CN113019381B - Three-dimensional porous self-supporting NiO/ZnO heterojunction material and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of porous materials, and provides a three-dimensional porous self-supporting NiO/ZnO heterojunction material and a preparation method thereof. In the present invention, the precursor solution containing high molecular polymer, nickel source, zinc source and water is subjected to freezing treatment to freeze the water in the solution into ice crystals, and then the ice crystals are removed by de-icing treatment to form macroporous channels, and finally the high pore size is removed by calcination. The molecular polymer forms micropores and mesopores, and at the same time, the nickel source is decomposed into NiO and the zinc source is decomposed into ZnO through calcination, and the accumulation of NiO particles and ZnO particles will also form macropores, thereby obtaining three-dimensional porous self-supporting NiO/ZnO Heterojunction materials. The examples show that the preparation method provided by the present invention is simple to operate, does not require template removal, and does not require strict control of experimental conditions.

Description

A three-dimensional porous self-supporting NiO/ZnO heterojunction material and preparation method thereof

technical field

The invention relates to the technical field of porous materials, in particular to a three-dimensional porous self-supporting NiO/ZnO heterojunction material and a preparation method thereof.

Background technique

Untreated urban domestic water, agricultural sewage, industrial sewage, etc. are discharged into rivers, which can lead to eutrophication of water bodies or excessive heavy metals, which will lead to the proliferation of bacteria in the water and the death of aquatic organisms, seriously affecting the ecosystem. As a safe, efficient and low-cost water pollution treatment method, semiconductor photocatalysis technology has broad application prospects in solving water pollution problems. The principle of semiconductor photocatalysis technology to treat water pollution is mainly to use the reduction and oxidation capabilities of photogenerated carriers to react with oxygen or water molecules at the interface between the catalyst and the water phase to generate active groups with strong oxidizing and reducing properties, which in turn react with oxygen or water molecules. Degradation or reduction of pollutants or heavy metal ions in water. Among many semiconductor catalyst materials, nickel oxide (NiO) and zinc oxide (ZnO) are widely used as photocatalysts due to their low cost and high chemical stability. However, since both ZnO and NiO are direct bandgap semiconductors with wide band gaps, the recombination efficiency of electrons and holes is high, and the light absorption range is narrow, which seriously affects their photocatalytic efficiency.

Semiconductor theory states that when two different types of semiconductors come into contact with each other, a heterojunction will be formed at the interface, and the diffusion and drift motion of carriers will cause the material to establish a stable built-in electric field at the interface. When the heterojunction is excited by light with energy higher than its bandgap energy, the nonequilibrium carriers are rapidly transferred under the modulation of the built-in electric field. The NiO/ZnO heterojunction has a typical type II heterojunction energy band structure, so the NiO/ZnO heterojunction can effectively hinder the ineffective recombination of photogenerated electrons and holes, resulting in a high photocatalytic efficiency. In addition, the microstructure of semiconductor catalysts also greatly affects the photocatalytic activity. The porous structure of semiconductor photocatalysts has high specific surface area and permeability, which makes it have more reactive sites and fast mass transfer channels, which contribute to the improvement of the performance of semiconductor photocatalysts. At present, the methods for preparing porous semiconductor photocatalysts mainly include template method and self-assembly method. However, the template method usually requires a complex de-template process, and the self-assembly method requires strict control of experimental conditions, which are not suitable for large-scale promotion. Therefore, it is necessary to develop a simple method for preparing porous NiO/ZnO heterojunction materials.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a three-dimensional porous self-supporting NiO/ZnO heterojunction material and a preparation method thereof. The preparation method provided by the present invention is simple to operate, does not require template removal, and does not require strict control of experimental conditions. The three-dimensional porous self-supporting NiO/ZnO heterojunction material exhibits excellent photocatalytic performance.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

The invention provides a preparation method of a three-dimensional porous self-supporting NiO/ZnO heterojunction material, comprising the following steps:

(1) mixing high molecular polymer, nickel source, zinc source and water to obtain a precursor solution;

(2) subjecting the precursor solution obtained in the step (1) to freezing treatment and deicing treatment in sequence to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor;

(3) calcining the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor obtained in the step (2) to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material.

