Formation of Stable Paramagnetic Nanocomposites Containing Zero

Article pubs.acs.org/JPCC

Formation of Stable Paramagnetic Nanocomposites Containing Zero-Valence Silver and Copper in a Polymeric Matrix Spartak S. Khutsishvili,* Tamara I. Vakul’skaya, Nadezhda P. Kuznetsova, Tamara G. Ermakova, Alexandr S. Pozdnyakov, and Galina F. Prozorova Irkutsk Institute of Chemistry of the Siberian Branch of the Russian Academy of Sciences, 1 Favorskogo Street, Irkutsk, 664033, Russia ABSTRACT: Magnetic properties of perspective nanocomposite materials based on copolymers of 1-vinyl-1,2,4-triazole with acrylonitrile and the formation of zero-valence metallic magnetic nanoparticles were investigated by electron paramagnetic resonance (EPR). In the EPR spectra of the nanocomposites intensive narrow singlets of conducting electrons with g = 2.00 were observed. The shape and width of the signals for silver and copper particles of the nanocomposites depended on microwave power. The Curie law character of the temperature dependences of intensity, g-factor value, and width of silver and copper nanoparticles’ signals were determined. Paramagnetic properties of the nanocomposites were found to remain constant over a long amount of time. X-ray diffraction (XRD), scanning electron microscope (SEM), teraohmmeter measurements, and atomic absorption analysis were also used to characterize these nanocomposites. The formation of the silver and copper nanoparticles from the rise of small clusters and their growth up to stabilization within the matrix under thermoreduction of initial complexes was monitored by EPR.

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INTRODUCTION Currently, nanomaterials are known to be used in many chemical processes which are beneficial for human beings:1−3 water purification, biodiesel production, fuel cell application, drug delivery, photocatalytic activity, thin film solar cell production, nanotoxicology, etc. In recent years, nanocomposite materials, containing metal particles and possessing complex properties, relevant to up-to-date catalysts, drugs, and optoelectronic devices, have received wide recognition and been successfully employed in industry.4−7 This trend is closely connected to the problem of the nanoparticles’ stabilization within a matrix, the generation of nanoclusters, their growth, supramolecular self-organization, and stability of the nanocomposites.8 It should be meantioned that, the nanoparticles’ sizes, which differ from the size of a bulk material, and the nature of the polymer matrix determine the unique properties of nanocomposites, in particular, the unusual magnetic properties. The homopolymer poly-1-vinyl-1,2,4-triazole possesses complexing ability, high chemical and thermal stability, biocompatibility,9 sorption properties,10 polymer electrolyte membrane properties,11,12 and high stabilizing ability at the formation of nanocomposites with metal nanoparticles.13,14 As for the polyacrylonitrile, it has properties such as conductivity, heat resistance, and hydrophilicity.15 Complex features of poly-1vinyl-1,2,4-triazole in combination with the properties of polyacrylonitrile allow us to obtain copolymers, where the mutual increase of useful individual properties is typical for the homopolymers. Nanocomposites based on poly-1-vinyl-1,2,4triazole and polyacrylonitrile with silver16 and copper17 © XXXX American Chemical Society

nanoparticles can have optical, electrical, and catalytic properties and are prospective materials for use in the microelectronics, techniques, and organic synthesis as a catalyst. Previously, we reported the successful synthesis of nanocomposites with a homogeneous narrow dispersed distribution of silver nanoparticles in the copolymer matrix of 1-vinyl-1,2,4triazole with acrylonitrile.18 A high ability for complexation, nontoxicity, as well as chemical and thermal stability are characterized for these polymers.10,19 The purpose of this work is the synthesis and study of new silver- and copper-containing polymer magnetic nanocomposites and dynamics of their formation in redox processes. In this paper, we present the detailed investigation of the behavior of EPR characteristics of paramagnetic polymeric nanocomposites based on copolymers of 1-vinyl-1,2,4-triazole with acrylonitrile that contain nanosized silver and copper particles under different temperature and microwave power as well as the initiation and growth of nanoparticles in time.

