CN108579746B - Preparation method and application of zinc oxide/silver oxide composite photocatalyst - Google Patents

Preparation method and application of zinc oxide/silver oxide composite photocatalyst Download PDF

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CN108579746B
CN108579746B CN201810353224.9A CN201810353224A CN108579746B CN 108579746 B CN108579746 B CN 108579746B CN 201810353224 A CN201810353224 A CN 201810353224A CN 108579746 B CN108579746 B CN 108579746B
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zinc oxide
silver oxide
zinc
silver
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黄六莲
肖禾
陈礼辉
马晓娟
林珊
刘胜楠
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Fujian Agriculture and Forestry University
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Abstract

The invention discloses a preparation method and application of a zinc oxide/silver oxide composite photocatalyst, wherein a zinc-based precursor is prepared by adopting a liquid-phase coprecipitation method, porous spongy zinc oxide is prepared by high-temperature calcination, silver nitrate is used as a precursor, sodium hydroxide is added to react under the alkaline environment condition of pH =13, silver oxide nanoparticles are obtained by drying, and the obtained porous spongy zinc oxide and silver oxide nanoparticles are subjected to physical mixing processes such as magnetic stirring under the alkaline condition to obtain the composite photocatalyst with silver oxide nanoparticles loaded on the surface of zinc oxide. ZnO/Ag prepared by the invention2The O composite material has the advantages of large specific surface area, high active sites of photocatalytic reaction and the like, and can be used for photocatalytic degradation of formaldehyde liquid under visible light.

Description

Preparation method and application of zinc oxide/silver oxide composite photocatalyst
Technical Field
The invention belongs to the field of catalysts, and particularly relates to a preparation method and application of a zinc oxide/silver oxide composite photocatalyst.
Background
In recent years, formaldehyde is used as a main chemical raw material and widely applied to various industries, such as printing, pesticides, building materials and other fields, and factories producing the products can discharge a large amount of untreated industrial wastewater into sewers, lakes, rivers and the like, and formaldehyde dissolved in water flows into the industrial wastewater, so that the industrial wastewater directly causes serious harm to aquaculture, human domestic water and agricultural irrigation, the health of human beings is seriously affected, and the industrial wastewater also poses a great threat to the ecological environment. The traditional formaldehyde removal methods comprise physical adsorption, biological purification, membrane separation technology and the like, but the methods only temporarily adsorb formaldehyde, do not fundamentally remove formaldehyde and cause secondary pollution. The semiconductor photocatalysis technology is a method capable of completely removing organic pollutants, electrons on a valence band of a semiconductor are excited to jump to a conduction band under illumination, holes are left on the valence band, photogenerated electrons and holes can oxidize surrounding water and oxygen into hydroxyl radicals and superoxide radicals with higher oxidizing performance, and the radicals can directly oxidize and decompose the organic pollutants to generate carbon dioxide and water, so that the formaldehyde can be removed essentially by adopting the photocatalysis technology. Among them, zinc oxide (ZnO) is one of the most commonly used photocatalytic semiconductors, has a forbidden band width of 3.37 eV at normal temperature, has the characteristics of good thermal stability and chemical stability, abundant sources, low price, no toxicity, and the like, is one of the most widely developed and applied semiconductors, and is widely applied to the aspects of sewage treatment, air purification, sensors, solar cells, gas-sensitive detection, and the like.
However, in the process of photocatalysis of semiconductor photocatalyst, the high recombination rate of photo-generated electrons and holes is one of the main defects existing in the semiconductor photocatalysis technology, zinc oxide is no exception, besides, as the photocatalysis reaction mainly occurs on the contact surface of the catalyst and organic pollutants, the size of the ZnO photocatalysis performance has a great relationship with the shape structure of the ZnO photocatalysis performance. Researchers have prepared ZnO with various morphologies, such as a hexagonal prism rod-shaped structure, a snowflake-shaped structure and a silver needle-shaped structure, but the ZnO with the morphologies tends to have a small specific surface area, affects the photocatalytic efficiency of the ZnO and cannot provide many active reaction sites for photocatalytic reaction. In addition, the forbidden band width of zinc oxide is relatively large, and most of photocatalytic reactions can only be carried out under ultraviolet light. Therefore, how to increase the specific surface area of ZnO, increase the active reaction sites in the photocatalytic reaction, how to expand the photocatalytic reaction of zinc oxide to the visible light region, and improve the utilization of solar energy, and how to perform the photocatalytic reaction of zinc oxide and suppress the recombination rate of photogenerated electrons and holes of ZnO is one of the requirements for improving the photocatalytic activity of ZnO.