Preferably, the mass concentration of the high molecular polymer in the precursor solution of the step (1) is 2-8%, the mass concentration of the nickel source is 0.7-1.0%, and the mass concentration of the zinc source is 0.4-0.7%.

Preferably, the high molecular polymer in the step (1) includes polyvinylpyrrolidone or polyvinyl alcohol; the nickel source includes nickel acetate or nickel nitrate; the zinc source includes zinc acetate or zinc nitrate.

Preferably, the temperature of the freezing treatment in the step (2) is below -196°C, and the freezing treatment time is 10-15 min.

Preferably, the temperature of the deicing treatment in the step (2) is -70 to -50° C., and the time of the deicing treatment is 24 to 48 h.

Preferably, the vacuum degree of the deicing treatment in the step (2) is 10-30 Pa.

Preferably, the calcination temperature in the step (3) is 500-550°C.

Preferably, the heating rate to the calcination temperature is 1-2.5°C/min.

The present invention also provides a three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared by the preparation method described in the above technical solution, wherein the three-dimensional porous NiO/ZnO heterojunction material has a hierarchical pore structure, and the hierarchical pores include Macroporous, mesoporous and microporous.

Preferably, the pore diameter of the micropores is 0.5-2 nm, the pore diameter of the mesopores is 2-50 nm, and the pore diameter of the macropores is 50 nm-10 μm.

The invention provides a preparation method of a three-dimensional porous self-supporting NiO/ZnO heterojunction material, comprising the following steps: mixing a high molecular polymer, a nickel source, a zinc source and water to obtain a precursor solution; The solution is sequentially subjected to freezing treatment and deicing treatment to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor; the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor is calcined to obtain a three-dimensional porous self-supporting NiO /ZnO heterojunction material. The present invention freezes the water in the solution into ice crystals by freezing the precursor solution containing the macromolecular polymer, nickel source, zinc source and water, then removes the ice crystals through de-icing treatment to form macroporous channels, and finally removes high pore size through calcination. The molecular polymer forms micropores and mesopores, and at the same time, the nickel source is decomposed into NiO and the zinc source is decomposed into ZnO through calcination, and the accumulation of NiO particles and ZnO particles will also form macropores, thereby obtaining three-dimensional porous self-supporting NiO/ZnO Heterojunction materials. The examples show that the preparation method provided by the present invention is simple to operate, does not require template removal, and does not require strict control of experimental conditions.

In addition, the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared by the present invention has excellent photocatalytic performance.

Description of drawings

FIG. 1 is a process flow diagram of preparing a three-dimensional porous self-supporting NiO/ZnO heterojunction material in Example 1 of the present invention;

2 is a SEM image of the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor and the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention, the inset is the three-dimensional porous self-supporting NiO/ZnO heterojunction SEM image of the junction material;

Fig. 3 is the SEM image of the side surface of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 2 of the present invention, and the inset is the SEM image of the cross-section of the three-dimensional porous self-supporting NiO/ZnO heterojunction material;

Fig. 4 is the SEM image of the side surface of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 3 of the present invention, and the inset is the SEM image of the cross-section of the three-dimensional porous self-supporting NiO/ZnO heterojunction material;

5 is an X-ray diffraction analysis pattern of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention, NiO prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2;

6 is an X-ray electron spectrogram of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention, NiO prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2;

7 is an X-ray electron spectrogram of Zn 2p of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention and ZnO prepared in Comparative Example 2;

8 is an X-ray electron spectrogram of Ni 2p of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention and NiO prepared in Comparative Example 1;

9 is the nitrogen adsorption and desorption curve of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention;

10 is a BET pore size distribution diagram of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention;

11 is a pore size distribution diagram obtained by mercury intrusion testing of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention;

12 is the photocatalytic performance curve of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention, NiO prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2;

13 is a linear fitting diagram of the first-order kinetics of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 of the present invention, NiO prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2 to degrade methyl orange;

14 is the photocatalytic performance curve of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 2 of the present invention and the powder NiO/ZnO material prepared in Comparative Example 3;

15 is a first-order kinetic linear fitting diagram of the degradation of Rhodamine B by the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 2 of the present invention and the powder NiO/ZnO material prepared in Comparative Example 3.

