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Sonochemical synthesis and characterization of nano-sized lead(II) 3D coordination polymer: Precursor for the synthesis of lead(II) oxybromide nanoparticles
Ultrasonics Sonochemistry 20 (2013) 1254–1260
Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Sonochemical synthesis and characterization of nano-sized lead(II) 3D coordination polymer: Precursor for the synthesis of lead(II) oxybromide nanoparticles Vahid Safarifard a, Ali Morsali a,⇑, Sang Woo Joo b,⇑ a b
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-4838, Tehran, Iran School of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, South Korea
a r t i c l e
i n f o
Article history: Received 9 December 2012 Received in revised form 17 January 2013 Accepted 29 January 2013 Available online 9 February 2013 Keywords: Coordination polymer Nano-structure Sonochemical Thermal decomposition
a b s t r a c t Nanoparticles of a three-dimensional coordination polymer, [Pb(L)(l2-Br)(H2O)]n (1), (L = 1H-1,2,4-triazole-3-carboxylate), have been synthesized by an ultrasonic method and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. The thermal stability of compound 1 both its bulk and nano-size has been studied by thermal gravimetric (TG) and differential thermal (DTA) analyses and compared each other. Concentration of initial reagents effects and the role of power ultrasound irradiation on size and morphology of nano-structured compound 1, have been studied. Calcination of the compound 1 at 500 °C under air atmosphere yields Pb3O2Br2 nanoparticles. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction In the last 10 years the field of coordination polymers has seen a tremendous expansion in research efforts [1]. Briefly, these materials consist of inorganic metal centers assembled by means of multifunctional polydentate organic ligands. These hybrid materials display a range of topologies resulting from these pairings, including one-, two-, and three-dimensional networks [2–4]. The considerable interest is driven by the impact on basic structural chemistry as well as by possible applications in a number of fields such as catalysis, molecular adsorption, luminescence, magnetism, nonlinear optics, and molecular sensing that are not found in mononuclear compounds [5–7]. Recently, nanosized coordination polymers with finite repeating units, have aroused a growing interest due to their special properties distinctive from conventional bulk coordination polymer [8]. Up to now, various coordination polymer nanocrystals including nanoparticles, nanocubes, nanorods, and nanotubes have been successfully synthesized. Nanoparticles of coordination polymers are fascinating to explore, because they are interesting candidates for applications in gas storage, conductivity, molecular recognition and separations, catalysis, chirality, photonics and magnetic materials [9–11]. Herein, we present a facile and environmentally friendly synthesis of nanocrystals of a 3D coordination polymer under ultra⇑ Corresponding authors. Tel.: +98 21 82884416; fax: +98 21 8009730 (A. Morsali). E-mail addresses: [email protected] (A. Morsali), [email protected] (S.W. Joo). 1350-4177/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ultsonch.2013.01.014
sonic irradiation. Although the sonochemical methods have been widely used for organic synthesis and the preparation of nanosized materials [12], to date the application of the ultrasonic method for the construction of coordination polymers remains unexplored. In this work, we would like to describe the rapid synthesis of nanocrystals of a lead(II) 3D coordination polymer, [Pb(L)(l2-Br)(H2O)]n (1) [13], (L = 1H-1,2,4-triazole-3-carboxylate). 1H-1,2,4-triazole3-carboxylic acid (HL) contains 1,2,4-triazole and one carboxylic acid functional group and to date some interesting coordination polymers with this ligand have been reported [14–16]. The results reveal that compared with traditional synthetic techniques, such as solvent diffusion technique, hydrothermal and solvothermal methods, ultrasonic synthesis is a simple, efficient, low cost, and environmentally friendly approach to nanoscale coordination polymers [17]. Sonochemical methods can lead to homogeneous nucleation and a substantial reduction in crystallization time compared with conventional oven heating when nanomaterials are prepared [18]. Many researchers have investigated the effect of ultrasound on chemical reactions, and most theories imply that the chemical or physical effects of ultrasound originate from acoustic cavitation within collapsing bubbles, which generates extremely localized hot spots having temperatures of roughly 5000 K, pressures of about 500 atm, and a lifetime of a few microseconds. Between the microbubble and the bulk solution, the interfacial region around the bubble has very large gradients of temperature, pressure, and the rapid motion of molecules leading to the production of excited states, bond breakage, the formation of free radicals, mechanical shocks, and high shear gradients [19]. The use of high-intensity ultrasound to enhance the reactivity of metals as a
V. Safarifard et al. / Ultrasonics Sonochemistry 20 (2013) 1254–1260
stoichiometric reagent has become a synthetic technique for many heterogeneous organic and organometallic reactions [20–26]. To proceed, we report the simple synthesis of Pb3O2Br2 nanoparticles by solid-state transformation of compound 1 calcined at 500 °C in air and without any surfactant or capping molecules. Lead oxyhalides represent an important class of inorganic materials with possible applications as ionic conductors and highly anisotropic nanomaterials. They are also interesting from the viewpoint of environmental chemistry and mineralogy [27]. Glasses based on Pb oxyhalides are widely used in the conversion of infrared light into visible light. The binary system PbO–PbBr2 based materials are used in the preparation of low melting glasses useful as glass scintillators in high energy physics [28]. However, compared with the great progress in the investigation of Pb3O2Br2 properties, studies on the synthesis of it, especially its nanostructures, have been lagging far behind. 