Disclosure of Invention
The invention aims to provide a preparation method of a zinc oxide/silver oxide composite photocatalyst which has high catalytic activity and is used for degrading formaldehyde under visible light aiming at the defects of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a zinc oxide/silver oxide composite photocatalyst comprises the steps of firstly preparing a zinc-based precursor by adopting a liquid-phase coprecipitation method, and preparing porous spongy zinc oxide by calcining; taking silver nitrate as a precursor, further adding sodium hydroxide to react in an environment with pH =13, and washing and drying to obtain silver oxide nanoparticles; finally, physically mixing the porous spongy zinc oxide and the silver oxide nanoparticles under an alkaline condition to obtain the zinc oxide/silver oxide composite photocatalyst with the silver oxide nanoparticles loaded on the surface of the zinc oxide; the method specifically comprises the following steps:
(1) preparation of porous spongy ZnO: weighing zinc nitrate hexahydrate, dissolving the zinc nitrate hexahydrate in deionized water, dropwise adding an aqueous solution containing hexamethylenetetramine and oxalic acid dihydrate, wherein the molar ratio of the zinc nitrate hexahydrate to the hexamethylenetetramine is 1:1-1:8, and carrying out magnetic stirring to fully dissolve the zinc nitrate hexahydrate; condensing and refluxing the mixed solution in an oil bath at 70-90 ℃ for 2-6 hours to obtain a white precipitate, washing the white precipitate with deionized water, and drying the white precipitate in a vacuum drying oven at 50 ℃ for 24 hours to obtain zinc oxide; then placing the obtained zinc oxide in a muffle furnace, calcining for 2-6 hours at the temperature of 600 ℃ in the air atmosphere to obtain a porous spongy ZnO product;
（2）Ag2preparing O nano particles: respectively weighing AgNO3And PEG-8000 are sequentially added into deionized water, magnetic stirring is carried out for 10min, NaOH solution with the concentration of 0.1mol/L is slowly dripped to enable the pH to be =13, dripping is stopped, and finally deionized water is used for washing, and constant temperature drying (the drying temperature is 60-90 ℃ and the drying time is 2 h) is carried out to obtain Ag2O nanoparticles;
（3）ZnO/Ag2preparing an O composite photocatalyst: firstly, weighing the porous spongy ZnO prepared in the step (1), putting the porous spongy ZnO into deionized water, adding PEG-8000 into the solution, and carrying out ultrasonic oscillation for 10 min; then weighing the Ag prepared in the step (2)2Adding O nanoparticles into the mixed solution, magnetically stirring for 30-60min, slowly dropping NaOH solution with concentration of 0.1mol/L to ensure that the pH is =13-14, stopping dropping, washing with deionized water, and drying at constant temperature (drying temperature is 60-90 ℃ and drying time is 2 h) to obtain ZnO/Ag loaded with silver oxide nanoparticles on the surface of zinc oxide2O composite photocatalyst.
The zinc oxide/silver oxide composite photocatalyst prepared by the preparation method is used for degrading formaldehyde under visible light, and the specific process is as follows: collecting 60-80mg ZnO/Ag2Placing the O composite photocatalyst in a quartz tube, measuring 100-150 mL of 10-20 mg/L formaldehyde solution, pouring the formaldehyde solution into the quartz tube, placing the quartz tube into a photocatalytic reaction device, magnetically stirring in the dark place, performing dark adsorption for 30min in the dark place, sampling for 4 mL, starting a visible light lamp to perform light irradiation for 120 min on the formaldehyde solution after sampling, and respectively sampling 4 mL when the illumination time reaches 15 min, 30min, 60min, 90min and 120 min, immediately placing all sampling solutions into a 5 mL centrifuge tube for shading and sealing after sampling, placing 2.5 mL reaction solution into a 25 mL graduated tube with a plug before testing, deionized water is added into the graduated tube to be diluted to the graduation line, 2.5 mL of prepared acetylacetone mixed solution is added, and the absorbance of the formaldehyde aqueous solution is measured by an ultraviolet visible absorption light detector.
