Nitrogen-doped BiOBr and its preparation method and application

Abstract

The present invention belongs to the field of semiconductor technology, and particularly relates to a nitrogen-doped BiOBr, a preparation method thereof and an application thereof. The nitrogen-doped BiOBr provided by the present invention can significantly improve the photocatalytic activity of BiOBr through various channels, and further significantly improve the ability of BiOBr to photocatalytically reduce CO2 to CO, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to nitrogen-doped BiOBr and a preparation method and application thereof. Background Art

[0002] At present, photocatalyst technology is widely used in the fields of organic pollutant degradation, photocatalytic water splitting to produce hydrogen, solar cells, etc. The development of efficient photocatalysts is the key factor in determining whether photocatalytic technology is feasible.

[0003] BiOX (X=F, Cl, Br, I) is a new type of photocatalyst, and its unique layered structure is conducive to the separation of photogenerated electrons and holes. Among them, BiOBr has a band gap of about 2.9eV and can effectively absorb visible light.

[0004] However, the photocatalytic activity of single BiOBr still needs to be further improved. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the photocatalytic activity of single BiOBr in the prior art is still low, thereby providing a nitrogen-doped BiOBr and a preparation method and application thereof.

[0006] To this end, the present invention provides the following technical solutions.

[0007] In a first aspect, the present invention provides a nitrogen-doped BiOBr, wherein N 3- Replace O 2- incorporated into the BiOBr structure, and / or, in N 3- The gaps between them are doped with [Bi2O2] 2+ .

[0008] In an optional embodiment, in the nitrogen-doped BiOBr, N 3- The incorporation amount is 8.73%~14.81%.

[0009] In an optional embodiment, in the XRD spectrum of the nitrogen-doped BiOBr, the 2θ value of the diffraction peak of the (102) plane is 31.691° to 31.660°, and the 2θ value of the diffraction peak of the (110) plane is 32.217° to 32.177°;

[0010] And / or, in the transmission electron microscope image of the nitrogen-doped BiOBr, the lattice spacing corresponding to the {102} crystal plane is 0.284 nm.

[0011] In a second aspect, the present invention provides a method for preparing the above-mentioned nitrogen-doped BiOBr, comprising the following steps:

[0012] S1. Contacting a bismuth nitrate raw material, urea and 2-bromoethylamine hydrobromide with each other, heating them until they melt, and obtaining an ionic liquid; wherein, based on bismuth nitrate, the molar ratio of the bismuth nitrate raw material, urea and 2-bromoethylamine hydrobromide is 1:(1.1-2):1;

[0013] S2. Continue to heat the ionic liquid obtained in step S1 until a self-ignition reaction occurs.

[0014] In an optional embodiment, in step S1, the heating temperature for heating to melt is 495°C to 505°C.

[0015] In an optional embodiment, the bismuth nitrate raw material includes bismuth nitrate and / or a bismuth nitrate precursor; the bismuth nitrate precursor includes Bi(NO3)3•5H2O.

[0016] In an optional embodiment, the preparation method further comprises the step of continuing to heat the solid sample obtained by the autocombustion reaction.

[0017] In an optional embodiment, the conditions for continuing heating include: a heating temperature of 499° C. to 501° C. and a heating time of 4 h.

[0018] In a third aspect, the present invention provides the use of the above nitrogen-doped BiOBr in the preparation of a photocatalyst.

[0019] In a fourth aspect, the present invention provides the use of the above-mentioned nitrogen-doped BiOBr in photocatalytic CO2 reduction.

