A carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst and its preparation method and application

Abstract

A carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst, its preparation method, and application relate to the field of photocatalytic materials. A bismuth complex is first prepared by ultrasonically heating hexadecyltrimethylammonium bromide, thiourea, and bismuth nitrate pentahydrate. The bismuth complex is then physically mixed with chitosan and annealed under vacuum conditions to produce a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst. This carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst consists of hollow elemental bismuth / bismuth oxycarbonate nanoshells anchored on the surface of an amorphous carbon bed. The nanoshells have an outer diameter of 100-200 nm and a thickness of approximately 20-30 nm. This composite photocatalyst has abundant active sites, significantly enhances visible light absorption, promotes the separation and transport of photogenerated carriers, and exhibits excellent catalytic activity in visible light photocatalytic reduction of CO2.

Description

Technical Field

[0001] The present invention relates to the field of photocatalytic materials, and in particular to a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst and a preparation method and application thereof. Background Art

[0002] In recent years, the rapid development of social forms and people's pursuit of a better life have led to the continuous advancement of society and technology, which has accelerated the consumption of fossil energy. The large-scale combustion of fossil energy such as oil and natural gas has caused a sharp increase in greenhouse gases, mainly CO2, in the atmosphere, exacerbating the energy crisis and the greenhouse effect. Through photocatalytic reduction technology, CO2 can be directly converted into renewable chemical fuels such as CO, CH4 and C x H y O z , achieving high-value-added conversion of CO2 while addressing the energy crisis and mitigating environmental issues caused by the greenhouse effect. In recent years, there has been increasing interest in photocatalytic CO2 reduction technology, but the conversion efficiency of photocatalytic CO2 reduction in practical applications remains low. Therefore, technologies that efficiently convert CO2 into hydrocarbons under sunlight have attracted considerable attention.

[0003] Bismuth oxycarbonate (Bi2O2CO3) is a Bi-OX bismuth-oxygen photocatalyst, and the tetragonal fluorochloroformite (PbFCl) phase Bi2O2CO3 has a typical layered structure. Its crystal structure consists of double CO3 - layer and [Bi2O2] 2+ The layers are alternately stacked along the c-axis, where [Bi2O2] 2+ Layer with double CO3 - The layers are connected by van der Waals forces, [Bi2O2] 2+ The Bi atoms and O atoms in the layer are connected in the form of covalent bonds. 2+ Strong covalent bond force within the layer and diCO3 - The difference in weak van der Waals forces between layers leads to [Bi2O2] 2+ Layer with double Br -The uneven charge distribution between layers will further polarize the related atoms and orbitals, thereby generating a static electric field inside the crystal, which is conducive to the effective separation of photogenerated electron-hole pairs. In order to reduce the recombination rate of photogenerated carriers in Bi2O2CO3 semiconductor materials, precious metal nanoparticles can be loaded on their surface for surface modification. The free electrons on the metal surface cause collective oscillations due to high-energy light irradiation, generating localized surface plasmon resonance (LSPR), which expands the light absorption range and enhances the photocatalytic performance. For example, Xia et al. successfully constructed an ultrathin BiOBr nanosheet heterostructure coupled with Au nanoparticles through an in situ photoreduction strategy, successfully enhancing the photocatalytic CO2 reduction activity of BiOBr (Liu GP, Wang L, Chen X, Zhu XW, Wang B, Xu XY, Chen ZR, Zhu WS, Li HM, Xia J X. Crafting of plasmonic Au nanoparticles coupled ultrathinBiOBrnanosheetsheterostructure: Steering charge transfer for efficient CO2 photoreduction[J]. Green Chem Eng, 2021)

[0004] The present invention uses a simple ultrasound-assisted heating reaction and annealing process to produce a novel composite material composed of hollow spherical nanostructured Bi@Bi2O2CO3 nanoshells anchored on a carbon bed surface. This carbon-supported elemental bismuth / bismuth oxycarbonate nanocomposite photocatalyst possesses abundant active sites, enhanced visible light absorption, and facilitates the separation and transport of photogenerated charge carriers, demonstrating excellent catalytic activity in visible light photocatalytic reduction of CO2. Summary of the Invention

