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Preparation and characterization of titanium dioxide nanotube array supported hydrated ruthenium oxide catalysts
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2012 Adv Nat Sci: Nanosci Nanotechnol 3 015008
(http://iopscience.iop.org/2043-6262/3/1/015008)
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Trang 2IOP P A N S N N
Preparation and characterization of
titanium dioxide nanotube array
supported hydrated ruthenium oxide
catalysts
Thi Phuong Ly Giang1, Thi Nhu Mai Tran2 and Xuan Tuan Le3
1University Paris-Sud, UMR-CNRS 8612, Laboratory of Proteins and Nanotechnologies in Separation
Sciences, 92296, Faculté de Pharmacie, Châtenay-Malabry, France
2Faculty of Chemistry, Hanoi University of Science, Vietnam National University in Hanoi,
19 Le Thanh Tong Street, Hanoi, Vietnam
3MiQro Innovation Collaborative Centre (C2MI), 45, boul de l’Aéroport, Bromont (Québec), Canada
E-mail:xuan.tuan.le@ulb.ac.beandmaitrannhu@gmail.com
Received 27 July 2011
Accepted for publication 26 September 2011
Published 6 March 2012
Online atstacks.iop.org/ANSN/3/015008
Abstract
This work aimed at preparing and characterizing TiO2nanotube supported hydrated ruthenium
oxide catalysts First of all, we succeeded in preparing TiO2nanotube arrays by
electrochemical anodization of titanium metal at 20 V for 8 h in a 1M H3PO4+ 0.5 wt% HF
solution as evidenced from scanning electron microscopy (SEM) and x-ray photoelectron
spectroscopy (XPS) results The hydrated ruthenium oxide was then deposited onto TiO2
nanotubes by consecutive exchange of protons by Ru3+ions, followed by formation of
hydrated oxide during the alkali treatment Further XPS measurements showed that the
modified samples contain not only hydrated ruthenium oxide but also hydrated ruthenium
species Ru(III)-OH
Keywords: TiO2nanotube, anodization, hydrated ruthenium, catalytic oxidation
Classification numbers: 2.03, 4.00, 5.06
1 Introduction
Incorporating metal-based species onto titanium dioxide
surface is one of the well-known methods to improve catalytic
activity of the resulting modified TiO2 materials [1 6]
Among various metals such as copper, nickel, tin, gold,
platinum, palladium the TiO2 supported Ru catalysts have
been proven to play an indispensable role with respect to
wastewater treatment and energy storage applications [7 10]
During the past ten years, TiO2nanotubes have been widely
investigated due to their practical applications in areas such
as biomaterials, solar cell, rechargeable lithium batteries, gas
sensor, and catalysts in particular [1, 10–14] Indeed, the
large cation exchange capacity of TiO2 nanotubes allows
a high loading of an active catalyst with even distribution
and high dispersion The open mesoporous morphology of
the nanotubes, absence of micropores, and high specific
surface area should facilitate transport of reagents during
a catalytic reaction The semiconducting properties of such new materials may result in strong electronic interaction between the support and a catalyst, which could improve catalytic performance in redox reactions [15] As a result, studies on supporting ruthenium-based compounds on TiO2
nanotubes are of potential interest [15–17] In this sense, this work focuses on preparation of titanium dioxide nanotube array supported hydrated ruthenium oxide catalysts
As a cost-effective and high rate method, the use of electrochemistry to prepare TiO2nanotube arrays is described
in the first section of the present paper Part of the work is then devoted to the loading of hydrated ruthenium oxides onto the electrochemically anodized TiO2nanotubes
It is remarkable to note that as a promising new catalyst for selective oxidation of many alcohols in aqueous media, hydrated ruthenium oxides have frequently been used in wastewater treatments [15] However, the role of
Content from this work may be used under the terms of the Creative Commons Attribution-NonCommercial ShareAlike 3.0 licence Any
Trang 3Adv Nat Sci.: Nanosci Nanotechnol 3 (2012) 015008 T P L Giang et al
Figure 1 Two-electrode electrochemical cell for preparation of
TiO2nanotube arrays
ruthenium supported catalysts towards methanol oxidation in
