S-type heterojunction composite photocatalyst of flower-shaped BN / TiO2 as well as preparation method and application of S-type heterojunction composite photocatalyst

Abstract

The invention discloses a flower-like BN / TiO2 S-type heterojunction composite photocatalyst and a preparation method and application thereof, the flower-like BN / TiO2 S-type heterojunction composite photocatalyst is formed by depositing a flower-like BN precursor on TiO2 particles, and an S-type heterojunction structure is formed between the flower-like BN precursor and the TiO2 particles. The preparation method comprises the following steps: S1, weighing TiO2 particles, melamine, boric acid and hexamethylenetetramine in proportion, adding into ultrapure water, carrying out mixing pretreatment, and then vacuumizing for freeze drying; and S2, drying, placing in an N2 atmosphere, carrying out high-temperature calcination at 948-952 DEG C, and naturally cooling to room temperature to obtain the flower-like BN / TiO2 S-type heterojunction composite photocatalyst. The catalyst is applied to production of ethanol by photocatalytic reduction of CO2. The photocatalytic activity of the composite photocatalyst is greatly improved, and the composite photocatalyst has stable high selectivity in ethanol production by reducing CO2.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photocatalytic materials, in particular to a flower-shaped BN / TiO2 S-type heterojunction composite photocatalyst and a preparation method and application thereof. TECHNICAL BACKGROUND

[0002] As the end product of combustion processes, the conversion of highly stable CO2 molecules into desired chemicals or fuels is a highly challenging problem. The solar-driven conversion of CO2 into C 2+ Solar fuels have attracted widespread interest as they offer a potential green route to alleviate the unprecedented pressure on global energy demand and the increasing impact of climate change.

[0003] The main products of the photocatalytic CO2 reduction reaction are currently limited to C1, such as CO, CH4, and HCOOH. The formation of valuable C 2+ The formation of products such as ethylene and ethanol remains challenging, with very low yields and selectivity. Ethanol is widely used as a clean fuel additive due to its high combustion enthalpy (-1366.8 kJ mol -1 (-1366.8 kJ mol-1), and is also used to synthesize a series of commodity chemicals. Ethanol production usually relies on the fermentation of environmentally harmful agricultural raw materials. Therefore, the use of carbon dioxide as a raw material to harvest solar radiation to produce ethanol has a significant advantage and great potential in future production.

[0004] Titanium dioxide (TiO2) is a common photocatalytic material, whose unique photocatalytic performance is not only affected by its inherent physical and chemical properties, but also by the morphology and structural properties of titanium dioxide particles. However, it has a high band gap (3.0 to 3.2 eV), so it can only absorb sunlight with a wavelength of less than 387.5 nm, limiting its utilization efficiency of visible light. Since titanium dioxide only responds to ultraviolet light, which accounts for only 5% of sunlight, the visible light, which accounts for 43% of the energy in sunlight, cannot be utilized. In order to further improve and enhance the photocatalytic activity of titanium dioxide and reduce the recombination rate of its photoelectrons and holes, ion doping, surface reduction, noble metal or metal loading, photosensitization, or the combination of different semiconductors to improve its utilization of visible light, to enhance the photocatalytic activity of titanium dioxide.

[0005] The Chinese patent document CN119897144A discloses a hexagonal boron nitride / titanium dioxide heterojunction doped material and a preparation method thereof. The material is formed by a heterojunction of hexagonal boron nitride (BN) and titanium dioxide, and the light absorption performance, carrier mobility and photocatalytic efficiency are optimized by doping nitrogen elements, iron elements and fluorine elements. The doping of nitrogen elements can reduce the band gap by introducing defect energy levels, and widen the light absorption range to the visible light and infrared light regions. The doping of iron elements can promote carrier separation by introducing intermediate energy levels. The doping of fluorine elements can reduce surface defects and inhibit carrier recombination. However, this technical solution cannot stably achieve high-selectivity photocatalytic reduction of CO2 to produce ethanol.