2. Experimental 2.1. Materials and physical techniques All reagents for the synthesis and analysis were commercially available from Merck Company and used as received. Doubly-distilled water was used to prepare aqueous solutions. Ultrasonic generators were carried out on a SONICA-2200 EP, (maximum 305 W at 40 kHz) and TECNO-GAZ, S.p.A., Tecna 6, (maximum 138 W at 35 kHz). Melting points were measured on an Electrothermal 9100 apparatus. Elemental analyses (carbon, hydrogen, and nitrogen) were performed using a Heraeus CHN–O– Rapid analyzer. The infrared spectra were recorded on a Nicolet Fourier Transform IR, Nicolet 100 spectrometer in the range 500–4000 cm1 using the KBr disk technique. Thermogravimetric analysis (TGA) and differential thermal analyses (DTA) of the title compound were performed on a computer-controlled PL-STA 1500 apparatus. Singlephased powder sample of 1 was loaded into alumina pans and heated with a ramp rate of 10 °C/min from room temperature to 700 °C under argon atmosphere. The simulated XRD powder pattern based on single crystal data were prepared using Mercury software [29]. X-ray powder diffraction (XRPD) measurements were performed using a Philips X’pert diffractometer with monochromated Cu-Ka radiation (k = 1.54056 Å). The samples were characterized by a scanning electron microscope (SEM) (Philips XL 30 and S-4160) with gold coating. 2.2. Synthesis of [Pb(L)(l2-Br)(H2O)]n (1) Single crystals of 1 were prepared by a branched tube method [13], 1H-1,2,4-triazole-3-carboxylic acid (0.117 g, 1 mmol), lead(II) nitrate (0.331 g, 1 mmol) and potassium bromide (0.119 g, 1 mmol) were placed in the bottom main of a branched tube. Water was carefully added to fill both arms, and then the arm to be heated was placed in oil bath at 60 °C. After 3 days, colorless crystals were deposited in the cooler arm which were filtered off, washed with water and air dried. (0.225 g, yield 54%),
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m.p. 195 °C. (Found C 8.55, H 0.99, N 10.43%. calculated for C3H4BrN3O3Pb; C 8.63, H 0.96, N 10.07%). IR (cm1) selected bands: 464(s), 651(s), 1100(s), 1303(m), 1370(m), 1457(vs), 1606(s) and 3370(br). 2.3. Synthesis of [Pb(L)(l2-Br)(H2O)]n (1) nanostructure by a sonochemical process To prepare the nanoparticles of 1, 50 ml solution of lead(II) nitrate (0.01 M) in water was positioned in a high-density ultrasonic probe, operating at 40 kHz with a maximum power output of 305 W. Into this aqueous solution a 50 ml solution of the ligand 1H-1,2,4-triazole-3-carboxylic acid (0.01 M) and sodium hydroxide (0.01 M) and potassium bromide (0.01 M) were added dropwise. The obtained precipitates were filtered off, washed with water and then dried in air. m.p. 180 °C. (Found C 8.61, H 0.89, N 10.12%). IR (cm1) selected bands: 466(s), 661(s), 1106(s), 1309(m), 1373(m), 1465(vs), 1610(s) and 3373(br). For the study of the effect of concentration the initial reagents and the role of power ultrasound irradiation on size and morphology of nano-structured compound 1, the above processes were done with concentrations of 0.05 and 0.1 M and electrical powers of 138 and 305 W from the ultrasonic generators. 2.4. Preparation of Pb3O2Br2 nanoparticles For preparation of lead(II) oxide bromide nanoparticles, calcination of the single crystals compound 1 was done at 500 °C in static atmosphere of air for 4 h. IR spectrum and powder XRD diffraction shows that calcination was completed and the entire organic compound was decomposed. 3. Results and discussion Reaction of 1H-1,2,4-triazole-3-carboxylate (L) and potassium bromide with lead(II) nitrate leads to formation of a 3D coordination polymer [Pb(L)(l2-Br)(H2O)]n (1). Nanocrystals of compound 1 were synthesized using the ultrasonic method at an ambient temperature and atmospheric pressure for different concentrations the initial reagents of 0.01, 0.05 and 0.1 M as well as different electrical powers of 138 and 305 W from the ultrasonic generators, respectively. A control experiment was also carried out to synthesize compound 1 single crystals using a heat gradient applied to a aqueous solution of the reagents (the ‘‘branched tube method’’), and the structures were confirmed by IR, elemental analysis and powder Xray diffraction (XRD) patterns. Scheme 1 gives an overview of the methods used for the synthesis of [Pb(L)(l2-Br)(H2O)]n (1) using the two different routes. The elemental analysis and IR spectra of the nano-structure produced by the sonochemical method and of the bulk material produced by the branched tube method are indistinguishable (Fig. 1). For the IR spectrum of 1, the triazole out of plane ring absorption can be observed at 651 cm1. The symmetric and asymmetric vibrations of the carboxylate group are observed as two
Scheme 1. Materials produced and synthetic methods.
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Fig. 1. IR spectra of (a) nano-particles of compound 1 produced by sonochemical method, (b) bulk materials as synthesized of 1.
strong bands at 1457 and 1606 cm–1, respectively. The D(tastsym) values of 149 cm1 indicate that the carboxylate anions coordinate to the Pb(II) center in bridging mode [30]. Fig. 2 shows the simulated XRD pattern from single crystal X-ray data of compound 1 (Fig. 2a) in comparison with the XRD pattern of the typical sample of compound 1 prepared by the sonochemical process (Fig. 2b). Acceptable matches, with slight differences in 2h, were observed between the simulated and
experimental powder X-ray diffraction patterns. This indicates that the compound obtained by the sonochemical process as nanostructures is identical to that obtained by single crystal diffraction. The significant broadening of the peaks indicates that the particles are of nanometer dimensions. The reaction between 1H-1,2,4-triazole-3-carboxylate (L) and potassium bromide with lead(II) nitrate provided a crystalline material of the general formula [Pb(L)(l2-Br)(H2O)]n (1). The
Fig. 2. XRD patterns; (a) simulated pattern based on single crystal data of compound 1, (b) nanostructure of compound 1 prepared by sonochemical process.
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%Frequency
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Diameter (nm)
% Frequency
Fig. 4. SEM photograph and the corresponding particle size distribution histogram of compound 1 nanoparticles prepared by ultrasonic generator 138 W in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.01 M.
