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Radiation-induced synthesis ofRuO2 nanoparticles by thermaldecomposition of Ru-tris-acetylacetonateR. M. Mahfouz a , M. Rafiq H. Siddiqui a & N. M. Abd El-Salam aa Department of Chemistry, College of Science, King SaudUniversity, PO Box 2455, Riyadh, 11451, Saudi Arabiab Department of Natural Sciences, Riyadh Community College,King Saud University, PO Box 28095, Riyadh, 11437, Saudi ArabiaVersion of record first published: 23 Sep 2011.

To cite this article: R. M. Mahfouz, M. Rafiq H. Siddiqui & N. M. Abd El-Salam (2011): Radiation-induced synthesis of RuO2 nanoparticles by thermal decomposition of Ru-tris-acetylacetonate,Radiation Effects and Defects in Solids: Incorporating Plasma Science and Plasma Technology,166:12, 951-958

To link to this article: http://dx.doi.org/10.1080/10420150.2011.608357

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Radiation Effects & Defects in SolidsVol. 166, No. 12, December 2011, 951–958

Radiation-induced synthesis of RuO2 nanoparticles by thermaldecomposition of Ru-tris-acetylacetonate

R.M. Mahfouza*, M. Rafiq H. Siddiquia and N.M. Abd El-Salamb

aDepartment of Chemistry, College of Science, King Saud University, PO Box 2455, Riyadh 11451,Saudi Arabia; bDepartment of Natural Sciences, Riyadh Community College, King Saud University,

PO Box 28095, Riyadh 11437, Saudi Arabia

(Received 3 May 2011; final version received 21 July 2011)

Pure-phase RuO2 nanoparticles were obtained by thermal decomposition of unirradiated and γ -irradiatedRu-tris-acetylacetonate precursors. Several influencing factors including absorbed dose, calcination timesand temperatures and addition of surfactants were thoroughly investigated. The newly synthesized RuO2nanoparticles were characterized by X-ray diffraction, scanning electron microscopy (SEM) and trans-mission electron microscopy (TEM) techniques. The results showed that the best conditions for thepreparation of mono-dispersed RuO2 nanoparticles were achieved by calcinations of unirradiated Ru-tris-acetylacetonate for 6 h at 600◦C. For γ -irradiated Ru-tris-acetylacetonate with 102 Gy total γ -raydoses, the optimal conditions for RuO2 preparation were calcination for 2 h at 200◦C. Thermal stabilityof RuO2 nanoparticles was studied using thermogravimetric (TG) and differential thermal analysis (DTA)techniques, and the results were evaluated and discussed.

Keywords: ruthenium oxide; acetylacetonate; thermal studies; nanoparticles; γ -irradiation

1. Introduction

Tris(acetylacetonate)ruthenium (III) (Ru(acac)3) is considered a promising precursor for the syn-thesis of heterogeneous ruthenium catalyst that is active in the hydrogenolysis, isomerization andhydrogenation of hydrocarbons (1–3).

Ru(acac)3 is a suitable metal-organic compound for the preparation of RuO2, which plays animportant role in many applications such as catalysis, electrochemistry and electronic technology(4, 5). The thermal decomposition of unirradiated Ru(acac)3 in air has been studied by Musicet al. (6). The thermolysis of Ru(acac)3 supported on silica and alumina has been investigatedby Plyuto et al. (7). The results of these studies indicate that RuO2 is the solid product of thedecomposition.

RuO2 is a highly heat-conductive oxide with a strong resistance against chemical corrosion andhas a good thermal stability. RuO2 is a rutile-structured transition oxide and has a bulk resistivity of35 μ� cm (8). While sol–gel methods for the preparation of RuO2 nanoparticles are documented,work on solid-state synthesis is scarce.

*Corresponding author. Email: rmhfouz@ksu.edu.sa

ISSN 1042-0150 print/ISSN 1029-4953 online© 2011 Taylor & Francishttp://dx.doi.org/10.1080/10420150.2011.608357http://www.tandfonline.com

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No previous work concerning radiation-induced synthesis of RuO2 nanoparticles has beenreported, except our previous work dealing with the thermal decomposition of Ru(acac)3 (9).