Detailed ways

The invention provides a preparation method of a three-dimensional porous self-supporting NiO/ZnO heterojunction material, comprising the following steps:

(1) mixing high molecular polymer, nickel source, zinc source and water to obtain a precursor solution;

(2) subjecting the precursor solution obtained in the step (1) to freezing treatment and deicing treatment in sequence to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor;

(3) calcining the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor obtained in the step (2) to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material.

In the present invention, high molecular polymer, nickel source, zinc source and water are mixed to obtain a precursor solution. The present invention has no special limitation on the mixing operation of the high molecular polymer, the nickel source, the zinc source and the water, and the technical solution of solid-liquid mixing well known to those skilled in the art can be adopted. In the present invention, the mixing of the high molecular polymer, the nickel source, the zinc source and the water is preferably carried out under stirring conditions. In the present invention, the stirring rate is preferably 500-600 r/min, more preferably 550-600 r/min; the stirring time is preferably 10-15 h, more preferably 12-14 h; the stirring temperature is Preferably it is room temperature; the stirring mode is preferably magnetic stirring.

In the present invention, the high molecular polymer preferably comprises polyvinylpyrrolidone or polyvinyl alcohol, more preferably polyvinylpyrrolidone. The source of the high molecular polymer is not particularly limited in the present invention, and commercially available products well known to those skilled in the art can be used. In the present invention, the high molecular polymer can hinder the agglomeration of the nickel source and the zinc source itself, promote the formation of heterojunction, and can also hinder the lateral growth of ice crystals, and serve as the skeleton constituting the pore structure.

In the present invention, the mass concentration of the high molecular polymer in the precursor solution is preferably 2-8%, more preferably 4-8%. In the present invention, the mass concentration of the high molecular polymer in the precursor solution is preferably controlled within the above range. If the mass concentration of the high molecular polymer is too high, the pores will collapse and the porous morphology cannot be maintained. The pore structure cannot be formed, and the resulting material exhibits the morphology of particle accumulation.

In the present invention, the nickel source preferably includes nickel acetate or nickel nitrate, more preferably nickel acetate. The source of the nickel source is not particularly limited in the present invention, and commercially available products well known to those skilled in the art can be used.

In the present invention, the mass concentration of the nickel source in the precursor solution is preferably 0.7-1.0%, more preferably 0.74-0.99%. In the present invention, the mass concentration of the nickel source in the precursor solution is preferably controlled within the above range. The concentration of the nickel source affects the mechanical strength of the material. The higher the concentration, the higher the hardness. However, if the concentration is too high, it will affect the photocatalysis of the material. performance.

In the present invention, the zinc source preferably includes zinc acetate or zinc nitrate, more preferably zinc acetate. The source of the zinc source is not particularly limited in the present invention, and commercially available products well known to those skilled in the art can be used.

In the present invention, the mass concentration of the zinc source in the precursor solution is preferably 0.4-0.7%, more preferably 0.44-0.65%. In the present invention, the mass concentration of the zinc source in the precursor solution is preferably controlled within the above-mentioned range. The concentration of the zinc source affects the mechanical strength of the material. The higher the concentration, the higher the hardness. However, if the concentration is too high, it will affect the photocatalysis of the material. performance.

In the present invention, the water is preferably deionized water.

After the precursor solution is obtained, the present invention sequentially performs freezing treatment and deicing treatment on the precursor solution to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor. In the present invention, the precursor solution containing the high molecular polymer, the nickel source, the zinc source and the water is subjected to freezing treatment to freeze the water in the solution into ice crystals, and then the ice crystals are removed by de-icing treatment to form macropores.

