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1.
Anisotropic self-diffusion of fluorinated poly(methacrylate) in metal-organic frameworks assessed with molecular dynamics simulation
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Utilizing the periodically structured metal–organic framework(MOF) as the reaction vessel is a promising technique to achieve the aligned polymer molecular chains, where the diffusion procedure of the polymer monomer inside MOF is one of the key mechanisms. To investigate the diffusion mechanism of fluorinated polymer monomers in MOFs, in this paper the molecular dynamics simulations combined with the density functional theory and the Monte Carlo method are used and the all-atom models of TFMA(trifluoroethyl methacrylate) monomer and two types of MOFs, [Zn_2(BDC)_2(TED)]n and[Zn_2(BPDC)_2(TED)]n, are established. The diffusion behaviors of TFMA monomer in these two MOFs are simulated and the main influencing factors are analyzed. The obtained results are as follows. First, the electrostatic interactions between TFMA monomers and MOFs cause the monomers to concentrate in the MOF channel, which slows down the monomer diffusion. Second, the anisotropic shape of the one-dimensional MOF channel leads to different diffusion speeds of monomers in different directions. Third, MOF with a larger pore diameter due to a longer organic ligand, [Zn_2(BPDC)_2(TED)]n in this paper, facilitates the diffusion of monomers in the MOF channel. Finally, as the number of monomers increases, the self-diffusion coefficient is reduced by the steric effect. 相似文献
2.
Tsung‐Han Yu Chin‐Hsian Ho Cheng‐You Wu Ching‐Hsuan Chien Chia‐Her Lin Szetsen Lee 《Journal of Raman spectroscopy : JRS》2013,44(11):1506-1511
We report the direct observation of surface‐enhanced Raman scattering (SERS) effect using metal–organic frameworks (MOFs) as substrates. Without the aid of any metal colloids or enhancing agents, the SERS signals of methyl orange (MO) adsorbed in MOFs were observed and even remained active if the organic linkers in MOFs were completely removed by high temperature and O2 plasma treatments. It implies that the SERS active site is at the metal oxide clusters. The ultraviolet‐visible spectra of MO, MOFs, and MO–MOF complexes show that absorption peaks are far from laser excitation line. Thus, conventional resonance enhancement effect should be ruled out, and charge‐transfer mechanism is the most likely scenario responsible for the observed SERS effect. Density functional theory (DFT) was used to interpret the chemical enhancement mechanism and the adsorption orientation‐dependent SERS spectra in our observation. The preferred adsorption orientations calculated by DFT method are consistent with the observed SERS results. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
3.
Xumiao Zhou Zejun Su Houyang Chen Xingqing Xiao Yuanhang Qin 《Molecular physics》2018,116(15-16):2095-2107
ABSTRACTIn the last three decades, the air pollution is the main problem to affect human health and the environment in China and its contaminants include SO2, NH3, H2S, NO2, NO and CO. In this work, we employed grand canonical Monte Carlo simulations to investigate the adsorption capability of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) for these toxic gases. Eighty-nine MOFs and COFs were studied, and top-10 adsorption materials were screened for each toxic gas at room temperature. Dependence of the adsorption performance on the geometry and constructed element of MOFs/COFs was determined and the adsorption conditions were optimised. The open metal sites have mainly influenced the adsorption of NH3, H2S, NO2 and NO. Especially, the X-DOBDC and XMOF-74 (X = Mg, Co, Ni, Zn) series of materials containing open metal sites are all best performance for adsorption of NH3 to illustrate the importance of electrostatic interaction. Our simulation results also showed that ZnBDC and IRMOF-13 are good candidates to capture the toxic gases NH3, H2S, NO2, NO and CO. This work provides important insights in screening MOF and COF materials with satisfactory performance for toxic gas removal. 相似文献
4.
Two-dimensional (2D) metal–organic framework (MOF) nanosheets have recently received extensive attention due to their ultra-thin thickness, large specific surface area, chemical and functional designability. In this study, an unconventional method using surface acoustic wave (SAW) technology is proposed to exfoliate large quantities and uniform layers of 2D MOF-Zn2(bim)4 nanosheets in a microfluidic system. We successfully demonstrated that the thickness of 2D MOF is effectively and accurately controlled by optimizing the SAW parameters. The mechanisms for the efficient exfoliation of 2D MOF nanosheets is attributed to both the electric and acoustic fields generated by the SAWs in the liquid. The electric field ionizes the methanol to produce H+ ions, which intercalate Zn2(bim)4 sheets and weaken the interlayer bonding, and the strong shear force generated by SAWs separates the MOF sheets. A yield of 66% for monolayer MOFs with a maximum size of 3.5 μm is achieved under the combined effect of electric and acoustic fields. This fast, low-energy exfoliation platform has the potential to provide a simple and scalable microfluidic exfoliation method for production of large-area and quantities of 2D MOFs. 相似文献
5.
