Electroless Deposition of Palladium at Bare and Templated Liquid/Liquid Interfaces

Article abstract of DOI:10.1021/ja037599y

A simple, electroless approach to metallize the liquid/liquid interface is reported. The method is illustrated with the deposition of Pd at the bare water/1,2-dichloroethane interface, and for the templated deposition of Pd within the 100 nm diameter pores of γ-alumina membranes. Copyright

Full text of DOI:10.1021/ja037599y

Published on Web 10/02/2003
Electroless Deposition of Palladium at Bare and Templated Liquid/Liquid
Interfaces
Robert A. W. Dryfe,* Andrew O. Simm, and Brett Kralj
Department of Chemistry, UniVersity of Manchester Institute of Science & Technology, P.O. Box 88,
Manchester M60 1QD, United Kingdom
Received July 29, 2003; E-mail: robert.dryfe@umist.ac.uk
The growth, and subsequent characterization, of metallic nano-
particles has received much attention in recent years.1,2 Solution
phase methods of deposition, generally involving the reduction of
a precursor cation, have been developed from two-phase liquid/
liquid3 (L/L) and colloidal systems.4 Electrochemical methods have
also been employed to reduce metals on solid substrates,5 with
templates such as porous films6,7 or lyotropic liquid crystalline
phases8 controlling the deposit structure on the nanometer scale.
Two-dimensional films have also been grown electrochemically by
bringing a working electrode in close proximity to a L/L inter-
face.9,10 Here, we report the combination of various aspects of the
above approaches to induce the electroless deposition of Pd at the
L/L interface, with and without the presence of a membrane
template.
Figure 2. Time-dependence of the absorption maximum for 1 mM aqueous
phase tetrachloropalladate solution, on contact with DCE containing 2 mM
An aqueous solution of ammonium tetrachloropalladate is
brought into contact with a solution of decamethylferrocene in 1,2-
decamethylferrocene. The DCE phase in both cases contained 0.1 M
dichloroethane (DCE).11 Within a few minutes, the straw-yellow
tetrabutylammonium perchlorate. The aqueous phase in the upper trace
contained 0.1 M lithium perchlorate and 1.0 M lithium chloride. In the
lower trace, the aqueous phase contained 1.0 M lithium perchlorate and
0.1 M lithium chloride. The aqueous phases in both cases also contained
0.05 M lithium sulfate.
aqueous phase loses it color, accompanied by a change in color of
the organic phase from amber to green. The simultaneous appear-
ance of a dark gray film at the L/L interface suggests that the
following heterogeneous reduction is operative:
Both the kinetics, and ultimately the equilibrium position, of a
heterogeneous electron-transfer process such as (1) ought to be a
function of the interfacial potential, ∆φ, of water relative to DCE.
A common ion, such as perchlorate, controls ∆φ via:14
2-
PdCl4 (aq) + 2Me10FeCp2(DCE) f
Pd(s) + 4Cl-(aq) + 2(Me)10FeCp2
(1)
+
(DCE)
ai,org
ln
zF ai,aq
RT
where Me10FeCp2 denotes the ferrocene derivative. The formation
of metallic Pd was supported by filtration of the solid species, using
a 100 nm pore diameter track-etched polyester membrane, and
energy-dispersive X-ray analysis of the solid residue, following
washing with water and acetone (Figure 1). The formation of
metallic Pd is consistent with the reduction potentials of the relevant
species, because the E0 value of the Pd precursor in 1 M chloride
solution is ca. 0.55 V more positive than that of the ferrocene
derivative in DCE.12,13
∆φ ) ∆φ°′ +
(2)
where ∆φ°′ is the formal distribution potential of ion i between
water (aq) and DCE (org) and other symbols have their usual
meanings. Equation 2 implies that an increase in the interfacial
potential results when the aqueous phase perchlorate concentra-
tion exceeds that of the organic phase (neglecting ion pairing and
the nonideality of the solutions). Given the high overall driving
force for Pd deposition, variation in ∆φ will be manifested as
changes in the rate, rather than the extent, of deposition. This
suggestion was borne out experimentally, as the time-dependence
of the visible absorption maximum of the aqueous solution reveals
(Figure 2).15 The morphology of the deposit also changed to a
denser, more compact form as ∆φ was increased, as optical
microscopy of the deposits following filtration suggests (see
Supporting Information).
The L/L electroless deposition process is potentially very useful,
because it may readily be combined with the template deposition
approach.6,7 Metallic particles are thus dispersed and retained within
a porous membrane, whereas the deposits formed at the bare
interface agglomerate to form ill-defined structures.
Figure 1. Energy dispersive X-ray analysis obtained for the metallic residue
formed at the L/L interface, following filtration.
We have recently reported the potentiostatically controlled growth
of dispersed Pd by deposition at the alumina-modified L/L interface,
