Carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst, preparation method and application thereof

Abstract

The application discloses a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst and a preparation method and application thereof, belongs to the technical field of catalyst materials, and is characterized in that porous tubular g-C3N4, high-exposure {001} crystal surface BiVO4 and UiO-66 are compounded to construct a ternary heterojunction system with a structure synergy and a closely coupled interface. The UIO-66 is used as an electronic medium and a structure support, the separation and migration efficiency of photo-generated carriers is significantly enhanced, the visible light absorption capacity and the redox potential of the material are synergistically improved through band matching, and therefore the catalytic activity of the material is superior to that of a single or binary component in multiple reactions such as organic pollutant degradation, CO2 reduction and water splitting to produce hydrogen / oxygen. The g-C3N4 with a unique porous tubular structure and the high specific surface area of the UIO-66 together strengthen the adsorption and mass transfer process of reactants and ensure good structural stability and recycling performance of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of catalyst materials technology, specifically relating to carbon nitride / bismuth vanadate / UiO-66 composite photocatalysts, their preparation methods, and applications. Background Technology

[0002] Photocatalysis technology can directly utilize solar energy to drive reactions such as water splitting to produce hydrogen, carbon dioxide reduction, and pollutant degradation, making it one of the green pathways to achieve energy conversion and environmental pollution control. However, traditional single-component photocatalysts generally suffer from bottlenecks such as limited visible light absorption, rapid recombination of photogenerated carriers, and insufficient surface active sites, resulting in their quantum efficiency and practical application performance failing to meet requirements.

[0003] In recent years, constructing heterojunction composite systems has been considered an effective strategy to improve photocatalytic performance. By coupling different semiconductor materials with matched band structures, the spatial separation of photogenerated electrons and holes can be promoted, thereby extending their lifetime and enhancing their redox capabilities. Several binary composite materials have been disclosed in the prior art. For example, the paper entitled "Fabrication of TernaryAg / g-C3N4 / BiVO4 Composites with Enhanced Visible-Light-Driven Photocatalytic Activity toward Rhodamine B Elimination" discloses a g-C3N4 / BiVO4 binary system. For BiVO4, the paper uses Bi(NO3)3·5H2O and NH4VO3 as raw materials to synthesize monoclinic BiVO4 by hydrothermal method at 160℃ for 4 hours. The high-activity crystal facets of BiVO4 prepared by this synthesis method are exposed in a small proportion, thus limiting its photocatalytic performance. For the g-C3N4 / BiVO4 binary system, a suspension of g-C3N4 powder is mixed with a suspension of BiVO4 powder, ultrasonically treated, stirred at room temperature, and the precipitate is collected by centrifugation and dried to obtain the g-C3N4 / BiVO4 binary composite material. The g-C3N4 / BiVO4 binary composite material prepared by the above synthesis method has problems such as weak interfacial bonding, single charge transport path and insufficient matching of light absorption range. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst, its preparation method, and its applications. This invention constructs a composite photocatalyst by combining porous tubular g-C3N4, BiVO4 with highly exposed {001} crystal planes, and UiO-66 with a regular porous structure. This provides abundant surface active sites, constructs multi-level charge transfer channels, significantly promotes the separation of photogenerated electrons and holes, broadens the visible light response range, and simultaneously endows the material with strong oxidation and reduction capabilities, thereby comprehensively improving its photocatalytic performance.

[0005] The first objective of this invention is to provide a method for preparing a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst, comprising the following steps: Using porous tubular graphitic carbon nitride as a carrier, an aqueous solution containing bismuth and vanadium sources was mixed with a surfactant solution to obtain a precursor solution, wherein the surfactant was sodium oleate. After mixing the precursor solution with the carrier dispersion, a hydrothermal reaction was carried out at 160℃~200℃ to synthesize bismuth vanadate with a lamellar structure in situ, which was simultaneously loaded onto the surface of porous tubular graphitic carbon nitride to obtain a binary composite material.

[0006] Using binary composite materials and metal-organic framework materials as raw materials, wherein the metal-organic framework material is UiO-66; the binary composite material and UiO-66 are reacted in a solvent system at 50℃~70℃, so that UiO-66 is loaded on the surface of the binary composite material to form Z-type and / or type II heterojunctions, thereby obtaining carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst.

[0007] In a preferred embodiment, the mass ratio of the graphitic carbon nitride, bismuth vanadate, and UiO-66 is 1:1.5 to 9:0.5 to 6.

[0008] In a preferred embodiment, the mass ratio of UiO-66 to the binary composite material is 0.2 to 0.6:1.

[0009] In a preferred embodiment, the ratio of the bismuth source, vanadium source and sodium oleate is 1 mmol: 1 mmol: 1.8 mg to 2 mg.

[0010] In a preferred embodiment, the {001} crystal plane family of the bismuth vanadate is bonded to the porous tubular graphite phase carbon nitride interface, wherein the {001} crystal plane family is at least one of the (004) crystal plane, (200) crystal plane and (020) crystal plane.

[0011] In a preferred embodiment, the hydrothermal reaction time is 8h to 12h; the reaction time at 50℃ to 70℃ is 10h to 14h.

[0012] In a preferred embodiment, the bismuth source is Bi(NO3)3. 5H2O, the vanadium source is NH4VO3.

[0013] As a preferred embodiment, the method for preparing the porous tubular graphitic carbon nitride includes the following steps: using urea and melamine as raw materials, a hydrothermal reaction is carried out at 160℃~180℃ to obtain a primary product, and the primary product is heated to 450℃~500℃ for heat treatment to obtain porous tubular graphitic carbon nitride.

[0014] A second objective of this invention is to provide a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst, prepared using the method described in any one of the preceding claims.

[0015] The third objective of this invention is to provide an application of the above-mentioned carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst in the catalytic degradation of organic pollutants. Specifically, the application method involves adding the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst to a solution containing organic pollutants, and then carrying out a photocatalytic degradation reaction under visible light.

[0016] Compared with the prior art, the present invention has the following beneficial effects: To address the problems of weak interfacial bonding, single charge transport path, and insufficient matching of light absorption range in existing binary composite photocatalysts, this invention provides a method for preparing a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst.

[0017] This invention employs a two-step loading method to prepare a ternary composite material. First, BiVO4 is synthesized in situ in a hydrothermal reaction and loaded onto the surface of porous tubular g-C3N4 (TCN). Subsequently, UiO-66 is loaded onto the surface of the binary composite material (TCN / BiVO4) via a water bath reaction. BiVO4 grows in situ on the g-C3N4 surface in a lamellar structure, and the {001} crystal planes of BiVO4 form a direct interfacial bond with g-C3N4, thereby significantly enhancing the interfacial bonding strength.

[0018] By loading UiO-66 onto the surface of a binary composite material, and utilizing the fact that the work function of UiO-66 is greater than that of g-C3N4 (i.e., the Fermi level of UiO-66 is lower), a new Fermi level and space charge region are formed between UiO-66 and TCN / BiVO4, with the electric field direction pointing from TCN / BiVO4 to UiO-66. Under photoexcitation conditions, electrons in the conduction band of UiO-66 recombine with holes in the valence band of TCN at the interface, while holes in the valence band of UiO-66 and electrons in the conduction band of TCN / BiVO4 are not easily transferred, thus forming Z-type and / or type II heterojunction charge transfer paths. Compared with the single charge transport channel of the binary system, the ternary system constructs a multi-level charge transfer channel, significantly suppressing the recombination of photogenerated electron-hole pairs.

[0019] The band structure of the g-C3N4 / BiVO4 binary composite material limits its utilization of visible light to a specific wavelength range, thus restricting its response to the solar spectrum. This invention introduces UiO-66, forming a tight heterojunction interface with the binary system, resulting in a synergistic rearrangement and coupling of the band structures of the three components. This band matching enables the composite material to generate photogenerated carriers over a wider photon energy range when photoexcited. Through charge transfer pathways forming Z-type and / or type II heterojunctions, the different components effectively utilize a portion of visible light energy that would otherwise be unabsorbed by the binary system alone, thereby expanding the light absorption range. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating the preparation process of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst of the present invention.

[0022] Figure 2 The XRD patterns of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst prepared in Example 2 of the present invention are shown in the figures. (a) shows the XRD patterns of BiVO4 and BiVO4{001}, (b) shows the XRD patterns of BiVO4{001} and 3TCN / BiOV4, and (c) shows the XRD patterns of UiO-66 and 4UiO / TCN / BiVO4.

