RU2592892C1 - Electrochemical method of producing nano-sized structures of nickel (ii) oxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to electrochemical production of active forms of nanoparticles of metal oxides. Electrochemical method of producing nano-sized structures of nickel (II) oxide involves oxidation of anode in ionic liquid in an air atmosphere. Nickel anode and cathode are used. Oxidation is performed at temperature 20-25 °C for 2-20 minutes, with density of direct current of 5-10 mA/cm² or at constant potential of 2.3-5 V. Ionic liquid is preferably with addition of distilled water or propylene glycol.

EFFECT: invention ensures production of highly ordered nano-sized structures.

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Description

The proposed method relates to the field of electrochemical preparation of active forms of nanoparticles of metal oxides, in particular, nickel oxide (II). Nanodispersed powder of nickel oxide is used in fuel cells as an electrode material consisting of a metal substrate and layers deposited on it based on nanoparticles of oxides and hydroxides of nickel, molybdenum or tungsten. Nanodispersed nickel oxide is used in catalysis, including the synthesis of carbon nanomaterials, as an active element of gas sensors. Based on complex mixtures of nickel and cobalt oxides, high-performance superfrequency dielectrics are being developed.

The features of the preparation of metal nanoparticles, including nickel nanooxide, by chemical methods are considered in detail in the monograph of A.B. Kilimnik and E.Yu. Ostrozhkova [Electrochemical synthesis of nanosized powders of metal oxides: monograph / A.B. Kilimnik, E.Yu. Ostrozhkova. - Tambov: Publishing House of FSBEI HPE "TSTU", 2012. - 144 p. - ISBN 978-5-8265-1100-8]. Chemical methods include gas phase deposition, solid and liquid reduction, pyrolysis of compounds and sol-gel technology.

Thanks to electron emission by one-dimensional metal oxide, periodic tip-like nanostructures are promising for use as electron emitters for X-ray sources, for flat screens, vacuum microelectronic devices, in catalysis, photonic crystals, and biosensors. Nickel oxide (NiO) is a transparent conductive oxide with a band gap in the range of 5 eV and has a low resistivity of approximately 0.14 Ohm · cm.

The technique for producing nanosites of nickel oxide with tip-like geometry is described in [S. Kei, K.-N. Kuo, C.-Y. Su, S.-T. Lee, C.-N. Hsiao, T.-P. Perng / Chem. Mater. 2006. V.18. P. 4544-4546]. Nickel oxide "nanosites" are obtained using an ultrasonic bath. Silica and optical glass B270 (Schott, Inc.) (hereinafter substrates) are purified by immersion in a solution (H ₂ SO ₄ /30% H ₂ O ₂ , 3: 1) at a temperature of 80 ° C for 5 minutes. Buffered oxide etching was applied to remove the surface oxide layer. Both substrates are then washed with a solution (H ₂ O / 30% H ₂ O ₂ / NH ₄ OH, 10: 2: 1) at 60 ° C. for 5 minutes and washed with distilled water. A suspension of polystyrene (PS) in water in the form of nanospheres 200 and 400 nm in size (10% by volume, Bangs Laboratories, Inc.) is diluted in a volume ratio of 1: 4 with a mixture of Triton X-100 (Aldrich) / methanol (1: 400 by volume ) A suspension of PS nanoparticles is applied to the substrate by rotation in a centrifuge at a speed of 2000 rpm for 10 seconds to obtain a nanosphere template. 200 ml organic and inorganic solutions are added dropwise to the nanosphere template. The sample is dried at room temperature, then heated in air at 350 ° C for 30 minutes to evaporate the nanospheres and solvent to form “nanosots” and the top layer. After sonication in distilled water for 30 seconds, the upper layer is removed, leaving a “nanosota” below. A nickel 2-ethylhexanoate solution was chosen as a precursor for the preparation of NiO nanosots.