[0006] Therefore, it is crucial to develop a stable and high-selectivity photocatalyst for photocatalytic reduction of CO2 to produce ethanol. SUMMARY

[0007] In view of the existing problems, the present application provides a flower-shaped BN / TiO2 S-type heterojunction composite photocatalyst, which improves the photocatalytic performance of TiO2 and simultaneously realizes stable and high-selectivity photocatalytic reduction of CO2 to produce ethanol.

[0008] To solve the above technical problems, the technical solution adopted by the present application is as follows: the catalyst is formed by depositing flower-shaped BN precursors on TiO2 particles, and an S-type heterojunction structure is formed between the flower-shaped BN precursors and the TiO2 particles.

[0009] By using the above technical solution, the flower-shaped BN precursors are used to disperse TiO2 nanoparticles, thereby inhibiting the agglomeration of TiO2 nanoparticles; and the effective contact of the binary photocatalyst is increased, and more reaction active sites are exposed. This technical solution selects two photocatalysts (BN and TiO2) with matched band gaps, forms a built-in electric field between the two, promotes the separation of electrons and holes in the photo-generated carriers produced by BN and TiO2, avoids carrier recombination, enhances the redox capacity of the system and the electron density of the reaction active center, and thus further improves the photocatalytic performance. That is, the flower-shaped BN has high chemical stability, thermal stability, wide band gap, biocompatibility and environmental friendliness, which can effectively make up for the shortcomings of traditional photocatalytic materials. By constructing a heterojunction, the energy band can be adjusted, the light absorption range can be widened, and the light absorption capacity can be enhanced. In addition, due to the built-in electric field formed by the difference in energy band structure, photo-generated electrons will migrate from the conduction band of TiO2 to the conduction band of the flower-shaped BN, and photo-generated holes will migrate from the valence band of the flower-shaped BN to the valence band of TiO2. This can improve the separation efficiency of photo-generated carriers, thereby significantly improving the light absorption efficiency and catalytic activity of the photocatalytic material.

[0010] Preferably, the formula of the flower-shaped BN precursor is 0.125-0.127 g of melamine, 0.123-0.125 g of boric acid, and 0.69-0.71 g of hexamethylenetetramine.

[0011] Preferably, the amount of the TiO2 particles is 0.01-0.07 g.

[0012] Preferably, the mass ratio of the TiO2 particles to the flower-shaped BN is 10%-50%.

[0013] Preferably, the amount of the TiO2 particles is 0.0399 g, and the mass ratio of the TiO2 particles to the flower-shaped BN is 30%.

[0014] The application also provides a preparation method of the flower-shaped BN / TiO2 S-type heterojunction composite photocatalyst.

[0015] To solve the above technical problems, the application adopts the technical scheme of the preparation method of the flower-shaped BN / TiO2 S-type heterojunction composite photocatalyst, which specifically comprises the following steps:

[0016] S1: TiO2 particles, melamine, boric acid, and hexamethylenetetramine are weighed according to the proportion, added into ultrapure water, mixed and pretreated, and then vacuumized to less than or equal to 1.0 Pa and freeze-dried;

[0017] S2: After drying, the mixture is placed in an N2 atmosphere, high-temperature calcined at 948-952 ℃, and naturally cooled to room temperature to obtain the flower-shaped BN / TiO2 S-type heterojunction composite photocatalyst.

[0018] Preferably, the specific steps of the step S1 are as follows:

[0019] S11: 0.125-0.127 g of melamine, 0.123-0.125 g of boric acid, 0.69-0.71 g of hexamethylenetetramine, and 0.01-0.07 g of TiO2 particles are weighed respectively and added into a beaker with 50 mL of ultrapure water;

[0020] S12: First, stirred in a water bath at 75-80 ℃ for 18-20 min; then stirred at 20-25 ℃ for 10-12 min; then placed in an ice water bath and stirred for 3 min; and finally placed in liquid nitrogen and frozen for 10-12 min;

[0021] S13: Finally, the frozen mixture is vacuumized to less than or equal to 1.0 Pa for continuous drying for 96 h.

