Structure of tubular halloysite-(10 Å) and its transition to halloysite-(7 Å) by infrared spectroscopy and X-ray diffraction

Sammanfattning

Halloysite nanotubes (often abbreviated as HNTs) are technologically important owing to their unique structural and morphological features. Some of these features pre-exist in the naturally hydrated halloysite-(10 Å) parent clay mineral; others may develop during its dehydration towards halloysite-(7 Å). This is the first infrared spectroscopic study of the transition to halloysite-(7 Å), which, in combination with X-ray diffraction (XRD), aimed at advancing the structural description of the process. Three cylindrical and two polygonal halloysite-(10 Å) samples, in both their H- and D-forms, were measured by attenuated total reflectance (ATR), non-invasively and in situ, following step-wise equilibration from 70% relative humidity (RH) to <10% RH and back to 70% RH at ambient temperature. This approach allowed for recording the spectrum of the dehydrating (but not rehydrating) interlayer in the nu O-D range, without interference from the inner nu OH groups, or from the inner-surface nu OH of anhydrous interlayers already present in the parent material. Besides the well-known 'hole' H2O species, a new type of H2O-decorated defect was detected at frequencies normally dominated by the inner nu OH. This defect is linked to the microenvironment created by the detachment between layer packets and forming 'crevices' or 'slits' upon dehydration. In addition, the study of the nu Si-O spectrum demonstrated that the dehydration of halloysite-(10 Å) leads to the parallel formation of localized, ordered, kaolinite-like domains co-existing with regions of accumulated disorder. The as-produced halloysite-(7 Å) had a non-ideal, open structure that resisted rehydration because the kaolinite-like domains do not rehydrate and act as permanent cross-links.

Nyckelord

10 Å to 7 Å transition; FT-IR spectroscopy; hydrogen/deuterium (H/D) exchange; halloysite nanotubes; HNTs; X-ray diffraction

Publicerad i

Clays and Clay Minerals
2024, volym: 72, artikelnummer: e33
Utgivare: CAMBRIDGE UNIV PRESS

SLU författare

• Hillier, Stephen

  • Institutionen för mark och miljö, Sveriges lantbruksuniversitet
    
  • The James Hutton Institute

UKÄ forskningsämne

Markvetenskap
Fysikalisk kemi

Publikationens identifierare

• DOI: https://doi.org/10.1017/cmn.2024.37

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/140001