Halloysite clay

All reactions were carried out
in a stainless-steel reaction vessel suspended in a stirred silicon
oil bath. Halloysite clay was purchased from Sigma-Aldrich (source:
Applied Minerals, Inc. Dragon Mine, Utah USA) and was used without
modification. All other chemicals were purchased from Alfa Aesar,
Sigma-Aldrich and VWR. All chemicals were used as received without
further purification or modification. Reaction mixtures were filtered
prior to work-up using Fisherbrand filter paper, P2-grade [porosity:
fine (particle retention: 1–5 μm)]. ¹H NMR
spectra were recorded at r.t. in DMSO-d₆ or CDCl₃ on a Bruker 400 MHz instrument operating at
a frequency of 300 MHz for ¹H NMR. ¹H chemical
shifts were referenced to the DMSO solvent signal (2.50 ppm) or the
CHCl₃ solvent signal (7.26 ppm). Halloysite XRD measurements
were performed on a Philips X’Pert diffractometer utilizing
Cu Kα radiation (λ = 1.5418 Å) and a curved graphite
monochromator at a voltage of 45 kV and a current of 40 mA. Halloysite
TEM images were obtained on a JEOL 2010 equipped with an EDAX genesis
energy-dispersive spectroscopy system, operated at an accelerating
voltage of 200 kV and an emission current of 109 μA.