[0022] Preferably, in the step S2, the flow rate of the N2 atmosphere is 180-200 mL / min, and the temperature is first kept at 20-25 DEG C for 25-35 min, the air in the tube furnace is evacuated, then the temperature of the tube furnace is raised to 948-952 DEG C at a rate of 5 DEG C / min, and then the calcination is performed at 948-952 DEG C for 3 h, and then the temperature is naturally lowered to room temperature, thereby obtaining the S-type heterojunction composite photocatalyst of flower-like BN / TiO2.

[0023] The application further provides an application of the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in photocatalytic reduction of CO2 to produce ethanol.

[0024] Preferably, the specific steps of the application of the catalyst are as follows: 8-12 mg of the catalyst and 10-12 mL of ultrapure water are added into a reaction device, the device is vacuumized to less than 3 Pa, then 1 atm of high-purity CO2 gas is introduced, a 300 W xenon lamp is turned on as an illumination light source, and the photocatalytic reduction of CO2 to produce ethanol is realized.

[0025] Compared with the prior art, the application has the beneficial effects that:

[0026] (1) The flower-like BN disperses the TiO2 nanoparticles, thereby inhibiting the agglomeration of the TiO2 nanoparticles, increasing the effective contact of the binary photocatalyst, and exposing more reaction active sites, i.e., significantly exposing the high-efficiency reaction sites;

[0027] (2) The two photocatalysts with matched band gaps are selected, a built-in electric field is formed between the two photocatalysts through the good contact of the two photocatalysts, the separation of the electrons and holes in the photo-generated carriers generated by the BN and TiO2 is promoted, the oxidation-reduction capacity of the system and the electron density of the reaction active center are increased while avoiding the recombination of the carriers, and thus the photocatalytic performance is further improved; i.e., the photocatalyst inhibits the recombination of the photo-generated electrons and holes, prolongs the lifetime of the photo-generated carriers, and thus improves the catalytic efficiency;

[0028] (3) In the application of photocatalytic reduction of CO2, the photocatalytic reduction of CO2 to produce ethanol is realized with high activity and high selectivity, which contributes to the resource utilization of CO2; i.e., under the condition of no sacrificial agent, the photocatalyst exhibits good photocatalytic activity and high selectivity, the yield of ethanol is about 51.1784 μmol g -1 h -1 , the electronic selectivity of ethanol is as high as about 99%, and the system has good stability; meanwhile, the absence of the sacrificial agent can greatly reduce the cost;

[0029] (4) The preparation method is simple in operation and good in repeatability, has great potential in future production, develops a stable and high-selectivity photocatalyst for photocatalytic reduction of CO2 to produce ethanol, and the selected materials are non-toxic and non-polluting, and simple to synthesize and easy to operate, meeting the environmental protection requirements. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the XRD pattern of the flower-like BN monomer catalyst in blank example 1, the TiO2 monomer catalyst in blank example 2 and the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in specific example 1 in the present application;

[0031] Figure 2 is the scanning electron microscope pattern of the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in specific example 1 in the present application;

[0032] Figure 3 is the transmission electron microscope pattern of the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in specific example 1 in the present application;

[0033] Figure 4 is the high-resolution transmission electron microscope pattern of the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in specific example 1 in the present application;

[0034] Figure 5 is the performance rate graph of photocatalytic reduction of CO2 of the monomer photocatalyst in blank examples 1-2 and the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in specific example 1 in the present application;

[0035] Figure 6 is the performance selectivity graph of photocatalytic reduction of CO2 of the monomer photocatalyst in blank examples 1-2 and the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in specific example 1 in the present application;

