A method for preparing bismuth-based two-dimensional vertical heterojunction catalysts using supercritical fluid technology

Abstract

The present invention discloses a method for preparing a two-dimensional vertical heterojunction catalyst by supercritical fluid, which comprises the following steps: dispersing Bi(NO3)3·5H2O and KIO3 in deionized water, with the molar ratio of Bi(NO3)3·5H2O to KIO3 being 0.5 - 2.0. After vigorous stirring, adjusting the pH of the solution to 1 - 3 to obtain a suspension; transferring the suspension to a supercritical reaction kettle, heating the reaction kettle to 40 - 200 °C, introducing CO2 into the reaction kettle to 8 - 30 MPa, and magnetically stirring for 1 - 6 h; after naturally cooling to room temperature, slowly releasing CO2 to relieve pressure, separating the precipitate from the supercritically treated suspension by centrifugation, and washing and drying the precipitate. The present invention utilizes the solvent properties of supercritical CO2 and the directional chemical adsorption reaction strategy of CO2 small molecules to achieve the two-dimensional directional self-assembly of Bi2O2CO3 on BiOIO3, and then successfully prepares a chemically bonded, large-size bismuth-based two-dimensional vertical heterojunction. The present invention can solve the problems such as low carrier separation efficiency caused by single interface, mismatched morphology and poor interface contact in the existing heterojunction catalysts, and significantly improve the CO2 photoreduction performance.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalyst preparation, and particularly relates to a method for preparing a bismuth-based two-dimensional vertical heterojunction catalyst with high CO 2 photoreduction performance. Background Art

[0002] Converting the greenhouse gas CO 2 into high-value-added chemicals is an important way to achieve sustainable environmental and energy development. Designing and synthesizing photocatalysts with excellent performance in aspects such as visible light absorption, CO 2 enrichment / activation, and electron-coupled proton transfer is the core of the successful development of this path. The two-dimensional vertical heterojunction catalyst with an ultra-high specific surface area can not only spontaneously form an internal electric field at the interface, effectively regulating the carrier dynamics and thermodynamic pathways of the CO 2 photoreduction process, but also provide abundant surface active sites for the adsorption and conversion of CO 2 , significantly improving the CO 2 photoreduction performance. However, non-coherent phase interfaces widely exist in the reported two-dimensional vertical heterojunctions, and the intermolecular layers are mostly weak van der Waals forces (vdW), showing poor lattice matching and interfacial interaction. The carrier capture defects generated at the non-coherent phase interfaces and the vdW gaps will significantly inhibit the charge carrier dynamics, resulting in low CO 2 photoreduction performance of the catalyst. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a bismuth-based two-dimensional vertical heterojunction catalyst by using supercritical fluid technology, so as to solve multiple technical problems existing in the application of the above two-dimensional vertical heterojunction in CO 2 photoreduction.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing a bismuth-based two-dimensional vertical heterojunction catalyst by using supercritical fluid technology, comprising the following steps:

[0006] Disperse Bi(NO 3 ) 3 ·5H 2 O and KIO 3 in deionized water, wherein the molar ratio of Bi(NO 3 ) 3 ·5H 2 O to KIO 3 is 0.5 - 2.0. After vigorous stirring, adjust the pH of the solution to 1 - 3 to obtain a suspension;

[0007] Transfer the suspension to a supercritical reactor, heat the reactor to 40 - 200 °C, and then introduce CO 2 into the reactor to 8 - 30 MPa, and stir magnetically for 1 - 6 h;

[0008] After natural cooling to room temperature, slowly release CO 2 to relieve pressure. The suspension after supercritical treatment is separated by centrifugation to obtain a precipitate, and the precipitate is washed and dried to obtain two-dimensional Bi 2 O 2 CO 3 / BiOIO 3 vertical heterojunction.

[0009] In some embodiments, the stirring speed is 500 - 1000 r / min.

[0010] In some embodiments, the solution pH is adjusted by adding HNO3.

[0011] In some embodiments, the centrifugation method is to centrifuge at a speed of 8000 rpm for 10 min.