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J. AM. CHEM. SOC. 2003, 125, 13014-13015
10.1021/ja037599y CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
particles develop a finite thickness and, hence, electronic conduction
pathways may allow deposit growth.17 We have thus transposed
the electroless deposition method to the alumina-modified L/L
interface with spontaneous Pd deposition being induced as above,
leading to the pale gray membranes taking on a progressively dark
gray luster as deposition proceeded. Time- and potential-dependent
deposition of Pd within the alumina pores is confirmed by scanning
electron microscopy (Figures 3 and 4, also confirmed by energy-
dispersive X-ray analyses).18 Liquid/liquid voltammetry, using the
tetraethylammonium ion, was used as a probe of the Pd-loaded
membranes (see Supporting Information),19 indicating that the final
deposit retained some porosity. For the early part of the deposition
at least, the template gives a simple way to localize the growth of
metal particles to a predefined dimension (in this case, 100 nm).
Finally, the electroless aspect of this procedure imparts exceeding
simplicity to the process.
We believe the route presented here, leading to the facile
deposition of nanometer scale metallic particles within an oxide
support, will be of technological utility, for example, in catalyst
preparation. We are currently investigating the relationship between
deposit structure and deposition conditions and the deposition of
other materials, in a variety of porous structures.
Acknowledgment. We thank EPSRC and the Leverhulme Trust
for financial support.
Supporting Information Available: Optical microscopy of filtered
Pd deposits and liquid/liquid voltammetry of ion transfer as a function
of deposition time (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
Figure 3. Scanning electron micrographs (SEM) of Pd deposited in alumina
membranes using the electroless method, after (a) 5 min and (b) 10 min of
contact between the DCE and aqueous solutions. The DCE phase contained
2 mM decamethylferrocene and 0.1 M tetrabutylammonium perchlorate.
The aqueous phase contained 1 mM tetrachloropalladate and 0.1 M lithium
perchlorate. The lighter color corresponds to Pd; the scale bar in the bottom
right of the images corresponds to 1 µm. Note in (b) that some “spillover”
of Pd to form larger aggregates is seen.
References
(1) Hicks, J. F.; Miles, D. T.; Murray, R. W. J. Am. Chem. Soc. 2002, 124,
13322-13328.
(2) Quinn, B. M.; Prieto, I.; Haram, S. K.; Bard, A. J. J. Phys. Chem. B 2001,
105, 7474-7476.
(3) Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. J. Chem.
Soc., Chem. Commun. 1994, 801-802.
(4) Patil, V.; Mayya, K. S.; Pradhan, S. D.; Sastry, M. J. Am. Chem. Soc.
1997, 119, 9281-9282.
(5) Penner, R. M. J. Phys. Chem. B 2002, 106, 3339-3353.
(6) Hulteen, J. C.; Martin, C. R. J. Mater. Chem. 1997, 7, 1075-1087.
(7) Nicewarner-Pen˜a, S. R.; Freeman, R. G.; Reiss, B. D.; Lin, H.; Pen˜a, D.
J.; Walton, I. D.; Cromer, R.; Keating, C. D.; Natan, M. J. Science 2001,
294, 137-141.
(8) Attard, G. S.; Bartlett, P. N.; Coleman, N. R. B.; Elliott, J. M.; Owen, J.
R.; Wang, J. H. Science 1997, 278, 838-840.
(9) Matsushita, M.; Sano, M.; Hayakawa, Y.; Honjo, H.; Sawada, Y. Phys.
ReV. Lett. 1984, 53, 286-289.
(10) Zeiri, L.; Younes, O.; Efrima, S.; Deutsch, M. J. Phys. Chem. B 1997,
101, 9299-9308.
(11) Ammonium tetrachloropalladate (Aldrich, Gillingham, U.K.) was prepared
as a 1 mM solution in “Milli-Q” water (Millipore, Watford, U.K.).
Decamethylferrocene (Aldrich) was used as a 2 mM solution in DCE
(Aldrich, HPLC grade). Neither solution was stirred in the deposition
experiments reported here.
(12) Eugster, N.; Ferm´ın, D. J.; Girault, H. H. J. Phys. Chem. B 2002, 106,
3428-3433.
(13) Johans, C.; Kontturi, K.; Schiffrin, D. J. J. Electroanal. Chem. 2002, 526,
29-35.
(14) Solomon, T.; Bard, A. J. J. Phys. Chem. 1995, 99, 17487-17489.
(15) The 462 nm aqueous phase absorbance was monitored in situ for 1 h,
using a Helios R spectrophotometer (Thermospetric, Cambridge, U.K.).
(16) Platt, M.; Dryfe, R. A. W.; Roberts, E. P. L. Chem. Commun. 2002, 2324-
2325.
Figure 4. SEM of Pd-loaded alumina membranes after 30 min of electroless
deposition. The organic phase was identical to Figure 3. The aqueous phase
contained 1 mM ammonium tetrachloropalladate and (a) 0.01 M lithium
perchlorate or (b) 0.05 M lithium perchlorate. The scale bar in the bottom
right of the images corresponds to 2 µm.
(17) Platt, M.; Dryfe, R. A. W.; Roberts, E. P. L. Electrochim. Acta 2003, 48,
3037-3046.
(18) SEM and energy dispersive X-ray analysis were performed using a Quanta
200 Environmental SEM (FEI Co., Hillsboro, OR).
(19) Platt, M.; Dryfe, R. A. W.; Roberts, E. P. L. Langmuir 2003, 19,
8019-8025.
formed by placing the denser DCE phase above the aqueous
phase.16,17 Transmission electron microscopy suggests that the
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