116
M. I. Qadir et al.
use of different ligands (phenanthroline) and functionalised ILs, such as nitrilefunctionalised or 2,2
-dipyridyl-amine-functionalised imidazolium salts, have been
used for the stabilisation and dispersion of Pd NPs in ILs [44–47].
Dupont et al. reported that the colloidal suspensions of cubic fcc Ni(cod) 2 NPs
of 5.0–6.0 nm were achieved in BMIm.NTf 2 and BMIm.BF 4 ILs using H 2 at 75 °C
(Table 4.1, entries 26–27) [37]. These ILs acted as stabilising agents for the NPs.
X-ray diffraction showed clearly Ni(0) NPs embedded in these ILs, avoiding their
agglomeration, whereas X-ray absorption spectroscopy evidenced that Ni(0) NPs
were surrounded by a cap layer due to steric and electrostatic interactions with the
ILs. They also observed that there were slight decreases in both the NP diameter and
the size distribution with an increase in the carbon numbers of the alkyl side chain
in the imidazolium cation up to 14 carbons [38].
Alloys and core–shell Co/Pt [40], Ru/Pt [41], Ru/Fe [20], Fe/Pt [42] and Ru/Ni
[43] bimetallic NPs are also easily accessible via simple decomposition of their
organometallic complexes in ILs using H 2 . The advantage of the use of these
organometallic complexes is that they possess only hydrocarbon-containing ligands
which, by reduction/decomposition, generate organic by-products with poor coordinating properties to the surface of the NPs and that can easily be removed from the
reaction mixture under vacuum. Consequently, ILs may provide adequate templates
for the generation of these bimetallic NPs. For example, Fe/Pt core–shell NPs
prepared in BMIm.NTf 2 have a diameter of 1.7 ± 0.2 nm, whereas the diameters of
those prepared in BMIm.PF 6 and BMIm.BF 4 IL are 1.8 ± 0.3 nm and 2.5 ± 0.4 nm,
respectively (Table 4.1, entries 35–37). Moreover, the thickness of the Pt shell layer
has a direct correlation with the water stability of the anion and increases in the
order PF 6 > BF 4 > NTf 2 , yielding the metal compositions Pt 4 Fe 1 , Pt 3 Fe 2 and Pt 1 Fe 1 ,
respectively [42].
4.4 Preparation of Naked NPs by Physical Methods
The fabrication of well-defined ‘surface-clean’ metal NPs still remains a challenge for
the chemical and engineering community [48]. In this respect, magnetron sputtering
deposition has emerged as a compromise physical technique that is a simple, clean
and provides an easy approach to prepare such nano-devices that may demonstrate
quite unique properties for several applications in fields such as electronics, sensors,
biomedicine and catalysis [49]. Indeed, this versatile method allows the fabrication of
‘naked’ NPs in a single step, generating highly pure metal-supported NPs using both
solid and liquid supports, as opposed to the chemical and electrochemical methods
that usually need further purification steps [50–54]. In particular, the fabrication
of metal nanoparticles in ILs or hybrid IL materials is a simple and controllable
process for several applications, with huge advantages compared to the classical wet
methods [21, 55–57]. In this technique, bombardment under vacuum of the metal
target (ultrapure, >99.99%) with energetic gaseous argon ions causes the physical
ejection of surface atoms and/or metal clusters. The generated sputtered metal species
M. I. Qadir et al.
use of different ligands (phenanthroline) and functionalised ILs, such as nitrilefunctionalised or 2,2
-dipyridyl-amine-functionalised imidazolium salts, have been
used for the stabilisation and dispersion of Pd NPs in ILs [44–47].
Dupont et al. reported that the colloidal suspensions of cubic fcc Ni(cod) 2 NPs
of 5.0–6.0 nm were achieved in BMIm.NTf 2 and BMIm.BF 4 ILs using H 2 at 75 °C
(Table 4.1, entries 26–27) [37]. These ILs acted as stabilising agents for the NPs.
X-ray diffraction showed clearly Ni(0) NPs embedded in these ILs, avoiding their
agglomeration, whereas X-ray absorption spectroscopy evidenced that Ni(0) NPs
were surrounded by a cap layer due to steric and electrostatic interactions with the
ILs. They also observed that there were slight decreases in both the NP diameter and
the size distribution with an increase in the carbon numbers of the alkyl side chain
in the imidazolium cation up to 14 carbons [38].
Alloys and core–shell Co/Pt [40], Ru/Pt [41], Ru/Fe [20], Fe/Pt [42] and Ru/Ni
[43] bimetallic NPs are also easily accessible via simple decomposition of their
organometallic complexes in ILs using H 2 . The advantage of the use of these
organometallic complexes is that they possess only hydrocarbon-containing ligands
which, by reduction/decomposition, generate organic by-products with poor coordinating properties to the surface of the NPs and that can easily be removed from the
reaction mixture under vacuum. Consequently, ILs may provide adequate templates
for the generation of these bimetallic NPs. For example, Fe/Pt core–shell NPs
prepared in BMIm.NTf 2 have a diameter of 1.7 ± 0.2 nm, whereas the diameters of
those prepared in BMIm.PF 6 and BMIm.BF 4 IL are 1.8 ± 0.3 nm and 2.5 ± 0.4 nm,
respectively (Table 4.1, entries 35–37). Moreover, the thickness of the Pt shell layer
has a direct correlation with the water stability of the anion and increases in the
order PF 6 > BF 4 > NTf 2 , yielding the metal compositions Pt 4 Fe 1 , Pt 3 Fe 2 and Pt 1 Fe 1 ,
respectively [42].
4.4 Preparation of Naked NPs by Physical Methods
The fabrication of well-defined ‘surface-clean’ metal NPs still remains a challenge for
the chemical and engineering community [48]. In this respect, magnetron sputtering
deposition has emerged as a compromise physical technique that is a simple, clean
and provides an easy approach to prepare such nano-devices that may demonstrate
quite unique properties for several applications in fields such as electronics, sensors,
biomedicine and catalysis [49]. Indeed, this versatile method allows the fabrication of
‘naked’ NPs in a single step, generating highly pure metal-supported NPs using both
solid and liquid supports, as opposed to the chemical and electrochemical methods
that usually need further purification steps [50–54]. In particular, the fabrication
of metal nanoparticles in ILs or hybrid IL materials is a simple and controllable
process for several applications, with huge advantages compared to the classical wet
methods [21, 55–57]. In this technique, bombardment under vacuum of the metal
target (ultrapure, >99.99%) with energetic gaseous argon ions causes the physical
ejection of surface atoms and/or metal clusters. The generated sputtered metal species