阅读说明：本技术 一种铜单原子催化材料与电极的制备方法及其在硝酸盐还原产氨中的应用 (Preparation method of copper monatomic catalytic material and electrode and application of copper monatomic catalytic material and electrode in production of ammonia by reduction of nitrate ) 是由 路建美 贺竞辉 于 2021-10-18 设计创作，主要内容包括：本发明公开了一种铜单原子催化材料与电极的制备方法及其在硝酸盐还原产氨中的应用,将2,5-二羟基对苯二甲醛,邻苯二胺与醋酸铜混合溶解于四氢呋喃(THF)中,在氩气保护下加热回流反应,过滤干燥得到前驱体材料,然后在氩气保护下,于管式炉中热解得到铜单原子催化材料。之后将铜单原子催化材料负载于亲水碳布表面,得到电催化还原硝酸盐产氨所使用的电极片,用于电催化硝酸盐还原产氨。本发明所公开的铜单原子催化材料所制备的电极具有极高的电催化硝酸盐还原产氨的活性以及循环稳定性。(The invention discloses a preparation method of a copper monatomic catalytic material and an electrode and application thereof in producing ammonia by reducing nitrate. And then loading the copper monatomic catalytic material on the surface of the hydrophilic carbon cloth to obtain an electrode plate used for producing ammonia by electrocatalytic reduction of nitrate, wherein the electrode plate is used for producing ammonia by electrocatalytic reduction of nitrate. The electrode prepared by the copper monatomic catalytic material disclosed by the invention has extremely high activity and cycling stability for electrocatalysis of nitrate reduction and ammonia production.)

1. A copper monatomic catalytic material, characterized in that, it is obtained by pyrolysis of a copper organic material in an inert gas; the copper organic material is obtained by reacting 2, 5-dihydroxy terephthalaldehyde, o-phenylenediamine and inorganic copper salt.

2. The copper monatomic catalytic material of claim 1, wherein the copper organic material is obtained by a reflux reaction of 2, 5-dihydroxyterephthalaldehyde, o-phenylenediamine and an inorganic copper salt in an organic solvent under the protection of an inert gas.

3. The copper monatomic catalytic material of claim 2, wherein the organic solvent is tetrahydrofuran; the inorganic copper salt is copper acetate; the reflux reaction time is 60-80 hours, and after the reaction is finished, the copper organic material is obtained by filtering and drying.

4. The copper monatomic catalytic material of claim 1, wherein the pyrolysis temperature is 500 to 600 ℃, the time is 2.5 to 3.5 hours, the temperature increase rate is 4 to 6 ℃ per minute, and the material is naturally cooled to room temperature after the pyrolysis.

5. A method of preparing a copper monatomic catalytic material as recited in claim 1, wherein the copper organic material is obtained by reacting 2, 5-dihydroxyterephthalaldehyde, o-phenylenediamine and an inorganic copper salt; and then carrying out pyrolysis on the copper organic material in inert gas to obtain the copper monatomic catalytic material.

6. An electrode for producing ammonia by electrocatalytic reduction of nitrate, which is obtained by supporting the copper monatomic catalytic material according to claim 1 on an electrically conductive substrate.

7. The method for preparing an electrode for producing ammonia by electrocatalytic reduction of nitrate according to claim 6, wherein the copper monatomic catalytic material according to claim 1 is supported on a conductive substrate to obtain the electrode for producing ammonia by electrocatalytic reduction of nitrate.

8. A method for producing ammonia by reducing nitrate, which comprises connecting a working electrode to the electrode for producing ammonia by electrocatalytic reduction of nitrate according to claim 6 in an electrochemical workstation, and carrying out an electrochemical reaction using nitrate as a raw material to obtain ammonia.

9. Use of the copper monatomic catalytic material of claim 1 for the preparation of electrodes for the electrocatalytic reduction of nitrates to produce ammonia, or for the reduction of nitrates to produce ammonia.

10. The use of the electrode for producing ammonia by electrocatalytic reduction of nitrate according to claim 6 in the electrocatalytic reduction of nitrate to produce ammonia.

