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Pore structural characteristics, size exclusion properties and column performance of two mesoporous amorphous silicas and their pseudomorphically transformed MCM‐41 type derivatives
Author(s) -
BayramHahn Zöfre,
Grimes Brian A.,
Lind Anna M.,
Skudas Romas,
Unger Klaus K.,
Galarneau Anne,
Iapichella Julien,
Fajula François
Publication year - 2007
Publication title -
journal of separation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.72
H-Index - 102
eISSN - 1615-9314
pISSN - 1615-9306
DOI - 10.1002/jssc.200700227
Subject(s) - mesoporous material , amorphous solid , porosity , materials science , chemical engineering , polystyrene , size exclusion chromatography , nanopore , porous medium , chromatography , chemistry , nanotechnology , polymer , crystallography , organic chemistry , composite material , enzyme , engineering , catalysis
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 μm 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.