Photocatalytic hydrogen production using TiO2–Pt aerogels

Chemical Engineering Journal 242 (2014) 96–101

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Chemical Engineering Journal

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Photocatalytic hydrogen production using TiO2–Pt aerogels

1385-8947/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.cej.2013.12.018

⇑ Corresponding authors. Address: Department of Chemical Engineering,University of Patras, 26500 Patras, Greece. Tel.: +30 2610997513 (P. Lianos).

E-mail addresses: [email protected] (V. Danciu), [email protected](P. Lianos).

1 Permanent address: Comenius University, Faculty of Natural Sciences, Depart-ment of Inorganic Chemistry, 84215 Bratislava, Slovakia.

Jarmila Puskelova a,1, Lucian Baia b,c, Adriana Vulpoi b,c, Monica Baia b,c, Maria Antoniadou a,Vassilios Dracopoulos d, Elias Stathatos e, Kovacs Gabor f, Zsolt Pap f, Virginia Danciu f,⇑,Panagiotis Lianos a,d,⇑a Department of Chemical Engineering, University of Patras, 26500 Patras, Greeceb Faculty of Physics, Babes-Bolyai University, M. Kogalniceanu 1, 400084 Cluj-Napoca, Romaniac Institute for Interdisciplinary Research in Bio-Nano-Sciences, Babes-Bolyai University, Treboniu Laurian 42, 400271 Cluj-Napoca, Romaniad FORTH/ICE-HT, P.O. Box 1414, 26504 Patras, Greecee Electrical Engineering Dept., Technological–Educational Institute of Patras, 26334 Patras, Greecef Faculty of Chemistry and Chemical Engineering, Babes-Bolyai University, Arany Janos 11, 400028, Cluj-Napoca, Romania

h i g h l i g h t s

� Synthesis and characterization ofTiO2–Pt aerogels.� Materials of high specific surface up

to 162 m2 g�1.� Hydrogen production by

photocatalytic ethanol reforming.� Colloidal Pt nanoparticle formation

and size control.� Importance of the number of active

catalytic sites.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 26 September 2013Received in revised form 4 December 2013Accepted 7 December 2013Available online 3 January 2014

Keywords:TiO2–PtAerogelsPhotocatalytic hydrogen productionEthanol reforming

a b s t r a c t

TiO2–Pt aerogel composites have been synthesized by mixing sol–gel titania with Pt colloidal suspensionsfollowed by supercritical drying. The highest specific surface achieved with these materials rangedbetween 550 and 600 m2 g�1 before annealing and stayed relatively high, i.e. 162 m2 g�1, after calcina-tion. The concentration of Pt nanoparticles ranged between 0.3 and 1.0 wt.% while their size rangedbetween 5.75 and 6.5 nm. These composites were employed as photocatalysts for room-temperaturephotocatalytic reforming of ethanol and hydrogen production. The highest hydrogen production rate,7.2 mmol H2 h�1 g�1, was obtained in the case of the smallest and most concentrated metal nanoparticlesunderlying the importance of the number of active sites on the TiO2–Pt composites. This rate of hydrogenproduction is relatively high and reflects the relatively high specific surface of the employedphotocatalysts.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

Photocatalytic reforming of organic substances for hydrogenproduction is carried out in the presence of a photocatalyst, typi-cally nanocrystalline titania, modified with deposited noble metalnanoparticles. The Fermi level of noble metals is much lower in en-ergy than the conduction band (CB) of titania (and other transitionmetal oxide semiconductors). When the semiconductor is excitedby absorption of photons, electron–hole pairs are generated.

