密度泛函与分子模拟计算介孔孔径分布比较

用巨正则系综Monte Carlo模拟(GCMC)方法和密度泛函理论（ DFT）结合统计积分方程（SIE）计算了介孔材料的孔径分布.为比较这两种方法,以77 K氮气在介孔活性碳微球中的吸附数据为依据,求出其孔径分布.在GCMC模拟和DFT计算中,流体分子模型化为单点的Lerrnard-Jones球;流体分子与吸附剂材料之间的作用采用平均场理论中的10-4-3模型.在DFT方法中,自由能采用Tarazona 提出的加权近似密度泛函方法(weighted density approximation,WDA)求解.结果表明,对于孔径大于1.125 nm的介孔材料,GCMC和DFT两种方法都可以用来研究介孔材料的孔径分布;对于小于1.125 nm的介孔材料,不能用DFT方法计算孔径分布（DFT方法本身的近似产生了误差）,只能用分子模拟方法.     

Porous structure of natural and modified clinoptilolites

The evaluation of the pore-size distribution (PSD) of natural and modified mesoporous zeolites, i.e., clinoptilolites is presented. We demonstrate the SEM results showing that the pores of fracture-type from 25-50 nm to 100 nm in size between clinoptilolite grains, as well as pores between crystal aggregates up to 500 nm in size are present in the studied material. The detailed distribution of pore sizes and tortuosity factor of the above-mentioned materials are determined from the adsorption-desorption isotherms of nitrogen measured volumetrically at 77 K. To obtain the reliable pore size distribution (PSD) of the above-mentioned materials both adsorption and desorption branches of the experimental hysteresis loop are described simultaneously by recently developed corrugated pore structure model (CPSM) of Androutsopoulos and Salmas. Evaluated pore size distributions are characterized by well-defined smooth peaks placed in the region of the mesoporosity. Moreover, the mean pore diameter calculated from the classical static measurement of nitrogen adsorption at 77 K correspond very well to the pore diameters from SEM, showing the applicability of the CPSM for characterization of the porosity of natural zeolites. We conclude that classical static adsorption measurements combined with the proper modeling of the capillary condensation/evaporation phenomena are a powerful method which can be applied for pore structure characterization of natural and modified clinoptilolites.     

Adsorption Study of Methane on Activated Meso-carbon Microbeads by Density Functional Theory

A combined method of density functional theory (DFT) and statistics integral equation (SIE) for the determination of the pore size distribution (PSD) is developed based on the experimental adsorption data of nitrogen on activated mesocarbon microbead (AMCMB) at 77K. The pores of AMCMB are described as slit-shaped with PSD.Based on the PSD, methane adsorption and phase behavior are studied by the DFT method. Both nitrogen and methane molecules are modeled as Lennard-Jones spherical molecules, and the well-known Steele‘s 10-4-3 potential is used to represent the interaction between the fluid molecule and the solid wall. In order to test the combined method and the PSD model, the Intelligent Gravimetric Analyzer (IGA-003) was used to measure the adsorption of methane on the AMCMB. The DFT results are in good agreement with the experimental data. Based on these facts,we predict the adsorption amount of methane, which can reach 32.3ω at 299K and 4 MPa. The results indicate that the AMCMBs are a good candidate for adsorptive storage of methane and natural gas. In addition, the capillary condensation and hysteresis phenomenon of methane are also observed at 74.05K.     

Synthesis, characterization, and adsorption properties of nanocrystalline ZSM-5

Nanocrystalline ZSM-5 with a Si/Al ratio of 20 was synthesized using clear solutions and a hydrothermal synthesis procedure. The resulting ZSM-5 materials were characterized by powder X-ray diffraction, scanning electron microscopy (SEM), nitrogen adsorption isotherms, solid-state nuclear magnetic resonance, and toluene adsorption. A commercial ZSM-5 sample was similarly characterized for comparison with the synthesized materials. The particle sizes of the synthesized ZSM-5 samples were calculated using the measured external surface areas and were determined to be 15 and 60 nm. SEM images indicated that the ZSM-5 samples consist of agglomerated and possibly intergrown particles. Toluene adsorption measurements showed that the ZSM-5 sample with a particle size of 15 nm adsorbed approximately 50% more toluene than the other ZSM-5 samples, most likely due to the adsorption of toluene on the external surface. For the toluene adsorbed on the internal zeolite surface, approximately one toluene molecule was adsorbed per channel intersection for each of the ZSM-5 samples.     