In the present invention, the temperature of the freezing treatment is preferably -196°C or lower. In the present invention, the freezing treatment is preferably performed in liquid nitrogen. In the present invention, the freezing treatment time is preferably 10-15 min, more preferably 10-12 min. In the present invention, the precursor solution is preferably placed at the above temperature for freezing treatment, so that the water in the precursor solution can be instantly frozen into ice crystals, and then the ice crystals are removed by de-icing treatment to form macropores.

After the freezing treatment is completed, in the present invention, the freezing treatment product is subjected to deicing treatment to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor. The present invention has no special limitation on the operation of the deicing treatment, as long as the ice crystals in the product can be removed. In the present invention, the method of the deicing treatment is preferably freeze-drying. In the present invention, the freeze-drying temperature is preferably -70--50°C, more preferably -70°C; the freeze-drying time is preferably 24-48h, more preferably 48h. In the present invention, the temperature of the freeze-drying is preferably controlled within the above range, so that the ice crystals can be directly sublimated without melting into water, which is beneficial to maintain the porous structure of the material. In the present invention, the freeze-drying device is preferably a vacuum freeze-drying machine.

In the present invention, the degree of vacuum in the deicing treatment is preferably 10 to 30 Pa, more preferably 20 to 30 Pa. The present invention preferably controls the vacuum degree of the de-icing treatment within the above-mentioned range. If the vacuum is too low, the sublimation rate of ice crystals is slow. At this time, the material itself may melt due to absorbing heat, which is not conducive to maintaining the porous structure of the material. Too high will affect the heat transfer, and will also slow down the sublimation rate of ice crystals and affect the maintenance of the porous structure of the material.

After obtaining the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor, the present invention calcines the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor to obtain the three-dimensional porous self-supporting NiO/ZnO heterojunction material. The invention removes the macromolecular polymer by calcination, and then forms micropores and mesopores. Meanwhile, the nickel source is decomposed into NiO and the zinc source is decomposed into ZnO through calcination, and the accumulation of NiO particles and ZnO particles also forms macropores.

In the present invention, the calcination temperature is preferably 500 to 550°C, more preferably 550°C. In the present invention, the heating rate to the calcination temperature is preferably 1 to 2.5°C/min, more preferably 2.5°C/min. In the present invention, the calcination temperature is preferably controlled within the above-mentioned range, so as to facilitate the complete removal of the high molecular polymer; however, if the calcination temperature is too high, the particles constituting the pore wall will become larger, the specific surface area of the material will decrease, and the final effect of the material will be affected. photocatalytic properties. In the present invention, the calcining device is preferably a muffle furnace.

After the temperature is raised to the calcination temperature, the present invention preferably maintains the temperature at the calcination temperature to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material. In the present invention, the holding time is preferably 1 to 5 hours, more preferably 2 to 3 hours. In the present invention, it is preferable to keep the temperature for a period of time in order to completely remove the high molecular polymer, while improving the crystallinity of the material.

In the present invention, the precursor solution containing the macromolecular polymer, the nickel source, the zinc source and the water is subjected to freezing treatment to freeze the water in the solution into ice crystals, and then the ice crystals are removed by de-icing treatment to form macropores, and finally the macromolecules are removed by calcination. The polymer forms micropores and mesopores, and at the same time, the nickel source is decomposed into NiO and the zinc source is decomposed into ZnO through calcination, and the accumulation of NiO particles and ZnO particles will also form macropores, thereby obtaining a macropore, mesopores. and microporous three-dimensional porous self-supporting NiO/ZnO heterojunction materials.

The present invention also provides a three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared by the preparation method described in the above technical solution, wherein the three-dimensional porous NiO/ZnO heterojunction material has a hierarchical pore structure, and the hierarchical pores include Macroporous, mesoporous and microporous. In the present invention, the micropores and mesopores are left by calcining to remove the high molecular polymer, which can greatly increase the specific surface area of the material and provide a large number of reaction sites for the photocatalytic reaction, and the macropores are left after deicing. The pore structure and the pore structure formed by particle accumulation can significantly improve the mass transfer efficiency of the reactants, thereby improving the efficiency of the photocatalytic reaction.