NiO powders were obtained by aerosol pyrolysis of an aqueous glycine-nitrate solution [A.P. Belosludtsev, D.V. Kuznetsov, D.V. Lysov, A.G. Yudin, S.E. Kondakov / NEWS. MOSCOW. UN-TA. SER. 2. CHEMISTRY. 2012.V. 53. No. 5. S. 339-343]. An aqueous solution of nickel nitrate salt (“analytical grade”) and glycine (“analytical grade”) was used as a starting material for the preparation of nickel oxide powders. Nickel nitrate was chosen because it decomposes at relatively low temperatures (56.5 ° C) and when using the method of pyrolysis of ultrasonic aerosols, nickel oxide particles with a hollow microsphere are formed. The apparatus for producing nanostructured microspheres by aerosol pyrolysis consists of ultrasonic generators, a cylindrical quartz reactor (length 510 mm, inner diameter 28 mm), a filter element and a vacuum pump. The distance from the surface of the solution to the ultrasonic emitter is 20 mm and is maintained by the dosed supply of the initial solution. The morphology of nanostructured microspherical particles of nickel oxide is studied depending on the composition of the initial solution. It was shown that this method forms hollow microspheres with a diameter of 0.5 to 5.0 μm, the walls of which consist of nanoparticles with a size of about 10-20 nm. It was found that the addition of glycine to the initial solution made it possible to achieve a uniformly porous structure of microspheres and significantly increase their specific surface area. The described method is devoid of one of the most significant drawbacks of producing nickel nanooxide from nitrate, namely, atmospheric pollution with nitrogen dioxide due to the addition of glycine, however, requires a rather complicated hardware design.

A method is proposed for modifying the surface of aluminum oxide or silicon by applying nickel nanooxide to it by pyrolysis [RF Patent No. 2496576 dated October 27, 2013, B01J, B82B, Levachev SM, Levacheva IS, Lanin SN, Vlasenko E. V., Bannykh A.A.]. The method includes treating the inorganic oxide with a water-soluble nickel (II) salt, followed by the formation of nickel (II) oxide nanoparticles on the surface of the inorganic oxide. In this case, an inorganic oxide and alkali are successively introduced into an aqueous solution of nickel (II) salt preheated to 50-90 ° C, and after cooling the resulting mixture, a solution of sodium tetrahydroborate in aliphatic alcohol is introduced. Then the aliphatic alcohol-water azeotropic mixture is distilled off from the obtained product, the product is kept at 70-90 ° C and washed successively in water and twice in aliphatic alcohol. The resulting alcohol-precipitate system is placed in an oven to remove the isopropyl alcohol-water azeotropic mixture, and then the washing step with isopropyl alcohol is repeated twice. The resulting solid residue is placed in a drying oven and maintained until the alcohol is completely removed. The dried sample is left in the air. In a day, all nickel nanoparticles are oxidized to nickel (II) oxide. As inorganic oxide, alumina or silica is used. The technical result of the invention is to reduce the energy intensity of the process. The disadvantages of this method include the duration (about a day) of the process, the frequency of leaching.

A method for producing arrays of zinc oxide nanorods is described [Patent KZ No. 26062 dated 09/14/2012, B81C, Kudaibergenov S.E. and etc.]. The method can be used to create solar cells, in optoelectronics, sensors. The technical result of the invention is to obtain ordered arrays of zinc oxide nanorods on non-oriented non-oriented substrates without the use of catalysts. The essence of the invention lies in the fact that vertically ordered arrays of zinc oxide nanorods are obtained by gas transport synthesis accelerated by the presence of carbon on the surface of the substrate, while the carbon surface layer is created by the pyrolysis of a layer of carbon-containing substance previously deposited on the substrate directly during synthesis. The disadvantage of this method is the use of high pressure and argon as a carrier gas.

Reducing the negative environmental impact of the chemical industry can be achieved by developing plants based on electrochemical processes that reduce the use of chemicals: oxidizing agents and reducing agents. Replacing chemical stages in technological processes for the synthesis of inorganic and organic substances with electrochemical ones allows:

- to develop universal technological schemes of production due to the universality of the oxidizing agent / reducing agent - electric current;

- increase the selectivity of the process, through the use of the required value of the potential of the electrode or current.