Technical Field

The invention belongs to the technical field of catalytic materials, and particularly relates to a synthesis method of a copper monatomic material, a preparation method of an electrode of the copper monatomic material, and application of the electrode in producing ammonia by reducing nitrate.

Background

Ammonia is an important chemical product production raw material, and the consumption of the ammonia is huge in the field of industrial production. At present, a Haber-Bosch process method is used for large-scale ammonia production, the synthesis condition of the process is harsh, the energy consumption is huge, and a large amount of air pollutants and greenhouse gases are generated while a large amount of fossil energy is combusted, so that increasingly severe environmental problems are caused. Under such circumstances, the electrocatalytic reduction of ammonia by electrochemical means using nitrate as a nitrogen source has attracted increasing research attention. The method has the advantages that firstly, the energy required for bond breaking in the nitrate radical deoxidation reaction process is low, the reaction is carried out at a solid-liquid interface, and the mass transfer effect in the reaction process is better; secondly, nitrate is the main component of nitrogen pollutants in the water body at present, excessive nitrate can cause eutrophication of the water body, and nitrite generated in the denitrification process can seriously threaten human health. However, at present, the problems of low conversion rate, low ammonia production efficiency, low ammonia production rate and the like still exist in the electrocatalytic degradation of nitrate, so that development of a new catalyst material for realizing efficient removal and resource utilization of nitrate is urgently needed.

Disclosure of Invention

The invention aims to provide a synthetic method of a copper monatomic catalytic material and an electrode preparation method. Compared with the existing report of producing ammonia by reducing nitrate, the electrode material prepared by the invention can efficiently reduce nitrate to produce ammonia, the ammonia production rate is higher than all the reported research results, and meanwhile, the electrode material has good cycle stability.

In order to achieve the purpose, the invention adopts the following specific technical scheme:

a copper monatomic catalytic material is obtained by pyrolyzing a copper organic material in inert gas; the copper organic material is obtained by reacting 2, 5-dihydroxy terephthalaldehyde, o-phenylenediamine and inorganic copper salt.

An electrode for producing ammonia by electrocatalytic reduction of nitrate is obtained by loading the copper monatomic catalytic material on a conductive substrate.

A method for producing ammonia by nitrate reduction comprises the following steps that in an electrochemical workstation, a working electrode is connected with an electrode for producing ammonia by electrocatalytic nitrate reduction, and nitrate is used as a raw material to carry out electrochemical reaction to obtain ammonia.

The invention discloses a copper monatomic catalytic material, an electrode based on the copper monatomic catalytic material, a preparation method of the copper monatomic catalytic material and application of the copper monatomic catalytic material in nitrate reduction and ammonia production.

In the invention, under the protection of inert gas, 2, 5-dihydroxy terephthalaldehyde, o-phenylenediamine and inorganic copper salt are subjected to reflux reaction in an organic solvent to obtain the copper organic material. Preferably, the organic solvent is Tetrahydrofuran (THF); the inorganic copper salt is copper acetate; the reflux reaction time is 60-80 hours, for example, 70-75 hours, and after the reaction is finished, the copper organic material is obtained by filtering and drying.

In the invention, the molar ratio of the 2, 5-dihydroxy terephthalaldehyde to the o-phenylenediamine to the inorganic copper salt is 1: 1 to (0.02-0.05), preferably 1: 1 to (0.025-0.035).

In the invention, the inert gas is argon; pyrolysis is carried out in a tube furnace; the pyrolysis temperature is 550 ℃, the holding time is 3 hours, the heating rate is 5 ℃ per min, and the material is naturally cooled to the room temperature after the pyrolysis is finished.

In the present invention, the conductive substrate used is a hydrophilic carbon cloth, and preferably, the carbon cloth is subjected to oxygen plasma treatment before use. Specifically, weighing the copper monatomic catalytic material, adding a binder (preferably a Nafion binder), conventionally dispersing, and then brushing the mixture on a conductive base material, wherein preferably the loading amount of the copper monatomic catalytic material on each piece of carbon cloth is 1.5-2.5 mg/cm²(ii) a And drying the brushed conductive base material at room temperature for 2-5 h to obtain the electrode for producing ammonia by electrocatalytic reduction of nitrate, wherein the electrode is used for electrochemical test to carry out nitrate reduction to produce ammonia.