fuel applications is still an open topic for discussion [18,19]
While some authors refer to the active ruthenium compound
mainly as metallic Ru0 in a bimetallic alloy, early research
revealed that hydrated ruthenium oxide as a part of bimetallic
Pt–Ru systems is the most active catalyst for methanol
oxidation [18] It is thus interesting to investigate the
oxidation state of the Ru components deposited on our TiO2
nanotube arrays In this work, the formation of Ru-based
species on the surface of TiO2 nanotubes will finally be
discussed as clearly as possible on the basis of x-ray
photoelectron spectroscopy (XPS) results
2 Experimental
2.1 Anodization of titanium metal
For the electrochemical anodization, a typical two-electrode
configuration (figure 1) was employed with platinum foil
as the counter electrode and titanium foil as the working
electrode Thickness of titanium foils (99.6% purity) was
0.5 mm Effective area of the O-ring on the working electrode
in contact with electrolyte solution (as shown in figure1) was
1.0 cm2 Prior to any electrochemical treatment the foils were
sonicated in acetone, isopropanol and methanol successively,
followed by rinsing with deionized (DI) water and drying in
a nitrogen stream All anodization experiments were realized
at room temperature in a 1 M H3PO4(Merck) + 0.5 wt% HF
(Sigma-Aldrich) solution A potential of 20 V was applied
through the system for 8 h After each anodization, the
obtained sample was rinsed by DI water and dried in a
nitrogen stream The as-anodized TiO2nanotubes were then
recrystallized by heating at 400◦C for 10 h under nitrogen
atmosphere The obtained samples were characterized by
means of scanning electron microscopy (SEM) and XPS
techniques
2.2 Deposition of hydrated ruthenium oxides onto T i O2
nanotubes
The hydrated ruthenium oxide was deposited on TiO2
nanotubes by consecutive exchange of protons by Ru3+
ions, followed by formation of hydrated oxide during the
alkali treatment 200 mg of RuCl3·3H2O (Sigma Aldrich) was
dissolved in 23 ml of water with addition of 2 ml of 0.5 M HCl Then TiO2 nanotube array samples were immersed in this solution for 60 min at 25◦C After washing with a large amount of DI water, the samples were put in a beaker containing 1.0 M NaOH (Sigma Aldrich) After 1 h, the samples were taken out of the solution, rinsed by DI water, and then dried at 80◦C under vacuum condition for 2 h
2.3 Microscopy study
The SEM images were recorded by a Hitachi S4800 equipped with a field emission gun (FEG-SEM)
2.4 XPS
XPS measurements were carried out with a Theta
300 (Thermo Scientific Instrument) equipped with a microfocusing monochromator x-ray source The data were collected at room temperature, and the operating pressure
in the analysis chamber was always below 10−9Torr The core level spectra were referenced to the pollution C 1 s binding energy at 284.9 eV Data treatment and peak-fitting procedures were performed using Avantage software
3 Results and discussions
3.1 Electrochemical preparation of T i O2nanotube arrays
When a potential of 20 V is applied through the two-electrode configuration described in the experimental section, first of all, TiO2 is electrochemically formed (Ti + H2O → TiO2+ 4e−) Dissolution of titania then takes place thanks to the presence of fluoride ions in the solution and leads to the formation of soluble hexafluorotitanium complexes (TiO2+ 6F−+ 4H+→ TiF2−6 + 2H2O) With the help of electrical field, TiO2 nanotubes finally formed as a function of the time [20, 21] Figure 2 presents the SEM images of the resulting layers at different scales The zoom-out SEM image (figure 2B) clearly shows the self-organized nanotubes as expected It is also observed that the nanotube diameter is of approximately 100 nm (figure 2C) Such an obtained result
is in a good agreement with the work of Bauer et al [22], where the TiO2nanotube diameter was reported to be linearly dependent on the applied voltages and a diameter of about
100 nm was obtained with an applied potential of 20 V
On the other hand, XPS measurements allow us to confirm that the self-organized nanotubes are titanium dioxide As can be seen in figure3 the survey spectrum of the sample is dominated by signals of titanium and oxygen
