Bismuth-doped vanadate-based environmental functional material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalytic materials, and discloses a bismuth-doped vanadate-based environmental functional material as well as a preparation method and application thereof. The material is Bi < x > (at) Mn < 2 > V < 2 > O < 7 >, wherein x is 1-7. The bismuth element is introduced on the premise of keeping the stability of the Mn2V2O7 main body crystal phase structure, so that the regulation and control of the material electronic structure and the activation of surface reaction active sites are realized. The preparation method comprises the following steps: by taking a sacrificial template as a carrier, introducing a manganese source, a vanadium source and a bismuth source through gas-phase ion exchange reaction at 425-550 DEG C to prepare the bismuth-doped manganese vanadate photocatalytic material. The material can efficiently drive a hydrogen evolution reaction and an oxygen evolution reaction at the same time under the condition of no sacrificial agent, the generation rate ratio of hydrogen to oxygen is close to the theoretical stoichiometric ratio of 2: 1, stable photocatalytic full decomposition of water is achieved, the overall photocatalytic activity of the material can reach 27.2 times that of undoped Mn2V2O7 at most, and the unexpected technical effect is achieved; the device is suitable for the field of solar-driven clean hydrogen production.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, and in particular to a bismuth-doped vanadate-based environmental functional material, its preparation method, and its application. Background Technology

[0002] Overall water splitting (OWS) technology, based on a single semiconductor light-absorbing material, can simultaneously generate hydrogen and oxygen through a one-step photoexcitation under illumination. It boasts advantages such as a simple reaction process, environmental friendliness, and the elimination of the need for external electricity, and is considered one of the important technological pathways for achieving renewable hydrogen production. This technology holds promise for directly converting water into clean hydrogen energy under solar power, thereby reducing dependence on fossil fuels and demonstrating broad application prospects.

[0003] Currently, some wide bandgap semiconductor materials have been proven to achieve photocatalytic water splitting, such as TiO2 and SrTiO3, which can achieve photocatalytic water splitting in the ultraviolet or ultraviolet-visible light regions. However, due to their wide bandgap, their absorption capacity for visible light is limited, resulting in low solar energy utilization efficiency and extremely low overall solar-to-hydrogen conversion efficiency (STH). Only when STH ≥ 10% does it have industrialization potential.

[0004] In contrast, narrow bandgap semiconductor materials have a wider visible light absorption range. When the bandgap of a semiconductor material is less than 2.1 eV, its theoretical STH efficiency can exceed 15%, making it a potential candidate material for achieving efficient photocatalytic water splitting. However, the number of existing narrow bandgap semiconductor materials capable of photocatalytic water splitting remains limited. Most reported narrow bandgap systems are constrained in actual reaction processes by factors such as slow oxygen evolution reaction (OER) kinetics, high reaction barriers, and insufficient effective active sites on the surface. This makes it difficult to simultaneously and efficiently complete the hydrogen evolution reaction (HER) and oxygen evolution reaction under sacrificial agent-free conditions, resulting in limited overall photocatalytic performance, or even exhibiting only half-reaction activity for hydrogen evolution.

[0005] Manganese vanadate Mn₂V₂O₇ is an n-type narrow bandgap semiconductor with a bandgap (Eg) of approximately 1.7 eV. The conduction band and valence band edges (Eg) are located at... CB ≈ -0.2 V, E VB Theoretically, a photocatalytic oxygen evolution reaction (OER) of approximately 1.5 V can simultaneously meet the thermodynamic requirements of both HER and OER, and has good visible light response. However, it still suffers from problems such as insufficient valence band reactivity and slow oxygen evolution reaction kinetics. Its intrinsic oxygen evolution activity is low, making it difficult to achieve efficient and stable photocatalytic total water splitting reaction. There are currently no publicly available reports on its ability to achieve efficient OWS under sacrificial agent-free conditions.

[0006] Therefore, how to effectively control the band structure and activate surface reactive sites of narrow bandgap semiconductor materials, especially systems with potential thermodynamic advantages such as Mn2V2O7, while maintaining the stability of their main structure, thereby breaking through the limitations of oxygen evolution reaction kinetics and achieving efficient photocatalytic water splitting under sacrificial agent-free conditions, remains a technical problem that urgently needs to be solved in this field.

[0007] The information disclosed in this background section is only intended to enhance the understanding of the background technology of this application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a bismuth-doped vanadate-based environmental functional material, its preparation method, and its applications.