A method for producing ultramicrodispersed nickel oxide powder on alternating current is proposed [RF patent No. 2503748 from 01/10/2014. Kilimnik A.B., Ostrozhkova E.Yu., Bakunin E.S.]. The method is as follows. The electrolysis is carried out on an alternating sinusoidal current on nickel electrodes, in a cell with a volume of 200 cm ³ , at a current density of 2.5 A / cm ² , a current frequency of 20 Hz and a temperature of 20-30 ° C, at a voltage of 4 V on the electrodes. Electrodes and thermometer fixed in an insulating cover, for example fluoroplastic or propylene. After a predetermined time of the process, the electrodes are removed from the cell, washed with distilled water and alcohol, and then weighed on an analytical balance. The resulting powder was separated by filtration, washed with distilled water, dried and weighed. The rate of destruction of Nickel and the formation of ultramicrodispersed powder of Nickel oxide is determined by the gravimetric method. The surface rate of nickel destruction is 75 mg / (cm ² · h). The disadvantage of this method is the use of gravimetry, as well as the lack of characteristics of the obtained nickel oxide (for example, the shape and size of the particles).

и др. В предлагаемом способе гидрофильную ионную жидкость 1-бутил-3-метилимидазолий тетрафторборат (BMIMBF₄) смешивают с дистиллированной водой в весовом отношении 0.276:1 и полученный раствор используют в качестве электролита. Рабочим электродом служит титановая фольга толщиной 0.5 мм, поверхность которой предварительно тщательно очищают ацетоном и этанолом. Фольгу помещают в двухэлектродную ячейку. Вспомогательным электродом является платиновая пластина. Электролиз проводят при комнатной температуре (21°C). Напряжение выбирают в ряду от 0 до 40 В. В течение электролиза поддерживают постоянное напряжение. Оптимизацию осуществляют подбором времени. Зависимость тока от времени фиксируют с помощью миллиамперметра. В начале синтеза ток составляет около 2 мА, постепенно падает за 80 минут до 0.5 мА, после чего резко возрастает до 20 мА, что служит сигналом окончания синтеза.Closest to the proposed method for the combination of essential features is a method for producing titanium oxide nanotubes in ionic liquids (US Patent 8,585,886, November 19, 2013, Jun Qu, Huimin Luo, and Sheng Dai). An electrochemical method is proposed for producing nanoscale structures of titanium (IV) oxide, including anodic oxidation of a titanium anode in an ionic liquid in an air atmosphere. The patent claims the use of various ILs of the general formula K ⁺ + A ^- , where K ^{+ is} selected from substituted imidazolium, pyridinium, quaternary ammonium ions with fluorine-containing anions from

and others. In the proposed method, the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF ₄ ) is mixed with distilled water in a weight ratio of 0.276: 1 and the resulting solution is used as an electrolyte. The working electrode is 0.5 mm thick titanium foil, the surface of which is thoroughly cleaned with acetone and ethanol. The foil is placed in a two-electrode cell. The auxiliary electrode is a platinum plate. The electrolysis is carried out at room temperature (21 ° C). The voltage is selected in the range from 0 to 40 V. During the electrolysis, a constant voltage is maintained. Optimization is carried out by the selection of time. The dependence of current on time is fixed using a milliammeter. At the beginning of the synthesis, the current is about 2 mA, gradually drops in 80 minutes to 0.5 mA, after which it rises sharply to 20 mA, which serves as a signal for the end of the synthesis.

Использование в качестве вспомогательного электрода платины ведет к удорожанию способа.The disadvantage of this method is that a mixture of ionic liquid with water is used as the electrolyte, although not all ILs mentioned in the patent are hydrophilic and are able to mix with water in the stated amounts, for example, IL with a bistriflatimide anion

The use of platinum as an auxiliary electrode leads to a higher cost of the method.

The objective of the proposed method is to obtain nanoscale oxides, specifically nickel oxide (II) in the nanodispersed state. The technical result consists in obtaining highly ordered nanoscale structures.

The problem is solved by this invention.