In the present invention, the pore size of the micropores is preferably 0.5-2 nm, more preferably 1-2 nm; the pore size of the mesopores is preferably 2-50 nm, more preferably 5-50 nm; the pore size of the macropores is preferably It is 50 nm to 10 μm, and more preferably 100 nm to 10 μm.

The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

Dissolve 0.372g nickel acetate, 0.328g zinc acetate and 4g polyvinylpyrrolidone in 50mL deionized water, stir magnetically at room temperature for 12h at a rate of 600r/min to obtain a precursor solution (polyvinylpyrrolidone in the precursor solution) The mass concentration of nickel acetate is 8%, the mass concentration of nickel acetate is 0.74%, and the mass concentration of zinc acetate is 0.65%);

The above precursor solution was injected into a centrifuge tube, and immersed vertically in liquid nitrogen at -196 °C at a speed of 1 cm/s for 10 min. After removing the cap of the centrifuge tube, the centrifuge tube was placed in a vacuum freeze dryer. The three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor was obtained by drying at a temperature of -70 °C for 48 h at a temperature of 20 Pa;

The above three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor was placed in a muffle furnace, and then the calcination temperature was increased from room temperature to 550 °C at a heating rate of 2.5 °C/min, and then kept for 2 h, and then naturally At room temperature, a three-dimensional porous self-supporting NiO/ZnO heterojunction material (denoted as NiO/ZnO-1) with macropores, mesopores and micropores was obtained. Among them, the macropore diameter is 7 μm, the mesopore diameter is 48 nm, and the micropore diameter is 1 nm.

Application example 1

The three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 was used for photocatalytic degradation of methyl orange, and a 50W UV lamp was used as the light source. 30mg of NiO/ZnO-1 prepared in Example 1 was added to 30mL of 10ppm methyl orange solution, adsorbed in the dark for 30min to reach adsorption-desorption equilibrium, then the mixed solution was placed under an ultraviolet lamp, and taken out every 15min. 2mL solution, the absorbance at 463nm of the solution was detected with a UH4150 spectrophotometer, the results are shown in Figure 12.

Example 2

Dissolve 0.496g nickel acetate, 0.219g zinc acetate and 4g polyvinylpyrrolidone in 50mL deionized water, stir magnetically at room temperature for 12h at a rate of 600r/min to obtain a precursor solution (polyvinylpyrrolidone in the precursor solution) The mass concentration of 8%, the mass concentration of nickel acetate is 0.99%, the mass concentration of zinc acetate is 0.44%);

The above precursor solution was injected into a centrifuge tube, and immersed vertically in liquid nitrogen at -196 °C at a speed of 1 cm/s for 10 min. After removing the cap of the centrifuge tube, the centrifuge tube was placed in a vacuum freeze dryer. The three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor was obtained by drying at a temperature of -70 °C for 48 h at a temperature of 20 Pa;

The above three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor was placed in a muffle furnace, and the calcination temperature was increased from room temperature to 550 °C at a heating rate of 2.5 °C/min, followed by holding for 2 h, and then naturally decreased. At room temperature, a three-dimensional porous self-supporting NiO/ZnO heterojunction material (denoted as NiO/ZnO-2) with macropores, mesopores and micropores was obtained. Among them, the macropore diameter is 6 μm, the mesopore diameter is 48 nm, and the micropore diameter is 1 nm.

Application example 2

The three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 2 was used for photocatalytic degradation of Rhodamine B, and a 50W UV lamp was used as the light source. 30mg of NiO/ZnO-2 prepared in Example 2 was added to 30mL of 10ppm Rhodamine B solution, adsorbed in the dark for 30min to reach adsorption-desorption equilibrium, then the mixed solution was placed under an ultraviolet lamp, and taken out every 15min. 2mL solution, the absorbance at 553nm of the solution was detected with a UH4150 spectrophotometer, the results are shown in Figure 14.