[0023] Figure 3The images show the FT-IR spectra of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst prepared in Example 2 of this invention, where (a) is the FT-IR spectrum of TCN, BiVO4{001} and 3TCN / BiOV4, and (b) is the FT-IR spectrum of UiO-66 and 4UiO / TCN / BiVO4.

[0024] Figure 4 The images show the SEM, TEM, and TEM mapping spectra of the TCN, BiVO4{001}, and 3TCN / BiOV4 photocatalysts prepared in the embodiments of the present invention. Among them, (a) is the SEM image of 3TCN / BiVO4, (b) is the TEM image of 3TCN / BiVO4, (c) is the TEM image of TCN and BiVO4{001}, (d) is the TEM image of TCN and BiVO4{001}, (e) is the TEM mapping spectrum of Bi element, and (f) is the TEM mapping spectrum of N element.

[0025] Figure 5 The images shown are SEM and TEM images of UiO-66 prepared in the embodiments of the present invention. (a) and (b) are SEM images of UiO-66 at different magnifications, and (c) is a TEM image of UiO-66.

[0026] Figure 6 The images show the SEM, TEM, TEM mapping, and HR-TEM spectra of the 4UiO / TCN / BiVO4 photocatalyst prepared in Example 2 of this invention. (a) and (b) are SEM images, (c) is a TEM (500 nm) image, (d) is a TEM mapping spectrum of 4UiO / TCN / BiVO4, (e) is a TEM (200 nm) image, and (f) is an HR-TEM spectrum of 4UiO / TCN / BiVO4.

[0027] Figure 7 The above are XPS spectra of the 3TCN / BiOV4 photocatalyst prepared in the embodiments of the present invention, wherein (a) is the full XPS spectrum of 3TCN / BiVO4, (b) is the XPS spectrum of C 1s, (c) is the XPS spectrum of N 1s, (d) is the XPS spectrum of O 1s, (e) is the XPS spectrum of Bi 4f, and (f) is the XPS spectrum of V 2p.

[0028] Figure 8 The UV-Vis DRS spectra of the TCN, BiVO4{001} and 3TCN / BiOV4 photocatalysts prepared in the embodiments of the present invention are shown, wherein (a) is the diffuse reflectance spectrum and (b) is the calculated band width spectrum.

[0029] Figure 9The UV-Vis DRS spectra of the UiO-66 and 4UiO / TCN / BiVO4 photocatalysts prepared in Example 2 of this invention are shown, where (a) is the diffuse reflectance spectrum and (b) is the calculated band width spectrum.

[0030] Figure 10 The PL spectra of the TCN, BiVO4{001} and 3TCN / BiOV4 photocatalysts prepared in the embodiments of the present invention, and the UiO-66, 3TCN / BiOV4 and 4UiO / TCN / BiVO4 photocatalysts prepared in Example 2 are shown in the figure. (a) shows the TCN, BiVO4{001} and 3TCN / BiOV4 photocatalysts, and (b) shows the UiO-66, 3TCN / BiOV4 and 4UiO / TCN / BiVO4 photocatalysts prepared in Example 2.

[0031] Figure 11 The images show the photocurrent density and electrochemical impedance spectra of the TCN, BiVO4{001} and 3TCN / BiOV4 photocatalysts prepared in the embodiments of the present invention, wherein (a) is the photocurrent density spectrum and (b) is the electrochemical impedance spectrum.

[0032] Figure 12 The photocurrent density and electrochemical impedance spectra of the UiO-66 and 4UiO / TCN / BiVO4 photocatalysts prepared in Example 2 are shown, where (a) is the photocurrent density spectrum and (b) is the electrochemical impedance spectrum.

[0033] Figure 13 The diagram shows the photocatalytic mechanism of the 3TCN / BiOV4 photocatalyst prepared in the examples.

[0034] Figure 14 The photocatalytic mechanism diagram is shown for the 4UiO / TCN / BiVO4 photocatalyst prepared in Example 2.

[0035] Figure 15 The figures show the degradation and kinetic curves of MB by the TCN, BiVO4{001} and xTCN / BiOV4 photocatalysts prepared in the examples. (a) shows the degradation effect of 1TCN / BiOV4, 2TCN / BiOV4, 3TCN / BiOV4, 4TCN / BiOV4, BiVO4{001} and TCN, and (b) shows the degradation kinetic curves of 1TCN / BiVO4, 2TCN / BiVO4, 3TCN / TCN / BiVO4, 4TCN / BiVO4, BiVO4{001} and TCN.

[0036] Figure 16The following are the degradation and corresponding kinetic curves of MB by the photocatalysts UiO-66, TCN, BiVO4{001}, 2UiO / TCN / BiVO4 (Example 1), 4UiO / TCN / BiVO4 (Example 2), and 6UiO / TCN / BiVO4 (Example 3) prepared in the examples. (a) is a graph showing the degradation effect on MB, and (b) is a graph showing the degradation kinetic curve of MB.

[0037] In the above figures, TCN represents porous tubular graphitic carbon nitride, BiVO4{001} represents bismuth vanadate monomer material with highly exposed {001} crystal planes, 3TCN / BiVO4 represents a binary composite photocatalyst of 30 mg porous tubular graphitic carbon nitride and highly exposed {001} crystal plane bismuth vanadate, 2UiO / TCN / BiVO4 represents a ternary composite photocatalyst of 200 mg content, i.e., the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst prepared in Example 1, 4UiO / TCN / BiVO4 represents a ternary composite photocatalyst of 400 mg content, i.e., the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst prepared in Example 2, and 6UiO / TCN / BiVO4 represents a ternary composite photocatalyst of 600 mg content, i.e., the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst prepared in Example 3. Detailed Implementation

[0038] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific 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. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods, and the materials and reagents used in the following embodiments are commercially available unless otherwise specified.

[0039] To address the problems of existing photocatalysts, such as weak interfacial bonding, a single charge transport path, and insufficient matching of light absorption ranges, this invention provides a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst, its preparation method, and its application.

[0040] The technical concept of the present invention will be described below.

[0041] This invention provides a method for preparing a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst, comprising the following steps: Using porous tubular graphitic carbon nitride as a carrier, an aqueous solution containing bismuth and vanadium sources was mixed with a surfactant solution to obtain a precursor solution, wherein the surfactant was sodium oleate. After mixing the precursor solution with the carrier dispersion, a hydrothermal reaction was carried out at 160℃~200℃ to synthesize bismuth vanadate with a lamellar structure in situ, which was simultaneously loaded onto the surface of porous tubular graphitic carbon nitride to obtain a binary composite material.

[0042] Using binary composite materials and metal-organic framework materials as raw materials, wherein the metal-organic framework material is UiO-66; the binary composite material and UiO-66 are reacted in a solvent system at 50℃~70℃, so that UiO-66 is loaded on the surface of the binary composite material to form Z-type and / or type II heterojunctions, thereby obtaining carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst.

[0043] In the aforementioned technical solution, a ternary heterojunction system with synergistic structure and tight interfacial coupling is constructed by combining porous tubular g-C3N4, BiVO4 with highly exposed {001} crystal planes, and UiO-66. This design not only utilizes UiO-66 as an electron medium and structural support, significantly enhancing the separation and migration efficiency of photogenerated carriers, but also synergistically improves the visible light absorption capacity and redox potential of the material through band matching. Therefore, it exhibits superior catalytic activity compared to single or binary components in multiple reactions such as organic pollutant degradation, CO2 reduction, and photocatalytic water splitting for hydrogen / oxygen production. Simultaneously, the unique tubular porous structure of graphitic carbon nitride and the high specific surface area of ​​UiO-66 jointly enhance the adsorption and mass transfer processes of reactants, while ensuring the good structural stability and recyclability of the composite material.

