RU2541798C1 - Method of preparing metal nanoparticle-modified carbon-containing indicator electrodes for voltammetric analysis of organic compounds - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of preparing carbon-containing indicator electrodes modified with nanoparticles of Au, Pt, Pd, Ni, Cu. Modification is carried out by depositing metal nanoparticles obtained by laser ablation of metal targets in clean solvents in the absence of stabilisers onto the working surface of the indicator electrode and holding (for not less than 5 minutes) the working surface in a respective dispersion (with concentration of not less than 0.05 g/l), followed by drying on air at room temperature.

EFFECT: method is simple, reactant-clean, and is not complicated by the need to use high temperatures and toxic organic substances.

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Description

The invention relates to the field of electrochemical analysis and is intended to produce carbon-containing electrodes modified with metal nanoparticles (Au, Pt, Pd, Ni, Cu), for the qualitative and quantitative determination of organic substances (hydroquinone, adrenaline, dopamine, ascorbic acid and glucose, etc. ) by voltammetric method in a wide range of objects (food products, pharmaceuticals, environmental objects, biological objects, etc.), as well as when conducting scientific research under research laboratories.

The presence of organic compounds in the analyzed sample is determined by the presence of peaks of the electrochemical transformations of the analyte on the indicator electrode or by the peaks of transformations of the modifiers in the presence of the analyte, and the concentration of the analytes is determined by the magnitude of the current peaks of the electrochemical conversion of the analyte or by the magnitude of the increment of the peak current of the conversion of the modifier in the presence of analyte. Modification of carbon-containing electrodes by the proposed method leads to an increase in the number of substances determined with their help and / or an increase in the sensitivity of the analysis compared to unmodified electrodes.

Abbreviations Used:

KhME - chemically modified electrodes;

CVA - cyclic voltammogram.

Voltammetry is a widely used electrochemical method for the analysis of organic compounds. Success in this area of electroanalysis is associated with the emergence of a new generation of electrodes - chemically modified electrodes (KhME) [Modified electrodes with catalytic properties in organic voltammetry // dissertation, L. Shaydarova. for the degree of Doctor of Chemistry, Kazan, 2008, 360 pp.]. Modification of the electrode surface increases the sensitivity, selectivity and reproducibility of the method. The electrocatalytic properties of CME are due to the introduction of a redox mediator that carries out electron transfer between the electrode and the analyte. This leads to a decrease in the potential of the redox reaction and an increase in its rate. In addition, the regeneration of the initial form of the mediator leads to an increase in the recorded current. Thus, redox mediators increase the sensitivity and, in some cases, the selectivity of the determination of organic compounds.

It is known that gold and platinum group metals are universal catalysts for many electrochemical reactions and serve as material for the manufacture of indicator electrodes [Modified electrodes with catalytic properties in organic voltammetry // dissertation, L. Shaydarova. for the degree of Doctor of Chemical Sciences, Kazan, 2008, 360 s]. However, electrodes with metal catalysts deposited on various supports or substrates have gained wider practical application. They exhibit special adsorption and electrocatalytic properties, different from compact and dispersed metals. This is associated with a change in the crystal orientation of the particles and their electronic structure. It has been established that the catalytic properties of metal particles are largely determined by their size and shape, degree of dispersion, the nature of the carrier, the nature of the precursor (the form of existence of a metal ion), the method of its deposition on the electrode surface [Modified electrodes with catalytic properties in organic voltammetry // Shaydarova L dissertation .G. for the degree of Doctor of Chemistry, Kazan, 2008, 360 pp.].

The voltammetric analysis of organic compounds using modified electrodes is based on the catalytic effect of modifier metals and is manifested in the appearance and / or shift of oxidation / reduction peaks of the analyte (potential catalysis) and / or in an increase in the currents of these peaks (current catalysis) [Modified electrodes with catalytic properties in organic voltammetry // dissertation by L. Shaydarova for the degree of Doctor of Chemistry, Kazan, 2008, 360 pp.].

