阅读说明：本技术 一种CuO QDs/CoAl-LDHs复合材料光催化剂的制备方法及用途 (Preparation method and application of CuO QDs/CoAl-LDHs composite material photocatalyst ) 是由 尹晓红 蒋玥 穆曼曼 于 2021-01-12 设计创作，主要内容包括：本发明提供了一种合成CuO QDs/CoAl-LDHs异质结的制备方法和应用,得到了x％CuO/CoAl-u的零维/二维(0D/2D)Z型异质结构复合材料,用于在紫外光下光催化还原二氧化碳研究。具体技术方案：通过相转移法得到CuO量子点(QDs)悬浮液,一步共沉淀法制备超薄的CoAl-LDHs(CoAl-u)；利用静电吸附作用将CuO QDs与CoAl-u结合构成具有Z型异质结构的复合催化剂x％CuO/CoAl-u,这种异质结构的形成,加快了电子传输速率,有效促进了电子空穴的分离,提高了光催化性能。本发明制备过程简单,催化剂稳定性高,利用氧化铜量子点取代贵金属光敏剂形成复合材料,将CO-2光催化还原为利用价值更高的有机燃料CH-3OH,为环境问题和能源短缺提供了解决方案,具有显著的经济效益和应用前景。(The invention provides a preparation method and application of a synthesized CuO QDs/CoAl-LDHs heterojunction, and obtains a zero-dimensional/two-dimensional (0D/2D) Z-type heterostructure composite material of x% CuO/CoAl-u, which is used for research on photocatalytic reduction of carbon dioxide under ultraviolet light. The specific technical scheme is as follows: obtaining CuO Quantum Dot (QDs) suspension by a phase transfer method, and preparing the super-quantum dot by a one-step coprecipitation methodThin CoAl-LDHs (CoAl-u); the CuO QDs and the CoAl-u are combined to form the composite catalyst x% CuO/CoAl-u with a Z-shaped heterostructure by utilizing the electrostatic adsorption effect, and the heterostructure is formed, so that the electron transmission rate is accelerated, the separation of electron holes is effectively promoted, and the photocatalytic performance is improved. The preparation method has simple preparation process and high catalyst stability, and the copper oxide quantum dots are used for replacing noble metal photosensitizer to form the composite material, so that CO is introduced 2 Photocatalytic reduction to organic fuel CH with higher utilization value 3 OH provides a solution for environmental problems and energy shortage, and has obvious economic benefit and application prospect.)

1. Photocatalytic reduction of CO₂The synthesis method of the CuO QDs/CoAl-LDHs composite material with the performance has the advantages that the Z-type heterojunction structure of the composite material is favorable for promoting the separation of photoproduction electrons and holes, the transmission rate of the photoproduction electrons is accelerated, and the photocatalytic reduction of CO is greatly improved₂And (4) performance.

2. The method for preparing CuO QDs/CoAl-LDHs composite material according to claim 1, comprising the steps of:

(1) synthesis of ultra-thin cobalt-aluminum hydrotalcite-like compound (CoAl-u) by one-step coprecipitation method

70mM Co (NO)₃)₂·6H₂O and 35mM Al (NO)₃)₃·9H₂Dissolving O in 25mL of deionized water, and naming the solution A; a0.25 mM NaOH aqueous solution was prepared and designated as solution B. Subsequently, the solutions A and B were simultaneously added dropwise at 85 ℃ to a four-necked flask containing 25mL of ultrapure water, and the pH was kept constant at 10 with vigorous stirring. Then, the precipitate was collected by centrifugation, washed twice with water, three times more with ethanol, and finally dispersed in 8mL of anhydrous ethanol for use, which was named as CoAl-u.

(2) Preparation of copper oxide quantum dot (CuO QDs) suspension by phase transfer method

Taking a certain amount of prepared 1M Cu (NO)₃)₂·3H₂The O solution was rapidly mixed with 50mL of an ethanol solution containing 1mL of dodecylamine (DDA). After vigorously stirring for 2min, adding 50mL of n-hexane solution into the mixed solution, and continuously and vigorously stirring for 1min to obtain blue flocculent Cu²⁺the-DDA complex is fully transferred from the water phase to the normal hexane phase, the mixed solution is divided into an upper layer and a lower layer after slight standing, the upper layer is the normal hexane phase containing the blue copper ion complex, and the lower layer is the water phase. The upper layer was then collected and transferred to a round bottom flask and heated at 55 ℃ with stirring for 100min to obtain a suspension of CuO QDsThe solution was designated CuO QDs-1/2/3 (corresponding to copper contents of 20, 60, 120. mu. mol, respectively).

