RU2729991C1 - Method of producing silver nanoparticles with size of 30 ± 3 nm - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to colloidal chemistry, particularly to production of conditioned colloidal silver nanoparticles by a nitrate method, which can be used in medicine, agriculture, biology, etc. Silver nanoparticles of size 30 ± 3 nm are obtained by reduction and stabilization of silver nitrate (AgNO₃) with sodium citrate (Na₃C₆H₅O₇) at ratio of concentrations of AgNO₃/Na₃C₆H₅O₇ solutions - 1:0.75 and their volumes of 5:1. In the Erlenmeyer flask one prepares 80 ml of 0.002 M AgNO₃ solution and adds a "stirring" rod of the magnetic mixer. Refluxer is put on flask and installed on magnetic stirrer with heating, where temperature is set to 300 °C and mixing mode is 375 rpm. When the first signs of boiling, which confirm the beginning of condensate flowing along the walls of the dephlegmator and/or bulb, 16 ml of 0.0075 M solution of Na₃C₆H₅O₇ are added. When colour of solution changes to yellowish one changes mixing mode by 500 rpm, temperature by 200 °C. From the moment of change of colour of the solution to its yellow one boils for 20 minutes, after which the return cooler is disconnected, the flask is removed from the magnetic mixer and allowed to cool at room temperature for 18–24 hours.

EFFECT: invention enables to obtain colloidal silver series standard series size 30 ± 3 nm without signs of aggregation and crystallisation.

1 cl, 2 dwg, 4 tbl

Description

This invention relates to the field of colloidal chemistry, immunochemistry, nanotechnology and solves the problem of obtaining nanoparticles of colloidal silver (NCS). Due to their unique physical, chemical and biological properties, silver nanoparticles are used in many fields of science and technology. They are part of spectrally selective coatings for absorbing solar energy, they are used as chemotherapeutic agents and catalysts for chemical reactions, and are also used for antimicrobial sterilization. This area of application includes the production of various packaging, dressing, textiles, water-based paints and enamels. It is also known that various preparations and cosmetics are produced on the basis of colloidal silver [Yamanova, P.P. On the use of silver nanoparticles in light industry / P.P. Yamanova, G.R. Nikolaenko // Bulletin of Kazan Technological University. - 2013. - No. 16. - S. 39-41].

Physical and chemical methods for obtaining silver nanoparticles are currently known. When using physical methods, nanoparticles are formed by dispersing large metal particles using colloid mills or ultrasound. Chemical methods make it possible to obtain nanoparticles as a result of a chemical reduction reaction in a solution of metal ions [Kolyada, L.G. Synthesis and research of silver nanoparticles and the possibility of their use in food packaging / L.G. Kolyada, N.L. Medyanik, Yu.Yu. Efimova, A.V. Kremnev // Bulletin of MSTU im. G.I. Nosov. - 2015. - No. 2. - S. 65-69].

Among the chemical ones, there is a known method for producing silver nanoparticles by the borohydride method, which is presented in the work of N.M. Drozdova et al. [Drozdova, N.M. Dependence of the properties of silver nanoparticles on the preparation method. Drozdova, N.A. Yashtulov // Scientific Almanac. - 2018. - No. 5-2 (43). - S. 137-139]. In this embodiment, colloidal silver nanoparticles are obtained by reduction of silver salts with sodium tetrahydride borate. For this, 15 ml of 2⋅10 ^-3 mol / l NaBH _{4 is} cooled to a temperature of 0 ° C by placing it in a crystallizer with ice. Next, cooled sodium tetrahydroborate is added to 5 ml of 1⋅10 ^-3 mol / l AgNO ₃ prepared in distilled water, and the mixture is quickly stirred with vigorous shaking.

This method is universal for obtaining silver nanoparticles in stable forms. This is due to the fact that sodium tetrahydriborate has a higher reducing ability compared to other reagents used [Podzharnaya, K.S. Analysis of methods for obtaining nanosized silver particles. Podzharnaya // Advances in chemistry and chemical technology. - 2012. - No. 7 (136). - S. 85-87].

