CN110813306A - Zinc ferrite/bismuth tungstate composite catalyst, preparation method thereof and application thereof in waste gas treatment - Google Patents

Abstract

_The invention discloses a zinc ferrite/bismuth _tungstate composite catalyst, a preparation method thereof and an application in waste gas treatment _; NO ₃ ) ₃ ·9H ₂ O) polyvinylpyrrolidone (PVP, K90) was used as raw material, and N,N-dimethylformamide (DMF) was used as solvent to prepare zinc ferrite ( ZnFe ₂ O ₄ ) nanofibers; using bismuth nitrate pentahydrate (Bi(NO ₃ ) ₃ ·5H ₂ O) and sodium tungstate dihydrate (Na ₂ WO ₆ ·2H ₂ O) as bismuth and tungsten sources, Dissolved in a mixed solvent of Ethanol and Ethylene glycol, and then added ZnFe ₂ O ₄ nanofibers into the above mixed solution to prepare Bi ₂ WO ₆ nanosheets grown on ZnFe ₂ O by heating reaction ₄ nanofibers were obtained to obtain a ZnFe ₂ O ₄ /Bi ₂ WO ₆ nanocomposite material, which was a zinc ferrite/bismuth tungstate composite catalyst. The ZnFe ₂ O ₄ /Bi ₂ WO ₆ nano-composite photocatalyst of the invention promotes the separation efficiency of photo-generated carriers in both Bi ₂ WO ₆ and ZnFe ₂ O ₄ , effectively increases the survival life of the photo-generated charges, and promotes the photocatalysis thereof. active.

Description

Zinc ferrite/bismuth tungstate composite catalyst and its preparation method and its application in waste gas treatment Applications

technical field

The invention belongs to the technical field of inorganic functional materials, in particular to a preparation method of a zinc ferrite/bismuth tungstate (ZnFe ₂ O ₄ /Bi ₂ WO ₆ ) composite catalyst and its application in waste gas treatment.

Background technique

With the rapid development of social economy and industrialization, the pollution of waste gas emitted by industry is becoming more and more serious, which brings great harm to human beings, animals and plants. In addition, the exhaust gas also causes environmental pollution such as acid rain, acid fog, and photochemical smog. Therefore, finding a cheap, efficient and energy-saving method to degrade waste gas has become a hot issue in environmental research. At present, semiconductor photocatalysis technology has the advantages of non-toxicity, high degradation efficiency, and strong redox ability, and is considered to be one of the most economical and effective methods to deal with exhaust gas pollution. Among the current photocatalysts, Bi ₂ WO ₆ is a widely studied oxide semiconductor photocatalyst. However, Bi ₂ WO ₆ also has its own shortcomings such as the easy and rapid recombination of photogenerated electrons and holes generated after illumination. Therefore, it is necessary to develop new methods to modify Bi ₂ WO ₆ in different ways to further improve the photocatalytic activity.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a nanocomposite ZnFe ₂ O ₄ /Bi ₂ WO ₆ capable of responding to visible light, a preparation method thereof, and visible light catalytic degradation of exhaust gas. The Bi ₂ WO ₆ nanosheet photocatalyst was modified on the ZnFe ₂ O ₄ nanofibers by solvothermal method to obtain ZnFe ₂ O ₄ /Bi ₂ WO ₆ nanocomposite material, and the exhaust gas was photocatalytically degraded, In order to achieve effective treatment of waste gas.

In order to achieve the above object, the concrete technical scheme of the present invention is as follows:

The preparation method of zinc ferrite/bismuth tungstate composite catalyst includes the following steps: adding ZnFe ₂ O ₄ nanofibers to a solution containing bismuth salt and tungsten salt, heating and reacting to obtain zinc ferrite/bismuth tungstate composite catalyst.

The invention also discloses a method for photocatalytic treatment of waste gas, comprising the following steps: adding ZnFe ₂ O ₄ nanofibers into a solution containing bismuth salt and tungsten salt, heating and reacting to obtain a zinc ferrite/bismuth tungstate composite catalyst; Then, the gas containing the exhaust gas is passed through the zinc ferrite/bismuth tungstate composite catalyst and illuminated to realize the photocatalytic treatment of the exhaust gas.

In the present invention, a solution containing zinc salt and iron salt is used as a spinning solution, and ZnFe ₂ O ₄ nanofibers are prepared by spinning and calcining. Preferably, the spinning solution is composed of zinc salt, iron salt, binder and solvent; preferably, the spinning is electrospinning.