[0005] The purpose of the present invention is to provide a simple method for preparing a carbon-supported elemental bismuth / bismuth oxycarbonate photocatalyst, and the prepared composite photocatalyst exhibits excellent catalytic activity in visible light catalytic reduction of CO2.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst comprises first preparing a bismuth complex by reacting cetyltrimethylammonium bromide (CTAB), thiourea (TU), and bismuth nitrate pentahydrate through ultrasonic heating, then physically mixing the bismuth complex with chitosan and annealing the mixture under vacuum conditions to prepare the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst. The specific preparation steps are as follows:

[0008] ① Preparation of bismuth complex:

[0009] An aqueous solution of cetyltrimethylammonium bromide (CTAB), thiourea (TU), and bismuth nitrate pentahydrate is prepared, stirred uniformly, and then subjected to ultrasonic heating reaction. After the reaction is completed, the bismuth complex is washed and dried to obtain the complex. The reaction temperature is 60-90° C., the reaction time is 30 minutes, and the molar ratio of cetyltrimethylammonium bromide (CTAB), thiourea (TU), and bismuth nitrate pentahydrate is 0.1-1:5-15:0.1-1.

[0010] ② Preparation of carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst:

[0011] The bismuth complex and chitosan are uniformly dispersed and mixed in a solvent by ultrasonic dispersion, wherein the weight ratio of the bismuth complex to chitosan is 1:5-25. The dispersed liquid droplets are then coated on a carrier, naturally dried, and vacuum annealed. After annealing, the powder on the carrier is collected, washed, and dried to obtain a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst.

[0012] As a preferred technical solution of the above preparation method, the ultrasonic heating reaction in step 1 is carried out in a KQ-50 constant temperature water bath ultrasonic instrument with a power of 50W. In step 2, the bismuth complex and chitosan are dispersed in ethanol and ultrasonically mixed uniformly. In step 2, annealing is performed under vacuum at a heating rate of 1-5°C / min, an annealing temperature of 400-500°C, and an annealing time of 1-5 hours.

[0013] The carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst proposed in this paper can be applied to visible light catalytic reduction of CO₂ and exhibits excellent catalytic activity. Its microstructure consists of hollow elemental bismuth / bismuth oxycarbonate nanoshells anchored to the surface of an amorphous carbon bed. The nanoshells have an outer diameter of 100-200 nm and a thickness of approximately 20-30 nm.

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

[0015] 1) In the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst structure prepared by the present invention, the hollow structure of elemental bismuth / bismuth oxycarbonate nanoshells is anchored on the surface of the amorphous carbon bed. This composite nanophotocatalyst has abundant active sites, enhances the absorption capacity of visible light, promotes the separation and transmission of photogenerated carriers, and exhibits excellent catalytic activity in the visible light catalytic reduction of CO2.

[0016] 2) The preparation method of the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst of the present invention has simple process equipment, easy operation, good repeatability, and cheap and readily available raw materials, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 11 is the X-ray diffraction analysis (XRD) spectrum of the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared in Examples 1, 2, and 3.

[0018] Figure 2 This is a field emission scanning electron microscope (FE-SEM) photograph of the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared in Example 1.

[0019] Figure 3 This is a field emission scanning electron microscope (FE-SEM) photograph of the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared in Example 2.

[0020] Figure 4 This is the Raman spectrum of the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared in Example 2.

[0021] Figure 5 This is a field emission scanning electron microscope (FE-SEM) photo of the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared in Example 3.

[0022] Figure 6 This is a graph showing the yield of CO and CH4 generated by the photocatalytic reduction of CO2 by the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared in Examples 1, 2, and 3. DETAILED DESCRIPTION

[0023] The carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst, its preparation method, and application proposed in the present invention are further described in detail below with reference to the examples and drawings.