Zhaodong Liu Mingguang Yao Ye Yuan Shuanglong Chen Ran Liu Shuangchen Lu Bo Zou Tian Cui Bingbing Liu 《Journal of Raman spectroscopy : JRS》2015,46(4):413-417
Raman spectroscopy of the one‐dimensional atomic or molecular chains, which are the attractive building blocks of advanced nanoscale materials, is crucial in understanding the physical properties of the one‐dimensional atomic or molecular chains. Here, we introduce the bromine into the one‐dimensional channels of AlPO4‐5 single crystals through a physical vapor diffusion method. Raman spectroscopy indicates that the confined bromine structures mainly exist as (Br2)n chains, individual Br2 molecules, and a small amount of Br3− chains inside the channels of AlPO4‐5 single crystals. Polarized Raman spectra demonstrate that the bromine molecular chains are approximately parallel to the channel direction of AlPO4‐5 single crystals. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
P. S. Timashev L. I. Krotova D. A. Lemenovskii V. K. Popov 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(7):1158-1163
A method for producing finely dispersed powders of methyl methacrylate (MMA)-styrene copolymer by radical polymerization in a supercritical carbon dioxide medium (SC-CO2) was proposed, studied, and experimentally implemented. The dispersing agent (surfactant), which made it possible to obtain nearly monodisperse size distribution of polymer particles, was poly(dimethylsiloxane methacrylate), a SC-CO2-soluble substance. The copolymer, synthesized with a molecular mass of M w ~ 36000 in the form of spherical particles with a characteristic size of ~1 μm, exhibited a higher thermal stability as compared to poly(methyl methacrylate) with a similar molecular mass. Varying the percentage ratio between MMA and styrene monomers, it was possible effectively control the integral hydrophobicity and physicomechanical characteristics of the methacrylate-styrene copolymer. 相似文献
7.
SMA-g-MPEG comb-like polymer is first employed as the dispersant of Al2O3 suspensions in this paper. The comb-like polymer has anionic polycarboxylate backbone, which makes the polymer easily absorbed on the cationic surface of Al2O3 particles; on the other hand, the comb-like polymer has hydrophilic MPEG side chains, which extend into the solution to provide steric repulsion after the comb-like polymer is absorbed on the surface of Al2O3 particles. The adsorption behavior, zeta potential, apparent viscosity, granularity and TEM images of the Al2O3 suspensions using SMA-g-MPEG as dispersant are investigated. The addition of SMA-g-MPEG improves the dispersibility and decreases the apparent viscosity of the Al2O3 suspension observably. The impacts of the length of side chains on the dispersion of Al2O3 suspensions are particularly discussed. The adsorbed molecular number of the dispersant decreased by increasing the length of side chains. The zeta potential of Al2O3 suspension is more negative by using comb-like polymer with shorter side chains. Based on the steric repulsion and adsorbed molecular number, SMA-g-MPEG with moderate length of side chain is found to have the best dispersibility for Al2O3 suspension. 相似文献
8.
Li‐Ping Zhang Chun‐E Mo Yan‐Ping Huang Zhao‐Sheng Liu 《Particle & Particle Systems Characterization》2019,36(1)
A novel molecularly imprinted polymer (MIP) coated metal organic framework (MOF) containing a liquid crystalline (LC) monomer is successfully synthesized for use in drug delivery systems. In this study, [Cu3(BTC)2(H2O)3] n (HKUST‐1) is chosen as the MOF support owing to its large pore volume, good diffusion, and thermostability. 4‐Methyl phenyl dicyclohexyl ethylene (MPDE) is used as a LC monomer to increase the solvent‐responsive floating of the composite. The preparation conditions of HKUST‐1@LC‐MIP with capecitabine (CAPE) as a template, including the types of functional monomer, the ratio between template and functional monomer, as well as the content of MPDE, are investigated. Characterizations of the HKUST‐1@LC‐MIP are explored using scanning electron microscopy and transmission electron microscope images, Fourier transform infrared spectroscopy, thermal gravimetric analysis, X‐ray diffraction, and nitrogen adsorption. Compared to the HKUST‐1, the HKUST‐1@LC‐MIP shows better stability in aqueous solution. In vitro release studies of CAPE of HKUST‐1@LC‐MIP show zero‐order release of profiles at the loaded concentration of 500 µg mL?1. From in vivo pharmacokinetic studies, the HKUST‐1@LC‐MIP displays higher relative bioavailability. It turns out that the HKUST‐1@LC‐MIP possesses the properties of controlled release and has the potentials for oral administration. 相似文献
9.