as expected Besides Ti and O peaks, we equally observe the presence of unavoidable contaminated carbon peak This peak will be further discussed in the next section of this work It
is important to point out that the Ti 2p core level spectrum (figure4(a)) shows the typical characteristics of titanium in TiO2 with the 2p3 /2 and 2p1 /2 peaks centred at 458.8 and 464.3 eV, respectively [23]
XPS analysis also revealed that fluoride ions are strongly absorbed on TiO2 surface, indicating the migration of F−
ions is driven by the electrical field (figure 4(b)) In fact, under the influence of the electrical field, fluoride ions can even penetrate into the bottom of the nanotube as reported
2
Trang 4Adv Nat Sci.: Nanosci Nanotechnol 3 (2012) 015008 T P L Giang et al
Figure 2 SEM images of TiO2nanotubes formed at 20 V for 8 h in
1M H3PO4+ 0.5 wt% HF at different scales
elsewhere [24] Furthermore, it should be kept in mind that
fluoride anions are involved in the dissolution process of TiO2
as mentioned above Here, the most important point to be
underlined is that simple anodization of titanium metal led to
the formation of TiO2film which consists of individual tubes
with a diameter of ≈100 nm as evidenced from the XPS and
SEM results
3.2 Titanium dioxide nanotube array supported hydrated
ruthenium oxide catalysts
Figure5 shows the XPS survey spectrum of TiO2 nanotube
arrays supported Ru As is seen here, the XPS survey spectrum
of TiO2 nanotubes modified with Ru-based species looks
very similar to that of pristine TiO2 nanotubes We do not
observe clearly the presence of ruthenium on the spectrum
This however can be easily understood by noting the fact that
the positions of Ru 3p are found to be very close to those
of Ti 2p and also the Ru 3d3 /2 peak appears superposed to
the C 1 s line In order to bing out the difference between
the two samples, we wish next to concentrate on the C 1 s
F
KLL
Ti
LMM
O KLL
F 1s
Ti 2p
O 1s
Ti 3p
Binding Energy /eV
40 kCPS
C 1s
Figure 3 XPS survey spectrum of anodized TiO2nanotube arrays
468 466 464 462 460 458 456
2p1/2
Binding energy /eV
a) Ti 2p
4 kCPS
2p3/2
Binding energy /eV
500 CPS b) F1s
Figure 4 Ti 2p and F 1 s high-resolution spectra of TiO2nanotube arrays
and C 1 s + Ru 3 d high-resolution spectra of the pristine and modified samples
Before modification with ruthenium, the C 1 s core level can be fitted by three components located at 284.9, 286.4 and 288.8 eV respectively (figure 6(a)) After modification,
a typical behaviour of C 1 s + Ru 3 d mixed spectrum as already reported in many published works [9, 25–27] is
Trang 5Adv Nat Sci.: Nanosci Nanotechnol 3 (2012) 015008 T P L Giang et al
Binding energy /eV
5 kCPS
Ti 2p + Ru 3p
F 1s
O 1s
C 1s + Ru 3d
Figure 5 XPS survey spectrum of TiO2nanotube arrays supported
Ru
290 288 286 284 282 280
C3
C1
Binding energy /eV
a) C 1s
C2
290 288 286 284 282 280
Ru2(3d3/2)
Ru1(3d3/2)
Ru2(3d5/2)
C3
C2
Binding energy /eV
1 (3d5/2)
b) C1s + Ru 3d
Figure 6 (a) Decomposed C 1 s core level spectra of pristine TiO2
nanotubes (b) Decomposed C 1 s and Ru 3 d core level spectra of
TiO2supported Ru nanotubes
depicted in figure 6(b) As expected, in addition to the C
peaks which are quasi-identical to those of the pristine sample,
the Ru 3 d peaks appear in the spectrum In particular, the
Ru 3 d core level spectrum is characterized by 2 pairs of
relatively narrow peaks which correspond to the 5/2 and 3/2
spin–orbits (the red and black lines presented in figure6(b))
The first pair of 3 d peak, Ru1(3d3 /2) and Ru1(3d5 /2), are
found at 281.0 and 285.2 eV, respectively while the second
one, Ru2(3d3 /2) and Ru2(3d5 /2), locate at 282.1 and 286.3 eV Note that a separation distance of 4.2 eV between 3d3 /2 and
5d5 /2 peaks found for both pairs in this work is very close
to the expected value of 4.1 eV [26] One can deduce that there are two components of Ru-species on the surface of the modified TiO2nanotube Nevertheless, discussion on the nature of the two components is quite complicated Mazzieri
et al[25] reported that by using RuCl3as precursor for catalyst preparation, ruthenium oxychloride species characterized by 3d3/2 peak at 280.9 eV are present on the sample surface.