Example 3

Dissolve 0.496g nickel acetate, 0.219g zinc acetate and 2g polyvinylpyrrolidone in 50mL deionized water, stir magnetically at room temperature for 12h at a rate of 600r/min to obtain a precursor solution (polyvinylpyrrolidone in the precursor solution) The mass concentration of nickel acetate is 4%, the mass concentration of nickel acetate is 0.99%, and the mass concentration of zinc acetate is 0.44%);

The above precursor solution was injected into a centrifuge tube, and immersed vertically in liquid nitrogen at -196 °C at a speed of 1 cm/s for 10 min. After removing the cap of the centrifuge tube, the centrifuge tube was placed in a vacuum freeze dryer. The three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor was obtained by drying at a temperature of -50 °C for 48 h at a temperature of 30 Pa;

The above-mentioned three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor was placed in a muffle furnace, and the calcination temperature was increased from room temperature to 500 °C at a heating rate of 1 °C/min, followed by holding for 2 h, and then naturally decreased. At room temperature, a three-dimensional porous self-supporting NiO/ZnO heterojunction material (denoted as NiO/ZnO-3) with macropores, mesopores and micropores was obtained. Among them, the macropore diameter is 2 μm, the mesopore diameter is 32 nm, and the micropore diameter is 1 nm.

Comparative Example 1

Dissolve 0.744g of nickel acetate and 4g of polyvinylpyrrolidone in 50mL of deionized water, and stir magnetically at room temperature for 12h at a rate of 600r/min to obtain a precursor solution;

The above precursor solution was injected into a centrifuge tube, and immersed vertically in liquid nitrogen at -196 °C at a speed of 1 cm/s for 10 min. After removing the cap of the centrifuge tube, the centrifuge tube was placed in a vacuum freeze dryer. The three-dimensional porous self-supporting NiO material precursor was obtained by drying at a temperature of -70 °C for 48 h at a temperature of 20 Pa;

The above-mentioned three-dimensional porous self-supporting NiO material precursor material is placed in a muffle furnace, and the calcination temperature is increased from room temperature to 550 °C at a heating rate of 2.5 °C/min, followed by holding for 2 hours, and then naturally lowered to room temperature to obtain Three-dimensional porous free-standing NiO with macropores, mesopores and micropores.

Comparative application example 1

The three-dimensional porous self-supporting NiO prepared in Comparative Example 1 was used for photocatalytic degradation of methyl orange with a 50W UV lamp as the light source. 30 mg of NiO prepared in Comparative Example 1 was added to 30 mL of 10 ppm methyl orange solution, adsorbed in the dark for 30 min to achieve adsorption-desorption equilibrium, then the mixed solution was placed under a UV lamp, and 2 mL of the solution was taken out every 15 min. UH4150 spectrophotometer detects the absorbance of the solution at 463 nm, and the results are shown in Figure 12.

Comparative Example 2

Dissolve 0.656g of zinc acetate and 4g of polyvinylpyrrolidone in 50mL of deionized water, and magnetically stir at room temperature for 12h at a rate of 600r/min to obtain a precursor solution;

The above precursor solution was injected into a centrifuge tube, and immersed vertically in liquid nitrogen at -196 °C at a speed of 1 cm/s for 10 min. After removing the cap of the centrifuge tube, the centrifuge tube was placed in a vacuum freeze dryer. The three-dimensional porous self-supporting ZnO material precursor was obtained by drying at a temperature of -70 °C for 48 h at a temperature of 20 Pa;

The above three-dimensional porous self-supporting ZnO material precursor was placed in a muffle furnace, and the calcination temperature was increased from room temperature to 550 °C at a heating rate of 2.5 °C/min, followed by holding for 2 h, and then naturally lowered to room temperature to obtain a Three-dimensional porous free-standing ZnO with macropores, mesopores and micropores.

Comparative application example 2

The three-dimensional porous self-supporting ZnO prepared in Comparative Example 2 was used for photocatalytic degradation of methyl orange with a 50W UV lamp as the light source. 30 mg of ZnO prepared in Comparative Example 2 was added to 30 mL of 10 ppm methyl orange solution, adsorbed in the dark for 30 min to achieve adsorption-desorption equilibrium, then the mixed solution was placed under an ultraviolet light source, and 2 mL of the solution was taken out every 15 min. UH4150 spectrophotometer detects the absorbance of the solution at 463 nm, and the results are shown in Figure 12.