[0020] The technical solution of the present invention has the following advantages:

[0021] The nitrogen-doped BiOBr provided by the present invention can significantly improve the photocatalytic activity of BiOBr through nitrogen doping in multiple ways, thereby significantly improving the ability of BiOBr to photocatalytically reduce CO2 to CO, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1is a graph of the X-ray diffraction analysis results in test example (1) of the present invention; wherein (a) is the XRD spectrum of each target product, and (b) is the XRD spectrum after partial enlargement of (a);

[0024] Figure 2 1 is a transmission electron microscopy analysis result diagram of test example (2) of the present invention; wherein (a) and (b) are TEM images of the target product of the comparative example and the target product of Example 3, respectively, and (c) and (d) are HRTEM images of the target product of the comparative example and the target product of Example 3, respectively;

[0025] Figure 3 1 is an element mapping analysis result diagram of the test example (3) of the present invention; wherein (a) is a Bi element mapping diagram, (b) is a Br element mapping diagram, (c) is an O element mapping diagram, and (d) is an N element mapping diagram;

[0026] Figure 4 is a graph of the electron spin resonance analysis results in test example (4) of the present invention;

[0027] Figure 5 is a graph of transient fluorescence analysis results in test example (5) of the present invention;

[0028] Figure 6 is a graph showing the UV-visible diffuse reflectance analysis results in test example (6) of the present invention; wherein (a) is a UV-visible diffuse reflectance spectrum (DRS), and (b) is a graph showing the band gap (Eg) analysis results based on the UV-visible diffuse reflectance spectrum;

[0029] Figure 7 is a graph of the solid fluorescence analysis results in test example (7) of the present invention;

[0030] Figure 8 is a photocurrent analysis result diagram in test example (8) of the present invention;

[0031] Fig. 9 is a dark impedance analysis result diagram in test example (9) of the present invention;

[0032] Fig.10 is a graph of the X-ray photoelectron spectroscopy analysis results in Test Example (10) of the present invention; wherein (a) is a high-resolution Bi 4f XPS spectrum of the target product of the comparative example and the target product of Example 3, (b) is a Br 3d spectrum of the target product of the comparative example and the target product of Example 3, (c) is an O 1s spectrum of the target product of the comparative example and the target product of Example 3, and (d) is a N1s spectrum of the target product of the comparative example and the target product of Example 3;

[0033] Fig.11 is a graph of the Mott-Schottky test results in test example (11) of the present invention;

[0034] Fig.12 is the energy band structure diagram obtained by testing in test example (12) of the present invention;

[0035] Fig.13 It is a graph of the photocatalytic CO2 reduction experiment results in the test example (13) of the present invention; wherein, (a) and (b) are line graphs showing the change in CO generation over time for different samples after 4 hours of Xe lamp irradiation and a bar graph showing the average CO generation rate; (c) and (d) are comparison graphs of the photocatalytic reduction CO2 activity experiment of the target product sample of Example 3 and the target product sample of the comparative example. DETAILED DESCRIPTION

[0036] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0037] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially. Example 1

[0038] Nitrogen-doped BiOBr was prepared as follows:

[0039] (1) Mix 3 mmol of Bi(NO3)3•5H2O, 3 mmol of C2H7Br2N and 3.3 mmol of CO(NH2)2, and heat them to 500 °C in an electric furnace to gradually melt them into an ionic liquid;

[0040] In this step, the molar ratio of Bi(NO3)3•5H2O, CO(NH2)2 and C2H7Br2N is 1:1.1:1, using bismuth nitrate as reference;

[0041] (2) continuing to heat the ionic liquid obtained in step (1) so that the ionic liquid undergoes a self-ignition reaction to obtain a solid sample;

[0042] (3) The solid sample obtained in step (2) was further heated in a muffle furnace at 500 °C for 4 h to obtain the target product.

[0043] After testing, the target product prepared in this example has N 3- The incorporation amount is 8.73%. Example 2

[0044] Nitrogen-doped BiOBr was prepared as follows:

[0045] (1) Mix 3 mmol of Bi(NO3)3•5H2O, 3 mmol of C2H7Br2N and 3.9 mmol of CO(NH2)2, and heat them to 500 °C in an electric furnace to gradually melt them into an ionic liquid;

[0046] In this step, the molar ratio of Bi(NO3)3•5H2O, CO(NH2)2 and C2H7Br2N is 1:1.3:1, using bismuth nitrate as reference;

[0047] (2) continuing to heat the ionic liquid obtained in step (1) so that the ionic liquid undergoes a self-ignition reaction to obtain a solid sample;

[0048] (3) The solid sample obtained in step (2) was further heated in a muffle furnace at 500 °C for 4 h to obtain the target product.