Here, we present the synthesis of RuO2 nanoparticles by solid-state decomposition of Ru(acac)3

as a precursor. Several influencing factors such as absorbed γ -ray doses, calcination temperatureand duration times of calcinations have been thoroughly investigated.

2. Experimental

Ruthenium acetylacetonate (99.99%) was obtained commercially from Aldrich LTD and usedwithout further purification. Samples were dried in a desiccator before analysis. For the thermalexperiments, a thermogravimetric analyzer was used (TGA-7, Perkin-Elmer). The amounts of thesamples were kept at 10 ± 0.1 mg.

For irradiation, samples were encapsulated under vacuum in glass vials and exposed to succes-sively increasing doses of radiation at constant intensity using a cobalt-60 γ -ray cell 220 (Nordion,INT-INC, Ontario, Canada) at a dose rate of 104 Gy/h. The source was calibrated against a Frickeferrous sulfate dosimeter, and the dose rate in the irradiated samples was calculated by applyingappropriate corrections on the basis of both the photon mass attenuation and energy absorptioncoefficient for the sample and dosimeter (10).

The infrared (IR) spectra were recorded at KBr pellets using a Perkin-Elmer 1000FT-IRspectrophotometer.

X-ray diffraction (XRD) measurements were carried out on a Siemens D5000 X-raydiffractometer using a nickel filter (Cu Kα at λ = 1.5418Å).

Scanning electron microscopy (SEM) was performed using JSM 6360 ASEM instrument.Transmission electron microscopy (TEM) was performed using TEM-200 CX instrument (Japan).

3. Results and discussion

Figure 1 shows typical TG and DTA curves for unirradiated Ru(acac)3 in static air. The TG curvesshow that the decomposition of Ru(acac)3 proceeds in one major step in the temperature range of150–250◦C with the formation of RuO2 as a solid residue according to the following equation:

Ru(acac)3 −→ RuO2 + Volatiles. (1)

The acetylacetonate ligand was found as the major gaseous product below 300◦C. At atemperature higher than 400◦C, the ligand decomposed mainly to CO, CO2 and H2O (11).The experimentally observed weight loss was found to exceed that predicated on the basis ofEquation (1). This disagreement is most likely due to the sublimation fraction of Ru(acac)3.

The DTA curves show the superposition of several endothermic peaks in the temperature rangeof �210◦C to �280◦C associated with the crystallization of RuO2 and decomposition of acety-lacetonate ligand. Figure 2 shows typical TG and DTA curves of γ -irradiated Ru(acac)3 with atotal dose of 102 KGy. In addition to a reduction in the induction period of the decompositionby irradiation, the TG curve shows three overlapped decomposition stages (I–III) in the range of150–320◦C with sublimation stage IV occurring at 330◦C. Three exothermic peaks centered at230, 260 and 280◦C were recorded in the DTA curve.

The significant changes in the features of the decomposition curves between unirradiated andγ -irradiated samples of Ru(acac)3 could be attributed to the formation of point defects and trappedelectrons induced by γ -irradiation in the host lattice of Ru(acac)3.

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Radiation Effects & Defects in Solids 953

Figure 1. TG and DTA curves of unirradiated Ru(acac)3.

Figure 2. TG and DTA curves of γ -irradiated Ru(acac)3.

XRD patterns of unirradiated andγ -irradiated Ru(acac)3 are presented in Figure 3. Both patternsdisplay the characteristic diffraction lines of a monoclinic (space group p21/c) system without anysignificant changes as a result of γ -irradiation, but only a decrease in the intensity of diffractionlines was observed for the γ -irradiated sample with 102 kGy total γ -ray dose.

The physical and chemical changes induced by γ -irradiation in Ru(acac)3 were followed byrecording IR spectra before and after γ -irradiation, and the spectra are shown in Figure 4. Bothspectra displayed the characteristic bands assigned to various vibration modes of the acetylace-tonate group. The band assigned to vRu−O at 660 cm−1 was the most affected by irradiation,and its decrease in intensity could be attributed to bond scission and degradation caused byγ -irradiation.