[0036] Figure 7 is the performance rate graph of photocatalytic reduction of CO2 of the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 with different proportions of TiO2 particles loaded in specific examples 1-5 in the present application;

[0037] Figure 8 is the mechanism of photocatalytic reduction of CO2 to produce ethanol realized by the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in specific examples 1-5 in the present application. DETAILED DESCRIPTION

[0038] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0039] Embodiment: The catalyst is formed by depositing flower-like BN precursors on TiO2 particles, and an S-type heterojunction structure is formed between the flower-like BN precursors and the TiO2 particles; the formula of the flower-like BN precursors is as follows: melamine 0.125-0.127 g, boric acid 0.123-0.125 g, and hexamethylenetetramine 0.69-0.71 g; the amount of the TiO2 particles is 0.01-0.07 g; and the mass fraction of the TiO2 particles and the flower-like BN is 10%-50%.

[0040] Preferably, the amount of the TiO2 particles is 0.0399 g; and the mass fraction of the TiO2 particles and the flower-like BN is 30%. Since the TiO2 particles are the matrix and do not participate in the reaction, the mass remains unchanged before and after the reaction. Therefore, the mass of the flower-like BN loaded on the TiO2 particles can be obtained by subtracting the mass of the TiO2 particles in the raw materials from the total mass of the product obtained after the reaction, so as to calculate the mass ratio of the TiO2 particles and the flower-like BN.

[0041] The preparation method of the S-type heterojunction composite photocatalyst of the flower-like BN / TiO2 specifically includes the following steps:

[0042] S1: The TiO2 particles, melamine, boric acid and hexamethylenetetramine are weighed according to the proportion, added into ultrapure water, mixed and pretreated, and then vacuum freeze-dried;

[0043] The specific steps of the step S1 are as follows:

[0044] S11: 0.125-0.127 g of melamine, 0.123-0.125 g of boric acid, 0.69-0.71 g of hexamethylenetetramine and 0.01-0.07 g of TiO2 particles are weighed respectively and added into a beaker with 50 mL of ultrapure water;

[0045] S12: First, stirring is performed in a water bath at 80°C for 20 min; then stirring is performed at 25°C for 10 min; then the mixture is placed in an ice water bath for stirring for 3 min, and finally the mixture is placed in liquid nitrogen for freezing for 10 min;

[0046] S13: Finally, the frozen mixture is vacuumed to less than or equal to 1.0 Pa for continuous drying for 96 h.

[0047] S2: After drying, high-temperature calcination was carried out at 948-952℃ under N2 atmosphere, and the natural cooling to room temperature obtained the S-type heterojunction composite photocatalyst of flower-like BN / TiO2;

[0048] In the step S2, under N2 atmosphere, the gas flow was 200 mL / min, first incubated at 25℃ for 30 min, evacuated the air in the tube furnace, then the temperature of the tube furnace was raised to 950℃ at a rate of 5℃ / min, and then the natural cooling to room temperature 25℃ after calcination at 950℃ for 3h, to obtain the S-type heterojunction composite photocatalyst of flower-like BN / TiO2.

[0049] The application of the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in photocatalytic reduction of CO2 to produce ethanol, the specific steps are: adding 10 mg of catalyst and 10 mL of ultrapure water in the reaction device, vacuuming to less than 3.0 Pa, then introducing 1 atmosphere of high-purity CO2 gas, turning on the 300W xenon lamp as the illumination light source, to realize the photocatalytic reduction of CO2 to produce ethanol.

[0050] The following will be further described by two blank comparative examples and five specific examples; the normal temperature or room temperature in these examples refers to 25℃.