[0009] This invention proposes a bismuth-doped vanadate-based environmental functional material, wherein the material is a bismuth-doped manganese vanadate (Bi). x @Mn2V2O7, where x is 1~7.

[0010] Preferably, x is 3 to 5.

[0011] When x is 1 to 7, the photocatalytic water splitting reaction can be achieved without sacrificial agents; when x is 3 to 5, the material exhibits the best synergistic activity in the hydrogen evolution and oxygen evolution reactions.

[0012] Preferably, the bismuth-doped manganese vanadate has a nanosheet, layered, or porous structure.

[0013] Preferably, the material contains a multi-component synergistic bonding structure formed by the interaction of Mn-O bonds, VO bonds, and Bi-Mn bonds.

[0014] Preferably, the material can simultaneously catalyze the hydrogen evolution reaction and the oxygen evolution reaction under sacrificial agent-free conditions.

[0015] A method for preparing bismuth-doped vanadate-based environmental functional materials as described above includes the following steps: (1) Sacrificial template construction steps: A metal oxide nanosheet array is grown on a conductive substrate by hydrothermal method to form a sacrificial template; (2) Gas-phase ion exchange conversion step: Under an inert atmosphere, the sacrificial template reacts with the manganese source, vanadium source and bismuth source through a gas-phase ion exchange reaction to form bismuth-doped manganese vanadate Bi in situ. x @Mn2V2O7, where x is 1~7.

[0016] Preferably, the sacrificial template is selected from one or more of ZnO, CoO, and WO3.

[0017] Preferably, the manganese source is selected from one or more of MnCl2, Mn(NO3)2, and manganese oxide.

[0018] Preferably, the vanadium source is selected from one or more of V2O3, VCl3, and VOC2O4·nH2O.

[0019] Preferably, the bismuth source is selected from one or more of Bi2O3, Bi(NO3)3·5H2O, and bismuth ammonium citrate.

[0020] Preferably, the temperature of the gas-phase ion exchange reaction is 425~550 °C, and the time of the gas-phase ion exchange reaction is 5~35 min.

[0021] Preferably, x is 3 to 5.

[0022] Based on the same inventive concept, this invention also proposes the application of the above-mentioned bismuth-doped vanadate-based environmental functional materials in the photocatalytic water splitting reaction.

[0023] Preferably, the photocatalytic water splitting reaction is carried out under sacrificial agent-free conditions.

[0024] Preferably, the photocatalytic water splitting reaction is carried out under visible light or simulated sunlight.

[0025] Preferably, the bismuth-doped vanadate-based environmental functional material is used to simultaneously catalyze the hydrogen evolution reaction and the oxygen evolution reaction.

[0026] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention constructs a Bi with a two-dimensional sheet-like array structure by using a sacrificial template-assisted gas-phase ion exchange method. x @Mn2V2O7 photocatalytic material significantly improves the specific surface area and light-available reaction interface of the material while maintaining the stability of the main crystal phase, providing a sufficient basis for the simultaneous occurrence of HER and OER. (2) By introducing a controllable proportion of Bi into Mn2V2O7, the band structure and surface electronic state distribution of the material were effectively regulated, significantly promoting the separation and migration of photogenerated electrons and holes, enabling the material to simultaneously and efficiently drive HER and OER without any sacrificial agents. Under visible light irradiation, the material of this invention exhibited a significantly improved hydrogen evolution rate (40.8 μmol·g⁻¹). -1 ·h -1 ) and oxygen evolution rate (20.4 μmol·g -1 ·h -1Its hydrogen evolution rate and oxygen evolution rate are significantly higher than those of the undoped Bi Mn2V2O7 control material, and the ratio of hydrogen to oxygen generation rate is close to the theoretical stoichiometric ratio of 2:1, indicating that a stable photocatalytic water splitting reaction has been achieved. (3) The Bi prepared in this invention x The Mn2V2O7 photocatalytic material achieved a simultaneous and significant increase in both the hydrogen evolution rate and oxygen evolution rate in the photocatalytic water splitting reaction, with the overall photocatalytic activity reaching up to 27.2 times that of undoped Mn2V2O7. This performance improvement is not only reflected in the hydrogen or oxygen evolution reactions individually, but also in the synergistic enhancement of both rates. This overcomes the inherent limitation of the slow oxygen evolution reaction kinetics in the Mn2V2O7 system, far exceeding what those skilled in the art could reasonably expect based on conventional elemental doping or morphology control methods, and represents an unexpected technical effect. Attached Figure Description

