Sonia: Ocho, Lee Whitemore, Ben Slater *, richard carter Lowe.
David Faraday Research Laboratory, Royal Society, 2 1 albemarle Street, London, UK, w 1s 4bs.
Received 5438+0 on April 25th, 2006; Accepted, June 25, 2006 5438+0
abstract
Atomic simulation has been used to study two completely different problems: (1) how to grow calcium carbonate and inhibitors, zeolites that can be operated at atomic scale and (2) the properties of external surfaces, and how to put these reactants or products on the surface. In the first study, we studied how monophosphonate-like growth inhibitors destroy the assembly of calcite that is emerging from the water. We have proved a growth inhibition mechanism, which emphasizes kinking and blockage, while toxicity is irreversible, and it is close to the site to prevent kinking and eliminate nearby impurities. Secondly, we prove that the two models proposed by terasaki (Australia terasaki, Williams Motor, Micro 43 (1994) 337) are stable and provide an outer surface with distinct stereochemical properties. In order to evaluate the traffic problem, we use the probe molecule benzene to go to the outer and inner surfaces of the energy barrier in person. We think that the partition wall is smaller than the volume, suggesting that the molecular dynamics radius is relatively small and the tax rate is determined. During transportation, it will be medium or crystal volume in the host country. ? 200 1 year editing science and other medical sciences, Elsevier SAS. property in copyright
Keywords: computer simulation; Calcite; zeolite
1 。 introduce
More and more computer simulation techniques are based on high-quality interatomic interaction potential, which provides new insights into the basic problems in crystal growth and nucleation of various materials. Recently, static energy calculation and classical molecular dynamics have been used to explore the time-dependent and time-free crystal surfaces alone or together. Among them, in the solid field generated by using atomic methods or even molecular mechanics according to this model, the more basic problem is that the cost of simulation usually increases on a superlinear scale. This limits the simulator to explore dimension-based system investigation and calculation of available resources in a limited length and time range. In the following two examples, it is difficult to simulate the time span of the phenomenon we are discussing, whether using Monte Carlo or molecular dynamics directly, but combining the combined energy reduction method with molecular dynamics. In these two cases, we have developed the ability of molecular dynamics to explore the spatial efficiency of regional images and strict energy minimization methods, such as atomic relaxation to zero net force. By coupling these methods, we will overcome the problem, otherwise we will face the challenge of calculation methods and available resources. In the second article, we describe the results of recent research on the growth inhibition mechanism of calcite surface, while in the third article, we study the physical properties and transport characteristics of zeolite surface.
2 。 Monophosphonate inhibitor ion inhibits the growth of calcium carbonate (1 0 ˉ 14) crystal.
2. 1 。 Background and methods
Experimental techniques for inhibiting calcite crystal growth, such as atomic force microscopy (AFM), have been widely studied. For example, if you are particularly interested in obtaining the most effective growth inhibitor, you can form calcite scale oil pipes and water treatment systems. The relationship between concentrated growth inhibitors and their effects on the size and morphology of crystal particles is analyzed, and the very complicated relationship between the functional groups of inhibitors, the intact calcite on the surface and the host country is revealed [2]. Atomic force microscopy provides spectacular images of calcite balance on the growth surface with and without growth inhibitors [3, 4]. Although these methods provide a lot of phenomenological evidence to support this assertion, from the contrast effect of experiments, it is obvious that there is a microscopic growth mechanism at the nuclear interface that needs to be solved. It is a very important milestone to develop BCF model [5] and study its application. These methods provide a scheme to predict crystal assembly, but because of the model, there is no clear characteristics of micro-growth stocks. It is not just intuition to predict how to suppress the interference of terraced fields, wall frame and kinks. In order to solve the mechanical details, some authors have used atomic simulation at the atomic level. De leeuw et al. [6,7] reported a series of comprehensive studies, focusing on the growth, morphology, defect chemistry and dissolution characteristics of calcite. Rohl et al. [8] studied the growth inhibition of barium sulfate by calculation and demonstrated how to affect the growth of bisphosphonate crystal on site. In addition, Nygren et al. [9] published a research report on the effect of diphosphonic acid growth inhibitors on calcite, and proposed that blocking kink websites is the most poisoned growth flame retardant mechanism. We extended this study to expect the role of bisphosphonic acid and a series of monophosphates as deconvolution agents and the inhibition efficiency of phosphonic acid groups. Although it is well known that the morphology of calcite is strongly influenced by temperature, pH value and supersaturation, product performance inhibitors (which have been determined to cause changes in crystal growth) are effective charges of inhibitors, stereochemistry and geometry. Step-by-step growth is particularly interesting, because gratz and Hillner [3 3,4] have established a time-resolved AFM, and the inhibitor HEDP (patented growth poison is widely used in industry) has accumulated step-by-step advantages. The most stable surface calcite (1 0. 14) presents a useful step (Figure 14), which is an obtuse angle, saluting grfig, the end part opposite to the balcony. 1 。 Slow and fast calcite (1 0. 1 4). 1 display
Slow reinforcement and b refer to acute steps.