[0012] In some embodiments, the washing step includes washing alternately with distilled ethanol and water 3 times, and the drying step includes drying under vacuum at 333 K for 6 h.

[0013] The present invention provides a method for preparing two-dimensional vertical heterojunction by using supercritical fluid technology. In a supercritical environment, the solvent properties of supercritical CO 2 can accelerate the synthesis reaction kinetics, and the chemical adsorption reaction strategy of CO 2 small molecules can achieve 2D directional self-assembly of Bi 2 O 2 CO 3 on BiOIO 3 to obtain a large-sized bismuth-based two-dimensional vertical heterojunction with chemical bonding.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] The advantages of supercritical CO 2 such as low viscosity, high diffusivity, and adjustable solvation ability of green solvents can accelerate the reaction kinetics of BiOIO 3 generation, shorten the reaction time, and the chemical adsorption reaction strategy of CO 2 small molecules can regulate the crystal growth orientation of BiOIO 3 to achieve 2D directional self-assembly at the molecular scale, and then precisely construct 2D Bi 2 O 2 CO 3 / BiOIO 3Vertical heterojunction. The large-sized 2D vertical heterojunction of chemical bonds can achieve the rapid transport of photo-generated carriers and their efficient separation in physical space, thereby solving the low CO 2 photoreduction efficiency caused by single interfaces, mismatched morphologies, and poor interface contacts in existing Bi-based heterojunctions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 XRD patterns of the target products obtained in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0017] Figure 2 SEM comparison diagrams of the target products obtained in Example 1 and Comparative Example 1 of the present invention: A) 2D Bi 2 O 2 CO 3 / BiOIO 3 vertical heterojunction, B) pure BiOIO prepared by the hydrothermal method 3 ;

[0018] Figure 3 TEM comparison diagrams of the target products obtained in Example 1 and Comparative Example 1 of the present invention: A) 2D Bi 2 O 2 CO 3 / BiOIO 3 vertical heterojunction, B) pure BiOIO prepared by the hydrothermal method 3 ;

[0019] Figure 4 Photocatalytic carbon dioxide reduction activity comparison diagrams of the target catalysts obtained in Examples 1-2 and Comparative Examples 1-2 of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be further described below in conjunction with the embodiments. The following embodiments are only used to more clearly illustrate the performance of the present invention and cannot be limited only to the following embodiments.

[0021] Example 1: Preparation of 2D vertical heterojunction by supercritical reaction for 2 h

[0022] Weigh 242.5 mg of Bi(NO 3 ) 3 ·5H 2 O and 107 mg of KIO 3 Add them to 20 mL of deionized water and stir vigorously for 10 minutes; then add 0.03 M of HNO 3 to the above solution; after stirring for 1 hour, transfer the formed suspension to a supercritical reaction kettle. Heat the reaction kettle to 180 °C, and then add CO 2Feed into the reaction kettle to 16 MPa, stir magnetically for 2 h; after naturally cooling to room temperature, slowly release carbon dioxide to relieve pressure. The suspension after supercritical treatment is separated by centrifugation to obtain a precipitate, and the product is collected by centrifugation at 8000 rpm for 10 min; wash alternately with distilled ethanol and water 3 times, and then dry under vacuum at 333 K for 6 h to obtain the target product, denoted as CO 2 -2h. As Figure 1 shown, CO 2 -2h is Bi 2 O 2 CO 3 / BiOIO 3 heterojunction.

[0023] Example 2: Preparation of 2D vertical heterojunction by supercritical reaction for 3 h