[0024] Example 1

[0025] ① Preparation of bismuth complex:

[0026] At room temperature and pressure, 0.4 mmol of Bi(NO₃)₃·5H₂O was mixed with 10 mL of deionized water in a 100 mL autoclaved bottle and stirred for 10 minutes. Subsequently, 20 mL of an aqueous solution of hexadecyltrimethylammonium bromide (containing 0.55 mmol of CTAB) and 30 mL of an aqueous solution of thiourea (containing 10 mmol of TU) were added with stirring. The bottle was sealed with the included screw cap and transferred to a 60°C water bath ultrasonicator (KQ-50, 50W) for 30 minutes. After the reaction, the solution was cooled to room temperature, washed sequentially with deionized water and anhydrous ethanol, and then dried at 60°C for 24 hours to obtain the bismuth complex.

[0027] ② Preparation of carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst:

[0028] 40 mg of the bismuth complex was mixed with 1 g of chitosan and added to 40 mL of ethanol for 30 minutes of ultrasonic dispersion. After stirring for 3 hours to thoroughly disperse the mixture, the mixture was drop-coated onto a 1 cm × 1 cm Si wafer. After natural drying, the mixture was vacuum annealed at 400°C for 1 hour at a heating rate of 3°C / min. The powder was collected from the Si wafer and washed sequentially with deionized water and anhydrous ethanol. The resulting powder was then dried at 60°C for 24 hours to obtain a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst.

[0029] See also Figure 1 The peak positions of the spectrum lines of Example 1 in the figure are consistent with the peak positions of the JCPDF standard card (41-1488) and the JCPDF standard card (44-1246), and no other impurity peaks are detected. There are three characteristic peaks of elemental bismuth at 2θ=27.16°, 37.94°, and 39.61°, corresponding to the (012), (104), and (110) crystal planes, respectively. There are three characteristic peaks of bismuth oxycarbonate at 2θ=23.90°, 30.25°, and 32.72°, corresponding to the (011), (013), and (110) crystal planes, respectively, proving that the bismuth / bismuth oxycarbonate composite photocatalyst was successfully prepared.

[0030] See also Figure 2 In the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst structure prepared in Example 1, the bismuth / bismuth oxycarbonate exhibited a highly dispersed hollow nanosphere shell morphology, anchored on the amorphous carbon bed surface. The nanosphere shells had an outer diameter of 100-200 nm and a thickness of approximately 20-30 nm. However, the nanospheres were not fully formed, with some bismuth / bismuth oxycarbonate flakes remaining on the carbon surface. This was attributed to the excessive amount of chitosan. During annealing, the carbon formed from the chitosan coated the bismuth complex, preventing the flakes from being evenly heated and causing them to curl into spheres.

[0031] Example 2

[0032] ① Preparation of bismuth complex:

[0033] At room temperature and pressure, 0.4 mmol of Bi(NO₃)₃·5H₂O was mixed with 10 mL of deionized water in a 100 mL autoclaved bottle and stirred for 10 minutes. Subsequently, 20 mL of an aqueous solution of hexadecyltrimethylammonium bromide (containing 0.55 mmol of CTAB) and 30 mL of an aqueous solution of thiourea (containing 10 mmol of TU) were added while stirring. The bottle was sealed with the included screw cap and transferred to a 70°C water bath ultrasonicator (KQ-50, 50W) for 30 minutes. After the reaction, the solution was cooled to room temperature, washed sequentially with deionized water and anhydrous ethanol, and then dried at 60°C for 24 hours to obtain the bismuth complex.

[0034] ② Preparation of carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst:

[0035] 40 mg of the bismuth complex was mixed with 0.4 g of chitosan and added to 40 mL of ethanol, ultrasonically dispersed for 30 minutes, stirred for another 3 hours to thoroughly disperse, and then drop-coated onto a 1 cm × 1 cm Si wafer. After natural drying, the powder was vacuum annealed at a heating rate of 3°C / min, an annealing temperature of 450°C, and a annealing time of 3 hours. After annealing, the powder was collected from the Si wafer, washed sequentially with deionized water and anhydrous ethanol, and then dried at 60°C for 24 hours to obtain a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst.