J. Puskelova et al. / Chemical Engineering Journal 242 (2014) 96–101 97

Electrons excited to the CB fall into the deep trap of attached metalnanoparticle and thus electron–hole separation is achieved. Fur-thermore, holes can be consumed by oxidation of the sacrificialagents, while trapped electrons interact with hydrogen ions pro-ducing molecular hydrogen. This model of photocatalytic hydrogenproduction is applicable to many different semiconductors, includ-ing transition metal oxides and sulfides. However, to this day, nobetter match has been found than the combination of nanocrystal-line titania with nanoparticulate platinum. Photocatalytic reform-ing remains a popular subject of research, even though, it goeson for several decades [1–15]. Recent works are geared by thesearch for new photocatalysts and combinations of photocatalystsas well as the search for sensitizers of large band gap semiconduc-tors to improve their solar responsive capacity [16–19]. However,concerning titania itself, there are still questions to answer. Com-mercial nanocrystalline titania has a limited specific surface area,for example, P25 is around 50 m2 g�1. Titania synthesized by softchemistry techniques like sol–gel in the presence of surfactanttemplates reaches higher specific surface and thus presents highactive interface with the reaction medium. Active interface isimportant for a photocatalyst since it defines its reaction front withits liquid or gaseous environment, determines the efficiency of theencounter with the reaction medium and affects the dispersion ofthe noble metal co-catalyst. This in turn helps avoiding aggregationof the noble metal nanoparticles and allows for higher lightabsorption cross-section. The deposited metal nanoparticles, theirelectrochemical potential, their size and distribution as well asthe kinetics of charge transfer have been and are being studiedwith a lot of interest in order to elucidate the implied processesand optimize photocatalytic hydrogen production [12,15,20,21].

With this in mind, in the present work, we have studied a com-bination between titania aerogels with platinum co-catalyst. TiO2

aerogels are a special class of materials, which are obtained bysupercritical drying of highly cross-linked inorganic gels, whosenetworks are built up from fundamental building blocks intercon-nected to form a well-defined porous structure [22–24]. In thepresent study, the involvement of this type of porous materials,which have been previously successfully used for pollutant photo-degradation [25–27], ensured a relatively high specific surface(162 m2 g�1), even when the samples were heat treated at a rela-tively elevated temperature (500 �C). The obtained aerogel-basedcomposites have been characterized by several techniques to en-sure their semiconductive and nanocrystalline properties, whiletheir photocatalytic capacity has been tested for hydrogen produc-tion applications. We have used ethanol as model ‘‘fuel’’ to be con-sumed by photodegradation. Ethanol is one of the modelsubstances obtained from biomass, therefore, renewable. The pres-ent results may then add to the effort of using renewable resourcesfor hydrogen production.

2. Experimental

2.1. Materials

Unless otherwise indicated, reagents were obtained from Al-drich and were used as received. Millipore water was used in allexperiments.

2.2. Preparation of Pt/TiO2 aerogels

2.2.1. Synthesis of TiO2 gelsTiO2 gels were prepared by one-step acid-catalyzed sol–gel pro-

cedure, using Ti[OCH(CH3)2]4, HNO3, C2H5OH (EtOH), and H2O atmolar ratios of 1:0.08:21:3.67. The obtained gels were kept foraging in a properly closed polyethylene box at room temperature

(21 days minimum) and then immersed in Pt colloidal solutionscontaining various amounts of platinum that were prepared as de-scribed in the following paragraph.

2.2.2. Synthesis of Pt colloidal solutions with added TiO2

Pt colloidal solutions were prepared by adapting an already re-ported protocol used for the synthesis of Au nanoparticles [28,29].Thus, 5.75, 6.0 and 6.5 nm Pt colloidal suspensions (their sizesdetermined by analyzing TEM data, see below) were obtained byadding 3.32, 1.66 and 0.83 mL of 25 � 10�3 mol L�1 trisodium cit-rate solution, respectively, to 332 mL of water. Then 25 g of TiO2

gel was introduced. After 30 min stirring, 3.35, 2.34 and 1 mL of25 � 10�3 mol L�1 hexachloroplatinic acid solution, respectively,was added to obtain 1.0%, 0.7% and 0.3% Pt nanoparticles concen-tration. After 30 min stirring, 3.35 mL of 0.3 mol L�1 NaBH4 (keptat 4 �C) was added to each solution and then stirred for 1 h. Theamount of platinum was thus controlled by the added quantityof hexachloroplatinic acid solution but the size of the formed plat-inum nanoparticles was controlled by the quantity of trisodiumcitrate [28,29].

2.2.3. Preparation of Pt/TiO2 aerogelsThe obtained modified TiO2 gels were washed 3–4 times with

EtOH, then kept overnight in EtOH and finally were supercriticallydried using liquid CO2 (313 K at 95.23 atm) in a homemade super-critical drying device. The dried Pt/TiO2 aerogels were thermallytreated with a rate of 1 �C/min until reaching 140 �C, and then at4 �C/min, until reaching the plateau of 500 �C, where they wereheld for 30 min. The samples were coded as follows: percent (Ptconcentration)–nm (Pt nanoparticles average size), e.g., 1.0%–6.5 nm means 1 wt.% of Pt concentration and Pt nanoparticles withan average size of 6.5 nm.

