Copper-based perovskite nanofiber, preparation method thereof, and application in electrocatalytic reduction of nitrate

Abstract

The present invention belongs to the technical field of nitrate reduction, and provides a copper-based perovskite nanofiber, a preparation method thereof, and application thereof in electrocatalytic reduction of nitrate. La(NO3)3·6H2O, Co(NO3)2·6H2O, and Cu(NO3)2·3H2O are added to a mixed solvent and stirred to obtain a precursor solution; the precursor solution is electrostatically spun to obtain nanofibers, and the nanofibers are calcined to obtain copper-based perovskite nanofibers. The LaCu x Co 1‑x O3 perovskite nanofibers are used as electrocatalysts for the electrocatalytic reduction of nitrate to produce ammonia. Copper-based perovskite nanofibers provide abundant active sites and contact areas in the electrocatalytic reduction of nitrate, have excellent performance in the electrocatalytic reduction of nitrate, have good cycle stability, practicality and long-term development prospects, and can solve the problem of excessively high nitrate content in wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of nitrate reduction, and in particular to a copper-based perovskite nanofiber, a preparation method thereof, and application thereof in electrocatalytic nitrate reduction. Background Art

[0002] Due to problems such as over-fertilization, substandard discharge of domestic sewage and industrial wastewater, nitrate pollution has become widespread in the global water environment. In order to solve this type of pollution problem, a variety of treatment technologies (such as biological denitrification, physical concentration, etc.) have been widely used in the treatment of nitrate pollution in water bodies. Among them, electrochemical nitrate reduction technology is driven by electricity and has the advantages of high reaction efficiency, simple operation, no need for chemical reducing agents and no secondary pollution. It is considered to be a "green" nitrate removal technology. As the key to electrochemical technology, the cathode catalyst material directly affects the reaction activity and product selectivity of nitrate reduction. Among them, copper-based catalysts have attracted much attention in the field of electrocatalytic reduction of nitrate to ammonia due to their excellent electrochemical activity, good ammonia production selectivity, controllable electronic structure and low cost. However, the following difficulties still exist: (1) Catalyst deactivation due to passivation, leaching and corrosion during long-term electrolysis; (2) Excessive accumulation of nitrite during the reaction; (3) The ammonia production Faradaic efficiency of Cu-based catalysts at low bias voltages is very low. This is because the nitrate reduction reaction to ammonia is a proton-coupled electron transfer reaction, which requires the participation of a large number of protons. Under alkaline conditions, Cu has a poor ability to catalyze the decomposition of water to produce protons. As a result, Cu-based catalysts can only show good ammonia production Faradaic efficiency in the hydrogen production potential range (<-0.4V (vs.RHE)).

[0003] Therefore, it is of great significance to study and obtain a copper-based perovskite nanofiber with improved reduction activity and cycle stability for electrocatalytic reduction of nitrate to produce ammonia. Summary of the Invention

[0004] The purpose of the present invention is to provide a copper-based perovskite nanofiber and a preparation method thereof and application in the electrocatalytic reduction of nitrate in order to overcome the deficiencies of the prior art.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing copper-based perovskite nanofibers, comprising the following steps:

[0007] 1) La(NO3)3·6H2O, Co(NO3)2·6H2O, and Cu(NO3)2·3H2O are added to a mixed solvent and stirred to obtain a precursor solution;

[0008] 2) electrospinning the precursor solution to obtain nanofibers, and calcining the nanofibers to obtain copper-based perovskite nanofibers.

[0009] Preferably, in step 1), the molar ratio of La(NO3)3·6H2O, Co(NO3)2·6H2O and Cu(NO3)2·3H2O is 6.5-8.5:2.25-6.75:0.75-5.25.

[0010] Preferably, in step 1), the molar mass ratio of La(NO3)3·6H2O to the mixed solvent is 6.5-8.5 mmol:15-25 g.

[0011] Preferably, the mixed solvent in step 1) comprises polyvinyl pyrrolidone and N,N-dimethylformamide, and the mass fraction of polyvinyl pyrrolidone in the mixed solvent is 10-14%.

[0012] Preferably, the stirring and mixing time in step 1) is 22 to 26 hours; and during the electrospinning process in step 2), the voltage is 12 to 20 kV and the spinning distance is 14 to 18 cm.

[0013] Preferably, the calcination treatment in step 2) comprises a first calcination treatment and a second calcination treatment; in the first calcination treatment, the temperature is 350-450° C. and the time is 1.5-2.5 h; in the second calcination treatment, the temperature is 550-650° C. and the time is 0.5-1.5 h.

