Preparation method and application of NiFe2O4 spinel / NiFe-hydrotalcite photocatalytic composite material

Abstract

The present invention belongs to the field of photocatalysis, and relates to a preparation method and application of NiFe2O4 spinel / NiFe‑hydrotalcite photocatalytic composite material. A soluble nickel salt and a soluble iron salt are dissolved in deionized water, a NaOH solution is added dropwise to the solution to make it alkaline, and Na2CO3 is added to the solution, stirred, and then transferred to a microwave hydrothermal reaction kettle; after cooling to room temperature, the reaction product is collected by centrifugation, cleaned, dried, and ground; and finally a NiFe2O4 spinel / NiFe‑hydrotalcite photocatalytic composite material is obtained. The NiFe2O4 / NiFe‑LDH photocatalytic composite material prepared by the present invention presents a regular hexagonal morphology, has a plasma resonance effect and abundant active sites, has a large specific surface area, can achieve near-infrared light response, effectively suppresses the recombination of photogenerated carriers, enhances the performance of the photocatalyst, and has excellent effect on the photocatalytic reduction of carbon dioxide to methane.

Description

Technical field:

[0001] The present invention belongs to the field of photocatalysis, and in particular relates to a NiFe2O4 spinel / NiFe-hydrotalcite photocatalytic composite material and a preparation method and application thereof. Background technology:

[0002] Due to the dramatic increase in global population and industrial activity, the burning of traditional fossil fuels, and the depletion of natural resources, the global increase in carbon dioxide emissions has placed significant pressure on the ecological environment. Developing low-cost, environmentally friendly, and industrial-scale new energy technologies to replace traditional fossil fuels is particularly important. It is worth noting that, compared with traditional thermal catalytic CO2 reduction processes, photocatalytic reduction of CO2 to high-value-added products is an effective strategy to alleviate environmental issues such as global warming and fossil fuel depletion.

[0003] Over the past few decades, people have developed efficient photocatalytic systems to reduce carbon dioxide emissions and have made significant progress. Reported photocatalysts include MOFs, metal oxides, g-C3N4, layered double hydroxides (LDHs), etc. Among them, LDHs are a class of layered columnar compounds with a special structure. Divalent metals and trivalent metals are evenly distributed. Their unique structure and multifunctional chemical composition make them widely used in catalysis, electrochemistry, drug delivery and other fields. It has been reported that the g-C3N4 foam / LDH heterojunction derived from melamine sponge has excellent CO2 photoreduction performance.

[0004] Chinese patent CN 112391649A provides a method for preparing a NiFe-LDH composite material. The method involves dispersing a Ni-BDC precursor, ferric nitrate, and ammonium fluoride in deionized water, adding a NaOH / Na2CO3 buffer solution, and hydrothermally reacting at 135-145°C for 10-12 hours to obtain a NiFe-LDH composite material with a MOF framework. However, the NiFe-LDH prepared by this method is complex, time-consuming, and inefficient. To date, no efficient method for preparing a NiFe-LDH composite material with plasmon resonance has been reported. Summary of the invention:

[0005] The present invention provides a NiFe2O4 spinel / NiFe-LDH photocatalytic composite material, its preparation method, and application. The present invention synthesizes the NiFe2O4 spinel / NiFe-LDH photocatalytic heterojunction material through a simple microwave hydrothermal method. By controlling the raw material ratio, microwave hydrothermal process parameters, and other process parameters, the NiFe2O4 spinel / NiFe-hydrotalcite composite material is obtained. The resulting catalyst can maximize the reduction and conversion of carbon dioxide.

[0006] In order to achieve the purpose of the present invention, the technical solution adopted is:

[0007] A method for preparing a NiFe2O4 spinel / NiFe-hydrotalcite catalytic composite material comprises the following steps:

[0008] (1) Weigh a certain amount of nickel salt and iron salt and dissolve them in deionized water to obtain solution A;

[0009] (2) adding a prepared pH adjuster (NaOH solution) dropwise to solution A to make solution A alkaline to obtain solution B;

[0010] (3) Add the prepared Na2CO3 solution to solution B and stir for a certain period of time to obtain mixed solution C;

[0011] (4) The mixed solution C is transferred to a reaction kettle, placed in a microwave hydrothermal reactor, and reacted at 140-180°C for 1-3 hours. After the reaction is completed, the mixture is cooled, the product is collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain a NiFe2O4 / NiFe-LDH photocatalytic composite material.