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Figure 3. XRD patterns of Ru(acac)3: (a) unirradiated and (b) γ -irradiated (102 kGy).

Figure 4. IR spectra of Ru(acac)3: (a) unirradiated and (b) γ -irradiated (102 kGy).

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3.1. Synthesis of RuO2 nanoparticles

The solid residue of the thermal decomposition of unirradiated and γ -irradiated ruthenium acety-lacetonate was chemically and physically investigated at different calcination temperatures anddifferent time intervals. It should be mentioned that the formation of the solid residue initiallystarted by the appearance of Ru metal. The Ru metal was oxidized into RuO2 on increasing theheating temperatures as well as on prolonged heating at the same temperature. This prospect has

Figure 5. XRD patterns of unirradiated Ru(acac)3 samples calcined at (a) 200◦C for 24 h, (b) 300◦C for 6 h and (c)600◦C for 6 h.

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Figure 6. XRD patterns of γ -irradiated Ru(acac)3 calcined at 200◦C for 6 h.

been demonstrated by recording XRD patterns of the solid residue after calcinations of rutheniumacetylacetonate at different calcination temperatures for different time intervals. Figure 5 showsthe XRD patterns of the unirradiated Ru(acac)3 sample calcined at 200◦C for 24 h and two othersamples calcined at 300◦C and 600◦C for 6 h, respectively. The sample calcined at 200◦C exhib-ited a non-crystalline behavior due to the formation of Ru metal nanoparticles. The Bragg angleof 2θ = 43.4◦ was consistent with Ru(0) diffraction (d = 0.208 nm). The particle size calculatedfrom the Debye-Scherrer formula using the information from this peak was ≈1.7 nm.

The XRD patterns of the sample calcined at 300◦C display diffraction lines attributed to theformation of a mixture of Ru(0) and RuO2 nanomaterials. The samples calcined at 600◦C exhibitedcomplete transformation to RuO2 nanoparticles as demonstrated by the XRD patterns shown inFigure 5. γ -Irradiation of the sample with 102 kGy total γ -ray dose led to the formation of purephase of RuO2 by calcination of the sample at 200◦C for 2 h as shown by the XRD patternsshown in Figure 6. This result illustrates the significant role of γ -irradiation in minimizing bothcalcination temperature and calcination time for the synthesis of RuO2 nanoparticles. To confirmthis, we calcined the γ -irradiated samples under the same conditions of temperature and time, andwe performed XRD and SEM measurements and the results collected were not in the nanolevel.

The IR spectra of the prepared RuO2 nanoparticles display the characteristic band at ≈300 cm−1

attributed to lattice vibration of RuO2.SEM measurements of the investigated nanoparticles using both unirradiated and γ -irradiated

Ru(acac)3 precursors are shown in Figure 7(a) and (b), respectively. The two images show differentmorphologies, affording further evidence for the influence of γ -irradiation on the shapes and sizesof the as-prepared nanoparticles.

Different experiments were performed starting with RuCl2(DMSO)4 as precursor for the prepa-ration of RuO2 nanoparticles. The results showed that calcination of RuCl2(DMSO)4 at 200◦Cfor five days leads to the formation of pure phase of RuO2 nanoparticles.

Further experiments concerning the preparation of RuO2 nanoparticles by the thermaldecomposition of Ru(DMSO)4 are in progress in our laboratory.

Measurements of the thermal stability of the as-prepared RuO2 nanoparticles using TG/DTAtechniques indicated that the particles are stable up to 600◦C, where a sudden collapse can bedetected in the temperature range of 600–700◦C due to the decomposition of Ru and O fromthe broken RuO2 bonds. The broad endothermic peak accompanying the decomposition processindicated that the particles are in the nanosize level. We performed kinetic analysis for isothermaland non-isothermal decomposition of RuO2 nanoparticles prepared using both unirradiated and

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Radiation Effects & Defects in Solids 957

Figure 7. SEM measurements of RuO2 nanoparticles using (a) unirradiated Ru(acac)3 precursor and (b) γ -irradiatedRu(acac)3 precursor.