[0049] After testing, the target product prepared in this example has N 3- The incorporation amount is 10.15%. Example 3

[0050] Nitrogen-doped BiOBr was prepared as follows:

[0051] (1) Mix 3 mmol of Bi(NO3)3•5H2O, 3 mmol of C2H7Br2N and 4.5 mmol of CO(NH2)2, and heat them to 500 °C in an electric furnace to gradually melt them into an ionic liquid;

[0052] In this step, the molar ratio of Bi(NO3)3•5H2O, CO(NH2)2 and C2H7Br2N is 1:1.5:1, using bismuth nitrate as reference;

[0053] (2) continuing to heat the ionic liquid obtained in step (1) so that the ionic liquid undergoes a self-ignition reaction to obtain a solid sample;

[0054] (3) The solid sample obtained in step (2) was further heated in a muffle furnace at 500 °C for 4 h to obtain the target product.

[0055] After testing, the target product prepared in this example has N 3- The incorporation amount is 11.54%. Example 4

[0056] Nitrogen-doped BiOBr was prepared as follows:

[0057] (1) Mix 3 mmol of Bi(NO3)3•5H2O, 3 mmol of C2H7Br2N and 6 mmol of CO(NH2)2, and heat them to 500 °C in an electric furnace to gradually melt them into an ionic liquid;

[0058] In this step, the molar ratio of Bi(NO3)3•5H2O, CO(NH2)2 and C2H7Br2N is 1:2:1, using bismuth nitrate as reference;

[0059] (2) continuing to heat the ionic liquid obtained in step (1) so that the ionic liquid undergoes a self-ignition reaction to obtain a solid sample;

[0060] (3) The solid sample obtained in step (2) was further heated in a muffle furnace at 500 °C for 4 h to obtain the target product.

[0061] After testing, the target product prepared in this example has N 3- The incorporation amount is 14.81%.

[0062] Comparative Example

[0063] Nitrogen-doped BiOBr was prepared as follows:

[0064] (1) Mix 3 mmol of Bi(NO3)3•5H2O, 3 mmol of C2H7Br2N and 3 mmol of CO(NH2)2, and heat them to 500 °C in an electric furnace to gradually melt them into an ionic liquid;

[0065] In this step, the molar ratio of Bi(NO3)3•5H2O, CO(NH2)2 and C2H7Br2N is 1:1:1, taking bismuth nitrate as reference;

[0066] (2) continuing to heat the ionic liquid obtained in step (1) so that the ionic liquid undergoes a self-ignition reaction to obtain a solid sample;

[0067] (3) The solid sample obtained in step (2) was further heated in a muffle furnace at 500 °C for 4 h to obtain the target product.

[0068] Test Case

[0069] (1) X-ray diffraction analysis

[0070] X-ray diffraction analysis was performed on the target products prepared in Examples 1-4 and the comparative example, and the results were as follows: Figure 1 As shown, (a) is the XRD spectrum of each target product, and (b) is the XRD spectrum after local enlargement in (a).

[0071] Depend on Figure 1 It can be seen that the 2θ value is 10.9 ◦ , 25.1 ◦ , 31.7 ◦ , 32.2 ◦ , 39.4 ◦ , 46.2 ◦ and 57.2 ◦ The diffraction peaks correspond to the (001), (101), (102), (110), (112), (200) and (212) planes. By comparison, it was found that a series of diffraction peaks matched well with the standard card (PDF#09-0393), and no impurity peaks were observed, indicating that the prepared sample had high purity (a), the photocatalyst material was successfully prepared, and the high diffraction peaks indicated good crystallinity.