[0012] The ratio of metal salt in step (1) is n(Fe 3+ ):n(Ni 2+ )=0.1~0.4:1, the iron salt can be ferric nitrate, ferric chloride, or ferric sulfate; the nickel salt can be nickel nitrate, nickel chloride, or nickel sulfate.

[0013] The pH value of solution B in step (2) is 9-14, and the concentration of NaOH is 0.2-0.5 mol / L

[0014] The concentration of Na2CO3 added in step (3) is 0.02-0.05 mol / L; n(Na2CO3):n(NaOH)=1:10. The washing method in step (4) is: first wash with deionized water 3 times, then wash with alcohol once.

[0015] The present invention also provides an application of the NiFe2O4 / NiFe-LDH photocatalytic composite material, that is, using the photocatalytic composite material to perform photocatalytic reduction of carbon dioxide to produce methane.

[0016] The specific application method is as follows: In a closed photochemical reactor at room temperature, a NiFe2O4 spinel / NiFe-LDH photocatalytic composite material is added to deionized water. After thorough ultrasonic dispersion, carbon dioxide gas is introduced to remove impurities. The product is then illuminated under simulated sunlight to photocatalytically reduce carbon dioxide to produce methane. Compared with existing technologies, the present invention has the following advantages:

[0017] (1) The microwave hydrothermal method used in the present invention is a one-step method for preparing NiFe2O4 / NiFe-LDH, which is shorter, more efficient, and reduces energy consumption compared to conventional hydrothermal methods for preparing NiFe-LDH. Under microwave conditions, microwaves generate an alternating electromagnetic field and utilize the thermal effect of electromagnetic radiation to rapidly increase the temperature of the reaction system in a very short period of time, causing NiFe2O4 spinel to precipitate in situ on the surface of the NiFe-LDH and grow uniformly. At the same time, the NiFe-LDH exhibits an ultra-thin two-dimensional hexagonal morphology.

[0018] (2) The NiFe2O4 / NiFe-LDH composite material prepared by the present invention has a larger specific surface area. NiFe2O4 is a narrow-bandgap semiconductor capable of near-infrared light response. Furthermore, the heterojunction formed by NiFe2O4 / NiFe-LDH enhances its ability to capture photogenerated electrons, accelerates the separation of photogenerated carriers, and improves the photocatalytic activity of the catalyst.

[0019] (3) The NiFe2O4 / NiFe-LDH composite material prepared by the present invention has a plasma resonance (SPR) effect, which can excite hot electrons and improve the catalytic efficiency of the composite photocatalyst. Description of the drawings:

[0020] Figure 1 XRD spectra of NiFe2O4, NiFe-LDH and NiFe2O4 / NiFe-LDH samples prepared in Example 1;

[0021] Figure 2 TEM image of the NiFe2O4 / NiFe-LDH sample prepared in Example 1 with a scale of 20 nm;

[0022] Figure 3 UV-Vis-NIR spectra of NiFe2O4, NiFe-LDH and NiFe2O4 / NiFe-LDH samples prepared in Example 1.

[0023] Figure 4 Thermal images of NiFe2O4, NiFe-LDH and the NiFe2O4 / NiFe-LDH sample prepared in Example 1. Specific implementation method:

[0024] Example 1

[0025] Ferric nitrate and nickel nitrate were weighed at a molar ratio of 0.4:1 and dissolved in deionized water. 0.2 mol / L NaOH solution was then added to the solution to raise its pH to 10. 0.02 mol / L Na2CO3 solution was then added and stirred at room temperature for 3 hours to obtain a mixed solution. The mixed solution was then transferred to a reactor and placed in a microwave hydrothermal reactor (Shanghai Xinyi Microwave Chemical Technology Co., Ltd., microwave power 1800 W) at 180°C for 1.5 hours. After the reaction was completed, the reaction was cooled, the product was collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain the NiFe2O4 / NiFe-LDH photocatalytic composite material.