The invention utilizes a simple liquid-phase coprecipitation method to form zinc-based composite salt, and gas in the composite salt escapes through high-temperature calcination to form a porous structureThe ZnO in the porous sponge structure is prepared by the zinc oxide, the structure greatly increases the contact area of the catalyst and the formaldehyde solution, and increases the reaction active sites of the photocatalytic reaction. Adding sodium hydroxide into silver nitrate solution, reacting in alkaline environment with pH =13, washing, and drying to obtain Ag2O nanoparticles; the obtained porous zinc oxide and silver oxide nanoparticles are subjected to physical mixing processes such as magnetic stirring and the like under an alkaline condition, and finally the zinc oxide composite photocatalyst with the silver oxide nanoparticles loaded on the surface is obtained, and the nano silver particles can capture photo-generated electrons and inhibit the recombination rate of the photo-generated electrons and holes, so that the photocatalysis efficiency is greatly improved. And the forbidden band width of the composite photocatalyst is relatively narrow, so that the forbidden band width of the formed composite photocatalyst is reduced, the photocatalytic reaction is expanded to a visible light region, the composite photocatalyst has great application value for degrading liquid formaldehyde under visible light, and a foundation is laid for developing a high-catalytic-activity semiconductor material capable of degrading liquid formaldehyde.
The invention has the beneficial effects that: compared with the traditional zinc oxide photocatalytic material, the porous spongy zinc oxide is prepared by a liquid-phase coprecipitation method, and then the porous zinc oxide and silver oxide nanoparticles are subjected to a simple physical mixing process under an alkaline condition to finally obtain the composite photocatalyst, so that the composite photocatalyst has the advantages of large specific surface area, high photocatalytic reaction activity, capability of performing a photocatalytic process under visible light and the like, the degradation rate of the formaldehyde liquid reaches 100% after the indoor formaldehyde liquid is subjected to visible-light catalytic degradation for 90min, no secondary pollution is caused, the formaldehyde can be completely removed essentially, and the composite photocatalyst is an environment-friendly photocatalytic material and can be used for photocatalytic degradation of liquid formaldehyde under visible light.
Detailed Description
The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples.
Example 1
(1) Preparation of porous spongy ZnO: weighing 2.7g of zinc nitrate hexahydrate, dissolving the zinc nitrate hexahydrate in 20mL of deionized water, dropwise adding 30mL of an aqueous solution containing 2.54g of hexamethylenetetramine and 0.32g of oxalic acid dihydrate (1 drop/second), and carrying out magnetic stirring to fully dissolve the zinc nitrate hexahydrate; condensing and refluxing the mixed solution in an oil bath at the temperature of 80 ℃ for 4 hours to obtain a white precipitate, washing the white precipitate with deionized water for multiple times, and drying the white precipitate in a vacuum drying oven at the temperature of 50 ℃ for 24 hours to obtain zinc oxide; then placing the obtained zinc oxide in a muffle furnace, and calcining for 4 hours at 300 ℃ in the air atmosphere to obtain a porous spongy ZnO product;
（2）Ag2preparing O nano particles: 1.7g AgNO was weighed out separately3And 0.1g PEG-8000 into 100mL deionized water, magnetically stirring for 10min, slowly adding 0.1mol/L NaOH solution dropwise to adjust pH =13, stopping adding dropwise, washing with deionized water for several times, and drying at 90 deg.C in air for 2h to obtain Ag2O nanoparticles;
（3）ZnO/Ag2preparing an O composite photocatalyst: firstly, weighing 0.4g of porous spongy ZnO prepared in the step (1), putting the porous spongy ZnO into 100mL of deionized water, adding 1g of PEG-8000 into the solution, and carrying out ultrasonic oscillation for 10 min; then 0.057g of Ag prepared in the step (2) is weighed2Adding O nano particles into the mixed solution, magnetically stirring for 30min, slowly dripping NaOH solution with the concentration of 0.1mol/L to ensure that the pH is =13, stopping dripping, washing by deionized water, and drying in a constant-temperature oven at 90 ℃ for 2h to obtain ZnO/Ag loaded with silver oxide nano particles on the surface of zinc oxide2O composite photocatalyst.
