CN117643905A

CN117643905A - Boron-doped bismuth oxybromide catalyst and preparation method and application thereof

Info

Publication number: CN117643905A
Application number: CN202311596467.2A
Authority: CN
Inventors: 蔡小龙; 申明智; 赵鹏; 曹锦波; 曹保卫; 许云华
Original assignee: Yulin University
Current assignee: Yulin University
Priority date: 2023-11-28
Filing date: 2023-11-28
Publication date: 2024-03-05

Abstract

The invention provides a boron-doped bismuth oxybromide catalyst and a preparation method and application thereof, wherein the mixed solution of raw materials is placed in an autoclave to react by a hydrothermal method under the conditions of constant temperature and sufficient reaction time, after the reaction is finished, reactants are cooled, and then precipitation, cleaning and drying are carried out, so that the boron-doped bismuth oxybromide catalyst is finally obtained; the preparation method is simple and convenient, raw materials are easy to obtain, and the preparation method is suitable for large-scale amplification. The boron doped bismuth oxybromide catalyst prepared by the invention is dispersed in absolute ethyl alcohol when in use, and is dried in a culture dish to obtain a catalyst film for photocatalytic decomposition of CO ₂ The use effect is better; the electron arrangement characteristic of the boron atom P orbit is beneficial to photogenerated current carryingThe boron doped bismuth oxybromide catalyst can increase the utilization rate of sunlight by reducing the band gap and improve CO by separating the seeds and increasing the coulomb efficiency ₂ Reduction efficiency, CO by photocatalysis ₂ Reducing into CO to achieve the purposes of carbon emission reduction, green and environmental protection.

Description

Boron-doped bismuth oxybromide catalyst and preparation method and application thereof

Technical Field

The invention belongs to the field of catalyst preparation, and particularly relates to a boron-doped bismuth oxybromide catalyst, and a preparation method and application thereof.

Background

China is a country using coal as main energy, and in recent years, along with rapid development of economy, the demand for energy is increased or not, and carbon dioxide (CO) is caused ₂ ) Excess emissions. CO of 2017 China ₂ The discharge amount reaches 92.326 ten thousand tons, due to CO ₂ Environmental problems caused by excessive emissions are becoming more serious, such as greenhouse effect, global warming, etc. Against this background, CO was developed ₂ Technologies such as trapping, sequestration, and reduction to high value chemicals (e.g., carbon monoxide, methane, formic acid, and methanol) are becoming urgent.

Carbon monoxide (CO) is an important raw material for chemical synthesis products, and CO ₂ Reduction to CO is realized by ₂ An important way of eliminating and reducing emissions. CO ₂ The reduction process comprises photocatalysis, electrocatalysis, electrochemical catalysis and the like, wherein the photocatalysis process can simulate photosynthesis of plants to utilize sunlight to convert CO ₂ And (5) reduction.

Bismuth oxybromide (BiOBr) is used as an N-type semiconductor and has excellent CO due to good chemical stability, proper energy band width (2.8-2.9 eV) and controllable morphological characteristics ₂ Photocatalytic reduction performance. However, researches show that the BiOBr conduction band potential is low, the BiOBr conduction band potential has selectivity to the range of light waves, and solar energy and CO can not be fully utilized ₂ The reduction efficiency is low, and the problems described above give the photocatalysis to CO ₂ The photoreduction into CO causes great difficulty, is to limit CO ₂ The main bottleneck of emission reduction.

Disclosure of Invention

In order to solve the problems, the invention provides a photocatalyst for reducing carbon dioxide by boron doped bismuth oxybromide and a preparation method thereof.

The non-metallic element boron (B) has good conductivity and small atomic radius, is easy to dope into a BiOBr crystal frame, and in addition, the electron arrangement characteristic of B atomic P orbit is beneficial to photon-generated carrier separation and increases coulomb efficiency, so that the B-doped BiOBr photocatalyst can increase the utilization rate of sunlight by reducing the band gap and improve CO ₂ Reduction efficiency.