[0072] The enlarged XRD spectrum (b) shows that the diffraction peaks of the (102) and (110) planes of the target product of the comparative example have not shifted, which indicates that the target product of the comparative example has not been doped with nitrogen. In the target products of Examples 1-4, as the amount of urea increases, the diffraction peaks of the (102) and (110) planes of the target products shift toward lower 2θ values, which indicates that nitrogen doping exists in the target products of Examples 1-4. Nitrogen doping leads to N 3- Replaced some O 2- , or N 3- The gaps between them are doped with [Bi2O2] 2+ According to the Bragg equation, when N 3- The ionic radius (1.71 Å) is larger than that of O 2- When the ionic radius (1.40 Å) of BiOBr is increased, the interplanar spacing of BiOBr increases, resulting in a decrease in the 2θ position.

[0073] (2) Transmission electron microscopy analysis

[0074] The target products obtained in Example 3 and the comparative example were analyzed by transmission electron microscopy. The analysis results are as follows: Figure 2 Wherein, (a) and (b) are TEM images of the target product of the comparative example and the target product of Example 3, respectively, and (c) and (d) are HRTEM images of the target product of the comparative example and the target product of Example 3, respectively.

[0075] As can be seen from (a) and (b), the sheet thickness of the target product of Example 3 is thinner than that of the target product of the comparative example, which indicates that after N doping, the sheet thickness of the prepared target product can be reduced, significantly shortening the distance for electrons to escape to the surface of the material, thereby better improving the performance of the material in photocatalytic reduction of CO2. In (c) and (d), the lattice spacing of the {102} crystal plane of the target product of the comparative example is 0.282 nm, and the lattice spacing of the {102} crystal plane of the target product of Example 3 is 0.284 nm, which further confirms the successful preparation of the BiOBr photocatalyst. It is also worth noting that the lattice spacing of the target product of Example 3 is greater than that of the target product of the comparative example, which indicates that the lattice constant of the target product of Example 3 becomes smaller, confirming that N is successfully doped into the unit cell of the target product of Example 3.

[0076] (3) Element mapping analysis

[0077] The target product of Example 3 was subjected to elemental mapping analysis, and the results were as follows: Figure 3 As shown, (a) is the Bi element mapping diagram, (b) is the Br element mapping diagram, (c) is the O element mapping diagram, and (d) is the N element mapping diagram. Figure 3 It can be seen that Bi, O, Br, and N are uniformly distributed in the target product of Example 3, which proves that N is uniformly doped into the BiOBr lattice of the target product of Example 3.

[0078] (4) Electron spin resonance analysis

[0079] In order to explore the structure and photoelectric properties of the samples, the target products obtained in Example 3 and the comparative example were subjected to electron spin resonance (ESR) tests. The test results are as follows: Figure 4 As shown. Figure 4 It can be seen that compared with the target product of the comparative example, the oxygen vacancy signal intensity of the target product of Example 3 is significantly enhanced, which indicates that N-doping of BiOBr will change [Bi2O2] 2+ The bonding environment leads to unit cell disorder and the generation of oxygen vacancies, which can greatly optimize the chemical bond structure and electron distribution of the BiOBr catalyst.

[0080] (5) Transient fluorescence analysis

[0081] Transient fluorescence analysis was performed on the target products obtained in Example 3 and the comparative example, and the results were as follows: Figure 5 As shown. Figure 5 It can be seen that the short lifetime (τ1) and long lifetime (τ2) of the target product of Example 3 (τ1 = 2.06, τ2 = 21.01) indicate that the lifetime of the photogenerated charges is prolonged compared with the target product of the comparative example (τ1 = 1.49, τ2 = 11.25).a =(A1τ1 2 + A2τ2 2 ) / (A1 τ1 + A2 τ2), the photogenerated charge lifetime (2.30 ns) of the target product in Example 3 is extended compared to the average lifetime (1.53 ns) of BiOBr. Based on the above results, it is inferred that N 3- The introduction of improves the separation efficiency of photogenerated electrons and holes in BiOBr photocatalysts, promotes charge transfer and obtains high photocatalytic activity.