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EXPERIMENTAL SECTION Materials and Synthesis. The starting homo- and copolymers on the basis of 1-vinyl-1,2,4-triazole are diamagnetic. Synthesis of the copolymer matrix of 1-vinyl-1,2,4-triazole (VT) with acrylonitrile (AN) of 11:89 and 51:49 mol % (Scheme 1): 1-vinyl-1,2,4-triazole (boiling temperature 43 °C/ 3 mmHg, nD20 1.5100) synthesized according to the previously Received: January 27, 2014 Revised: July 21, 2014

A

dx.doi.org/10.1021/jp5045207 | J. Phys. Chem. C XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry C

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Scheme 1

developed technique,20 acrylonitrile from “Aldrich”, 2,2′azoisobutyronitrile (AIBN, recrystallized from ethanol and dried in a vacuum oven to constant mass), chemically pure silver nitrate AgNO3, and chemically pure CuCl2·H2O were used as starting reagent for synthesis of copolymers VT−AN and nanocomposites. Dimethylformamide (DMF) was purified by a known methodology,21 and chemically pure nitric acids of 37% concentration were used as solvents. Radical polymerization of 1-vinyl-1,2,4-triazole with acrylonitrile was conducted in an ampule in the presence of AIBN (0.5 wt %) in DMF under argon at 80 °C for 0.4 h. After the reaction mixture was precipitated in distilled water, it was washed twice with ethanol and dried in a vacuum oven at 50 °C to constant mass. The obtained compounds were white powders that are soluble in DMF, dimethyl sulfoxide, and nitric acid and can be used as stabilizing matrixes for novel nanocomposites, containing Ag(0) and Cu(0) particles. The copolymers have the properties of a high-resistance organic semiconductor. Their electroconductivity is 10−12−10−14 S/cm. Synthesis of the Silver-Containing Nanocomposite of the Copolymer VT−AN on the Example of Copolymer of 51:49 mol %. Copolymer VT−AN (0.3 g, 2.02 mmol) was dissolved in 10 mL of nitric acid (C = 37%, ρ = 1.23 g/cm3). Under stirring AgNO3 (0.162 g, 0.95 mmol) was added to the resulting solution and kept at 25 °C for 5 h. The formation of light yellow solution was observed; nitric acid was evaporated at 90 °C; and the solid substance of polymer silver complex heated at 210 °C for 1 h was isolated. The silver-containing nanocomposite of the copolymer VT−AN was obtained in the form of dark brown powder with silver content of 35 wt %. Synthesis of the Copper-Containing Nanocomposite of the Copolymer VT−AN on the Example of Copolymer of 11:89 mol % Content. Copolymer VT−AN (0.5 g, 3.38 mmol) was dissolved in 10 mL of nitric acid (C = 37%, ρ = 1.23 g/ cm3) for 5 h to full dissolution, but CuCl2·H2O (0.3 g, 1.76 mmol) was dissolved in 6 mL of HNO3. At mixing blue solution was instantly formed, from which nitric acid was evaporated at 90 °C, then dried in a vacuum oven to constant mass. The solid copper-containing polymer complex was heated at 210 °C for 1 h. Consequently, the copper-containing nanocomposite of the copolymer VT−AN was formed as the fine-dispersed black powder with copper content of 38 wt %. Characterizations and Measurements. The X-ray diffraction analysis has been made on powder diffractometers D8 ADVANCE (Cu radiation). The estimated size of metal nanoparticles was confirmed by XRD analysis. Diffraction patterns of the nanocomposites show a strongly broadened peak (Figure 1a) in the region where bulk silver has the most intense (111) reflection with d = 2.35 Å, which verifies the presence of nanosize metallic Ag in the samples. The XRD patterns showing the diffraction peak that correspond to metallic copper are observed at 2θ values of 46.7° and 50.8° (Figure 1b). We used the Debye−Scherrer formula22 to calculate their linear dimensions, which are 17−20 nm and 25−26 nm for the sizes of silver and copper nanoparticles, respectively.