ZnO/Ag2And (3) testing the performance of the O composite photocatalyst in degrading liquid formaldehyde by visible light: 80mg of ZnO/Ag is taken2Placing an O composite photocatalyst in a quartz tube, measuring 150 mL of 10 mg/L formaldehyde solution, pouring the formaldehyde solution into the quartz tube, placing the quartz tube into a photocatalytic reaction device, carrying out magnetic stirring in the dark, carrying out dark adsorption for 30min in the dark, then sampling for 4 mL, starting a visible light lamp after sampling to carry out light irradiation for 120 min on the formaldehyde solution, respectively sampling for 4 mL when the light irradiation time reaches 15 min, 30min, 60min, 90min and 120 min, immediately placing all the sampling solutions into a 5 mL centrifuge tube after sampling, carrying out light shielding sealing, configuring a series of formaldehyde solutions with different concentrations before sample measurement, measuring the absorbance of the formaldehyde solutions by an acetylacetone method, and drawing a standard according to the concentration and the measured absorbance dataAnd (3) calibrating a curve, putting 2.5 mL of reaction liquid into a 25 mL graduated tube with a plug after testing, adding deionized water into the graduated tube to dilute the solution to a scale mark, adding 2.5 mL of prepared acetylacetone mixed solution, measuring the absorbance of the formaldehyde aqueous solution by using an ultraviolet visible absorption light detector, substituting the absorbance of different time periods into a standard curve to calculate the concentration of formaldehyde, calculating the formaldehyde degradation rate at different moments, wherein the degradation rate can reach 100% after 90 min.
Example 2
(1) Preparation of porous spongy ZnO: weighing 2.7g of zinc nitrate hexahydrate, dissolving the zinc nitrate hexahydrate in 20mL of deionized water, dropwise adding 30mL of an aqueous solution containing 5.09g of hexamethylenetetramine and 0.3g of oxalic acid dihydrate (1 drop/second), and carrying out magnetic stirring to fully dissolve the zinc nitrate hexahydrate; condensing and refluxing the mixed solution in an oil bath at 90 ℃ for 4 hours to obtain a white precipitate, washing the white precipitate with deionized water for multiple times, and drying the white precipitate in a vacuum drying oven at 50 ℃ for 24 hours to obtain zinc oxide; then placing the obtained zinc oxide in a muffle furnace, and calcining for 4 hours at 400 ℃ in the air atmosphere to obtain a porous spongy ZnO product;
（2）Ag2preparing O nano particles: 1.7g AgNO was weighed out separately3And 0.1g of PEG-8000 are sequentially added into 100mL of deionized water, the mixture is magnetically stirred for 10min, NaOH solution with the concentration of 0.1mol/L is slowly dripped to enable the pH to be =13, the dripping is stopped, finally, the mixture is washed by the deionized water and dried for 2h at the constant temperature of 90 ℃ in the air to obtain Ag2O nanoparticles;
（3）ZnO/Ag2preparing an O composite photocatalyst: firstly, weighing 0.4g of porous spongy ZnO prepared in the step (1), putting the porous spongy ZnO into 100mL of deionized water, adding 1g of PEG-8000 into the solution, and carrying out ultrasonic oscillation for 10 min; then 0.113g of Ag prepared in the step (2) is weighed2Adding O nano particles into the mixed solution, magnetically stirring for 30min, slowly dripping NaOH solution with the concentration of 0.1mol/L to ensure that the pH is =14, stopping dripping, washing by deionized water, and drying in a 90 ℃ oven at constant temperature for 2h to obtain ZnO/Ag loaded with silver oxide nano particles on the surface of zinc oxide2O composite photocatalyst.
