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INVESTIGATION OF ARGENTUM, COPPER, COBALT AND NICKEL NANOPARTICLES BY TRANSPARENT ELECTRONIC MICROSCOPY

УДК 541.64.539.3:537.8

Методом просвечивающей электронной микроскопии изучены наночастицы серебра, меди, кобальта и никеля, полученные из ацетатов этих металлов в растворах поливинилпирролидона в диметилформамиде и диметилсульфоксиде.

ЖЭM әдісі орқылы куміс, мыс, кобальт және никельдің нанобөлшектері зерттеліп, осы металлдардың ацетаттарынан алынған поливинилпирролидоннің диметилформамид және диметилсульфоксид ерітінділері.

ABSTRACT

Nanoparticles of argentums, copper, cobalt and nickel obtained from acetates of these metals in polyvinylpirrolidone solutions in dimethylformamide and dimethylsulfoxide were studied by transparent electronic microscopy.

Keywords: metals, nanoparticles, stabilizing polymers, aprotic solvents, electronic microscopy

INTRODUCTION

Usually nanoparticles of noble metals are synthesed by reflux in alcohol solutions of stabilizing polymers as polyvinylalcohol, polyvinylpirrolidone etc.[1, 2].

In case of copper,cobalt and nickel their nanoparticles can be obtained by using strong reducers as hydrazine, sodium borhydride in the same media [3, 4].

Here we present simple method of nanoparticles synthesis with using aprotic solvents as dimethylformamide and dimethylsulfoxide.

EXPERIMENTAL

Argentums, copper, cobalt and nickel acetates of “Sigma Chemicals” (USA) were used. Polyvinylpirrolidone of “Sigma Chemicals” with molecular weight M = 40000 was used. Dimethylformamide (DMF) of “Guangdong Gguanghua” and dimethylsulfoxide (DMSO) of “Fisher” were used.

Transparent electronic microscopy and diffraction pictures were obtained with using microscopes EM-125K and JEOL JEM1200EXII at 60-120kV.

RESULTS AND DISCUSSIONS

Earlier it was shown that reducing of argentums acetate at boiling in ethanol solution of polyvinylpirrolidone goes more fast than in case of argentums nitrate [5, 6]. Also it is interesting to check that in DMF and DMSO it is possible to obtain argentums nanoparticles without boiling at room temperature.

At Figure1 transparent electronic microscopy pictures of argentums nanoparticles obtained from argentums acetate in DMF are shown. If at component ratio R = PVPd /Ag equal 80 the formation of spherical nanoparticles occurs, but at R = 40 nanoparticles of different forms appear: triangles, pentagons, rods etc. (Figure 1b, c and d). Calculations of interplanar distances in crystal lattice from diffractograms demonstrate the metallic nature of nanoparticles.


Figure 1. TEM picture and diffractograms of argentums nanoparticles in DMF. PVPd, M = 40000, R = 40,     standard deviation σ = 20,5 %. Magnification 100000x.


Figure 2. TEM picture of argentums nanoparticles in DMSO PVPd, M = 40000, R = 40 (a), R = 10 (б), σ = 54,3 %. Magnification 100000x (a) and 30000x (b).


Figure 3. TEM picture (a), diffractograms (b) and sizes distribution (c) of copper nanoparticles in DMSO. PVPd,  M =40000, R =   40, σ = 22,5 %. Magnification 100000x.


Figure 4. TEM picture (a), diffractograms (b) and sizes distribution (c) of copper nanoparticles in DMF. PVPd, M = 40000, R = 40, σ = 12,8 %. Magnification 120000x.


Figure 5. TEM picture (a), diffractograms (b) and sizes distribution (c) of cobalt nanoparticles in DMF. PVPd, M = 40000, R = 40, σ = 9,6 %. Magnification 100000x.


Figure 6. TEM picture (a), diffractograms (b) and sizes distribution (c) of cobalt nanoparticles in DMSO. PVPd, M = 40000, R = 40, σ = 32,2%. Magnification 100000x.


