Effect of interlayer cations on exfoliating 2D montmorillonite nanosheets with high aspect ratio: From experiment to molecular calculation

In this work, the montmorillonite (MMT) with different interlayer ions (Na⁺ and Ca²⁺) were exfoliated to prepare high aspect ratio 2D montmorillonite nanosheets (MMTNS). The effect of interlayer cations was experimentally and theoretically studied through the atomic force microscope (AFM) and molecular simulation. Na-MMT could be more easily exfoliated to monolayer with the thickness of 0–1 nm compared to Ca-MMT, and the exfoliated Na-MMTNS have higher lateral diameter than Ca-MMTNS under the same condition, leading to that the Na-MMTNS with high aspect ratio can be more readily obtained. This observation was sufficiently interpreted by molecular dynamic simulation and first principles calculations including band structure, density of states, electron density difference and electron localization function. It is indicated that the interlayer binding energy of Na-MMT was weaker while its in-plane structure was stronger compared with Ca-MMT. The strong interacting force between interlayer Ca atoms and the in-plane atoms will cause structural failure after exfoliating Ca-MMT off to 2D nanosheets. It is suggested that the interaction between the extranuclear electrons of atoms in MMT layer and interlayer cations will affect the overall intensity and apparent exfoliation properties.     

Liquid-phase exfoliation method to access cobalt oxide nanosheets in pH-neutral solutions

Two-dimensional materials have gained significant attention across the materials community due to their remarkable physical, chemical, electronic, and optical properties. With many two-dimensional materials discovered each year, investigations into their processing, scalability, and resulting properties are important to fully realize their potential in next-generation technologies. While numerous exfoliation techniques are available for a variety of two-dimensional materials, liquid-phase exfoliation techniques offer many advantages, particularly high throughput and scalability. Herein, we report a liquid-phase exfoliation method to access multilayer cobalt oxide nanosheets in pH-neutral aqueous solutions varying in size, concentration, and application. The size, thickness, and morphology of the multilayer nanosheets were confirmed using atomic force microscopy and transmission electron microscopy. Finally, selected cobalt oxide nanosheets underwent additional analysis of the crystallinity, structure, and cobalt valance.     

Gas-assisted exfoliation of boron nitride nanosheets enhancing adsorption performance

A gas exfoliation strategy for controllable preparation of boron nitride (BN) nanosheets with few-layered structure were reported. The green exfoliation process provides the BN nanosheets remarkable increment of adsorption capacities to organic contaminants, which is ascribed to better exposure of active sites originating from the larger surface area and thinner layer. Moreover, the prepared BN also exhibits outstanding recyclability.     

Graphene nanosheets production using liquid-phase exfoliation of pre-milled graphite in dimethylformamide and structural defects evaluation

The non-oxidation-based procedure is proposed for the production of high-quality graphene nanosheets using graphite as the raw materials. This research demonstrated a hybrid two-step production method by liquid-phase exfoliation (LPE) of Premilled graphite in Dimethylformamide (DMF) and compared it with the purely milled and just sonicated samples. However, a simple physical separation procedure composed of two centrifuge processes also designed for the separation of the products in each step. By this process, the exfoliated graphite, less-exfoliated ones and produced nanoparticles are separated, and the less-exfoliated ones are reused again in moderate sonication process. Two grades of graphene nanosheets and a grade of graphitic nanoparticles result at the end. The quality and the nature of defects in all graphene samples produced from LPE, wet milling of graphite and a combination of both, was investigated and discussed by Raman spectroscopy related indices. Raman spectra analysis indicates the adverse effect of sonication power on the in-plane defects formation in the graphene nanosheets which could be hindered by the reduction in power of sonication along with the pre-milling of the graphite. Also inductively-coupled plasma (ICP) and field emission scanning electron microscopy (FE-SEM) analysis used for further characterization of the milled-sonicated sample.     