Diameter (nm) Fig. 3. SEM photographs and the corresponding particle size distribution histogram of compound 1 nanoparticles prepared by ultrasonic generator 305 W in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.01 M in two different scale bars.
morphology and size of compound 1 prepared by the sonochemical method was characterized by scanning electron microscopy (SEM) and shows that it is composed of particles with sizes of about 40 nm. Fig. 3 shows the scanning electron microscopy (SEM) and the corresponding particle size distribution histograms of the compound 1. Another high-density ultrasonic probe, operating at 35 kHz with a maximum power output of 138 W and different concentrations of lead(II) nitrate and ligands 1H-1,2,4-triazole-3carboxylate (L) and potassium bromide solution (0.1, 0.05 and 0.01 M) were tested (Figs. 4–6). Appropriate nano-sized particles of compound 1 were obtained at a smaller concentration of 0.01 M and with both different powers of ultrasound irradiation (Figs. 3 and 4). Particle sizes and morphology of the nanoparticles depend on the power of ultrasound
Fig. 5. SEM image of agglomerated microsized compound 1 particles prepared by ultrasonic generator 138 W in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.05 M.
irradiation. In order to investigate the role of power ultrasound irradiation on the nature of products, reactions were performed under different power ultrasound irradiation. Comparison between the samples with different power ultrasound irradiation shows that high power ultrasound irradiation decreased particles size. Thus, smaller crystals with narrower size distribution (for 305 W, see Fig. 4) were achieved by sonocrystallization at higher power ultrasound irradiation when compared with other power (138 W, Fig. 5) due to a promotion of the faster nucleation process in solution [31]. The size of the nanoparticles compound 1 increased with increasing concentration of initial reagents. Fig. 5 illustrates
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Fig. 6. SEM image of compound 1 microrods prepared by ultrasonic generator 138 W in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.1 M.
Fig. 7. SEM image of compound 1-bulk powder prepared via simple mixing of precursors in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.1 M.
agglomerated microsized particles obtained under 0.05 M concentration of initial reagents. According to Fig. 6, the increase in the concentration of initial reagents to 0.1 M lead to formation of microrods compound 1. For comparison the sonochemical synthesis, a compound 1 sample was also prepared via simple mixing of precursors, without ultrasonic irradiations, under 0.1 M concentration of initial reagents at an ambient temperature and atmospheric pressure for 1 h (1-bulk). Fig. 7 shows the SEM image of the 1-bulk powder sample. In comparison, the particles size of 1-bulk is 300–600 nm (Fig. 7), which is approximately 4–6 times bigger than the sample prepared by a sonochemical process with same concentration of initial reagents (0.1 M, Fig. 6). Such a observed size difference shows effect of sonochemical process [12]. The IR spectrum and XRD pattern of typical samples of compound 1 prepared by the sonochemical process at concentrations of 0.01, 0.05 and 0.1 M as well as 1-bulk powder sample prepared via simple mixing are also same with the crystalline sample. The structure of compound 1 has been reported by our group previously [13]. In 1, the coordination number is 7 and each PbII ion is in the holodirected geometry, and coordinated by two oxygen atoms, two nitrogen atoms of the L anions act as bridging ligands via a tetra-donor coordination mode and one oxygen atom of aqua ligand. Also two bridged bromide ions have coordinated to lead(II) ion forming quite distorted pentagonal bipyramid geometry, thus forming infinite 3D neutral network as illustrated in Fig. 8. The title complex crystallizes in the orthorhombic space group Pna21. To examine the thermal stability of the nano-sized particles and the single crystals of compound [Pb(L)(l2-Br)(H2O)]n (1), thermal gravimetric (TG) and differential thermal analyses (DTA) were carried out between 25 and 700 °C under argon flow (Fig. 9). Compound 1 is stable up to 145 °C at which temperature the water molecule begins to be removed. The solid residue formed at around 145 °C is suggested to be the water-free compound, [Pb(L)(l2-Br)]n. At higher temperatures, the decomposition of the water-free compound occurs to ultimately give solid that appears to be PbO (observed: 52.04, calcd: 53.50%). Nano-sized compound 1 is less stable and start to decompose at 105 °C. Detectable decomposition of the nano-particles of 1 thus starts about 40 ° earlier than that of its bulk counterparts, probably due to the much higher surface to volume ratio of the nano-sized particles, as more heat is needed to annihilate the lattices of the single crystals. Mass loss
Fig. 8. A fragment of the 3D framework in compound 1, viewed along c direction.
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Fig. 9. Thermal behavior of compound 1 as bulk and nanoparticle.
Fig. 10. XRD pattern of Pb3O2Br2 nanoparticles prepared by calcination of compound 1 at 500 °C.
the nano-structured material has the same appearance as those of their single crystalline counterparts and the endo- and exothermic effects are retained for nano-structured 1. Some differences between the maximum intensities indicate, in agreement with TGA results, a somehow lower stability of the nanostructures when compared with their single crystals. Fig 10 provides the XRD pattern of the residue obtained from calcination of compound 1. The obtained pattern matches with the standard pattern of Pb3O2Br2 with the lattice parameters (a = 9.8162 Å, b = 12.253 Å, c = 5.8754 Å, S.G. = Pbnm and z = 4) which is the same as the reported values (JCPDS card number 17-0241). An SEM image of the residue which is obtained from the direct calcination single crystals of compound 1 at 500 °C shows the formation of Pb3O2Br2 nanoparticles (Fig. 11). 4. Conclusions Fig. 11. SEM image of Pb3O2Br2 nanoparticles prepared by calcination of compound 1 at 500 °C.