[0014] Preferably, the rate of heating from room temperature to the first calcination temperature and the rate of heating from the first calcination temperature to the second calcination temperature are independently 4-6°C / min; the first calcination treatment is carried out in a nitrogen atmosphere; and the second calcination treatment is carried out in an air atmosphere.

[0015] The present invention also provides copper-based perovskite nanofibers prepared by the method for preparing the copper-based perovskite nanofibers.

[0016] Preferably, the copper-based perovskite nanofiber is LaCu x Co 1-x O3 perovskite nanofibers, wherein x is 0.1 to 0.7.

[0017] The present invention also provides the use of the copper-based perovskite nanofibers in the electrocatalytic reduction of nitrate.

[0018] The beneficial effects of the present invention include:

[0019] The present invention prepares LaCu by electrostatic spinning and high temperature calcination. x Co 1-xO3 (x = 0.1 ~ 0.7) perovskite nanofibers. x Co 1-x O3 perovskite nanofibers were used as electrocatalysts for the electrocatalytic reduction of nitrate to ammonia, and Cu doping significantly improved the electrocatalytic performance. Copper-based perovskite nanofibers provide abundant active sites and contact area for the electrocatalytic reduction of nitrate, demonstrating excellent electrocatalytic performance, good cycle stability, practicality, and long-term development prospects, potentially addressing the problem of excessive nitrate levels in wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 LaCu prepared in Example 3 0.7 Co 0.3 Scanning electron microscopy image of O3 perovskite nanofibers;

[0021] Figure 2 LaCu prepared in Examples 1 to 3 x Co 1-x LSV curves of electrocatalytic reduction of nitrate by O3 (x = 0.1, 0.5, 0.7) perovskite nanofibers;

[0022] Figure 3 LaCu prepared in Examples 1 to 3 x Co 1-x O3 (x=0.1, 0.5, 0.7) perovskite nanofiber electrocatalytic reduction of nitrate to produce NH4 + Yield diagram. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing copper-based perovskite nanofibers, comprising the following steps:

[0024] 1) La(NO3)3·6H2O, Co(NO3)2·6H2O, and Cu(NO3)2·3H2O are added to a mixed solvent and stirred to obtain a precursor solution;

[0025] 2) electrospinning the precursor solution to obtain nanofibers, and calcining the nanofibers to obtain copper-based perovskite nanofibers.

[0026] In the present invention, the molar ratio of La(NO3)3·6H2O, Co(NO3)2·6H2O and Cu(NO3)2·3H2O in step 1) is preferably 6.5-8.5:2.25-6.75:0.75-5.25, more preferably 7.0-8.0:2.25-6.75:0.75-5.25, and more preferably 7.5:6.75:0.75, 7.5:3.75:3.75 or 7.5:2.25:5.25.

[0027] In the present invention, the molar mass ratio of La(NO3)3·6H2O and the mixed solvent in step 1) is preferably 6.5-8.5 mmol:15-25 g, more preferably 7.0-8.0 mmol:18-22 g, and more preferably 7.5 mmol:20 g.

[0028] In the present invention, the mixed solvent preferably comprises polyvinyl pyrrolidone (PVP) and N,N-dimethylformamide (DMF), and the mass fraction of polyvinyl pyrrolidone in the mixed solvent is preferably 10-14%, more preferably 11-13%, and even more preferably 12%.

[0029] In the present invention, the stirring and mixing time in step 1) is preferably 22 to 26 hours, more preferably 23 to 25 hours, and more preferably 24 hours; the stirring and mixing is preferably carried out at room temperature, and the stirring and mixing speed is preferably 260 to 350 r / min, more preferably 280 to 320 r / min, and more preferably 300 r / min.

[0030] In the present invention, during the electrospinning process of step 2), the voltage is preferably 12 to 20 kV, more preferably 14 to 18 kV, more preferably 15 to 16 kV, and the spinning distance is preferably 14 to 18 cm, more preferably 15 to 17 cm, more preferably 16 cm.

[0031] In the present invention, the calcination treatment in step 2) preferably includes a first calcination treatment and a second calcination treatment; in the first calcination treatment, the temperature is preferably 350-450°C, more preferably 370-430°C, more preferably 390-400°C, and the time is preferably 1.5-2.5h, more preferably 1.7-2.2h, more preferably 2h; in the second calcination treatment, the temperature is preferably 550-650°C, more preferably 570-630°C, more preferably 590-600°C, and the time is preferably 0.5-1.5h, more preferably 0.7-1.2h, more preferably 1h.