插层法制备环氧树脂/蒙脱土纳米复合材料的研究

选用有机化蒙脱土,分别利用溶液插层和熔融插层法制备了环氧树脂／蒙脱土纳米复合材料,研究了上述复合体系的黏度、插层体系的固化反应性及插层方法对于相结构的影响。结果表明：插层剂对环氧树脂在低温时的反应性将产生一定的影响,但在高温反应时的影响不大;其黏度随着蒙脱土的引入而增大,并显现出触变性;采用不同的插层方法均可得到类似的复合体系的相结构。     

二维金属有机骨架材料制备技术的研究进展

金属有机骨架（MOFs）材料是一种由金属离子或团簇通过配位键与有机配体自组装形成的有机-无机杂化多孔材料。二维MOFs材料具有比表面积大、孔隙率高、孔结构可调、电子传递能力强以及活性位点直接暴露在二维平面上等独特优点,这使得它们在气体吸附、催化、储能及传感等多个领域均有很好的应用前景。随着二维材料的迅速发展,越来越多的新型二维MOFs材料被合成制备出来。结合近几年国内外研究现状,综述了界面生长法、表面活性剂辅助法和剥离法等3种二维MOFs材料的制备方法,分析了各种方法的优点和不足之处,并对其未来的发展进行了展望。今后,开发一种成本低、产率高、易于工业化生产且环境友好的二维MOFs材料制备技术将是该研究领域的重点发展方向。     

超薄氧掺杂g-C3N4纳米片的制备及其光催化性能

采用H2SO4与KMnO4为氧化剂，通过对热聚合法合成的原始石墨相氮化碳（g-C3N4）超声辅助氧化剥离，制备了超薄氧掺杂g-C3N4纳米片。基于HRTEM、XRD、AFM、XPS表征，考察了超声辅助氧化剥离对原始g-C3N4形貌、结构的影响；通过可见光催化降解刚果红分析了超薄氧掺杂g-C3N4纳米片的光催化性能；通过UV-vis-DRS、EIS、PL分析，探究了超薄氧掺杂g-C3N4纳米片光催化性能的增强机制。结果表明，对原始g-C3N4超声辅助氧化剥离6 h，可获得比表面积为58.45 cm2 g-1、厚度为1.08 nm的超薄氧掺杂g-C3N4纳米片；超薄氧掺杂g-C3N4纳米片（200 mg L-1）对刚果红（20 mg L-1）在120 min内可实现83%的降解，具有良好的光催化性能；与原始g-C3N4相比，超薄氧掺杂g-C3N4纳米片更有利于催化活性位点的暴露与光生载流子的分离传输，从而具有更好的光催化性能。     

蒙脱石预处理对制备柱撑蒙脱石的促进作用研究

在制备柱撑蒙脱石的过程中，首次提出了蒙脱石的预处理工艺，并以莱西钙基膨润土为原料，研究了预处理方法、预处理时间、料浆浓度、分散剂种类及用量对蒙脱石分散程度的影响，将钙基蒙脱石颗粒分散达到0.964 μm。经过预处理后，用钙基蒙脱石直接制备柱撑蒙脱石，并用SEM、XRD、DTA-TG和SRF等进行了表征。经300 ℃焙烧2 h后，其层间距为1.262 nm，热稳定性达588 ℃，此法省去了蒙脱石的钠化改性，简化了制备工艺。     

Facile preparation of epoxy-based composite with oriented graphite nanosheets

A facile technique was built to fabricate epoxy-based composite film with graphite nanosheets (GN) alignment. GN were coated with magnetite nanoparticles and dispersed ultrasonically in epoxy resin. The homogeneous suspension was then cast on a poly(tetrafluoroethylene) substrate and subjected to an external unidirectional magnetic field before the mixture got solidified. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the modified GN embedded in epoxy resin were aligned along the magnetic field direction, which was perpendicular to the film plane. The transmittances of the film samples, measured by UV-visible spectrometer, were improved due to the orientation of the GN fillers.     