[0082] (6) UV-visible diffuse reflectance analysis

[0083] UV-visible diffuse reflectance analysis was performed on the target products obtained in Example 3 and the comparative example, and the analysis results obtained are as follows: Figure 6 As shown, (a) is the UV-visible diffuse reflectance spectrum (DRS), and (b) is the band gap (Eg) analysis result diagram based on the UV-visible diffuse reflectance spectrum. As can be seen from (a), the absorbance of the comparative target product in the UV region is weak, and the absorbance in the visible region is also low, indicating that it is difficult for the comparative target product to achieve the purpose of reducing CO2 under visible light. After N doping, the target product of Example 3 has an enhanced absorption capacity for visible light, proving that nitrogen doping can effectively regulate the energy band structure.

[0084] UV-Vis diffuse reflectance spectroscopy is also used to analyze the band gap (Eg) of the prepared photocatalyst. Eg can be calculated by the formula α(hν)=A(hν-Eg) n / 2 Obtained. Where α, h, ν, A and Eg represent coefficient, Planck constant, optical frequency, band constant and band gap energy, respectively. When the catalyst is a direct semiconductor, n is 1; when the catalyst is an indirect semiconductor, n is 4. Since BiOBr is an indirect semiconductor, α(hν)=A(hν-Eg) n / 2 After rearrangement, we get [α(hν)] 1 / 2 Proportional to hν. [α(hν)] 1 / 2 As the ordinate and hν as the abscissa, the intersection of the tangent and the abscissa is Eg. As shown in (b), the Eg of the target product of the comparative example and the target product of Example 3 are 2.73 eV and 2.58 eV, respectively.

[0085] (7) Solid-state fluorescence analysis

[0086] The separation and migration of photoinduced carriers were studied by steady-state photoluminescence (PL) spectroscopy at 290 nm excitation. The samples were the target products obtained in Example 3 and the comparative example. The results are shown in FIG. Figure 7 As shown. Figure 7In the example, BiOBr exhibits a PL signal at 465 nm. The emission intensity of the target product of Example 3 is much lower than that of the target product of the comparative example, which means that the e − –h + The lowest recombination rate indicates that the photoinduced charge separation efficiency is high, which indicates that the separation of carriers is significantly promoted after N-doping of BiOBr samples.

[0087] (8) Photocurrent analysis

[0088] In order to study the effect of doping on the carrier separation efficiency, a photochemical experiment was conducted. Transient photocurrent is commonly used to directly illustrate the separation efficiency of photogenerated electrons and holes. The samples are the target products obtained in Example 3 and the comparative example. The results are shown in Figure 8 shown. Figure 8 The photocurrent response of the prepared samples is shown. It can be seen that compared with the target product of the comparative example, the photocurrent intensity of the target product of Example 3 is significantly enhanced, proving that nitrogen doping reduces the electron migration resistance of the material and significantly improves the separation and transfer of carriers (the same as the impedance conclusion below).

[0089] (9) Dark impedance analysis

[0090] The charge transfer kinetics between the photocatalysts was evaluated by electrochemical impedance spectroscopy (EIS) test. The samples were the target products obtained in Example 3 and the comparative example. The results are shown in FIG. Fig. 9 As shown. Fig. 9 It can be seen that compared with the target product of the comparative example, the semicircle of the target product nanomaterial of Example 3 is smaller and the photocurrent intensity is significantly enhanced, which proves that the target product nanocomposite material of Example 3 reduces the electron migration resistance of the material and significantly improves the separation and transfer of carriers.

[0091] (10) X-ray photoelectron spectroscopy analysis

[0092] The structures of the target product of the comparative example and the target product of Example 3 were studied by X-ray photoelectron spectroscopy (XPS). Fig.10 As shown, (a) is the high-resolution Bi 4f XPS spectrum of the target product of the comparative example and the target product of Example 3, (b) is the Br 3d spectrum of the target product of the comparative example and the target product of Example 3, (c) is the O 1s spectrum of the target product of the comparative example and the target product of Example 3, and (d) is the N1s spectrum of the target product of the comparative example and the target product of Example 3. The XPS measurement spectrum shows that the Bi, O, Br and N elements of the target product of the comparative example and the target product of Example 3 have good EDX spectra.

