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Download fileGlucan Adsorption on Mesoporous Carbon Nanoparticles: Effect of Chain Length and Internal Surface
journal contribution
posted on 30.10.2012, 00:00 authored by Po-Wen Chung, Alexandre Charmot, Oz M. Gazit, Alexander KatzThe adsorption of cellulose-derived long-chain (longer
than ten
glucose repeat units on size) glucans onto carbon-based acid catalysts
for hydrolysis has long been hypothesized; however, to date, there
is no information on whether such adsorption can occur and how glucan
chain length influences adsorption. Herein, in this manuscript, we
first describe how glucan chain length influences adsorption energetics,
and use this to understand the adsorption of long-chain glucans onto
mesoporous carbon nanoparticles (MCN) from a concentrated acid solution,
and the effect of mesoporosity on this process. Our results conclusively
demonstrate that mesoporous carbon nanoparticle (MCN) materials adsorb
long-chain glucans from concentrated acid hydrolyzate in amounts of
up to 30% by mass (303 mg/g of MCN), in a manner that causes preferential
adsorption of longer-chain glucans of up to 40 glucose repeat units
and, quite unexpectedly, fast adsorption equilibration times of less
than 4 min. In contrast, graphite-type carbon nanopowders (CNP) that
lack internal mesoporosity adsorb glucans in amounts less than 1%
by mass (7.7 mg/g of CNP), under similar conditions. This inefficiency
of glucan adsorption on CNP might be attributed to the lack of internal
mesoporosity, since the CNP actually possesses greater external surface
area relative to MCN. A systematic study of adsorption of glucans
in the series glucose to cellotetraose on MCN shows a monotonically
decreasing free energy of adsorption upon increasing the glucan chain
length. The free energy of adsorption decreases by at least 0.4 kcal/mol
with each additional glucose unit in this series, and these energetics
are consistent with CH−π interactions providing a significant
energetic contribution for adsorption, similar to previous observationsin
glycoproteins. HPLC of hydrolyzed fragments in solution, 13C Bloch decay NMR spectroscopy, and GPC provide material balance
closure of adsorbed glucan coverages on MCN materials. The latter
and MALDI-TOF-MS provide direct evidence for adsorption of long-chain
glucans on the MCN surface, which have a radius of gyration larger
than the pore radius of the MCN material.
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Keywords
surface areaMCN surfacemesoporous carbon nanoparticlesGlucan Adsorptionadsorption equilibration timesmesoporous carbon nanoparticleHPLCGPCobservationsin glycoproteinsglucan adsorptionglucan chain length influences adsorption energeticsMesoporous Carbon Nanoparticles13 C Bloch decay NMR spectroscopyadsorption decreasesglucan chain length influences adsorptionMCN materialsacid hydrolyzateMCN material40 glucoseacid solutionseries glucoseCHmesoporosity adsorb glucans4 minInternal SurfaceThe adsorptionglucan coveragesCNPglucose unitglucan chain lengthmaterial balance closureChain Lengthpore radius