[0051] Blank Example 1: This example is the preparation of monomer flower-like BN photocatalyst, the specific steps are:

[0052] S1: Taking 0.126g of melamine, 0.124g of boric acid, 0.7g of hexamethylenetetramine and 50mL of ultrapure water into a 100mL beaker, under 80℃ water bath, stirring for 20min, then stirring at room temperature for 10min, then putting into ice water bath for 3min, finally putting into liquid nitrogen for 10min; then vacuum drying to less than or equal to 1.0 Pa, and then continuously drying for 96h;

[0053] S2: Finally, under N2 atmosphere, the gas flow was 200 mL / min, first incubated at room temperature for 30 min to evacuate the air in the tube furnace, then raised to 950℃ at a rate of 5℃ / min, and then the natural cooling to room temperature 25℃ after calcination at 950℃ for 3h, to obtain the flower-like BN monomer photocatalyst (marked as BNF).

[0054] The obtained monomer flower-like BN photocatalyst was subjected to photocatalytic reduction of CO2 performance test. The specific steps were as follows: 10 mg of the above catalyst was ultrasonically dispersed in 10 mL of ultrapure water, the reaction device was vacuumed to less than 3 Pa, then 1 atm of high-purity CO2 gas was introduced, a 300 W xenon lamp equipped with a filter was turned on as an irradiation light source, after 5 h of reaction, the reaction solution was collected, and the production amount of ethanol was calculated by integrating the area of the ethanol triplet peak in the hydrogen nuclear magnetic resonance spectrum.

[0055] Blank Example 2: This example was for preparing a monomer TiO2 photocatalyst. The specific steps were as follows: 1 g of TiO2 (P25) was placed in a porcelain boat, under N2 atmosphere, the gas flow was 200 mL / min, the temperature was first kept at room temperature for 30 min to exhaust the air in the tube furnace, then the temperature was raised to 950 ℃ at a rate of 5 ℃ / min, after calcination at 950 ℃ for 3 h, the temperature was naturally lowered to room temperature, and a high-temperature calcined monomer TiO2 photocatalyst (denoted as TiO2) was obtained.

[0056] The obtained monomer TiO2 photocatalyst was subjected to photocatalytic reduction of CO2 performance test, and the specific process was the same as that of blank example 1.

[0057] Specific Example 1: An S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 30% TiO2 by mass fraction was prepared. The specific steps were as follows:

[0058] S1: 0.0399 g of P25, 0.126 g of melamine, 0.124 g of boric acid, 0.7 g of hexamethylenetetramine and 50 mL of ultrapure water were placed in a 100 mL beaker, stirred under a water bath at 80 ℃ for 20 min, then stirred at room temperature for 10 min, then placed in an ice water bath and stirred for 3 min, and finally placed in liquid nitrogen and frozen for 10 min; then vacuum dried to less than or equal to 1 Pa, and continuously dried for 96 h;

[0059] S2: Finally, under N2 atmosphere, the gas flow was 200 mL / min, the temperature was first kept at room temperature for 30 min to exhaust the air in the tube furnace, then the temperature was raised to 950 ℃ at a rate of 5 ℃ / min, after calcination at 950 ℃ for 3 h, the temperature was naturally lowered to room temperature, and an S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 30% TiO2 by mass fraction (denoted as B-30T) was obtained.

[0060] The obtained S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 30% TiO2 by mass fraction was subjected to photocatalytic reduction of CO2 performance test. The specific process was the same as that of blank example 1.

[0061] Specific Example 2: An S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 10% TiO2 by mass fraction was prepared. The specific steps were as follows:

[0062] S1: take 0.0133g P25, 0.126g melamine, 0.124g boric acid, 0.7g hexamethylenetetramine and 50mL ultrapure water into a 100mL beaker, under 80℃ water bath, stir for 20min, then stir for 10min at room temperature, then put into ice water bath and stir for 3min, finally put into liquid nitrogen and freeze for 10min, then freeze-drying, vacuum to less than or equal to 1Pa, and then continue drying for 96h;

[0063] S2: finally under N2 atmosphere, the gas flow is 200 mL / min, the temperature is first at room temperature for 30min to exhaust the air in the tube furnace, then heated to 950℃ at a rate of 5℃ / min, calcined at 950℃ for 3h, then naturally cooled to room temperature, to obtain the S-type heterojunction composite photocatalyst of 10% TiO2 loaded flower-like BN / TiO2 (marked as B-10T).