In the invention, the hydrophilic carbon cloth and the electrochemical workstation are the existing products, and the working electrode, the counter electrode, the reference electrode, the electrolyte and the like are all the existing conventional products.

Compared with the prior art, the invention utilizing the technical scheme has the following advantages:

(1) the copper monatomic catalytic material disclosed by the invention is simple in synthetic method and easy to operate;

(2) compared with the existing research reports, the copper monatomic catalytic material disclosed by the invention has the highest ammonia generation rate, and meanwhile, the copper monatomic catalytic material has excellent ammonia production efficiency, and the byproduct production amount is low;

(3) the electrode prepared by the copper monatomic catalytic material disclosed by the invention has the characteristics of good cycling stability and high electrochemical activity.

Drawings

FIG. 1 is a TEM image of a copper monatomic catalytic material;

FIG. 2 is a HAADF-STEM diagram of a copper monatomic catalytic material;

FIG. 3 is an XRD pattern of a copper organic material and a copper monatomic catalytic material;

FIG. 4 is a Raman spectrum of a copper monatomic catalytic material;

FIG. 5 is a linear sweep voltammogram of the copper monatomic catalytic material (linear sweep rate: 20 mV/s, voltage range: 0V to-2.60V, nitrogen-nitrate concentration of 1000 mg/L, electrolyte concentration of 0.5mol/L Na₂SO₄）；

FIG. 6 shows the change of the ammonia generating efficiency and ammonia generating rate with voltage (1 hour of electrolysis in constant voltage mode, nitrogen-nitrate concentration is 1000 mg/L, electrolyte is 0.5mol/L Na)₂SO₄）；

FIG. 7 is a graph showing the kinetics of transformation of nitrate and generation of ammonia and nitrite by a copper monatomic catalytic material (6 hours of electrolysis in constant voltage mode, voltage of-2.20V, electrolyte of 0.5mol/L Na)₂SO₄The nitrogen-nitrate radical concentration is 1000 mg/L);

FIG. 8 is a graph showing the cycle stability performance of the copper monatomic catalytic material electrode (each cycle was performed in a constant voltage mode for 1 hour, the voltage was-2.20V, the nitrogen-nitrate concentration was 1000 mg/L, and the electrolyte was 0.5mol/L Na₂SO₄）。

Detailed Description

The copper monatomic catalyst is used for electrochemical reduction of nitrate to generate ammonia, has high nitrate radical removal efficiency and ammonia generation rate, and has important significance for harmlessness and recycling of nitrate. In the invention, the hydrophilic carbon cloth and the electrochemical workstation are the existing products, and the working electrode, the counter electrode, the reference electrode, the electrolyte and the like are all the existing conventional products.

The technical scheme of the invention is further explained by combining the attached drawings and specific examples. Unless otherwise indicated, reagents, materials, and apparatuses used in the following examples are commercially available; the specific operating methods and test methods involved are conventional.

In the invention, the electrode substrate used is the conventional hydrophilic carbon cloth, the carbon cloth is treated by oxygen plasma for 10 min before use, and the size of the carbon cloth substrate is 1 cm multiplied by 1 cm.

Example one synthesis of a copper monatomic catalytic material, the specific steps are as follows:

166.13 mg (1 mmol) of 2, 5-dihydroxy terephthalaldehyde, 108.14 mg (1 mmol) of o-phenylenediamine and 5.45 mg (0.027 mmol) of copper acetate are added into 100 mL of Tetrahydrofuran (THF), and the mixture is heated under reflux for 72 hours under the protection of argon; then, the mixture was filtered, and the filter cake was washed with methanol and then vacuum-dried at 75 ℃ for 6 hours to obtain a copper organic material.

The copper organic material is placed in a porcelain boat and pyrolyzed in a tube furnace under the protection of argon, the temperature is increased to 550 ℃ from room temperature and kept for 3 hours, and then the material is naturally cooled to room temperature to obtain the copper monatomic catalytic material which is used for the following experiment, wherein the temperature increase rate is 5 ℃/min.