calculations of the end residue and the XRD pattern of the final decomposition product (Fig. 10) show the formation of Pb3O2Br2. The DTA curve of compound 1 indicates the decomposition of compound takes place with one endothermic effect at 166 °C and three exothermic effects at 282, 343 and 602 °C (Fig. 9). The DTA curve of
A nano-sized Pb(II) 3D coordination polymer, [Pb(L)(l2-Br) (H2O)]n (1), L = 1H-1,2,4-triazole-3-carboxylate, was synthesized by sonochemical irradiation and compared with its crystalline structure [13]. Compound 1 was characterized by X-ray powder diffraction (XRD), IR spectroscopy and thermal gravimetric (TG) and differential thermal analysis (DTA). To proceed, compound 1 was decomposed at 500 °C under air atmosphere to produce Pb3O2Br2 nanoparticles. To prepare the nanostructure of compound 1, three different concentrations of initial reagents, 0.1,
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0.05 and 0.01 M, were tested. Appropriate nano-sized particles of compound 1 were obtained at a concentration of 0.01 M. Sizes and morphologies of the nanostructures depend on the concentration of initial reagents as well as the power of ultrasound irradiation used. The results of crystallization as a function of concentration of initial reagents as well as power of ultrasound irradiation show that for compound 1 the nucleation rate controls the crystallization process. Results show a decrease in the particles size as the power of ultrasound irradiation is increased. It is an interesting point that high concentration of initial reagents led to rod-like nanostructures morphology. All these results reveal that ultrasonic synthesis can be employed successfully as a simple, efficient, low cost, environmentally friendly and very promising method for the fabrication of nanoscale coordination polymers with tunable size and morphology by varying the reaction conditions. Acknowledgements The authors thank Tarbiat Modares University for all the supports. The work was supported by the World Class University Grant R32-2008-000-20082 of the National Research Foundation of Korea. References [1] R. Chakrabarty, P.S. Mukherjee, P.J. Stang, Supramolecular coordination: selfassembly of finite two- and three-dimensional ensembles, Chem. Rev. 111 (2011) 6810–6918. [2] A. Erxleben, Structures and properties of Zn(II) coordination polymers, Coord. Chem. Rev. 246 (2003) 203–228. [3] C.L. Cahill, D.T. de Lill, M. Frisch, Homo- and heterometallic coordination polymers from the f elements, CrystEngComm 9 (2007) 15–26. [4] A. Morsali, L.-G. Zhu, (4,40 -Bipyridine)mercury(II) coordination polymers, syntheses, and structures, Helv. Chim. Acta 89 (2006) 81–93. [5] S.R. Batten, S.M. Neville, D.R. Turner, Coordination polymers: design, analysis and application, The Royal Society of Chemistry 89 (2009). [6] C. Janiak, Engineering coordination polymers towards applications, Dalton Trans. (2003) 2781–2804. [7] H. Li, J. Zhai, X. Sun, Large-scale synthesis of coordination polymer microdendrites and their application as a sensing platform for fluorescent DNA detection, RSC Adv. 1 (2011) 725–730. [8] T. Uemura, S. Kitagawa, Nanocrystals of coordination polymers, Chem. Lett. 34 (2005) 132–137. [9] N. Soltanzadeh, A. Morsali, Sonochemical synthesis of a new nano-structures bismuth(III) supramolecular compound: new precursor for the preparation of bismuth(III) oxide nano-rods and bismuth(III) iodide nano-wires, Ultrason. Sonochem. 17 (2010) 139–144. [10] H. Sadeghzadeh, A. Morsali, Hedge balls nano-structure of a mixed-ligand lead(II) coordination polymer; thermal, structural and X-ray powder diffraction studies, CrystEngComm 12 (2010) 370–372. [11] W. Lu, S.S.-Y. Chui, K.-M. Ng, C.-M. Che, A Submicrometer wire-to-wheel metamorphism of hybrid tridentate cyclometalated platinum(II) complexes, Angew. Chem. Int. Ed. 47 (2008) 4568–4572.
[12] A. Gedanken, Using sonochemistry for the fabrication of nanomaterials, Ultrason. Sonochem. 11 (2004) 47–55. [13] V. Safarifard, A. Morsali, Reversible crystal-to-crystal transformation of a 3D– 3D coordination polymer by solid state anion-replacement with no change in nano-particle morphology, CrystEngComm 13 (2011) 4817–4819. [14] V. Safarifard, A. Morsali, Mechanochemical solid-state transformations from a 3D lead(II) chloride triazole carboxylate coordination polymer to its bromide/ thiocyanate analogs via anion-replacements: precursors for the preparation of lead(II) chloride/bromide/sulfide nanoparticles, CrystEngComm 14 (2012) 5130–5132. [15] D.-P. Li, X.-H. Zhou, X.-Q. Liang, C.-H. Li, C. Chen, J. Liu, X.-Z. You, Novel structural diversity of triazolate-based coordination polymers generated solvothermally with anions, Cryst. Growth Des. 10 (2010) 2136–2145. [16] V. Safarifard, A. Morsali, Sonochemical syntheses of a nanoparticles cadmium(II) supramolecule as a precursor for the synthesis of cadmium(II) oxide nanoparticles, Ultrason. Sonochem. 19 (2012) 1227–1233. [17] J.H. Bang, K.S. Suslick, Applications of ultrasound to the synthesis of nanostructured materials, Adv. Mater. 22 (2010) 1039–1059. [18] W.-J. Son, J. Kim, J. Kim, W.-S. Ahn, Sonochemical synthesis of MOF-5, Chem. Commun. (2008) 6336–6338. [19] L.-G. Qiu, Z.-Q. Li, Y. Wu, W. Wang, T. Xu, X. Jiang, Facile synthesis of nanocrystals of a microporous metal-organic framework by an ultrasonic method and selective sensing of organoamines, Chem. Commun. (2008) 3642– 3644. [20] A. Aslani, A. Morsali, M. Zeller, Nano-structures of two new lead(II) coordination polymers: new precursors for preparation of PbS nanostructures, Solid State Sci. 10 (2008) 1591–1597. [21] M.A. Alavi, A. Morsali, Syntheses and characterization of Mg(OH)2 and MgO nanostructures by ultrasonic method, Ultrason. Sonochem. 17 (2010) 441– 446. [22] A. Askarinejad, A. Morsali, Synthesis of cadmium(II) hydroxide, cadmium(II) carbonate and cadmium(II) oxide nanoparticles; investigation of intermediate products, Chem. Eng. J. 150 (2009) 569–571. [23] A. Aslani, A. Morsali, Sonochemical synthesis of nano-sized metal-organic lead(II) polymer: a precursor for the preparation of nano-structured lead(II) iodide and lead(II) oxide, Inorg. Chim. Acta 362 (2009) 5012–5016. [24] V. Safarifard, A. Morsali, Sonochemical syntheses of a nano-sized copper(II) supramolecule as a precursor for the synthesis of copper(II) oxide nanoparticles, Ultrason. Sonochem. 