In order to achieve the above object, the present invention provides the following technical solutions:

the preparation method of the boron-doped bismuth oxybromide catalyst comprises the following steps:

s1: mixing an aqueous solution of boric acid with a nitric acid solution of bismuth nitrate, and stirring to obtain a solution A;

s2: mixing and uniformly stirring an alkali metal bromide aqueous solution with the solution A to obtain a solution B, wherein the alkali metal bromide is potassium bromide or sodium bromide;

s3: transferring the solution B into an autoclave for hydrothermal reaction, and cooling after the reaction is finished to obtain a reaction product C;

s4: and centrifuging the reaction product C, washing with absolute ethyl alcohol, and drying to obtain the boron doped bismuth oxybromide catalyst.

Further, the molar ratio of boric acid to bismuth nitrate in S1 is 0.25-1:100.

Further, the molar ratio of the amount of the alkali metal bromide to the amount of the bismuth nitrate in the S2 is 5-10:1.

In S3, the hydrothermal reaction condition is that the temperature is 150-180 ℃ and the reaction time is 10-14 h.

The invention also provides a boron-doped bismuth oxybromide catalyst which is characterized by being prepared by the method, wherein the boron-doped bismuth oxybromide catalyst is sheet-shaped, the average thickness of a sheet layer is 18.9-45.3 nm, and the average diameter of the sheet layer is 176-331 nm.

The invention also provides an application of the boron-doped bismuth oxybromide catalyst, which comprises the following steps:

s1: dispersing the boron-doped bismuth oxybromide catalyst into absolute ethyl alcohol to obtain a catalyst suspension;

s2: pouring the catalyst suspension into a culture dish and drying to obtain a catalyst film;

s3: putting the catalyst film into a light-transmitting closed reactor, and filling CO ₂ And water vapor, under sun light or simulated sun light.

The invention has the beneficial effects that:

the invention provides a boron doped bismuth oxybromide catalyst and a preparation method and application thereof, wherein the boron doped bismuth oxybromide catalyst is prepared by uniformly mixing boric acid aqueous solution and bismuth nitrate nitric acid solution in proportion, adding alkali bromide solution into the mixture, uniformly stirring the mixture, placing the obtained mixed solution into an autoclave, carrying out hydrothermal reaction under the conditions of constant temperature and sufficient reaction time, cooling reactants after the reaction is finished, precipitating, cleaning and drying the cooled reactants, and finally obtaining the boron doped bismuth oxybromide catalyst; the preparation method is simple and convenient, raw materials are easy to obtain, and the preparation method is suitable for large-scale amplification.

The boron doped bismuth oxybromide catalyst prepared by the invention is dispersed in absolute ethyl alcohol when in use, and is dried in a culture dish to obtain a catalyst film for photocatalytic decomposition of CO ₂ The use effect is better; the electron arrangement characteristic of the boron atom P orbit is beneficial to the separation of photon-generated carriers and the increase of coulomb efficiency, and the boron doped bismuth oxybromide catalyst can increase the utilization rate of sunlight and improve CO by reducing the band gap ₂ Reduction efficiency, CO by photocatalysis ₂ Reducing into CO to achieve the purposes of carbon emission reduction, green and environmental protection.

Compared with bismuth oxybromide photocatalysts doped with other elements, the non-metallic element boron atom has small radius, is easy to dope into bismuth oxybromide crystal lattice, and adopts B ³⁺ Substituted part Bi ³⁺ The energy band structure of the bismuth oxybromide is changed, the band gap energy is reduced, the absorption range of the bismuth oxybromide to light waves is widened, and the light utilization rate is improved; b (B) ³⁺ Substituted part Bi ³⁺ Impedance is reduced, charge migration rate is increased, photo-generated carrier separation rate is improved, and photocatalysis efficiency is improved; compared with pure phase bismuth oxybromide, B ³⁺ The doping of (2) improves the yield of carbon monoxide; in addition, the boron cost is lower, the cost of the doped bismuth oxybromide catalyst is reduced, and the catalyst has the advantages ofGood economic benefit development prospect.