[0026] An X-ray powder diffraction experiment was performed on the NiFe2O4 / NiFe-LDH composite material prepared in this example. Its morphology and structure were observed under a transmission electron microscope, and its light absorption was tested under an ultraviolet-visible diffuse reflectance spectrometer.

[0027] XRD patterns such as Figure 1 As shown: The characteristic diffraction peaks of NiFe2O4 and NiFe-LDH appear in the NiFe2O4 / NiFe-LDH composite material, indicating that the composite material has been successfully synthesized; In addition, the TEM image of the NiFe2O4 / NiFe-LDH sample is shown in Figure 2 As can be seen from the figure, the prepared NiFe-LDH has a regular hexagonal morphology, and NiFe2O4 particles are uniformly dispersed on the NiFe-LDH, which is consistent with the XRD results.

[0028] The UV-vis-NIR spectra and thermal imaging of NiFe2O4 / NiFe-LDH and NiFe2O4 and NiFe-LDH prepared in this example are as follows: Figure 3 and Figure 4 As shown in the figure, the NiFe-LDH light response absorption edge is around 650nm, and the temperature rises to 100.6℃ under illumination. NiFe-LDH has a plasmon resonance effect in the near-infrared, and the temperature rises to 96.1℃ under illumination. The NiFe2O4 / NiFe-LDH light response absorption edge extends to around 900nm. At the same time, it also well inherits the plasmon resonance effect of NiFe-LDH, enabling the NiFe2O4 / NiFe-LDH composite material to achieve a full spectrum absorption range, and the temperature rises to 107.3℃ under illumination.

[0029] Through the above experimental method, the yield of methane from photocatalytic reduction of CO2 in pure water under 4 hours of simulated sunlight was 35.3 μmol·g -1 ·h -1 .

[0030] Example 2

[0031] Ferric nitrate and nickel nitrate were weighed at a molar ratio of 0.1:1 and dissolved in deionized water. 0.3 mol / L NaOH solution was then added to the solution to raise its pH to 9. 0.03 mol / L Na2CO3 solution was then added and stirred at room temperature for 1 hour to obtain a mixed solution. The mixed solution was then transferred to a reaction vessel and placed in a microwave hydrothermal reactor. The reaction was carried out at 160°C for 1.5 hours. After the reaction was completed, the reaction was cooled, and the product was collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain the NiFe2O4 / NiFe-LDH photocatalytic composite material.

[0032] After 4 hours of simulated sunlight irradiation, the yield of methane from photocatalytic reduction of CO2 in pure water was 34.1 μmol·g -1 ·h -1 .

[0033] Example 3

[0034] Nickel nitrate and ferric nitrate were weighed at a molar ratio of 0.2:1 and dissolved in deionized water. 0.4 mol / L NaOH solution was then added to the solution to raise its pH to 12. 0.04 mol / L Na2CO3 solution was then added and stirred at room temperature for 2 hours to obtain a mixed solution. The mixed solution was then transferred to a reaction vessel and placed in a microwave hydrothermal reactor. The reaction was carried out at 170°C for 1.5 hours. After the reaction was completed, the product was cooled, collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain the NiFe2O4 / NiFe-LDH photocatalytic composite material.

[0035] After 4 hours of simulated sunlight irradiation, the yield of methane from photocatalytic reduction of CO2 in pure water was 34.7 μmol·g -1 ·h -1 .

[0036] Example 4

[0037] Ferric nitrate and nickel nitrate at a molar ratio of 0.3:1 were dissolved in deionized water. 0.5 mol / L NaOH solution was then added to the solution to raise its pH to 11. 0.05 mol / L Na2CO3 solution was then added and stirred at room temperature for 2.5 hours to obtain a mixed solution. The mixed solution was then transferred to a reaction vessel and placed in a microwave hydrothermal reactor. The reaction was carried out at 150°C for 3 hours. After the reaction was completed, the reaction was cooled, and the product was collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain a NiFe2O4 / NiFe-LDH photocatalytic composite material.