FIG. 1 is a TEM image of a copper monatomic catalytic material, from which the formation of nanoparticles can be seen; FIG. 2 is a HAADF-STEM diagram of a copper monatomic catalytic material, with the bright spots being copper monatomics. FIG. 3 is an XRD pattern of the copper organic material and the copper monatomic catalytic material, from which it can be seen that the copper monatomic has no crystalline morphology of the precursor material after pyrolysis, and no copper nanoparticles are formed; FIG. 4 is a Raman spectrum of a copper monatomic catalytic material, confirming its state of carbonization, and I_D/I_G=1.06, indicating that there are many defects in the catalyst material structure.

Example two synthesis of copper monatomic catalytic material, the specific steps are as follows:

166.13 mg (1 mmol) of 2, 5-dihydroxy terephthalaldehyde, 108.14 mg (1 mmol) of o-phenylenediamine and 5.0 mg of copper acetate are added into 100 mL of Tetrahydrofuran (THF), and the mixture is heated and refluxed for 72 hours under the protection of argon; then filtered, and the filter cake was washed with methanol and then vacuum-dried at 75 ℃ for 5 hours to obtain a copper organic material.

And (2) putting the copper organic material into a porcelain boat, pyrolyzing the copper organic material in a tube furnace under the protection of argon, raising the temperature from room temperature to 550 ℃, keeping the temperature for 3.5 hours, and naturally cooling the copper organic material to room temperature to obtain the copper monatomic catalytic material, wherein the temperature raising rate is 5 ℃/min.

Example synthesis of a three-copper monatomic catalytic material, the specific steps are as follows:

166.13 mg (1 mmol) of 2, 5-dihydroxy terephthalaldehyde, 108.14 mg (1 mmol) of o-phenylenediamine and 7.0 mg of copper acetate are added into 100 mL of Tetrahydrofuran (THF), and the mixture is heated and refluxed for 70 hours under the protection of argon; then, the mixture was filtered, and the filter cake was washed with methanol and then vacuum-dried at 70 ℃ for 7 hours to obtain a copper organic material.

Putting the copper organic material into a porcelain boat, pyrolyzing the copper organic material in a tube furnace under the protection of argon, raising the temperature from room temperature to 550 ℃, keeping the temperature for 3 hours, and naturally cooling the copper organic material to room temperature to obtain the copper monatomic catalytic material, wherein the temperature raising rate is 4.5 ℃/min.

Tests can show that the catalysts of the second embodiment and the third embodiment have no generation of copper nanoparticles.

Comparative example

The amount of copper acetate used in example one was increased to 10.9mg, the remainder was unchanged, and the catalytic material obtained by pyrolysis was tested to find copper nanoparticles.

Example four preparation of an electrode for producing ammonia by electrocatalytic reduction of nitrate, comprising the following specific steps:

weighing the copper monatomic catalytic material (example one) after vacuum drying, and mixing the copper monatomic catalytic material with 100 microliters of Nafion binder solution (serving as a binder and serving as a commercially available product) to obtain catalyst slurry; then brush-coating on a piece of hydrophilic carbon cloth treated by oxygen plasma; the carbon cloth after being coated was dried at room temperature for 3 hours to prepare a copper monatomic catalytic material electrode, which was an electrode for producing ammonia by electrocatalytic reduction of nitrate, and was used in the following experiment, with a copper monatomic catalytic material loading of 2 mg on the carbon cloth.

EXAMPLE V reduction of nitrate to Ammonia

The copper monatomic catalytic material was tested by an electrochemical workstation (model CorrTest CS 310). Before testing, the working electrode was connected to a carbon cloth (example four) of an electrode for producing ammonia by electrocatalytic reduction of nitrate, a platinum sheet was used as a counter electrode, a calomel electrode was used as a reference electrode, and the electrolytic cell was an H-type electrolytic cell. After the assembly is finished, 0.5mol/L sodium sulfate is used as an electrolyte, 1000 mg/L nitrogen-nitrate (potassium nitrate) is used as an electrolyte, and the main electrochemical test is a linear voltammetry scanning method, wherein the scanning potential range is 0 to-2.60V, and the constant voltage method is applied with the voltage range of-1.60 to-2.60V.