Cl^- и др. Выбор ионных жидкостей как электролитических сред для синтеза нанооксида никеля обусловлен их свойствами, удовлетворяющими требованиям «green chemistry». Различные ионные жидкости на основе катиона имидазолия, в том числе [BMIM][NTf₂] и 1-бутил-3-метилимидазолий хлорид [BMIM]Cl, не только негорючи, но и стабильны в широком диапазоне температур: от комнатной температуры до 400°C. Они обладают достаточной электропроводностью, что в общем случае не требует введения постороннего фонового электролита. В то же время ионные жидкости характеризуются большими «окнами» электрохимической устойчивости (от -2 до +2 В относительно потенциала хлорсеребряного электрода) и одновременно выполняют роль среды, формирующей и стабилизирующей наночастицы оксидов металлов. Высокая вязкость ионной жидкости способствует тому, что в ее присутствии формирование наночастиц оксидов металлов происходит в виде отдельных зерен на поверхности электрода, а не в виде тонкого слоя из компактного оксида. Предлагаемый способ получения нанооксида никеля не ограничивает возможности использования как гидрофильных ([BMIM]Cl), так и гидрофобных ([BMIM][NTf₂]) ионных жидкостей. Содержание воды в находящейся в равновесии с атмосферой [BMIM]Cl составляет около 60000 ppm, а в [BMIM][NTf₂] около 500 ppm [А.М. O'Mahony, D.S. Silvester, L. Aldous, С. Hardacre, RG. Compton / J. Chem. Eng. Data 2008. V. 53. P. 2884-2891].In the electrochemical method for producing nanosized particles of nickel (II) oxide, comprising oxidizing the anode in an ionic liquid in an atmosphere of air, according to the invention, a nickel anode is used as the anode, the oxidation is carried out at a temperature of 20-25 ° C for 2-20 minutes, at a constant density current 5-10 mA / cm ² or at a constant potential of 2.3-5 V, a nickel cathode is used as a cathode. Nickel foil with a thickness of up to 0.5 mm is used as a nickel cathode and anode. Preferably, an ionic liquid with the addition of distilled water (in a volume ratio of ionic liquid / water up to 10: 1) or propylene glycol (in a volume ratio of ionic liquid / propylene glycol from 1: 0.5 to 1: 1) is used. The ionic liquid cation is selected from substituted alkylimidazolium, alkylpyridinium, alkylpiperidinium, etc., the anion is selected from

Cl ^- and others. The choice of ionic liquids as electrolytic media for the synthesis of nickel nanooxide is due to their properties that meet the requirements of "green chemistry". Various ionic liquids based on the imidazolium cation, including [BMIM] [NTf ₂ ] and 1-butyl-3-methylimidazolium chloride [BMIM] Cl, are not only non-combustible, but also stable over a wide temperature range: from room temperature to 400 ° C. They have sufficient electrical conductivity, which in the General case does not require the introduction of extraneous background electrolyte. At the same time, ionic liquids are characterized by large "windows" of electrochemical stability (from -2 to +2 V relative to the potential of a silver chloride electrode) and at the same time serve as a medium that forms and stabilizes metal oxide nanoparticles. The high viscosity of the ionic liquid contributes to the fact that in its presence the formation of metal oxide nanoparticles occurs as individual grains on the surface of the electrode, and not as a thin layer of compact oxide. The proposed method for producing nickel nanooxide does not limit the possibility of using both hydrophilic ([BMIM] Cl) and hydrophobic ([BMIM] [NTf ₂ ]) ionic liquids. The water content in [BMIM] Cl, which is in equilibrium with the atmosphere, is about 60,000 ppm, and in [BMIM] [NTf ₂ ] about 500 ppm [A.M. O'Mahony, DS Silvester, L. Aldous, C. Hardacre, RG. Compton / J. Chem. Eng. Data 2008. V. 53. P. 2884-2891].