Drawings

FIG. 1 is an XRD pattern for bismuth oxybromide and boron doped bismuth oxybromide catalysts;

FIG. 2 is a scanning electron microscope image of a boron doped bismuth oxybromide catalyst;

FIG. 3 is an XPS spectrum of bismuth oxybromide and a boron doped bismuth oxybromide catalyst;

FIG. 4 is a graph of band gap energies for bismuth oxybromide and boron doped bismuth oxybromide catalysts;

FIG. 5 is a graph of the impedance of bismuth oxybromide and boron doped bismuth oxybromide catalysts;

FIG. 6 is a graph showing the effect of light exposure time on the yield of photocatalytic carbon dioxide reduction products.

Detailed Description

In order that the manner in which the above-recited features and advantages of the present invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings, in which, as a result, all embodiments of the invention are illustrated in the appended drawings.

All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Example 1

s1: mixing 0.1g of 5% aqueous boric acid solution with 78.5g of 10% bismuth nitrate nitric acid solution, and stirring to obtain solution A;

s2: 77.0g of 20% potassium bromide aqueous solution and the solution A are mixed and stirred uniformly to obtain a solution B;

s3: transferring the solution B into an autoclave, preserving heat at 160 ℃ for 12 hours, and cooling to room temperature after the reaction to obtain a reaction product C;

s4: centrifugally precipitating the reaction product C for 2min at the rotating speed of 1500r/min, washing with absolute ethanol for 8 times, and drying at 60 ℃ for 10 hours to obtain the boron doped bismuth oxybromide catalyst;

the boron doped bismuth oxybromide catalyst described in example 1 had a boron to bismuth doping level of 0.5%, and was then designated as 0.5B/BiOBr;

FIG. 1 is an XRD pattern of bismuth oxybromide and boron doped bismuth oxybromide catalyst, as shown in FIG. 1, the bismuth oxybromide is of tetragonal structure, and the boron doped bismuth oxybromide is also of tetragonal structure, indicating that boron doping enters the crystal lattice of bismuth oxybromide, but does not affect the crystal structure of bismuth oxybromide;

FIG. 2 is a scanning electron microscope image of a boron doped bismuth oxybromide catalyst, as shown in FIG. 2, the boron doped bismuth oxybromide catalyst has a two-dimensional nano-lamellar morphology, the average thickness of the lamellar is about 20.4nm, the average diameter of the lamellar is about 186nm, and the boron doped bismuth oxybromide catalyst used in FIG. 2 is 0.5B/BiOBr prepared in example 1;

FIG. 3 is an XPS spectrum of bismuth oxybromide and boron doped bismuth oxybromide catalyst, as shown in FIG. 3, the elements of the boron doped bismuth oxybromide catalyst include B, O, bi and Br, indicating that boron atoms were successfully incorporated into the bismuth oxybromide lattice, wherein the binding energy corresponding to B1s indicates that boron is in the form of B ³⁺ A crystal lattice of bismuth oxybromide in the form;

FIG. 4 is a graph of band gap energies of bismuth oxybromide and boron doped bismuth oxybromide catalysts, as shown in FIG. 4, the band gaps of bismuth oxybromide and boron doped bismuth oxybromide are 2.86eV and 2.65eV, respectively, indicating B ³⁺ Doping forms a new energy level between the valence and conduction bands of the BiOBr, which results in a decrease in the band gap energy of the boron doped bismuth oxybromide catalyst, also indicating B ³⁺ The doping of the (2) is beneficial to the efficient separation of photogenerated carriers;

FIG. 5 is a graph showing the impedance of bismuth oxybromide and boron doped bismuth oxybromide catalysts, as shown in FIG. 5, the internal charge transfer resistance of the boron doped bismuth oxybromide catalysts is reduced and the interfacial charge transfer rate is increased, indicating B ³⁺ Can excite charge transfer;

the boron-doped bismuth oxybromide catalyst (0.5B/BiOBr) prepared in example 1 was used for photocatalytic CO decomposition ₂ Comprising the following steps:

s1: 10mg of 0.5B/BiOBr is added into 10g of absolute ethyl alcohol, and the mixture is subjected to ultrasonic vibration for 2 hours to obtain a catalyst suspension;

s2: pouring the catalyst suspension into a culture dish, and drying at 60 ℃ to obtain a catalyst film;

s3: putting the catalyst film into a light-transmitting closed reactor, and filling CO ₂ And steam (ratio about 1:10), the reactor is closed, and the reaction is carried out for 5 hours under the irradiation of sun light;

the composition of the gases in the reactor was analyzed per hour, the main component being CO ₂ ，CO，O ₂ And CH (CH) ₄ ；