The disadvantages of the borohydride method are the high toxicity and aggressiveness of the reducing agents, as well as the impossibility of achieving high concentrations of nanoparticles in the final solutions.

The citrate-sulfate method of obtaining nanoparticles of colloidal silver (Keri Lee's method) is based on the reduction of silver ions with ferrous sulfate and stabilization of the resulting particles with sodium citrate [Carey, LM // American Journal of Science. - 1889. - V. 37 - P. 476-491]. This technique is carried out as follows. Two preparations are prepared: a 0.02% solution of AgNO ₃ and a mixture consisting of two solutions taken in equal volumes - Na ₃ C ₆ H ₅ O ₇ ⋅2H ₂ O and FeSO ₄ ⋅7H ₂ O with a final concentration of the substance in solution 6 g / l. The prepared mixture is quickly added to the AgNO ₃ solution, stirring vigorously on a magnetic stirrer for 1 hour [Drozdova, NM Dependence of the properties of silver nanoparticles on the preparation method. Drozdova, N.A. Yashtulov // Scientific Almanac. - 2018. - No. 5-2 (43). - S. 137-139].

Silver nanoparticles obtained by the Keri Lee method are significantly superior in optical and morphological characteristics, as well as in homogeneity, to conventional nitrate sols; however, the main disadvantage of this method is the use of high concentrations of reagents, which necessitates a series of successive deposition cycles of metal particles.

The closest to the claimed method is a method for producing colloidal silver nanoparticles by the Turkevich citrate method. Initially, this method was developed to obtain nanoparticles of colloidal gold, which consisted in the reduction of hydrochloric acid with sodium citrate by boiling in an aqueous solution [Turkevich J. A Study of the Nucleation and Growth Processes in the Synthesis of Colloidal Gold. Discuss / J. Turkevich, P.S. Stevenson, J. Hiller // Faraday Soc. - 1951. - No. 11. - P. 55-75]. Subsequently, the citrate method of Turkevich was applied to the synthesis of silver nanoparticles [Tripatni G.N.R. Adsorption of 2-Mercaptopyrimidine on Silver Nanoparticles in Water / G.N.R. Tripatni, V. Clements // J. Phys. Chem. - 2003. - V. 107. - No. 40. - P. 1125-11132].

This method was used in the work of O.V. Dementieva [Dementyeva O. The. Comparative study of the properties of silver hydrosols obtained by citrate and citrate-sulfate methods / O.V. Dementyeva, A.V. Malkovsky, M.A. Filippenko, V.M. Ore // Colloid Journal. - 2008. - T. 70. - No. 5. - S. 607-619]. The advantage of this work is the preparation and evaluation of various sols that differ in the molar and volume ratio of the reagents, as well as depending on the sampling time during the boiling of the reaction mixture. However, when evaluating the results of the work by the method of spectrophotometry and electron microscopy, the inhomogeneity of the hydrosol was revealed, with a spread in the particle diameter from 5 nm to 60 nm.

According to scientific literature, there are various modifications of the citrate method, differing in the time of boiling the reaction mixture and sampling with or without the use of cooling a solution of silver nanoparticles to stop the reduction reaction [Evdokimov, AA Obtaining and research of nanostructures: laboratory workshop on nanotechnology / A.A. Evdokimov, A.S. Sigov. - M: BINOM. Knowledge laboratory. - 2011. - 146 p.].

The main advantage of Turkevich's citrate method is that the citrate anion acts simultaneously as a reducing agent and a stabilizing agent for the resulting particles. However, when sodium citrate is both a stabilizer and a reducing agent, the nanoparticle formation process becomes especially sensitive to the synthesis conditions. The ratio of the concentrations of silver and citrate ions, as well as the boiling time of the solution and the mixing rate of the reagents, has a great influence on the size of nanoparticles.