用实验和模拟计算确定SiO2空心微球的孔径分布

用巨正则系综蒙特卡罗（GCMC）模拟方法结合统计积分方程（SIE）计算了SiO2空心微球球壳上的孔径分布（PSD）.HRTEM、XRD及氮气吸附等实验测试表明,SiO2空心微球的球壳上有无序的介孔孔道.在模拟中,基于实验数据,将SiO2空心微球模型化为具有一定孔径分布的园柱孔,流体模型化为Lennard-Jones(LJ)球,流体分子和孔壁间的相互作用采用Wang等人[10]最近提出的完全解析的势函数描述.模拟结果显示,用孔径分布拟合的吸附数据和实验吸附等温线吻合良好,说明PSD能够十分有效地表示SiO2空心微球的微孔结构.     

Immersion Calorimetry: Molecular Packing Effects in Micropores

Repeated and controlled immersion calorimetry experiments were performed to determine the specific surface area and pore‐size distribution (PSD) of a well‐characterized, microporous poly(furfuryl alcohol)‐based activated carbon. The PSD derived from nitrogen gas adsorption indicated a narrow distribution centered at 0.57±0.05 nm. Immersion into liquids of increasing molecular sizes ranging from 0.33 nm (dichloromethane) to 0.70 nm (α‐pinene) showed a decreasing enthalpy of immersion at a critical probe size (0.43–0.48 nm), followed by an increase at 0.48–0.56 nm, and a second decrease at 0.56–0.60 nm. This maximum has not been reported previously. After consideration of possible reasons for this new observation, it is concluded that the effect arises from molecular packing inside the micropores, interpreted in terms of 2D packing. The immersion enthalpy PSD was consistent with that from quenched solid density functional theory (QSDFT) analysis of the nitrogen adsorption isotherm.     

Employment of Molecularly Imprinted Polymers to High‐Throughput Screen nNOS‐PSD‐95 Interruptions: Structure and Dynamics Investigations on Monomer–Template Complexation

Molecularly imprinted polymers (MIPs) are employed to screen nNOS‐PSD‐95 (neuronal nitric oxide synthase post‐synaptic density protein‐95) interruptions. 5‐(3,5‐Dichloro‐2‐hydroxybenzylamino)‐2‐hydroxybenzoic acid (ZL006; a potential drug candidate for the treatment of stroke, depression, and pain) is employed as a template. Four kinds of functional monomers (2‐VP: 2‐vinylpyridine; 4‐VP: 4‐vinylpyridine; MMA: methyl methacrylate; and MAAM: methacrylamide) are designed, and their complexation with ZL006 in various solvents (methanol, acetonitrile, toluene, chloroform) is investigated by molecular dynamics simulations and quantum mechanics calculations. Both 4‐VP and MAAM have stronger interactions with ZL006 than those of 2‐VP and MMA. The appropriate ratio of monomer to template is 3:1. Intermolecular hydrogen bonds play a dominant role in monomer–template complexation. Ideal solvents are toluene and chloroform, and the solvation effect on monomer–template complexation is revealed. Both molecular modeling and adsorption experiments demonstrate that as‐synthesized ZL006‐MIP with 4‐VP as a monomer has better selectivity than that employing MAAM to screen for nNOS‐PSD‐95 interruptions.     

Pore size distribution analysis of selected hexagonal mesoporous silicas by grand canonical Monte Carlo simulations

We combine here a regularization procedure with individual adsorption isotherms obtained from grand canonical Monte Carlo simulations in order to obtain reliable pore size distributions. The methodology is applied to two hexagonal high-ordered silica materials: SBA-15 and PHTS, synthesized in our laboratory. Feasible pore size distributions are calculated through an adaptable procedure of deconvolution over the adsorption integral equation, with two necessary inputs: the experimental adsorption data and individual adsorption isotherms, assuming the validity of the independent pore model. The application of the deconvolution procedure implies an adequate grid size evaluation (i.e., numbers of pores and relative pressures to be considered for the inversion, or kernel size), the fulfillment of the discret Picard condition, and the appropriate choice of the regularization parameter (L-curve criteria). Assuming cylindrical geometry for both porous materials, the same set of individual adsorption isotherms generated from molecular simulations can be used to construct the kernel to obtain the PSD of SBA-15 and PHTS. The PSD robustness is measured imposing random errors over the experimental data. Excellent agreement is found between the calculated and the experimental global adsorption isotherms for both materials. Molecular simulations provide new insights into the studied systems, pointing out the need of high-resolution isotherms to describe the presence of complementary microporosity in these materials.     

