Electrosynthesis of silver metallonanocomposites in the 1-vinyl-1.2.4-triazole copolymer matrix with methacrylic acid

Abstract

Silver nanocomposites were synthesized by the electrochemical method in the matrix of a copolymer of 1-vinyl-1,2,4-triazole with methacrylic acid, by combining the process of electrochemical polymerization with cathodic precipitation of metals on metal electrodes. In the electronic spectra of nanocomposites, absorption bands appear with a maximum in the region of 417–421 nm, which is typical for systems with zero valence silver. The IR spectra show that the polymer structure hardly changes during the formation of nanocomposites and films. The presence of silver in the amorphous polymer phase is indicated by the results of X-ray diffraction studies. The silver content in nanocomposites is 0–9%, which leads to an increase in the viscosity of nanocomposite solutions compared to solutions of the initial copolymers. Transmission electron microscopy data show that the synthesized nanocomposites consist of particles with a diameter of 1–12 nm, predominantly spherical.

Introduction

Electrochemical synthesis and the structure of nanocomposites are very important for modern Material Science. The properties of the obtained compounds depend on the nature of the monomeric units and the dimensions of the clusters.^1–5

The formed materials are used in medicine as thromboresistant, biocompatible, antiviral materials, and in the creation of biosensors – in catalysis, as well as in other spheres of science.^2–12

Based on poly-1-vinyl-1.2.4-triazole, effective flocculants have been developed for clarification and stabilization of juices and wines, and monomolecular layers and films are formed from copolymers of 1-vinyl-1.2.4-triazole with styrene, methyl, and fluoroalkyl methacrylates. The high efficiency of poly-1-vinyl-1.2.4-triazole as a polymeric stabilizing matrix of silver and gold nanoparticles was found.

Nanomaterials used in medicine should possess hydrophilicity, thromboresistance, bioactivity and biocompatibility, and should also be easily combined with medicines and other substances. Copolymers, in particular the copolymer of 1-vinyl-1.2.4-triazole (VT) with methacrylic acid (MA), are used in the manufacture of surgical masks, wound coverings, and various medical devices; they are studied little, and their use in medicine is promising.^13–21

By using silver nanoparticles in the synthesis process, it is possible to obtain functional, thromboresistant, non-toxic polymers, whose production will greatly expand the range of materials used in pharmacy.

In most cases, the silver metal phase in the presence of a stabilizing polymer is formed using reducing agents (sodium borohydride, formaldehyde, glucose, etc.). This approach complicates the synthesis (additional reagents are introduced) and requires thorough purification of target compounds, which is accompanied by their loss. Therefore, approaches based on the reduction of silver ions both due to the medium in which the formation of nanocomposites is carried out and due to stabilizing polymers are of great interest.

The method of particle formation and the functionality of the polymer phase affect the properties of nanocomposites.

Since VT polymers and copolymers have high film formation, solubility, biocompatibility, in this study properties, and are nontoxic (LD₅₀ > 3000 mg∙kg⁻¹),^22,23 they were used as a polymer matrix.

The electrochemical method can form silver-containing compounds, nanocomposite coatings based on vinylazole copolymers.^22,24

A priority direction of modern science is the synthesis of nanostructured functional systems and the study of their properties – biomedical, nanocatalytic, etc.

Due to the peculiarity of their physical and chemical properties and the difference from the properties of a bulk metal, metal nanoparticles can be widely used in various areas of science.^25–35

As a rule, nanosized metal particles are thermodynamically unstable, and they can be obtained in a relatively pure form only when fixed on a solid, immobile carrier. To obtain the required size of particles on the carrier, the electrochemical method in different modifications is used.^9,35,36 The electrochemical method is one-stage and environmentally friendly. To obtain polymer nanocomposites with effective antimicrobial and antiviral properties, it is necessary to use particles containing zero-valent silver.^27–29

In this work, functional matellon nanocomposites based on a copolymer of 1-vinyl-1,2,4-triazole and MA with silver nanoparticles were synthesized by the electrochemical method. The structure and composition of the synthesized silver nanocomposites were confirmed by various physicochemical methods. Some properties of nanocomposites have been studied.