In the proposed method, water or propylene glycol is added to the solvent (ionic liquid). The Ni ²⁺ ions formed during the anodic dissolution of nickel in the presence of water form aqua complexes of the composition [Ni (Н ₂ О) ₄ ] ²⁺ , which form nickel oxide upon hydrolysis. Glycols and polyols are also important in the synthesis of well-characterized nanostructured oxide materials, since they are chelating ligands of the metal ion, which makes it possible to control the rate of hydrolysis of transition metal alkoxides [T. Fröschl, U. Hörmann, P. Kubiak, G. Kučerova ', M. Pfanzelt, C.K. Weiss, RJ Behm, N. Hüsing, U. Kaiser, K. Landfesterd, M. Wohlfahrt-Mehrens / Chem. Soc. Rev. 2012. v. 41. R. 5313-5360].

The cathode can be used electrodes, for example, of graphite, glassy carbon, copper, cobalt and other materials that have sufficient electrical conductivity and do not interact with the ionic liquid. The reference electrode is silver wire.

Electrochemical anodizing of nickel is carried out in an air atmosphere.

The list of illustrative materials.

In fig. 1 is a photomicrograph of a surface fragment of a starting nickel anode degreased in acetone and dried to constant weight.

In fig. Figure 2 shows a micrograph of a fragment of the surface of a nickel anode obtained after 15 minutes of anodic exposure at a potential of E = 2.8 V in an ionic liquid [BMIM] Cl in an air atmosphere at a temperature of 25 ° C. In fig. 2, on the surface of the nickel electrode, orderedly arranged nickel oxide rods with a diameter of 50 nm and a length of over 200 nm are visible.

In fig. Figure 3 shows a micrograph of a fragment of the surface of a nickel anode obtained after 5 min of exposure at a potential of E = 2.3 V in [BMIM] Cl ionic liquid in the presence of propylene glycol additive (volume ratio 1: 1) in an air atmosphere at a temperature of 20 ° C. In fig. 3, on the surface of the nickel electrode, orderly arranged nickel oxide nanorods ranging in size from 50 to 200 nm are visible.

In fig. Figure 4 shows a micrograph of a fragment of the surface of a nickel anode obtained after 5 min of exposure to an anode current of 7.5 mA cm ^–2 in ionic liquid [BMIM] Cl in the presence of propylene glycol additive (volume ratio 1: 1) in an air atmosphere at a temperature of 25 ° C. In fig. 4, nickel oxide nanorods 30–30 nm in diameter and 100–200 nm in length arranged in layers on the surface of a nickel electrode are visible.

In fig. Figure 5 shows a micrograph of a fragment of the surface of a nickel anode after anodic exposure at a constant current density of 7.5 mA cm ^-2 for 100 seconds in an ionic liquid [BMIM] NTf ₂ in the presence of propylene glycol (volume ratio 1: 1) in an air atmosphere at a temperature of 25 ° C. In fig. Figure 5 shows the formation of nickel nanooxide in the form of "nanosets" with "tip-like" geometry with a diameter of about 100 nm.

The data obtained by anodic electrochemical treatment of a nickel anode in an ionic liquid medium indicate that, as a result of this process, nickel oxide nanoparticles in the form of "nanosets" with tip-like geometry or nanorods with a diameter of 30-100 nm are formed on the nickel surface depending on the conditions of the synthesis.

The proposed method is illustrated by the following examples.

Example 1

Electrochemical preparation of nickel oxide was carried out from a solution of ionic liquid 1-butyl-3-methylimidazolium chloride [BMIM] Cl containing water in an amount of 60,000 ppm. The process was carried out at a temperature of 25 ° C for 15 min at a potential of E = 2.8 V. A nickel foil (S = 0.4 cm ² ), previously degreased in acetone and dried to constant weight, was used as an anode (Fig. 1). Nickel foil was used as a cathode. The reference electrode is silver wire.

Electron microscopy data of the nickel anode (Fig. 2) were obtained after 15 minutes of anode exposure. In fig. Figure 2 shows the products of the complete oxidation of nickel with a highly developed surface on the nickel electrode. In fig. 2, on the surface of a nickel electrode, orderly vertically arranged nickel oxide rods with a diameter of 50 nm and a length of over 200 nm are visible. According to elemental analysis, the content of oxygen (35-43% atomic), nickel (40-47% atomic) and the remaining is adsorbed chloride ion.