改性剂及高密度聚乙烯插层和剥离蒙脱石的分子动力学模拟

为研究高密度聚乙烯/有机改性蒙脱石(PE-HD/OMMT)复合材料中改性剂及PE-HD对蒙脱石(MMT)插层和剥离的影响,采用分子动力学方法模拟了OMMT中不同负载量的十八烷基三甲基氯化铵阳离子(OTAC+)在MMT中的排列方式以及对MMT插层的影响.此外,搭建了PE-HD/OMMT复合材料模型,编写MS Perl脚本...     

Physicochemical driving forces behind exfoliation process of a synthetic montmorillonite in PDMS polymers

The conditions under which exfoliation of organo-montmorillonite in Poly(dimethylsiloxane) elastomers may occur were investigated via a three approaches: determination of the inter-platelet distance (as measured by WAXS), the surface energy evaluation (via inverse gas chromatography) of the polymer matrix and the clays, and measurement of heat of interaction (using a flow microcalorimeter in heptane) between polymers and the clay. The exfoliation efficiency is estimated by performing dynamic mechanical measurements. The results indicate that compatibilization and geometrical considerations are not sufficient requirements to transform clay particles into platelets. It evidences the determinant role of specific interactions between the reactive polymer end-groups and the filler surface. Polymer conformation on the clay surface and heat of adsorption associating “dispersive or London” forces and hydrogen bonding of respectively trimethyl- and hydroxyl-terminated polymer are evaluated.     

Characterization of boron nitride nanosheets synthesized by boron-ammonia reaction

Boron nitride nanosheets (BNNS) with thickness 5–11 nm were successfully produced when pure boron powder (1–2 μm) interacted with ammonia gas in chemical vapour deposition set up. Under the optimized parameters, at 1200 °C and for uninterrupted 1 h of reaction duration, 2D BNNS with thickness of ca.11 nm were synthesized. BNNS were characterized by X-ray diffraction (XRD) for crystal structure, scanning electron microscopy for dimensions and morphology, energy dispersive X-ray analysis for chemical composition and Fourier transform infrared spectroscopy for sp² BN bond detection. The thickness of BNNS determined from both XRD data (using Scherrer equation) and atomic force microscopic analysis confirmed the stated product thickness. The BNNS obtained at 1200 °C had high crystallinity, purity and yield.     

三聚阳离子表面活性剂改性蒙脱土的制备与表征

合成了一种含六氢三嗪的新型三聚季铵盐阳离子表面活性剂T16,以13C NMR和ESI-MS表征其结构,并作为有机插层剂应用于蒙脱土的改性。红外光谱(FTIR)、热重分析(TGA)表明,T16已插层到蒙脱土片层间。X射线粉末衍射(XRD)表明,T16改性后蒙脱土层间距从原来的1.486 nm增加到3.324 nm。沉降实验表明,改性后蒙脱土在苯乙烯和甲苯中形成凝胶体系,表现出很好的相容性和分散性,有利于聚合物或其单体进入蒙脱土层间形成纳米复合材料。     

PEO/蒙脱土液态热熔胶的制备与性能研究

以聚氧化乙烯(PEO)与钠基蒙脱土为主要原料,在室温时,于固体状态下充分混合30 m in,将混合好的PEO与钠基蒙脱土溶于50 mL蒸馏水中,加入一定量的VAE乳液和少量助剂,制得PEO/蒙脱土液态热熔胶。各组分的最佳质量比为水∶PEO∶VAE乳液∶钠基土=50∶1∶0.3∶0.5,热熔胶溶液经涂布烘干后,制成胶膜,对牛皮纸的T型剥离强度达到0.14 kN/m。粘接的样品,在室温水中浸泡24 h,能自然分开,无残留胶体。     

聚酰胺改性用插层蒙脱石制备和性能研究

介绍了聚酰胺改性用插层蒙脱石制备方法、性能和应用。其中将自制的非反应型插层蒙脱石用熔体挤出法制备蒙脱石／尼龙6纳米复合材料,其拉伸强度为84．41MPa、抗弯强度为115．40MPa、热变形温度(0．45MPa)为189℃。     