19 (2012) 823–829. [25] A.R. Abbasi, K. Akhbari, A. Morsali, Dense coating of surface mounted CuBTC metal-organic framework nanostructures on silk fibers, prepared by layer-bylayer method under ultrasound irradiation with antibacterial activity, Ultrason. Sonochem. 19 (2012) 846–852. [26] Z.-Q. Li, L.-G. Qiu, T. Xu, Y. Wu, W. Wang, Z.-Y. Wu, X. Jiang, Ultrasonic synthesis of the microporous metal–organic framework Cu3(BTC)2 at ambient temperature and pressure: an efficient and environmentally friendly method, Mater. Lett. 63 (2009) 78–80. [27] S.V. Krivovichev, O.I. Siidra, E.V. Nazarchuk, P.C. Burns, W. Depmeier, Particular topological complexity of lead oxide blocks in Pb31O22X18 (X = Br, Cl), Inorg. Chem. 45 (2006) 3846–3848. [28] O. Siidra, S. Krivovichev, Crystal chemistry of oxocentered chain lead oxyhalides and their importance as perspective materials, minerals as advanced materials I, Springer, 2008. pp. 129–141. [29] Mercury 1.4.1, Copyright Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK, 2001–2005. [30] K. Nakamoto, ‘Infrared and Raman Spectra of Inorganic and Coordination Compounds’, 5th ed., John Wiley and Sons, New York, 1997. [31] B. Seoane, J.M. Zamaro, C. Tellez, J. Coronas, Sonocrystallization of zeolitic imidazolate frameworks (ZIF-7, ZIF-8, ZIF-11 and ZIF-20), CrystEngComm 14 (2012) 3103–3107.
Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Sonochemical synthesis and characterization of nano-sized lead(II) 3D coordination polymer: Precursor for the synthesis of lead(II) oxybromide nanoparticles Vahid Safarifard a, Ali Morsali a,⇑, Sang Woo Joo b,⇑ a b
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-4838, Tehran, Iran School of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, South Korea
a r t i c l e
i n f o
Article history: Received 9 December 2012 Received in revised form 17 January 2013 Accepted 29 January 2013 Available online 9 February 2013 Keywords: Coordination polymer Nano-structure Sonochemical Thermal decomposition
a b s t r a c t Nanoparticles of a three-dimensional coordination polymer, [Pb(L)(l2-Br)(H2O)]n (1), (L = 1H-1,2,4-triazole-3-carboxylate), have been synthesized by an ultrasonic method and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. The thermal stability of compound 1 both its bulk and nano-size has been studied by thermal gravimetric (TG) and differential thermal (DTA) analyses and compared each other. Concentration of initial reagents effects and the role of power ultrasound irradiation on size and morphology of nano-structured compound 1, have been studied. Calcination of the compound 1 at 500 °C under air atmosphere yields Pb3O2Br2 nanoparticles. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction In the last 10 years the field of coordination polymers has seen a tremendous expansion in research efforts [1]. Briefly, these materials consist of inorganic metal centers assembled by means of multifunctional polydentate organic ligands. These hybrid materials display a range of topologies resulting from these pairings, including one-, two-, and three-dimensional networks [2–4]. The considerable interest is driven by the impact on basic structural chemistry as well as by possible applications in a number of fields such as catalysis, molecular adsorption, luminescence, magnetism, nonlinear optics, and molecular sensing that are not found in mononuclear compounds [5–7]. Recently, nanosized coordination polymers with finite repeating units, have aroused a growing interest due to their special properties distinctive from conventional bulk coordination polymer [8]. Up to now, various coordination polymer nanocrystals including nanoparticles, nanocubes, nanorods, and nanotubes have been successfully synthesized. Nanoparticles of coordination polymers are fascinating to explore, because they are interesting candidates for applications in gas storage, conductivity, molecular recognition and separations, catalysis, chirality, photonics and magnetic materials [9–11]. Herein, we present a facile and environmentally friendly synthesis of nanocrystals of a 3D coordination polymer under ultra⇑ Corresponding authors. Tel.: +98 21 82884416; fax: +98 21 8009730 (A. Morsali). E-mail addresses: [email protected] (A. Morsali), [email protected] (S.W. Joo). 1350-4177/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ultsonch.2013.01.014
sonic irradiation. Although the sonochemical methods have been widely used for organic synthesis and the preparation of nanosized materials [12], to date the application of the ultrasonic method for the construction of coordination polymers remains unexplored. In this work, we would like to describe the rapid synthesis of nanocrystals of a lead(II) 3D coordination polymer, [Pb(L)(l2-Br)(H2O)]n (1) [13], (L = 1H-1,2,4-triazole-3-carboxylate). 1H-1,2,4-triazole3-carboxylic acid (HL) contains 1,2,4-triazole and one carboxylic acid functional group and to date some interesting coordination polymers with this ligand have been reported [14–16]. The results reveal that compared with traditional synthetic techniques, such as solvent diffusion technique, hydrothermal and solvothermal methods, ultrasonic synthesis is a simple, efficient, low cost, and environmentally friendly approach to nanoscale coordination polymers [17]. Sonochemical methods can lead to homogeneous nucleation and a substantial reduction in crystallization time compared with conventional oven heating when nanomaterials are prepared [18]. Many researchers have investigated the effect of ultrasound on chemical reactions, and most theories imply that the chemical or physical effects of ultrasound originate from acoustic cavitation within collapsing bubbles, which generates extremely localized hot spots having temperatures of roughly 5000 K, pressures of about 500 atm, and a lifetime of a few microseconds. Between the microbubble and the bulk solution, the interfacial region around the bubble has very large gradients of temperature, pressure, and the rapid motion of molecules leading to the production of excited states, bond breakage, the formation of free radicals, mechanical shocks, and high shear gradients [19]. The use of high-intensity ultrasound to enhance the reactivity of metals as a
