Pore structural characteristics, size exclusion properties and column performance of two mesoporous amorphous silicas and their pseudomorphically transformed MCM-41 type derivatives

Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Mainz, Germany.
Journal of Separation Science (Impact Factor: 2.74). 12/2007; 30(18):3089-103. DOI: 10.1002/jssc.200700227
Source: PubMed


Highly ordered mesoporous silicas such as, mobile composition of matter, MCM-41, MCM-48, and the SBA-types of materials have helped to a large extent to understand the formation mechanisms of the pore structure of adsorbents and to improve the methods of pore structural characterization. It still remains an open question whether the high order, the regularity of the pore system, and the narrow pore size distribution of the materials will lead to a substantial benefit when these materials are employed in liquid phase separation processes. MCM-41 type 10 microm beads are synthesized following the route of pseudomorphic transformation of highly porous amorphous silicas. Highly porous silicas and the pseudomorphically transformed derivatives are characterized by nitrogen sorption at 77 K and by inverse size-exclusion chromatography (ISEC) employing polystyrene standards. Applying the network model developed by Grimes, we calculated the pore connectivity n(T) of the materials. The value of n(T) varies between the percolation threshold of the lattice and values of n(T) > 10, the latter being the limiting value above which the material can be considered to be almost infinitely connected such that the ISEC behavior of the material calculated with the pore network model is the same when calculated with a parallel pore model which assumes an infinite connectivity. One should expect that the pore connectivity is reflected in the column performance, when these native and unmodified materials are packed into columns and tested with low molecular weight analytes in the Normal Phase LC mode. As found in a previous study on monolithic silicas and highly porous silicas, the slope of the plate height (HETP) - linear velocity (u) curve decreased significantly with enhanced pore connectivity of the materials. First results on the pseudomorphically transformed MCM-41 type silicas and their highly porous amorphous precursors showed that (i) the transformation did not change the pore connectivity (within the limits detectable by ISEC) from the starting material to the final product and (ii) the slope of the HETP versus u curve for dibutylphtalate did not change significantly after the pseudomorphic transformation.

Download full-text


Available from: Anne Galarneau, Oct 07, 2015
36 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: A set of chromatographic materials for bioseparation were characterised by various methods. Both commercial materials and new supports presenting various levels of rigidity were analysed. The methods included size-exclusion and capillary phenomena based techniques. Both batch exclusion and inverse size-exclusion chromatography were used. Gas adsorption, mercury porosimetry and thermoporometry were applied as well as a new method based on water desorption starting from the saturated state. When the rigidity of adsorbents is high enough, the agreement is reasonable between the values of the structural parameters that were determined (surface area, porosity, and pore size) by various methods. Nevertheless, a part of macroporosity may not be evidenced by inverse size-exclusion chromatography whereas it is visible by batch exclusion and the other methods. When the rigidity decreases, for example with soft swelling gels, where standard nitrogen adsorption or mercury porosimetry are no more reliable, two main situations are encountered: either the methods based on capillary phenomena (thermoporometry or water desorption) overestimate the pore size with an amplitude that depends on the method, or in some cases it is possible to distinguish water involved in the swelling of pore walls from that involved in pore filling by capillary condensation.
    Journal of Chromatography A 09/2009; 1216(41):6906-16. DOI:10.1016/j.chroma.2009.07.075 · 4.17 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The mass transfer kinetics of toluene and polystyrenes (of which the M(w) varies from 162 to 1.85 x 10(6) g mol(-1)) through columns filled with silica porous spheres were studied by inverse size exclusion chromatography. The mass transfer parameters were measured by modeling the band broadening of the chromatograms. The experimental height equivalent to a theoretical plate (HETP) data were analyzed using the general rate model in order to determine the effective diffusion coefficient in porous particles as a function of molecular size. The bulk molecular diffusion coefficients were experimentally determined by dynamic light scattering (DLS) and Taylor dispersion analysis (TDA). The topological tortuosity of the porous particles was determined by electrical measurements. The effective molecular diffusion coefficient through porous particles was modeled taking into account exclusion, friction, and at last tortuosity effects. A phenomenological law is proposed to model the evolution of the tortuosity experienced by a molecule in a porous particle as a function of its size. It gives a good prediction of the evolution of effective diffusion coefficient with the molecule/pore size ratio.
    Analytical Chemistry 02/2010; 82(7):2668-79. DOI:10.1021/ac902858b · 5.64 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The efficacy of nanoporous inorganic MCM-41 membrane as a new separator material for electrochemical cell has been investigated. The hexagonally ordered, narrow pore structure of MCM-41 membrane serves as ion exchange channels between the anolyte and catholyte of an electrochemical cell. Besides, it also acts as the electrolyte matrix or reservoir due to the hydrophilic nature of the as-synthesized MCM-41 and along with the high surface area and pore volume density characteristics. MCM-41 membrane has been employed as separator in zinc–air electrochemical system. MCM-41 was synthesized on the zinc substrate by dip-coating method and its thickness was ca. 5μm. The Zn/MCM-41/air cell was able to produce a maximum power density of 32mWcm−2 and possessed a volumetric energy density of 300Whl−1, which are considered comparable to the published product datasheet of commercial zinc–air button cells of equivalent size.
    Fuel and Energy Abstracts 02/2011; 367(1):152-157. DOI:10.1016/j.memsci.2010.10.061
Show more