The known method [Modified electrodes with catalytic properties in organic voltammetry // thesis Shaydarova LG for the degree of Doctor of Chemistry, Kazan, 2008, 360 pp.] the preparation of carbon-containing electrodes modified with metal nanoparticles by electrochemical polarization in solutions of modifier metal salts. A potentiostatic or potentiometric mode of producing metal nanoparticles on the surface of a carbon-containing indicator electrode is carried out. The particle size and degree of surface filling are controlled by the time of electrochemical deposition. Pt, Pd, Au, Rh, Ru, Ir, and Os were used as modifier metals. Modified by this method, carbon-containing electrodes can be used in the determination of a wide range of organic substances. In particular, the authors proposed using a glassy carbon electrode coated with platinum particles to determine ethanol; the best catalytic effect for determining hydroquinone was observed for a gold modified electrode; in the case of dopamine and adrenaline, among the metals considered in the work, the catalytic effect was shown by rhodium, platinum and gold deposited on a glassy carbon electrode (the maximum effect was determined for gold by the determination of dopamine for gold, and on platinum when determining adrenaline). In the determination of ascorbic acid, Pt, Pd, and Au exhibit great catalytic activity when they are present in the form of nanoparticles.

However, this method of preparing modified electrodes has several disadvantages:

- The modifier must be applied immediately before the analysis, which complicates the procedure for the analysis itself and makes it difficult to standardize such electrodes.

- The uniformity of the coating of the electrode with modifier particles strongly depends on the surface imperfection due to the fact that the maximum current density is observed on the defects.

- The applied particles of the modifier are present on the surface of the modified electrodes in the form of multilayer agglomerates, which leads to the fact that not all of them have contact with the basic material of the electrode. While it is known [Voltammetry with modified and ultramicroelectrodes // Budnikov G.K., Maistrenko V.N., Murinov Yu.I. M .: Nauka, 1994. 240 p.], That the most favorable conditions for electron transfer in the case of electrodes modified with metal nanoparticles are provided for monolayer coatings, which are characterized by a high degree of energy equivalence.

The main disadvantage of the analysis using the electrodes described above is that voltammograms show peaks of electrochemical transformations of metal modifiers that are oxidized and reduced during the analysis. The presence of these peaks complicates the interpretation of the obtained voltammograms, since it is necessary to separate the peaks of the modifier and the analyte, provided that the former are able to shift in the presence of the analyte and change the current value regardless of the concentration of the depolarizer. This complicates the procedure for interpreting the results and may lead to errors.

More attractive from the point of view of simplicity and reproducibility of the form and particle size of the modifiers are methods for modifying the electrodes using finished metal nanoparticles from dispersions in various solvents.

So, the known method [Patent: Method for determining cysteine in aqueous solutions by cyclic voltammetry on a graphite electrode modified with colloidal gold particles // Perevezentseva D.O., Mironets E.V., Gorchakov E.V. RF patent No. 2463587, dated 05.24.2011; Publication: Voltammetry of glutathioin on graphite electrodes modified with gold nanoparticles // Seitzhanova MA, Perevezentseva D.O. Proceedings of the IX International Conference of Students and Young Scientists "Prospects for the Development of Basic Sciences", Tomsk, 2012] modification of graphite electrodes to determine organic substances such as cysteine and glutathioin by gold nanoparticles from sols prepared by chemical reduction from HAuCl ₄ with a mixture citrate and sodium borohydride. The modifier was applied by electrochemical deposition on the background of a 0.1 M NaOH solution at a potential of -1.0 V for 300 s. Despite the fact that ready-made metal nanoparticles were used to modify the electrode in this method, since the modifier was deposited electrochemically, it had the same drawbacks as in the case of the method [Modified electrodes with catalytic properties in organic voltammetry // dissertation L. L. Shaydarova. for the degree of Doctor of Chemistry, Kazan, 2008, 360 pp.].