[0044] In this ternary heterojunction architecture, porous tubular graphitic carbon nitride (g-C3N4) not only provides a high specific surface area and abundant mass transport channels, but its suitable conduction band position can also serve as the main reduction reaction center for photogenerated electrons. Bismuth vanadate (BiVO4), with its highly exposed {001} crystal planes, becomes a strong oxidation reaction active site due to its optimized band structure and excellent hole migration ability. Meanwhile, the metal-organic framework UIO-66 plays a dual role as a "molecular sponge" and structural support in the system due to its highly ordered hierarchical channels, extremely large specific surface area, and tunable surface chemical properties. On the one hand, it efficiently adsorbs and enriches reactants (such as CO2, organic molecules, and water molecules), and on the other hand, it acts as an electron transfer medium and interfacial coupling agent, promoting the formation of efficient stepwise charge transfer channels between g-C3N4 and BiVO4. The three components employed in this invention construct Z-type or II-type heterojunction charge transfer paths through the synergistic design of band structure and morphology, achieving efficient spatial separation and long lifetime maintenance of photogenerated electron-hole pairs, while fully utilizing the advantages of each component in spectral absorption, carrier migration and surface reaction.

[0045] The ternary heterojunction system provided by this invention can not only promote the efficient separation and migration of electron-hole pairs through the band ladder arrangement, but also enhance the adsorption and activation of reactants by utilizing the porous tubular structure of graphitic carbon nitride and the confinement effect of metal-organic framework UiO-66, thereby comprehensively improving the photocatalytic performance.

[0046] This invention develops a ternary composite photocatalyst with controllable structure and strong interfacial coupling. Through microstructural design, porous tubular g-C3N4 is constructed to increase the specific surface area and expose active sites. Simultaneously, it is ternarily composited with BiVO4, which has highly exposed {001} crystal planes, and UiO-66, which has a regular porous structure. This broadens the spectral response range, constructs multi-level charge transfer channels, and provides abundant surface active sites. This invention provides new ideas and material basis for designing efficient and stable solar energy conversion materials.

[0047] The carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst of the present invention can simultaneously drive multiple photocatalytic reactions under visible light irradiation, including the efficient degradation of organic pollutants, the selective reduction of CO2 to carbon-based fuels, and the decomposition of water to produce H2 and O2, providing a promising new material platform for realizing multi-path resource utilization driven by solar energy.

[0048] The photocatalytic mechanism of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst of the present invention is as follows: Let TCN represent porous tubular graphitic carbon nitride, BiVO4{001} represent bismuth vanadate with highly exposed {001} crystal planes, and TCN / BiVO4 represent a binary composite photocatalyst of porous tubular graphitic carbon nitride and bismuth vanadate with highly exposed {001} crystal planes. When TCN and BiVO4{001} form a composite material, a new Fermi level is formed between the Fermi levels of TCN and BiVO4{001}. Simultaneously, the valence band and conduction band of TCN shift downwards, while the valence band and conduction band of BiVO4{001} shift upwards. At this point, the valence band and conduction band of TCN near the BiVO4{001} bend upwards, and the valence band and conduction band of BiVO4{001} near the TCN bend downwards. Furthermore, during the above process, space charge regions are formed on both sides of the interface between TCN and BiVO4{001}. Because of the lower Fermi level of sm-BiVO4, electrons can more easily transfer from TCN to BiVO4{001}, thus forming a positive space charge region on the TCN side and a negative space charge region on the BiVO4{001} side, creating a built-in electric field pointing from TCN to BiVO4{001}. When light irradiates the TCN / BiVO4 binary composite photocatalyst and the photon energy is greater than the band gaps of TCN and BiVO4{001}, valence band electrons in TCN and BiVO4{001} transition to their conduction bands, creating holes in the valence band. According to the principle of minimum energy, electrons in the BiVO4{001} conduction band and holes in the TCN valence band simultaneously move towards their respective lower energy directions, and this process is facilitated by the built-in electric field. At this point, electrons in the BiVO4{001} conduction band recombine with holes in the TCN valence band. Holes in the BiVO4{001} valence band require significantly more energy to move towards lower energies (the difference between the Fermi levels of TCN and BiVO4{001}), and similarly, electrons in the TCN conduction band also require greater energy to move towards lower energies. This process is not easily achieved. At this point, there are a large number of holes in the BiVO4{001} valence band and a large number of electrons in the TCN conduction band, giving TCN / BiVO4 strong oxidizing and reducing properties.

[0049] The work function of UiO-66 is larger than that of g-C3N4, meaning that the Fermi level of UiO-66 is lower than that of TCN. When UiO-66 combines with TCN / BiVO4, the energy bands of UiO-66 and TCN / BiVO4 shift upwards and downwards respectively, forming a new Fermi level between them. This causes the energy band of UiO-66 near TCN / BiVO4 to bend downwards, while the energy band of TCN / BiVO4 near UiO-66 bends upwards. Simultaneously, a space charge region is generated at the interface between UiO-66 and TCN / BiVO4, with the electric field direction from TCN / BiVO4 to UiO-66. When illuminated, electrons in the valence band absorb photons with energy greater than or equal to the band gap and transition from the valence band to the conduction band, creating holes in the valence band. Furthermore, because the band gap of UiO-66 nanomaterials is larger than that of TCN / BiVO4, it can only absorb energy in the ultraviolet region, thus generating only a small number of photogenerated electrons and holes, while TCN / BiVO4 generates more electrons and holes. According to the principle of minimum energy, electrons in the conduction band of UiO-66 and holes in the valence band (TCN's valence band) of TCN / BiVO4 simultaneously transfer to lower energy directions, recombinating at the interface between UiO-66 and TCN / BiVO4, and the built-in electric field promotes this process. However, holes in the valence band of UiO-66 and electrons in the conduction band of TCN / BiVO4 require much higher energy (the Fermi level difference between UiO-66 and TCN / BiVO4), making their transfer less likely. Therefore, compared with the TCN / BiVO4 / UiO-66 nanocomposite material prepared by TCN / BiVO4, UiO-66 has improved oxidation capacity, while inhibiting the recombination of photogenerated electron-hole pairs and promoting their transfer, thus giving TCN / BiVO4 / UiO-66 stronger photocatalytic performance.

[0050] The technical effects of the present invention will be described below through specific embodiments and comparative examples.

[0051] Example 1 A method for preparing a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst includes the following steps: S1, 4g of urea and 1g of melamine were dissolved separately in 35mL of deionized water and sonicated for 15min, then stirred with a magnetic stirrer for 30min. The urea solution and melamine solution were mixed and stirred continuously for 30min to ensure thorough mixing. The mixture was then transferred to a 100mL reactor lined with polytetrafluoroethylene. The reactor was then placed in an electrically heated drying oven at 180℃ for 24h. After the reaction, the mixture was allowed to cool to room temperature naturally, washed twice with deionized water, then washed again with a small amount of a mixture of ethanol and water, and dried in a 60℃ oven for 12h. The dried product was collected and placed in a 15mL covered crucible and kept at 450℃ for 3h in a muffle furnace at a heating rate of 5℃ / min. After the reaction, the mixture was allowed to cool to room temperature naturally, then washed, dried, and collected for characterization. Porous tubular graphitic carbon nitride, denoted as TCN, was obtained.

[0052] S2, Weigh 300 mg of TCN and ultrasonically disperse it in 10 mL of deionized water to obtain a TCN dispersion. Add 5 mmol of Bi(NO3)3 5H₂O was added to 25 mL of 36% acetic acid solution, sonicated for 30 min, and continuously stirred at room temperature for 60 min, denoted as solution A. 5 mmol of NH₄VO₃ was added to 25 mL of deionized water, sonicated for 15 min, and continuously stirred at 65°C for 60 min, denoted as solution B. 10 mg of sodium oleate was added to 10 mL of deionized water, sonicated for 15 min, and continuously stirred at room temperature for 30 min, denoted as solution C. Then, solution B was slowly added dropwise to solution A, while simultaneously adding an appropriate amount of NaOH to adjust the pH to 7, and stirred for 60 min. Solution C was then added, and stirring continued for another 30 min. Finally, TCN dispersion was added to the above solutions, and stirring continued for another 30 min. After the four solutions were thoroughly mixed, the solution was poured into a 100 mL reaction vessel, and the oven initial temperature was set to 30°C with a heating rate of 5°C / min. The reaction was carried out at a constant temperature of 180°C for 10 h, followed by natural cooling to room temperature. Finally, the yellow reaction product was obtained by centrifugation. The product was then washed three times with deionized water and anhydrous ethanol, and dried in a drying oven at 60°C for 12 hours to obtain a yellow powder, which is the binary composite photocatalyst, denoted as 3TCN / BiVO4.