[0064] The obtained S-type heterojunction composite photocatalyst of 10% TiO2 loaded flower-like BN / TiO2 is subjected to photocatalytic reduction of CO2 performance test process: the specific process is the same as blank example 1.

[0065] Specific embodiment 3: preparation of S-type heterojunction photocatalyst of 20% TiO2 loaded flower-like BN / TiO2, the specific steps are:

[0066] S1: take 0.0266g P25, 0.126g melamine, 0.124g boric acid, 0.7g hexamethylenetetramine and 50mL ultrapure water into a 100mL beaker, under 80℃ water bath, stir for 20min, then stir for 10min at room temperature, then put into ice water bath and stir for 3min, finally put into liquid nitrogen and freeze for 10min, then freeze-drying, vacuum to less than or equal to 1Pa, and then continue drying for 96h;

[0067] S2: finally under N2 atmosphere, the gas flow is 200 mL / min, the temperature is first at room temperature for 30min to exhaust the air in the tube furnace, then heated to 950℃ at a rate of 5℃ / min, calcined at 950℃ for 3h, then naturally cooled to room temperature, to obtain the S-type heterojunction composite photocatalyst of 20% TiO2 loaded flower-like BN / TiO2 (marked as B-20T).

[0068] The obtained S-type heterojunction composite photocatalyst of 20% TiO2 loaded flower-like BN / TiO2 is subjected to photocatalytic reduction of CO2 performance test process: the specific process is the same as blank example 1.

[0069] Specific embodiment 4: preparation of S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 40% TiO2 by mass fraction, the specific steps are as follows:

[0070] S1: 0.0532 g of P25, 0.126 g of melamine, 0.124 g of boric acid, 0.7 g of hexamethylenetetramine and 50 mL of ultrapure water were weighed into a 100 mL beaker, stirred under a water bath at 80°C for 20 min, then stirred at room temperature for 10 min, then put into an ice water bath and stirred for 3 min, finally put into liquid nitrogen and freeze for 10 min, then freeze-dried under vacuum to less than or equal to 1 Pa, and then continuously dried for 96 h;

[0071] S2: Finally, under N2 atmosphere, the gas flow is 200 mL / min, the temperature is first kept at room temperature for 30 min to exhaust the air in the tube furnace, then heated to 950°C at a heating rate of 5°C / min, and then naturally cooled to room temperature after calcination at 950°C for 3 h, to obtain S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 40% TiO2 by mass fraction (marked as B-40T).

[0072] The obtained S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 40% TiO2 by mass fraction was tested for photocatalytic reduction of CO2 performance: the specific process is the same as that of blank embodiment 1.

[0073] Specific embodiment 5: preparation of S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 50% TiO2 by mass fraction, the specific steps are as follows:

[0074] S1: 0.0665 g of P25, 0.126 g of melamine, 0.124 g of boric acid, 0.7 g of hexamethylenetetramine and 50 mL of ultrapure water were weighed into a 100 mL beaker, stirred under a water bath at 80°C for 20 min, then stirred at room temperature for 10 min, then put into an ice water bath and stirred for 3 min, finally put into liquid nitrogen and freeze for 10 min, then freeze-dried under vacuum to less than or equal to 1 Pa, and then continuously dried for 96 h;

[0075] S2: Finally, under N2 atmosphere, the gas flow is 200 mL / min, the temperature is first kept at room temperature for 30 min to exhaust the air in the tube furnace, then heated to 950°C at a heating rate of 5°C / min, and then naturally cooled to room temperature after calcination at 950°C for 3 h, to obtain S-type heterojunction composite photocatalyst of flower-like BN / TiO2 loaded with 50% TiO2 by mass fraction (marked as B-50T).

