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Factor analysis of 27 Al MAS NMR spectra for identifying nanocrystalline phases in amorphous geopolymers
Author(s) -
Urbanova Martina,
Kobera Libor,
Brus Jiri
Publication year - 2013
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.4009
Subject(s) - nanocrystalline material , amorphous solid , crystallite , nmr spectra database , aluminosilicate , phase (matter) , geopolymer , chemistry , chemical engineering , solid state nuclear magnetic resonance , materials science , spectral line , crystallography , nuclear magnetic resonance , organic chemistry , physics , catalysis , astronomy , engineering , fly ash
Nanostructured materials offer enhanced physicochemical properties because of the large interfacial area. Typically, geopolymers with specifically synthesized nanosized zeolites are a promising material for the sorption of pollutants. The structural characterization of these aluminosilicates, however, continues to be a challenge. To circumvent complications resulting from the amorphous character of the aluminosilicate matrix and from the low concentrations of nanosized crystallites, we have proposed a procedure based on factor analysis of 27 Al MAS NMR spectra. The capability of the proposed method was tested on geopolymers that exhibited various tendencies to crystallize (i) completely amorphous systems, (ii) X‐ray amorphous systems with nanocrystalline phases, and (iii) highly crystalline systems. Although the recorded 27 Al MAS NMR spectra did not show visible differences between the amorphous systems (i) and the geopolymers with the nanocrystalline phase (ii), the applied factor analysis unambiguously distinguished these materials. The samples were separated into the well‐defined clusters, and the systems with the evolving crystalline phase were identified even before any crystalline fraction was detected by X‐ray powder diffraction. Reliability of the proposed procedure was verified by comparing it with 29 Si MAS NMR spectra. Factor analysis of 27 Al MAS NMR spectra thus has the ability to reveal spectroscopic features corresponding to the nanocrystalline phases. Because the measurement time of 27 Al MAS NMR spectra is significantly shorter than that of 29 Si MAS NMR data, the proposed procedure is particularly suitable for the analysis of large sets of specifically synthesized geopolymers in which the formation of the limited fractions of nanocrystalline phases is desired. Copyright © 2013 John Wiley & Sons, Ltd.