[0053] S3, 1 mmol of ZrCl4 (zirconium chloride) and 1 mmol of BDC (terephthalic acid) were added to 60 mL of DMF (N,N-dimethylformamide) and sonicated for 30 min, followed by continuous stirring for 1 h to ensure thorough mixing. Then, the mixed solution was transferred to a 100 mL stainless steel reactor lined with polytetrafluoroethylene and kept in an oven at 120 °C for 24 h. After natural cooling to room temperature, the reaction was completed. Finally, the reaction product was collected by centrifugation, washed three times with deionized water, methanol, and DMF, and placed in a drying oven at 60 °C for 12 h to obtain a white powder, denoted as UiO-66.

[0054] S4. 200 mg of UiO-66 was added to 30 mL of DMF solution, sonicated for 30 min, and then stirred for 60 min, denoted as solution A. 1 g of 3TCN / BiVO4 sample was added to 30 mL of deionized water, sonicated for 30 min, and then stirred for 60 min, denoted as solution B. Then, solution B was added dropwise to solution A to obtain a mixed solution. The mixture was stirred continuously at 60℃ in a water bath for 12 h, and then naturally cooled to room temperature. Finally, the precipitate was separated by centrifugation, washed three times with ethanol and deionized water, and collected after being placed in a 60℃ drying oven for 12 h. The resulting product was denoted as 2UiO / TCN / BiVO4.

[0055] Example 2 A method for preparing a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst includes the following steps: S1, 4g of urea and 1g of melamine were dissolved separately in 35mL of deionized water and sonicated for 15min, then stirred with a magnetic stirrer for 30min. The urea solution and melamine solution were mixed and stirred continuously for 30min to ensure thorough mixing. The mixture was then transferred to a 100mL reactor lined with polytetrafluoroethylene. The reactor was then placed in an electrically heated drying oven at 180℃ for 24h. After the reaction, the mixture was allowed to cool to room temperature naturally, washed twice with deionized water, then washed again with a small amount of a mixture of ethanol and water, and dried in a 60℃ oven for 12h. The dried product was collected and placed in a 15mL covered crucible and kept at 450℃ for 3h in a muffle furnace at a heating rate of 5℃ / min. After the reaction, the mixture was allowed to cool to room temperature naturally, then washed, dried, and collected for characterization. Porous tubular graphitic carbon nitride, denoted as TCN, was obtained.

[0056] S2, Weigh 300 mg of TCN and ultrasonically disperse it in 10 mL of deionized water to obtain a TCN dispersion. Add 5 mmol of Bi(NO3)3 5H₂O was added to 25 mL of 36% acetic acid solution, sonicated for 30 min, and continuously stirred at room temperature for 60 min, denoted as solution A. 5 mmol of NH₄VO₃ was added to 25 mL of deionized water, sonicated for 15 min, and continuously stirred at 65°C for 60 min, denoted as solution B. 10 mg of sodium oleate was added to 10 mL of deionized water, sonicated for 15 min, and continuously stirred at room temperature for 30 min, denoted as solution C. Then, solution B was slowly added dropwise to solution A, while simultaneously adding an appropriate amount of NaOH to adjust the pH to 7, and stirred for 60 min. Solution C was then added, and stirring continued for another 30 min. Finally, TCN dispersion was added to the above solutions, and stirring continued for another 30 min. After the four solutions were thoroughly mixed, the solution was poured into a 100 mL reaction vessel, and the oven initial temperature was set to 30°C with a heating rate of 5°C / min. The reaction was carried out at a constant temperature of 180°C for 10 h, followed by natural cooling to room temperature. Finally, the yellow reaction product was obtained by centrifugation. The product was then washed three times with deionized water and anhydrous ethanol, and dried in a drying oven at 60°C for 12 hours to obtain a yellow powder, which is the binary composite photocatalyst, denoted as 3TCN / BiVO4.

[0057] S3, 1 mmol of ZrCl4 (zirconium chloride) and 1 mmol of BDC (terephthalic acid) were added to 60 mL of DMF (N,N-dimethylformamide) and sonicated for 30 min, followed by continuous stirring for 1 h to ensure thorough mixing. Then, the mixed solution was transferred to a 100 mL stainless steel reactor lined with polytetrafluoroethylene and kept in an oven at 120 °C for 24 h. After natural cooling to room temperature, the reaction was completed. Finally, the reaction product was collected by centrifugation, washed three times with deionized water, methanol, and DMF, and placed in a drying oven at 60 °C for 12 h to obtain a white powder, denoted as UiO-66.

[0058] S4. 400 mg of UiO-66 was added to 30 mL of DMF solution, sonicated for 30 min, and then stirred for 60 min, denoted as solution A. 1 g of 3TCN / BiVO4 sample was added to 30 mL of deionized water, sonicated for 30 min, and then stirred for 60 min, denoted as solution B. Then, solution B was added dropwise to solution A to obtain a mixed solution. The mixture was stirred continuously at 60℃ in a water bath for 12 h, and then allowed to cool naturally to room temperature. Finally, the precipitate was separated by centrifugation, washed three times with ethanol and deionized water, and collected after being placed in a 60℃ drying oven for 12 h. The resulting product was denoted as 4UiO / TCN / BiVO4.

[0059] Example 3 A method for preparing a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst includes the following steps: S1, 4g of urea and 1g of melamine were dissolved separately in 35mL of deionized water and sonicated for 15min, then stirred with a magnetic stirrer for 30min. The urea solution and melamine solution were mixed and stirred continuously for 30min to ensure thorough mixing. The mixture was then transferred to a 100mL reactor lined with polytetrafluoroethylene. The reactor was then placed in an electrically heated drying oven at 180℃ for 24h. After the reaction, the mixture was allowed to cool to room temperature naturally, washed twice with deionized water, then washed again with a small amount of a mixture of ethanol and water, and dried in a 60℃ oven for 12h. The dried product was collected and placed in a 15mL covered crucible and kept at 450℃ for 3h in a muffle furnace at a heating rate of 5℃ / min. After the reaction, the mixture was allowed to cool to room temperature naturally, then washed, dried, and collected for characterization. Porous tubular graphitic carbon nitride, denoted as TCN, was obtained.

[0060] S2, Weigh 300 mg of TCN and ultrasonically disperse it in 10 mL of deionized water to obtain a TCN dispersion. Add 5 mmol of Bi(NO3)3 5H₂O was added to 25 mL of 36% acetic acid solution, sonicated for 30 min, and continuously stirred at room temperature for 60 min, denoted as solution A. 5 mmol of NH₄VO₃ was added to 25 mL of deionized water, sonicated for 15 min, and continuously stirred at 65°C for 60 min, denoted as solution B. 10 mg of sodium oleate was added to 10 mL of deionized water, sonicated for 15 min, and continuously stirred at room temperature for 30 min, denoted as solution C. Then, solution B was slowly added dropwise to solution A, while simultaneously adding an appropriate amount of NaOH to adjust the pH to 7, and stirred for 60 min. Solution C was then added, and stirring continued for another 30 min. Finally, TCN dispersion was added to the above solutions, and stirring continued for another 30 min. After the four solutions were thoroughly mixed, the solution was poured into a 100 mL reaction vessel, and the oven initial temperature was set to 30°C with a heating rate of 5°C / min. The reaction was carried out at a constant temperature of 180°C for 10 h, followed by natural cooling to room temperature. Finally, the yellow reaction product was obtained by centrifugation. The product was then washed three times with deionized water and anhydrous ethanol, and dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, which is the binary composite photocatalyst, denoted as 3TCN / BiVO4.

[0061] S3, 1 mmol of ZrCl4 (zirconium chloride) and 1 mmol of BDC (terephthalic acid) were added to 60 mL of DMF (N,N-dimethylformamide) and sonicated for 30 min, followed by continuous stirring for 1 h to ensure thorough mixing. Then, the mixed solution was transferred to a 100 mL stainless steel reactor lined with polytetrafluoroethylene and kept in an oven at 120 °C for 24 h. After natural cooling to room temperature, the reaction was completed. Finally, the reaction product was collected by centrifugation, washed three times with deionized water, methanol, and DMF, and placed in a drying oven at 60 °C for 12 h to obtain a white powder, denoted as UiO-66.