[0036] See also Figure 1 In the figure, the peak positions of the spectrum of Example 2 correspond one-to-one with all diffraction crystal planes of the JCPDF standard card (41-1488) and the JCPDF standard card (44-1246). There are three characteristic peaks of elemental bismuth at 2θ = 27.16°, 37.94°, and 39.61°, corresponding to the (012), (104), and (110) crystal planes, respectively. There are three characteristic peaks of bismuth oxycarbonate at 2θ = 23.90°, 30.25°, and 32.72°, corresponding to the (011), (013), and (110) crystal planes, respectively. This proves that the bismuth / bismuth oxycarbonate composite photocatalyst was successfully prepared. Compared with Examples 1 and 3, the diffraction peak of Example 2 is sharper, indicating better crystallinity.

[0037] See also Figure 3 In the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst structure prepared in Example 2, the bismuth / bismuth oxycarbonate exhibited a highly dispersed hollow nanoshell morphology, anchored on the amorphous carbon bed surface. The spherical shells had an outer diameter of 100-200 nm and a thickness of approximately 20-30 nm. Furthermore, compared to Example 1, the number of bismuth / bismuth oxycarbonate flakes on the carbon surface was significantly reduced.

[0038] See also Figure 4 From the Raman spectrum of the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared in Example 2, it can be seen that the peaks at 1350 and 1600 cm -1 There are two characteristic spectral peaks of carbon materials, called D peak and G peak. D / I G The value is 0.679, which proves that the flakes anchored by bismuth / bismuth oxycarbonate in Example 2 are carbon materials, and are carbon materials with graphite phase structure.

[0039] Example 3

[0040] ① Preparation of bismuth complex:

[0041] At room temperature and pressure, 0.4 mmol of Bi(NO₃)₃·5H₂O was mixed with 10 mL of deionized water in a 100 mL autoclaved bottle and stirred for 10 minutes. Subsequently, 20 mL of an aqueous solution of hexadecyltrimethylammonium bromide (containing 0.55 mmol of CTAB) and 30 mL of an aqueous solution of thiourea (containing 10 mmol of TU) were added with stirring. The bottle was sealed with the included screw cap and transferred to a 90°C water bath ultrasonicator (KQ-50, 50W) for 30 minutes. After the reaction, the solution was cooled to room temperature, washed sequentially with deionized water and anhydrous ethanol, and then dried at 60°C for 24 hours to obtain the bismuth complex.

[0042] ② Preparation of carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst:

[0043] 40 mg of the bismuth complex was mixed with 0.2 g of chitosan and added to 40 mL of ethanol for 30 minutes of ultrasonic dispersion. After stirring for 3 hours to thoroughly disperse the mixture, the mixture was drop-coated onto a 1 cm × 1 cm Si wafer. After natural drying, the mixture was vacuum annealed at 500°C for 5 hours at a heating rate of 3°C / min. The powder was collected from the Si wafer and washed sequentially with deionized water and anhydrous ethanol. The resulting powder was then dried at 60°C for 24 hours to obtain a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst.

[0044] See also Figure 1 In the figure, the spectral peaks of Example 3 correspond one-to-one with the diffraction crystal planes of the JCPDF standard card (41-1488) and the JCPDF standard card (44-1246). There are three characteristic peaks of elemental bismuth at 2θ=27.16°, 37.94°, and 39.61°, corresponding to the (012), (104), and (110) crystal planes, respectively. There are three characteristic peaks of bismuth oxycarbonate at 2θ=23.90°, 30.25°, and 32.72°, corresponding to the (011), (013), and (110) crystal planes, respectively. No other impurity peaks were detected, proving that the bismuth / bismuth oxycarbonate composite photocatalyst was successfully prepared.