Despite the abundance of methods for the synthesis of silver nanoparticles in various media (aqueous and organic), using various reducing agents, obtaining conditioned particles of a certain size remains a rather difficult task.

The lack of a clear algorithm for the production of silver nanoparticles justifies the feasibility of working out a step-by-step method for obtaining NPK, which is optimal for using nanoparticles in various fields of science, in medicine, industry, agriculture, due to the proven presence of antimicrobial, antiviral, antitoxic action in silver nanoparticles.

The technical result of the invention is the development of a step-by-step method for producing LCHS by the citrate method and the assessment of preparations obtained using the proven technique.

The technical result is achieved by reducing and stabilizing silver nitrate with sodium citrate, expressed in a step-by-step algorithm for obtaining preparations of colloidal silver with a size of 30 ± 3 nm, which represents the worked out stages of preparing silver nanoparticles taking into account all the necessary parameters in terms of the ratio of volumes and concentrations of reagents AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ , temperature and time parameters, as well as mixing modes, set at each stage.

To confirm the objectivity of the choice of optimal conditions for the preparation of NPK, the results of evaluating the series of preparations obtained under various conditions are presented.

During the development of the invention, the influence of the following parameters and conditions on the quality of the preparation of LCP was determined:

1) the ratio of the concentrations of the reagents AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ ;

2) the ratio of volumes of reagents AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ ;

3) the boiling time of the solution from the moment the yellow color appears until the end of the experiment.

We used silver nitrate AgNO ₃ (Sigma-Aldrich, USA), sodium citrate Na ₃ C ₆ H ₅ O ₇ anhydrous (Sigma-Aldrich, USA), distilled water (GOST 6709-72), dionized water ( GOST 11.029.003-80), hydrochloric and nitric acid (Reakhim, Russia).

An Adventurer electronic analytical balance (OHAUS, USA) was used to weigh the reagents. All reagents were prepared in deionized water. To obtain deionized water, we used the UF Arium 611 UF system (Sartorius, Germany).

Colloidal silver nanoparticles were prepared in 100 ml Erlenmeyer flasks using a magnetic stirrer (Meidolph, Germany) and a ball reflux condenser. Glass pipettes for 5 and 10 ml, dispensers with variable volume, and plastic tips (Eppendorf, Germany) were used to add reagents. For sampling and storage of samples, foil-covered penicillin vials were used. Colloidal silver nanoparticles were prepared using a heated magnetic stirrer (Heidolph, Germany). The sizes and electron density of nanoparticles were analyzed on a JEM-1011 electron transmission microscope (Jeol, Japan).

All laboratory glassware intended for the preparation of NPK preparations was pretreated with a mixture of concentrated hydrochloric and nitric acids in a ratio of 3: 1 - "aqua regia". All the dishes were processed in a dry heat oven at 180 ° C for 60 min.

To prepare a 1 M matrix solution of silver nitrate (M = 169.87 g / mol), 10 ml of deionized water was added to 1.69 g of AgNO ₃ . The finished solution was stored in a dark glass vial in a refrigerator at a temperature of 4 ° C.

A solution of 1 M matrix sodium citrate (M = 258.0 g / mol) was prepared immediately before performing each experiment. For this, 10 ml of deionized water was added to 2.58 g of Na ₃ C ₆ H ₅ O ₇ .

For each series, the same temperature regime was used for boiling AgNO ₃ (300 ° C) and the stirring speed on a magnetic stirrer (375 rpm), relying on the previously developed method of obtaining colloidal gold nanoparticles by the citrate method [Bogacheva N. V., Darmov I. V., Krupina K.A., Smirnova D.N. Patent No. 2644466 "Method for producing colloidal gold nanoparticles with an average diameter of 25-30 nm" / Kirov, VyatSU]. The prepared solution of AgNO _{3 was} brought to a boil, then Na ₃ C ₆ H ₅ O ₇ was added dropwise into it and the color of the solution was observed to change to a yellowish color. When a yellow color appeared, the temperature regime was changed from 300 ° C to 200 ° C, the number of stirrer revolutions was changed from 375 rpm to 500 rpm.