In the above technical scheme, the dosage ratio of zinc salt, iron salt and adhesive is (0.5-5) mmol: (1-5) mmol: (1-10) g; the voltage of electrospinning is 10-20 kV, The injection rate is 0.15-0.25 mm/min; the calcination temperature is 500-800°C, and the time is 1-3h.

In the above technical scheme, the mass ratio of the bismuth salt and the tungsten salt is (100-500): (10-100); the temperature of the heating reaction is 30-200°C, and the time is 12-48 h.

In the above technical solution, the mass ratio of bismuth salt, tungsten salt and ZnFe ₂ O ₄ nanofiber is 6:2:(0.6-1.5).

In the present invention, the zinc salt is zinc nitrate hexahydrate, the iron salt is iron nitrate nonahydrate, the binder is polyvinylpyrrolidone, the solvent is N,N-dimethylformamide; the bismuth salt is bismuth nitrate pentahydrate, and the tungsten salt It is sodium tungstate dihydrate; in the solution containing bismuth salt and tungsten salt, the solvent is a mixed solvent of absolute ethanol (Ethanol) and ethylene glycol (Ethylene glycol).

The preparation method of the zinc ferrite/bismuth tungstate composite catalyst of the present invention is as follows:

(1) Using zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ ·6H ₂ O), ferric nitrate nonahydrate (Fe(NO ₃ ) ₃ ·9H ₂ O) polyvinylpyrrolidone (PVP, K90) as raw materials, and using Zinc ferrite (ZnFe ₂ O ₄ ) nanofibers were prepared by electrospinning and high temperature calcination with N,N-dimethylformamide (DMF) as solvent;

(2) Using bismuth nitrate pentahydrate (Bi(NO ₃ ) ₃ .5H ₂ O) and sodium tungstate dihydrate (Na ₂ WO ₆ .2H ₂ O) as bismuth and tungsten sources, they were dissolved in absolute ethanol. In the mixed solvent of Ethanol and Ethylene glycol, ZnFe ₂ O ₄ nanofibers were added to the above mixed solution, and Bi ₂ WO ₆ nanosheets were prepared by heating reaction and grown on the ZnFe ₂ O ₄ nanofibers to obtain The ZnFe ₂ O ₄ /Bi ₂ WO ₆ nanocomposite material is a zinc ferrite/bismuth tungstate composite catalyst.

The method for photocatalytic treatment of exhaust gas disclosed in the present invention is specifically as follows:

(1) Using zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ ·6H ₂ O), ferric nitrate nonahydrate (Fe(NO ₃ ) ₃ ·9H ₂ O) polyvinylpyrrolidone (PVP, K90) as raw materials, and using Zinc ferrite (ZnFe ₂ O ₄ ) nanofibers were prepared by electrospinning and high temperature calcination with N,N-dimethylformamide (DMF) as solvent;

(2) Using bismuth nitrate pentahydrate (Bi(NO ₃ ) ₃ .5H ₂ O) and sodium tungstate dihydrate (Na ₂ WO ₆ .2H ₂ O) as bismuth and tungsten sources, they were dissolved in absolute ethanol. In the mixed solvent of Ethanol and Ethylene glycol, ZnFe ₂ O ₄ nanofibers were added to the above mixed solution, and Bi ₂ WO ₆ nanosheets were prepared by heating reaction and grown on the ZnFe ₂ O ₄ nanofibers to obtain The ZnFe ₂ O ₄ /Bi ₂ WO ₆ nanocomposite material is a zinc ferrite/bismuth tungstate composite catalyst;

(3) The gas containing the exhaust gas is flowed through the zinc ferrite/bismuth tungstate composite catalyst and illuminated to realize the photocatalytic treatment of the exhaust gas.

The invention also discloses the application of the above zinc ferrite/bismuth tungstate composite catalyst in waste gas treatment.

In the present invention, the exhaust gas is nitrogen monoxide, and the illumination is visible light illumination.

The preparation method of the visible light-responsive nanocomposite material ZnFe ₂ O ₄ /Bi ₂ WO ₆ in the present invention can be carried out as follows:

_1. Preparation of _ZnFe2O4 nanofibers

First, Zn(NO ₃ ) ₂ .6H ₂ O and Fe(NO ₃ ) ₃ .9H ₂ O were dissolved in a DMF solution. After stirring for several hours at room temperature, PVP was added to the solution, and the mixture was continuously magnetically stirred for several hours to obtain a brown-red homogeneous precursor solution. Then, the precursor solution was transferred into a plastic syringe fitted with a steel needle for electrospinning. Finally, the obtained nanofibers _were calcined in air to obtain _ZnFe2O4 nanofibers.

