Synthesis method of carbon nitride quantum dot / cu / biVO4 composite photocatalyst

Abstract

The application belongs to the field of photocatalytic materials, and relates to a synthesis method of a carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst. The method comprises the following steps: firstly, synthesizing carbon nitride quantum dots and BiVO4 respectively; then, preparing a Cu / BiVO4 composite by using the BiVO4; and finally, compounding the Cu / BiVO4 composite with the carbon nitride quantum dots to obtain the carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst. The synthesis method is easy to operate and has good repeatability. Through composition and structure regulation, the up-conversion luminescence performance of the carbon nitride quantum dots and Cu doping are utilized, new energy bands are generated in the composite, the band gap is reduced, and the photocatalytic performance is improved. Compared with the BiVO4 and the Cu / BiVO4 composite, the composite can widen the light response range, inhibit the recombination of photo-generated electrons and holes, and thus improve the photocatalytic performance of the BiVO4.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials, and in particular to a method for synthesizing carbon nitride quantum dot / Cu / BiVO4 composite photocatalysts. Background Technology

[0002] Photocatalytic conversion of carbon dioxide (CO2) into renewable fuels is one of the most effective strategies to simultaneously lead humanity out of the dual dilemmas of the greenhouse effect and the energy crisis. Mimicking natural photosynthesis, the photocatalytic conversion of CO2 into carbon-containing fuels requires overcoming the thermodynamic and kinetic barriers involved in the reactions. Achieving this reaction via photocatalysis also relies on the development of highly efficient and stable photocatalysts.

[0003] BiVO4 is a visible light-driven photocatalyst with advantages such as narrow band gap (approximately 2.4 eV), high abundance in the Earth's crust, low cost, high chemical stability, and good dispersibility in water, and is widely used in the field of photocatalysis. However, although BiVO4 alone can effectively utilize solar energy, it still has some shortcomings in the field of photocatalytic CO2 reduction, such as low photogenerated carrier migration efficiency, poor surface adsorption of CO2 molecules, and the need to improve the separation efficiency of photogenerated charges. Therefore, it is necessary to specifically regulate its morphology, structure, and composition to improve the performance of photocatalytic CO2 reduction. For example, Li et al. prepared N and Fe co-doped BiVO4 using the sol-gel method. The co-doped energy level generated helps to increase visible light absorption and suppress photogenerated charge recombination, which significantly improves the yield of hydrocarbon fuels (Li F, et al., Physical Chemistry Chemical Physics, 2017, 19(32): 21862-21868.). Furthermore, constructing heterojunction systems allows for the manipulation of the active site distribution in catalytic systems by utilizing the structural characteristics of other semiconductors. For example, Wu et al. prepared BiVO4 / C4N3 direct Z-type heterojunctions using template-induced and in-situ polymerization methods, leveraging the tight interface between the two heterojunctions to retain the more potent oxidizing and reducing agents. + and e - It participates in photocatalytic reduction reactions, significantly enhancing the CO yield (Wu J, et al., Applied Catalysis B: Environmental, 2021, 295: 120277.). Huang et al. synthesized porous mulberry-like BiVO4-Bi2O3 pn heterojunction materials using a one-step hydrothermal method. Compared with BiVO4, the heterojunction exhibited good photocatalytic performance for CO2 reduction under visible light irradiation, with CH4 and CO yields being 47 times and 25.7 times that of BiVO4 alone, respectively (Huang L, et al., ChemCatChem, 2021, 13(14): 3357-3367.).

[0004] Doping BiVO4 with copper ions can generate a new valence band, reduce the band gap of BiVO4, and suppress the recombination of photogenerated carriers. Carbon nitride quantum dots (CNQDs) have upconversion luminescence and quantum size effects, which can further excite BiVO4 to generate more electrons and holes. Therefore, combining the two can further enhance the photocatalytic performance of BiVO4.

[0005] This invention utilizes upconversion luminescence of carbon nitride quantum dots and Cu doping to further construct a multi-component BiVO4 complex with excellent photocatalytic performance, which can effectively enhance the photocatalytic reduction performance of CO2. Summary of the Invention

[0006] The purpose of this invention is to provide a method for synthesizing a carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst, which enhances the photocatalytic reduction performance of BiVO4 for CO2 by regulating its structure and composition. The preparation method of the carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst is easy to operate, exhibits high catalytic efficiency, and good activity.