[0032] In the present invention, the rate of heating from room temperature to the first calcination temperature and the rate of heating from the first calcination temperature to the second calcination temperature are independently preferably 4-6°C / min, more preferably 4.5-5.5°C / min, and more preferably 5°C / min.

[0033] In the present invention, the first calcination treatment is preferably carried out in a nitrogen atmosphere; the second calcination treatment is preferably carried out in an air atmosphere; the process of heating from room temperature to the first calcination temperature is preferably carried out in a nitrogen atmosphere, and the process of heating from the first calcination temperature to the second calcination temperature is preferably carried out in an air atmosphere.

[0034] The present invention also provides copper-based perovskite nanofibers prepared by the method for preparing the copper-based perovskite nanofibers.

[0035] In the present invention, the copper-based perovskite nanofiber is LaCu x Co 1-x O3 perovskite nanofibers, wherein x is preferably 0.1 to 0.7.

[0036] The present invention also provides the use of the copper-based perovskite nanofibers in the electrocatalytic reduction of nitrate.

[0037] The copper-based perovskite nanofiber electrocatalytic reduction of nitrate to produce NH4 + The specific steps are as follows: (1) ultrasonically mixing copper-based perovskite nanofibers (catalyst), anhydrous ethanol and Nafion membrane solution to obtain catalyst ink; (2) dropping the catalyst ink onto carbon paper to obtain catalyst-loaded carbon paper; (3) using the catalyst-loaded carbon paper as a working electrode, an Ag / AgCl electrode as a reference electrode, a graphite rod as a counter electrode, and a sodium sulfate solution as an electrolyte to perform an electrochemical catalytic reduction of nitrate and determine the content of ammonium ions in the solution.

[0038] In the present invention, the mass volume ratio of copper-based perovskite nanofibers, anhydrous ethanol and Nafion membrane solution is preferably 3-5 mg: 300-400 μL: 35-45 μL; the Nafion membrane solution is an aqueous solution of Nafion membrane; the mass fraction of the Nafion membrane solution is preferably 4-6%, more preferably 5%.

[0039] In the present invention, the ultrasonic mixing time is preferably 15 to 25 minutes, more preferably 18 to 22 minutes, and more preferably 20 minutes; the ultrasonic mixing power is preferably 50 to 80 W, more preferably 60 to 70 W.

[0040] In the present invention, the catalyst loading amount in the catalyst-loaded carbon paper is preferably 0.35 to 0.45 mg / cm 2 , more preferably 0.39 to 0.42 mg / cm 2 , more preferably 0.4 mg / cm 2 .

[0041] In the present invention, the molar concentration of the sodium sulfate solution is preferably 0.45 to 0.55 mol / L, more preferably 0.5 mol / L; the sodium sulfate solution is an aqueous solution of sodium sulfate.

[0042] In the present invention, the steps of the electrochemical performance test are as follows: introducing 99.9% pure argon into the electrolyte for 0.5 h, performing 20 cycles of CV activation; recording by linear sweep voltammetry (LSV) at a scan rate of 5 mV / s; and electrocatalytic testing using chronoamperometry with an electrolysis time of 2 h.

[0043] In the present invention, the potential of the working electrode to the reversible hydrogen electrode is calculated using formula 1:

[0044] E RHE =E Ag / AgCl +0.0591pH+0.197VFormula 1

[0045] Among them, E RHE is the potential of the working electrode to the reversible hydrogen electrode (RHE), E Ag / AgCl is the Ag / AgCl electrode potential, and pH is the pH value of the electrolyte solution.

[0046] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] 0.75mmolLa(NO3)3·6H2O, 0.675mmolCo(NO3)2·6H2O and 0.075mmolCu(NO3)2·3H2O were added to a mixed solvent of 2gPVP(K90) and DMF (the mass fraction of PVP in the mixed solvent was 12%), and the mixture was stirred at room temperature at a rate of 300r / min for 24h to obtain a precursor solution.

[0049] The precursor solution was transferred to a spinning tube and electrospun at a voltage of 16 kV and a spinning distance of 16 cm. The nanofibers obtained by electrospinning were calcined in a tubular furnace. The specific steps of the calcination process were as follows: heating from room temperature to 400 ° C at a rate of 5 ° C / min in a nitrogen atmosphere, calcining at 400 ° C in a nitrogen atmosphere for 2 hours; then heating from 400 ° C to 600 ° C at a rate of 5 ° C / min in an air atmosphere, calcining at 600 ° C in air for 1 hour to obtain LaCu 0.1 Co 0.9 O3 perovskite nanofibers.

