密度泛函理论研究离子在碳材料上的吸附行为

发布时间：2018-02-16 22:06

本文关键词： 土壤污染物离子吸附碳材料密度泛函理论计算　出处：《西南大学》2017年硕士论文　论文类型：学位论文

【摘要】：土壤是人类赖以生存的物质基础和财富源泉。但我国在工农业生产迅猛发展和城镇化进程日益加快的同时,土壤也受到了严重污染,这极大地威胁到生态安全和人类健康。无机污染物在土壤各种污染物中所占比重最大,其主要包括重金属离子和阴离子污染物。人们在一直探索土壤无机污染物的去除方法,经研究证实碳材料是一种很有潜力的无机污染物去除材料。现今,碳材料吸附离子的研究工作已被广泛开展,但大多数工作是从宏观角度出发,研究离子吸附过程中的吸附量、吸附强度以及吸附过程等。本论文运用了密度泛函理论计算方法,从分子尺度上研究并阐明碳材料的离子吸附相关机制。论文以多环芳烃团簇结构作为碳材料的研究模型,选择结构相对简单的卤素离子(X-=F~-,Cl~-,Br~-和I~-)作为阴离子代表;选择碱金属离子(M~+=Li~+、Na~+和K~+)、碱土金属(M~(2+)=Be~(2+)、Mg~(2+)和Ca~(2+))及三价镧离子(La~(3+))为金属离子代表;以六个离子对(MX=LiF,NaF,KF,Li I,NaF,KF)作为阴阳离子对代表,运用密度泛函理论(DFT)深入而系统地研究了碳材料与它们之间的相互作用,并得出以下主要结论:(1)卤素离子与金属离子在碳材料表面的吸附行为具有一定的相似之处,但在本质上明显不同。二者在碳材料表面的吸附强度均随着离子半径的增大而减弱,表现为为F~-Cl~-Br~-I~-和Li~+Na~+K~+(或Be~(2+)Mg~(2+)Ca~(2+));通过比较结合能的大小可知,卤素离子中仅有F~-与碳材料的相互作用较强(Eb=-97.0 kJ·mol~(-1)),其它的吸附作用都很弱,因此可以轻松地从碳材料表面脱附,而金属离子则都可以稳定地吸附在碳材料表面。碳材料与阴离子、金属离子的作用机制本质区别在于:与卤素离子作用时为电子受体,电荷从卤素离子转移到碳材料表面,而在与金属离子作用时为电子供体,电子由碳材料表面转移到金属离子上;(2)本论文进一步地分析了碳材料电子性质的改变对离子吸附行为的影响,选择了常见的电子受体F原子对碳材料进行边界官能化修饰。结果表明,当碳材料与离子相互作用时,卤素离子在碳材料表面的吸附强度随边界官能化比例(Θ)的增大而逐渐增强,而金属离子的吸附强度却逐渐减弱。当Θ=100%时,F~-与碳材料表面的结合能已经增大到接近原来的两倍(-186.3 kJ·mol~(-1)),而金属离子Li~+、Na~+和K~+离子的结合能却分别降低到-95.7、-44.8和-25.9 kJ·mol~(-1),已经明显低于F~-的结合能大小。由此可知,官能团修饰及改变官能化比例可以调节碳材料的电子性质,进而调控卤素离子和金属离子的优先吸附顺序。(3)碳材料对水合离子吸附的研究表明,水合作用减弱了离子与碳材料间的直接作用强度。碳材料在与水合卤素离子作用时,H_2O不仅可以与卤素离子形成氢键,而且还通过O原子与碳材料发生相互作用。但当碳材料与水合金属离子作用时,金属离子与H_2O分子中的O原子形成化学键,然后H_2O再通过H原子与碳材料发生作用。也正因如此,水合作用对卤素离子在未官能化碳材料表面的吸附强度影响较大,而对金属离子则在完全官能化碳材料表面的吸附强度影响较大。(4)所有阴阳离子对都可以通过两侧以及同侧垂直方式稳定地吸附在碳材料表面,但垂直构型稳定性要明显的强于两侧构型,且金属离子直接与碳材料直接的垂直构型结构更为稳定。进一步研究表明,两种垂直构型的相对稳定性差异由与之对应的金属离子和阴离子在碳材料表面的吸附强度之差所决定。当金属离子的吸附作用明显较强时,金属离子直接与碳材料直接作用的构型为优势构型,而阴离子的吸附作用更强时,优势构型则转变为阴离子离子直接与碳材料直接作用的构型;当二者的结合能相当时,两种垂直构型的稳定性比较接近。(5)碳材料的原子掺杂改变了离子的吸附模式,其中水平构型最为稳定,而垂直构型的稳定性较差甚至在某些情况下不能存在。结合能的计算结果表明,所有原子掺杂都增强了NaF在碳材料表面的吸附,且吸附强度按NOBBe顺序依次增强。但是,含掺杂原子的碳材料对离子对吸附的调节机制并不相同,缺电子原子Be和B掺杂对NaF吸附的促进源于掺杂原子与F~-的直接作用,而富电子原子N和O掺杂则主要是通过改变碳材料体系π电子共轭促进NaF吸附,这也是它们对NaF的吸附强度弱于缺电子Be和B掺杂的原因。综上所述,本论文深入而系统地研究了金属离子、阴离子以及阴阳离子对在碳材料表面的吸附行为及吸附机制,比较它们吸附特性的异同,并揭示碳材料电子性质、水合作用、补偿离子等因素对离子吸附行为及吸附效果的影响。研究结果对认识离子在碳材料上的吸附理论支撑和科学依据,也为今后有针对性的选择和制备碳材料提供了一些参考方向。
[Abstract]:The soil is the material basis of human survival and the source of wealth. But our country is accelerating in the industrial and agricultural production and the rapid development of the urbanization process at the same time, the soil has been seriously polluted, which greatly threaten the ecological safety and human health. The inorganic pollutants in the soil of various pollutants in the largest proportion, the main including heavy metal ions and anionic pollutants. People have been exploring methods for removal of inorganic contaminants in soil, the study confirmed that the carbon material is a kind of promising material removal of inorganic pollutants. Nowadays, ion adsorption of carbon materials in the research work has been carried out widely, but most of the work is from a macro perspective, the adsorption capacity of ion adsorption in the process of adsorption strength and adsorption process. This paper uses density functional theory calculation method, research and clarify the ion adsorption of carbon materials from molecular scale Based on the related mechanism. PAHs cluster structure as the research model of carbon materials, halogen ion selective relatively simple structure (X-=F~-, Cl~-, Br~- and I~-) as the representative of anion; alkali metal ions (M~+=Li~+, Na~+ and K~+), alkaline earth metal (M~ (2+) =Be~ (2+), Mg~ (2+) and Ca~ (2+)) and trivalent lanthanide ions (La~ (3+)) is a metal ion with six representatives; ion pair (MX=LiF, NaF, KF, Li, I, NaF, KF) as the representative of ions, using density functional theory (DFT) thorough and systematic research of carbon materials and the interaction between them, and the main conclusions are as follows: (1) halogen ions and metal ions have some similarities in the adsorption behavior of carbon materials on the surface, but in essence are obviously different. The two adsorption on the surface of the carbon material strength are increased with the increase of ionic radius and the decrease of the performance for F~-Cl~-Br~-I~- and Li~+Na~+K~+ (or Be~ (2+) Mg~ (2+) Ca~ (2+)); by comparing the binding energy of F~-, only with a carbon material in the strong interaction of halogen ions (Eb=-97.0 kJ - mol~ (-1)), the other adsorption effect is very weak, so we can easily from the surface of the carbon material desorption of metal ions can be stably adsorbed on the surface of the carbon material. The carbon