Qi Yang Fubing Yao Yu Zhong Fei Chen Xiaoyu Shu Jian Sun Li He Bo Wu Kunjie Hou Dongbo Wang Xiaoming Li 《Particle & Particle Systems Characterization》2019,36(6)
Heterogeneous palladium (Pd)‐based catalysts are extensively applied to improve the catalytic performance and/or expand the reaction scope in many catalytic processes, involving the cross‐coupling, hydrogenation, reduction, and oxidation reactions. Among them, metal–organic framework (MOF)‐supported Pd nanoparticles (Pd NPs) are becoming the most popular one for their excellent catalytic performance and reusable property. To motivate the development of this technology, the applications of MOF‐supported Pd NPs (Pd NPs/MOFs) in heterogeneous catalysis are critically summarized herein, including the hydrogenation reduction of nitro‐ and polyunsaturated compounds, synthesis of carbon–carbon (C? C) bonds compounds, chromium (Cr(VI)) reduction, dehalogenation, alcohol oxidation, CO2 conversion, and CO oxidation. The influences of base, solvents, electron character of substitutes, and type of halogen on the catalytic performance are comprehensively discussed. Finally, the application prospects of Pd NPs/MOFs and existing shortcomings in the catalytic field are proposed. 相似文献
10.
Shuanglong Chen Mingguang Yao Ye Yuan Fengxian Ma Zhaodong Liu Bing Li Ran Liu Quanjun Li Bo Zou Tian Cui Bingbing Liu 《Journal of Raman spectroscopy : JRS》2015,46(4):400-405
Raman spectra of iodine species confined in one‐dimensional elliptical channels of AlPO4‐11 (AEL) crystals have been studied from room temperature down to −196 °C. As temperature decreases, thermal fluctuations of individual iodine molecules confined in AEL channels are slowed down and they prefer to rotate to channel axis direction, which increases the population of iodine molecules along channel axis (i.e., lying molecules and chains). Such temperature‐driven orientation transformation of iodine molecules is found to be reversible upon heating up to room temperature. The experimental observations are in good agreement with our theoretical simulations by molecular dynamics on low density iodine‐filled AEL crystals. We thus provide a new way to modulate the orientation of iodine molecules in nanochannels, which may have implications in low‐temperature‐sensitive nanoscale devices. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
11.
Gayatri Kumari N. R. Patil Venkata Srinu Bhadram Ritesh Haldar Satyanarayana Bonakala Tapas Kumar Maji Chandrabhas Narayana 《Journal of Raman spectroscopy : JRS》2016,47(2):149-155
Interpenetrating metal organic frameworks are interesting functional materials exhibiting exceptional framework properties. Uptake or exclusion of guest molecules can induce sliding in the framework making it porous or non‐porous. To understand this dynamic nature and how framework interaction changes during sliding, metal organic framework (MOF) 508 {Zn(BDC)( 4,4′‐Bipy)0.5 · DMF(H2O)0.5} was selected for study. We have investigated structural transformation in MOF‐508 under variable conditions of temperature, pressure and gas loading using Raman spectroscopy and substantiated it with IR studies and density functional theory (DFT) calculations. Conformational changes in the organic linkers leading to the sliding of the framework result in changes in Raman spectra. These changes in the organic linkers are measured as a function of high pressure and low temperature, suggesting that the dynamism in MOF‐508 framework is driven by ligand conformation change and inter‐linker interactions. The presence of Raman signatures of adsorbed CO2 and its librational mode at 149 cm−1 suggests cooperative adsorption of CO2 in the MOF‐508 framework, which is also confirmed from DFT calculations that give a binding energy of 34 kJ/mol. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
12.
