不同价态Fe在煤系高岭石中晶格取代的DFT研究
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摘要
为探索不同价态Fe在高岭石中晶格取代的形式及其对高岭石界面结构性质的影响,采用密度泛函理论(DFT)方法对不同价态Fe在高岭石晶体中的晶格取代进行了模拟计算,通过晶格取代能计算分析Fe元素的3种晶格取代的难易程度,并通过计算能带结构和前线轨道,分析了Fe元素的3种晶格取代对高岭石界面结构性质的影响.结果表明:不同价态Fe在高岭石晶体中的晶格取代形式主要有Fe~(2+)取代铝氧八面体中的Al~(3+)(Fe~(2+)→Al~(3+))、Fe~(3+)取代铝氧八面体中的Al~(3+)(Fe~(3+)→Al~(3+))及Fe~(3+)取代硅氧四面体中的Si~(4+)(Fe~(3+)→Si~(4+))3种,其取代程度由易到难为:Fe~(2+)→Al~(3+)> Fe~(3+)→Si~(4+)> Fe~(3+)→Al~(3+);高岭石经过不同价态Fe元素取代后,将导致高岭石晶格的能带带隙减小,最高占有分子轨道(HOMO)和最低占有分子轨道(LUMO)的反应活性发生改变.通过穆斯堡尔(M?ssbauer)谱仪对淮北矿区煤系高岭石中的铁占位进行了分析,淮北矿区煤系高岭石中的Fe占位主要为六配位Fe~(2+)和四配位Fe~(3+),及极少量的六配位Fe~(3+),3种Fe的含量从大到小为:六配位Fe~(2+)>四配位Fe~(3+)>六配位Fe~(3+);同时,M?ssbauer谱测试结果进一步验证了DFT计算的正确性.
In order to study the lattice substitution forms of Fe with different valences in kaolinite and the influence on the structural properties of kaolinite interface, the density functional theory(DFT) calculation was performed to explore the lattice substitution of Fe with different valences in kaolinite and the influence on the structural properties of kaolinite interface. In this calculation, the possibilities of three lattice substitutions by Fe element were analyzed by lattice substitution energies, and the effects of the three lattice substitutions on the structural properties of kaolinite were predicted by the energy band structures and frontier orbitals. The results show that Fe~(2+) substituted principally the Al~(3+) in alumina octahedral(Fe~(2+)→Al~(3+)), while Fe~(3+) could replace both the Al~(3+) in alumina octahedral(Fe~(3+)→Al~(3+)) and the Si~(4+) in silica tetrahedron(Fe~(3+)→Si~(4+)). The substitution occurred according to the following order: Fe~(2+)→Al~(3+)>Fe~(3+)→Si~(4+)>Fe~(3+)→Al~(3+). It was found that a decrease on the band gap of kaolinite lattice and a variation on the reactivity of HOMO and LUMO orbitals took place after the substitution with Fe. The space occupancy of iron in the coal measures kaolinite in Huaibei mining area was also analyzed by M?ssbauer spectrometer. The results showed that the space occupancy of iron mainly existed in the forms of six-coordination Fe~(2+), tetra-coordination Fe~(3+) and little amount of six-coordination Fe~(3+). The Fe content of the three forms was six-coordination Fe~(2+)> tetra-coordination Fe~(3+)> six-coordination Fe~(3+). The results from M?ssbauer spectrum were in good agreement with those from density functional theory calculation.
In order to study the lattice substitution forms of Fe with different valences in kaolinite and the influence on the structural properties of kaolinite interface, the density functional theory(DFT) calculation was performed to explore the lattice substitution of Fe with different valences in kaolinite and the influence on the structural properties of kaolinite interface. In this calculation, the possibilities of three lattice substitutions by Fe element were analyzed by lattice substitution energies, and the effects of the three lattice substitutions on the structural properties of kaolinite were predicted by the energy band structures and frontier orbitals. The results show that Fe~(2+) substituted principally the Al~(3+) in alumina octahedral(Fe~(2+)→Al~(3+)), while Fe~(3+) could replace both the Al~(3+) in alumina octahedral(Fe~(3+)→Al~(3+)) and the Si~(4+) in silica tetrahedron(Fe~(3+)→Si~(4+)). The substitution occurred according to the following order: Fe~(2+)→Al~(3+)>Fe~(3+)→Si~(4+)>Fe~(3+)→Al~(3+). It was found that a decrease on the band gap of kaolinite lattice and a variation on the reactivity of HOMO and LUMO orbitals took place after the substitution with Fe. The space occupancy of iron in the coal measures kaolinite in Huaibei mining area was also analyzed by M?ssbauer spectrometer. The results showed that the space occupancy of iron mainly existed in the forms of six-coordination Fe~(2+), tetra-coordination Fe~(3+) and little amount of six-coordination Fe~(3+). The Fe content of the three forms was six-coordination Fe~(2+)> tetra-coordination Fe~(3+)> six-coordination Fe~(3+). The results from M?ssbauer spectrum were in good agreement with those from density functional theory calculation.