2. Preparation of ZnFe ₂ O ₄ /Bi ₂ WO ₆ composites

First, bismuth nitrate pentahydrate and sodium tungstate dihydrate were ultrasonically dissolved in ethylene glycol. Then, ethanol was slowly added to the mixed solvent. Then, the prepared ZnFe ₂ O ₄ nanofibers were added and mixed uniformly under stirring conditions. Finally, the obtained solution was transferred to a reaction kettle for heating reaction, and the solid product was washed by centrifugation to obtain a ZnFe ₂ O ₄ /Bi ₂ WO ₆ composite material.

3. Photocatalytic degradation of waste gas

The operation of photocatalytic degradation of heavy metal wastewater is as follows. The degradation effects of ZnFe ₂ O ₄ , Bi ₂ WO ₆ and a series of ZnFe ₂ O ₄ /Bi ₂ WO ₆ (100 mg) on waste gas were investigated at the same concentration.

Advantages of this program:

1. The present invention adopts an easy-to-operate electrospinning and solvothermal method to prepare a ZnFe ₂ O ₄ /Bi ₂ WO ₆ composite photocatalyst. The preparation process is simple and the cost of raw materials is low, which is conducive to reducing the preparation cost and is easy to realize large-scale production. mass production.

2. The ZnFe ₂ O ₄ /Bi ₂ WO ₆ nanocomposite photocatalyst of the present invention promotes the separation efficiency of photo-generated carriers in both Bi ₂ WO ₆ and ZnFe ₂ O ₄ , effectively increases the survival life of photo-generated charges, and promotes their photocatalytic activity.

3. The ZnFe ₂ O ₄ /Bi ₂ WO ₆ nanocomposite material obtained by the present invention can improve the absorption and utilization of visible light, and can effectively carry out photocatalytic degradation of exhaust gas.

Description of drawings

Figure 1 is a scanning electron microscope (SEM) image of ZnFe ₂ O ₄ nanofibers;

Figure 2 is a transmission electron microscope (TEM) image of ZnFe ₂ O ₄ nanofibers;

Fig. 3 is the scanning electron microscope (SEM) image of ZnFe ₂ O ₄ /Bi ₂ WO ₆ composite;

Fig. 4 is the scanning electron microscope (SEM) image of flower-like Bi ₂ WO ₆ material;

Fig. 5 is the catalytic effect diagram of ZnFe ₂ O ₄ , Bi ₂ WO ₆ and ZnFe ₂ O ₄ /Bi ₂ WO ₆ composite;

Figure 6 is the cyclic degradation diagram of the ZnFe ₂ O ₄ /Bi ₂ WO ₆ composite.

Detailed ways

The preparation method of the zinc ferrite/bismuth tungstate composite catalyst of the present invention is as follows: adding ZnFe ₂ O ₄ nanofibers to a solution containing bismuth salt and tungsten salt, heating and reacting to obtain a zinc ferrite/bismuth tungstate composite catalyst.

The present invention will be further described below in conjunction with the examples.

Example 1

Preparation of ZnFe ₂ O ₄ nanofibers: First, 1 mmol of Zn(NO ₃ ) ₂ ·6H ₂ O and 2 mmol of Fe(NO ₃ ) ₃ ·9H ₂ O were dissolved in 10 mL of DMF solution at room temperature After stirring for 1 hour, 2 g of PVP was added, and the magnetic stirring was continued for 12 hours to obtain a brown-red homogeneous precursor solution, which was the spinning solution; then, the spinning solution was transferred to 5 mL of a steel needle with a diameter of 0.5 mm. Electrospinning was performed in a plastic syringe (voltage: 15 kV, injection rate: 0.2 mm min ^-1 ) to obtain nanofibers; finally, the obtained nanofibers were calcined in air at 600 °C for 2 h with a heating rate of 1 °C min ^-1 (room temperature to 600 °C), ZnFe ₂ O ₄ nanofibers were obtained.

In order to observe the morphology of the material, SEM and TEM were used to characterize the products prepared in this example. Figure 1 is the SEM images of the ZnFe ₂ O ₄ nanofibers prepared in this example, (a) and (b) represent The ZnFe ₂ O ₄ nanofibers prepared in this example. FIG. 2 is a transmission electron microscope image of the ZnFe ₂ O ₄ nanofibers prepared in this example, and (a) and (b) represent the ZnFe ₂ O ₄ nanofibers prepared in this example.