The present work is devoted to a study of the molecular mechanisms of the crystallization of polymer chains induced by graphene by using molecular dynamics (MD) simulations. From the atomic configuration translation, the number distri- bution of the atoms, and the order parameter S, the crystallization process can be summarized in two steps, the adsorption and the orientation. By analyzing the diffusion properties of the polymer chains, we find that a graphene substrate has a great adsorption for the polymer molecules and the polymer molecules need more time to adjust their configurations. Therefore, the adsorption step and the orientation step are highly cooperative. 相似文献
13.
Matthias Mendt Bettina Jee Dieter Himsl Lutz Moschkowitz Tim Ahnfeldt Norbert Stock Martin Hartmann Andreas Pöppl 《Applied magnetic resonance》2014,45(3):269-285
Continuous-wave electron paramagnetic resonance spectroscopy is applied to explore the adsorption of carbon dioxide (CO2) over the metal organic framework (MOF) MIL-53. Therefore, paramagnetic Cr3+ ions, which replace a small amount of the bulk Al3+ ions in MIL-53(Al/Cr), are used as magnetically active probes. CO2 was adsorbed on samples of MIL-53(Al/Cr) at equilibrium pressures between 0 and 2.5 bar. The transformation from the large pore phase to the narrow pore phase of MIL-53 was observed by electron paramagnetic resonance spectroscopy at small CO2 pressures between 0.2 and 0.4 bar, which is in accordance with adsorption results reported in literature. By analyzing the electron paramagnetic resonance signal intensities of the corresponding Cr3+ probes, the ratio between the amount of the narrow pore phase and the large pore phase before and after this phase transformation was quantified. A small fraction of the large pore phase remains even after this phase transition. CO2 adsorption at 77 K indicates the occurrence of the transformation of this MOF from a narrow pore phase to a large pore phase triggered by the adsorbed CO2. Similar observations were already made using powder X-ray diffraction or infrared spectroscopy. But in contrast to these methods electron paramagnetic resonance spectroscopy on Cr3+ seems to be very sensitive not only to large differences between crystallographic conformations like large pores and narrow pores but also to different amounts and configurations of CO2 molecules trapped in the same structural phase of MIL-53, taking advantage of the high sensitivity of the fine structure interaction of Cr3+. 相似文献
14.
What is believed to be the first evidence of an all-optical orientation of a highly transparent polymer is presented. The samples are bulk rods of poly(methyl methacrylate) grafted with paranitroaniline (PNA) obtained by use of copolymerization of methyl methacrylate (MMA) monomers mixed with grafted MMA-PNA monomers. Bulk samples were obtained after molding and polishing of the copolymer with standard techniques. Experiments show that the photoinduced second-order(1) susceptibility chi((2)) may occur through molecular reorientation following selective polar excitation of the nonlinear chromophores by simultaneous two- and three-photon absorption on the same electronic level. 相似文献
15.
利用三维朗之万动力学模拟研究了多价态高分子链在受体平面上的吸附行为。其在受体平面上的吸附具有超选择性,随着高分子链上配体浓度的增大,发生超选择性吸附时的平面受体浓度范围变窄;而超选择性吸附最显著时的平面受体浓度,即最佳平面受体浓度随着链上配体浓度的增大而减小。对处于吸附态的多价态高分子链的构象性质进行了系统地研究,发现链的平衡回转半径Rg及其水平分量Rg},随着平面受体浓度的增大都存在极大值。其平衡回转半径Rg与其链长N间的标度指数表明当平面受体浓度的增大时,处于吸附态的链构象介于二维链构象和三维链构象之间;随着平面受体浓度的进一步增大,吸附在平面上的多价态高分子链发生轻微的塌缩 相似文献
16.
本文应用分子理论,研究中性(A)/聚电解质(B)高分子混合刷对蛋白质的吸附/解吸附特性.理论模型考虑蛋白质与中性高分子A的排斥、以及与聚电解质高分子B的静电吸引.研究发现,在pH=4~6、中性高分子A处于弱水合状态时,混合刷中A高分子链塌缩,B聚电解质链溶胀.由于蛋白质和B聚电解质链间的静电吸引,导致高分子混合刷对蛋白质的吸附.当A高分子水合性增强时,A高分子链溶胀,B聚电解质链塌缩.由于蛋白质与A高分子链间的排斥作用增强,与B聚电解质链间的静电吸引减弱,混合刷对蛋白质解吸附. 相似文献
17.