γ -irradiated Ru(acac)3. The analysis was done by applying a model-free approach using linearFlynn–Wall–Ozawa and nonlinear Vyazovkin iso-conversional methods (12–15). The results ofapplication of these free models on the investigated data showed a systematic dependence of Ea

on α, indicating a simple decomposition process. The entropy of activation (�S) of the thermaldecomposition was also calculated for each nanoparticle using the following relationship:

A =(

KTs

h

)e�S

R,

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Table 1. Data of activation energy (Ea), Arrhenius parameter (A) and the entropychange (�S).

DTA peak temperature (◦C) Ea (kJ mol−1) A (s−1) �S (J◦C−1 mol−1)

530 140 4121 −170

where A is the Arrhenius parameter, K is the Boltzmann constant, Ts is the peak temperature, h isthe Plank constant and R is the gas constant.

The data of activation energy (Ea), Arrhenius parameter (A) and the entropy change (�S) aresummarized in Table 1.

The data showed high thermal stability of the prepared RuO2 nanoparticles, phenomena whichcould be of potential use in technological applications of RuO2 nanoparticles.

Acknowledgement

This project was supported by King Saud University, Deanship of Scientific Research, College of Science Research Center.

References

(1) Vlaic, G.; Bart, J.C.J.; Cavigiolo, W.; Furesi, A.; Ragaini, V.; Cattania Sabbadini, M.G.; Burattini, E. J. Catal. 1987,107, 263–274.

(2) Tijani, A.; Coq, B.; Figueras, F. Appl. Catal. 1991, 76, 255–266.(3) Coq, B.; Crabb, E.; Warawdekar, M.; Bond, G.C.; Slaa, J.C.; Garagno, S.; Mercadante, L.; Ruitz, J.G.; Sierra, M.C.S.

J. Mol. Catal. 1994, 92, 107–121.(4) Eom, C.B.; Dover, R.D.; Philips, J.H.; Werder, D.J.; Marshall, J.H.; Chen, C.H.; Cava, R.J.; Fleming, R.M.; Fork,

D.K. Appl. Phys. Lett. 1993, 63, 2570–2572.(5) Vijay, D.P.; Desu, S.B. J. Electrochem. Soc. 1993, 140, 2640–2645.(6) Music, S.; Popoviæ, S.; Maljkoviæ, M.; Furiæ, K.; Gajoviæ, A. Materials Science Letters 2002, 21, 1131–1134.(7) Plyuto, Y.V.; Babic, I.V.; Sharanda, L.F.; Marcodewit, L.F.; Johannes, C. Thermochim. Acta 1999, 335, 87–91.(8) Pagnaer, J.J.; Nelis, D.; Mondelaers, D.; Vanhoyland, G.; D’Haen, J.; Van, M.K.; Bael, Van den Rul, H.; Mullens,

J.; Van Poucke, L.C. J. Eur. Ceram. Soc. 2004, 24, 919–923.(9) Mahfouz, R.M.; Al-Ahmari, Sh.A.; Warad, I.Kh.; Al-Resayes, S.I.; Alkayali, W.Z.; Raslan, K.R.; Al-Otaibi, A.M.

Radiat. Eff. Def. Solids 2008, 163, 115–125.(10) Spinks, J.W.T.; Woods, R.J. An Introduction to Radiation Chemistry; John Wiley & Sons: New York, 1990.(11) Vyazovkin, S.; Linert, W. J. Solid State Chem. 1995, 114, 392–398.(12) Flynn, J.H.; Wall, L.A. J. Res. Natl. Bur. Stand. 1966, 70A, 487–523.(13) Ozawa, T. Bull. Chem. Soc. Jpn. 1965, 38, 1881–1886.(14) Vyazovkin, S.; Linert, W. Chem. Phys. 1995, 193, 109–118.(15) Vyazovkin, S.; Dollimore, D. J. Chem. Inf. Comput. Sci. 1966, 36, 42–45.

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