4-CO3-HCO3-H2O system[J].J Chem Thermodyn,2019,131:88-96.DOI:10.1016/j.jct.2018.10.029.
[2]Ayoob S,Gupta A K.Fluoride in drinking water:A review on the status and stress effects[J].Crit Rev Env Sci Tec,2006,36(6):433-487.DOI:10.1080/10643380600678112.
[3]孙红丽,马峰,刘昭,等.西藏高温地热显示区氟分布及富集特征[J].中国环境科学,2015,35(1):251-259.Sun H L,Ma F,Liu Z,et al.The distribution and enrichment characteristics of fluoride in geothermal active area in Tibet[J].China Environmental Science,2015,35(1):251-259.
[4]谢兴能,杨秀忠,杨胜元,等.贵州地氟病氟源探讨--以黔中地氟病区地质环境调查为例[J].中国地质,2010,37(3):696-703.DOI:10.3969/j.issn.1000-3657.2010.03.024.Xie X N,Yang X Z,Yang S Y,et al.A tentative discussion on the source of endemic fluorosis:geo-environmental evidence from three counties in Guizhou Province[J].Geology in China,2010,37(3):696-703.
[5]Eigen M,Tamm K Z.Schallabsorption in elektrolytl?sungen als folge chemischer relaxation II.Me?ergebnisse und relaxationsmechanismen für 2-2-wertige elektrolyte[J].Elektrochemie,1962,66(2):107-121.
[6]Eigen M,Tamm K Z.Schallabsorption in elektrolytl?sungen als folge chemischer relaxation I.Relaxationstheorie der mehrstufigen dissoziation[J].Elektrochemie,1962,66(2):93-107.
[7]张强,李燕均,庄巍.离子对水溶液微观结构和动力学的影响[J].中国科学:化学,2016,46(1):51-58.Zhang Q,Li Y J,Zhuang W.Ion effect on the structures and dynamics of aqueous solutions[J].Scientia Sinica:Chimica,2016,46(1):51-58.
[8]Fleissner G,Hallbrucker A,Mayer E.Increasing contact ion pairing in the supercooled and glassy states of“dilute”aqueous magnesium,calcium,and strontium nitrate solution:implications for biomolecules[J].JPhys Chem,1993,97(18):4 806-4 814.DOI:10.1021/j100120a037.
[9]Hage W,Hallbrucker A,Mayer E.Increasing ion pairing and aggregation in supercooled and glassy dilute aqueous electrolyte solution as seen by FTIR spectroscopy of alkali metal thiocyanates[J].J Phys Chem,1992,96(15):6 488-6 493.DOI:10.1021/j100194a070.
[10]Simonet V,Calzavara Y,Hazemann J L,et al.X-ray absorption spectroscopy studies of ionic association in aqueous solutions of zinc bromide from normal to critical conditions[J].J Phys Chem,2002,117(6):2 771-2781 .DOI:10.1063/1.1490588.
[11]Ciccotti G,Ferrario M,Hynes J T,et al.Constrained molecular dynamics and the mean potential for an ion pair in a polar solvent[J].Chem Phys,1989,129(2):241-251.DOI:10.1016/0301-0104(89)80010-2.
[12]Chialvo A A,Cummings P T,Cochran H D,et al.Na+-Cl-ion pair association in supercritical water[J].JChem Phys,1995,103(21):9 379-9 387.DOI:10.1063/1.470707.
[13]Driesner T,Seward T M,Tironi I G.Molecular dynamics simulation study of ionic hydration and ion association in dilute and 1 molal aqueous sodium chloride solutions from ambient to supercritical conditions[J].Geochim Cosmochim Ac,1998,62(18):3 095-3 107.DOI:10.1016/S0016-7037(98)00207-5.
[14]He M,Liu X,Lu X,et al.Molecular simulation study on K+-Cl-ion pair in geological fluids[J].Acta Geochim,2017,36(1):1-8.DOI:10.1007/s11631-016-0130-6.
[15]Zhang Z,Duan Z.Lithium chloride ionic association in dilute aqueous solution:a constrained molecular dynamics study[J].Chem Phys,2004,297(1):221-233.
[16]Chlalvo A A,Simonson J M M.Ion association in aqueous LiCl solutions at high concentration:Predicted results via molecular simulation[J].J Chem Phys,2006,124(15):154 509-154 517.DOI:10.1063/1.2186641.
[17]Xu M,Larentzos J P,Roshdy M,et al.Aqueous divalent metal-nitrate interactions:hydration versus ion pairing[J].Phys Chem Chem Phys,2008,10(32):4 793-4 801.DOI:10.1039/b807090n.