[0050] Example 2

[0051] The Co(NO3)2·6H2O and Cu(NO3)2·3H2O in Example 1 were changed to 0.375mmol and 0.375mmol respectively, and the other conditions were the same as in Example 1 to obtain LaCu 0.5 Co 0.5O3 perovskite nanofibers.

[0052] Example 3

[0053] The Co(NO3)2·6H2O and Cu(NO3)2·3H2O in Example 1 were changed to 0.225mmol and 0.525mmol respectively, and the other conditions were the same as in Example 1 to obtain LaCu 0.7 Co 0.3 O3 perovskite nanofibers.

[0054] The LaCu prepared in this example 0.7 Co 0.3 Scanning electron microscopy images of O3 perovskite nanofibers Figure 1 As shown, from Figure 1 It can be seen that the prepared electrocatalyst has a nanofiber shape, which can provide abundant active sites and contact area as a catalyst in the electrocatalytic process.

[0055] Example 4

[0056] 0.72mmolLa(NO3)3·6H2O, 0.625mmolCo(NO3)2·6H2O and 0.078mmolCu(NO3)2·3H2O were added to a mixed solvent of 1.8gPVP(K90) and DMF (the mass fraction of PVP in the mixed solvent was 11%), and stirred at room temperature at a rate of 280r / min for 25h to obtain a precursor solution.

[0057] The precursor solution was transferred to a spinning tube and electrospun at a voltage of 14 kV and a spinning distance of 15 cm. The nanofibers obtained by electrospinning were calcined in a tubular furnace. The specific steps of the calcination treatment were as follows: in a nitrogen atmosphere, the temperature was raised from room temperature to 370 ° C at a rate of 4.5 ° C / min, and calcined at 370 ° C in a nitrogen atmosphere for 1.7 h; then in an air atmosphere, the temperature was raised from 370 ° C to 570 ° C at a rate of 4.5 ° C / min, and calcined at 570 ° C in air for 0.7 h to obtain LaCu 0.1 Co 0.9 O3 perovskite nanofibers.

[0058] Example 5

[0059] 0.78 mmol La(NO3)3·6H2O, 0.375 mmol Co(NO3)2·6H2O and 0.375 mmol Cu(NO3)2·3H2O were added to a mixed solvent of 2.2 g PVP (K90) and DMF (the mass fraction of PVP in the mixed solvent was 13%), and stirred at room temperature at a rate of 320 r / min for 23 h to obtain a precursor solution.

[0060] The precursor solution was transferred to a spinning tube and electrospun at a voltage of 17 kV and an electrospinning distance of 17 cm. The nanofibers obtained by electrospinning were calcined in a tubular furnace. The specific steps of the calcination treatment were as follows: in a nitrogen atmosphere, the temperature was raised from room temperature to 430 ° C at a rate of 5.5 ° C / min, and calcined at 430 ° C in a nitrogen atmosphere for 2.2 hours; then in an air atmosphere, the temperature was raised from 430 ° C to 630 ° C at a rate of 5.5 ° C / min, and calcined at 630 ° C in air for 1.2 hours to obtain LaCu 0.5 Co 0.5 O3 perovskite nanofibers.

[0061] The perovskite nanofibers of Examples 1 to 3 were used as electrocatalysts for electrocatalytic reduction of nitrate to produce NH4 + Performance test: 4.0 mg of the electrocatalyst of Example 1, 360 μL of anhydrous ethanol, and 40 μL of Nafion membrane solution of model D520 (mass fraction of Nafion membrane solution is 5%) were mixed by ultrasound (power of 60 W) for 20 min to obtain a uniformly mixed catalyst ink. 200 μL of the catalyst ink was dropped onto 1 cm × 1 cm carbon paper to obtain a catalyst loading of 0.4 mg / cm 2 of carbon paper.