[0093] The high-resolution Bi 4f XPS spectrum of the target product of the comparative example shows peaks at 159.43 eV and 164.69 eV, which are attributed to the Bi 3+ Bi 4f 7 / 2 and Bi 4f 5 / 2 Example 3 Bi 4f of the target product 7 / 2 and Bi 4f 5 / 2 Located at 159.19 eV and 164.46 eV respectively, the two peaks are attributed to Bi 3+ (a), which shows that N doping does not change the valence state of Bi. 3+ form. However, it can be clearly seen that the Bi 4f peak of the target product in Example 3 moves to a lower binding energy, indicating that the electron density of the Bi ion increases. According to the definition of electronegativity, the more electronegative an atom is, the greater its attraction to the bonding electrons. The electronegativity of oxygen (3.44) is greater than that of nitrogen (3.04), so in the Bi-O bond, oxygen will attract more electron pairs, causing the electron density of Bi to decrease relatively. After N is doped in BiOBr, N replaces the O atom to form a Bi-N bond. Since the electronegativity of nitrogen is less than that of oxygen, nitrogen has a weaker ability to attract electron pairs, so the electron density of Bi increases relatively. Therefore, after changing from a Bi-O bond to a Bi-N bond, the electron density of Bi will increase.

[0094] The Br 3d spectrum of the target product of the comparative example has two peaks at around 68.50 eV and 69.56 eV, corresponding to Br - Br 3d 5 / 2 and Br 3d 3 / 2 Example 3 Br 3d in the target product 5 / 2 and Br 3d 3 / 2 The peak of Br − The charge of N-doped BiOBr increases (b), indicating that the N-doped BiOBr reacts with [Bi2O2] 2+ O in the form of [Bi2O2N] 2+ layer, [Bi2ON] 2+ and [Br2] 2- The structural rearrangement of the plates is beneficial to the polarization effect between the layers and enables fast charge transfer.

[0095] The O 1s peak can also be fitted into three peaks near 530 eV, 532 eV and 533 eV (c), which are attributed to lattice oxygen (Bi-O), chemically adsorbed oxygen species (Ov) and hydroxyl (OH), respectively. It can be seen that the peak of the Bi-O bond has a significant decrease, indicating that N replaces O atoms and inserts into [Bi2O2] 2+Compared with the target product of the comparative example, the Ov peak of the target product of Example 3 increases (c), and the ESR results can more intuitively show that the number of oxygen vacancies in the target product sample of Example 3 increases ( Figure 4 In addition, the main peak of O 1s in the target product of Example 3 shifts to a lower binding energy, indicating that N 3- The introduction of has a great influence on the local chemical environment, making the charge of O more negative.

[0096] (d) shows the high-resolution XPS spectrum of N 1s, with a micro-peak observed at 399.74 eV and a signal at 398.6 eV associated with the Bi-N bond in the nitride, confirming the presence of N in the target product of Example 3. In this study, no signal corresponding to N was detected in the spectrum of the target product sample of the comparative example, while N signal was detected in the target product sample of Example 3, indicating that the addition of excess urea can serve as a N source for N-doping BiOBr.

[0097] (11) Mott-Schottky test

[0098] The flat band potential (Efb) was measured using the Mott-Schottky plot collected by the electrochemical workstation. The samples were the target products obtained in Example 3 and the comparative example. The results are shown in Fig.11 As shown. Fig.11 As shown, the intersection of the tangent line of the image and the abscissa is the flat band potential value of the catalyst relative to the Ag / AgCl electrode. The flat band potential values ​​of the target product of the comparative example and the target product of Example 3 relative to the Ag / AgCl electrode are -1.21 eV and -1.32 eV, respectively, and the slope of the image is positive, indicating that BiOBr is an n-type semiconductor. The flat band potential value relative to the hydrogen electrode can be calculated by the following formula:

[0099] ERHE=EAg / AgCl+0.059pH+EAg / AgCl 0 ,

[0100] Among them, EAg / AgCl 0 =+0.199 V, pH=6.8, RHE corresponds to normal hydrogen electrode (NHE) at pH=0.