[0027] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the following description is only a part of the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 For the synthesis and characterization of catalysts; Note: (a) Schematic diagram of the synthesis process of Mn2V2O7 and Bi@Mn2V2O7 catalysts; (b) Mn2V2O7 and Bi 4.78 XRD pattern of the Mn2V2O7 sample; (c) Bi 4.78 SEM image of @Mn2V2O7; (d~e)Bi 4.78 TEM image of @Mn2V2O7; (f~g)Bi 4.78 HRTEM image of @Mn2V2O7; (h) corresponding selected area electron diffraction (SAED) pattern; (i) EDS surface distribution of Mn, V, O and Bi elements.

[0029] Figure 2 Structural characterization of Mn2V2O7; Note: (a) HRTEM image of Mn2V2O7, with inset being TEM image of Mn2V2O7; (b) lattice fringe spacing of Mn2V2O7.

[0030] Figure 3 Characterization of the chemical state of the catalyst surface; Note: Mn2V2O7 and Bi 4.78High-resolution XPS spectra of (a) Mn 2p, (b) V 2p, and (c) Bi 4f in Mn2V2O7; (d) MnO, Mn3O4, MnO2, Mn2O3, Mn2V2O7, and Bi. 4.78 (e) Mn K-edge normalized XANES spectrum of Mn2V2O7; (f) locally magnified XANES spectrum in the 6540~6560 eV range; 4.78 The k²-weighted EXAFS Fourier transform spectra of @Mn2V2O7 and reference samples MnO, Mn3O4, MnO2, and Mn2O3; (g~i) is the vector wavelet transform diagram of the k²-weighted EXAFS of the above samples.

[0031] Figure 4 A comparison of the photocatalytic performance of Mn2V2O7 and Bi@Mn2V2O7; Note: (a) Mn2V2O7, Bi 1.05 @Mn2V2O7、Bi 2.87 @Mn2V2O7、Bi 4.78 @Mn2V2O7 and Bi7. 01 (a) Comparison of H2 and O2 yields of Mn2V2O7 in photocatalytic water splitting; (b) Mn2V2O7 and Bi under illumination 4.78 @Mn2V2O7 complete water splitting performance test; (c)Bi 4.78 Cyclic stability test of @Mn2V2O7; (d)Bi 4.78 UV-Vis absorption spectrum and wavelength-dependent apparent quantum yield of @Mn2V2O7.

[0032] Figure 5 Mn2V2O7 and Bi 4.78 Photophysical and electrochemical characterization of @Mn2V2O7; Note: (a) UV-Vis absorption spectrum (the inset shows the corresponding Tauc curve); (b) Valence band XPS spectrum; (c) Mn2V2O7 and Bi 4.78 (d) Schematic diagram of the band structure of Mn2V2O7; (e) Photoluminescence spectrum; (f) Time-resolved photoluminescence spectrum; (c) Mn2V2O7 and Bi 4.78 Electrochemical impedance Nyquist plot of @Mn2V2O7.

[0033] Figure 6 For (a) Mn2V2O7 and (b) Bi 4.78 Water contact angle test of Mn2V2O7 sample.

[0034] Figure 7 The theoretical HER mechanism for Mn2V2O7 and Bi@Mn2V2O7; Note: (a) Atomic configuration of hydrogen adsorption on the surface of Bi@Mn2V2O7; (b) Calculation of d-band centers of Mn2V2O7; (c) Calculation of d-band centers of Bi@Mn2V2O7; (d) Gibbs free energy diagram of HER reaction between Mn2V2O7-V site and Bi@Mn2V2O7-V site; (e) PDOS diagram of Mn2V2O7; (f) PDOS diagram of Bi@Mn2V2O7.

[0035] Figure 8 The OER theoretical mechanism for Mn2V2O7 and Bi@Mn2V2O7; Note: (a) OER Gibbs free energy diagrams of Mn2V2O7-Mn2 and Bi@Mn2V2O7-Mn3 sites; (b) OER Gibbs free energy diagrams of Mn2V2O7-Mn1 and Bi@Mn2V2O7-Bi1 sites; (c) OER active sites in the Mn2V2O7 structural model; (d) OER active sites in the Bi@Mn2V2O7 structural model; (e) Comparison of adsorption energies of *O for Mn2V2O7-Mn1 and Bi@Mn2V2O7-Bi1 sites; (f) PDOS diagram of Mn2V2O7; (g) PDOS diagram of Bi@Mn2V2O7.