ZnO/Ag2O composite photocatalyst photodegradable liquid APerformance testing of aldehydes: 80mg of ZnO/Ag is taken2Placing the O composite photocatalyst in a quartz tube, measuring 150 mL of formaldehyde solution with the concentration of 10 mg/L, pouring the formaldehyde solution into the quartz tube, placing the quartz tube into a photocatalytic reaction device, carrying out magnetic stirring in the dark, carrying out dark adsorption for 30min in the dark, then sampling 4 mL, starting a visible light lamp after sampling, carrying out light irradiation on the formaldehyde solution for 120 min, respectively sampling 4 mL when the light irradiation time reaches 15 min, 30min, 60min, 90min and 120 min, immediately placing all the sampled solutions into a 5 mL centrifuge tube after sampling, carrying out light shielding and sealing, placing 2.5 mL of reaction solution into a 25 mL graduated tube with a plug before testing, adding deionized water into the graduated tube to dilute to a scale mark, adding 2.5 mL of prepared acetylacetone mixed solution, measuring the absorbance of the formaldehyde solution by using an ultraviolet visible absorption light detector, substituting the absorbance of the formaldehyde solution into a standard curve for calculating the concentration of formaldehyde in different time periods, and (3) calculating the formaldehyde degradation rate at different moments, wherein the degradation rate can reach 100% after 90 min.
Example 3
(1) Preparation of porous spongy ZnO: weighing 2.7g of zinc nitrate hexahydrate, dissolving the zinc nitrate hexahydrate in 20mL of deionized water, dropwise adding 30mL of an aqueous solution containing 5.09g of hexamethylenetetramine and 0.572g of oxalic acid dihydrate (1 drop/second), and carrying out magnetic stirring to fully dissolve the zinc nitrate hexahydrate; condensing and refluxing the mixed solution in an oil bath at 90 ℃ for 4 hours to obtain a white precipitate, washing the white precipitate with deionized water for multiple times, and drying the white precipitate in a vacuum drying oven at 50 ℃ for 24 hours to obtain zinc oxide; then placing the obtained zinc oxide in a muffle furnace, and calcining for 4 hours at 400 ℃ in the air atmosphere to obtain a porous spongy ZnO product;
（2）Ag2preparing O nano particles: 1.7g AgNO was weighed out separately3And 0.1g of PEG-8000 are sequentially added into 100mL of deionized water, the mixture is magnetically stirred for 10min, NaOH solution with the concentration of 0.1mol/L is slowly dripped to enable the pH to be =13, the dripping is stopped, finally, the mixture is washed by the deionized water and dried for 2h at the constant temperature of 90 ℃ in the air to obtain Ag2O nanoparticles;
（3）ZnO/Ag2preparing an O composite photocatalyst: firstly, 0.4g of porous spongy ZnO prepared in the step (1) is weighed and put into 100mL of deionized water, and thenAdding 1g of PEG-8000 into the solution, and performing ultrasonic oscillation for 10 min; then 0.5683g of Ag prepared in the step (2) are weighed2Adding O nano particles into the mixed solution, magnetically stirring for 30min, slowly dripping NaOH solution with the concentration of 0.1mol/L to ensure that the pH is =13, stopping dripping, washing by deionized water, and drying in a 90 ℃ oven at constant temperature for 2h to obtain ZnO/Ag loaded with silver oxide nano particles on the surface of zinc oxide2O composite photocatalyst.