Embodiment 2

Preparation of ZnFe ₂ O ₄ /Bi ₂ WO ₆ composites: First, 240 mg of Bi(NO ₃ ) ₃ · 5H ₂ O and 80 mg of Na ₂ MoO ₄ · 2H ₂ O were ultrasonically dissolved in 5 mL of ethylene glycol Then, slowly add 30 mL of ethanol into the above mixed solvent; then add the prepared ZnFe ₂ O ₄ nanofibers (Example 1) under stirring conditions, transfer to the reaction kettle and heat to 160 ℃ after mixing The reaction was carried out for 24 h; then naturally cooled to room temperature, the obtained solid product was repeatedly washed with deionized water and ethanol for 3 times, and then dried in a 60 °C oven to obtain ZnFe ₂ O ₄ /Bi ₂ WO ₆ (simply marked as ZnFe 2 O 4 /Bi 2 WO 6 ) ZFO/BWO) composite material, which is a zinc ferrite/bismuth tungstate composite catalyst. Depending on the quality of the ZnFe ₂ O ₄ added, ZnFe ₂ O ₄ /Bi ₂ WO ₆ composites with different ZnFe ₂ O ₄ contents can be obtained, including 15% ZFO/BWO, 20% ZFO/BWO, 30% ZFO/BWO , where 20% ZFO/BWO represents ZnFe ₂ O ₄ nanofibers with an added amount of 40 mg and a pure flower-like Bi ₂ WO ₆ material yield of 160 mg, ZnFe ₂ O ₄ in ZnFe ₂ O ₄ /Bi ₂ WO ₆ composite The mass fraction in the material is 20%.

In order to observe the morphology of the composite materials, the products prepared in this example were characterized by scanning electron microscopy. Figure 3 is a scanning electron microscopy image of the visible light-responsive ZnFe ₂ O ₄ /Bi ₂ WO ₆ composite catalyst prepared in this example, (a ) and (b) represent the ZnFe ₂ O ₄ /Bi ₂ WO ₆ composite catalyst prepared in this example.

Embodiment 3

Preparation of flower-like Bi ₂ WO ₆ material: First, 240 mg of Bi(NO ₃ ) ₃ ·5H ₂ O and 80 mg of Na ₂ MoO ₄ ·2H ₂ O were sonicated in 5 mL of ethylene glycol. Then, 30 mL of ethanol was slowly added to the above mixed solvent. Finally, the obtained solution was transferred to the reaction kettle and heated to 160 °C for 24 h. When the belt system was naturally cooled to room temperature, the obtained solid product was repeatedly washed with deionized water and ethanol for 3 times, and dried in an oven at 60 °C to obtain flower-shaped Bi ₂ WO ₆ material with a yield of 160 mg.

In order to observe the morphology of the material, SEM was used to characterize the product prepared in this example. Figure 4 is the SEM image of the flower-shaped Bi ₂ WO ₆ catalyst prepared in this example, (a) represents the prepared catalyst in this example. Flower-like Bi ₂ WO ₆ catalyst.

Based on the above, it can be seen from Fig. 1(ab) and Fig. 2(ab) that the prepared ZnFe ₂ O ₄ nanofibers have a one-dimensional fiber morphology, with a diameter of 100-200 nm and a length of several micrometers; from the accompanying drawings 3(a) and (b) found that Bi ₂ WO ₆ nanosheets were uniformly supported on ZnFe ₂ O ₄ nanofibers; Fig. 4(a) showed that the curd-shaped Bi ₂ WO ₆ was composed of a large amount of Bi ₂ WO ₆ composed of nanosheets.

Embodiment 4

The specific steps for photocatalytic treatment of exhaust gas are as follows: 100 mg of the catalyst to be tested is spread on a wooden board in a closed cylindrical detection chamber with a volume of 2.26 L, and a 300 W xenon lamp is placed vertically above it. The gas flow was controlled to a concentration of 600 ppb by mixing air and nitric oxide in a compressed bottle and passed through the reaction chamber at a flow rate of 1.2 L/min. When the catalyst reached adsorption-desorption equilibrium (about 0.5 h), the xenon lamp was turned on, and the photocatalytic measurements were started on the _NOx analyzer. The measurement time was 30 min, and the sampling interval was 1 min, and a total of 30 sets of data were obtained.