[0045] See also Figure 5 In the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst structure prepared in Example 3, bismuth / bismuth oxycarbonate presents a hollow nanoshell morphology with high dispersion, anchored on the surface of the amorphous carbon bed, with an outer diameter between 100-200 nm and a thickness of about 20-30 nm.

[0046] Example 4

[0047] The visible light photocatalytic CO2 reduction activity of the catalysts prepared in Examples 1-3 above was tested in an online photocatalytic reaction system (MC-SPB10-AG) designed by Beijing Magnesium Corporation.

[0048] 10 mg of catalyst and 1 mL of deionized water were added to a centrifuge tube and sonicated continuously for 15 minutes until the catalyst was completely dispersed. The mixture was then evenly added dropwise onto a sieve plate and placed in a glass reactor connected to a photocatalytic reaction system. High-purity CO₂ (99.999%) was introduced as the reaction gas. The CO₂ flow was stopped when the pressure reading reached 15 kPa. The purge cycle was repeated three times until the system pressure stabilized. A 300 W xenon lamp (MC-XF300) was used as the light source. Throughout the photoreaction phase, the reactor temperature was maintained at approximately 6°C using a circulating condensate water system. The production of reducing gas products was analyzed every hour using an online gas chromatograph (GC9790Ⅱ) equipped with an FID and TCD detectors.

[0049] See also Figure 6 The carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalysts prepared in the three examples all have excellent CO2 reduction ability, especially the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared in Example 2 by adding 0.4g of chitosan has the best photocatalytic CO2 reduction performance.

[0050] The above examples confirm that the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared by the ultrasound-assisted liquid phase synthesis method of the present invention has good visible light catalytic reduction of CO2 ability, and the production process is simple and has the possibility of large-scale synthesis.

[0051] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst, characterized in that: A bismuth complex is first prepared by ultrasonically heating hexadecyltrimethylammonium bromide, thiourea, and bismuth nitrate pentahydrate. The bismuth complex is then physically mixed with chitosan and annealed under vacuum conditions to produce a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst. The specific preparation steps are as follows: ① Preparation of bismuth complex: An aqueous solution of hexadecyltrimethylammonium bromide, thiourea, and bismuth nitrate pentahydrate is prepared, stirred uniformly, and then subjected to ultrasonic heating reaction. After the reaction, the bismuth complex is washed and dried to obtain the complex. The reaction temperature is 60-90° C., the reaction time is 30 minutes, and the molar ratio of hexadecyltrimethylammonium bromide, thiourea, and bismuth nitrate pentahydrate is 0.1-1:5-15:0.1-1. ② Preparation of carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst: The bismuth complex and chitosan are uniformly dispersed and mixed in a solvent by ultrasonic dispersion, wherein the weight ratio of the bismuth complex to chitosan is 1:5-25. The dispersed liquid droplets are then coated on a support, naturally dried, and then vacuum annealed at 400-500°C for 1-5 hours. After annealing, the powder on the support is collected, washed, and dried to obtain a carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst. The composite photocatalyst microstructure consists of hollow elemental bismuth / bismuth oxycarbonate nanoshells anchored on the surface of an amorphous carbon bed. The outer diameter of the nanoshells is between 100-200 nm and the thickness is 20-30 nm.

2. The preparation method according to claim 1, wherein The ultrasonic heating reaction in step ① is carried out in a constant temperature water bath ultrasonic instrument with a model of KQ-50 and a power of 50W.

3. The preparation method according to claim 1, wherein In step ②, the bismuth complex and chitosan are dispersed in ethanol and ultrasonically mixed uniformly.

4. The preparation method according to claim 1, wherein In step ②, the vacuum annealing heating rate is 1~5℃ / min.

5. Use of the carbon-supported elemental bismuth / bismuth oxycarbonate composite photocatalyst prepared by the method of claim 1 in visible light catalytic reduction of CO2.

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