Table 1
Based on pentaphosphonate ion, this work has been carried out.
[(po3) pH] Step acute angle is formed. Atomic force microscopy also shows that slow steps become faster and sharper. Therefore, we consider the interaction inhibitor and this step, because the fastest growth step, that is, the slow step, will have the strongest growth inhibition. Based on pentaphosphonate, the work here is listed in table 1. Hemp, sand control scheme and pemp are monosubstituted analogues of bisphosphonates of Nygren et al. Both HEDP and PMP have been reported in the study of experimental inhibitors, so we have studied them so that we can prove the observed effect and our calculation results. Obviously, these molecules have unrelated physical properties, although it is a hidden feature that all these molecules have different charge distributions because of the existence of strong electron-withdrawing or electron-donating groups. The adsorption inhibitor of this model is located on the surface of calcite. Let's discuss three-dimensional and electrostatic factors and their functions, as well as their inhibitory effects on growth. The structure of calcite is modeled after the atomic potential set widely used at present, because pavese et al. [10]; This force field uses a shell model to describe highly polar oxygen carbonate atoms. The inhibitor is described by the force field cvff diagram of molecular mechanics. 2 。 The figure shows the simulation strategy. Step 1 is a geometric optimization impurity, close to the site. The second step is to optimize the impurities beside the calcium carbonate plant. [1 1], in which the interactive calcite surface and inhibitor are described as cvff clauses with scale. There are comprehensive and detailed force fields in the reference materials. [ 12 ] 。 On the surface, the numerical simulation is carried out by Zhang Jiandong's program [13], while on the surface, the simulated units are described in two areas. The lower layer is fixed and the upper layer is relaxed to mechanical balance. Among them, on the surface, 4000 ions are repeatedly described in two aspects. Comprehensive and detailed simulation conditions can be found elsewhere [12]. We have carried out various simulations, but focusing on the mechanism here shows that Nygren is the most effective one-step assembly containing calcite according to the basic conditions. Our research process is exactly the same as Nygren, and it is described by the schematic diagram in the figure. 2 。 In essence, the simulation process can catch up with the one-step assembly mechanism, but phosphonates are being studied and placed next to the ground as impurities. This arrangement is then geometrically optimized, and a calcium carbonate charge neutral chain will be added, which is placed next to the bound phosphonate. Combine energy with calcium carbonate building blocks, and then calculate and compare the binding force and energy, and kink with another calcium carbonate unit, a calcite.
2.2 。 result
Referring to Table 2, we can infer that all phosphonic acid ions lead to a great decrease in the binding energy of calcium carbonate raw materials. This result can be explained as an unstable one-step assembly process. On this basis, we expect the intensified assembly process to be dull purely for the sake of energy. If we now study the relative degree of binding force
Table 2
Calculation of binding energy calcium carbonate unit will inevitably kink. The website contains the ion binding energy (kjmol- 1) of adions on the surface of dark light-strengthened (14).