Figure 1. XRD pattern for silver- (a) and copper-containing (b) nanocomposites of the copolymer VT−AN.

The metal percentage of nanocomposites has been determined by atomic absorption analysis using a PerkinElmer AAnalyst 200 spectrometer. The elemental analysis has shown that mass percentages of silver and copper in the nanocomposites on the basis of the copolymer VT−AN matrix are 35% and 38%, respectively. The electrical conductivity has been measured on the constant current with an E6-13A teraohmmeter use. The electroconductivity of nanocomposites for the silver-containing sample is 10−9−10−10 S/cm, and for the copper-containing one it is 10−6−10−7 S/cm. The SEM micrographs have been made on HITACHI TM 3000, detector SDD XFlash 430-H (Figure 2). The sizes of the cavities formed in the silver- and copper-containing nanocomposites are in the range of 0.8−32.0 μm and 0.3−12.0 μm, respectively. CW and pulse EPR spectra were recorded with an FT Xband Brüker ELEXSYS E-580 spectrometer (X-wave range 9.7 GHz). The precision of the measurement of g-factor was ±0.0002. CW EPR spectra were recorded at the following conditions: amplitude modulation 1.0 G, receiver gain 50 dB, time constant 0.02 s, conversion time 0.04 s, microwave power 0.6325 mW at room temperature. The monitoring of the nanocomposites obtained was carried out at 470 and 520 K for silver- and copper-containing nanocomposites, respectively, in quartz ampules (diameter of 3 mm) directly in the resonator of an EPR spectrometer at the modulation amplitude 1.0−5.0 G, receiver gain 30 dB, time constant 0.02−0.04 s, conversion time 0.07−0.08 s, and microwave power 0.6325 mW. The temperature dependences were studied in the 113−223 K range, slowly decreasing the temperature by 20° steps at B



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broad isotropic signal of the Cu2+ polymeric complex (g = 2.17, ΔH = 142 G). EPR characteristics of the complexes accord with the available literature data for analogous two-valence silver24,25 and copper26,27 complexes. Whereas the relaxation time for these complexes is quite short, it leads to the broadening of EPR signals.28 Signals of the nanocomposite materials (g = 2.00), which are recorded after thermal reduction of the complexes, belong to the conduction electrons of zero-valence metals, forming nanoclusters stabilized by the polymeric matrix, which is in agreement with data.29−32 For the investigation of nanoparticles’ initiation and their growth, the monitoring of polymeric complex reduction directly in the resonator of the EPR spectrometer has been carried out. Observations were made with a gradually increasing temperature, ranging from 373 to 470 K for silver- and to 520 K for copper-containing samples (the temperature limits were chosen at active reduction moments). Decreasing of the intensity of the wide complex signal close to zero and increasing of the narrow singlet are observed in both cases in 1 h (Figure 3). The g-factor’s shift and the broadening of its

Figure 2. SEM micrographs for silver- (a) and copper-containing (b) nanocomposites of the copolymer VT−AN.

amplitude modulation 1.0 G, receiver gain 30 dB, time constant 0.02 s, conversion time 0.07 s, and microwave power 0.6325 mW. The relaxation characteristics of nanocomposites were determined by pulse patterns of π−T−π/2−τ−π for T1, π/ 2−τ−π for T2, where π/2 = 0.02 μs, τ = 0.20 μs, and T = 1.00 μs. The concentrations of paramagnetic centers were calculated by the known method23 with the use of diphenylpicrylhydrazyl as a standard.