Another method is known [Article: Au-nanoparticle-bis-bipyridinum cyclophane superstructures: assembly, characterization and sensoric applications // Lahav M., Shipway AN, Willner I. Journal of Chemical Society. 1999. V. 2. P. 1925-1931.], Also based on the deposition on the surface of the electrodes of gold nanoparticles prepared by chemical reduction (sodium citrate from HAuCl ₄ ). In this method, tin-based electrodes doped with indium were modified. The method of applying Au modifying nanoparticles to the surface consists in preliminary 2-minute silylation of the electrode surface by exposure to 3-aminopripyltriethoxysilane, followed by exposure to the dispersion of gold nanoparticles for 2 hours and placing cyclophane tetrachloride in a solution for 30 minutes. After washing three times, the electrodes were placed in water, where they were stored before and after use. Unlike the previous one [Patent: A method for determining cysteine in aqueous solutions by cyclic voltammetry on a graphite electrode modified with colloidal gold particles // Perevezentseva D.O., Mironets E.V., Gorchakov E.V. RF patent No. 2463587, dated 05.24.2011.], In this method of modifying gold nanoparticles are present on the surface in a state bound by organic compounds. Such particles have a sufficiently strong fastening on the working surface of the electrode, but are present in the form of multilayer aggregates. These modified electrodes are designed to determine hydroquinone, dopamine and adrenaline at pH 7.2 (phosphate buffer). The main disadvantage of this method is the presence of organic “fixers” on the surface of the electrode. In some cases, this may interfere with the analysis, and the stability of the electrode and the stability of its operation in aggressive environments are significantly affected, since strong acids and alkalis can affect the composition and surface properties of the electrode.

Another method is known [Article: Gold nanoparticle arrays for the voltammetric sensing of dopamine // Raj C.R., Okajima T., Ohsaka T. Journal of Electrochemical Chemistry. 2003. V. 543. P. 127-133] modification of the electrodes by metal nanoparticles, based on the attachment of nanoparticles to the surface of the gold electrode by the amino terminal groups of cystamine. A colloidal solution of Au nanoparticles was prepared by reducing gold with citrate and sodium borohydride from gold tetrahydrochloride. Gold particles were deposited onto a pre-modified cystamine electrode by holding the first in a colloidal solution for 12 hours. Next, a thorough flush was performed to remove loose cystamine. The electrode modified in this way is intended for electrochemical analysis of dopamine. Unlike previous methods, this option allows you to get a monolayer of modifier nanoparticles on the surface, but the above-mentioned disadvantages associated with the presence of an organic component on the surface are preserved.

Closest to the modification method proposed by the authors is [Article: Electrocatalytic oxidation of glucose at gold nanoparticle-modified carbon electrodes in alkaline and neutral solutions // Tominaga M., Shimazoe T., Nagashima M., Taniguchi I. 2005. V. 7. P. 189-193]. The method is based on applying to the carbon-containing electrode pre-prepared by two-phase synthesis [Article: Alcanethiolate gold cluster molecules with core diameter from 1.5 to 5.2 nm: Core and monolayer properties as a function of core size //M.J. Hostetler, J.E. Wingate, C.J. Zhong, J.E. Harris, R.W. Vachet, M.R. Clark, J.D. Londono, S.J. Green, J.J. Stokes, G..D. Wignall, G.L. Glish, M.D. Porter, N.D. Evans, R.W. Murray Langmuir. 1998. V.14. P. 17-30] gold nanoparticles with a diameter of 2 nm, coated with a monolayer of decantiolate anions from a dispersion in hexane, followed by drying in air at room temperature. To remove the organic encapsulating agent, the electrodes, after applying the modifier, were heat treated at 300 ° C for 2 hours. The obtained carbon-containing electrode modified with gold nanoparticles was used to determine glucose in alkaline and neutral environments.