[0024] Weigh 242.5 mg of Bi(NO 3 ) 3 ·5H 2 O and 107 mg of KIO 3 Add them to 20 mL of deionized water and stir vigorously for 10 minutes; then add 0.03 M of HNO 3 to the above solution; after stirring for 1 hour, transfer the formed suspension to a supercritical reaction kettle. Heat the reaction kettle to 180 °C, and then feed CO 2 into the reaction kettle to 16 MPa, stir magnetically for 3 h; after naturally cooling to room temperature, slowly release carbon dioxide to relieve pressure. The suspension after supercritical treatment is separated by centrifugation to obtain a precipitate, and the product is collected by centrifugation at 8000 rpm for 10 min; wash alternately with distilled ethanol and water 3 times, and then dry under vacuum at 333 K for 6 h to obtain the target product, denoted as CO 2 -3h. As Figure 1 shown, CO 2 -3h is Bi 2 O 2 CO 3 / BiOIO 3 heterojunction; as Figure 2 shown, the scanning electron microscope (SEM) of the 2D Bi 2 O 2 CO 2 CO 3 / BiOIO 3 vertical heterojunction shows stacked nanosheets with irregular edges, and the average lateral size is about 5 μm; as Figure 3 shown, the lattice-matched Bi 2 O 2 CO 3 grows closely on BiOIO 3On the surface, 2D / 2D contacts are formed. It is worth noting that through supercritical CO 2 Introduce Bi by reactive epitaxial attachment 2 O 2 CO 3 Can significantly change the crystal orientation of BiOIO 3 .

[0025] Comparative Example 1: Preparation of pure BiOIO by hydrothermal method 3

[0026] The difference from Examples 1-2 is that it is not treated under supercritical conditions; the specific steps are as follows: Weigh 242.5 mg of Bi(NO 3 ) 3 ·5H 2 O and 107 mg of KIO 3 Add to 20 mL of deionized water and stir vigorously for 10 minutes; then add 0.03 M of HNO 3 to the above solution; after stirring for 1 hour, transfer the formed suspension to a hydrothermal reaction kettle and react at 180 °C for 3 h; after natural cooling to room temperature, separate the precipitate by centrifugation, collect the product by centrifugation at 8000 rpm for 10 min; wash it alternately with distilled ethanol and water 3 times, and then dry it under vacuum at 333 K for 6 h to obtain the control product. As Figure 1 shown, the product prepared by the hydrothermal method is pure BiOIO 3 ; as Figure 2 shown, the pure BiOIO 3 with an aspect ratio of about 2.5 presents a uniform nanosheet morphology.

[0027] Comparative Example 2: Supercritical reaction for 7 h

[0028] Weigh 242.5 mg of Bi(NO 3 ) 3 ·5H 2 O and 107 mg of KIO 3 Add to 20 mL of deionized water and stir vigorously for 10 minutes; then add 0.03 M of HNO 3 to the above solution; after stirring for 1 hour, transfer the formed suspension to a supercritical reaction kettle. Heat the reaction kettle to 180 °C, then introduce CO 2 into the reaction kettle to 16 MPa, and stir magnetically for 7 h; after natural cooling to room temperature, slowly release carbon dioxide to relieve pressure, and separate the precipitate from the suspension after supercritical treatment by centrifugation, collect the product by centrifugation at 8000 rpm for 10 min; wash it alternately with distilled ethanol and water 3 times, and then dry it under vacuum at 333 K for 6 h to obtain the target product, denoted as CO 2 -7h. As Figure 1 shown, CO2 -7h is pure Bi 2 O 2 CO 3 Product.

[0029] Performance test: Photocatalytic CO in pure water 2 Reduction performance test

[0030] The photocatalytic carbon dioxide reduction system was used to evaluate the catalyst activity, including a simulated solar light source, a 100 mL quartz reactor, a circulating cooling system, a Beijing Sevenstar Huachuang Electronics D08-1F mass flowmeter, and a Fuli gas chromatograph (GC9790). The simulated solar light source was realized by a 300 W xenon lamp light source with an AM 1.5G filter, and the light intensity was 100 mW cm -2 .