[0062] S4. 600 mg of UiO-66 was added to 30 mL of DMF solution, sonicated for 30 min, and then stirred for 60 min; this solution is denoted as Solution A. 1 g of 3TCN / BiVO4 sample was added to 30 mL of deionized water, sonicated for 30 min, and then stirred for 60 min; this solution is denoted as Solution B. Then, Solution B was added dropwise to Solution A to obtain a mixed solution. The mixture was continuously stirred at 60℃ in a water bath for 12 h, and then allowed to cool naturally to room temperature. Finally, the precipitate was separated by centrifugation, washed three times with ethanol and deionized water, and collected after being placed in a 60℃ drying oven for 12 h. The resulting product is denoted as 6UiO / TCN / BiVO4.

[0063] To illustrate the catalytic effect of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst prepared in this invention, application examples are also provided, as follows.

[0064] Application Example 1 Application of a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst in the photocatalytic degradation of methylene blue (MB), the application comprising the following steps: Using MB as the target degradation product, a 100W LED light strip was used to simulate visible light for photocatalytic reaction. A water-cooling device was added during the photocatalytic degradation process to maintain room temperature and prevent temperature from affecting the degradation efficiency. The photocatalytic performance testing procedure was as follows: First, a certain amount of 30 mg / L MB solution was prepared. Second, 30 mg of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst prepared in Example 1 was added to 50 mL of the pollutant solution (MB solution). The mixture was stirred continuously for 30 min in the dark to allow the photocatalyst and the target degradation product to reach adsorption-desorption equilibrium. 3 mL of the liquid was centrifuged and used as the initial concentration test sample. The initial concentration was recorded as [initial concentration value missing]. C 0; then, the light source was turned on to carry out the photocatalytic reaction. Every 15 minutes, 3 mL of the solution after the photocatalytic reaction was taken and centrifuged. The supernatant was used for pollutant concentration testing. Finally, the absorbance of the supernatant at 554 nm at time t was measured using a UV-Vis spectrophotometer to obtain the concentration of the target dye at time t. Ct (represented), and according to the Beer-Lambert law D(%) = ( C 0- C t ) / C The degradation rate of the target substance was calculated using the Langmuir-Hinshelwood pseudo-first-order reaction model (ln( C 0 / Ct The degradation rate k of the target pollutant is obtained by )=kt), so as to realize the photocatalytic performance of the prepared photocatalyst.

[0065] The performance of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalysts prepared in Examples 1 to 3 above was characterized, and the results are as follows.

[0066] XRD analysis: like Figure 2 Figure (a) shows the XRD patterns of the BiVO4{001} sample and BiVO4. The characteristic peaks of the BiVO4{001} sample are compared with those of the standard PDF card (space group: I 2 / b Comparative analysis with JCPDS No. 83-1699 shows that the peaks of the BiVO4{001} sample at 15.1°, 19.0°, 28.9°, 30.5°, and 46.7° are consistent with the characteristic peaks of the (002), (011), (112), (004), and (204) crystal planes on the standard PDF card. The characteristic peak of the (112) crystal plane is the highest, followed by the characteristic peaks of the (013) and (011) crystal planes. Therefore, it can be proven that the BiVO4{001} sample is a monoclinic scheelite structure BiVO4 nanomaterial. Figure 2As can be seen intuitively in (a), the intensity of the characteristic peak of the (004) crystal plane of BiVO4{001} is significantly higher than that of BiVO4. Further analysis of the XRD data of BiVO4{001} and BiVO4 was conducted, and the ratio of the main characteristic peak of BiVO4{001} and BiVO4 to the characteristic peak (strongest peak) of their respective (112) crystal planes was calculated. The results are shown in Table 1. The characteristic peaks of the (002) and (004) crystal planes of BiVO4{001} account for 41.2% of the (112) crystal plane, which is much higher than that of BiVO4 (20.0%). Compared with the standard PDF card, BiVO4{001} is nearly 10% higher. Taking into account the proportions of the (020) and (200) crystal planes, the characteristic peaks of the (002), (004), (020), and (200) crystal planes of BiVO4{001} account for 72.4% of the (112) crystal plane. Based on the above analysis, both BiVO4{001} and BiVO4 samples are monoclinic scheelite BiVO4 structures, and BiVO4{001} has a higher proportion of {001} crystal plane exposure than BiVO4. The XRD patterns of the prepared 3TCN / BiVO4 samples are shown in [image / image / description]. Figure 2 In (b), with sm-BiVO4 (JCPDS No. 83-1699, space group: I 2 / b The XRD standard PDF cards of 3TCN / BiVO4 and g-C3N4 (JCPDS No. 87-1526) were compared. The XRD of the 3TCN / BiVO4 sample contained characteristic peaks of BiVO4{001} and g-C3N4 (002) crystal plane. This indicates that BiVO4{001} and TCN did not affect each other's structures during the preparation of the 3TCN / BiVO4 sample, and the structure of the 3TCN / BiVO4 sample is mainly composed of TCN and BiVO4{001}. Figure 2Figure (c) shows the XRD test results of the UiO-66 sample and the 4UiO / TCN / BiVO4 sample from Example 2. The positions of the four strongest characteristic peaks of the UiO-66 sample are approximately 7.4°, 8.6°, 25.8°, and 30.9°, respectively, which are consistent with the previously reported XRD of UiO-66 nanomaterials. These peaks correspond to the (110), (200), (442), and (711) crystal planes of UiO-66 nanomaterials, respectively. In the XRD of the 4UiO / TCN / BiVO4 sample, the characteristic peaks of UiO-66 can be seen. Compared with the BiVO4 standard card JCPDS No. 83-1699, the corresponding characteristic peaks of BiVO4{001} can be observed, but the characteristic peaks of TCN are not observed. This is mainly due to the relatively reduced content of TCN and the low characteristic peak value of TCN in the XRD. This phenomenon often occurs in other composite materials.

[0067] Table 1. XRD data of BiVO4{001} and BiVO4. FT-IR analysis: The FT-IR spectra of TCN, BiVO4{001}, 3TCN / BiVO4, and 4UiO / TCN / BiVO4 samples are as follows: Figure 3 As shown. Figure 3 In (a) the BiVO4{001} sample at 738 cm -1 The peak at that point is VO4 -3 In the group v The asymmetric tensile vibrations of 3 are generated. This can be seen in the FT-IR spectrum of the TCN sample at 812 cm⁻¹. -1 The peak at approximately 1317 cm⁻¹ represents a typical vibrational peak of the heptaazine ring, the basic structural unit of the g-C₃N₄ tris-triazine structure. -1 and 1238cm -1 The characteristic peaks at 2800 cm⁻¹ represent CN(-C)-C (complete condensation) and C-CH-C (partial condensation), respectively. -1 ~3300cm -1The peaks within the range are generated by the vibration of NH (or NH2) groups, i.e., residual amino groups (C-NH2 or 2C-NH) after calcination, or related to OH stretching and adsorbed water. The FT-IR of the 3TCN / BiVO4 sample contains characteristic peaks of both monomeric TCN and BiVO4{001} nanomaterials. Combined with XRD analysis results, this indicates the presence of TCN and BiVO4{001} structures in the 3TCN / BiVO4 sample, and that the preparation of the 3TCN / BiVO4 sample did not destroy the basic structures of TCN and BiVO4{001} materials. Comparison of the characteristic peaks of the three samples also shows a slight blue shift in the position of the main characteristic peak of the 3TCN / BiVO4 sample relative to the peak position of BiVO4{001}, which may be due to the interaction between TCN and BiVO4{001} at the interface. This also indicates the successful preparation of the TCN / BiVO4 nanocomposite material. Figure 3 (b) shows the FT-IR test results for the UiO-66 sample and the 4UiO / TCN / BiVO4 sample. A distinct broad peak can be observed in the FT-IR spectrum of the UiO-66 sample, at 3600 cm⁻¹. -1 ~3300cm -1 The range represents the stretching vibration peak of the hydroxyl group (-OH), at 1596 cm⁻¹. -1 and 1506cm -1 The peak at 1391 cm⁻¹ is caused by the asymmetric tensile vibration of C=O. -1 The peak at 750 cm⁻¹ is related to the asymmetric stretching vibration of CO in terephthalic acid. -1 and 552cm -1 The nearby peaks correspond to the vibrations of δ(CH) and ν(Zr-O), respectively. Combined with XRD analysis, the results indicate that the UiO-66 sample is a UiO-66 nanomaterial. The typical characteristic peaks of UiO-66 nanomaterials, as well as the characteristic peaks of TCN and BiVO4{001} nanoparticles, are clearly observed in the FT-IR spectrum of the 4UiO / TCN / BiVO4 sample. At 1600 cm⁻¹... -1 ~1400cm -1 The vibration peak at 738 cm⁻¹ is generated by the typical tensile vibration of the g-C₃N₄ heterocycle. -1 The vibration peak at that location belongs to BiVO4{001} nanomaterials. v 3(VO4 -3 The asymmetric tensile vibration of ) was observed. Therefore, the presence of UiO-66, TCN and BiVO4{001} nanostructures in the 4UiO / TCN / BiVO4 sample was further confirmed.