2.3. Photocatalytic installation for hydrogen production and detection

The reactor was of cylindrical shape, made of Pyrex glass andcarrying fittings allowing gas inlet–outlet. It was placed in frontof a UV-enhanced light source (Osram Ultramed 400 W) withoutfilters. Light was concentrated on the reactor by means of a cylin-drical lens. The intensity of radiation at the center of the reactor, asmeasured with a radiometer, was approximately 80 mW cm�2.100 mg of the TiO2–Pt photocatalyst were dispersed in 100 mL ofwater containing 1% vol. of ethanol. The slurry was continuouslystirred during the measurements. The solution was first degasedby an Ar flow and then the light was turned on. During measure-ments, the Ar flow was maintained at 20 cm3 min�1. Hydrogenwas detected on line by using a SRI 8610C gas chromatograph. Cal-ibration of the chromatograph signal was accomplished by com-parison with a standard of 0.25% H2 in Ar.

2.4. Characterization methods

The band gap energy (Eg) of the investigated samples was calcu-lated from their diffuse reflectance spectra, recorded by employinga Perkin Elmer Lambda 45 spectrophotometer in the wavelengthrange of 200–800 nm. Reflectance data were converted accordingto the Kubelka–Munk theory to F(R), and the band gap energiescorresponding to both direct and indirect transitions were calcu-lated from the individual plots of [F(R)�E]2 and [F(R)�E]1/2 versus en-ergy of the exciting light (E), respectively. A Tecnai F20 fieldemission, high resolution Transmission Electron Microscope(TEM) operating at an accelerating voltage of 200 kV and equippedwith Eagle 4 k CCD camera was employed to obtain the TEMimages. The samples were suspended in distillated water and thendeposited on Cu grids with carbon film evaporated on freshlycleaved mica. The sizes of the Pt nanoparticles were determined

200 260 320 380 440 500 560 620 680 740 8001015

2025

3035

404550

5560

6570

5.75 nm 0.7% 5.75nm 1% 6 nm 0.3% 6 nm 0.7% 6 nm 1% 6.5 nm 0.3% 6.5 nm 0.7% 6.5 nm 1% 5.75 nm 0.3%

Ref

lect

ance

Wavelength [nm]

Fig. 1. Diffuse reflectance spectra of the TiO2–Pt aerogel composites in relation tothe average particle and doping concentration.

15 25 35 45 55 65

6.5 nm

6 nm

Inte

nsity

2θ (degrees)

5.75 nm

1%

0.7%

0.3%

1%

0.7%0.3%

1%0.7%0.3%

Fig. 2. XRD patters of TiO2–Pt aerogel composites in relation to the average particleand doping concentration.

98 J. Puskelova et al. / Chemical Engineering Journal 242 (2014) 96–101

by using software TIA that is dedicated to the TEM Imaging andAnalysis processing. Field Emission Scanning Electron Microscope(FE-SEM) images were recorded with a ZEISS SUPRA 35VP device.XRD patterns were recorded with a Shimadzu XRD-6000 diffrac-tometer, using Cu Ka radiation (k = 1.5418 Å), with Ni-filter. Thecrystallites mean size for each sample was calculated accordingto the Scherrer’s equation. Specific surface area, pore size distribu-tion, and pore volume determinations were obtained by perform-ing N2 sorption/desorption measurements with a Sorptomatic1990 apparatus and using Brunauer–Emmett–Teller (BET), Bar-rett–Joyner–Halenda (BJH) and Horvath–Kawazoe (HK) calculationmethods. The samples were pretreated at 120 �C for a few hours toremove moisture and contaminants and the mass of powder wasaccurately measured before and after pretreatment.

3. Results and discussion

3.1. Photocatalysts characterization

TiO2–Pt aerogel composite photocatalysts were characterizedby several different techniques. The results revealed that Pt distri-bution follows a good dispersability, while the presence of Pt had asmall but detectable and reproducible effect on the nanocrystal-lites size and energy gap.