FIG. 5 is a linear sweep voltammogram of a copper monatomic catalytic material, from which it can be seen that a higher reduction current density is exhibited after nitrate is added, confirming the occurrence of the nitrate reduction reaction. Figure 6 shows the faradaic efficiency and the ammonia production rate under different voltages, the highest faradaic efficiency is under the condition of-1.80V, the highest ammonia production rate is under the voltage of-2.60V, and the working voltage range of-2.00 to-2.20V can give consideration to the higher faradaic efficiency and the ammonia production rate. FIG. 7 is a graph showing the kinetics of conversion of nitrate into ammonia and nitrite with a copper monatomic catalytic material, and it can be seen that as time increases, nitrate is continuously reduced, converted into ammonia and nitrite, and nitrite is always maintained at a lower concentration and ammonia concentration is continuously increased. FIG. 8 is a graph showing the cycling stability performance of a Cu monatomic catalytic material electrode, wherein constant voltage electrolysis is performed for 1 hour under the conditions of-2.20V and 1000 mg/L of nitrogen-nitrate as a reduction substrate in each cycle, new electrolyte is applied to both sides of a cathode and an anode after each cycle is completed, and electrolysis is performed again for 1 hour under the condition that other conditions are not changed. The graph shows that after 20 times of cycle tests, the catalyst still can show excellent ammonia production rate and ammonia production efficiency, and the catalyst can work stably for a long time and efficiently reduce nitrate to produce ammonia.

The concentration detection of ammonia, nitrate and nitrite in the experiment is tested and quantified by an ultraviolet spectrophotometry. The conversion rate of nitrate is calculated according to the equation (1):

wherein c is₀And c are the initial and test concentrations of nitrate (mg/L), respectively.

The Faraday efficiency calculation method for ammonia is as in equation (2):

wherein F is the Faraday constant, c_NH3Is the concentration of ammonia produced (mg/L) at the time of the test, V is the volume of the electrolyte (L), and Q is the total charge (C) of the electrolysis process.

The yield of ammonia gas was calculated as in equation (3):

wherein c is the concentration of ammonia (mg/L) at the time of test, V is the volume of electrolyte (L), and S is the electrode area (cm)²) And t is the test time (h).

Through the analysis, the copper monatomic catalytic material prepared by the technical scheme and the electrode prepared by the copper monatomic catalytic material show excellent nitrate removal rate and extremely high ammonia production rate (23.36 mg h)^-1 cm^-2). Applicant previously disclosed "Cu (I) @ Ti₃C₂T_xMXene catalytic material "" 20% CuPc @ Ti₃C₂T_xMXene catalytic material ", the same experiment for reducing nitrate to produce ammonia was carried out, and Cu (I) @ Ti was found₃C₂T_xThe ammonia production rate of the MXene catalytic material is 2.15 mg h at most^-1cm^-2，20%[email protected] Ti₃C₂T_xThe ammonia production rate of the MXene catalytic material is 2.72 mg h at most^-1 cm^-2. The same nitrate reduction ammonia production experiment is carried out on the copper organic material, and the ammonia production rate is found to be 10.27mg h at most^-1 cm^-2。

On the basis of the first example, the copper acetate is replaced by 17.4mg of ferrous acetate, and the rest is unchanged to obtain the iron monatomic catalytic material, and the same nitrate reduction ammonia production experiment is carried out, and the ammonia production rate is found to be 17.80 mg h at most^-1 cm^-2. On the basis of the first example, the copper acetate is replaced by 20.7mg of ruthenium trichloride, and the rest is not changed to obtain the ruthenium monatomic catalytic material, and the same experiment for reducing nitrate and generating ammonia is carried out, and the ammonia generation rate is found to be 11.26 mg h at most^-1 cm^-2。

The electrode catalyst material disclosed by the invention has excellent catalytic performance and good cycle stability. The method not only solves the problem of degradation of nitrate pollutants, but also generates ammonia with useful value, provides an extremely effective reference for the cyclic utilization of future energy, and has good prospect in practical application.