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RESULTS AND DISCUSSION The combination of 1,2,4-triazole and nitrile units in copolymers provides the macromolecules with high coordination ability toward the metal ions and decreases the nanoparticles’ agglomeration. Their coordination ability is explained both by nitrogen atom in the position 4 of the heterocycle, because it is the most electronegative atom of the 1,2,4-triazole cycle, and by cyano groups of acrylonitrile (Scheme 2). Indeed, the copolymers VT−AN show high activity toward the metal atoms by forming charge transfer complexes. Their EPR spectra depend on a sample orientation in the magnetic field. As a result, the polymer complexes of divalence silver have ascertained the anisotropy with g∥ = 2.2623 and g⊥ = 2.0762. On the contrary, copper-containing prototypes of copolymers VT−AN in the EPR spectrum give a

Figure 3. EPR monitoring of thermal reductions measured at 470 and 500 K for silver- (a) and copper-containing (b) polymeric complexes of the copolymer VT−AN.

Scheme 2

narrow line during the growth of the signal’s intensity occurs, which can be explained by such processes as the rise of small nanoclusters, their growth, stabilization of nanoparticles within the matrix, supramolecular self-organization, etc. Thus, the nanocomposite formation is realized in several stages and accompanied by the decrease of g-factor from 2.0043 to 2.0039 and linear increase of the intensity and double integral of the narrow signal. On the first stage (10−15 min) the width and parameter of asymmetry are also decreased, and then this process becomes slower. After 45−50 min the signal becomes symmetrical Lorentzian shape with ΔH = 5.5 G. The changes C



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Figure 4. EPR spectra measured at room temperature for silver- (a) and copper-containing (b) nanocomposites of the copolymer VT−AN at various microwave powers (mW).

have been obtained by the pulsed EPR method at 113 K (T1′ = 6.874 (±0.628) μs and T1″ = 38.573 (±1.559) μs, T2′ = 0.009 (±0.004) μs and T2″ = 0.192 (±0.003) μs). Since the EPR signals of zero-valence metals are registered in a range close to the g-factor of the free electron and they are similar to the signals of polyconjugated polymers (the triple CN bond of acrylonitrile can be polymerized under certain conditions forming double-chain conjugate polymers),39,40 it is necessary to exclude or determine the contributions of the latter into the narrow signals of nanocomposites. To check this, the copolymer VT−AN of composition 11:89 with high content of acrylonitrile obtained at a high-temperature regime up to 573 K during 1.5 h is used. To control the sample of the starting copolymer, after heating at 563−573 K, we have shown a weak narrow singlet (N = 1016 spin/g, g = 2.0050, ΔH = 5.3 G, A/B = 1.0). Noteworthy, unlike the nanocomposite systems, the obtained copolymer VT−AN even under so hard conditions gives a negligibly weak signal. Moreover, the exploration of completely reduced complexes of poly-1-vinyl1,2,4-triazole allows the EPR signals of metal nanoclusters to be registered and analyzed. Nevertheless, the spectra observed can be regarded as a superposition of two kinds of signals (mainly from different size zero-valence metal nanoparticles and also from the improbable signal of the polymer matrix). For this purpose, we have studied the dependency of EPR characteristics of the signals on microwave power (the so-called saturation effect) which is presented in Figure 4. The effect of saturation by microwave power on the samples containing zero-valence silver and copper is described by the different complicated curves in coordinates SQRT mW (Figure 5). For silver-containing samples, there are inflection points on the dependency of line widths at 0.8 and 4.5 implying that the signal is a superposition of at least two signals of similar gfactors and widths, which belong to different paramagnetic centers (Figure 5a). As for the dependency of the signals’ intensities on microwave power, the saturation curve has the inflection point at 4.5 and further almost approaches the plateau. For copper-containing nanocomposites, the inflection point on the dependency of line widths shifts to 0.45 (Figure 5b). In regard to dependency of the signal intensity at different microwave power values, the saturation occurs faster for silvercontaining nanocomposites, but full saturation caused by microwave power does not occur even at 8.0 for both silverand copper-containing nanocomposites. This means that the obtained samples contain free electrons of zero-valence metal nanoparticles with different sizes and probably organic radicals related to the polymeric matrix (the above-mentioned