[0062] A traditional three-electrode system was used, with an Ag / AgCl electrode as the reference electrode, a graphite rod as the counter electrode, and catalyst-loaded carbon paper as the working electrode to assemble an electrolytic cell. A 0.5 mol / L sodium sulfate solution was used as the electrolyte. Electrocatalytic reduction of nitrate was performed on a Wuhan Coster CS350H electrochemical workstation to test the ammonium ion content in the solution. First, nitrogen gas with a purity of 99.9% was introduced into a bottle containing 0.5 mol / L sodium sulfate solution for 0.5 h, followed by 20 cycles of CV activation. LSV was then used for recording, with a scan rate of 5 mV / s. The electrochemical test used the chronoamperometry method, and the electrolysis time was 2 h.

[0063] LaCu prepared in Examples 1 to 3 x Co 1-x The LSV curves of the electrocatalytic reduction of nitrate by O3 (x = 0.1, 0.5, 0.7) perovskite nanofibers are shown in Figure 2. Figure 2 As shown. x Co 1-x The electrocatalyst made of O3 perovskite nanofibers was used as the working electrode, and the LSV curve showed that the LaCu x Co 1-x O3 perovskite nanofibers have excellent reduction performance for nitrate. Compared with other copper content catalysts, LaCu 0.7 Co0.3 O3 catalyst has better reduction performance for nitrate.

[0064] LaCu prepared in Examples 1 to 3 x Co 1-x O3 (x=0.1, 0.5, 0.7) perovskite nanofiber electrocatalytic reduction of nitrate to produce NH4 + The yield diagram is as follows Figure 3 The results show that LaCu 0.1 Co 0.9 O3, LaCu 0.5 Co 0.5 O3 and LaCu 0.7 Co 0.3 O3 perovskite nanofibers have excellent electrocatalytic reduction performance of nitrate. 0.7 Co 0.3 O3 has the highest ammonium production efficiency, with a yield of 88.2 μg·h at a high potential (-0.9 V vs. Ag / AgCl). -1 mg -1 Compared with other catalysts, LaCu 0.7 Co 0.3 The Faradaic efficiency of O3 electrocatalytic production of ammonium is as high as 85%, and the Faradaic efficiency of by-products is low. It is an excellent catalyst for the electrocatalytic reduction of nitrates with good practicality and long-term development prospects.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing copper-based perovskite nanofibers, characterized in that: The following steps are included: 1) La(NO3)3·6H2O, Co(NO3)2·6H2O, and Cu(NO3)2·3H2O are added to a mixed solvent and stirred to obtain a precursor solution; 2) electrospinning the precursor solution to obtain nanofibers, and calcining the nanofibers to obtain copper-based perovskite nanofibers; Step 1) The molar ratio of La(NO3)3·6H2O, Co(NO3)2·6H2O and Cu(NO3)2·3H2O is 6.5-8.5:2.25-6.75:0.75-5.25; Step 1) The mixed solvent comprises polyvinyl pyrrolidone and N,N-dimethylformamide; Step 2) The calcination treatment includes a first calcination treatment and a second calcination treatment; in the first calcination treatment, the temperature is 350-450°C and the time is 1.5-2.5 hours; in the second calcination treatment, the temperature is 550-650°C and the time is 0.5-1.5 hours; the nanofibers are calcined in a tubular furnace; The rate of heating from room temperature to the first calcination temperature and the rate of heating from the first calcination temperature to the second calcination temperature are independently 4-6 ° C / min; the first calcination treatment is carried out in a nitrogen atmosphere; the second calcination treatment is carried out in an air atmosphere; The copper-based perovskite nanofiber is LaCu x Co 1-x O3 perovskite nanofibers, wherein x is 0.1, 0.5 or 0.

7.

2. The method for preparing copper-based perovskite nanofibers according to claim 1, wherein: In step 1), the molar mass ratio of La(NO3)3·6H2O to the mixed solvent is 6.5-8.5 mmol: 15-25 g.

3. The method for preparing copper-based perovskite nanofibers according to claim 2, wherein: The mass fraction of polyvinyl pyrrolidone in the mixed solvent is 10-14%.

4. The method for preparing copper-based perovskite nanofibers according to claim 1 or 3, characterized in that: The stirring and mixing time in step 1) is 22 to 26 hours; during the electrospinning process in step 2), the voltage is 12 to 20 kV, and the spinning distance is 14 to 18 cm.

5. The copper-based perovskite nanofiber prepared by the method for preparing the copper-based perovskite nanofiber according to any one of claims 1 to 4, characterized in that: The copper-based perovskite nanofiber is LaCu x Co 1-x O3 perovskite nanofibers, wherein x is 0.1, 0.5 or 0.

7.

6. Use of the copper-based perovskite nanofibers according to claim 5 in the electrocatalytic reduction of nitrate.

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