In the course of the work, we consistently worked out the conditions influencing the condition of the NCHS.

At the first stage, while maintaining other equal parameters, different concentrations of reagents were used (Table 1). In this case, in 100 ml of a solution of colloidal silver, the final concentration of silver nitrate in the solution was 0.002 M, and the concentration of sodium citrate changed from 0.002 M in batch No. 1 to 0.0015 M in batch No. 2 and to 0.001 M in batch No. 3. The volumes of sodium citrate and silver nitrate in each batch were constant.

According to the results of electron microscopy, it was found that the preparation No. 1 contained a low concentration of heterogeneous particles, there was their aggregation, they were of various shapes - triangular, rod-shaped, oval; in preparation No. 3, conglomerates of unformed particles were observed; preparation No. 2 contained a high concentration of particles, their shape was more uniform and regular, aggregation was observed much less.

The results obtained are illustrated in FIG. 1, which is the dependence of the size of silver nanoparticles on the ratio of the concentrations of AgNO ₃ and Na3C6H5O7.

In the first stage for further working out a method of producing nanoparticles of colloidal silver was chosen ratio AgNO ₃ / Na3C6H5O7 concentrations - 1 / 0.75, resulting in uniform particles were obtained, of regular shape with a small degree of aggregation of 35 ± 5.

At the next stage, the effect of the ratio of the volumes of the reagents while maintaining the concentration ratio AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ (1 / 0.75) on the conditionality of the obtained series of preparations of colloidal silver nanoparticles was evaluated (Table 2).

According to the results of electron microscopy, it was found that in the preparation No. 3, in the preparation of which the volume ratio AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ 1/1 was chosen, a significantly larger number of conglomerates was observed than in the preparation No. 5 (the volume ratio reagents 5/1), where they were present, but in smaller quantities. The shape of the particles in both cases is correct, rounded, size 32.3-33.5 nm. Silver nanoparticles in preparation No. 4 had an irregular shape and large size - more than 50.0 nm. According to the results of this stage, preparation No. 5 was assessed as the most conditioned. The parameters used to obtain it were chosen for the third stage of the study.

At the third stage of the development of a step-by-step method for obtaining a conditioned preparation of silver nanoparticles, the parameters selected in the first two stages of the study were used (the concentration ratio AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ - 1: 0.75; the ratio of volumes AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ - 5: l) and the choice of the optimal boiling time of the solution after the beginning of the appearance of a yellowish color was carried out.

For this, when a yellow color of the solution appeared, the temperature regime on a magnetic stirrer was changed from 300 ° C to 200 ° C, the number of revolutions of the stirrer was changed from 375 rpm to 500 rpm, and sterile vials were sampled with an interval of 4 min for evaluation by electron microscopy. As a result, it was found that in samples No. 7 and 8 there was aggregate stability of the particles. When the solution was boiled for 20 minutes, the particles in the field of view were scattered, were of the correct rounded shape, approximately the same size - 30-33 nm.

The characteristics of 1-9 series of preparations obtained during the development of a step-by-step method for obtaining silver nanoparticles as a result of using various conditions is presented in Table 4.

According to the results of the experiment, it was found that the optimal parameters for the preparation of colloidal silver nanoparticles are as follows:

1) The ratio of concentrations of solutions AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ - 1: 0.75.

2) The ratio of the volumes of solutions AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ - 5: 1.

3) Optimum temperature and stirring mode of the magnetic stirrer: 300 ° C and 375 rpm - from the beginning of the experiment; 200 ° С and 500 rpm - from the moment the yellowish color appears.

4) The boiling time of the solution to stabilize the particles after the appearance of a yellowish color is 20 minutes.

