Characterization Of Nanoporous Materials Research Articles

Characterization of Nanoporous Materials.

Detailed analysis of textural properties, e.g., pore size and connectivity, of nanoporous materials is essential to identify correlations of these properties with the performance of gas storage, separation, and catalysis processes. The advances in developing nanoporous materials with uniform, tailor-made pore structures, including the introduction of hierarchical pore systems, offer huge potential for these applications. Within this context, major progress has been made in understanding the adsorption and phase behavior of confined fluids and consequently in physisorption characterization. This enables reliable pore size, volume, and network connectivity analysis using advanced, high-resolution experimental protocols coupled with advanced methods based on statistical mechanics, such as methods based on density functional theory and molecular simulation. If macro-pores are present, a combination of adsorption and mercury porosimetry can be useful. Hence, some important recent advances in understanding the mercury intrusion/extrusion mechanism are discussed. Additionally, some promising complementary techniques for characterization of porous materials immersed in a liquid phase are introduced.

Nanoporous Alumina Fabrication: A Short Review

Aims: Since the 19th century, there has been considerable research effort in the fabrication, and characterization of nanoporous materials. These nanoporous materials are highly scientifically and technologically relevant as a result of the surface openings that have controllable dimensions at both the micrometer and nanometer scales. Nanoporous alumina foil has been a template of choice in various applications due to its simplicity and ease of fabrication. Keywords: Anodic aluminum oxide, anodization, barrier oxide, electrolytes, nanoporous, mechanical property.

Characterization of Nanoporous Materials with Atom Probe Tomography.

A method to characterize open-cell nanoporous materials with atom probe tomography (APT) has been developed. For this, open-cell nanoporous gold with pore diameters of around 50 nm was used as a model system, and filled by electron beam-induced deposition (EBID) to obtain a compact material. Two different EBID precursors were successfully tested-dicobalt octacarbonyl [Co2(CO)8] and diiron nonacarbonyl [Fe2(CO)9]. Penetration and filling depth are sufficient for focused ion beam-based APT sample preparation. With this approach, stable APT analysis of the nanoporous material can be performed. Reconstruction reveals the composition of the deposited precursor and the nanoporous material, as well as chemical information of the interfaces between them. Thus, it is shown that, using an appropriate EBID process, local chemical information in three dimensions with sub-nanometer resolution can be obtained from nanoporous materials using APT.

Importance of the αs-plot Method in the Characterization of Nanoporous Materials

Fil: Villarroel Rocha, Jhonny. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico San Luis. Instituto de Fisica Aplicada; Argentina

Characterization of nanoporous monoliths using nitrogen adsorption and positronium annihilation lifetime spectroscopy

The characterization of nanoporous materials is essential for their application as model systems. In this study, nanoporous glass monoliths with a pore diameter below 10 nm were used as model system to compare the pore size analysis performed via nitrogen adsorption and positronium annihilation lifetime spectroscopy (PALS). For determination of pore size distribution via nitrogen sorption, B.J.H. method and DFT method were used. By applying positronium annihilation lifetime spectroscopy as independent characterization technique, DFT method was validated to provide more realistic results for the pore size distribution of the model material.

Simple synthesis and characterization of nanoporous materials from talc

AbstractSynthetic siliceous mesoporous materials are of great value in many different applications, including nanotechnology, biotechnology, information technology, and medical fields, but historically the resource materials used in their synthesis have been expensive. Recent efforts have focused on indirect synthesis methods which utilize less expensive silicate minerals as a resource material. The purpose of the present study was to investigate talc, a natural silicate mineral, as one such resource. It was used as raw material to prepare two advanced materials: porous silica (PS) and ordered mesoporous silica (MCM-41). The PS, with a specific surface area of 260 m2/g and bimodal pore-size distribution of 1.2 nm and 3.7 nm, was prepared by grinding and subsequent acid leaching. The MCM-41, with a large surface area of 974 m2/g and a narrow pore-size distribution of 2.8 nm, was obtained using a surfactant, cetyltrimethylammonium bromide (CTAB), by hydrothermal treatment using the as-prepared PS as a source of Si. The two resultant materials were characterized by small angle X-ray diffraction (SAXRD) and wide-angle X-ray diffraction (WAXRD), high-resolution transmission electron microscopy (HRTEM), solid-state magic-angle-spinning nuclear magnetic resonance (MAS NMR), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption-desorption measurements. Based on these measurements, possible processes of transformation of PS from talc, upon acid treatment, and the formation of MCM-41 were investigated systemically. Acid leaching induced the transformation of a rigid layered structure to a nearly amorphous one, with micropores formed by a residual layered structure and mesopores formed from a condensed framework. The MCM-41 was a mixture of silanol groups (Si(SiO)3(OH)) and a condensed Q4 framework structure (Si(SiO)4), with a small amount of remaining Q3 layered structure (Si(SiO)3OMg). The increased Q4/Q3 value confirmed greater polymerization of MCM-41 than of PS. At the low CTAB concentration used (2 wt.%), the highly charged silicate species controlled the surfactant geometry. Charge-density matching, together with the degree of polymerization of the silicates, determined the resultant mesophase.