In our case, it is however worth mentioning that we do not observe any significant amount of chloride on the spectrum This allows us to exclude the presence of the chloride compounds (ruthenium oxychloride and ruthenium chloride)
in our catalysts Actually, the Ru component standing for
a 3d3/2 peak at 281.4 eV can be assigned to ruthenium in
RuO2 [26] or in RuO2.xH2O [28] This peak is slightly higher than our first Ru component (Ru1(3d3 /2) found at 281.0
in comparison with contaminated C peak of 284.9 eV) In
a separative work published by Bavykin et al [15], it was reported that Ru(III)-hydrated oxide could be obtained on the TiO2 surface through the same preparation process used in the present work On account of those facts, it is believed that the first Ru component appeared at low binding energies (281.0 and 285.2 eV) in our spectrum should be attributed to the hydrated ruthenium oxides
With the aim of clarifying the nature of the second component with Ru2(3d3 /2) and Ru2(3d5 /2) binding energies
of 282.1 and 286.3 eV, it is important to note that the peaks are not at all linked to RuCl3 as mentioned above In this case, the peaks can be attributed to the Ru (III) from hydrous
Ru (III) – OH incorporated on the lattice of TiO2 nanotubes through the ion exchange reactions between the Ru3+cations
in the solution and protons in the TiO2nanotube framework Nanotubular ‘titanium dioxide’ is indeed a protonated form
of a layered titanic acid The exact crystal structure of the nanotubes is a matter of current dispute; it probably corresponds either to the layered titanate H2Ti3O7 which has
a monoclinic structure with stepwise layers of three lengths
in each step, or to H2Ti2O4(OH)2 in which the unit cell has an orthorhombic symmetry The nanotube walls have a multilayered structure in which protons occupy positions on either side of the wall surface (convex and concave), as well
as in the interstitial cavities between the layers of the nanotube walls Therefore, protons and cations from aqueous solutions (H+, Men+) could easily be exchanged for protons in the nanotube wall, according to the following equation [15]:
xMen++ H2Ti3O7→ MexH2−xTi3Ox (n−1)+
The obtained XPS data indicate that the resulting
Ru/TiO2 nanotube arrays contain both hydrated ruthenium oxide and hydrated ruthenium species Ru(III)-OH
4 Conclusion
A one-step electrochemical method has been used to prepare TiO2 layers that consist of arrays of individual tubes with a diameter of ≈100 nm Thanks to the ion exchange reaction between the proton of the protonated
4
Trang 6Adv Nat Sci.: Nanosci Nanotechnol 3 (2012) 015008 T P L Giang et al
form of a layered titanic acid and Ru3+ cation in the
bulk solution, hydrated ruthenium species Ru(III)-OH can
be easily incorporated on TiO2 nanotube surface Part of
such a ruthenium species was subsequently converted to
hydrated ruthenium oxide by simple alkali and thermal
treatments Aside from Ru(III)-OH species, XPS allowed us
to evidence the presence of hydrated ruthenium oxide on
the surface of supported Ru/TiO2 nanotube catalysts As
mentioned in the introduction, supported Ru/TiO2 catalysts
have been proven efficient in the selective oxidation of several
organic alcohols Testing the catalytic activity of the obtained
Ru/TiO2 nanotube catalysts is obviously the subject of our
further works
References
[1] Varghese O K, Paulose M, LaTempa T J and Grimes C A 2009
Nano Lett.9 731
[2] Yu K-P, Yu W-Y, Kuo M-C, Liou Y-C and Chien S-H 2008
Appl Catal.B84 112
[3] Torrente-Murciano L, Lapkin A A, Bavykin D V, Walsh F C
and Wilson K 2007 J Catal.245 272
[4] Luu C L, Nguyen Q T and Ho S T 2010 Adv Nat Sci.:
Nanosci Nanotechnol.1 015008
[5] Vu A T, Nguyen Q T, Bui T H L, Tran M C, Dang T P and Tran
T K H 2010 Adv Nat Sci.: Nanosci Nanotechnol.1 015009
[6] Dang T M D, Nguyen T M H and Nguyen H P 2010 Adv Nat.
