Photochemical synthesis of nano-phase palladium films on quartz

Article abstract of DOI:10.1134/S1070427209050322

Processes of photochemical deposition of palladium films on quartz from solutions of palladium(II) perchlorate and bis(ethylenediamine)palladium(II) tetraphenylborate in dimethyl formamide solutions and dimethyl formamide-ethanol mixtures were studied. Th

Full text of DOI:10.1134/S1070427209050322

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 5, pp. 915−917. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © E.A. Lifanova, V.V. Gorbunova, T.B. Boitsova, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 5, pp. 859−862.
BRIEF
COMMUNICATIONS
Photochemical Synthesis of Nano-Phase Palladium
Films on Quartz
E. A. Lifanova, V. V. Gorbunova, and T. B. Boitsova
Gertsen Russian State Pedagogical University, St. Petersburg, Russia
Received January 21, 2008
Abstract—Processes of photochemical deposition of palladium films on quartz from solutions of palladium(II)
perchlorate and bis(ethylenediamine)palladium(II) tetraphenylborate in dimethyl formamide solutions and
dimethyl formamide–ethanol mixtures were studied. The efficiency of the film deposition increases depending
on the solvent nature.
DOI: 10.1134/S1070427209050322
99.5%) a light-beige precipitate was formed. The
precipitate was filtered, washed out by water, dried, and
stored in darkness in a desiccator. All solutions were
prepared on the basis of bidistilled water.
Synthesis of palladium nanostructures is of interest
from the viewpoint of their application as catalysts [1,
2]. Palladium colloidal particles are known to be inferior
to traditionally used palladium complexes in catalytic
activity, being simultaneously highly stable and capable
of regenerating. As a rule, metal particles obtained in the
synthesis of such catalysts are encapsulated in matrixes
of block copolymers [3] or dendrimer structures [4], that
considerably reduces their reactivity due to blocking the
catalyst surface. The deposition of palladium nanoparticles
on the surface of such mesoporous structures as TiO2 [5],
Al2O3 [6], and SiO2 [7] is also widely used.
Palladium perchlorate was synthesized from PdCl2
(Aldrich, 99.9%) by the procedure described in [9].
Palladium films were obtained from photolytes by the
dissolution of synthesized solid salts Pd(ClO4)2 and
[PdEn2](BPh4)2 in N,N-dimethyl formamide (DMF) and
its mixtures with methanol, ethanol, and propanol-2 in
proportions from 20 : 1 up to 1 : 1 (by volume). The
solvents were purified according to known procedures
[10]. The systems were irradiated by monochromic light
of a Philips TUV 4W/G4 05 lamp with the excitation
wavelength λexc of 254 nm. The light quantity was 2.0 ×
1015 quant cm2 s−1. Polished quartz was used as a solid
support. The formation of films on a quartz surface was
recorded by spectrophotometry (Shimadzu UV-2401).
The size of particles, the processes of their formation,
growth, and aggregation were recorded with a Hitachi
HU-11 electron microscope.
The aim of this work was to study the kinetics of
photochemical deposition of palladium films on quartz
depending on a photolyte composition.
EXPERIMENTAL
We used palladium perchlorate Pd(ClO4)2 and
bis(ethylenediamine)palladium(II) tetraphenylborate
[PdEn2](BPh4)2 (En, ethylenediamine C2H8N2; BPh4−,
tetraphenylborate ion B(C6H5)4−) as initial compounds
for the film deposition. To obtain [PdEn2](BPh4)2, we
used the procedure described in [8] for the synthesis
of a [PdEn2]Cl2 ethylenediamine solution. As a result
of the exchange reaction of the obtained [PdEn2]Cl2
ethylenediamine solution and a solution containing
a stoichiometric amount of NaB(C6H5)4 (Sigma-Aldrich,
The UV irradiation of DMF solutions of palladium(II)
perchloratePd(ClO4)2 incontactwithaquartzsupportleads
to a deposition of a grey metalescent film on its surface.
According to the X-ray photoelectronic spectroscopy data
[11], the film represents pure palladium. Examination
of kinetic curves of the formation of palladium films on
quartz depending on initial palladium concentration has
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LIFANOVA et al.
The use of ethylenediaminepalladium(II) tetraphenyl-
borate [PdEn2](BPh4)2 as an initial compound also leads
to the deposition of a palladium film on a quartz surface.
The intensity of the film coloration increases as the
irradiation duration increases. In this case the deposition
proceeds more effectively: reached optical densities of
films are 1.5-2-fold greater than for films obtained in
similar conditions using palladium(II) perchlorate. The
film formation occurs without an induction period, kinetic
curves flatten for 15 min of the irradiation. No deposits are