Materials and experimental techniques

Electrosynthesis was carried out in a glass electrolyzer with and without a diaphragm. IR spectra of polymers and films were recorded with Specord M-80 and Bruker Vertex 70 spectrometers in KBr pellets. The absorption spectra were recorded on a Perkin Elmer Lambda 35 UV/VIS spectrophotometer. The metal content in the formed nanocomposites was determined by the atomic absorption and elemental analysis using Perkin Elmer Analyst 200 instruments. The distributions of metal nanoparticles were determined using a TEM transmission electron microscope. The thermal properties of the films and nanocomposites were studied on a MOM derivatograph (Hungary). The temperature increased by 5 deg⋅min⁻¹ each time.

VT was synthesized according to the procedure described in, ³⁶ and MA was purified according to the general procedure.

The general technique for the formation of nanocomposites and films. In an electrochemical chamber with a capacity of 0.05 L, electrolysis was carried out [E = −0.1 … −1.2 V (c.s.e.) or j = 1–25 mA⋅cm⁻²] in an aqueous or water-ethanol solution containing 0.5–1 mol⋅l⁻¹ 1-vinyl-1.2.4-triazole, 0.5–1 mol⋅l⁻¹ MA, 1.5–3 mol⋅l⁻¹ AgNO₃, 0.03–0.06 wt% 4-tert-butylperoxy-4-oxobutanoic acid (TBOBA) and in some cases 0.07–0.1 wt.% chitosan. The working electrodes were iron or steel plates with dimensions of 1-2 cm⁻², and the anode was a platinum or glassy carbon (SU-12, SU-20) plate with the same area. The current density was more than 10 mA⋅cm⁻², the metal composite was deposited on the bottom of the cell. After completion of electropolymerization, the electrode package was removed, the cathode with the resulting coating was separated, washed thoroughly with distilled water and dried to constant weight, and studied.

Results and discussions

At the electrochemical polymerization of the VT-MK system and their mixtures in the presence of AgNO₃ and the initiator TBOBA at potentials E = 0.6–1.2 V, nanocomposites and their films are formed in which the amount of silver varies from 1 to 10 wt.%. Nanocomposite films obtained on the electrodes are insoluble in water and organic solvents. When heated, the copolymer is crosslinked.

In the electronic spectra of nanocomposites with silver, in comparison with aqueous solutions of the original copolymers and AgNO₃, bands of limiting plasmon absorption are visible in the region of silver-containing nanocomposite coatings. Absorption bands with a limit appear in the region of 417–421 nm. This is characteristic of the systems with isolated metallic silver nanoparticles (Figure 1, curve 2).

Figure 1.

Electronic spectra of the VT-MA copolymer (1) and silver nanocomposite: (2) 7.6% Ag, (3) 8.5% Ag.

The IR spectrum shows that absorption bands appear in VT-MK copolymers, peculiar vibrations of the triazole ring: 1506 (C = N), 1435 (C-N), 1277, 1004 (C-H), 660 cm⁻¹ (C-N), 1275 cm⁻¹ (NN), 3112 (CH), and a band – at 1714 cm⁻¹ – stretching vibrations $-COOH$ (Figure 2).

Figure 2.

IR spectra of VT-MA copolymer (1) and nanocomposite (2).

As can be seen from Figure 2, the structure of the polymer does not change during the formation of the nanocomposite. This shows that the structure of the VT-MA copolymer does not change during electrosynthesis and the original properties of the polymer matrix are preserved.

According to elemental analysis and atomic – absorption spectroscopy, the silver content in nanocomposite films is 1–9%. Compared to the original copolymers, the viscosity of polymer nanocomposites increases on average by 10–20%. This is expressed by the fact that numerous interactions of polymer macromolecules with nanosized metal particles occur (Table 1).