(3) Preparation of composite catalyst copper oxide quantum dot loaded cobalt-aluminum hydrotalcite

0.1g of the prepared CoAl-u was dispersed in absolute ethanol (150mL) by sonication and stirred for another 30 min. And then dropwise adding the normal hexane suspension of the CuO QDs into the CoAl-u ethanol suspension, and continuously and vigorously stirring the mixed solution at room temperature for 6 hours to ensure that the CuO QDs are fully adsorbed on the CoAl-u nano-sheets through electrostatic action. Then centrifuging to collect the product, washing with anhydrous ethanol for more than 3 times, and vacuum drying the obtained product at 80 ℃ for 12 h. The obtained products correspond to the above-mentioned CuO QDs-1, 2, 3, respectively named x% CuO/CoAl-u (x ═ 1.4%, 4.5%, 8.7%).

3. The method for synthesizing CuO QDs/CoAl-LDHs composite material as claimed in claim 1 and photocatalytic reduction of CO under UV light₂Produce CH₃Application to OH performance.

Technical Field

The invention belongs to the technical field of catalytic materials, and particularly relates to a photocatalyst applied to photocatalytic reductionCO₂The preparation method and the application of the composite catalyst.

Background

Since the industrial revolution, along with the rapid development of science and technology and human productivity, the scale of industrial production in each country is rapidly expanded, and the living standard of human materials is greatly improved. However, this not only provides the human productive life with the scarce development opportunity and strong power, but also brings the increasingly serious challenge. Carbon dioxide (CO)₂) Is an important product for the combustion of fossil fuel and is also a greenhouse gas with the largest proportion. Statistics show that 2018 the CO produced by energy consumption globally₂The greenhouse gas reaches 331 hundred million tons, and the growth rate is 1.7 percent, which is the largest greenhouse gas (72 percent of the total). Therefore, people are already in CO₂A great deal of work is done on the aspects of capture, storage and conversion. Inspired by plant photosynthesis, people reduce CO by artificial simulation of photocatalysis₂The conversion to more valuable carbon-based fuels has been successfully achieved and is an important research topic in the world today.

Hydrotalcite-like compounds (LDHs) are important two-dimensional layered materials, and due to the characteristics of structural multifunctionality, cationic component adjustability, adjustable energy band structure and the like, the hydrotalcite-like compounds (LDHs) are in the presence of CO₂Has great application potential in photocatalytic reduction. The LDHs material is composed of ultrathin composite metal plate layers, provides favorable conditions for efficient diffusion and separation of current carriers, and can increase CO content by exposing a large number of hydroxyl groups on the surface₂Adsorption and resistance to solvents such as water. Because of these unique advantages, various LDH materials are in CO₂The field of photoreduction is widely researched, but because the photocatalytic activity of a single LDHs material is not ideal due to the problems of low charge separation efficiency and the like, effective modification strategies for the LDHs material are applied to improving the performance, such as constructing a heterojunction, loading a cocatalyst and the like.

In addition, Quantum Dot (QDs) semiconductor materials have been widely studied due to their strong light trapping ability and effective promotion of charge transport ability. In particular, CuO QDs are receiving a great deal of attention due to their narrow band gap and wide optical response range. However, it is not limited toIn the photocatalytic reduction of CO due to its inherent instability and agglomeration-prone properties₂The aspect is limited as a catalyst or cocatalyst. Therefore, CuO QDs are dispersed on the surface of LDHs, and an interface heterojunction is constructed under the action of electrostatic force, so that the CuO QDs are an effective strategy for improving the conversion efficiency of carbon dioxide.

Disclosure of Invention

The invention provides a preparation method and application of a novel photocatalyst, wherein the photocatalyst avoids using a noble metal photosensitizer and reduces CO by light₂Is CH₃OH has higher activity, keeps good stability after a cycle test, has simple preparation process and low cost, and provides a new research and development idea for the development of new energy and a novel catalyst.

In order to solve the technical problems, the invention adopts the following technical scheme:

the technical scheme is as follows:

the invention provides a preparation method of a novel photocatalyst, which comprises the following steps:

(1) synthesis of ultra-thin cobalt-aluminum hydrotalcite-like compound (CoAl-u) by one-step coprecipitation method

70mM Co (NO)₃)₂·6H₂O and 35mM Al (NO)₃)₃·9H₂Dissolving O in 25mL of deionized water, and naming the solution A; a0.25 mM NaOH aqueous solution was prepared and designated as solution B. Subsequently, the solutions A and B were simultaneously added dropwise at 85 ℃ to a four-necked flask containing 25mL of ultrapure water, and the pH was kept constant at 9 to 10 with vigorous stirring. Then, the precipitate was collected by centrifugation, washed twice with water, three times more with ethanol, and finally dispersed in 8mL of anhydrous ethanol for use, which was named as CoAl-u.