[0036] Figure 9 The d-band centers are (a) Mn2V2O7-Mn2 sites and (b) Bi@Mn2V2O7-Mn3 sites.

[0037] Figure 10 The PDOS diagrams are for (a) Bi@Mn2V2O7 and (b) Mn2V2O7. Detailed Implementation

[0038] This invention proposes a bismuth-doped vanadate-based environmental functional material, its preparation method, and its application. To facilitate understanding of this invention by those skilled in the art, the specific embodiments of this invention are described below with reference to the accompanying drawings.

[0039] In this invention, unless otherwise specified, the equipment and raw materials used are commercially available or commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0040] The sacrificial template used in this example is a ZnO nanosheet.

[0041] Example 1: Bi 4.78 Preparation of @Mn2V2O7 The specific steps are as follows: (1) Preparation of ZnO nanosheet sacrificial template First, weigh out a certain amount of urea and zinc nitrate hexahydrate and dissolve them in deionized water to prepare precursor solutions of 0.15 mol / L and 1.5 mol / L, respectively. Stir magnetically for 20 min. Add 30 mL of the above solutions in a 1:1 ratio to a 50 mL reaction vessel. Place the cleaned FTO conductive glass into the reaction vessel with its conductive surface facing down, seal it, and place it in a vacuum drying oven at 100 ℃ for 5 hours (the reaction time can be adjusted from 4 to 8 hours). Allow it to cool naturally. After the reaction is complete, remove the sample. Rinse the non-conductive surface with deionized water to remove any deposits, and then gently remove any remaining impurities with a lint-free wiping paper to obtain a uniformly distributed array of basic zinc carbonate nanosheets.

[0042] Then, a pyrolysis conversion process is carried out. The FTO substrate with the supported precursor is placed in a temperature-controlled muffle furnace and heated to 400 °C at a heating rate of 3 °C / min and held for 30 min (the annealing temperature can be adjusted between 300 and 500 °C). After natural cooling to room temperature, a well-crystallized ZnO nanosheet film is obtained.

[0043] (2) Synthesis of bismuth-doped manganese vanadate Bi by gas-phase ion exchange method 4.78 @Mn2V2O7 like Figure 1 As shown in Figure a, an FTO conductive glass with a sacrificial template is placed in the middle of a quartz tube. Approximately 10 cm upstream, 0.16 g of MnCl2 and 0.04 g of dry VCl3 are uniformly placed, with 0.03 g of BiCl3 additionally added to the VCl3. The mixture is then incubated at 10 °C for 1 min under a protective N2 atmosphere of 50 sccm. - ¹Heating to 525 °C and holding at that temperature for 30 min, followed by natural cooling, yields Bi. 4.78 @Mn2V2O7.

[0044] Example 2: Bi 1.05 Preparation of @Mn2V2O7 The difference between Example 2 and Example 1 is that 0.01 g BiCl3 is added to VCl3 in step (2).

[0045] Example 3: Bi 2.87 Preparation of @Mn2V2O7 The difference between Example 3 and Example 1 is that 0.02 g BiCl3 was added to VCl3 in step (2).

[0046] Example 4: Bi 7.01 Preparation of @Mn2V2O7 The difference between Example 4 and Example 1 is that 0.04 g of BiCl3 was added to VCl3 in step (2).

[0047] Comparative Example 1: Preparation of Mn2V2O7 The difference between Comparative Example 1 and Example 1 is that no additional BiCl3 was added to VCl3 in step (2).

[0048] Material characterization 1.1 Crystal Structure The crystal structure of the obtained catalyst was characterized using X-ray diffraction (XRD), such as... Figure 1 As shown in b, Mn2V2O7 and Bi 4.78 All diffraction peaks of @Mn2V2O7 are consistent with those of monoclinic Mn2V2O7 (JCPDS No. 73-1806). Characteristic diffraction peaks corresponding to the (021), (-201), and (130) crystal planes appear at 27.5°, 29.2°, and 33.8°, indicating that no other crystal phases are generated during the doping process and the main structure of the material is stable, providing a structural basis for subsequent electronic structure regulation and reaction activity enhancement.