Study on adsorption kinetic of aromatic hydrocarbons onto activated carbon in gaseous flow method

The adsorption behavior of benzene, toluene, o-xylene, m-xylene, and p-xylene onto activated carbon was investigated using the flow method. The removal efficiency of aromatic hydrocarbons in the gaseous phase was estimated based on the adsorption kinetic constants and the saturated amount of aromatic hydrocarbons adsorbed on the activated carbon. The saturated amount of benzene and toluene adsorbed was greater than that of xylene adsorbed because the molecular sizes of benzene and toluene are smaller than that of xylene. The adsorption kinetic constant increased in the order of xylene, toluene, and benzene. Those of the three xylene isomers were similar. These results indicated that the adsorption rate of benzene by the activated carbon was the fastest and the kinetic constant depended upon the different between the boiling point and the melting point and the molecular size of the aromatic hydrocarbons.     

Monte Carlo Simulation and Experimental Studies of CO2, CH4 and Their Mixture Capture in Porous Carbons

Adsorption of carbon dioxide and methane in porous activated carbon and carbon nanotube was studied experimentally and by Grand Canonical Monte Carlo (GCMC) simulation. A gravimetric analyzer was used to obtain the experimental data, while in the simulation we used graphitic slit pores of various pore size to model activated carbon and a bundle of graphitic cylinders arranged hexagonally to model carbon nanotube. Carbon dioxide was modeled as a 3-center-Lennard-Jones (LJ) molecule with three fixed partial charges, while methane was modeled as a single LJ molecule. We have shown that the behavior of adsorption for both activated carbon and carbon nanotube is sensitive to pore width and the crossing of isotherms is observed because of the molecular packing, which favors commensurate packing for some pore sizes. Using the adsorption data of pure methane or carbon dioxide on activated carbon, we derived its pore size distribution (PSD), which was found to be in good agreement with the PSD obtained from the analysis of nitrogen adsorption data at 77 K. This derived PSD was used to describe isotherms at other temperatures as well as isotherms of mixture of carbon dioxide and methane in activated carbon and carbon nanotube at 273 and 300 K. Good agreement between the computed and experimental isotherm data was observed, thus justifying the use of a simple adsorption model.     

Fluids in nanospaces: molecular simulation studies to find out key mechanisms for engineering

We have analyzed various phenomena that occur in nanopores, focusing on elucidating their key mechanisms, to advance the effective engineering use of nanoporous materials. As ideal experimental systems, molecular simulations can effectively provide information at the molecular level that leads to mechanistic insight. In this short review, several of our recent results are presented. The first topic is the critical point depression of Lennard-Jones fluid in silica slit pores due to finite size effects, studied by our original Monte Carlo (MC) technique. We demonstrate that the first layers of adsorbed molecules in contact with the pore walls act as a “fluid wall” and impose extra finite size effects on the fluid confined in the central portion of the pore. We next present a new kernel for pore size distribution (PSD) analysis, based entirely on molecular simulation, which consists of local isotherms for nitrogen adsorption in carbon slit pores at 77 K. The kernel is obtained by combining grand canonical Monte Carlo (GCMC) method and open pore cell MC method that was developed in the previous study. We show that overall trends of the PSDs of activated carbons calculated with our new kernel and with conventional kernel from non-local density functional theory are nearly the same; however, apparent difference can be seen between them. As the third topic, we apply a free energy analysis method with the aid of GCMC simulations to investigate the gating behavior observed in a porous coordination polymer, and propose a mechanism for the adsorption-induced structural transition based on both the theory of equilibrium and kinetics. Finally, we construct an atomistic silica pore model that mimics MCM-41, which has atomic-level surface roughness, and perform molecular simulations to understand the mechanism of capillary condensation with hysteresis. We calculate the work required for the gas–liquid transition from the simulation data, and show that the adsorption branch with hysteresis for MCM-41 arise from spontaneous capillary condensation from a metastable state.     