(2) Preparation of copper oxide quantum dot (CuO QDs) suspension by phase transfer method

Taking a certain amount of prepared 1M Cu (NO)₃)₂·3H₂The O solution was rapidly mixed with 50mL of an ethanol solution containing 1mL of dodecylamine (DDA). After vigorously stirring for 2min, adding 50mL of n-hexane solution into the mixed solution, and continuously and vigorously stirring for 1min to obtain blue flocculent Cu²⁺Sufficient transfer of the DDA complex from the aqueous phase to n-hexaneAnd the mixed solution is divided into an upper layer and a lower layer after slightly standing, wherein the upper layer is a normal hexane phase containing the blue copper ion complex, and the lower layer is a water phase. The collected upper layer was then transferred to a round bottom flask and heated at 55 ℃ for 100min with stirring to obtain a CuO QDs suspension, designated CuO QDs-1/2/3 (corresponding to copper contents of 20, 60, 120. mu. mol, respectively).

(3) Preparation of composite catalyst copper oxide quantum dot loaded cobalt-aluminum hydrotalcite

0.1g of the prepared CoAl-u was dispersed in absolute ethanol (150mL) by sonication and stirred for another 30 min. And then dropwise adding the normal hexane suspension of the CuO QDs into the CoAl-u ethanol suspension, and continuously and vigorously stirring the mixed solution at room temperature for 6 hours to ensure that the CuO QDs are fully adsorbed on the CoAl-u nano-sheets through electrostatic action. Then centrifuging to collect the product, washing with anhydrous ethanol for more than 3 times, and vacuum drying the obtained product at 80 ℃ for 12 h. The obtained products correspond to the above-mentioned CuO QDs-1, 2, 3, respectively named x% CuO/CoAl-u (x ═ 1.4%, 4.5%, 8.7%).

Second, the photocatalysis of nano photocatalyst x% CuO/CoAl-u reduces CO₂The performance evaluation method comprises the following steps:

photocatalytic reduction of CO₂The reaction is carried out in a closed normal-pressure quartz reactor by taking isopropanol as a solvent. The device is divided into five parts: high purity CO₂Gas steel cylinder (99.999%), photocatalytic quartz reactor, high-pressure mercury lamp (250W), high-purity N₂Gas cylinder (99.999%), gas chromatograph (BRUKER, 456-GC).

The specific experimental operations were as follows:

1) weighing 0.025g of catalyst powder to be detected, placing the catalyst powder into a reactor, adding 20mL of isopropanol, and carrying out ultrasonic treatment for 30s to obtain a fully dispersed catalyst-isopropanol suspension;

2) at 300 mL/min^-1Introducing CO into the sealed reactor at a flow rate₂To remove air and make the system reach CO₂For the purpose of saturation, turning on a light source to perform photocatalytic reaction;

4) after 10h of reaction, the lamp was turned off. Centrifuging to separate liquid product and solid catalyst, and detecting liquid product by gas chromatography (BRUKER, 456-GC)CH₃OH yield;

5) collecting the reacted solid catalyst, and circulating the test steps to evaluate the stability of the catalyst; and the above operations were repeated to carry out the control tests with catalyst-no light and with light-no catalyst, using high purity gas N₂Substitute for high purity CO₂A control experiment was performed.

Drawings

FIG. 1 is an X-ray diffraction (XRD) pattern of a CoAl-u photocatalyst and an X% CuO/CoAl-u composite photocatalyst prepared according to the present invention, i.e., XRD patterns of example 1 and example 2;

FIG. 2 is a Transmission Electron Microscope (TEM) image of a CoAl-u photocatalyst prepared according to the present invention, i.e., a TEM image of example 1;

FIG. 3(a-c) is a TEM of a composite x% CuO/CoAl-u photocatalyst prepared according to the present invention, i.e., a TEM of example 2;

FIG. 4 shows the original CoAl-u photocatalyst prepared by the present invention and the composite material of different proportions of x% CuO/CoAl-u for photocatalytic reduction of CO₂Is CH₃Yield of OH, i.e., performance test plots for example 1 and example 2;

FIG. 5 is a graph showing the results of activity cycle tests of 4.5% CuO/CoAl-u photocatalysts of the composite prepared according to the present invention, i.e., a graph showing the performance tests of the composite of example 2;

Detailed Description

Aiming at the defects of the prior art, the invention provides an x% CuO/CoAl-u composite material with a heterostructure for photocatalytic reduction of CO₂The preparation method of (1). The invention is further illustrated by the following specific examples.

Example 1

Photocatalytic reduction of CO₂Preparation and performance test of ultrathin cobalt-aluminum hydrotalcite materials and copper oxide quantum dots.