As shown in fig. 6, CO and CH ₄ The yields of (2) are linear over time and the data are shown in Table 1:

TABLE 1 Effect of illumination time on photocatalytic carbon dioxide reduction product yield

The boron doped bismuth oxybromide photocatalyst (0.5B/BiOBr) is irradiated for 1h under the sunlight to treat CO ₂ Reduction to the main product CO (21.72. Mu. Mol. G) ^-1 ·h ^-1 ) At the same time accompanied by a small amount of CH ₄ (2.15μmol·g ^-1 ·h ^-1 ) The boron doped bismuth oxybromide catalyst has good selectivity to the product and higher yield.

The photocatalytic decomposition of CO ₂ The sunlight in the process is changed into simulated sunlight, and the photocatalytic decomposition of CO is repeated ₂ The light time was set to 1h, and experimental data are shown in table 2:

TABLE 2 influence of the number of photocatalytic cycles on CO yield

Number of cycles	CO yield (mu mol g) ^-1 ·h ^-1 )
		1	21.72
2	21.03
		3	20.45
4	19.16
		5	19.14

As can be seen from Table 1, the cycle times are different for the photocatalytic reduction of CO at 0.5B/BiOBr ₂ The effect of the CO yield of the product is small, and the CO yield exhibits a slight decay as the number of cycles increases.

Example 2

s2: mixing 66.6g of 20% sodium bromide aqueous solution with the solution A and uniformly stirring to obtain a solution B;

the boron-doped bismuth oxybromide catalyst prepared in example 2 wasThe boron-doped bismuth oxybromide catalyst prepared in example 1 was used for the photocatalytic decomposition of CO ₂ The catalytic effect was substantially equivalent in the process of (1) CO ₂ The yield of CO reduced to the main product was 21.72. Mu. Mol g ^-1 ·h ^-1 At the same time accompanied by a small amount of CH ₄ Yield was 2.15. Mu. Mol g ^-1 ·h ^-1 The same conditions are used in example 2, CO ₂ The yield of CO reduced to the main product was 21.58. Mu. Mol g ^-1 ·h ^-1 At the same time accompanied by a small amount of CH ₄ Yield of 2.06. Mu. Mol g ^-1 ·h ^-1 。

Examples 3 to 6

The preparation method of the boron doped bismuth oxybromide catalyst is different from that of the example 1 in that the amount of boric acid in S1 is different, the example 6 is a comparative example, no boron is doped, the bismuth oxybromide is directly prepared, and the average thickness and average diameter data of the sheet layers of the B/BiOBr with different boron doping amounts are shown in Table 3:

TABLE 3 influence of the average thickness and average diameter of the sheets of B/BiOBr with different boron doping levels

Examples	Boron doping amount (%)	Average thickness of sheet (nm)	Average diameter of lamellar (nm)
				1	0.50	20.4	186
3	0.25	42.1	331
				4	0.75	36.2	217
5	1.00	45.3	230
				6	0.00	55.8	425

As can be seen from the data in table 2, the average thickness of the sheet layer of the boron doped bismuth oxybromide catalyst with the boron doping amount of 0.5% is smaller, and the corresponding sheet layer diameter is smaller;

the boron-doped bismuth oxybromide catalyst is used for photocatalytic decomposition of CO ₂ Experimental conditions were as in example 1 photocatalytic decomposition of CO ₂ The conditions of (2) are identical and the data are shown in Table 4;

TABLE 4 influence of boron doping on carbon monoxide and methane yields

As can be seen from the data in table 4, the photocatalytic effect of the boron doped bismuth oxybromide catalyst with the boron doping amount of 0.5% is optimal, and the photocatalytic effect is doubled compared with that of bismuth oxybromide per se;

experimental results show that the smaller the average thickness of the boron-doped bismuth oxybromide photocatalyst sheet layer is, the larger the average diameter of the sheet layer is, the more excellent the photocatalysis effect is shown, and the influence of the average thickness of the sheet layer on the reaction is larger; the effect of the preparation conditions on the catalyst performance can be indirectly illustrated by comparing the average thickness and average diameter of the boron doped bismuth oxybromide photocatalyst sheet.