[0101] Therefore, the flat band potential values ​​of the target product of the comparative example and the target product of Example 3 relative to the hydrogen electrode are respectively -0.61 V and -0.72 V. Since the flat band potential of the n-type semiconductor relative to the hydrogen electrode is very close to the conduction band position, the conduction band potential ECB of the target product of the comparative example and the target product of Example 3 catalysts are respectively -0.61 V and -0.72 V vs NHE.

[0102] (12) Energy band structure diagram

[0103] The band gap energies Eg of the comparative target product and the target product of Example 3 were obtained by DRS, which were 2.73 eV and 2.58 eV, respectively. According to the formula EVB=ECB+Eg, the valence band potentials of the comparative target product and the target product of Example 3 were 2.12 V and 1.86 V, respectively. Therefore, it can be concluded that the introduction of N will shorten the band gap distance ( Fig.12 ), electrons can more easily jump from the valence band to the conduction band, thereby improving the activity of photocatalytic CO2 reduction. Fig.12 It is shown that the target product of the comparative example and the target product of Example 3 can effectively reduce CO2 to CO under visible light because their conduction band and valence band span the redox potential of CO2 to CO.

[0104] (13) Photocatalytic CO2 reduction experiment

[0105] In order to evaluate the photocatalytic CO2 activity of the target product of the comparative example and the target product of Examples 1-4 after N doping, a photoreduction experiment was carried out in a gas-solid reactor without using any sacrificial agent under full spectrum irradiation of a Xe lamp, with a CO2 concentration of 15% and a time of 2 h. The results are as follows Fig.13 Among them, (a) and (b) show the line graph of CO generation amount and average CO generation rate of different samples after 4 hours of Xe lamp irradiation. It can be seen that the activity of the target product in Example 3 is the best, and the average CO generation rate is 51.3 μmol·g -1 ·h -1 (c) and (d) are comparison diagrams of the photocatalytic reduction of CO2 activity of the target product sample of Example 3 and the target product sample of the comparative example. From the corresponding CO generation amount and CO average generation rate of the two samples, it can be seen that the activity of the target product sample of Example 3 is 7.1 times that of the target product sample of the comparative example.

[0106] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for preparing nitrogen-doped BiOBr, characterized in that: In the nitrogen-doped BiOBr, N 3- Replace O 2- into the structure of BiOBr, or in N 3- The gaps between them are doped with [Bi2O2] 2+ , the preparation method comprises the following steps: S1. Contacting a bismuth nitrate raw material, urea and 2-bromoethylamine hydrobromide with each other, heating them until they melt, and obtaining an ionic liquid; wherein the molar ratio of the bismuth nitrate raw material, urea and 2-bromoethylamine hydrobromide is 1:(1.1-2):1; S2. Continue to heat the ionic liquid obtained in step S1 until a self-ignition reaction occurs, and continue to heat the solid sample obtained by the self-ignition reaction. The conditions for continued heating include: a heating temperature of 499° C. to 501° C. and a heating time of 4 h.

2. The preparation method according to claim 1, characterized in that In the nitrogen-doped BiOBr, N 3- The incorporation amount is 8.73%~14.81%.

3. The preparation method according to claim 1, characterized in that: In the XRD spectrum of the nitrogen-doped BiOBr, the 2θ value of the diffraction peak of the (102) plane is 31.691° to 31.660°, and the 2θ value of the diffraction peak of the (110) plane is 32.217° to 32.177°; And / or, in the transmission electron microscope image of the nitrogen-doped BiOBr, the lattice spacing corresponding to the {102} crystal plane is 0.284 nm.

4. The preparation method according to claim 1, characterized in that In step S1, the heating temperature for heating to melt is 495°C to 505°C.

5. The preparation method according to claim 1, characterized in that: The bismuth nitrate raw material includes bismuth nitrate and / or a bismuth nitrate precursor; the bismuth nitrate precursor includes Bi(NO3)3•5H2O.

6. Use of nitrogen-doped BiOBr prepared by the preparation method according to any one of claims 1 to 5 in preparing a photocatalyst.

7. Use of nitrogen-doped BiOBr prepared by the preparation method according to any one of claims 1 to 5 in photocatalytic CO2 reduction.

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