[18]Matthews R P,Naidoo K J.Experimentally consistent ion association predicted for metal solutions fromfree energy simulations[J].J Phys Chem B,2010,114(21):7 286-7 293.DOI:10.1021/jp911823x.
[19]Iskrenova-Tchoukova E,Kalinichev A G,Kirkpatrick RJ.Metal cation complexation with natural organic matter in aqueous solutions:molecular dynamics simulations and potentials of mean force[J].Langmuir,2010,26(20):15 909-15 919.DOI:10.1021/la102535n.
[20]Larentzos J P,Criscenti L J.A molecular dynamics study of alkaline earth metal-chloride complexation in aqueous solution[J].J Phys Chem B,2008,112(45):14 243-50.DOI:10.1021/jp802771w.
[21]Faridi J,EI Guendouzi M.Study of ion-pairing and thermodynamic properties of sodium fluoride in aqueous solutions at temperatures from 298.15 to353.15 K[J].J Solution Chem,2015,44(11):2 194-2 207.DOI:10.1007/s10953-015-0405-2.
[22]Aghaie M,Samaie E.Non-ideality and ion-pairing in saturated aqueous solution of sodium fluoride at 25℃[J].J Mol Liq,2006,126(1):72-74.
[23]Fennell C J,Bizjak A,Vlachy V,et al.Ion pairing in molecular simulations of aqueous alkali halide solutions[J].J Phys Chem B,2009,113(19):6 782-6 791.DOI:10.1021/jp809782z.
[24]Timko J,Bucher D,Kuyucak S.Dissociation of NaCl in water from ab initio molecular dynamics simulations[J].J Chem Phys,2010,132(11):114 510-114 517.DOI:10.1063/1.3360310.
[25]Guardia E,Rey R,Padro J A.Na+-Na+and Cl--Cl-ion pairs in water:Mean force potentials by constrained molecular dynamics[J].J Chem Phys,1991,95(4):2 823-2 831.DOI:10.1063/1.460934.
[26]Ikeda T,Hirata M,Kimura T.Hydrolysis of Al3+from constrained molecular dynamics[J].J Chem Phys,2006,124(7):74 503-74 509.DOI:10.1063/1.2168459.
[27]Zhang Q,Zhang R,Zhao Y,et al.Pairing preferences of the model mono-valence mono-atomic ions investigated by molecular simulation[J].J Chem Phys,2014,140(18):184 504-184 512.DOI:10.1063/1.4874255.
[28]Abraham M J,Schulz R,et al.GROMACS:High performance molecular simulations through multi-level parallelism from laptops to supercomputers[J].Software X,2015,1-2:19-25.DOI:10.1016/j.softx.2015.06.001.
[29]Berendsen H J,Grigera J R,Straatsma T P.The missing term in effective pair potentials[J].J Phys Chem,1987,91(24):6 269-6 271.DOI:10.1021/j100308a038.
[30]Jorgensen W L,Maxwell D S,Tirado-Rives J.Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids[J].J Am Chem Soc,1996,118(45):11 225-11 236.DOI:10.1021/ja9621760.
[31]Lukyanova E V,Zotov A V.Determination of the NaF(aq)association constant for the NaF-NaCl-H2OSystem at 25-75℃by means of potentiometry[J].Russ J Phys Chem A,2017,91(4):672-677.DOI:10.1134/S0036024417040148.
[32]Fuoss R M.Conductimetric determination of thermodynamic pairing constants for symmetrical electrolytes[J].P Natl Acad Sci USA,1980,77(1):34-38.DOI:10.1073/pnas.77.1.34.
[33]Fuoss R M.Ionic Association.III.The equilibrium between ion pairs and free ions[J].J Am Chem Soc,1958,80(19):5 059-5 061.DOI:10.1021/ja01552a016.
[34]代倩.氯化物盐水溶液微观结构特征的动力学模拟[D].长沙:湖南大学,2015.Dai Q.Theoretical study the structural characteristics of hydration of Chloride brine solution[D].Changsha:Hunan University,2015.
[35]Wang L J,Zhang W,Yang B,et al.Solubility measurements in Na-F-CO3-HCO3-H2O system at(308.15and 323.15)K and development of a Pitzer-based equilibrium model for the Na-F-Cl-SO4-CO3-HCO3-H2O system[J].J Chem Thermodyn,2019,131:88-96.DOI:10.1016/j.jct.2018.10.029.