Fig. 5 is the effect diagram of ZnFe ₂ O ₄ , Bi ₂ WO ₆ and ZnFe ₂ O ₄ /Bi ₂ WO ₆ for the treatment of exhaust gas, through the effect Fig. 5 it is found that the catalytic efficiency of ZnFe ₂ O ₄ /Bi ₂ WO ₆ to exhaust gas is obviously better in ZnFe ₂ O ₄ (25%) and Bi ₂ WO ₆ (29%). And by adjusting the content of ZnFe ₂ O ₄ added, the degradation effect of up to 53% can be achieved. It shows that ZnFe ₂ O ₄ /Bi ₂ WO ₆ complex has high catalytic degradation activity for nitric oxide.

Figure 6 is the cycle effect diagram of ZnFe ₂ O ₄ /Bi ₂ WO ₆ (20% ZFO/BWO) on waste gas degradation. It can be seen from the figure that after 5 cycles, the degradation effect is only reduced by 6%, and the good degradation effect. Therefore, the catalyst can be reused and has good stability.

The composite catalyst of the prior art is used for parallel test comparison: CN108273515A Embodiment 1 discloses a zinc ferrite doped bismuth tungstate photocatalyst, using the same photocatalytic treatment exhaust gas test method as above, basically reaches the degradation balance after 45 minutes, 60 The final degradation efficiency in minutes was 33%; indicating that the morphology of the composite has a great influence on the performance.

Through the above analysis, the present invention successfully prepared ZnFe ₂ O ₄ /Bi ₂ WO ₆ nanocomposite material by simple and easy-to-operate electrospinning and solvothermal method. Moreover, the composite material disclosed in the present invention has strong visible light catalytic degradation for exhaust gas. In addition, the present invention has the advantages of simple production process, economical and environmental protection, and low production cost, so it will have a good application prospect in waste gas treatment.

Claims (10)

1. The zinc ferrite/bismuth tungstate composite catalyst is characterized in that the preparation method of the zinc ferrite/bismuth tungstate composite catalyst comprises the following steps of mixing ZnFe₂O₄Adding the nano-fiber into a solution containing bismuth salt and tungsten salt, and heating for reaction to obtain the zinc ferrite/bismuth tungstate composite catalyst.

2. The zinc ferrite/bismuth tungstate composite catalyst as claimed in claim 1, wherein the ZnFe is prepared by spinning and calcining a solution containing zinc salt and iron salt as a spinning solution₂O₄And (3) nano fibers.

3. The zinc ferrite/bismuth tungstate composite catalyst as claimed in claim 2, wherein the spinning solution is composed of zinc salt, iron salt, binder and solvent; the spinning is electrostatic spinning; the calcining temperature is 500-800 ℃, and the time is 1-3 h.

4. The zinc ferrite/bismuth tungstate composite catalyst as claimed in claim 2, wherein the ratio of the zinc salt to the iron salt to the binder is (0.5-5) mmol to (1-10) g; the voltage of electrostatic spinning is 10-20 kV, and the injection speed is 0.15-0.25 mm/min; the zinc salt is zinc nitrate hexahydrate, the ferric salt is ferric nitrate nonahydrate, and the adhesive is polyvinylpyrrolidone.

5. The zinc ferrite/bismuth tungstate composite catalyst as claimed in claim 1, wherein the mass ratio of the bismuth salt to the tungsten salt is (100-500) to (10-100); the heating reaction temperature is 30-200 ℃, and the time is 12-48 h.

6. The zinc ferrite/bismuth tungstate composite catalyst as claimed in claim 1, wherein the bismuth salt, the tungsten salt, and the ZnFe salt are used as the catalyst₂O₄The mass ratio of the nano fibers is 6: 2: 0.6-1.5.

7. The zinc ferrite/bismuth tungstate composite catalyst as claimed in claim 1, wherein the bismuth salt is bismuth nitrate pentahydrate, and the tungsten salt is sodium tungstate dihydrate; in the solution containing bismuth salt and tungsten salt, the solvent is a mixed solvent of absolute ethyl alcohol and glycol.

8. The use of the zinc ferrite/bismuth tungstate composite catalyst as set forth in claim 1 for the treatment of exhaust gas.

9. Use according to claim 8, wherein the exhaust gas is a nitride.

10. The preparation method of the zinc ferrite/bismuth tungstate composite catalyst is characterized by comprising the following steps of mixing ZnFe₂O₄The nano-fiber is added with a solution containing bismuth salt and tungsten saltIn the solution, heating and reacting to obtain the zinc ferrite/bismuth tungstate composite catalyst.

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