This method has no drawbacks of the previous ones, in particular, there are no extraneous organic compounds on the working surface of the electrode, however, it is complicated by the need to use organic solvents (toluene when preparing nanoparticles, hexane when applied to the surface), as well as the presence of an additional stage during modification, due to the need removal of the encapsulating agent (decantiolate anions) by heat treatment requiring high temperatures. Since not all carbon-containing electrodes are resistant to high-temperature effects, they can be destroyed, structure of the surface layer of the electrode (agglomeration of nanoparticles, overgrowing of defects) and other undesirable changes can occur, which can lead to deterioration of the characteristics of the electrodes and poor reproducibility of the results. Also, in the case of high-temperature exposure, it is impossible to use metals that can oxidize under such conditions as modifiers — deep oxidation can lead to loss of adhesion of nanoparticles to the surface of the indicator electrode.

A common drawback of all of the above methods for the preparation of electrodes using finished nanoparticles is the use of various organic substances when modifying as stabilizers, fixers, etc. In addition, all the above methods of depositing nanoparticles from their dispersions onto the electrode require a long (from 2 to 12 hours) contact of the surface of the modified electrode with the dispersion of nanoparticles, which is hardly acceptable for using these methods on an industrial scale.

The present invention solves the problem of the need for use in the process of modification and / or subsequent presence on the surface of the electrodes of additional organic substances. There is also the possibility of using other, cheaper metals, in addition to gold and platinum group metals.

The objective of the invention is the creation of a simple, reagent-friendly, not complicated by the need to use high temperatures and toxic organic substances method of preparing carbon-containing electrodes modified with nanoparticles of various metals for voltammetric analysis of organic substances.

A positive result is achieved by the fact that:

- Firstly, inexpensive and widespread carbon-containing electrodes are used as a base: impregnated graphite electrodes (IGE) (impregnated with a mixture of polyethylene and paraffin), carbon paste electrodes (UPE), glassy carbon electrodes (SU), carbon composite electrodes (on based on graphite powder and a solid polymer binder). This class of electrodes is characterized by high chemical and electrochemical stability and a wide range of working potentials.

- Secondly, charge-stabilized finished dispersions of metal nanoparticles (Au, Pt, Pd, Ni, Cu) obtained by laser ablation of bulk metal targets in pure solvents (alcohol, water or any other) in lack of stabilizing or encapsulating agents. Particle size is governed by the conditions for obtaining their dispersions [Article: Synthesis of metal nanoparticles during laser ablation of solids in liquids by nanosecond radiation of the 2nd harmonic of an Nd-YAG laser // Svetlichny VA, Isaak TI, Babkina OV, Shabalina A.V. University News. Physics. 2009, No. 12/2].

- Thirdly, applying the modifier to the surface is carried out by maintaining the working surface of the electrode in a colloidal solution, followed by drying in air at room temperature. The concentration of particles on the surface is determined by the aging time (for maximum filling does not exceed 30 minutes) and the concentration of particles in the solution.

A distinctive feature of the proposed method is the use of pure metal nanoparticles having a spherical or close to spherical shape, ranging in size from 2 to 100 nm (depending on the nature of the metal and production conditions, Figure 1) and having a fairly narrow size distribution and active surface. This leads to the formation of a monolayer coating of nanoparticles on the working surface of the carbon-containing electrode (Figure 2). In turn, this type of coating in the absence of additional binders ensures maximum contact of the modifier nanoparticles with the electrode and can significantly facilitate electron transfer in the system, which is manifested in the catalytic effect of the use of electrodes modified in this way in the electrochemical analysis of organic substances.

The proposed method is illustrated by a diagram (Figure 3), which depicts the process of modifying the electrode.

(1) Prepared surface of the carbon-containing electrode (a - contact; b - electrode body; c - protective coating; d - working surface of the electrode);

(2) maintaining the dispersion of nanoparticles;

(3) drying to remove solvent from the work surface and rinsing with distilled water to remove particles from non-working surfaces of the electrode;

(4) re-drying the surface of the electrode to remove residual water.

The proposed method is as follows and includes the steps:

1. Preparation of the surface of carbon-containing electrodes for applying the modifier by grinding and polishing with abrasive materials, paper.

