The
synthesis of selectively deposited palladium nanoparticles (PdNPs)
inside tubular halloysite lumens is reported. This specific localization
was directed by the selective modification of the aluminol surfaces
of the clay mineral through stable Al–O–C bonds. An
ionic liquid (1-(2-hydroxyethyl)-3-methylimidazolium) was grafted
onto halloysite following the guest displacement method (generally
used for kaolinite) using halloysite–DMSO preintercalate. The
characterization of this clay nanohybrid material (XRD, NMR, TGA)
showed characteristics reminiscent of similar materials synthesized
from kaolinite. The grafting on halloysite lumens was also effective
without using the DMSO preintercalate. The presence of these new functionalities
in halloysite directs the synthesis of uniform PdNPs with size ranging
between 3 and 6 nm located exclusively in the lumens. This results
from the selective adsorption of PdNPs precursors in functionalized
lumens through an anion exchange mechanism followed by in situ reduction.
In contrast, the unmodified clay mineral displayed nanoparticles both
inside and outside the tubes. These catalysts showed significant catalytic
activity for the reduction of 4-nitrophenol (4-NP). The most efficient
catalysts were recycled up to three times without reducing significantly
the catalytic activities