[0031] Specifically, the 35 mg products obtained in Examples 1-2 and Comparative Examples 1-2 and 70 mL of deionized water were ultrasonically homogenized and then transferred to a 100 mL quartz reactor, respectively. Before the reaction, high-purity CO was passed at a flow rate of 20 ml min -1 to expel the air in the reactor. During the whole reaction process, the CO 2 flow rate was 7 ml min 2 , and at the same time, the circulating cooling system was used to maintain the reactor temperature at 25 °C. A gas chromatograph equipped with TCD and FID detectors was used to monitor the photocatalytic products online. -1 The experimental results are as

[0032] shown. The 2DBi Figure 4 formed during the supercritical carbon dioxide treatment process 2 O 2 CO 3 / BiOIO 3 vertical heterojunction (CO 2 -2h, CO 2 -3h) has significantly enhanced CO 2 photoreduction performance. Specifically, the CO yield of the CO 2 -3h sample was 118.15 μmol g -1 h -1 , which were 3.6 and 3.8 times that of pure BiOIO 3 and pure Bi 2 O 2 CO 3 (CO 2 -7h), respectively. At the same time, the selectivity of CO 2 converted to CO was close to 100%, and no H 2 or CH 4 by-products were observed. This means Bi 2 O2 CO 3 / BiOIO 3 The formation of the heterojunction can effectively reduce the energy barrier for proton transfer to CO 2 . In addition, the average yield ratio of CO and O 2 is 2.16:1, close to the ideal stoichiometric ratio, confirming the effective photoreduction of CO 2 in pure water.

[0033] In summary, the present invention provides a method for preparing two-dimensional vertical heterojunctions using supercritical fluid technology. In a supercritical environment, the solvent properties of supercritical CO 2 can accelerate the synthesis reaction kinetics, while the chemical adsorption reaction strategy of CO 2 small molecules can achieve the 2D directional self-assembly of Bi 2 O 2 CO 3 on BiOIO 3 to obtain a large-sized chemically bonded bismuth-based two-dimensional vertical heterojunction.

[0034] Among them, the advantages of supercritical CO 2 such as the low viscosity, high diffusivity, and tunable solvation ability of green solvents can accelerate the reaction kinetics of BiOIO 3 formation, shorten the reaction time, while the chemical adsorption reaction strategy of CO 2 small molecules can regulate the crystal growth orientation of BiOIO 3 , achieve 2D directional self-assembly at the molecular scale, and then precisely construct 2D Bi 2 O 2 CO 3 / BiOIO 3 vertical heterojunction. The chemically bonded large-sized 2D vertical heterojunction can achieve rapid transport of photo-generated carriers and their efficient separation in physical space, thereby solving the low CO 2 photoreduction efficiency caused by reasons such as single interface, mismatched morphology, and poor interface contact in existing Bi-based heterojunctions.

[0035] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bismuth-based two-dimensional vertical heterojunction catalyst using supercritical fluid technology, characterized in that, it comprises the following steps: Disperse Bi(NO 3 ) 3 ·5H 2 O and KIO 3 in deionized water. The molar ratio of Bi(NO 3 ) 3 ·5H 2 O to KIO 3 is 0.5 - 2.

0. After vigorous stirring, adjust the pH of the solution to 1 - 3 to obtain a suspension; Transfer the suspension to a supercritical reactor, heat the reactor to 40 - 200 °C, and then introduce CO 2 into the reactor to 8 - 30 MPa, and stir magnetically for 1 - 6 h; Slowly release CO after natural cooling to room temperature 2 Release pressure. The suspension after supercritical treatment is separated by centrifugation to obtain a precipitate, and the precipitate is washed and dried to obtain two-dimensional Bi 2 O 2 CO 3 / BiOIO 3 Vertical heterojunction.

2. The method for preparing a bismuth-based two-dimensional vertical heterojunction catalyst using supercritical fluid technology according to claim 1, characterized in that, the stirring speed is 500 - 1000 r / min.

3. The method for preparing a bismuth-based two-dimensional vertical heterojunction catalyst using supercritical fluid technology according to claim 1, characterized in that, By adding HNO 3 Adjust the pH of the solution.

4. The method for preparing a bismuth-based two-dimensional vertical heterojunction catalyst using supercritical fluid technology according to claim 1, characterized in that, the centrifugation method is to centrifuge at a speed of 8000 rpm for 10 min.

5. The method for preparing a bismuth-based two-dimensional vertical heterojunction catalyst using supercritical fluid technology according to claim 1, characterized in that, the washing step includes washing alternately with distilled ethanol and water 3 times, and the drying step includes drying under vacuum at 333 K for 6 h.

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