V. Safarifard et al. / Ultrasonics Sonochemistry 20 (2013) 1254–1260
stoichiometric reagent has become a synthetic technique for many heterogeneous organic and organometallic reactions [20–26]. To proceed, we report the simple synthesis of Pb3O2Br2 nanoparticles by solid-state transformation of compound 1 calcined at 500 °C in air and without any surfactant or capping molecules. Lead oxyhalides represent an important class of inorganic materials with possible applications as ionic conductors and highly anisotropic nanomaterials. They are also interesting from the viewpoint of environmental chemistry and mineralogy [27]. Glasses based on Pb oxyhalides are widely used in the conversion of infrared light into visible light. The binary system PbO–PbBr2 based materials are used in the preparation of low melting glasses useful as glass scintillators in high energy physics [28]. However, compared with the great progress in the investigation of Pb3O2Br2 properties, studies on the synthesis of it, especially its nanostructures, have been lagging far behind. 2. Experimental 2.1. Materials and physical techniques All reagents for the synthesis and analysis were commercially available from Merck Company and used as received. Doubly-distilled water was used to prepare aqueous solutions. Ultrasonic generators were carried out on a SONICA-2200 EP, (maximum 305 W at 40 kHz) and TECNO-GAZ, S.p.A., Tecna 6, (maximum 138 W at 35 kHz). Melting points were measured on an Electrothermal 9100 apparatus. Elemental analyses (carbon, hydrogen, and nitrogen) were performed using a Heraeus CHN–O– Rapid analyzer. The infrared spectra were recorded on a Nicolet Fourier Transform IR, Nicolet 100 spectrometer in the range 500–4000 cm1 using the KBr disk technique. Thermogravimetric analysis (TGA) and differential thermal analyses (DTA) of the title compound were performed on a computer-controlled PL-STA 1500 apparatus. Singlephased powder sample of 1 was loaded into alumina pans and heated with a ramp rate of 10 °C/min from room temperature to 700 °C under argon atmosphere. The simulated XRD powder pattern based on single crystal data were prepared using Mercury software [29]. X-ray powder diffraction (XRPD) measurements were performed using a Philips X’pert diffractometer with monochromated Cu-Ka radiation (k = 1.54056 Å). The samples were characterized by a scanning electron microscope (SEM) (Philips XL 30 and S-4160) with gold coating. 2.2. Synthesis of [Pb(L)(l2-Br)(H2O)]n (1) Single crystals of 1 were prepared by a branched tube method [13], 1H-1,2,4-triazole-3-carboxylic acid (0.117 g, 1 mmol), lead(II) nitrate (0.331 g, 1 mmol) and potassium bromide (0.119 g, 1 mmol) were placed in the bottom main of a branched tube. Water was carefully added to fill both arms, and then the arm to be heated was placed in oil bath at 60 °C. After 3 days, colorless crystals were deposited in the cooler arm which were filtered off, washed with water and air dried. (0.225 g, yield 54%),
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m.p. 195 °C. (Found C 8.55, H 0.99, N 10.43%. calculated for C3H4BrN3O3Pb; C 8.63, H 0.96, N 10.07%). IR (cm1) selected bands: 464(s), 651(s), 1100(s), 1303(m), 1370(m), 1457(vs), 1606(s) and 3370(br). 2.3. Synthesis of [Pb(L)(l2-Br)(H2O)]n (1) nanostructure by a sonochemical process To prepare the nanoparticles of 1, 50 ml solution of lead(II) nitrate (0.01 M) in water was positioned in a high-density ultrasonic probe, operating at 40 kHz with a maximum power output of 305 W. Into this aqueous solution a 50 ml solution of the ligand 1H-1,2,4-triazole-3-carboxylic acid (0.01 M) and sodium hydroxide (0.01 M) and potassium bromide (0.01 M) were added dropwise. The obtained precipitates were filtered off, washed with water and then dried in air. m.p. 180 °C. (Found C 8.61, H 0.89, N 10.12%). IR (cm1) selected bands: 466(s), 661(s), 1106(s), 1309(m), 1373(m), 1465(vs), 1610(s) and 3373(br). For the study of the effect of concentration the initial reagents and the role of power ultrasound irradiation on size and morphology of nano-structured compound 1, the above processes were done with concentrations of 0.05 and 0.1 M and electrical powers of 138 and 305 W from the ultrasonic generators. 2.4. Preparation of Pb3O2Br2 nanoparticles For preparation of lead(II) oxide bromide nanoparticles, calcination of the single crystals compound 1 was done at 500 °C in static atmosphere of air for 4 h. IR spectrum and powder XRD diffraction shows that calcination was completed and the entire organic compound was decomposed. 3. Results and discussion Reaction of 1H-1,2,4-triazole-3-carboxylate (L) and potassium bromide with lead(II) nitrate leads to formation of a 3D coordination polymer [Pb(L)(l2-Br)(H2O)]n (1). Nanocrystals of compound 1 were synthesized using the ultrasonic method at an ambient temperature and atmospheric pressure for different concentrations the initial reagents of 0.01, 0.05 and 0.1 M as well as different electrical powers of 138 and 305 W from the ultrasonic generators, respectively. A control experiment was also carried out to synthesize compound 1 single crystals using a heat gradient applied to a aqueous solution of the reagents (the ‘‘branched tube method’’), and the structures were confirmed by IR, elemental analysis and powder Xray diffraction (XRD) patterns. Scheme 1 gives an overview of the methods used for the synthesis of [Pb(L)(l2-Br)(H2O)]n (1) using the two different routes. The elemental analysis and IR spectra of the nano-structure produced by the sonochemical method and of the bulk material produced by the branched tube method are indistinguishable (Fig. 1). For the IR spectrum of 1, the triazole out of plane ring absorption can be observed at 651 cm1. The symmetric and asymmetric vibrations of the carboxylate group are observed as two
Scheme 1. Materials produced and synthetic methods.
