A reassessment of the 29Si MAS-NMR spectra of sepiolite and aluminated sepiolite

Abstract A 29 Si MAS-NMR one-pulse and ﹛ 1 H﹜ CP comparative study of sepiolite, folded sepiolite, aluminated sepiolite, and palygorskite was conducted. The three main resonances of sepiolite at -92.0 ± 0.1, —94.3 + 0.1, and — 97.8 ± 0.1 p.p.m. were assigned with respect to the position of the Si atoms within the three pairs of symmetrical sites in the basal plane. The line at —97.8 p.p.m. was attributed to the central sites by comparison with the resonances and chemical environments of Si in talc and palygorskite. The line at —94.3 p.p.m. was attributed to the edge sites, because it is strongly reinforced by cross-polarization. Alumination of sepiolite led to a broadening of the peaks and new downfield resonances in line with what can be observed in other phyllosilicates and zeolites.