Adsorption of C7 hydrocarbons on biporous SBA-15 mesoporous silica

In our recent studies (Vinh-Thang, H.; Huang, Q.; Eic, M.; Trong-On, D.; Kaliaguine, S. Langmuir 2005, 21, 2051-2057; Vinh-Thang, H.; Huang, Q.; Eic, M.; Trong-On, D.; Kaliaguine, S. Stud. Surf. Sci. Catal. 2005, in press), a series of synthesized SBA-15 materials were characterized using nitrogen adsorption/desorption isotherms at 77 K and SEM images. In the present paper, four of them (MMS-1-RT, MMS-1-60, MMS-1-80, and MMS-5-80) were further investigated with regard to their equilibrium characteristics using n-heptane and toluene as sorbates by the standard gravimetric technique. SBA-15 materials proved to have a broad pore size distribution within the micropore/small-mesopore range in the walls of their main mesoporous channels. The adsorption capacities for toluene were found to be higher than for n-heptane. The isosteric heats of adsorption, estimated by the Clausius-Clapeyron equation, are also higher for toluene compared to n-heptane. They were found to depend on framework microporosity of the relevant SBA-15 samples. The isosteric heats of adsorption for all sorbates decrease with increased loading and approach the heats of evaporation of the respective sorbate. The adsorption capacities of SBA-15 samples are significantly higher than those of silicalite, i.e., the MFI zeolite silica analogue. In contrast to that, the isosteric heats of adsorption in the mesopore channels of SBA-15 were found to be much smaller. This result also suggests that SBA-15 can potentially be a good candidate for separation of C(7) hydrocarbons.     

Characterization of a delaminated clay and pillared clays by adsorption of probe molecules

Characterization of the textural and structural properties of a sodium form of a delaminated calcic montmorillonite, and of aluminium pillared materials prepared with and without amine pre-adsorption, was made using the adsorption of different probe molecules (nitrogen, toluene, methyl ethyl ketone and 1,1,1-trichloroethane). Due to the delaminated character of the prepared solids, the characterization by X-ray diffraction of the pillared materials was not possible. In this context, the adsorption of probe molecules revealed to be informative since, although the prepared materials were mainly mesoporous solids in consequence of their delaminated nature, when the amine pre-adsorption was used before the pillaring, microporosity was also formed.     

Monte carlo simulation and pore-size distribution analysis of the isosteric heat of adsorption of methane in activated carbon

The isosteric heat of adsorption of methane in an activated carbon adsorbent has been modeled by Monte Carlo simulation, using a pore-size distribution (PSD) to relate simulation results for pores of different sizes to the experimental adsorbent. Excellent fits were obtained between experimental and simulated isosteric heats of adsorption of methane in BPL activated carbon. The PSD was then used to predict the adsorption of methane and ethane in the same carbon adsorbent, with good results. The PSD derived from isosteric heat data was shown to be richer in information than PSDs obtained by the more conventional method of fitting to isotherm data.     

Fluorous metal-organic frameworks with superior adsorption and hydrophobic properties toward oil spill cleanup and hydrocarbon storage

We demonstrate that fluorous metal-organic frameworks (FMOFs) are highly hydrophobic porous materials with a high capacity and affinity to C(6)-C(8) hydrocarbons of oil components. FMOF-1 exhibits reversible adsorption with a high capacity for n-hexane, cyclohexane, benzene, toluene, and p-xylene, with no detectable water adsorption even at near 100% relative humidity, drastically outperforming activated carbon and zeolite porous materials. FMOF-2, obtained from annealing FMOF-1, shows enlarged cages and channels with double toluene adsorption vs FMOF-1 based on crystal structures. The results suggest great promise for FMOFs in applications such as removal of organic pollutants from oil spills or ambient humid air, hydrocarbon storage and transportation, water purification, etc. under practical working conditions.     

Distribution of carbon nanotube sizes from adsorption measurements and computer simulation

The method for the evaluation of the distribution of carbon nanotube sizes from the static adsorption measurements and computer simulation of nitrogen at 77 K is developed. We obtain the condensation/evaporation pressure as a function of pore size of a cylindrical carbon tube using Gauge Cell Monte Carlo Simulation (Gauge Cell MC). To obtain the analytical form of the relationships mentioned above we use Derjaguin-Broekhoff-deBoer theory. Finally, the pore size distribution (PSD) of the single-walled carbon nanohorns (SWNHs) is determined from a single nitrogen adsorption isotherm measured at 77 K. We neglect the conical part of an isolated SWNH tube and assume a structureless wall of a carbon nanotube. We find that the distribution of SWNH sizes is broad (internal pore radii varied in the range 1.0-3.6 nm with the maximum at 1.3 nm). Our method can be used for the determination of the pore size distribution of the other tubular carbon materials, like, for example, multiwalled or double-walled carbon nanotubes. Besides the applicable aspect of the current work the deep insight into the problem of capillary condensation/evaporation in confined carbon cylindrical geometry is presented. As a result, the critical pore radius in structureless single-walled carbon tubes is determined as being equal to three nitrogen collision diameters. Below that size the adsorption-desorption isotherm is reversible (i.e., supercritical in nature). We show that the classical static adsorption measurements combined with the proper modeling of the capillary condensation/evaporation phenomena is a powerful method that can be applied for the determination of the distribution of nanotube sizes.     