Comparative Example 3

Dissolve 0.496g of nickel acetate, 0.219g of zinc acetate and 4g of polyvinylpyrrolidone in 50mL of deionized water, and magnetically stir at room temperature for 12h at a rate of 600r/min to obtain a precursor solution;

The above-mentioned precursor solution was injected into a centrifuge tube, the cap of the centrifuge tube was removed, and the centrifuge tube was placed in an oven, and dried at 60° C. for 48 hours to obtain a powder NiO/ZnO material precursor;

The above-mentioned powder NiO/ZnO material precursor was placed in a muffle furnace, and the calcination temperature was increased from room temperature to 550 ° C according to the heating rate of 2.5 ° C/min, followed by holding for 2 hours, and then naturally lowered to room temperature to obtain powder. Bulk NiO/ZnO material (referred to as NiO/ZnO-E).

Comparative application example 3

The powder NiO/ZnO heterojunction material prepared in Example 3 was used for photocatalytic degradation of Rhodamine B, and a 50W UV lamp was used as the light source. 30 mg of NiO/ZnO-E prepared in Comparative Example 3 was added to 30 mL of 10 ppm Rhodamine B solution, and adsorbed in the dark for 30 min to reach the adsorption-desorption equilibrium. After that, the mixed solution was placed under an ultraviolet lamp, and 2 mL of the solution was taken out every 15 minutes, and the absorbance of the solution at 553 nm was detected with a UH4150 spectrophotometer. The results are shown in Figure 14.

FIG. 1 is a process flow diagram of preparing a three-dimensional porous self-supporting NiO/ZnO heterojunction material in Example 1. As shown in Figure 1, nickel acetate, zinc acetate, polyvinylpyrrolidone and water were first mixed to obtain a precursor solution, and then the precursor solution was placed in liquid nitrogen for freezing treatment, and then placed in a freeze dryer for de-icing After treatment, it was finally calcined in a muffle furnace to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material.

2 is the SEM image of the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor and the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1, wherein the inset is the three-dimensional porous self-supporting NiO/ZnO heterojunction The SEM image of the junction material; it can be seen from Figure 2 that the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor and the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 all have a pore structure, and the pore walls Thin and smooth, and the pore structure left after ice sublimation can be observed on the side.

3 is a SEM image of the side surface of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 2, wherein the inset is an SEM image of the cross-section of the three-dimensional porous self-supporting NiO/ZnO heterojunction material. It can be seen from Figure 3 that the microstructure of NiO/ZnO-2 prepared in Example 2 is similar to that of NiO/ZnO-1 prepared in Example 1, and both have abundant pore structures.

4 is a SEM image of the side of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 3, wherein the inset is an SEM image of the cross-section of the three-dimensional porous self-supporting NiO/ZnO heterojunction material. It can be seen from Figure 4 that the microstructure of NiO/ZnO-3 prepared in Example 3 is similar to that of NiO/ZnO-1 prepared in Example 1 and NiO/ZnO-2 prepared in Example 2, and both have rich The pore structure is different, but the size of the pore is different, indicating that the preparation method provided by the present invention can control the size of the pore structure.

5 is the X-ray diffraction analysis pattern of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1, NiO prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2; X-ray electron spectra of the self-supporting NiO/ZnO heterojunction material, NiO prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2; FIG. 7 is the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1. and the X-ray electron spectrum of Zn 2p of ZnO prepared in Comparative Example 2; Figure 8 is the X-ray of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 and NiO of Ni 2p prepared in Comparative Example 1. Electron spectrogram. It can be seen from FIGS. 5 to 8 that the preparation method provided by the present invention successfully prepares a three-dimensional porous self-supporting NiO/ZnO heterojunction material.

9 is the nitrogen adsorption and desorption curve of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1; FIG. 10 is the BET pore size distribution diagram of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 . It can be seen from FIG. 9 and FIG. 10 that the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 has microporous and mesoporous structures.