[0007] This invention provides a method for synthesizing a carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst, comprising the following steps: First, using polymer semiconductor g-C3N4 as raw material, an initial solution is prepared using concentrated sulfuric acid and concentrated nitric acid as solvents. The white precipitate collected from the initial solution is then reacted with concentrated ammonia via hydrothermal reaction to obtain carbon nitride quantum dots (CNQDs). Second, Bi(NO3)3 and EDTA are used to prepare a Bi acid-containing solution. The Bi acid-containing solution is then reacted with an aqueous solution of NH4VO3 to obtain BiVO4. Next, BiVO4 and an aqueous solution of Cu(NO3)2 are used as raw materials to react with an aqueous solution of NaBH4 to obtain the Cu / BiVO4 composite CBVO. Finally, CBVO is dispersed in the CNQDs solution and reacted to obtain the carbon nitride quantum dot / Cu / BiVO4 composite. The morphology, structure and composition of the target products were characterized using scanning electron microscopy (SEM, JSM-6360LV, JEOL, Japan), high-resolution transmission electron microscopy (HRTEM, JEM-2100F, JEOL, Japan) and X-ray diffraction (XRD, Empyrean XRD-6000, BRUKER AXS, Germany).

[0008] The preparation method of the above-mentioned carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst includes the following steps:

[0009] (1) Melamine powder was placed in a covered crucible and then transferred to a muffle furnace for annealing at 550℃ for 4 hours to obtain bulk phase g-C3N4. 0.25 g of bulk phase g-C3N4 was weighed and dispersed in 20 mL of concentrated sulfuric acid and 20 mL of concentrated nitric acid. After ultrasonic exfoliation for 4 hours, a milky white solution was obtained. This solution was added dropwise to 1000 mL of distilled water, magnetically stirred for 0.5 hours, allowed to stand, and centrifuged to obtain a white precipitate. The precipitate was washed with water until neutral and dried at 60℃. 0.40 g of the white precipitate was weighed and dispersed in 50 mL of concentrated ammonia water and reacted solvatindically at 180℃ for 12 hours. After the reaction was complete, the solution was dialyzed for 72 hours to obtain 1 mg·L⁻¹. -1 Carbon nitride quantum dots, denoted as CNQDs.

[0010] (2) Weigh 2.00 g Bi(NO3)3·5H2O and 1.00 g EDTA and dissolve them in 20 mL of dilute nitric acid solution (0.5 mol·L⁻¹). -1 Then slowly add it to 20 mL of NH4VO3 aqueous solution (containing 1.00 g NH4VO3), and use 1 mol·L⁻¹ water. -1 The pH of the solution was adjusted to 1 with ammonia, and then a solvothermal reaction was carried out at 180℃ for 6 hours. The resulting precipitate was separated, washed, and dried, and then heat-treated at 450℃ for 2 hours to finally obtain a yellow powder, BiVO4, denoted as BVO. A certain amount of BiVO4 powder with a Cu content of 1-10 wt% was weighed and mixed with 10 mL of Cu(NO3)2·xH2O aqueous solution in an ice bath, and then 10 mL of NaBH4 aqueous solution (0.1 mol·L⁻¹) was added. -1 The precipitate was quickly added to the above solution and continuously magnetically stirred in an ice bath for 4 hours. The precipitate was then separated and dried, and then heat-treated in a muffle furnace at 450°C for 4 hours to obtain the Cu / BiVO4 complex, denoted as CBVO.

[0011] (3) Weigh 0.10 g of the Cu / BiVO4 complex prepared in step (2) and ultrasonically disperse it in 20-60 mL of the CNQDs solution obtained in step (1). React hydrothermally at 100-140 °C for 1-5 h. After the reaction is complete, the precipitate is separated, washed and dried to obtain the carbon nitride quantum dot / Cu / BiVO4 complex, denoted as CCBVO.

[0012] The advantages of the carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst prepared by this invention are:

[0013] (1) The synthesis method is easy to operate and has good repeatability.

[0014] (2) By regulating the composition and structure, the upconversion luminescence properties of carbon nitride quantum dots and Cu doping are utilized to generate new energy bands in the composite, reduce the band gap, and improve photocatalytic performance.

[0015] (3) Compared with BiVO4 alone and Cu / BiVO4 complex, it was found that carbon nitride quantum dot / Cu / BiVO4 complex can broaden the photoresponse range and suppress the recombination of photogenerated electrons and holes, thereby improving the photocatalytic performance of BiVO4. Attached Figure Description

[0016] Figure 1 This is a scanning electron microscope (SEM) image of the product in Example 1.

[0017] Figure 2 The images shown are (a) a high-resolution transmission electron microscope (HRTEM) image, (b) an energy spectrum, and (ch) an elemental distribution map of the product in Example 1.