(1) Synthesis of ultra-thin cobalt-aluminum hydrotalcite-like compound (CoAl-u) by one-step coprecipitation method

70mM Co (NO)₃)₂·6H₂O and 35mM Al (NO)₃)₃·9H₂Dissolving O in 25mL of deionized water, and naming the solution A;a0.25 mM NaOH aqueous solution was prepared and designated as solution B. Subsequently, the solutions A and B were simultaneously added dropwise at 85 ℃ to a four-necked flask containing 25mL of ultrapure water, and the pH was kept constant at 10 with vigorous stirring. Then, the precipitate was collected by centrifugation, washed twice with water, three times more with ethanol, and finally dispersed in 8mL of anhydrous ethanol for use, which was named as CoAl-u.

(2) Photocatalytic reduction of CO by nano photocatalyst ultrathin cobalt-aluminum hydrotalcite₂Study of Properties

Taking a 25mg CoAl-u sample and 20mL isopropanol in a photocatalytic quartz reactor, and introducing high-purity CO into the quartz reactor₂The gas duration was 30min to exclude internal air and the reaction system was closed. Then, the light source is turned on for reaction, and the light source is turned off after the reaction is carried out for 10 hours. The methanol product yield was analyzed by gas chromatography (BRUKER, 456-GC).

Example 2

Has excellent photocatalytic reduction of CO₂Preparing a performance nano composite photocatalyst x% CuO/CoAl-u and testing the performance.

(1) Taking a certain amount of prepared 1M Cu (NO)₃)₂·3H₂The O solution was rapidly mixed with 50mL of an ethanol solution containing 1mL of dodecylamine (DDA). After vigorously stirring for 2min, adding 50mL of n-hexane solution into the mixed solution, and continuously and vigorously stirring for 1min to obtain blue flocculent Cu²⁺the-DDA complex is fully transferred from the water phase to the normal hexane phase, the mixed solution is divided into an upper layer and a lower layer after slight standing, the upper layer is the normal hexane phase containing the blue copper ion complex, and the lower layer is the water phase. The upper layer was then collected and transferred to a round bottom flask and heated at 55 ℃ for 100min with stirring to obtain a CuO QDs suspension. 0.1g of the prepared CoAl-u was dispersed in absolute ethanol (150mL) by sonication and stirred for another 30 min. And then dropwise adding the normal hexane suspension of the CuO QDs into the CoAl-u ethanol suspension, and continuously and vigorously stirring the mixed solution at room temperature for 6 hours to ensure that the CuO QDs are fully adsorbed on the CoAl-u nano-sheets through electrostatic action. The product was then collected by centrifugation, washed 3 more times with absolute ethanol, and dried under vacuum at 80 ℃ for 12h, named x% CuO/CoAl-u (x ═ 1.4%, 4.5%, 8.7%).

(2) Photocatalytic reduction of CO by nano photocatalyst x% CuO/CoAl-u₂Study of Properties

Taking 25mg of x% CuO/CoAl-u sample and 20mL of isopropanol in a photocatalytic quartz reactor, and introducing high-purity CO into the quartz reactor₂The gas duration was 30min to exclude internal air and the reaction system was closed. Then, the light source is turned on for reaction, and the light source is turned off after the reaction is carried out for 10 hours. The methanol product yield was analyzed by gas chromatography (BRUKER, 456-GC).

FIG. 1 is an XRD pattern of ultra-thin cobalt aluminum hydrotalcite (CoAl-u) prepared in example 1 and example 2 and x% CuO/CoAl-u composite material, and the crystal structure of the ultra-thin cobalt aluminum hydrotalcite is changed along with the increase of the CuO QDs loading amount.

FIG. 2 is a TEM image of the CoAl-u photocatalyst obtained in example 1, and it can be seen from the TEM image that the CoAl-u photocatalyst shows an ultrathin nanosheet structure, the thickness range is about 2.3-4.8 nm, the particle size is about 50nm, and the ultrathin lamella structure is very beneficial to CO₂Adsorption of (3).

FIG. 3 is a TEM image of the 4.5% CuO/CoAl-u composite obtained in example 2. Among them, FIG. 3(a-b) shows the distribution of particles of CuO QDs on a CoAl-u sheet, which has a particle size of about 2.9 nm; FIG. 3(c) allows observation of the lattice spacing of the CuO and CoAl-u nanomaterials, indicating successful preparation of the composite.

FIG. 4 shows the results of activity tests on the catalysts prepared in examples 1 and 2, which shows that the composite photocatalyst, 4.5% CuO/CoAl-u, can be used for photocatalytic reduction of CO₂The yield of the produced methanol is obviously higher than that of other catalysts, and the yield reaches 283.26 mu mol g^-1·h^-1。

FIG. 5 shows that the methanol yield of the composite material 4.5% CuO/CoAl-u can reach more than 95% of the initial photocatalytic yield after four activity cycle tests, which indicates that the photocatalyst has good stability.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.