Energy, we think the most unstable ion is the proxy HEDP species, which is well known as a fairly strong growth blocker. Monophosphonate species are not so effective in preventing one-step assembly, which is consistent with the experimental results. Surprisingly, the relatively large primitive man of PMP is considered to be the most effective inhibitor, although it is three-dimensional and not too heavy. One possible explanation is that the phenyl group is determined to be perpendicular to the one-step assembly carrier, so that the repulsive force with calcium carbonate units can be avoided, which is stronger than that of pemp. Because calcium ions are attracted by dihydroxy groups, DMP with large binding energy is produced. The gap between cannabis and HEDP is partly due to the fact that one species has phosphonate groups, while the other species has two. In addition, due to the advantage of electrostatic force, the calcium carbonate share is poor in binding energy. It is more generally observed that such long bisphosphonic acid is larger than monophosphonic acid, that is, the favorable electrostatic interaction between calcite growing chain and kink is more effective at present, and bisphosphonic acid reduces the binding energy of calcium carbonate growing chain. We also note that these binding energies do not take into account the energy of solvents, whether calcium carbonate units or phosphonate units, but recent calculations [1 1] show that for all poisons considered here, the binding net energy definitely increases calcium carbonate units, that is, it is endothermic, which means that the growth of additional steps may only be greater than the length of poisons. Therefore, it is expected that this step will become an experimental aiming head. In fact, the confirmation of this phenomenon can be found in gratz and Hillner [4] of afmwork, which shows that the advantage of blunt step is becoming more and more innovative as a functional influence agent of HEDP concentration (in the study of effective poison concentration).
2.3 。 Conclusion: Calcite growth inhibition In a word, our calculation shows that how to explain kink retardation from the microscopic point of view can explain the experimental observation that phosphonates delay crystal growth and reduce particle size, and refer to the crystal congress theory and the potential abacus between atoms.
3 。 Adsorption and migration, silica faujasite on the outer surface
3. 1 。 Background and methods, understanding the transport properties of microporous and mesoporous materials is still a challenge to theoretical skills, and it is extremely important for catalytic industry. Although there are many examples of diffusion research in zeolite blocks, R? The external surface of le is not discussed in detail in terms of the influence of molecules on traffic. However, people are increasingly interested in external surfaces, which are considered to be available in micro-crucibles, where "pore catalysis" is possible. This concept is particularly relevant to layered zeolite materials, especially those synthesized by corma et al. [14], such as itq2. In order to simulate the transport on zeolite surface, it is obviously necessary to establish an external surface model. Although many studies have described the necessary conditions, especially the terminal can be stabilized into ionic oxide (relative to the bulk), for example, if the chemical properties of zeolite are not considered, the same conditions cannot be directly applied. The development of accurate surface terminals is not as easy as the textbook of this course, and it is hindered by the lack of reports and studies, which are considered to be able to solve the classification termination problem of surface microporous structures. In particular, atomic force microscopy (see, for example, Nasalmond et al.' s gas cell [15]) and high-resolution microscopy (see, for example, terasaki et al. [16]) have proved to be valuable reference points. In the next section, we will introduce the study of silica faujasite crystals and the migration of benzene on the outer surface. Migration characteristics of benzene in x, y zeolite and NaY diagram. 3 。 Terasaki [1] is recommended for type III surfaces. It has been widely studied, experimented and simulated. We have previously reported a possible termination of the surface of faujasite (1 1 1) studied in [17], and the adsorbed benzene is on the surface. Here we describe another type of termination (terasaki [1] type III below), in which high-quality and high-resolution data [1] supports a termination graph. 3 。 This termination is different from previous studies, in which bis-hexacyclic (d6r) was expressed on the surface. The morphology of faujasite is mainly (1 1 1) surface, which makes it spread at home and abroad, and the crystal only passes through (1 1) surface, so the key to understand the absorption characteristics and migration obstacles of knowledge is to understand the transport characteristics of crystal interface. Full details of this method can be found elsewhere [18]. We use the shell model potential [19], which has been successfully used to replicate a wide range of pure silica microporous structures. In addition, we also consider the surface hydroxyl groups and the parameter report of Schroeder [20] to describe the intermolecular and intramolecular hydroxyl groups. Benzene molecule is called by forcefield because of Hansen et al. [2 1], but the scale of charge, considering the fact, is based on the potential model, with formal charge, rather than the local cost of Hansen et al. Before using the software described by Zhang Jiandong, in this article, we used ***8 layers, of which 4 people regularly hold geometry in batches, while the other 4 layers are optimized.