observed may be explained by the formation of a great number of very small nanoparticles at once, with their following stabilization. During the thermal influence on the complexes there are intra- and intermolecular cyclization of acrylonitrile fragments,33 generating hydrogen whereby the reduction of two-valence metal ions to the zero-valence state is carried out. The transformation of the EPR spectrum of the two-valence copper complex at thermal reduction to the typical singlet from Cu0 is observed earlier in ref 34. Complexity assessment of these processes requires a separate investigation, and it is out of the frame of this work. However, hypothetically the reduction mechanism can be described relying on the electron transfer theory,35 when the temperature influence on the two-valence metal complex increases the energy of both the central ion and ligands (matrix), thereby making the transport of electrons from the hydrogen atom easier. In this case, the reduction process of the metal ion in the complex at elevated temperature has to be of dissociative intraspheric form and accompanied by zero-valence metal formation. The study of the reduction process starting at 500 K in both systems after 15 min has shown the only intensive narrow singlet conditioned by nanocomposite-containing metal particles. Electron spin resonance spectra for metal nanoparticles are very different from the behavior of bulk metals and depend on the sizes of nanoparticles. The narrow EPR signals observed with g-factor close to the free electron are most likely determined by the conduction electrons of zero-valence metals.36 As opposed to starting copolymers, the synthesized novel stable nanocomposites are paramagnetic deep brown and black powders, fine-dispersed, insoluble in water and the organic solvents. The preparation of nanocomposites is accompanied by almost complete metal reduction, and paramagnetism of the obtained nanocomposites is 1019−1020 spin/g. The EPR characteristics of the narrow singlets (symmetric for silverand asymmetric (A/B = 0.7) for copper-containing nanocomposites) are g-factor of 2.005 and width of 5−8 G (Figure 4), and such singlets are presented within the range between 1 and 30 nm of nanoparticles’ sizes.29,32,37 The studies of the EPR signals’ temperature dependency, their shape, and width in microwave saturation have proved that these signals refer to zero-valence metals that form clusters stabilized by the copolymer matrix. The complicated dependencies of the intensity of signals and width on microwave power can be explained by the size variations of the clusters (from one to several nanoparticles) and by some other factors.32,38 The relaxation characteristics of silver-containing nanocomposites D



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Table 1. Experimental EPR Characteristics for Silver- and Copper-Containing Nanocomposites on the Basis of the VT−AN Copolymer silver T, K

intensity, r.u.

g-factor

ΔH, G

intensity, r.u.

g-factor

ΔH, G

293 223 203 183 163 143 123 113

1.00 1.42 1.52 1.78 1.97 2.15 2.46 2.88

2.0050 2.0052 2.0053 2.0053 2.0054 2.0054 2.0055 2.0056

5.30 5.55 5.57 5.60 5.64 5.68 5.70 5.72

1.00 2.15 2.65 3.23 3.78 4.46 5.19 5.89

2.0056 2.0058 2.0058 2.0059 2.0059 2.0059 2.0060 2.0060

8.05 8.07 8.09 8.16 8.18 8.21 8.25 8.31

respectively, and the orders of magnitude are in agreement with energy activation for the conduction electrons.45−47 Characteristics of a narrow singlet of the silver-containing nanocomposite at 40 K are g = 2.0061, ΔH = 7.33 G, and A/B = 1.05, which significantly differ from the same parameters obtained at room temperature. Shifts of g-factors from ge and the dependences of width signal on the size of metal clusters are described in refs 37 and 48. It should be noted that weak doublet satellites’ lines of 107Ag and 109Ag isotopes with constants of 671 and 773 G, respectively,49−51 have been registered in the EPR spectrum at 113 K at high and low fields in only just obtained Ag(0)containing nanocomposites. This effect is typical for very small nanoparticles at low temperature.37,50,52 The ratio between their constants is 1.15 which coincides with one of the magnetic moments of the silver isotopes and, thus, confirms the lines’ references. However, the observation of these satellites over time is more difficult, which can be attributed to an agglomeration of small nanoparticles with further evolution of the nanosystem.29,32,51 The EPR signals of obtained compounds possess reversibility of the temperature dependence. Moreover, the studied nanocomposites show high stability during at least two years and keep practically invariable paramagnetic properties. Even hard UV-irradiation of the obtained nanocomposites with an LSB610 100 W Hg lamp (UV irradiation system, ER 203 UV) had no effect on the observed signals. However, in the case of silver-containing complexes the same UV-irradiation provokes the appearance of a weak symmetric singlet with characteristics identical to the signal of zero-valence silver.