[0049] 1.2 Microstructure The microstructures of Mn2V2O7 and Bi@Mn2V2O7 were systematically characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), such as... Figure 1 As shown in c, Mn2V2O7 and Bi 4.78 @Mn2V2O7 exhibits a plate-like structure composed of stacked nanoparticles (200~300 nm), with abundant pores between the particles (Fig. 1d) increasing the reactive surface area; in high-resolution TEM (HRTEM), the interplanar spacings of 0.33 nm and 0.49 nm correspond to Bi 4.78 The (021) and (001) faces of @Mn2V2O7 ( Figure 1 e~g). Furthermore, the (001) interplanar spacing increased from 0.48 nm for Mn2V2O7 to Bi. 0.48 @Mn2V2O7 at 0.49 nm ( Figure 1 g and Figure 2 ).like Figure 1 As shown in h, the selected area electron diffraction (SAED) pattern also confirms Bi 4.78 The fact that Mn2V2O7 maintains a single-crystal structure indicates that Bi doping did not disrupt the original atomic arrangement of the Mn2V2O7 nanosheets. Figure 1As shown in Figure i, elemental imaging using energy-dispersive X-ray spectroscopy (EDS) reveals a uniform distribution of Mn, V, O, and Bi. Tables 1 and 2 show the mass fraction of Bi at different doping concentrations: as the Bi doping concentration increases, the Mn content decreases rapidly while V remains almost unchanged, indicating that Bi selectively substitutes for Mn sites.

[0050] Table 1 Bi 4.78 EDS elemental analysis results of the Mn2V2O7 sample

[0051] Table 2. Mass fractions (wt.%) of Mn, V, O, and Bi in Bi@Mn2V2O7 as determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0052] 1.3 Surface Chemical State X-ray photoelectron spectroscopy (XPS) was used to analyze the relationship between Mn₂V₂O₇ and Bi. 4.78 The chemical state of Mn2V2O7. For example... Figure 3 As shown in a~b, Bi 4.78 The binding energies of Mn 2p and V 2p in @Mn2V2O7 are slightly higher than those in the original Mn2V2O7. Considering that Bi's Alley-LuoZhou electronegativity (1.67) is greater than that of Mn (1.60) and V (1.45), the bonding electrons of Bi tend to accumulate in Bi after replacing Mn, leading to a decrease in the electron cloud density of Mn and V and an increase in the binding energy. Furthermore, Bi... 4.78 The Bi 4f peaks in the Mn2V2O7 sample are located at 156.11 eV and 161.25 eV ( Figure 3 c), corresponding to Bi 4f7 / 2 and Bi 4f5 / 2, indicates that Bi is in the form of Bi³ + It exists in form.

[0053] Synchrotron X-ray absorption spectroscopy (SR-XAS) was used to characterize the local chemical environment of Mn sites in depth. In the X-ray absorption near-edge structure (XANES) spectrum of the Mn K-side (… Figure 3 (d~e), the absorption edge position is between MnO and Mn2O3 and closer to MnO, combined with Mn2 in Mn2p XPS. + The signal confirms that the average oxidation state of Mn is close to +2. Fourier transform extended X-ray absorption fine structure (FT-EXAFS) shows that the main peak at 1.52 Å corresponds to Mn-O coordination ( Figure 3 f). It is worth noting that Bi 4.78In addition to the Mn-O characteristics, the FT-EXAFS spectrum of @Mn2V2O7 also shows a weak Bi-Mn peak at approximately 2.36 Å, indicating a weak interaction between Mn and Bi atoms. To accurately resolve the complex multi-element coordination structure, vector wavelet transform (WT-EXAFS) analysis was performed on the EXAFS. Figure 3 As shown by g~i, Bi 4.78 The main scattering peaks of the @Mn2V2O7 system correspond to Mn-V, Mn-O, and Mn-Bi bonds, which are significantly different from the Mn-O in MnO and the Mn-Mn in Mn2O3, thus confirming that Bi... 4.78 The formation of @Mn2V2O7.