3.2 。 Results Using various molecular dynamics and energy minimization techniques to find the best adsorption site on the outer surface, we identified three possible sites, which are similar but not identical. Because of the existence of d6r, type III surface is more jagged than type I surface, and d6r is surrounded by 12 yuan ring (Sir). Table 3 shows that the best combination can find the type III surface, and also compares the type I surface. Fourth, describe the location of the absorption site. It is found that the member 12 (elective 3) which is the most unfavorable for finding the absorption part is very similar, that is, 30.3 kjmol- 1 [17] which was found in batches before. The second most stable position is higher than d6r (optional one), and the energy judgment is similar to that found by Mr. 600, which is on the I-plane. Most importantly, it is found that the best absorption site is lower than d6r, more than one 6-ring, and some of them are more than four rings (selectivity 2). The combination can be found on this website very similar, only a few people are lower than the comparable website bulk.what, which is particularly interesting. For this result, there are two different terminals, which have been observed. There is a completely different absorption site in the high-resolution electron microscope [1], so there will be different persistence probabilities. The energy transfer calculated by constraint minimization method is benzene, 12 member transfer. The pseudoatom in the center of benzene molecule keeps a fixed displacement on the vertical surface, which looks like Cartesian Z coordinates, and the molecule can rotate freely around the pseudoatom in the center of benzene ring. We find that the order of the maximum energy barrier migration through the outer surface of 12 member is18 kj mol-1. This value is consistent with this discovery of type I surface water. As mentioned above, it is about 13 kJ mol- 1 low energy ratio cage. Pre-stack migration technology is adopted in the crystal body.
3.3 。 Conclusion: Zeolite surface
These results show that when the diffusion process enters or leaves the crystal, sorbate approaches 12mr, which is equivalent to the terminal observed in the two countries, but most importantly, it is far below the bulk migration energy of 3 1 kjmol- 1, which indicates that the time scale of diffusion entering or leaving the crystal will be much faster than that of diffusion in the body. However, for the third kind, on the surface, alive.
Table 3
Calculation of benzene absorption energy in hydroxyl faujasite
(1 1 1) surface
Site adsorption energy (kjmol- 1)
Figure. 4 。 Optimize the adsorption of type III faujasite (1 1 1) on the construction site. Vertex view. At that time, the benzene in 6/4 speech positions will therefore be comparable as a whole until the concentration of benzene is enough to fill all 6/4 speech positions; The diffusion parallel to the surface will be slightly faster than the observed mass, while in a similar process, the diffusion from the outer surface to the first super will be faster than the mass, and vice versa, that is, perpendicular to the ground.
4 。 General discussion
Thus, the power of computer simulation technology has been clearly demonstrated here, and at the same time, we can investigate complex microscopic processes and study a wide range of research materials on the surface. Our research results show that nucleation on calcite surface can slow down the introduction of various phosphonate additives. In fact, this calculation also provides a reasonable explanation for the existence of sawtooth, which has been observed by atomic force microscope that HEDP is added to the mother liquor. In addition, our research results show that the outer surface of zeolite has its distinct physical and chemical properties and is relatively large. These properties are difficult to establish by experimental methods, but the model is here. Let's discuss the superficial articles with characteristics. Although the result of adsorption is specific to an adsorbate, our model can be used to explore various adsorbents and heuristically infer the transport of reagents, products and by-products through crystals.
Express one's gratitude formally
S.a.o and L.W. would like to thank epsrc for their funding. L.W.B.S. and c.r.a.c would like to thank Professor terasaki for providing the high-resolution image analysis unit (1 1). We thank epsrc for providing local computing resources and visualization software provided by MSI.