引文
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[2] 陈军,闵凡飞,刘令云,等.高泥化煤泥水的疏水聚团沉降试验研究[J].煤炭学报,2014,39(12):2507-2512.CHEN Jun,MIN Fanfei,LIU Lingyun,et al.Study on hydrophobic aggregation settlement of high muddied voal slurry water[J].Journal of China Coal Society,2014,39(12):2507-2512.
[3] ISRAELACHVILI J N,MCGUIGGAN P M.Forces between surfaces in liquids [J].Science,1988,16(1):31-47.
[4] PENG C,SONG S,FORT T.Study on hydration layers near a hydrophilic surface in water through AFM imaging[J].Surface and Interface Analysis,2006,38(5):975-980.
[5] MIN F,PENG C,LIU L.Investigation on hydration layers of fine clay mineral particles in different electrolyte aqueous solutions[J].Powder Technology,2015,283:368-372.
[6] 崔吉让,方启学,黄国智.一水硬铝石与高岭石的晶体结构与表面性质[J].有色金属,1999,51(4):25-30.CUI Jirang,FANG Qixue,HUANG Guozhi.Crystal structures and surface properties of diaspore and kaolinite[J].Nonferrous Metals,1999,51(4):25-30.
[7] JIANG H,SUN Z,XU L,et al.A comparison study of the flotation and adsorption behaviors of diaspore and kaolinite with quaternary ammonium collectors[J].Minerals Engineering,2014,65:124-129.
[8] PERDEW J P,KURTH S.Density functionals for non-relativistic coulomb systems in the New Century[J].Lecture Notes in Physics,2003,620:1-51.
[9] WANG X,QIAN P,SONG K,et al.The DFT study of adsorption of 2,4-dinitrotoluene on kaolinite surfaces[J].Computational and Theoretical Chemistry,2013,1025:16-23.
[10] 闵凡飞,彭陈亮,刘令云,等.微细蒙脱石颗粒界面疏水改性机理研究[J].材料导报,2017,31(16):150-155.MIN Fanfei,PENG Chenliang,LIU Lingyun,et al.Interfacial hydrophobicity modification of fine montmorillonite particles:A mechanism study[J].Materials Review,2017,31(16):150-155.
[11] CHEN J,MIN F,LIU L,et al.Experimental investigation and DFT calculation of different amine/ammonium salts adsorption on kaolinite[J].Applied Surface Science,2017,419:241-251.
[12] CLARK S J,SEGALL M D,PICKARD C J,et al.First principles methods using CASTEP[J].Zeitschrift Fuer Kristallographie,2005,220(5/6):567-570.
[13] PERDEW J P,BURKE K,ERNZERHOF M.Generalized gradient approximation made simple[J].Physical Review Letters,1996,77:3865-3868.
[14] VANDERBILT D.Soft self-consistent pseudopotentials in a generalized eigenvalue formalism[J].Physical Review B,1990,41:7892 -7895.
[15] 韩永华,刘文礼,陈建华,等.羟基钙在高岭石两种(001)晶面的吸附机理[J].煤炭学报,2016,41(3):743-750.HAN Yonghua,LIU Wenli,CHEN Jianhua,et al.Adsorption mechanism of hydroxyl calcium on two kaolinite (001) surface[J].Journal of China Coal Society,2016,41(3):743-750.
[16] MONKHORST H J,PACK J D.Special points for Brillouin-zone integrations[J].Physical Review B,1976,13:5188-5192.
[17] 陈建华.硫化矿物浮选晶格缺陷理论[M].长沙:中南大学出版社,2012:51-64.CHEN Jianhua.Principles of the flotation of sulphide minerals bearing lattice defects[M].Changsha:Central South University Press,2012:51-64.
[18] HU X L,MICHAELIDES A.Water on the hydroxylated (001) surface of kaolinite:From monomer adsorption to a flat 2D wetting layer[J].Surface Science,2008,602(4):960-974.
[19] BISH D L.Rietveld refinement of the kaolinite structure at 1.5 K[J].Clays & Clay Miner,1993,41:738-744.
[20] 陈建华.硫化矿物浮选固体物理研究[M].长沙:中南大学出版社,2015:61-62.CHEN Jianhua.The solide physics of sulphide minerals flotation[M].Changsha:Central South University Press,2015:61-62.
[21] 陈军,闵凡飞,刘令云,等.不同胺/铵阳离子在高岭石(001)面吸附的密度泛函[J].煤炭学报,2016,41(12):3115-3121.CHEN Jun,MIN Fanfei,LIU Lingyun,et al.The DFT calculations of different amine/ammonium cations adsorption on kaolinite (001) surface[J].Journal of China Coal Society,2016,41(12):3115-3121.
[22] 杨晓杰,丁述理.京西煤系高岭石的铁占位[J].河北建筑科技学院学报,2005,22(3):73-75.YANG Xiaojie,DING Shuli.Study on the kaolinite in coal measures of West Beijing by M?ssbauer spectroscopy[J].Journal of Hebei Institute of Architectural Science and Technology,2005,22(3):73-75.
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