[0038] After 4 hours of simulated sunlight irradiation, the yield of methane from photocatalytic reduction of CO2 in pure water was 33.8 μmol·g -1 ·h -1 .

[0039] Example 5

[0040] Ferric nitrate and nickel nitrate were weighed at a molar ratio of 0.15:1 and dissolved in deionized water. 0.1 mol / L NaOH solution was then added to the solution to raise its pH to 13. 0.01 mol / L Na₂CO₃ solution was then added and stirred at room temperature for 3 hours to obtain a mixed solution. The mixed solution was then transferred to a reaction vessel and placed in a microwave hydrothermal reactor. The reaction was carried out at 140°C for 2 hours. After the reaction was completed, the reaction was cooled, and the product was collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain the NiFe₂O₄ / NiFe-LDH photocatalytic composite material.

[0041] After 4 hours of simulated sunlight irradiation, the yield of methane from photocatalytic reduction of CO2 in pure water was 33.2 μmol·g -1 ·h -1 .

[0042] Example 6

[0043] Ferric nitrate and nickel nitrate were weighed at a molar ratio of 0.25:1 and dissolved in deionized water. 0.1 mol / L NaOH solution was then added to the solution to raise its pH to 14. 0.01 mol / L Na2CO3 solution was then added and stirred at room temperature for 3 hours to obtain a mixed solution. The mixed solution was then transferred to a reaction vessel and placed in a microwave hydrothermal reactor. The reaction was heated at 180°C for 1 hour. After the reaction was completed, the reaction was cooled, and the product was collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain the NiFe2O4 / NiFe-LDH photocatalytic composite material.

[0044] After 4 hours of simulated sunlight irradiation, the yield of methane from photocatalytic reduction of CO2 in pure water was 34.6 μmol·g -1 ·h -1 .

[0045] Comparative Example 1

[0046] Ferric nitrate and nickel nitrate were weighed at a molar ratio of 0.4:1 and dissolved in deionized water. 0.2 mol / L NaOH solution was then added to the solution to raise its pH to 10. 0.02 mol / L Na2CO3 solution was then added and stirred at room temperature for 3 hours to obtain a mixed solution. The mixed solution was then transferred to a reaction kettle and placed in a conventional hydrothermal reactor. The reaction was carried out at 180°C for 12 hours. After the reaction was completed, the reaction was cooled, and the product was collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain the NiFe2O4 / NiFe-LDH photocatalytic composite material.

[0047] This comparative example was not carried out under microwave hydrothermal reaction, which requires a long reaction time. Conventional hydrothermal reaction cannot rapidly increase the temperature of the reaction system in a very short time, and only NiFe-LDH can be obtained. After 4 hours of simulated solar light irradiation, the yield of methane produced by photocatalytic reduction of CO2 in pure water was 14.1 μmol·g -1 ·h -1 .

[0048] Comparative Example 2

[0049] Ferric nitrate and nickel nitrate were weighed at a molar ratio of 0.5:1 and dissolved in deionized water. 0.2 mol / L NaOH solution was then added to the solution to raise its pH to 10. 0.02 mol / L Na2CO3 solution was then added and stirred at room temperature for 3 hours to obtain a mixed solution. The mixed solution was then transferred to a reaction vessel and placed in a microwave hydrothermal reactor. The reaction was carried out at 180°C for 1.5 hours. After the reaction was completed, the reaction was cooled, the product was collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain the NiFe-LDH photocatalytic composite material.

[0050] This comparative example n(Fe 3+ ):n(Ni 2+ ) is 0.5:1, only NiFe-LDH can be obtained. After 4 hours of simulated sunlight, the yield of methane produced by photocatalytic reduction of CO2 in pure water was 16.9μmol·g -1 ·h -1 .

[0051] Comparative Example 3

[0052] Ferric nitrate and nickel nitrate at a molar ratio of 0.5:1 were weighed and dissolved in deionized water. Citric acid was then added to the solution and stirred at 80°C until the water completely evaporated. The mixture was then calcined in a muffle furnace at 400°C for 3 hours to obtain a NiFe2O4 photocatalytic composite material.