Example 2

Under experimental conditions similar to Example 1, nanosized particles of nickel oxide were synthesized in a solution of [BMIM] Cl containing water in an amount of 60,000 ppm. The process was carried out at a temperature of 20 ° C for 20 min at a potential of E = 2.6 V. A nickel foil (S = 0.4 cm ² ), previously degreased in acetone and dried to constant weight, was used as an anode (Fig. 1). Nickel foil was used as a cathode. The reference electrode is silver wire. On the surface of the nickel electrode, ordered nickel oxide rods with a diameter of 50 nm and a length of over 200 nm are formed.

Example 3

Under experimental conditions similar to example 1, the preparation of nanosized particles of nickel oxide was carried out from a solution of [BMIM] Cl containing propylene glycol (volume ratio 1: 1). The process was carried out at a temperature of 25 ° C for 5 min at a potential of E = 2.3 V. Nickel foil was used as the anode (S = 0.4 cm ² ). Nickel foil was used as a cathode. The reference electrode is silver wire. In fig. Figure 3 shows a micrograph of a fragment of the surface of a nickel anode obtained after 5 min of exposure at a potential of E = 2.3 in [BMIM] Cl ionic liquid in the presence of a propylene glycol additive (volume ratio 1: 1) in an air atmosphere at a temperature of 25 ° C. In fig. 3, on the surface of the nickel electrode, orderly arranged nickel oxide nanorods ranging in size from 50 to 200 nm are visible.

Example 4

Under experimental conditions similar to Example 1, the synthesis of nanosized particles of nickel oxide was carried out from a solution of [BMIM] Cl containing propylene glycol (volume ratio 1: 1). The process was carried out at a temperature of 25 ° C for 5 min at an anode current of 7.5 mA · cm ^-2 . In fig. Figure 4 shows a micrograph of a fragment of the surface of a nickel anode obtained after 5 min of exposure to an anode current of 7.5 mA cm ^–2 in ionic liquid [BMIM] Cl in the presence of propylene glycol additive (volume ratio 1: 1) in an air atmosphere at a temperature of 25 ° C. In fig. 4, nickel oxide nanorods 30–30 nm in diameter and 100–200 nm in length arranged in layers on the surface of a nickel electrode are visible.

Example 5

Under experimental conditions similar to Example 1, nanosized particles of nickel oxide were prepared from a solution of [BMIM] NTf ₂ containing propylene glycol (volume ratio 1: 1). The process was carried out at a temperature of 25 ° C for 120 seconds at an anode current of 7.5 mA · cm ^-2 . Electron microscopy data are shown in Fig. 5.

In fig. Figure 5 shows a micrograph of a fragment of the surface of a nickel anode after anodic exposure at a constant current density of 7.5 mA cm ^-2 for 120 seconds in an ionic liquid [BMIM] NTf ₂ in the presence of propylene glycol (volume ratio 1: 1) in an air atmosphere at a temperature of 25 ° C. In fig. Figure 5 shows the formation of nickel nanooxide in the form of "nanosets" with tip-like geometry with a diameter of about 100 nm.

Claims (4)

1. The electrochemical method for producing nanoscale structures of nickel oxide (II), including the oxidation of the anode in an ionic liquid in an atmosphere of air, characterized in that a nickel anode and cathode are used, the oxidation is carried out at a temperature of 20-25 ° C for 2-20 minutes, at DC density 5-10 mA / cm ² or at a constant potential of 2.3-5 V. 2. The method according to claim 1, characterized in that nickel foil with a thickness of up to 0.5 mm is used as a nickel cathode and anode. 3. The method according to p. 1, characterized in that they use an ionic liquid with the addition of distilled water in a volume ratio of ionic liquid / water up to 10: 1. 4. The method according to p. 1, in which an ionic liquid with the addition of propylene glycol in a volume ratio of ionic liquid / propylene glycol from 1: 0.5 to 1: 1 is used.

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