Figure 5. Dependency (measured at room temperature) of signal width (solid blue line) and double integral (broken red line) on microwave power for silver- (a) and copper-containing (b) nanocomposites of the copolymer VT−AN.

polyconjugated polymer) due to the formation of the doublechain structures by the CN bond (possible source of additional stabilization centers). During the saturation process, the g-factor remains unchanged, and the signal is symmetric. The line shape is almost Lorentzian at saturation, which points to 1−2 nm of metal clusters’ sizes.29,41 According to Kawabata’s theory42 for small particles size estimation the relationship ΔH =

copper

1.78 × 1011 × (Δg )2 × d 2 × ρ VF × M

where the metal density ρ, the Fermi velocity VF, the peak-topeak line width ΔH, and the atomic mass of the metal M are known, values of Δg, which is the difference between the g value of the metal considered and the free-electron g-factor (2.0023), have been found by the experiments.43,44 Thus, we estimated the particle diameter d of stabilized nanoparticles as 1.10 and 0.73 nm for silver- and copper-containing nanocomposites, respectively. It is necessary to note that the EPR method detects only paramagnetic nanoparticles. If the calculated results of nanoparticle sizes by Kawabata’s theory are considered to be correct, then nanoparticles with larger sizes are diamagnetic. As the temperature decreases, the intensity of the EPR signals, g-factors, and widths increases. The data and the EPR spectra are given in Table 1 and Figure 6. The alteration of the EPR signals’ intensities follows the Curie law, which allows energy characteristics of the nanocomposites to be determined by the Boltzmann distribution N1/N2 = exp(−ΔE/kT). Thus, the thermoactivation energies calculated from the diagram (see Figure 6) in coordinates ln(N) − (1/T) are 13.5 and 19.9 meV for silver and copper clusters in the range of 113−223 K,

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CONCLUSIONS We have demonstrated that thermal reduction of copolymer complexes VT−AN with AgNO3 and CuCl2 leads to new paramagnetic (N = 1019−1020 spin/g) nanocomposite materials containing zero-valence silver and copper particles (17−20 nm and 25−26 nm for the sizes of silver and copper nanoparticles, respectively) stabilized by the polymeric matrix, with the metal content up to 38%. Average diameters of paramagnetic clusters around 1 nm of silver and copper nanocomposites were determined on the basis of EPR experimental data by Kawabata’s theory. Monitoring of the nanoparticle formation in a polymer matrix in a resonator of the EPR spectrometer has shown the regularity of variation of signal characteristics, which are determined by the sizes of the clusters. The thermal activation energies of free electrons 13.5 and 19.9 meV for silver and copper clusters in the range of 113−223 K, respectively, were estimated. The obtained nanocomposites E