[0054] Performance Characterization 2.1 Photocatalytic performance Under simulated sunlight irradiation and with the same cocatalyst system and loading conditions, the effects of Mn2V2O7 and Bi were systematically compared. 1.05 @Mn2V2O7、Bi 2.87 @Mn2V2O7、Bi 4.78 @Mn2V2O7 and Bi 7.01 The photocatalytic OWS activity of @Mn2V2O7 was assessed. A dual-co-catalyst system (Ru+Pt) was used for co-catalyst support. Photocatalytic activity was evaluated using an online gas chromatography system equipped with a Shimadzu GC2014 thermal conductivity detector (TCD) and argon as the carrier gas. All water splitting experiments were conducted under continuous irradiation with a 300 W xenon lamp at an intensity of 430 mW·cm⁻¹. -2 .

[0055] like Figure 4 As shown in figure a, the hydrogen production rate of Mn2V2O7 is only 1.5 μmol·g. -1 ·h -1 Bi doping significantly improved both HER and OER activities. When the Bi doping concentration reached 4.78% (Bi... 4.78 The catalyst performed best when using Mn2V2O7, achieving a hydrogen production rate of 40.8 μmol·g. -1 ·h -1 The oxygen production rate was 20.4 μmol·g. -1 ·h -1 It is 27.2 times higher than Mn2V2O7. Figure 4 b). This performance also surpasses most recently reported narrow-bandgap metal oxide photocatalytic systems (Table 3), highlighting the superiority of this catalyst. Excess doping (Bi7). 01 @Mn2V2O7) actually led to a decrease in activity, attributed to the formation of carrier recombination centers due to lattice distortion caused by excessive doping. Stability tests showed that Bi 4.78The activity of @Mn2V2O7 remained almost unchanged after five cycles. Figure 4 c). In addition, such as Figure 4 As shown in d, the apparent quantum yield (AQY) measured in the range of 400–700 nm is consistent with the trend of the absorption spectrum, and the AQY reaches 3.87% at 450 nm, confirming that the OWS reaction is driven by the absorption of photons.

[0056] Table 3 Comparison of reported water splitting performance of narrow bandgap metal oxide photocatalysts

[0057] 2.2 Mechanism Investigation Bi 4.78 @Mn2V2O7 exhibits unique water-decomposing activity compared to Mn2V2O7, and the reasons for its enhanced effect were investigated. Figure 5 The UV-Vis absorption spectrum of a shows that Bi 4.78 The absorption edge of Mn2V2O7 exhibits a blue shift of approximately 100 nm, indicating a broadening of the band gap. Tauc curves based on the Kubelka-Munk equation show the relationship between Mn2V2O7 and Bi... 4.78 The band gaps (Eg) of @Mn2V2O7 are 1.67 eV and 1.99 eV, respectively. Figure 5 (a diagram). Valve band XPS (VBXPS) gives the valence band tops of 1.50 eV and 1.78 eV respectively. Figure 5 b). According to Eg = EVB - ECB, the conduction band bottom positions are -0.17 V and -0.21 V, respectively. Figure 5 c summarizes the band structure and water redox potential: Bi doping significantly raises the valence band top, providing a stronger driving force for OER.

[0058] Steady-state photoluminescence (PL) spectroscopy shows that Bi 4.78 The luminescence intensity of @Mn2V2O7 is much lower than that of Mn2V2O7, indicating that photogenerated carrier recombination is significantly suppressed. Figure 5 d). Time-resolved PL (TRPL) further gives the carrier lifetime: Bi 4.78 The migration-transmission time for @Mn2V2O7 is 8.87 ns, which is much higher than that for Mn2V2O7 (1.35 ns), indicating an improvement in migration-transmission performance. Figure 5 e). Electrochemical impedance spectroscopy (EIS) Nyquist plot shows Bi 4.78 @Mn2V2O7 has a smaller charge transfer resistance ( Figure 5 f). Furthermore, water contact angle testing indicates that Bi... 4.78 The contact angle of @Mn2V2O7 is smaller than that of Mn2V2O7, and the surface hydrophilicity is enhanced, which is beneficial to the adsorption and activation of H2O molecules. Figure 6 ).

[0059] 2.3 Theoretical Calculation To elucidate the effect of Bi doping on the photocatalytic water splitting of Mn2V2O7, density functional theory (DFT) calculations were performed using Vienna ab initio Simulation Package (VASP) software. First, structural models of Mn2V2O7 and Bi@Mn2V2O7 were constructed, and the adsorption configurations during the HER and OER processes were optimized.