In order to explore the in uence of modification sites of functional groups on landfill gas (CO2/CH4) separation performance of metal-organic frameworks (MOFs), six types of organic linkers and three types of functional groups (i.e. -F, -NH2, -CH3) were used to construct 36 MOFs of pcu topology based on copper paddlewheel. Grand canonical Monte Carlo simulations were performed in this work to evaluate the separation performance of MOFs at low (vacuum swing adsorption) and high (pressure swing adsorption) pressures, respectively. Simulation results demonstrated that CO2 working capacity of the unfunctionalized MOFs generally exhibits pore-size dependence at 1 bar, which increases with the decrease in pore sizes. It was also found that -NH2 functionalized MOFs exhibit the highest CO2 uptake due to the enhanced Coulombic interactions between the polar -NH2 groups and the quadrupole moment of CO2 molecules, which is followed by -CH3 and -F functionalized ones. Moreover, positioning the functional groups -NH2 and -CH3 at sites far from the metal node (site b) exhibits more significant enhancement on CO2/CH4 separation performance compared to that adjacent to the metal node (site a). 相似文献
18.
The adsorption of cationic and neutral R6G molecules on Au nanoparticles was elucidated by surface enhanced Raman scattering (SERS). The steric hindrance at hydroethyl amino (‐N(H)Et) groups in R6G was evidenced by the observation that R6G+ adsorb on as‐prepared gold nanoparticles (AuNPs) only with electrostatic forces, in contrast to the electrostatic and chemical adsorption of R123+ with dihydro amino (‐NH2) groups on as‐prepared AuNPs. Large steric hindrance at the amino groups in R6G yielded saturated coverage of 700 molecules/AuNP for R6G+ significantly fewer than 1000 molecules/AuNP for R123+. In addition, neutral R6G0 on AuNPs showed markedly enhanced peaks at 1200–1600 cm−1, which were not observed in Raman spectra of R6G0 in bulk solution, and also in SERS of R6G+ on AuNPs. These bands are attributed to vibrational modes of an outer phenyl ring and ethyl amino groups, which are vertical to a xanthene plane, on the basis of theoretical analysis of molecular vibrations. Thus, Raman scattering of these bands is enhanced under an inclined orientation of R6G0 molecules chemisorbed on AuNPs via lone pair electrons at amino groups. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
Mehdi Shakourian‐Fard Alireza Fattahi Zahra Jamshidi 《Journal of Physical Organic Chemistry》2012,25(2):153-161
Binding of Mg2+, Ca2+, Zn2+, and Cu+ metal ions with 2′‐deoxythymidine (dT) nucleoside was studied using a density functional theory method and a 6‐311++G(d,p) basis set. This work demonstrated that the interaction of dT with these cations is tri‐coordinated η (O2, O4′, O5′). Among the four types of cations, Zn2+ cation exhibited the most tendency to interact with the dT. Cations via their interaction with dT can affect the N‐glycosidic bond length, the values of pseudorotation of the sugar ring, the orientation of the base unit with respect to the sugar ring, and the acidity of the O5′H, O3′H, and N3H groups in the dT nucleoside. Natural bond orbital analysis was performed to calculate the charge transfer and natural population analysis of the complexes. Quantum theory of atoms in molecules was also applied to determine the nature of interactions. It was shown that in dT–Mg2+ and dT–Ca2+ complexes, the bonds are electrostatic (closed‐shell) interactions, although they are partially covalent and partially electrostatic interactions in dT–Zn2+ and dT–Cu+ complexes. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
20.
Yang Yong Yongxiao Bai Yanfeng Li Lei Lin Yanjun Cui Chungu Xia 《Journal of magnetism and magnetic materials》2008
Functionalized superparamagnetic particles were prepared by graft polymerization of glycidyl methacrylate and methacryloxyethyl trimethyl ammonium chloride onto the surface of modified-Fe3O4 nanoparticles. The resultant particles were characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. The results indicate that the polymer chains had been effectively grafted onto the surface of Fe3O4 nanoparticles. The functionalized particles remained dispersive and superparamagnetic. Lipase was immobilized on the magnetic particles under mild conditions by electrostatic adsorption and covalent binding with the activity recovery up to 70.4%. The immobilized lipase had better thermal stability compared to free lipase. 相似文献