[0068] SEM, TEM, and TEM Mapp analysis: like Figure 4 Image (a) is a SEM image of the 3TCN / BiVO4 sample, showing tubular and lamellar structures, with the lamellars adhered to the surface of the tubes. The results of TEM characterization of the 3TCN / BiVO4 sample are as follows... Figure 4 As shown in (b), the sheet-like structure adhered to the tube wall can be observed more clearly. To further confirm whether it is BiVO4{001} and TCN nanomaterials, TEM images of the 3TCN / BiVO4 sample were obtained. Figure 4 (b) scanned for Bi and N elements respectively, and obtained Figure 4 (e) and (f). To avoid the influence of nitrogen in the air, the N element ratio was lowered and the contrast was increased during scanning. It can be clearly seen from the images that the Bi atom scan is plate-like, while the N atom scan is strip-like (tubular). Combined with the morphology of the monomer material, this further illustrates that the plate-like structure is BiVO4{001}, and the tubular structure is TCN. HR-TEM was used to... Figure 4 The boundary (red box) between the sheet material and the tubular material in (b) was characterized and analyzed, and the results are as follows: Figure 4 (c) and (d). The lattice fringe spacings were measured to be 0.289 nm, 0.261 nm, and 0.252 nm, respectively, consistent with the standard PDF card (JCPDS No. 83-1699). I 2 / b By comparing the space groups, they correspond to the (004), (200), and (020) crystal planes of BiVO4{001}, respectively. Therefore, it can be confirmed that the lamellar structure is BiVO4{001} nanomaterial. Upon closer observation of the lattice fringes of the (200) and (020) crystal planes of BiVO4{001}, it can be seen that they are perpendicular to each other, which further confirms that the lamellar structure is BiVO4{001} nanomaterial. Combined with the XRD and FT-IR analysis results, the combination of TCN and BiVO4{001} does not affect its structure and morphology. From the above analysis results, it can be seen that the interfaces of the {001} crystal plane family ((004), (200), and (020) crystal planes belong to the {001} crystal plane family) of BiVO4{001} are combined with TCN.

[0069] SEM and TEM analyses: Figure 5 (a) and (b) are SEM images of the UiO-66 sample, showing that the UiO-66 sample exists as particles. Figure 5 (c) clearly shows the boundaries of the particles, which are polyhedral and have a diameter of about 100 nm. This is consistent with the morphology of UiO-66 nanomaterials reported in the past. Combined with the XRD analysis results, it is further confirmed that the UiO-66 sample is a UiO-66 nanomaterial.

[0070] SEM, TEM, and TEM Mapp analysis: like Figure 6 SEM, TEM, TEM elemental scanning, and HR-TEM images of the 4UiO / TCN / BiVO4 sample are shown. Tubular, lamellar, and granular structures are clearly observed in the SEM and TEM images, with lamellar and granular structures attached to the tubular surface. Comparing the morphology with that of monomeric TCN, BiVO4{001}, and UiO-66 nanomaterials, the tubular structure is TCN, the lamellar structure is BiVO4{001}, and the granular structure is UiO-66. (TEM elemental scanning images are shown.) Figure 6 (d) indicates that the red and green colors represent Zr and Bi elements, respectively, further confirming that they are UiO-66 and BiVO4{001} nanomaterials. The morphology and location of Zr and Bi elements can be clearly distinguished through the Zr and Bi element scans. (HR-TEM) Figure 6 Analysis of (f) shows the presence of lattice fringes with widths of 0.321 nm, 0.260 nm, and 0.252 nm. Comparison with literature and standard cards (JCPDS No. 83-1699) indicates that 0.321 nm corresponds to the lattice fringes of UiO-66, while 0.260 nm and 0.252 nm correspond to the (200) and (020) crystal planes of BiVO4{001}. Based on the above analysis results and XRD and FT-IR analyses, it can be concluded that the 4UiO / TCN / BiVO4 sample contains nanostructures of UiO-66, TCN, and BiVO4{001}, without altering the structure and morphology of the monomer materials.

[0071] XPS Analysis: Figure 7 (a) shows the full XPS spectrum of 3TCN / BiVO4, confirming that only Bi, V, O, C, and N elements exist on the sample surface. The XPS spectrum of C1s is as follows... Figure 7 As shown in (b), the characteristic peak at 284.5 eV is caused by the amorphous carbon on the surface of the prepared sample, while the peaks at 285.9 eV and 288.5 eV represent sp in the N-containing aromatic ring (NC=N). 2 Hybrid carbon. In Figure 7 In (c), the characteristic peak of N 1s at 397.6 eV represents the C=NC bond, and the peak at 400.0 eV originates from N-(N3). The O 1s peak at 529.6 eV represents lattice O in BiVO4{001}, and the peaks at 531.7 eV and 533.9 eV represent hydroxyl groups and surface adsorbed water, respectively. Figure 7 (d)). In the Bi 4f spectrum ( Figure 7The peaks at 164.0 eV and 158.7 eV (e) correspond to Bi4f. 5 / 2 and Bi 4f 7 / 2 This indicates that Bi is mainly present in the 3TCN / BiVO4 sample as Bi. 3+ Form exists; such as Figure 7 In (f), the V 2p characteristic peaks appear at 524.0 eV and 516.3 eV, which are attributed to V 2p, respectively. 1 / 2 and V 2p 3 / 2 Furthermore, in the 3TCN / BiVO4 sample, V mainly exists as V3. 5+ The characteristic peaks confirm the presence of g-C3N4 and sm-BiVO4 structures in the 3TCN / BiVO4 sample, but no new chemical bonds are formed between them.

[0072] Specific surface area, pore volume, and average pore diameter: Table 2 shows the specific surface area, pore volume, and pore size of the BiVO4{001}, UiO-66, and 4UiO / TCN / BiVO4 samples. The specific surface area, pore volume, and average pore size of the UiO-66 sample were 886 μm. 2 / g, 0.15cm 2 The specific surface area of ​​the 4UiO / TCN / BiVO4 sample was 552 m² / g and 1.31 mm. 2 The specific surface area of ​​the 4UiO / TCN / BiVO4 sample is smaller than that of the UiO-66 sample but much larger than that of the BiVO4{001} sample, although the average pore size is larger than that of the UiO-66 sample. The large specific surface area of ​​the 4UiO / TCN / BiVO4 sample is due to the contribution of UiO-66, while the pore size and pore volume are mainly contributed by TCN.

[0073] Table 2 Data of BiVO4{001}, UiO-66 and 4UiO / TCN / BiVO4 samples UV-Vis DRS analysis: Figure 8 These are the UV-Vis DRS spectra of TCN, BiVO4{001}, and 3TCN / BiVO4 samples, from... Figure 8 As can be seen, their absorption band edges are approximately 475 nm, 506 nm, and 560 nm, respectively. Compared to TCN and BiVO4{001}, the 3TCN / BiVO4 sample can absorb a wider range of sunlight. According to the Tauc formula ( The band gap of 3TCN / BiVO4 is 2.21 eV, which is 0.24 eV smaller than that of BiVO4{001} and 0.40 eV smaller than that of TCN. Furthermore, according to the empirical formula ( , By using this method, we can obtain the positions of the valence band top and conduction band bottom for TCN and BiVO4{001}. We know that the X value for g-C3N4 is 4.67 eV, and the X value for sm-BiVO4 is 6.04 eV. The calculated results show that the conduction band top and valence band bottom positions for TCN are 1.48 eV and -1.13 eV, respectively, and for BiVO4{001}, they are 2.77 eV and 0.33 eV, respectively.