ZnO/Ag2Testing the performance of the O composite photocatalyst for degrading liquid formaldehyde by using visible light: 80mg of ZnO/Ag is taken2Placing the O composite photocatalyst in a quartz tube, measuring 150 mL of formaldehyde solution with the concentration of 10 mg/L, pouring the formaldehyde solution into the quartz tube, placing the quartz tube into a photocatalytic reaction device, carrying out magnetic stirring in the dark, carrying out dark adsorption for 30min in the dark, then sampling 4 mL, starting a visible light lamp after sampling, carrying out light irradiation on the formaldehyde solution for 120 min, respectively sampling 4 mL when the light irradiation time reaches 15 min, 30min, 60min, 90min and 120 min, immediately placing all the sampled solutions into a 5 mL centrifuge tube after sampling, carrying out light shielding and sealing, placing 2.5 mL of reaction solution into a 25 mL graduated tube with a plug before testing, adding deionized water into the graduated tube to dilute to a scale mark, adding 2.5 mL of prepared acetylacetone mixed solution, measuring the absorbance of the formaldehyde solution by using an ultraviolet visible absorption light detector, substituting the absorbance of the formaldehyde solution into a standard curve for calculating the concentration of formaldehyde in different time periods, and (3) calculating the formaldehyde degradation rate at different moments, wherein the degradation rate can reach 100% after 90 min.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims (3)

1. A preparation method of a zinc oxide/silver oxide composite photocatalyst is characterized by comprising the following steps: firstly, preparing a zinc-based precursor by adopting a liquid-phase coprecipitation method, and preparing porous spongy zinc oxide by calcining; taking silver nitrate as a precursor, further adding sodium hydroxide to react in an environment with pH =13, and washing and drying to obtain silver oxide nanoparticles; finally, physically mixing the porous spongy zinc oxide and the silver oxide nanoparticles under an alkaline condition to obtain the zinc oxide/silver oxide composite photocatalyst with the silver oxide nanoparticles loaded on the surface of the zinc oxide;
the preparation method of the zinc oxide/silver oxide composite photocatalyst specifically comprises the following steps:
(1) preparation of porous sponge zinc oxide: weighing zinc nitrate hexahydrate, dissolving the zinc nitrate hexahydrate in deionized water, dropwise adding an aqueous solution containing hexamethylenetetramine and oxalic acid dihydrate, and carrying out magnetic stirring to fully dissolve the zinc nitrate hexahydrate; condensing and refluxing the mixed solution in an oil bath at 70-90 ℃ for 2-6 hours to obtain a white precipitate, washing the white precipitate with deionized water, and drying the white precipitate in a vacuum drying oven to obtain zinc oxide; then placing the obtained zinc oxide in a muffle furnace, and calcining for 2-6 hours at the temperature of 600 ℃ in the air atmosphere to obtain porous spongy zinc oxide;
(2) preparing silver oxide nanoparticles: respectively weighing AgNO3And PEG-8000 are sequentially added into deionized water, magnetic stirring is carried out for 10min, NaOH solution with the concentration of 0.1mol/L is slowly dripped to enable the pH to be =13, dripping is stopped, and finally, deionized water is used for washing, and constant temperature drying is carried out to obtain silver oxide nanoparticles;
(3) preparing a zinc oxide/silver oxide composite photocatalyst: firstly, weighing the porous spongy zinc oxide prepared in the step (1), putting the porous spongy zinc oxide into deionized water, adding PEG-8000 into the solution, and carrying out ultrasonic oscillation for 10 min; weighing the silver oxide nanoparticles prepared in the step (2), putting the silver oxide nanoparticles into the mixed solution, magnetically stirring for 30-60min, slowly dropping NaOH solution with the concentration of 0.1mol/L to ensure that the pH value is =13-14, stopping dropping, washing with deionized water, and drying at constant temperature to obtain the zinc oxide/silver oxide composite photocatalyst with the silver oxide nanoparticles loaded on the surface of zinc oxide;
in the step (1), the molar ratio of the zinc nitrate hexahydrate to the hexamethylenetetramine is 1:1-1: 8;
in the step (1), the temperature of vacuum drying is 50 ℃, and the drying time is 24 h.
2. The preparation method of the zinc oxide/silver oxide composite photocatalyst according to claim 1, characterized in that: in the step (2) and the step (3), the constant-temperature drying process parameters are as follows: the drying temperature is 60-90 ℃, and the drying time is 2 h.
3. The zinc oxide/silver oxide composite photocatalyst prepared by the preparation method of any one of claims 1-2.
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