material with anion, mechanism of metal ions is the essential difference between function and halogen ions for electron acceptor charge transfer from halogen ions to the surface of the carbon material, and with metal ions as electron donor, electron transfer from the surface of the carbon material to the metal ions (; 2) this paper analyses the influence of electronic properties of carbon materials on the adsorption behavior of the ion, choose the common electron acceptor F atom boundary functionalized modification of carbon materials. The results show that when the carbon materials and ionic interaction, from halogen With the boundary of functionalized proportion in the adsorption strength of carbon materials (PE) surface increases gradually increased, while the adsorption strength of metal ion is weakened gradually. When introducing =100%, the combination of F~- and carbon material surface energy has increased to nearly two times the original (-186.3 kJ - mol~ (-1)), and the metal ions of Li~+, combined with Na~+ and K~+ ions was decreased to -95.7, -44.8 and -25.9 kJ mol~ (-1), has been significantly lower than the F~- combined size. Therefore, the electronic properties of modified and functionalized carbon material ratio can be adjusted, and then adjust the priority sequence control and metal halide ion adsorption ion. (3) research of carbon materials on the hydration of ion adsorption showed that hydration weakens the direct effect of ionic strength and carbon materials. Carbon material with hydrated ions, H_2O can not only form hydrogen bond and halogen ions, but also by O Interact with carbon materials. But when carbon materials and hydrated metal ions, metal ions and H_2O molecules in O atoms form chemical bonds, then H_2O effect of H atoms and carbon materials through. Because of this, the hydration effect on the adsorption strength of halogen ions of carbon material on the surface non functional, and metal ions in fully functionalized carbon adsorption strength of material surface has great influence. (4) of all ions on can be stably adsorbed on the surface of the carbon material by both sides and the same side vertical mode, but the vertical configuration stability are stronger than both sides of configuration, vertical configuration and structure of metal ions direct and direct carbon material is more stable. Further study showed that the relative stability of the difference between the two vertical configuration by the corresponding metal ions and anions on the adsorption strength of carbon materials on the surface of the difference Decided. When the adsorption of metal ions was strong, metal ions and carbon materials directly for the advantage of the configuration configuration, and stronger adsorption of anions, the advantage configuration was transformed into anion ion directly with the direct effect of carbon materials with configuration; when the two can be quite close to two, stability vertical configuration. (5) carbon atom doped ion adsorption mode change, the level of configuration of the most stable, and poor stability of vertical structure exists even in some cases not. Combined with the calculation results can show that all atoms have enhanced the adsorption of NaF on the surface of the carbon material, and the adsorption according to the NOBBe sequence of strength enhancement. However, carbon material containing doping on the regulation mechanism of ions on the adsorption is not the same, electron deficient atom Be and B doping on the adsorption of NaF on promoting source doping With the direct effect of F~-, and the electron rich atom N and O doping is mainly through the change of carbon material system pi electron conjugated promoted NaF adsorption, which is their adsorption strength on NaF weak in electron deficient Be and B doping. In summary, this thesis in-depth and systematic study of metal ions, anions, Yin and Yang the ions on the adsorption behavior and mechanism of carbon material surface, compare their adsorption properties, and reveal the electronic properties of carbon materials, hydration, compensation effect of ions on ion adsorption behavior and adsorption effect. The results of studying on the adsorption of ions in carbon materials, theoretical support and scientific basis for the future the selection and preparation of carbon materials provide some reference.

【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O647.3;X53

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