3.1.1. UV–Vis spectrophotometryDRS spectra recorded on the TiO2–Pt aerogel composites are

presented in Fig. 1 and the calculated direct and indirect Eg values

Table 1Values of the energy gap obtained from the DRS measurements for indirect and direct transdimension range as derived from XRD and HRTEM measurements.

Pt concentration and nanoparticle size Eg (eV)

Direct Indirect

Pt 0.3%–5.75 3.34 3.14Pt 0.7%–5.75 3.29 2.91Pt 1.0%–5.75 3.31 3.02

Pt 0.3%–6 3.30 3.05Pt 0.7%–6 3.31 3.00Pt 1.0%–6 3.30 2.96

Pt 0.3%–6.5 3.33 3.07Pt 0.7%–6.5 3.36 3.06Pt 1.0%–6.5 3.34 3.07

are listed in Table 1. Direct Eg values were all the same withinexperimental error. However, indirect Eg values did vary fromone sample to the other indicating that the presence of Pt had acertain influence on the combined photocatalyst behavior. Suchan influence was also previously observed for quantities of Pt lowerthan 1 wt.% [30,31]. As it will be seen below, the differentiation be-tween the titania nanoparticles, expressed by the different indirectEg values, reflects also on the photocatalytic properties. Therefore,it is concluded that indirect transitions is expected to play a role inthe present case.

3.1.2. XRD patternsFig. 2 shows XRD patterns obtained with all nine different TiO2–

Pt combinations. All samples crystallized in the anatase phase.Analysis of the main peak by the Scherrer’s equation yielded theTiO2 crystallite mean sizes listed in Table 1. Their values ranged be-tween 8 and 11 nm. It is seen that larger Pt nanoparticles induced adecrease in TiO2 size. Thus the smallest TiO2 sizes were observedwith 6.5 nm Pt. Similar influence was previously evidenced[32,33], when various noble metal nanoparticles were loaded ondifferent oxides. The concentration of Pt did not affect titania nano-particle size within experimental error.

3.1.3. SEM and TEM imagesSEM and TEM images are presented in Fig. 3 for a few character-

istic TiO2–Pt composites. SEM image (Fig. 3A) revealed a porousnanostructure built up of small nanoparticles of size 610 nm. Even

itions alongside the anatase crystalline mean size and corresponding Pt nanoparticles

TiO2 crystallites mean size (nm) Pt nanoparticles size (nm)

11 5.75 ± 1.259

10

9 6.0 ± 1.510

9

9 6.5 ± 288

Fig. 3. SEM (A) and TEM (B, C) images of TiO2–Pt aerogel composites. Image (B) corresponds to 0.7%–6.5 nm and image (C) to 1.0%–6 nm composite. The scale bars are: (A)200 nm; (B) 10 nm; and (C) 100 nm.

0

100

200

300

400

500

0.0 0.2 0.4 0.6 0.8 1.0

p/p0

V ads

/cm

3 g-1

Fig. 4. Adsorption/desorption isotherm of TiO2–Pt (1%)–6.5 nm aerogel.

J. Puskelova et al. / Chemical Engineering Journal 242 (2014) 96–101 99

though, accurate determination of crystallite size cannot be madeby SEM, the obtained values were very close to those calculatedby Scherrer’s equation. This was subsequently verified by

Table 2Specific surface area (SBET), average mesopore size (d), maxim mesopore siz

Pt concentration and nanoparticle size SBET (m2 g�1)

Pt 0.3%–5.75 91Pt 0.7%–5.75 138Pt 1.0%–5.75 99Pt 0.3%–6 109Pt 0.7%–6 118Pt 1.0%–6 124Pt 0.3%–6.5 138Pt 0.7%–6.5 162Pt 1.0%–6.5 145

recording TEM images. Indeed the latter clearly show the presenceof dark-colored Pt nanoparticles that have a relatively sphericalshape (see Fig. 3B) and are well distributed over the titania phase(Fig. 3C). The sizes of the Pt nanoparticles were determined fromthe TEM images by using the dedicated to the instrument softwareand are shown in Table 1. Even though, the error in calculating Ptsizes is very large, the average size is well distinguished in eachcase. Thus for the three different Pt concentrations the correspond-ing average Pt sizes were 5.75, 6.0 and 6.5 nm.