2. The deposition of metal nanoparticles on the working surface of carbon-containing electrodes was carried out by keeping the working surface of the indicator electrode in a dispersion (water, alcohol or other) of nanoparticles with a concentration of at least 0.05 g / l for at least 5 minutes. Then, drying was carried out in air at room temperature until the solvent was completely removed from the electrode surface. After drying by washing with distilled water, nanoparticles were deposited on the side surfaces of the electrode.

3. Activation of the surface of the indicator electrode. To fix nanoparticles on the surface of a carbon-containing electrode, a single scan was performed in the potential region determined by the working range of the electrode in the background electrolyte, which was subsequently used in the analysis (for example, in the analysis of ascorbic acid, 0.1 M sulfuric acid is used as the background electrolyte).

4. The surface regeneration of the indicator electrode, if necessary, is carried out by standard mechanical cleaning using abrasive materials, followed by grinding and polishing (the specific cleaning technology depends on the type of carbon-containing electrode used).

Example 1

The surface of the carbon paste electrode preliminarily prepared by grinding and polishing was kept in an alcohol dispersion of palladium nanoparticles ranging in size from 3 to 70 nm (Figure 1b) with a concentration of 0.2 g / l for 10 minutes. After drying and washing, activation was performed by scanning in the potential range from 2.5 to -1.5 V at a speed of 30 mV / s in 0.1 M sulfuric acid. Next, cyclic voltammograms of the background electrolyte and analyte - dopamine solution, 0.005 M, were shot in the range from 0 to + 1.0 V at a speed of 30 mV / s. Figure 4 shows the sections of CVA with dopamine peaks on a pure impregnated graphite electrode and on the electrode after modification with palladium nanoparticles. In the presence of the modifier, an anode peak is shifted by 100 mV to a less positive region, a cathode peak is also shifted by 100 mV in the opposite direction and a significant increase in the currents of both peaks. Thus, when using electrodes modified by the proposed method in the analysis of dopamine, the interpretation of the obtained data is significantly simplified due to a clearer peak shape of the analyte, and an increase in currents indicates the possibility of a higher sensitivity of the analysis of dopamine using a modified electrode.

Example 2

The surface of the impregnated graphite electrode was prepared by grinding and polishing, after which it was modified by 10-minute exposure of nickel nanoparticles (0.05 g / l) from 8 to 30 nm in alcohol dispersion (Figure 1c), followed by drying at room temperature and washing. Next, the potential scan was activated in the range from 2.5 to -1.5 V at a speed of 30 mV / s in 0.1 M sulfuric acid. Cyclic voltammograms of the background electrolyte and a solution of hydroquinone in the background electrolyte with a concentration of 0.005 M were recorded in the range from 0 to + 1.0 V at a speed of 30 mV / s. Figure 5 shows CVA plots with peaks of hydroquinone on a pure impregnated graphite electrode and on the electrode after modification with nickel nanoparticles.

The presence of a modifier on the surface leads to a shift of the anode peak by 50 mV to a less positive region, of the cathode peak by 100 mV in the opposite direction. There is also an improvement in the shape of both peaks, which can facilitate the interpretation of the results and an increase in the current values, which indicates a possible increase in the detection limit and sensitivity of the analysis method using electrodes modified by the proposed method.

Example 3

Gold nanoparticles from 2 to 25 nm in size (Figure 1a) were applied to the prepared surface of the carbon-composite electrode from an aqueous dispersion with a concentration of 0.1 g / l for 10 minutes. After drying in air at room temperature and washing, a potential scan was performed in the range from 2 to -1.5 V at a speed of 10 mV / s in 0.1 M sulfuric acid.

Next, cyclic voltammograms of the background electrolyte and solutions of ascorbic acid in the background electrolyte with various concentrations were obtained. The survey was carried out in the potential range from 0 to + 1.0 V at a speed of 10 mV / s.