电化学剥离黑磷制备纳米黑磷研究进展

纳米黑磷具有可调节直接带隙、高载流子迁移率等优点,在储能、催化等领域具有广阔的应用前景。然而,纳米黑磷应用的前提在于其高效制备。在制备纳米黑磷的诸多方法中,电化学剥离法通常在温和的反应条件下进行,操作简单、高效、可控性较强,是目前最有可能实现纳米黑磷低成本、规模化的可控制备方法。根据电化学剥离过程中原料黑磷的位置,电化学剥离可分为阳极剥离、阴极剥离和电解液剥离。为系统了解电化学剥离制备纳米黑磷的研究现状与发展前景,综述了3种不同电化学剥离方式制备纳米黑磷的研究进展,同时分析了3种剥离方式的优缺点及对应的剥离机制。最后对未来电化学剥离黑磷进行了展望,并提出阴极剥离由于制备的纳米黑磷种类丰富且氧缺陷少,是一种相对较优的实现纳米黑磷高效制备的电化学剥离方式。     

有机改性蒙脱土的制备及其吸附性能研究

以信阳上天梯矿钙基膨润土为原料,经提纯钠化后用十六烷基三甲基澳化铵(CrMAB)作有机插层剂与蒙脱土层间的阳离子进行交换,制备出层间距不同的有机蒙脱土,用XRD、TG、DSC对产品进行表征.探讨了有机改性的工艺条件及所得有机蒙脱土的吸附性能.结果表明,对50 mL质量浓度为50 mg/1,的苯酚溶液,在温度35℃、吸附时间50 min、有机蒙脱土投加量1.0 g条件下,对苯酚的脱除率可达76%～78%左右.     

不同表面活性剂制备有机蒙脱土

分别利用阳离子表面活性剂十六烷基三甲基溴化铵、十六烷基三甲基氯化铵和阴离子表面活性剂十二烷基磺酸钠制备了有机蒙脱土,并通过红外光谱分析和X-射线衍射分析对其进行了表征。结果表明,有机插层剂已进入蒙脱土的层间,蒙脱土的层间距由1.24 nm分别增加到2.14,2.20和2.51 nm。沉降实验结果表明,这种有机蒙脱土在有机介质中表现出很好的分散性。     

Study of the factors influencing the exfoliation of an organically modified montmorillonite in methyl methacrylate/poly(methyl methacrylate) mixtures

The factors that affect the dispersion of exfoliated organically modified montmorillonite in a solution of poly(methyl methacrylate) in methyl methacrylate are explored. Exfoliation of montmorillonite in the solution is achieved with the assistance of ultrasound, and rheological measurements indicate a very significant increase in the viscosity, a dramatic shear thinning behavior, and a finite yield stress, all of which are direct consequences of the exfoliated state of the clay platelets. A number of factors, including the sonication power, clay loading, use of a swelling agent, and moisture content of the modified montmorillonite, are found to influence the exfoliation process. The effect of addition of a range of titanate coupling agents (LICA‐01, 12, 38, 44, and 97) on the viscosity of the nanoclay dispersions was investigated. It was found that LICA‐44 had the effect of reducing the viscosity of the exfoliated montmorillonite dispersion without apparently influencing the extent of the exfoliation. Molecular modeling, UV–visible and Fourier transform infrared spectrometry were used to investigate the possible reasons for efficacy of this LICA. The LICA appears to act through a combination of steric effects and the presence of certain charges on the organic molecule. The magnitude of the negative charges on elements of the LICA appears to influence its ability to bind to the clay and also its ability to reduce the viscosity of the nanoclay. This article indicates how the apparently conflicting requirements of achieving a highly exfoliated state and also maintaining a viscosity low enough for processing can be effectively addressed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Utilization of multiple graphene layers in fuel cells. 1. An improved technique for the exfoliation of graphene-based nanosheets from graphite

An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tulle-like translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp² domains of graphene nanosheets obtained after the reduction of graphite oxide.