3.1.4. BET measurementsAdsorption and desorption isotherms of N2 are presented in

Fig. 4. According to IUPAC classification (1985), the physisorptionisotherms of TiO2–Pt (6.5 nm) aerogels correspond to type IV withthe H2 hysteresis loop. In this case, the pore structures are complexand tend to be made up of interconnected networks of pores of dif-ferent size and shape [34]. The corresponding values are listed inTable 2. All samples were porous and developed a high specificarea, which in the case of 0.7%–6.5 nm reached 162 m2 g�1. Oneshould mention that the as-prepared titania aerogel sample exhib-its a specific surface of 550–600 m2 g�1 [27], which after thermaltreatment at 500 �C for 2 h drastically diminishes reaching about120–160 m2 g�1 [30]. The decrease then of the specific surface is

e (dmax) and mesopore volume (Vp) of the TiO2–Pt samples.

d (nm) dmax (nm) Vp (cm3 g�1)

9.8 10.6 0.448.6 11.6 0.368.3 7.1 0.338 8.1 0.368.3 8.6 0.338.3 8.4 0.411.1 11.3 0.5311.1 11.4 0.6310.6 10.9 0.61

Fig. 5. Evolution of hydrogen by ethanol photocatalytic reforming in the presenceof TiO2–Pt (1%) composite photocatalyst with various Pt sizes: (1) 5.75 nm; (2)6 nm; and (3) 6.5 nm. The photodegradable solution contained 1% ethanol.

Fig. 6. Evolution of hydrogen by ethanol photocatalytic reforming in the presenceof TiO2–Pt composite photocatalyst carrying 5.75 nm Pt nanoparticles at variousconcentrations: (1) 1.0%; (2) 0.7%; and (3) 0.3%. The photodegradable solutioncontained 1% ethanol.

100 J. Puskelova et al. / Chemical Engineering Journal 242 (2014) 96–101

expected for calcinated aerogels. The merits of the present aerogelapproach relate with the fact that even with calcination at 500 �Cthe materials manage to preserve a substantial specific surface.The size of the pores was comparable with the titania nanoparticlesize. As a general remark, one observes that both the Pt nanoparti-cles size and their concentration affect the specific surface andpore volume, but it is worth mentioning that the highest valuesof the two morphological parameters were obtained for the biggestPt nanoparticles.

In conclusion, the characterization of the TiO2–Pt compositeswith various techniques revealed a porous structure with ratheruniform Pt distribution. We believe that this uniform distributionis the result of mixing metal and titania nanoparticles in the colloi-dal phase and the subsequent supercritical drying. Titania nano-crystal sizes ranged between 8 and 11 nm, the smallest sizesobserved when Pt nanoparticles were the largest. The highest val-ues of the two morphological parameters were obtained for thebiggest Pt nanoparticles (6.5 nm), while the highest specific surfacewas reached for the 0.7%–6.5 nm composite (162 m2 g�1). This suc-cessful mixing of titania with Pt nanoparticles is expected to have

beneficial consequences to the photocatalytic functioning of thecomposite photocatalysts. This is discussed in the next section.

3.2. Photocatalytic hydrogen production by ethanol reforming

Photocatalytic degradation of aqueous ethanol under anaerobicconditions follows an alcohol reforming model frequently dis-cussed in the past [3–7,11–13,17]. The overall mineralizationscheme obeys the following equation [6,13]:

C2H5OHþ 3H2O! 2CO2 þ 6H2 DH ¼ 173:1 kJ mol�1 ð1Þ

This endergonic reaction receives all necessary energy throughphotons absorbed by the photocatalyst. Photogenerated holesinteract with and oxidize the organic content while photogenerat-ed electrons reduce hydrogen ions and produce molecular hydro-gen. Pure photocatalysts are not capable of carrying out thesereactions because of extensive electron–hole recombination. Com-bined photocatalysts do enjoy electron–hole separation as alreadydiscussed. The present combined TiO2–Pt aerogel photocatalystswere proven especially successful in this functionality. The tempo-ral evolution of hydrogen in the presence of TiO2–Pt aerogel phot-ocatalysts are presented in Figs. 5 and 6. All curves could bedivided into three major parts: the rising part, corresponding tothe time needed for hydrogen build up within the reaction solutionand the tubing to the detection compartment; the peak rate, whichgives an indication of the maximum possible hydrogen productionrate under the present conditions; and the declining part, whichcorresponds to ‘‘fuel’’ consumption. If the quantity of ethanol weresubstantially larger, the production rate decline would have beenslower or the curve would have formed a plateau [13–15]. Theexistence or not of a plateau depends on the relative quantity ofcatalyst and fuel and the intensity of incident radiation or, insimple words, on how fast the photocatalyst can degrade fuel. Inall studied cases, smaller Pt nanoparticles gave more hydrogen.Thus, in Fig. 5, showing results obtained with the same (1%) Pt con-centration, the highest rate was obtained with 5.75 nm Pt nanopar-ticles. This result may be readily explained by the followingreasoning: smaller Pt nanoparticles means a broader Pt distribu-tion thus creating more combined photocatalyst-co-catalyst sites,therefore, more reaction sites. When the size of the Pt nanoparti-cles was kept constant but their concentration increased, a similartrend was observed. That is, the more numerous Pt nanoparticles,for the same quantity of titania, were more effective. On thecontrary, at the lowest Pt concentration, a marked drop of effi-ciency was demonstrated (Fig. 6). It is obvious that in the presentrange of concentrations and sizes, smaller and more numerousnanoparticles gave the highest hydrogen production rate, i.e.12 lmol min�1. In a recent review paper [35], the role of Pt nano-particle size is nicely explained as follows. When the size of Ptnanoparticles becomes smaller than about 1 nm, quantum confine-ment effects raise the Pt work function very high (�2.13 eV w.r.t.vacuum) while for the bulk platinum or for large nanoparticlesthe work function is �5.65 eV. The corresponding CB level fornanocrystalline titania is �4.4 eV while the valence band (VB) liesat �7.6 eV. When the Pt particles become too small, no injection ofelectrons can take place since the metal then lies too high. Whenthe particles are too large, then in addition to injection of electrons,holes can also be injected from the VB of titania onto the close-ly-ing energy state of the metal. This, however, corresponds to facili-tating electron–hole recombination. For this reason, metal particlesshould not be either too large or too small but be moderately small.Interestingly, the presently synthesized Pt nanoparticles, espe-cially, the smaller ones seem to lie in the proper size range. Indeed,since the quantity of photocatalyst was 100 mg, the rate of12 lmol min�1 corresponds to 7.2 mmol H2 h�1 g�1. This is a high

J. Puskelova et al. / Chemical Engineering Journal 242 (2014) 96–101 101

rate for photocatalytic hydrogen production, much higher than ithas been recorded in some cases [10,13–15,36,37] and comparablewith some optimized other cases [12]. Some control experimentswere also conducted using commercial titania Degussa P25 modi-fied with Pt for further appreciation of the importance of the pres-ent results. Indeed, maximum rate of hydrogen production wasthen 4.8 mmol H2 h�1 g�1, lower than the lowest quantity ofhydrogen produced with aerogel samples. It is then obvious thatthe aerogels route produces more efficient photocatalysts forhydrogen production.

4. Conclusions

Room temperature photocatalytic reforming of ethanol can besuccessfully realized using TiO2–Pt aerogel composites. These com-posites were obtained by mixing sol–gel synthesized titania withPt colloidal suspension followed by supercritical drying andannealing at 500 �C. The employed method of preparation of thecomposites allowed a relatively high catalyst specific surface andcontrol of size and concentration of metal nanoparticles. Thus Ptnanoparticle size was controlled by the quantity of added triso-dium citrate. Highest hydrogen production rate was reached inthe case of the smallest size and the most concentrated Ptnanoparticles.

Acknowledgements

We acknowledge financial aid from the Greece–Romania R&Dcooperation program 2012–2014. Jarmila Puskelova acknowledgesthe National scholarship programme of the Slovak Republic for thesupport of mobility of students, PhD students, university teachersand researchers, for a scholarship that allowed her stay in theUniversity of Patras. Authors L.B., A.V., G.K., Zs.P and V.D. highlyacknowledge the financial support by a grant of the RomanianNational Authority for Scientific Research, CNCS – UEFISCDI,project number PN-II-ID-PCE-2011-3-0442.

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