formed in this case. The size of particles forming a film
is 5−10 nm, particles being homogeneously distributed
over the quartz surface.
Fig. 1. Dependence of optical density D360 measured at λ =
360 nm for colloidal palladium deposited on a quartz surface
from 0.01 M [Pd(En)2](BPh4)2 solutions on the DMF : alcohol
volume ratio α. Wavelength λexc = 254 nm, τirr = 5 min.Alcohol:
(1) propanol-2, (2) methanol, (3) ethanol.
Thus, the efficiency of the metal film deposition is
determined by the nature of a palladium initial compound.
Metal particles are formed in a near-surface layer of the
photolyte. It is essential for the film formation that rates
of the diffusion of palladium intermediates to the quartz
surface and their sorption on it should be higher than
the rate of their growth. Possessing catalytic properties,
palladium particles can become larger not only as a result
of the photolysis of DMF solutions, but also due to the
autocatalytic reduction of Pd(II) ions on their surface.
In the case of palladium(II) perchlorate the reduction of
ions is rather fast.Agglomerates formed in a near-surface
photolyte layer are incapable of sorption and sedimentate
on the photochemical cell bottom. Binding of Pd(II) ions
in a stable ethylenediamine complex results in slowing
down growth processes.
Fig. 2. Kinetic curves of palladium film photodeposition on
quartz from 0.01 M [Pd(En)2](BPh4)2 solutions within 60 min.
Wavelength λexc=254 nm. D360 is optical density measured at
λ=360 nm; (τ) irradiation duration (min). Solvent: (1) DMF, (2)
DMF : propanol-2, (3) DMF : methanol, (4) DMF : ethanol.
Low values of optical densities of the films are
caused by the fact that the rate of nanoparticles growth
and agglomeration exceeds the rate of their sorption on
a quartz surface. The formation of palladium particles
proceeds presumably in bulk photolyte.
shown that the films are deposited without an induction
period. After 1 min irradiation kinetic curves flatten out,
i.e. the amount of metal precipitated as a film does not
change during the further irradiating up to 15 min. The
increase in palladium(II) perchlorate concentration in
photolyte from 5 × 10−3 up to 5 × 10−2 M allows optical
density of a film to be doubled. Nevertheless D values
do not exceed 0.2 units. According to the electronic
microscopy data, the film consists of isolated particles of
5−10 nm in diameter. In the case of a 3 min irradiation
the film deposition is accompanied by the formation
of agglomerates of particles of 50−70 nm in diameter,
their size and number increasing during the further
irradiation. Formed agglomerates are sedimentated
on the photochemical cell bottom to form black loose
deposits.
Metal deposition can be accelerated if substances
capable of regulating sorption and growth processes are
added to the photolyte. It is known [12] that alcohols,
being secondary reducing agents, can increase the
efficiency of the reduction of metal ions to the metal form.
In this work we have analyzed the influence of the alcohol
nature on the palladium film formation. The addition of
alcohols to a DMF solutions of [PdEn2](BPh4)2 in the ratio
1:20 (by volume) affects the kinetics of film formation
only slightly, whereas the increase in the alcohol content
in the system up to the 1:1 ratio results in the 2.5-fold
increase in the optical density of the films (Fig. 1).
We have found that the efficiency of film deposition
from photolytes containing equal volumes of the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 5 2009

PHOTOCHEMICAL SYNTHESIS OF NANO-PHASE PALLADIUM FILMS
917
components increases in the sequence DMF–propanol-
2–methanol–ethanol (Fig. 2).
REFERENCES
The obtained results can be explained as follows. The
presence of the DMF carbonyl chromophore group with
the absorption maximum in the near UV region provides
a possibility for occurring sensitized photolysis
(λexc=254 nm) [13] of alcohols with the formation of
radicals. Stability of alcohol radicals increases in the
sequence CH2OH < CH2CH2OH < CH3COHCH3.
As secondary alcohol radicals are stable, propanol-2 in
comparison with DMF provides a more effective film
formation. It should be expected that the efficiency of
film deposition increases in the sequence propanol-
2−ethanol−methanol. However, a high volatility of
methanol leads to a decrease in the rate of film formation
under equal irradiation conditions.
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(1) Efficiency of the palladium film deposition
depends on the solvent nature and increases in the
sequence propanol-2 - methanol−ethanol.
(2) The deposition process proceeds without an
induction period.
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