[0074] UV-Vis DRS analysis: Figure 9 The UV-vis DRS test results for the UiO-66 sample and the 4UiO / TCN / BiVO4 sample are presented. Figure 9 As can be observed in (a), the absorption band edge of the UiO-66 sample is in the ultraviolet region, while the absorption band edge of the 4UiO / TCN / BiVO4 sample is in the visible region (approximately 585 nm), and its absorption range is larger than that of the 3TCN / BiVO4 sample. Using UV-vis DRS absorption spectral data and based on the Tauc equation (… The x-coordinate was calculated as follows: hv The vertical axis is ( ahv ) 2 The curve. The result is as follows. Figure 9 As shown in (b), the band gap values ​​were obtained by extending the rising curve of the first peak and intersecting it with the horizontal axis. The band gap of the UiO-66 sample was 3.91 eV, and the band gap of the 4UiO / TCN / BiVO4 sample was 2.04 eV, which were smaller than those of UiO-66 and 3TCN / BiVO4. These results indicate that the TCN / BiVO4 / 4UiO composite material has better photocatalytic performance than the UiO-66 monomer and the 3TCN / BiVO4 composite material. Furthermore, the positions of the conduction band bottom and valence band top of UiO-66 can be determined using an empirical formula: According to the literature, the X of UiO-66 is 5.6 eV. Calculations show that its valence band top is 3.06 eV and its conduction band bottom is -0.86 eV.

[0075] PL Analysis: Figure 10(a) shows the photoluminescence (PL) spectra of TCN, BiVO4{001}, and 3TCN / BiVO4 samples, with spectral intensities in descending order: TCN > BiVO4{001} > 3TCN / BiVO4. Lower PL peak intensities indicate fewer photogenerated electron-hole recombinations. According to UV-Vis DRS measurements, the 3TCN / BiVO4 sample absorbs more photon energy and generates more photogenerated electron-hole pairs. The PL test shows that the 3TCN / BiVO4 sample has the fewest photogenerated electron-hole recombinations, indicating a greater number of separated photogenerated electron-hole pairs. This suggests that the interface between TCN and BiVO4{001} provides a channel for the separation of photogenerated electron-hole pairs, or that the formation of a heterojunction structure between the two promotes the separation of photogenerated electrons and holes. The higher the photogenerated carrier separation rate, the greater the probability of electrons and holes reaching the catalyst surface, the more electrons and holes participate in the photocatalytic reaction, and the stronger its photocatalytic performance.

[0076] like Figure 10 As shown in (b), the photoluminescence (PL) spectra of the UiO-66, 3TCN / BiVO4, and 4UiO / TCN / BiVO4 samples are presented. Compared with the UiO-66 and 3TCN / BiVO4 samples, the PL intensity of 4UiO / TCN / BiVO4 is significantly lower. This is because the addition of UiO-66 further promotes the separation of photogenerated electron-hole pairs in 3TCN / BiVO4, resulting in only a small number of photogenerated electron-hole pairs recombinating. Therefore, it can be inferred that the 4UiO / TCN / BiVO4 sample contains more separated photogenerated electrons and holes than UiO-66 and TCN / BiVO4, thus resulting in a greater number of electrons and holes reaching the photocatalyst surface to participate in the photocatalytic reaction, and its photocatalytic performance may be stronger.

[0077] Current density and electrochemical impedance analysis: like Figure 11(a) compares the transient photocurrent responses of TCN, BiVO4{001}, and 3TCN / BiVO4 samples under four cycles of illumination. It can be seen that when illumination is turned on, the current values ​​of all samples initially spike and then stabilize at a certain value. When illumination is turned off, the current values ​​drop to near zero. The reason for the spike followed by a decrease to a constant value at the initial stage of illumination is that a large number of electrons and holes are generated instantaneously during illumination. Photogenerated electrons and holes recombine rapidly within a short time, and after reaching equilibrium, the photocurrent tends to be constant. Comparing the constant currents of TCN, BiVO4{001}, and TCN / BiVO4 samples, the current of the 3TCN / BiVO4 sample is 1.5 times that of the monolithic BiVO4{001} sample and approximately twice that of TCN, and they exhibit good reproducibility. This further demonstrates that the composite material of TCN and BiVO4{001} can effectively promote the separation of photogenerated electrons and holes, allowing more free electrons to participate in conductivity. Furthermore, electrochemical impedance spectroscopy is also an effective method for analyzing charge separation efficiency. Figure 11 (b) shows the electrochemical impedance spectroscopy (EIS) curves of TCN, BiVO4{001}, and 3TCN / BiVO4 samples. A larger radius of the EIS curve indicates greater resistance during electron-hole separation; conversely, a smaller radius indicates more electrons can participate in the photocatalytic reaction. The EIS curve radii of the TCN, BiVO4{001}, and 3TCN / BiVO4 samples, from largest to smallest, are TCN > BiVO4{001} > 3TCN / BiVO4, indicating that the 3TCN / BiVO4 sample exhibits a higher number of photogenerated electron-hole pairs. This result is consistent with the conclusions drawn from transient photocurrent and PL analyses. This suggests that heterojunction formation in the TCN / BiVO4 composite material promotes the separation of photogenerated electrons and holes or inhibits their recombination.

[0078] Current density and electrochemical impedance analysis: Figure 12 (a) shows the transient photocurrent response of the UiO-66 sample and the 4UiO / TCN / BiVO4 sample under four cycles of intermittent illumination. It can be seen that when illumination is turned on, the photocurrent of all samples reaches its peak and then gradually decreases until it reaches a constant photocurrent; when illumination is turned off, the photocurrent rapidly drops to near zero. The change process is the same for each cycle, and there is no significant difference in the photocurrent value change, indicating that all samples have good reproducibility. Compared with the photocurrent test results of UiO-66 and 3TCN / BiVO4, the stable current value of the 4UiO / TCN / BiVO4 sample under illumination is larger, indicating that the addition of UiO-66 results in more mobile charges in 3TCN / BiVO4. This further proves that the 4UiO / TCN / BiVO4 sample suppresses the recombination of photogenerated electron-hole pairs, allowing more photogenerated electrons to participate in conduction. Figure 12 (b) shows the electrochemical impedance spectroscopy (EIS) curves of UiO-66 and 4UiO / TCN / BiVO4 samples. The radius of the EIS curve for 4UiO / TCN / BiVO4 is significantly smaller than that for UiO-66. Comparing with previous test results, the EIS radius of 4UiO / TCN / BiVO4 is also smaller than that of 3TCN / BiVO4, and a smaller radius indicates less resistance during charge transfer. This suggests that photogenerated carriers in the 4UiO / TCN / BiVO4 sample transfer more easily than those in UiO-66 and 3TCN / BiVO4. It also indicates that the addition of UiO-66 results in more conductive ions in 3TCN / BiVO4, reducing the impedance. Based on the above analysis and combined with UV-vis DRS and PL test results, it can be concluded that the TCN / BiVO4 / 4UiO composite material exhibits better photoelectric and electrochemical properties than UiO-66 and 3TCN / BiVO4, and its photocatalytic performance may also be better.

[0079] Photocatalytic mechanism analysis: The conduction band positions of TCN and BiVO4{001} are 0.33 eV and 2.77 eV, respectively, and the valence band positions are -1.13 eV and 1.48 eV, respectively. vs . NHE, pH=7). Figure 13 (a) shows the band arrangement of TCN and BiVO4{001}. The work function of sm-BiVO4 is greater than that of g-C3N4, meaning that the Fermi level of sm-BiVO4 is lower than that of g-C3N4. When TCN and BiVO4{001} form a composite material, a new Fermi level is formed between the Fermi levels of TCN and BiVO4{001}. Simultaneously, the valence band and conduction band of TCN shift downwards, while the valence band and conduction band of BiVO4{001} shift upwards. At this point, the valence band and conduction band of TCN near the BiVO4{001} bend upwards, while the valence band and conduction band of BiVO4{001} near the TCN bend downwards. Furthermore, during the above process, space charge regions are formed on both sides of the interface between TCN and BiVO4{001}. Because sm-BiVO4 has a lower Fermi level, electrons can more easily transfer from TCN to BiVO4{001}, thus forming a positive space charge region on the TCN side and a negative space charge region on the BiVO4{001} side, creating a built-in electric field pointing from TCN to BiVO4{001}. The conclusion that the built-in electric field direction of the g-C3N4 and BiVO4 composite materials is from g-C3N4 to BiVO4 is consistent with this. Figure 13(b) shows the band arrangement and space charge distribution at the interface of the TCN / BiVO4 composite material. When light irradiates the TCN / BiVO4 composite material and the photon energy is greater than the band gap of TCN and BiVO4{001}, valence band electrons in TCN and BiVO4{001} transition to their conduction bands, creating holes in the valence band. According to the principle of minimum energy, electrons in the BiVO4{001} conduction band and holes in the TCN valence band simultaneously move towards their respective lower energy directions, and this process is facilitated by the built-in electric field. At this time, electrons in the BiVO4{001} conduction band recombine with holes in the TCN valence band, while holes in the BiVO4{001} valence band require greater energy to move towards lower energy directions (the difference between the Fermi levels of TCN and BiVO4{001}). Similarly, electrons in the TCN conduction band also require greater energy to move towards lower energy directions, making this process difficult to occur. At this point, there are a large number of holes in the BiVO4{001} valence band and a large number of electrons in the TCN conduction band, which makes TCN / BiVO4 have strong oxidizing and reducing properties.