[0018] Figure 3 The X-ray diffraction (XRD) patterns of the products in Example 1 and Comparative Example 2 are shown.

[0019] Figure 4 A comparison of the CO2 photocatalytic reduction performance of carbon nitride quantum dot / Cu / BiVO4 composites. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: Melamine powder was placed in a covered crucible and then annealed in a muffle furnace at 550°C for 4 hours to obtain bulk phase g-C3N4. 0.25 g of bulk phase g-C3N4 was weighed and dispersed in 20 mL of concentrated sulfuric acid and 20 mL of concentrated nitric acid. After ultrasonic exfoliation for 4 hours, a milky white solution was obtained. This solution was added dropwise to 1000 mL of distilled water, magnetically stirred for 0.5 hours, allowed to stand, and centrifuged to obtain a white precipitate. The precipitate was washed with water until neutral and dried at 60°C. 0.40 g of the white precipitate was weighed and dispersed in 50 mL of concentrated ammonia water and reacted solvatindically at 180°C for 12 hours. After the reaction was complete, the resulting solution was dialyzed for 72 hours to obtain 1 mg·L⁻¹. -1 Carbon nitride quantum dots, denoted as CNQDs.

[0022] Weigh 2.00 g Bi(NO3)3·5H2O and 1.00 g EDTA and dissolve them in 20 mL of dilute nitric acid solution (0.5 mol·L⁻¹). -1 Then slowly add it to 20 mL of NH4VO3 aqueous solution (containing 1.00 g NH4VO3), and use 1 mol·L⁻¹ water.-1 The pH of the solution was adjusted to 1 with ammonia, and then a solvothermal reaction was carried out at 180°C for 6 hours. The resulting precipitate was separated, washed, and dried, and then heat-treated at 450°C for 2 hours to finally obtain a yellow powder BiVO4, denoted as BVO.

[0023] A certain amount of BiVO4 powder with a Cu content of 3wt% was weighed and mixed with 10 mL of Cu(NO3)2·xH2O aqueous solution in an ice bath. Then, 10 mL of NaBH4 aqueous solution (0.1 mol·L⁻¹) was added. -1 The precipitate was quickly added to the above solution and continuously magnetically stirred in an ice bath for 4 hours. The precipitate was then separated and dried, and then heat-treated in a muffle furnace at 450°C for 4 hours to obtain the Cu / BiVO4 complex, denoted as CBVO.

[0024] 0.10 g of the Cu / BiVO4 composite was ultrasonically dispersed in 40 mL of CNQDs solution and subjected to hydrothermal reaction at 120 °C for 3 h. After the reaction was completed, the resulting precipitate was separated, washed, and dried to obtain the carbon nitride quantum dot / Cu / BiVO4 composite, denoted as CBVO.

[0025] Comparative Example 1: Weigh 2.00 g Bi(NO3)3·5H2O and 1.00 g EDTA and dissolve them in 20 mL of dilute nitric acid solution (0.5 mol·L⁻¹). -1 Then slowly add it to 20 mL of NH4VO3 aqueous solution (containing 1.00 g NH4VO3), and use 1 mol·L⁻¹ water. -1 The pH of the solution was adjusted to 1 with ammonia, and then a solvothermal reaction was carried out at 180°C for 6 hours. The resulting precipitate was separated, washed, and dried, and then heat-treated at 450°C for 2 hours to finally obtain a yellow powder BiVO4, denoted as BVO.

[0026] Comparative Example 2: Weigh 2.00 g Bi(NO3)3·5H2O and 1.00 g EDTA and dissolve them in 20 mL of dilute nitric acid solution (0.5 mol·L⁻¹). -1 Then slowly add it to 20 mL of NH4VO3 aqueous solution (containing 1.00 g NH4VO3), and use 1 mol·L⁻¹ water. -1 The pH of the solution was adjusted to 1 with ammonia, and then a solvothermal reaction was carried out at 180°C for 6 hours. The resulting precipitate was separated, washed, and dried, and then heat-treated at 450°C for 2 hours to finally obtain a yellow powder BiVO4, denoted as BVO.

[0027] A certain amount of BiVO4 powder with a Cu content of 3wt% was weighed and mixed with 10 mL of Cu(NO3)2·xH2O aqueous solution in an ice bath. Then, 10 mL of NaBH4 aqueous solution (0.1 mol·L⁻¹) was added. -1The precipitate was quickly added to the above solution and continuously magnetically stirred in an ice bath for 4 hours. The precipitate was then separated and dried, and then heat-treated in a muffle furnace at 450°C for 4 hours to obtain the Cu / BiVO4 complex, denoted as CBVO.