Examples 7 to 9

The process for preparing the boron doped bismuth oxybromide catalyst differs from that of example 1 in that the amount of potassium bromide used in S2 is different;

the data are shown in table 5:

TABLE 5 influence of Potassium bromide usage on average platelet thickness and average diameter of boron doped bismuth oxybromide catalysts

Examples	Potassium bromide: bismuth nitrate (molar ratio)	Average thickness of sheet (nm)	Average diameter of lamellar (nm)
				7	5	20.2	183
8	6	20.1	180
				1	8	20.4	186
9	10	20.6	187

As can be seen from the data in Table 5, the amount of potassium bromide used has less effect on the average thickness of the platelets and the average diameter of the platelets of the boron-doped bismuth oxybromide catalyst, and only a large excess of potassium bromide relative to bismuth nitrate is required.

Examples 10 to 15

The difference from the preparation method of the boron-doped bismuth oxybromide catalyst in example 1 is that the reaction conditions of the S3 hydrothermal reaction are different;

the data are shown in table 6:

TABLE 6 influence of reaction conditions on average thickness and average diameter of platelets of boron doped bismuth oxybromide catalysts

Examples	Reaction temperature (. Degree. C.)	Reaction time (h)	Average thickness of sheet (nm)	Average diameter of lamellar (nm)
					10	150	10	18.9	176
11	155	10	19.6	181
					1	160	12	20.4	186
12	165	11	20.9	187
					13	170	12	21.7	195
14	175	13	23.2	208
					15	180	14	25.4	214

As can be seen from the data of table 6, the average thickness of the sheets and the average diameter of the sheets of the boron-doped bismuth oxybromide catalyst tended to increase as the reaction temperature increased and the reaction time increased.

Finally, it should be noted that the above description is only for illustrating the technical solution of the present invention, and not for limiting the scope of the present invention, and that the technical solution of the present invention may be modified or replaced by the same simple modification by those skilled in the art without departing from the essential scope of the technical solution of the present invention.

Claims

1. A method for preparing a boron-doped bismuth oxybromide catalyst, which is characterized by comprising the following steps:

S1: Mix the aqueous solution of boric acid and the nitric acid solution of bismuth nitrate and stir to obtain solution A;

S2: Mix and stir the alkali metal bromide aqueous solution and solution A evenly to obtain solution B. The alkali metal bromide is potassium bromide or sodium bromide;

S3: Transfer solution B to an autoclave for hydrothermal reaction. After the reaction is completed, cool to obtain reaction product C;

S4: Centrifuge the reaction product C, wash with absolute ethanol, and dry to obtain a boron-doped bismuth oxybromide catalyst.

2. The preparation method of the boron-doped bismuth oxybromide catalyst as claimed in claim 1, wherein the molar ratio of boric acid to bismuth nitrate in S1 is 0.25 to 1:100.

3. The preparation method of the boron-doped bismuth oxybromide catalyst according to claim 1, wherein the molar ratio of the amount of alkali metal bromide to the amount of bismuth nitrate in S2 is 5 to 10:1.

4. The preparation method of the boron-doped bismuth oxybromide catalyst according to claim 1, characterized in that in S3, the hydrothermal reaction conditions are: temperature 150-180°C, reaction time 10-14 hours.

5. A boron-doped bismuth oxybromide catalyst, characterized in that it is prepared using the method described in any one of claims 1 to 4. The boron-doped bismuth oxybromide catalyst is in the shape of a sheet, and the average thickness of the lamellae is 18.9 ~45.3nm, and the average diameter of the lamellae is 176~331nm.

6. The application of a boron-doped bismuth oxybromide catalyst, which is characterized by comprising the following steps:

S1: Dispersing the boron-doped bismuth oxybromide catalyst according to claim 5 into absolute ethanol to obtain a catalyst suspension;

S2: Pour the catalyst suspension into a petri dish and dry to obtain a catalyst film;

S3: Place the catalyst film into a light-transmitting closed reactor, fill it with CO ₂ and water vapor, and react under sunlight or simulated sunlight.