[0080] Photocatalytic mechanism analysis: UiO / TCN / BiVO4 UiO-66 readily combines with the π-π conjugated structure in TCN, thus it can be concluded that TCN and UiO-66 combine in the TCN / BiVO4 composite material to form a UiO / TCN / BiVO4 composite material. Their band arrangement is shown in Figure 14(a). The work function of UiO-66 is larger than that of g-C3N4, meaning that the Fermi level of UiO-66 is lower than that of TCN. When UiO-66 combines with TCN / BiVO4, the bands of UiO-66 and TCN / BiVO4 shift upwards and downwards respectively, forming a new Fermi level between them. This causes the band of UiO-66 near TCN / BiVO4 to bend downwards, while the band of TCN / BiVO4 near UiO-66 bends upwards. Simultaneously, a space charge region is generated at the interface between UiO-66 and TCN / BiVO4, with the electric field direction from TCN / BiVO4 to UiO-66, as shown in Figure 14(a). Figure 14As shown in (b), when illuminated, electrons in the valence band absorb photons with energy greater than or equal to the band gap and transition from the valence band to the conduction band, creating holes in the valence band. Because the band gap of UiO-66 nanomaterials is larger than that of TCN / BiVO4, it can only absorb energy in the ultraviolet region, thus generating only a small number of photogenerated electrons and holes, while TCN / BiVO4 generates more. According to the principle of minimum energy, electrons in the conduction band of UiO-66 and holes in the valence band of TCN / BiVO4 (TCN's valence band) simultaneously transfer to the lower energy direction, recombine at the interface between UiO-66 and TCN / BiVO4, and the built-in electric field promotes this process. However, holes in the valence band of UiO-66 and electrons in the conduction band of TCN / BiVO4 require much higher energy (the Fermi level difference between UiO-66 and TCN / BiVO4), making transfer less likely. (Comparison) Figure 14 In (a) and (b), the BiVO4{001} valence band position shifts towards higher energy (downward), enhancing the oxidation capacity of TCN / BiVO4. Furthermore, when UiO-66 generates photogenerated electrons and holes, even the small number of holes exhibit strong oxidation capacity. Therefore, the TCN / BiVO4 / UiO nanocomposite material prepared by this invention, using UiO-66 and TCN / BiVO4, demonstrates improved oxidation capacity compared to TCN / BiVO4, while simultaneously suppressing the recombination of photogenerated electron-hole pairs and promoting their transfer, resulting in stronger photocatalytic performance for TCN / BiVO4 / UiO.

[0081] Photocatalytic degradation analysis of MB: TCN, BiVO4{001} and 3TCN / BiVO4 The photocatalytic performance of TCN / BiVO4 samples was evaluated by photocatalytic degradation of MB solution under simulated visible light irradiation. The results are as follows: Figure 15 As shown in the figure. After 60 minutes of light irradiation, the 3TCN / BiVO4 sample showed the best degradation effect on MB, reducing the MB concentration by more than 95%, while the BiVO4{001} and TCN samples reduced the MB concentration by 73% and 47%, respectively. (See the first-order linear kinetic curve...) Figure 15 The reaction constant k value is shown in (b). Within 60 min of photocatalytic reaction time, the k value of 3TCN / BiVO4 is 0.049, which is 4.5 times that of TCN and 2.3 times that of BiVO4{001}. Other TCN ratios of TCN / BiVO4 also showed better MB degradation performance than TCN and BiVO4{001}.

[0082] Photocatalytic degradation analysis of MB: UiO-66 and 4UiO / TCN / BiVO4 The photocatalytic performance of UiO / TCN / BiVO4 samples with different contents of UiO-66 was evaluated by simulating the degradation of MB solution under visible light. The results are as follows: Figure 16 As shown, in the 30-minute dark reaction, the decrease in solution concentration is negligible compared to photocatalytic degradation. The figure clearly shows that UiO / TCN / BiVO4 significantly degrades 30 mg / L MB within 45 minutes compared to UiO-66, BiVO4{001}, and TCN monomer materials. Specifically, in Example 2, the 400 mg UiO-66 content of 4UiO / TCN / BiVO4 can achieve approximately 95% degradation, while UiO-66 only achieves approximately 32%. Figure 16 (b) shows the reaction constant k values ​​of the first-order linear kinetic curves of the photocatalytic degradation of MB by UiO-66, BiVO4{001}, TCN, and xUiO / TCN / BiVO4 (the composite photocatalysts of Examples 1 to 3) over 45 min, which are 0.008, 0.018, 0.012, 0.043, 0.050, and 0.067, respectively. Calculations show that the degradation rate of MB by 4UiO / TCN / BiVO4 prepared in Example 2 is approximately 8.4 times, 3.7 times, and 5.6 times that of UiO-66, BiVO4{001}, and TCN, respectively.

[0083] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst, characterized in that, Includes the following steps: Using porous tubular graphitic carbon nitride as a carrier, an aqueous solution containing bismuth and vanadium sources is mixed with a surfactant solution to obtain a precursor solution, wherein the surfactant is sodium oleate. After mixing the precursor solution with the carrier dispersion, a hydrothermal reaction was carried out at 160℃~200℃ to synthesize bismuth vanadate with a lamellar structure in situ. Simultaneously, it was loaded onto the surface of porous tubular graphitic carbon nitride to obtain a binary composite material. Using binary composite materials and metal-organic framework materials as raw materials, wherein the metal-organic framework material is UiO-66; the binary composite material and UiO-66 are reacted in a solvent system at 50℃~70℃, so that UiO-66 is loaded on the surface of the binary composite material to form Z-type and / or type II heterojunctions, thereby obtaining carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst.

2. The preparation method of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst according to claim 1 is characterized in that, The mass ratio of the porous tubular graphitic carbon nitride, bismuth vanadate, and UiO-66 is 1:1.5-9:0.5-6.

3. The preparation method of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst according to claim 2, characterized in that, The mass ratio of UiO-66 to the binary composite material is 0.2 to 0.6:

1.

4. The preparation method of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst according to claim 1 is characterized in that, The ratio of bismuth source, vanadium source and sodium oleate is 1 mmol: 1 mmol: 1.8 mg to 2 mg.

5. The preparation method of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst according to claim 1, characterized in that, The {001} crystal plane family of the bismuth vanadate is bonded to the porous tubular graphite phase carbon nitride interface, wherein the {001} crystal plane family is at least one of the (004) crystal plane, (200) crystal plane and (020) crystal plane.

6. The preparation method of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst according to claim 1, characterized in that, The hydrothermal reaction time is 8h to 12h; the reaction time at 50℃ to 70℃ is 10h to 14h.

7. The preparation method of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst according to claim 1, characterized in that, The bismuth source is Bi(NO3)3. 5H2O, the vanadium source is NH4VO3.

8. The method for preparing the biochar-doped aluminum-cobalt spinel catalyst according to claim 1, characterized in that, The method for preparing porous tubular graphitic carbon nitride includes the following steps: using urea and melamine as raw materials, a hydrothermal reaction is carried out at 160℃~180℃ to obtain a primary product, and the primary product is heated to 450℃~500℃ for heat treatment to obtain porous tubular graphitic carbon nitride.

9. A carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst, characterized in that, The composite photocatalyst was prepared using the method described in any one of claims 1 to 8.

10. The application of the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst according to claim 9 in the catalytic degradation of organic pollutants, characterized in that, The application method is as follows: the carbon nitride / bismuth vanadate / UiO-66 composite photocatalyst is added to a solution containing organic pollutants, and a photocatalytic degradation reaction is carried out under visible light.

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