Figure 6 shows that in the absence of a modifier, a peak in the potential region + 0.5 V is not observed on the electrode surface. This peak is also absent when a voltammogram for a pure background electrolyte solution is obtained. Therefore, the emerging peak is explained by the catalytic effect of the oxidation of ascorbic acid on the electrode in the presence of gold nanoparticles.

Figure 7a shows CVA with peaks of oxidation of ascorbic acid from solutions of various concentrations on a modified electrode against a background of 0.1 M sulfuric acid. There is a noticeable increase in the peak current of the analyte transformation as its concentration increases. Figure 7b shows a calibration dependence for determining the concentration of ascorbic acid from the current value. The correlation coefficient was 0.999. This dependence can be used to analyze ascorbic acid solutions by the voltammetric method using carbon-containing electrodes modified with gold nanoparticles obtained by laser ablation.

Example 4

Gold nanoparticles ranging in size from 2 to 25 nm from an alcohol dispersion of a concentration of 0.2 g / l were applied to the prepared surface of the impregnated graphite electrode by aging for 10 minutes. This was followed by air drying and washing. The electrode surface was activated by scanning the potential in the range from 2.5 to -1.5 V at a speed of 20 mV / s: in the case of adrenaline analysis, in 0.1 M sulfuric acid; for glucose analysis - in 0.1 M NaOH. Next, cyclic voltammograms of the background electrolyte and analyte solutions in the above background electrolytes were obtained. Figure 8 shows the obtained CVA.

In the presence of the modifier, the peak of adrenaline conversion in the region of 730 mV, which is absent when using an unmodified electrode, is observed, as well as the peak of the electrochemical conversion of glucose at 200 mV, which is also uncharacteristic of the electrode before its modification with gold nanoparticles. Thus, it is possible to use electrodes modified by the claimed method for voltammetric analysis of these substances.

Example 5

Platinum nanoparticles (from 2 to 25 nm - Figure 1d) were deposited on the prepared surface of the glassy carbon electrode by 15 min aging in an alcohol dispersion, 0.05 g / L. After drying and washing, a potential scan was performed in the range from 2.5 to -1.5 V (30 mV / s) in the background electrolyte — 0.1 M sulfuric acid. Next, cyclic voltammograms of the background electrolyte and solutions of ascorbic acid in the background electrolyte with various concentrations were obtained. in the range from 0 to + 1.0 V at a speed of 30 mV / s. Figure 9 shows CVA with analyte peaks on the electrode after modification with platinum nanoparticles. A peak is observed in the region of 500 mV, the magnitude of which depends on the analyte concentration; therefore, the proposed method for modifying carbon-containing electrodes with platinum can be used to prepare electrodes for analyzing solutions for ascorbic acid content.

Example 6

On the surface of the impregnated graphite electrode, previously prepared by polishing, copper nanoparticles (20-100 nm) from an alcohol dispersion (0.15 g / l) were deposited for 10 minutes. This was followed by air drying and washing with distilled water. To activate the electrode surface, a single potential scan was performed in 0.1 M sulfuric acid in the range from 2.5 to -1.5 V at a speed of 30 mV / s. Next, cyclic voltammograms of the background electrolyte and ascorbic acid solutions in the background electrolyte with different analyte concentrations were obtained (range from 0 to + 1.0 V; speed 30 mV / s). Figure 10 shows CVA with analyte peaks to the electrode after modification with copper nanoparticles.

As in the previous example, in this case, there is a peak in the oxidation of ascorbic acid, the current value of which increases with increasing analyte concentration, which indicates the possibility of using electrodes modified with copper nanoparticles in this analysis.

Claims (1)

A method of preparing carbon-containing indicator electrodes modified with Au, Pt, Pd, Ni, Cu, metal nanoparticles, characterized in that the modification is carried out by deposition of metal nanoparticles obtained by laser ablation of metal targets in pure solvents in the absence of stabilizers on the working surface of the indicator electrode during aging (not less than 5 minutes) of the working surface in the corresponding dispersion (with a concentration of at least 0.05 g / l), followed by drying in air at room temperature ur

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