[0076] The obtained mass fraction 50% TiO2-loaded flower-like BN / TiO2 S-type heterojunction composite photocatalyst was subjected to a photocatalytic reduction of CO2 performance test process: the specific process was the same as that of blank example 1.

[0077] The structure and performance of blank examples 1-2 and specific examples 1-5 were analyzed below in combination with the drawings.

[0078] Figure 1 is the XRD pattern of the flower-like BN monomer photocatalyst of blank example 1, the TiO2 monomer photocatalyst of blank example 2 and the flower-like BN / TiO2 S-type heterojunction composite photocatalyst in specific example 1; the obtained composite material has characteristic peaks of both flower-like BN and TiO2, wherein the peak at 27.45° represents the (110) crystal face of rutile TiO2, and the peak at 36.5° represents the (101) crystal face of rutile TiO2; the XRD result shows that the composite material is composed of flower-like BN and TiO2.

[0079] Figure 2 is the scanning electron microscope pattern of the flower-like BN / TiO2 S-type heterojunction composite photocatalyst in specific example 1, from which it can be seen that the flower-like BN disperses the TiO2 nanoparticles and inhibits the agglomeration of the TiO2 nanoparticles. Figure 2

[0080] Figure 3 is the transmission electron microscope pattern of the flower-like BN / TiO2 S-type heterojunction composite photocatalyst in specific example 1; from it can be found that the flower-like BN and TiO2 nanoparticles are well combined and form a heterojunction structure. Figure 3

[0081] Figure 4 is the high-resolution transmission electron microscope pattern of the flower-like BN / TiO2 S-type heterojunction composite photocatalyst in specific example 1, wherein the lattice fringe spacing of 0.327 nm is the (110) crystal face of rutile TiO2, and the lattice fringe spacing of 0.334 nm is the (002) crystal face of boron nitride BN. Through it can be further proved that the flower-like BN and TiO2 nanoparticles are in good contact, and the heterojunction structure is formed. Figure 4

[0082] Figure 5 is the performance rate diagram of photocatalytic reduction of CO2 of the flower-like BN monomer photocatalyst of blank example 1, the TiO2 monomer photocatalyst of blank example 2 and the flower-like BN / TiO2 S-type heterojunction composite photocatalyst in specific example 1; the flower-like BN / TiO2 S-type heterojunction composite photocatalyst can realize photocatalytic reduction of CO2 to produce ethanol, and the rate is as high as ~51.1784 μmol g -1 h -1 ​​​.

[0083] Figure 6 is a performance selectivity graph of photocatalytic reduction of CO2 of the flower-like BN monomer photocatalyst of blank example 1, the TiO2 monomer photocatalyst of blank example 2 and the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 in specific embodiment 1, from Figure 6 It can be seen from the figure that the selectivity of the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 for producing ethanol is as high as ~99%.

[0084] Figure 7 is a performance rate graph of photocatalytic reduction of CO2 of the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 with different proportions of TiO2 particles loaded in specific embodiments 1-5, from Figure 7 It can be seen from the figure that the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 with 30% TiO2 loaded has the highest reaction activity.

[0085] Figure 8 is a mechanism of realizing photocatalytic reduction of CO2 to produce ethanol in specific embodiments 1-5; through construction of the S-type heterojunction, the environments of oxidation and reduction reactions are separated, and the recombination of photo-generated electron-hole pairs is successfully inhibited by using the built-in electric field formed, realizing efficient use of photo-generated electrons and production of ethanol.

[0086] For those skilled in the art, the specific embodiments are only exemplary descriptions of the present application, and it is obvious that the specific implementation of the present application is not limited by the above-mentioned modes, as long as various non-essential improvements are made by using the method concept and technical solution of the present application, such as replacing the mass of a certain substance or a certain reaction parameter, or directly applying the concept and technical solution of the present application to other occasions without improvement, which are all within the protection scope of the present application.