[0028] Figure 1 The image shows a SEM image of the carbon nitride quantum dot / Cu / BiVO4 composite. As can be seen from the image, the synthesized product has a spherical structure with a rough surface and non-uniform size. Figure 2 This is confirmed by the HRTEM plot of a. According to the energy spectrum ( Figure 2 b) Analysis shows that the product is composed of Bi, V, O, Cu, C, and N elements, and the elements are evenly distributed. Figure 3 The XRD pattern of the carbon nitride quantum dot / Cu / BiVO4 composite shows that the composite exhibits diffraction peaks at 18.71°, 19.02°, 28.28°, 30.58°, 34.50°, 35.26°, 39.78°, 42.44°, 46.02°, 46.68°, 47.22°, 50.31°, 53.26°, 58.40°, and 59.62°. The diffraction peaks correspond to the (110), (011), (121), (040), (200), (002), (211), (051), (132), (240), (042), (202), (161), (321), and (123) crystal planes of BiVO4 (JCPDS No. 14-0688), respectively, confirming the presence of the monoclinic scheelite phase BiVO4 in the composite. No characteristic peaks of carbon nitride quantum dots or elemental Cu or its oxides were detected, which may be due to their low content, poor crystallinity, or high dispersibility. Comparative Example 2 also exhibits similar diffraction peaks, indicating that the introduction of carbon nitride quantum dots did not alter the crystal structure of BiVO4.

[0029] In the carbon dioxide photocatalytic reduction experiment, 20 mg of sample was dispersed in a mixed solvent consisting of 10 mL of triethanolamine (TEOA) and 20 mL of ultrapure water. High-purity CO2 gas (99.999%) was introduced, and after stirring for 30 min, the light source (300 W xenon lamp, operating current 20 mA) was turned on to carry out photocatalytic reduction of CO2. Figure 4 The graph shows a comparison of the CO2 photocatalytic reduction performance of the carbon nitride quantum dot / Cu / BiVO4 composite. As can be seen, CO2 is almost impossible to reduce under conditions of no light and no catalyst, indicating that light and catalyst are extremely important for the photocatalytic reduction of CO2. Replacing CO2 with N2 also yields almost no detectable products, confirming that the products CH4 and CO are indeed due to the photocatalytic reduction of CO2. Compared with BVO and CBVO, CCBVO exhibits enhanced photocatalytic CO2 reduction performance, achieving a CH4 and CO yield of 97.0 μmol·g after 5 hours of illumination. -1 and 93.0 μmol·g-1 The above results indicate that the photocatalytic performance of the carbon nitride quantum dot / Cu / BiVO4 composite catalyst is significantly higher than that of BiVO4 alone and the Cu / BiVO4 composite.

[0030] Example 2-26

[0031] Using the experimental conditions in Table 1, the desired carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst can also be obtained by following the preparation process described in Example 1.

[0032] Table 1 Comparison of various experimental conditions and photocatalytic CO2 reduction performance in Examples 2-26

[0033]

[0034] According to the experimental data in Table 1:

[0035] (1) Under the same conditions, as the volume of the carbon nitride quantum dot solution increased, the yield of the carbon nitride quantum dot / Cu / BiVO4 composite for photocatalytic reduction of CO2 to CH4 and CO first increased and then decreased, with the highest yield when the volume of the carbon nitride quantum dot solution was 40 mL. This may be because as the content of carbon nitride quantum dots in the composite increases, its upconversion luminescence effect gradually strengthens, enhancing the composite's light absorption capacity and generating more photogenerated charges, thus improving photocatalytic performance. However, excessive carbon nitride quantum dots in the composite can become charge recombination centers, which can inhibit the separation of photogenerated charges and reduce photocatalytic activity.

[0036] (2) Under the same conditions, as the solvothermal temperature increased, the yield of the carbon nitride quantum dot / Cu / BiVO4 composite for photocatalytic reduction of CO2 to CH4 and CO first increased and then decreased, with the highest yield at a solvothermal temperature of 120℃. This may be because the interaction between carbon nitride quantum dots and Cu / BiVO4 gradually forms as the solvothermal temperature increases. When the solvothermal temperature is too high, it will destroy the original morphology and structure of the crystals and the interaction between multiple components, affecting the photocatalytic activity.

[0037] (3) Under the same conditions, with the extension of solvothermal time, the yield of the photocatalytic reduction of CO2 to CH4 and CO by the carbon nitride quantum dot / Cu / BiVO4 composite first increases and then decreases, with the highest yield observed at a solvothermal time of 3 h. This may be because with the extension of solvothermal time, a tight interface gradually forms between the carbon nitride quantum dots and Cu / BiVO4, which helps to separate the photogenerated charges and prolongs the charge lifetime. When the solvothermal time is too long, it will destroy the interfacial interactions between the multiple components and reduce the photocatalytic activity.