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Fig. 1. IR spectra of (a) nano-particles of compound 1 produced by sonochemical method, (b) bulk materials as synthesized of 1.
strong bands at 1457 and 1606 cm–1, respectively. The D(tastsym) values of 149 cm1 indicate that the carboxylate anions coordinate to the Pb(II) center in bridging mode [30]. Fig. 2 shows the simulated XRD pattern from single crystal X-ray data of compound 1 (Fig. 2a) in comparison with the XRD pattern of the typical sample of compound 1 prepared by the sonochemical process (Fig. 2b). Acceptable matches, with slight differences in 2h, were observed between the simulated and
experimental powder X-ray diffraction patterns. This indicates that the compound obtained by the sonochemical process as nanostructures is identical to that obtained by single crystal diffraction. The significant broadening of the peaks indicates that the particles are of nanometer dimensions. The reaction between 1H-1,2,4-triazole-3-carboxylate (L) and potassium bromide with lead(II) nitrate provided a crystalline material of the general formula [Pb(L)(l2-Br)(H2O)]n (1). The
Fig. 2. XRD patterns; (a) simulated pattern based on single crystal data of compound 1, (b) nanostructure of compound 1 prepared by sonochemical process.
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%Frequency
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Diameter (nm)
% Frequency
Fig. 4. SEM photograph and the corresponding particle size distribution histogram of compound 1 nanoparticles prepared by ultrasonic generator 138 W in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.01 M.
Diameter (nm) Fig. 3. SEM photographs and the corresponding particle size distribution histogram of compound 1 nanoparticles prepared by ultrasonic generator 305 W in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.01 M in two different scale bars.
morphology and size of compound 1 prepared by the sonochemical method was characterized by scanning electron microscopy (SEM) and shows that it is composed of particles with sizes of about 40 nm. Fig. 3 shows the scanning electron microscopy (SEM) and the corresponding particle size distribution histograms of the compound 1. Another high-density ultrasonic probe, operating at 35 kHz with a maximum power output of 138 W and different concentrations of lead(II) nitrate and ligands 1H-1,2,4-triazole-3carboxylate (L) and potassium bromide solution (0.1, 0.05 and 0.01 M) were tested (Figs. 4–6). Appropriate nano-sized particles of compound 1 were obtained at a smaller concentration of 0.01 M and with both different powers of ultrasound irradiation (Figs. 3 and 4). Particle sizes and morphology of the nanoparticles depend on the power of ultrasound
Fig. 5. SEM image of agglomerated microsized compound 1 particles prepared by ultrasonic generator 138 W in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.05 M.
irradiation. In order to investigate the role of power ultrasound irradiation on the nature of products, reactions were performed under different power ultrasound irradiation. Comparison between the samples with different power ultrasound irradiation shows that high power ultrasound irradiation decreased particles size. Thus, smaller crystals with narrower size distribution (for 305 W, see Fig. 4) were achieved by sonocrystallization at higher power ultrasound irradiation when compared with other power (138 W, Fig. 5) due to a promotion of the faster nucleation process in solution [31]. The size of the nanoparticles compound 1 increased with increasing concentration of initial reagents. Fig. 5 illustrates
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Fig. 6. SEM image of compound 1 microrods prepared by ultrasonic generator 138 W in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.1 M.
Fig. 7. SEM image of compound 1-bulk powder prepared via simple mixing of precursors in concentration of initial reagents [Pb2+] = [L] = [Br] = 0.1 M.
agglomerated microsized particles obtained under 0.05 M concentration of initial reagents. According to Fig. 6, the increase in the concentration of initial reagents to 0.1 M lead to formation of microrods compound 1. For comparison the sonochemical synthesis, a compound 1 sample was also prepared via simple mixing of precursors, without ultrasonic irradiations, under 0.1 M concentration of initial reagents at an ambient temperature and atmospheric pressure for 1 h (1-bulk). Fig. 7 shows the SEM image of the 1-bulk powder sample. In comparison, the particles size of 1-bulk is 300–600 nm (Fig. 7), which is approximately 4–6 times bigger than the sample prepared by a sonochemical process with same concentration of initial reagents (0.1 M, Fig. 6). Such a observed size difference shows effect of sonochemical process [12]. The IR spectrum and XRD pattern of typical samples of compound 1 prepared by the sonochemical process at concentrations of 0.01, 0.05 and 0.1 M as well as 1-bulk powder sample prepared via simple mixing are also same with the crystalline sample. The structure of compound 1 has been reported by our group previously [13]. In 1, the coordination number is 7 and each PbII ion is in the holodirected geometry, and coordinated by two oxygen atoms, two nitrogen atoms of the L anions act as bridging ligands via a tetra-donor coordination mode and one oxygen atom of aqua ligand. Also two bridged bromide ions have coordinated to lead(II) ion forming quite distorted pentagonal bipyramid geometry, thus forming infinite 3D neutral network as illustrated in Fig. 8. The title complex crystallizes in the orthorhombic space group Pna21. To examine the thermal stability of the nano-sized particles and the single crystals of compound [Pb(L)(l2-Br)(H2O)]n (1), thermal gravimetric (TG) and differential thermal analyses (DTA) were carried out between 25 and 700 °C under argon flow (Fig. 9). Compound 1 is stable up to 145 °C at which temperature the water molecule begins to be removed. The solid residue formed at around 145 °C is suggested to be the water-free compound, [Pb(L)(l2-Br)]n. At higher temperatures, the decomposition of the water-free compound occurs to ultimately give solid that appears to be PbO (observed: 52.04, calcd: 53.50%). Nano-sized compound 1 is less stable and start to decompose at 105 °C. Detectable decomposition of the nano-particles of 1 thus starts about 40 ° earlier than that of its bulk counterparts, probably due to the much higher surface to volume ratio of the nano-sized particles, as more heat is needed to annihilate the lattices of the single crystals. Mass loss
Fig. 8. A fragment of the 3D framework in compound 1, viewed along c direction.