The invention is illustrated by an example of obtaining three series of preparations of colloidal silver with a nanoparticle diameter of 30 ± 3 nm in a volume of 96 ml, prepared under the following conditions:

1) Prepare 16 ml of 0.0075 M Na ₃ C ₆ H ₅ O ₇ solution. To do this, add 0.031 g of Na ₃ C ₆ H ₅ O ₇ salt and 16 ml of deionized water at room temperature to a 100 ml Erleinmeyer flask, add a sterile "stirring" rod of a magnetic stirrer. Place the flask with the contents on a magnetic stirrer and dissolve the salt for 2 minutes with constant stirring.

2) Prepare 80 ml of 0.002 M AgNO ₃ solution. To do this, add 0.027 g of AgNO ₃ and 80 ml of deionized water at room temperature to a 100 ml Erleinmeyer flask, add a sterile "stirring" rod of a magnetic stirrer.

3) Put on a flask containing a 0.002 M solution AgNO ₃ solution, a reflux condenser. Place the flask with a reflux condenser on a magnetic stirrer and set the stirring mode to 375 rpm and the temperature to 300 ° С;

4) When the first signs of boiling appear (the beginning of condensate flowing down the walls of the reflux condenser and / or flask) add 16 ml of 0.0075 M Na ₃ C ₆ H ₅ O ₇ solution.

5) When the color of the solution changes to yellowish, change the operating mode of the magnetic stirrer to the following: stirring mode at 500 rpm and temperature at 200 ° C.

6) From the moment the solution color changes to yellow, boil the solution for another 20 minutes. Remove the flask from the magnetic stirrer. Cover the NHCS solution with foil and leave to cool for a day at room temperature, then store in a refrigerator at 4 ° C.

If it is necessary to prepare another volume of the drug, it is necessary to recalculate, observing the ratio of volumes and concentrations of reagents AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ .

The results obtained, confirming the efficiency of the method for step-by-step preparation of colloidal silver nanoparticles by the citrate method, are illustrated in Fig. 2, which is a table with photographs of the obtained conditioned series of NsCS preparations.

Thus, the developed step-by-step technique made it possible to obtain conditioned preparations of silver nanoparticles of the same rounded shape, 30 ± 3 nm in size, without signs of aggregation and crystallization.

The technical result of the invention is the development of a step-by-step method for the preparation of LPCS of size 30 ± 3, which represents the worked out stages of preparation of silver nanoparticles, taking into account all the necessary parameters in terms of the ratio of volumes and concentrations of reagents AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ , temperature and time parameters as well as mixing modes established at each stage - is achieved by the essential features indicated in the claims.

Claims (1)

A method of obtaining silver nanoparticles with a size of 30 ± 3 nm by reduction and stabilization of silver nitrate (AgNO ₃ ) with sodium citrate (Na ₃ C ₆ H ₅ O ₇ ) at a concentration ratio of solutions AgNO ₃ / Na ₃ C ₆ H ₅ O ₇ - 1: 0 , 75 and their volumes 5: 1, including the following stages: in an Erlenmeyer flask, prepare 80 ml of 0.002 M AgNO ₃ solution and add a stirring rod of a magnetic stirrer, put a reflux condenser on the flask and put it on a heated magnetic stirrer, set the temperature on the magnetic stirrer to 300 ° С and stirring mode 375 rpm, when the first signs of boiling appear, which confirm the beginning of condensate flowing down the walls of the reflux condenser and / or flask, add 16 ml of 0.0075 M Na ₃ C ₆ H ₅ O ₇ solution, when the color of the solution changes change the stirring mode to yellowish at 500 rpm, the temperature to 200 ° C, from the moment the solution color changes to yellow, it is boiled for 20 minutes, then the reflux condenser is disconnected, the flask is removed from the magnetic stirrer and allowed to cool at room temperature. temperature for 18-24 hours.

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