Figure 7. TEM picture (a), diffractograms (b) and sizes distribution (c) of nickel nanoparticles in DMF. PVPd, M = 40000, R = 40, σ = 16,0%. Magnification 100000x.

In DMSO argentums nanoparticles with relative narrow sizes distribution are forming only at R = 40 (Figure 2a).The decrease of R to 10 leads to decrease of stabilization and to aggregation of nanoparticles (Figure 2b).

Synthesis of copper, cobalt and nickel nanoparticles is not possible by simple reflux method in alcohols. It may be explained by more electronegative potentials of these metals in comparison with noble ones. Usually nitrates of these metals are reduced at elevated temperatures by using such strong reducers as hydrazine or sodium borhydride [3, 4].

We obtained copper, cobalt and nickel nanoparticles by reducing their acetates in polyvinylpirrolidone solutions in DMF and DMSO at elevated temperatures. As in the case of argentums nanoparticles during synthesis of copper, cobalt and nickel nanoparticles in DMF and DMSO the solvents play dual role as solvents and as reducers simultaneously.

Heating of copper acetate in DMF and in DMSO solutions of polyvinylpirrolidone at 150ºC during about 40 minutes leads to formation of red-orange colloid solutions of copper nanoparticles. Reducing is not observed for other copper salts. At Figure 3a and 4a TEM pictures of copper nanoparticles are presented. Diffractograms of Figure 3b and 4b demonstrate the metallic nature of obtained nanoparticles with narrow sizes distribution especially for DMF (Figure 3c and 4c) and average sizes about 2-3 nm.

Synthesis of cobalt nanoparticles were conducted in DMF and DMSO at 110-120ºC. Light-brown colored solutions were obtained.

TEM pictures (Figure 5a and 6a) and diffractograms (Figure 5b and 6b) show the formation of metallic nanoparticles with average sizes 2-3 nm and narrow sizes distribution (Figure 5c and 6c).

Nanoparticles of nickel were obtained in DMF at 150ºC. Light-brown solutions are forming. At Figure 7a TEM pictures of nickel nanoparticles and diffractograms (Figure 7b) demonstrate the formation of metallic particles with average sizes 2-3 nm and narrow sizes distribution (σ = 16,0 %).

Nickel nanoparticles were not obtained in DMSO.

Summary of obtained results is presented in Table 1.

From Table 1 it can see that:

1. Copper, cobalt and nickel nanoparticles obtained in DMF have a more narrow size distribution in comparison with results in DMSO.

2. Argentums nanoparticles obtained in DMF and in DMSO have a greater sizes and more wide sizes distribution.

CONCLUSION

Nanoparticles of argentums were obtained in soft conditions in aprotic solvents from acetate salt at room temperature.

Also copper, cobalt and nickel nanoparticles were synthesed in aprotic solvents from metal acetates at elevated temperatures without using the strong reducers as hydrazine or sodium borhydride.

Thus simple and easy reducing method for obtaining of argentums, cobalt and nickel nanoparticles was presented.

Table 1. Size characteristics of argentums, copper, cobalt and nickel nanoparticles. PVPd M = 40000, R = 40

Salt

Solvent

d, nm

σ, %

1

AgAc

DMF

9,1

20,5

2

Cu(Ac)2

DMF

2-3

12,8

3

Co(Ac)2

DMF

2-3

9,6

4

Ni(Ac)2

DMF

2-3

16,0

5

AgAc

DMSO

3,5

54,3

6

Cu(Ac)2

DMSO

2-3

22,5

7

Co(Ac)2

DMSO

2

32,2

REFERENCES

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4. Caro D., Bradley J.S. // Langmuir. 1998. V.14. P.295.

5. Shmakov S.N., Yagovkina A.A., Iskakov R.M., Zhubanov B.A., Bekturov E.A. // Izv.NAN RK, Ser.Chim. 2008. N 4. P.54.

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