[0038] (4) Under the same conditions, as the copper content in the composite increases, the yield of the photocatalytic reduction of CO2 to CH4 and CO by the carbon nitride quantum dot / Cu / BiVO4 composite first increases and then decreases, with the highest yield when the copper content is 3wt%. This may be because as the copper content in the composite increases, copper is effectively incorporated into the BiVO4 lattice, which helps to reduce the band gap and suppress the recombination of photogenerated charges. However, further increases in copper content may alter the interaction between Cu and BiVO4 grains, or even become recombination centers for photogenerated charges, thus reducing the photocatalytic activity.

[0039] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for synthesizing a carbon nitride quantum dot / Cu / BiVO4 composite photocatalyst, characterized in that, The process includes the following steps: First, using polymer semiconductor g-C3N4 as raw material, an initial solution is prepared using concentrated sulfuric acid and concentrated nitric acid as solvents. The white precipitate collected from the initial solution is then reacted with concentrated ammonia via hydrothermal reaction to obtain carbon nitride quantum dots (CNQDs). Second, Bi(NO3)3 and EDTA are used to prepare a Bi acid-containing solution. The Bi acid-containing solution is then reacted with an aqueous solution of NH4VO3 to obtain BiVO4. Next, BiVO4 and an aqueous solution of Cu(NO3)2 are used as raw materials and reacted with an aqueous solution of NaBH4 to obtain the Cu / BiVO4 composite CBVO. Finally, CBVO is dispersed in the CNQDs solution and reacted to obtain the carbon nitride quantum dot / Cu / BiVO4 composite. Specifically, the following steps are included: (1) Weigh 0.25g of bulk phase g-C3N4 and disperse it in a mixed concentrated acid. After ultrasonic exfoliation for 4h, a milky white solution is obtained. Add the solution dropwise to 1000mL of distilled water, stir magnetically for 0.5h, let stand, and centrifuge to obtain a white precipitate. Wash with water until neutral, and then... o Dry at C; weigh 0.40 g of the white precipitate and disperse it in 50 mL of concentrated ammonia water; solvate at 180 °C. o The reaction proceeds for 12 hours; after the reaction is complete, the resulting solution is dialyzed for 72 hours to obtain 1 mg·L⁻¹. -1 Carbon nitride quantum dots, denoted as CNQDs; (2) Weigh 2.00g Bi(NO3)3·5H2O and 1.00g EDTA and dissolve them in 20mL of 0.5mol·L⁻¹ -1 Add the precipitate to a dilute nitric acid solution, then slowly add it to 20 mL of an aqueous solution containing 1.00 g of NH₄VO₃, and use 1 mol·L⁻¹ water. -1 The pH of the solution was adjusted to 1 with ammonia, and then solvothermal treatment was performed at 180°C. o The reaction was carried out at C for 6 hours; the resulting precipitate was then separated, washed, and dried, and subjected to a 450°C reaction. o After heat treatment at C for 2 hours, a yellow powder BiVO4, denoted as BVO, was finally obtained. A certain amount of BiVO4 powder was weighed and mixed with 10 mL of Cu(NO3)2·xH2O aqueous solution in an ice bath, and then 10 mL of 0.1 mol·L⁻¹ water was added. -1 A NaBH4 aqueous solution was rapidly added to the above solution, and the mixture was continuously magnetically stirred in an ice bath for 4 hours. The precipitate was then separated and dried, and then subjected to further treatment in a muffle furnace at 450°C. o After heat treatment at C for 4 h, a Cu / BiVO4 complex was obtained, denoted as CBVO; (3) Weigh 0.10g of the Cu / BiVO4 complex prepared in step (2) and ultrasonically disperse it in the CNQDs solution obtained in step (1). After the hydrothermal reaction is completed, the precipitate is separated, washed and dried to obtain the carbon nitride quantum dot / Cu / BiVO4 complex, denoted as CCBVO. In step (1), melamine powder is placed in a covered crucible and then transferred to a muffle furnace for annealing at 550°C for 4 hours to obtain bulk phase g-C3N4; In step (1), the mixed concentrated acid consists of 20 mL of concentrated sulfuric acid and 20 mL of concentrated nitric acid; In step (2), BiVO4 powder is weighed according to a Cu content of 3wt%; In step (3), the CNQDs solution is 40 mL, the hydrothermal temperature is 120 °C, and the time is 3 h.

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