Claims

1. A flower-like BN / TiO2 S-type heterojunction composite photocatalyst, characterized in that, The catalyst is formed by depositing flower-like BN precursors on TiO2 particles, and an S-type heterojunction structure is formed between the flower-like BN precursors and the TiO2 particles. 2.The flower-like BN / TiO2 S-type heterojunction composite photocatalyst of claim 1, wherein The formula of the flower-like BN precursors is as follows: 0.125-0.127 g of melamine, 0.123-0.125 g of boric acid, and 0.69-0.71 g of hexamethylenetetramine. 3.The flower-like BN / TiO2 S-type heterojunction composite photocatalyst of claim 1, characterized in that, The amount of the TiO2 particles is 0.01-0.07 g. 4.The flower-like BN / TiO2 S-type heterojunction composite photocatalyst of claim 3, characterized in that, The mass ratio of the TiO2 particles to the flower-like BN is 10%-50%. 5.The flower-like BN / TiO2 S-type heterojunction composite photocatalyst of claim 4, characterized in that, The amount of the TiO2 particles is 0.0399 g, and the mass ratio of the TiO2 particles to the flower-like BN is 30%.

6. A method for preparing a flower-like BN / TiO2 S-type heterojunction composite photocatalyst, characterized in that, Specifically, the following steps are included: S1: The TiO2 particles, melamine, boric acid, and hexamethylenetetramine are weighed in proportion, added to ultrapure water, and mixed for pretreatment, followed by vacuum freezing drying; S2: After drying, the mixture is placed in an N2 atmosphere, high-temperature calcination is performed at 948-952 ℃, and the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 is obtained after natural cooling to room temperature.

7. The method for preparing the flower-like BN / TiO2 S-type heterojunction composite photocatalyst according to claim 6, characterized in that, The specific steps of S1 are as follows: S11: 0.125-0.127 g of melamine, 0.123-0.125 g of boric acid, 0.69-0.71 g of hexamethylenetetramine, and 0.01-0.07 g of TiO2 particles are weighed and added to a beaker containing 50 mL of ultrapure water; S12: Stirring is performed in a water bath at 75-80 ℃ for 18-20 min, stirring is performed at 20-25 ℃ for 10-12 min, then the mixture is placed in an ice water bath for stirring for 3 min, and finally the mixture is frozen in liquid nitrogen for 10-12 min; S13: Finally, the frozen mixture is vacuumed to less than or equal to 1.0 Pa for continuous drying for 96 h.

8. The method for preparing the flower-like BN / TiO2 S-type heterojunction composite photocatalyst according to claim 6, characterized in that, In S2, the gas flow rate under N2 atmosphere is 180-200 mL / min, the temperature is first kept at 20-25 ℃ for 25-35 min to evacuate the air in the tube furnace, then the temperature of the tube furnace is raised to 948-952 ℃ at a rate of 5 ℃ / min, and the S-type heterojunction composite photocatalyst of flower-like BN / TiO2 is obtained after natural cooling to room temperature after calcination at 948-952 ℃ for 3 h.

9. The S-type heterojunction composite photocatalyst of flower-like BN / TiO2 according to any one of claims 1-5 is used in photocatalytic reduction of CO2 to produce ethanol. 10.The application of the flower-like BN / TiO 2 S-type heterojunction composite photocatalyst according to claim 9, characterized in that, The specific steps of the application of the catalyst are as follows: 8-12 mg of the catalyst and 10-12 mL of ultrapure water are added to a reaction device, vacuum is applied to less than 3 Pa, 1 atm of high-purity CO2 gas is introduced, a 300 W xenon lamp is turned on as an illumination light source, and photocatalytic reduction of CO2 to produce ethanol is achieved.

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