[0053] Comparative Example: NiFe2O4 was obtained by sol-gel method. The yield of methane produced by photocatalytic reduction of CO2 in pure water under 4 hours of simulated sunlight was 6.8 μmol·g -1 ·h -1 .

[0054] Comparative Example 4

[0055] Ferric nitrate and nickel nitrate at a molar ratio of 0.05:1 were dissolved in deionized water. 0.2 mol / L NaOH solution was then added to the solution to raise its pH to 10. 0.02 mol / L Na2CO3 solution was then added and stirred at room temperature for 3 hours to obtain a mixed solution. The mixed solution was then transferred to a reaction vessel and placed in a microwave hydrothermal reactor. The reaction was carried out at 180°C for 1.5 hours. After the reaction was completed, the product was cooled, collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain the NiFe-LDH photocatalytic composite material.

[0056] This comparative example n(Fe 3+ ):n(Ni 2+ ) was 0.05:1, and only NiFe-LDH with low crystallinity could be obtained. After 4 hours of simulated sunlight irradiation, the yield of methane produced by photocatalytic reduction of CO2 in pure water was 5.8 μmol·g -1 ·h -1 .

[0057] Comparative Example 5

[0058] Ferric nitrate and nickel nitrate were weighed at a molar ratio of 0.4:1 and dissolved in deionized water. 0.2 mol / L NaOH solution was then added to the solution to raise its pH to 10. 0.02 mol / L Na2CO3 solution was then added and stirred at room temperature for 3 hours to obtain a mixed solution. The mixed solution was then transferred to a reaction vessel and placed in a microwave hydrothermal reactor. The reaction was carried out at 130°C for 1.5 hours. After the reaction was completed, the reaction was cooled, the product was collected by centrifugation, washed to remove impurities, and finally vacuum dried to obtain a NiFe oxide photocatalytic composite material.

[0059] In this comparative example, the microwave hydrothermal temperature was 130°C, and only composite oxides of NiO and Fe2O3 were obtained. After 4 hours of simulated sunlight irradiation, the yield of methane produced by photocatalytic reduction of CO2 in pure water was only 4.3 μmol·g -1 ·h -1 .

Claims

1. A method for preparing a NiFe2O4 spinel / NiFe-hydrotalcite photocatalytic composite material, characterized by: The specific preparation steps are: (1) Soluble nickel salt and soluble iron salt are dissolved in deionized water to obtain solution A; the ratio of soluble nickel salt to soluble iron salt is n(Fe 3+ ):n(Ni 2+ ) = 0.1~0.4:1; (2) Add a pH regulator to solution A to make solution A alkaline, thereby obtaining solution B; (3) Add Na2CO3 to solution B and stir to obtain mixed solution C; (4) The mixed solution C was transferred to a reactor, placed in a microwave hydrothermal reactor, and reacted at 140-180 °C. After the reaction was completed, the mixture was cooled and the product was collected by centrifugation. After washing to remove impurities, the product was finally vacuum dried to obtain a NiFe2O4 spinel / NiFe-hydrotalcite photocatalytic composite material.

2. The method for preparing the NiFe2O4 spinel / NiFe-hydrotalcite photocatalytic composite material according to claim 1, characterized in that: In step (2), alkalinity is achieved when the pH value is 9 to 14, and the pH regulator is a NaOH solution with a concentration of 0.2 to 0.5 mol / L.

3. The method for preparing the NiFe2O4 spinel / NiFe-hydrotalcite photocatalytic composite material according to claim 1, characterized in that: The amount of Na2CO3 added in step (3) is: n(Na2CO3):n(pH adjuster)=1:

10.

4. Use of the NiFe2O4 spinel / NiFe-hydrotalcite photocatalytic composite material prepared by the method according to any one of claims 1 to 3, characterized in that: The NiFe2O4 spinel / NiFe-hydrotalcite photocatalytic composite material is used for the photocatalytic reduction of carbon dioxide to produce methane.

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