Development Of Novel Biomimetic Membrane Designs For Separation And Biosensor Applications

Integral membrane proteins have a variety of functions e.g. as channels, transporters or receptors. In order to study transmembrane proteins under controlled circumstances they must be embedded into a matrix mimicking their in vivo environment. There has been a growing interest in developing a biomimetic platform technology for biosensor and separation applications.Current design criteria for free-spanning artificial membrane platform technologies are low leak membrane sealing, membrane stabilities above 1 day, absolute reproducibility, a scaffold consisting of multiple functional units, enablement of reconstitution of membrane spanning molecules, be robust for transportation and cost effective. For mass transfer flow and high throughput screening applications additional design criteria are required. These include a high perforation level of the membrane scaffold material, the functional membrane units are arranged in arrays to facilitate a screening platform (e.g. for microplate readers) and the artificial membrane platform is scalable to met various requirements for the individual technical applications.Recently, we have developed a model biomimetic membrane design and an automation technique for establishing multiple black lipid membranes (BLMs) in arrays of micro structured ethylene tetrafluoroethylene films, and supported by a micro porous material. Success rates for establishment of supported BLMs across multiple aperture arrays were above 95%.Currently, work is focused on characterization of nanoporous materials and surface modifications together with different lipid compositions. Furthermore, to develop methods for the encapsulation of established membranes and for the controlled incorporation and distribution of transmembrane proteins into such encapsulated biomimetic membranes. Combined this work aims to meet all of the current design criteria for free-spanning artificial membrane platforms.

On the characterization of nanoporous materials by means of empirical and intrinsic transport coefficients

Nanoporous materials need to be classified and characterized both for scientific research and applications in industrial production and environmental protection. Nanoporous materials with simple geometries (e.g. channel pores, slit pores) can be characterized by means of transport coefficients such as diffusion and viscosity coefficients of the fluid and gas flows through these materials. To this end, empirical transport coefficients defined by the Einstein relation and the Green–Kubo formula are frequently used. In the present study, it will be shown that the applicability of empirical transport coefficients is limited because of the confinement of fluid molecules in nanopores and the direct and indirect molecule–molecule interactions. It will be advocated that transport properties of nanoporous materials are better described by transport coefficients different from empirical transport coefficients such as intrinsic transport coefficient defined by Brownian dynamics models.

Physisorption Hysteresis Loops and the Characterization of Nanoporous Materials

The classification of adsorption hysteresis loops recommended by the IUPAC in 1984 was based on experimental observations and the application of classical principles of pore filling (notably the use of the Kelvin equation for mesopore analysis). Recent molecular simulation and density functional (DFT) studies of the physisorption of gases by model pore structures have greatly improved our understanding of the mechanisms of hysteresis and it is therefore timely to revisit the IUPAC recommendations. In this review, we conclude that there is no immediate need to change the IUPAC classification of physisorption isotherms and hysteresis loops. However, in the light of recent advances, we are able to offer a revised checklist for the analysis of nitrogen isotherms on nanoporous solids: this includes a carefully regulated application of DFT in place of a classical procedure such as the well-known Barrett-Joyner-Halenda (BJH) method.

Characterization of nanoporous materials from adsorption and desorption isotherms

We present a consistent method for calculation of pore size distributions in nanoporous materials from adsorption and desorption isotherms, which form the hysteresis loop H1 by the IUPAC classification. The method is based on the nonlocal density functional theory (NLDFT) of capillary condensation hysteresis in cylindrical pores. It is implemented for the nitrogen and argon sorption at their boiling temperatures. Using examples of MCM-41 type and SBA-15 siliceous materials, it is shown that the method gives the consonant pore size distributions calculated independently from the adsorption and desorption branches of the sorption isotherm. The pore size distributions, pore volumes and specific surface areas calculated from nitrogen and argon data are consistent. In the case of SBA-15 materials, the method evaluates also the amount of microporosity. The results of the NLDFT method are in agreement with independent estimates of pore sizes in regular nanoporous materials.