11 is a pore size distribution diagram obtained by mercury intrusion testing on the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1. It can be seen from FIG. 11 that the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1 has a macroporous structure.

Figure 12 shows the photocatalytic degradation of methyl orange by the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1, NiO prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2 under ultraviolet light (λ<420 nm). Figure 13 is a linear fitting diagram of the first-order kinetics of the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 1, NiO prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2 to degrade methyl orange. It can be seen from Figure 12 and Figure 13 that the NiO/ZnO-1 prepared in Example 1 has better photocatalytic efficiency than NiO and ZnO with the same structure.

Fig. 14 is the photocatalytic degradation curve of rhodamine B under ultraviolet light (λ<420nm) by the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 2 and the powder NiO/ZnO material prepared in Comparative Example 3; 15 is a linear fitting diagram of the first-order kinetics of the degradation of Rhodamine B by the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 2 and the powder NiO/ZnO material prepared in Comparative Example 3. It can be seen from Figure 14 and Figure 15 that the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in Example 2 has a higher photocatalytic rate than the powder NiO/ZnO heterojunction prepared in Comparative Example 3, The degradation rate is about 3 times that of powder NiO/ZnO material. It can be seen that the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared by the preparation method provided by the present invention exhibits more excellent photocatalytic performance due to its unique hierarchical porous structure.

It can be seen from the above examples that the preparation method of the three-dimensional porous self-supporting NiO/ZnO heterojunction material provided by the present invention is simple to operate, does not require template removal, and does not require strict control of experimental conditions. In addition, the three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared in the present invention has excellent photocatalytic performance.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (9)

1. A preparation method of a three-dimensional porous self-supporting NiO/ZnO heterojunction material comprises the following steps:

(1) mixing a high molecular polymer, a nickel source, a zinc source and water to obtain a precursor solution; the mass concentration of the high molecular polymer in the precursor solution is 2-8%, the mass concentration of the nickel source is 0.74-0.99%, and the mass concentration of the zinc source is 0.4-0.7%;

(2) sequentially freezing and deicing the precursor solution obtained in the step (1) to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor;

(3) calcining the three-dimensional porous self-supporting NiO/ZnO heterojunction material precursor obtained in the step (2) to obtain a three-dimensional porous self-supporting NiO/ZnO heterojunction material;

the three-dimensional porous self-supporting NiO/ZnO heterojunction material has a hierarchical pore structure, and the hierarchical pore comprises macropores, mesopores and micropores.

2. The method according to claim 1, wherein the high molecular weight polymer in step (1) comprises polyvinylpyrrolidone or polyvinyl alcohol; the nickel source comprises nickel acetate or nickel nitrate; the zinc source includes zinc acetate or zinc nitrate.

3. The method according to claim 1, wherein the temperature of the freezing treatment in the step (2) is-196 ℃ or less, and the time of the freezing treatment is 10-15 min.

4. The preparation method according to claim 1, wherein the temperature of the deicing in the step (2) is-70 to-50 ℃, and the time of the deicing is 24 to 48 hours.

5. The method according to claim 1 or 4, wherein the vacuum degree of the de-icing treatment in the step (2) is 10 to 30 Pa.

6. The method according to claim 1, wherein the calcination temperature in the step (3) is 500 to 550 ℃.

7. The method according to claim 6, wherein the rate of temperature increase to the calcination temperature is 1 to 2.5 ℃/min.

8. The three-dimensional porous self-supporting NiO/ZnO heterojunction material prepared by the preparation method of any one of claims 1 to 7, wherein the three-dimensional porous self-supporting NiO/ZnO heterojunction material has a hierarchical pore structure, and the hierarchical pores comprise macropores, mesopores and micropores.

9. The three-dimensional porous self-supporting NiO/ZnO heterojunction material according to claim 8, wherein the pore diameter of the micropores is 0.5-2 nm, the pore diameter of the mesopores is 2-50 nm, and the pore diameter of the macropores is 50 nm-10 μm.

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