Silica imprinted materials containing pharmaceuticals as a template: textural aspects

Silica-based materials were prepared by the acid catalyzed sol?Cgel method using different pharmaceuticals as a template. The template molecules investigated were fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol and tetracycline. The resulting hybrid silicas underwent ultrasound extraction in the presence of several solvents and were characterized by elemental analysis, porosimetry by adsorption/desorption of nitrogen (BET method), small-angle X-ray scattering and X-ray diffraction. Drug extraction was carried out by the combination of solvent and ultra-sound. The textural characteristics of the hybrid xerogels and resulting imprinted materials were shown to be highly dependent on the molecular weight and molecular volume of the drug template. Increasing the molecular weight of the template results in a decrease in the encapsulation content of the resulting material. In the case of paracetamol and fluoxetine, the dimensions of the surface area are not sufficient to guarantee the adsorption of the smaller molecule. Instead, the shape generated through encapsulation and extraction during the production of the imprinted silica dictates the adsorption behavior.     

Water adsorption and desorption on microporous solids at elevated temperature

Summary An accurate gravimetric method was used to explore water adsorption/desorption isotherms between 105 and to 250°C for a number of synthetic and natural porous solids including controlled pore glass, activated carbon fiber monoliths, natural zeolites, pillared clay, and geothermal reservoir rocks. The main goal of this work was to evaluate water adsorption results, in particular temperature dependence of hysteresis, for relatively uniform, nano-structured solids, in the context of other state-of-the-art experimental and modeling methods including nitrogen adsorption, spectroscopy, neutron scattering, and molecular simulation. Since no single method is able to provide a complete characterization of porous materials, a combination of approaches is needed to achieve progress in understanding the fluid-solid interactions on the way to developing a predictive capability.     

Application of hydrophobic silica based aerogels and xerogels for removal of toxic organic compounds from aqueous solutions

This work is devoted to the application of hydrophobic silica based aerogels and xerogels for the removal of three toxic organic compounds from aqueous solutions. These materials were tested and characterized regarding their morphology, particle size distribution, surface area and porous structure. The equilibrium tests were carried out at different adsorbate concentrations and the experimental data were correlated by means of Langmuir and Freundlich isotherms. The equilibrium data were well described by Langmuir and Freundlich in most cases. The maximum adsorption capacity by Langmuir model was observed for the adsorption of benzene onto aerogel (192.31 mg/g), though the most promising results were obtained for toluene adsorption due to the greater adsorption energy involved. Comparing these results with other reported results, the hydrophobic silica based aerogels/xerogels were found to exhibit a remarkable performance for the removal of benzene and toluene. In addition, the regeneration of previously saturated aerogel/toluene was also investigated by using an ozonation process. The adsorption/regeneration tests with ozone oxidation showed that the aerogel might be regenerated, nevertheless the materials lost their hydrophobicity and thus different methods should be evaluated in forthcoming investigations.     

Room-temperature ammonia formation from dinitrogen on a reduced mesoporous titanium oxide surface with metallic properties

Mesoporous titanium oxide was treated with bis(toluene) titanium under nitrogen at room temperature in toluene, leading to a new blue black material possessing conductivity values of up to 10(-)(2) Omega(-)(1) cm(-)(1). XRD and nitrogen adsorption showed that the mesostructure was fully retained. Elemental analysis indicated that the material absorbed Ti from the organometallic, without any incorporation of the toluene ligand. There was also an increase of nitrogen from below the detection limit to 1.16%. XPS studies showed that the Ti framework was reduced by the organometallic and that the material had reduced nitride on the surface. There was also an emission at the Fermi level, suggesting metallic behavior. This was confirmed by variable-temperature conductivity studies, which showed a gradual decrease of resistivity with temperature. SQUID magnetometer studies revealed spin glass behavior with a degree of temperature independent paramagnetism, consistent with metallic properties. Solid-state (15)N NMR studies on materials synthesized in the presence of labeled dinitrogen showed that the source of the nitride was the reaction atmosphere. IR and (15)N NMR demonstrated that this nitrogen species was surface ammonia, suggesting that the initially formed nitride species had reacted with moisture imbedded in the walls of the mesostructure. The direct conversion of dinitrogen to ammonia is a very rare process and this work represents the first example of this process mediated by a molecular sieve.