Sci.: Nanosci Nanotechnol.1 025011
[7] Perkas N, Pham M D, Gallezot P, Gedanken A and Besson M
2005 Appl Catal B59 121
[8] Pham M D, Aubert G, Gallezot P and Messon M 2007 Appl.
Catal.B73 236
[9] Elmasides C, Kondarides D, Grunert W and Verykios X E
1999 J Phys Chem B103 5227
[10] Grimes C A 2007 J Mater Chem.17 1451
[11] Song Y-Y, Schmidt-Stein F, Bauer S and Schmuki P 2009
J Am Chem Soc.131 4230
[12] Mor G K, Shankar K, Paulose M, Varghese O K and Grimes
C A 2006 Nano Lett.6 215
[13] Zhang Q, Dandeneau C S, Candelaria S, Liu D, Garcia B B,
Zhou X, Jeong Y-H and Cao G 2010 Chem Mater.22 2427
[14] Song H, Qiu X, Guo D and Li F 2008 J Power Sources178 97
[15] Bavykin D V, Lapkin A A, Plucinski P K, Friedrich J M and
Walsh F C 2005 J Catal.235 10
[16] Liming W and Binghua Y 2010 4th Int Conf on
Bioinformatics and Biomedical Engineering (4th iCBBE, 18–20 June 2010, Chengdu, China) Proc.ed W Lu (Piscataway, NJ: IEEE)
DOI.:10.1109/ICBBE.2010.5514829
[17] Bandara J, Shankar K, Basham J, Wietasch H, Paulose M,
Varghese O K, Grimes C A and Thelakkat M 2011 Eur.
Phys J Appl Phys.53 20601
[18] Gomez de la Fuente J L, Martinez-Huerta M V, Rojas S, Hernadez-Fernandez P, Terreos P, Fierro J L G and Pena
M A 2009 Appl Catal B88 505
[19] Huang S Y and Yeh C T 2010 J Power Sources195 2638
[20] Ghicov A, Tsuchiya H, Macak J M and Schmuki P 2005
Electrochem Commun.7 505
[21] Liu Y, Zhou B, Li J, Can X, Bai J and Cai W 2009 Appl Catal.
B92 326
[22] Bauer S, Kleber S and Schmuki P 2006 Electrochem.
Commun.8 1321
[23] Moulder J F, Stickle W F, Sobol P E and Bomben K D 1992
Handbook of X-Ray Photoelectron Spectroscopy(Eden, Prarie, MN: Perkin-Elmer)
[24] Li D, Chang P-C, Chien C-J and Lu J G 2010 Chem Mater.
22 5707
[25] Mazzieri V, Coloma-Pascual F, Arcoya A, L’Argentiere P C
and Figoli N S 2003 Appl Surf Sci.210 222
[26] Rochefort D, Dabo P, Guay D and Sherwood P M A 2003
Electrochim Acta48 4245
[27] Mun C, Ehrhardt J J, Lambert J and Madic C 2007 Appl Surf.
Sci.253 7613
[28] Kim K S and Winograd N 1974 J Catal.35 66