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Figure 6. Temperature dependency EPR spectra for silver- (a) and copper-containing (b) nanocomposites of the copolymer VT−AN, at 1−223 K, 2−203 K, 3−183 K, 4−163 K, 5−143 K, 6−123 K, and 7−113 K. Membranes based on Copolymer Composites. In Carbon Nanomaterials in Clean Energy Hydrogen Systems; Baranovski, B., Zaginaichenko, S., Schur, D., Skorokhod, V., Veziroglu, A., Eds.; Springer: Berlin, 2008, NATO Science for Peace and Security Series C: Environmental Security, pp 379−384. (12) Aslan, A.; Ç elik, S. Ü .; Şen, Ü .; Haser, R.; Bozkurt, A. Intrinsically Proton-Conducting Poly(1-vinyl-1,2,4-triazole)/Triflic Acid Blends. Electrochim. Acta 2009, 54, 2957−2961. (13) Prozorova, G. F.; Pozdnyakov, A. S.; Emel’yanov, A. I.; Korzhova, S. A.; Ermakova, T. G.; Trofimov, B. A. Water-soluble Silver Nanocomposites with 1-Vinyl-1,2,4-triazole Copolymer. Dokl. Chem. 2013, 449, 87−88. (14) Pozdnyakov, A. S.; Emel’yanov, A. I.; Ermakova, T. G.; Prozorova, G. F. Functional Polymer Nanocomposites Containing Triazole and Carboxyl Groups. Polym. Sci. B 2014, 56, 238−246. (15) Güvendik, G.; Boşgelmez, I. I. Acrylonitrile. J. Fac. Pharm. Ankara Univ. 2000, 29, 31−58. (16) Zhang, Z.; Zhang, L.; Wang, S.; Chen, W.; Lei, Y. A Convenient Route to Polyacrylonitrile/Silver Nanoparticle Composite by Simultaneous Polymerization-Reduction Approach. Polymer 2001, 42, 8315− 8318. (17) Kozhitov, L. V.; Karpukhin, V. V.; Kozlov, V. V.; Karpacheva, G. P. Method of Obtaining Thermostable Nanocomposite Cu/Polyacrylonitrile. Russia. Patent RU 2,330,864 C1, August 10, 2008. (18) Kuznetsova, N. P.; Ermakova, T. G.; Pozdnyakov, A. S.; Emel’yanov, A. I.; Prozorova, G. F. Synthesis and Characteristics of Silver-Containing Polymer Nanocomposites on the basis of Copolymer of 1-Vynil-1,2,4-triazole with Acrylonitrile. Russ. Chem. Bull. 2013, 11, 2509−2513. (19) Pozdnyakov, A. S.; Ermakova, T. G.; Kanitskaya, L. V.; Kuznetsova, N. P.; Korzhova, S. A.; Prozorova, G. F. The Reactivity of 1-Vinyl-1,2,4-triazole in the Radical Copolimerization with Crotonic Aldehyde. Russ. J. Gen. Chem. 2012, 82, 87−90. (20) Makhno, L. P.; Ermakova, T. G.; Domnina, E. S.; Tatarova, L. A.; Skvortsov, G. G.; Lopyrev, V. A. Preparation Method of 1-vinyl1,2,4-triazole. Patent SU 464584, March 25, 1975. (21) Becker, H.; Berger, W.; Domschke, G.; Fanghänel, E.; Faust, J.; Fischer, M.; Gentz, F.; Gewald, K.; Gluch, R.; Mayer, R. et al. Organikum; VEB Deutscher Verlag der Wissenschaften: Berlin, 1976. (22) Barret, C. A.; Massalsky, T. B. Structure of Metalls; McGraw-Hill: New York, 1966. (23) Poole, C. P. Electron Spin Resonance: A Comprehensive Treatise on Experimental Techniques, 2nd ed.; Dover Publications: Dover, 1997. (24) Ali, M.; Shames, A. I.; Gangopadhyay, S.; Saha, B.; Meyerstein, D. Silver(II) Complexes of Tetraazamacrocycles: Studies on E.P.R. and Electron Transfer Kinetics with Tiosulfate Ion. Trans. Met. Chem. (Dordrecht, Neth.) 2004, 29, 463−470. (25) McMilan, J. A.; Smaler, B. Paramagnetic Resonance of Some Silver(II) Compounds. J. Chem. Phys. 1961, 35, 1698−1701. (26) Gonzalez-Alvarez, M.; Alzuet, G.; Borra, J.; Macias, B.; del Olmo, M.; Liu-Gonzalez, M.; Sanz, F. Nuclease Activity of

possess stable paramagnetic properties for at least two years, which testify to the invariability in the size of silver and copper nanoparticles, high stabilizing features of the matrix on the basis of copolymers 1-vinyl-1,2,4-triazole with acrylonitrile, and their perspective and attractivity for practical purposes.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Russian Foundation for Basic Research (Grants 08-03-00021 and 11-03-00022). REFERENCES

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