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Fig. 9. Thermal behavior of compound 1 as bulk and nanoparticle.
Fig. 10. XRD pattern of Pb3O2Br2 nanoparticles prepared by calcination of compound 1 at 500 °C.
the nano-structured material has the same appearance as those of their single crystalline counterparts and the endo- and exothermic effects are retained for nano-structured 1. Some differences between the maximum intensities indicate, in agreement with TGA results, a somehow lower stability of the nanostructures when compared with their single crystals. Fig 10 provides the XRD pattern of the residue obtained from calcination of compound 1. The obtained pattern matches with the standard pattern of Pb3O2Br2 with the lattice parameters (a = 9.8162 Å, b = 12.253 Å, c = 5.8754 Å, S.G. = Pbnm and z = 4) which is the same as the reported values (JCPDS card number 17-0241). An SEM image of the residue which is obtained from the direct calcination single crystals of compound 1 at 500 °C shows the formation of Pb3O2Br2 nanoparticles (Fig. 11). 4. Conclusions Fig. 11. SEM image of Pb3O2Br2 nanoparticles prepared by calcination of compound 1 at 500 °C.
calculations of the end residue and the XRD pattern of the final decomposition product (Fig. 10) show the formation of Pb3O2Br2. The DTA curve of compound 1 indicates the decomposition of compound takes place with one endothermic effect at 166 °C and three exothermic effects at 282, 343 and 602 °C (Fig. 9). The DTA curve of
A nano-sized Pb(II) 3D coordination polymer, [Pb(L)(l2-Br) (H2O)]n (1), L = 1H-1,2,4-triazole-3-carboxylate, was synthesized by sonochemical irradiation and compared with its crystalline structure [13]. Compound 1 was characterized by X-ray powder diffraction (XRD), IR spectroscopy and thermal gravimetric (TG) and differential thermal analysis (DTA). To proceed, compound 1 was decomposed at 500 °C under air atmosphere to produce Pb3O2Br2 nanoparticles. To prepare the nanostructure of compound 1, three different concentrations of initial reagents, 0.1,
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0.05 and 0.01 M, were tested. Appropriate nano-sized particles of compound 1 were obtained at a concentration of 0.01 M. Sizes and morphologies of the nanostructures depend on the concentration of initial reagents as well as the power of ultrasound irradiation used. The results of crystallization as a function of concentration of initial reagents as well as power of ultrasound irradiation show that for compound 1 the nucleation rate controls the crystallization process. Results show a decrease in the particles size as the power of ultrasound irradiation is increased. It is an interesting point that high concentration of initial reagents led to rod-like nanostructures morphology. All these results reveal that ultrasonic synthesis can be employed successfully as a simple, efficient, low cost, environmentally friendly and very promising method for the fabrication of nanoscale coordination polymers with tunable size and morphology by varying the reaction conditions. Acknowledgements The authors thank Tarbiat Modares University for all the supports. The work was supported by the World Class University Grant R32-2008-000-20082 of the National Research Foundation of Korea. References [1] R. Chakrabarty, P.S. Mukherjee, P.J. Stang, Supramolecular coordination: selfassembly of finite two- and three-dimensional ensembles, Chem. Rev. 111 (2011) 6810–6918. [2] A. Erxleben, Structures and properties of Zn(II) coordination polymers, Coord. Chem. Rev. 246 (2003) 203–228. [3] C.L. Cahill, D.T. de Lill, M. Frisch, Homo- and heterometallic coordination polymers from the f elements, CrystEngComm 9 (2007) 15–26. [4] A. Morsali, L.-G. Zhu, (4,40 -Bipyridine)mercury(II) coordination polymers, syntheses, and structures, Helv. Chim. Acta 89 (2006) 81–93. [5] S.R. Batten, S.M. Neville, D.R. Turner, Coordination polymers: design, analysis and application, The Royal Society of Chemistry 89 (2009). [6] C. Janiak, Engineering coordination polymers towards applications, Dalton Trans. (2003) 2781–2804. [7] H. Li, J. Zhai, X. Sun, Large-scale synthesis of coordination polymer microdendrites and their application as a sensing platform for fluorescent DNA detection, RSC Adv. 1 (2011) 725–730. [8] T. Uemura, S. Kitagawa, Nanocrystals of coordination polymers, Chem. Lett. 34 (2005) 132–137. [9] N. Soltanzadeh, A. Morsali, Sonochemical synthesis of a new nano-structures bismuth(III) supramolecular compound: new precursor for the preparation of bismuth(III) oxide nano-rods and bismuth(III) iodide nano-wires, Ultrason. Sonochem. 17 (2010) 139–144. [10] H. Sadeghzadeh, A. Morsali, Hedge balls nano-structure of a mixed-ligand lead(II) coordination polymer; thermal, structural and X-ray powder diffraction studies, CrystEngComm 12 (2010) 370–372. [11] W. Lu, S.S.-Y. Chui, K.-M. Ng, C.-M. Che, A Submicrometer wire-to-wheel metamorphism of hybrid tridentate cyclometalated platinum(II) complexes, Angew. Chem. Int. Ed. 47 (2008) 4568–4572.
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