12.3 Deposition at the Liquid–Liquid Interface
445
The range of polarization in any aqueous/non-aqueous liquid pair studied so far is
around 1 V, which imposes a strong limitation onto the particles that can be deposited.
Examples studied so far include Pd [70, 73, 74, 86], Pt [81], Ag [92] and Cu [88, 91]
when the precursor was in the aqueous phase and Au when the precursor was in the
organic phase [68, 69, 85, 87]. A detailed overview of the systems studied, including
the reducing compounds applied in the organic phase, has been published elsewhere
[102].
The reaction pathway of the formation of Au (where the precursor ion is [AuCl 4 ]
–
in the organic phase) differed significantly from the case when the precursor ion was
in the aqueous phase. For Au deposition, the first step was the transfer of the Aucontaining complex across the interface and its reduction to [AuCl 2 ]
– that can be
reduced later to obtain nanoparticles. This was strongly evidenced with combined
spectroelectrochemical studies [66, 68].
The theory of the particle nucleation at the free, large surface area liquid–liquid
interface has been elaborated in detail [70, 73, 74]. Special attention was given to the
role of the interfacial tension on the nucleation behaviour [74]. This is particularly
important for the nucleation at the liquid–liquid interface since the relative surface
area of the particle floating at the interface strongly depends on the wetting ability of
both liquid phases. Having no energetically favourable surface sites for the nucleus
formation at the liquid–liquid boundary, the results for the nucleation have an unusually large scatter [81], and the importance of the purity during the experimental work
is to be emphasized [85].
Shortly after the appearance of the studies of electrodeposition at ITIES, a few
studies showed up where the deposition at the liquid phase boundary took place
in porous nanochannel membranes [75, 77, 79, 82] instead of an open surface of
large surface area. In the case of the membrane-supported ITIES, the mass transport
conditions are clearly different, and the hemispherical diffusion problem prevailing
around the particle formed at the open surface is reduced to a one-dimensional linear
one. The application of the membrane was also hoped to prevent the aggregation of
the particle that highly influences the overlap of the diffusion fields at open surfaces
and hence impacts also the chronoamperometric transients. Beside the ease of the
theoretical approach, the advantage of the membrane-supported systems was that a
regular set of particles could be obtained within a well-defined support but without
the necessity of another metal as electrical lead. It was shown that the relative position
of the liquid phases with respect to the template was controlled by the surface wetting
properties of the liquids, rather than gravity [75]; hence, the particles could be formed
at the orifice of the channels of the membrane. The membrane as a support made
it easy to collect particles for TEM studies, which showed that the agglomerates
produced were composed of particles of 3 to 5 nm diameter [77]. This was much
smaller than the pore diameter applied (~100 nm). This was in an approximate
agreement with the results obtained for Au particle deposition at ITIES of large
surface area [87].
Another interesting field within the ITIES-related deposition studies is the parallel
electrochemical reaction of polymer-forming monomers and metal salts resulting
in nanoparticle formation during their reduction. This approach may have various
445
The range of polarization in any aqueous/non-aqueous liquid pair studied so far is
around 1 V, which imposes a strong limitation onto the particles that can be deposited.
Examples studied so far include Pd [70, 73, 74, 86], Pt [81], Ag [92] and Cu [88, 91]
when the precursor was in the aqueous phase and Au when the precursor was in the
organic phase [68, 69, 85, 87]. A detailed overview of the systems studied, including
the reducing compounds applied in the organic phase, has been published elsewhere
[102].
The reaction pathway of the formation of Au (where the precursor ion is [AuCl 4 ]
–
in the organic phase) differed significantly from the case when the precursor ion was
in the aqueous phase. For Au deposition, the first step was the transfer of the Aucontaining complex across the interface and its reduction to [AuCl 2 ]
– that can be
reduced later to obtain nanoparticles. This was strongly evidenced with combined
spectroelectrochemical studies [66, 68].
The theory of the particle nucleation at the free, large surface area liquid–liquid
interface has been elaborated in detail [70, 73, 74]. Special attention was given to the
role of the interfacial tension on the nucleation behaviour [74]. This is particularly
important for the nucleation at the liquid–liquid interface since the relative surface
area of the particle floating at the interface strongly depends on the wetting ability of
both liquid phases. Having no energetically favourable surface sites for the nucleus
formation at the liquid–liquid boundary, the results for the nucleation have an unusually large scatter [81], and the importance of the purity during the experimental work
is to be emphasized [85].
Shortly after the appearance of the studies of electrodeposition at ITIES, a few
studies showed up where the deposition at the liquid phase boundary took place
in porous nanochannel membranes [75, 77, 79, 82] instead of an open surface of
large surface area. In the case of the membrane-supported ITIES, the mass transport
conditions are clearly different, and the hemispherical diffusion problem prevailing
around the particle formed at the open surface is reduced to a one-dimensional linear
one. The application of the membrane was also hoped to prevent the aggregation of
the particle that highly influences the overlap of the diffusion fields at open surfaces
and hence impacts also the chronoamperometric transients. Beside the ease of the
theoretical approach, the advantage of the membrane-supported systems was that a
regular set of particles could be obtained within a well-defined support but without
the necessity of another metal as electrical lead. It was shown that the relative position
of the liquid phases with respect to the template was controlled by the surface wetting
properties of the liquids, rather than gravity [75]; hence, the particles could be formed
at the orifice of the channels of the membrane. The membrane as a support made
it easy to collect particles for TEM studies, which showed that the agglomerates
produced were composed of particles of 3 to 5 nm diameter [77]. This was much
smaller than the pore diameter applied (~100 nm). This was in an approximate
agreement with the results obtained for Au particle deposition at ITIES of large
surface area [87].
Another interesting field within the ITIES-related deposition studies is the parallel
electrochemical reaction of polymer-forming monomers and metal salts resulting
in nanoparticle formation during their reduction. This approach may have various