Table 1.

Composites of copolymers VT-MK.

Nanocom-posite no	- Electrode potentiol (ch.s.e.)/V	Ag content, wt. %	Yield, %	η/dl·g−1	λmax/nm	Sizes of nanosized particles, nm
1	0.65	7.6	88.6	1.83	417	2–12
2	0.75	8.5	83.4	0.90	417	2–8
3	0.95	9.3	78.2	0.21	421	2–6

The obtained results are confirmed by the structure of the copolymer:

There are few nanoparticles involved in an organized relationship; therefore, loose copolymer coils appear in aqueous solutions in an expanded form, and the solubility of nanocomposites is created to a greater extent by intramolecular interactions of copolymer macromolecules with silver nanoparticles.

Copolymer coils are a small arrangement of polymer nanocomposite macromolecules, which, compared to the initial copolymer, appears due to fragmentary crosslinking of nanosized particles.

At a silver content above 9%, at first a fragmentary and then an absolute loss of solubility is visible. This is caused by an increase in intermolecular solvation due to the crosslinking of polymer macromolecules by metal nanoparticles under the influence of plural cooperative forces.

Since the solubility of copolymers occurs due to the formation of hydrogen bonds between carboxyl groups and the triazole ring,^37,38 the hydration process is significantly competed with the intermolecular bonding of macromolecules with the help of surface silver nanoparticles.

The hydration of the polymer nanocomposite decreases, up to its absolute deprivation of water, with an increase in the content of nanosized silver particles (the vast majority of triazole and carboxyl groups are in an organized interaction with silver nanoparticles and do not involve in the creation of hydrogen bonds with water molecules).

The generation of organic-inorganic composites, that is, the presence of silver nanoparticles and a shapeless polymer stage, is finally substantiated by X-ray analysis. As can be seen from Figure 3, distinguishes between the shapeless polymer part and the deep dermographs of metal nanoparticles, characteristic of the planes of the crystalline stage of zero-valent silver are distinguished.

Figure 3.

Diffractograms of nanocomposites (1) and (2) I – intensity, 2θ – Bragg angle (deg).

The sizes of silver nanoparticles are calculated according to. ³⁹ As transmission electron microscopy has shown (Figure 4(a)), the nanocomposites contain silver nanoparticles, 2–12 nm in size, predominantly elliptical in shape. They are uniformly distributed in the polymer matrix (Figure 4(b)).

Figure 4.

The electron micrographs (a) and the distribution scheme of silver nanoparticles by size (b) in VT-MA copolymers.

When checking the thermal stability of polymer nanocomposites, it was found that in the temperature range of 320°C–400°C, a gradual loss of mass occurs, up to 40%, and the first stage of destruction of the polymer matrix is observed, because during this period, methyl and carboxyl groups are split off and oxidized (Figure 5).

Figure 5.

Thermogravimetric curves: 1 – VT-MA copolymer, 2 - silver-containing (8.5%) nanocomposite, $\mathrm{\Delta }m$ – weight loss, T – temperature (°C).

The next stage of degradation occurs at 430–500°C. The electrical conductivity of nanocomposites is determined, – it is 8.9∙10⁻¹⁰–7.2∙10⁻⁹ S·cm⁻. This is three orders of magnitude greater than the initial electrical conductivity. The increase in electrical conductivity is apparently due to individual local tunneling currents that arise in the samples between the electrically conductive nanoparticles of metallic silver.

Conclusions

Thus, from the monomeric systems 1-vinyl-1.2.4-triazole and MA, silver metal nanocomposites and films were synthesized by the direct (electrochemical) method, and some properties of the obtained nanocomposites were studied. The formed silver nanocomposites and films are promising for use in medicine, in the development of antimicrobial, biocompatible, thromboresistant polymeric materials. They can serve as effective flocculants for clarification of wines and juices.