[0060] The influence of Bi doping on the electronic structure and HER performance was investigated by calculating the d-orbit partial wave density of states (PDOS) at the V site. Figure 7 a). The results show that after Bi doping, the d-band center of the V site increased from -0.47 eV to -0.29 eV ( Figure 7 (b~c). To further verify the effect of this change on catalytic activity, the hydrogen adsorption free energy (|ΔGH|) was calculated. The closer the value is to zero, the more favorable it is for surface H adsorption and H2 desorption. The ΔGH of the original Mn2V2O7 is 0.422 eV, indicating poor adsorption activity. Figure 7 d); while the ΔG*H of Bi@Mn2V2O7 decreased to 0.188 eV, showing stronger adsorption capacity and a lower HER energy barrier. This is attributed to the increased d-band center at the V site enhancing its adsorption performance and strengthening the interaction between the V-dz² orbital and the H-1 orbital ( ). Figure 7 e~f).

[0061] To investigate the regulation of the electronic structure of adjacent Mn sites by Bi doping and its effect on OER activity, the Gibbs free energy changes in the four-electron OER process were compared between the doped adjacent Mn sites (Bi@Mn2V2O7-Mn3 site) and the undoped same site (Mn2V2O7-Mn2 site). Figure 8 As shown in figure a, the maximum free energy difference (η) at the Mn2V2O7-Mn2 sites OER = 0.834 V) appears in the *OH → *O step, indicating that the strong adsorption of *O is the potential-determining step (PDS) of OER. However, the overpotential of Bi@Mn2V2O7-Mn3 site decreases to 0.698 V, indicating that Bi doping significantly enhances the OER catalytic activity of the adjacent Mn site. More importantly, the d-band center of the Mn site shifts significantly upward, enhancing the adsorption capacity of Mn, lowering the activation barrier of *O, and even shifting the rate-determining step to the formation of *OOH ( Figure 9 ).

[0062] Furthermore, the changes in OER activity at the doping sites were compared. For example... Figure 8As shown in b, the Mn2V2O7-Mn1 site ( Figure 5 c) with the Bi@Mn2V2O7-Bi1 site ( Figure 8 The potential-determining steps (PDS) of d) all occur in the *OH → *O process. However, the overpotential of Bi@Mn2V2O7 at the PDS (η = 0.615 V) is lower than that of pristine Mn2V2O7 (0.936 V), indicating that Bi doping enhances the adsorption capacity of *O. Figure 8 e). The orbital interactions and bonding strengths of Bi-6p, Mn-3d, and O-2p in the *O intermediate were analyzed using PDOS mapping. Figure 10 As shown, O-2p exhibits more peaks near the Fermi level, overlapping with Mn-3d or Bi-6p, consistent with frontier orbital theory. The overlap between Bi-pz orbitals and O-2p at the Fermi level is greater than that between Mn-3d and O-2p. Therefore, according to the symmetry matching principle of molecular orbital theory, Bi@Mn2V2O7 exhibits stronger O adsorption.

[0063] Crystal orbital Hamiltonian layout functions can be used to quantitatively analyze the bonding strength between Bi-O and Mn-O. For Mn₂V₂O₇, the spin-down channels are filled with electrons, while the spin-up channels contain a large number of antibonding electrons. This is consistent with... Figure 4 The weak orbital overlap between Mn-3d and O-2p at the Fermi level leads to a decrease in the Mn-O bonding strength. Figure 8 f). In Bi@Mn2V2O7, the spin-down COOHP value (-2.782) is close to that of Mn2V2O7 (-2.866). Figure 8 g); however, the bonding states of the spin-up channel are completely occupied, while the antibonding states are almost vacant, resulting in a significantly lower spin-up COOHP (-2.974) for Bi@Mn2V2O7 compared to Mn2V2O7 (-2.325). Figure 8 (f~g). This result further confirms that the Bi-O bond is stronger than the Mn-O bond. Therefore, Bi doping enhances the OER catalytic activity by strengthening the orbital interaction with O and reducing the adsorption energy of the oxygen intermediate.

[0064] In summary, this embodiment achieves a significant improvement in photocatalytic water splitting performance by introducing Bi element to deeply reconstruct the electronic structure while maintaining the main crystal phase and crystal plane structure of Mn2V2O7. This is done without sacrificial agents. The resulting Bi@Mn2V2O7 photocatalyst achieves a maximum hydrogen production rate of 40.8 μmol·g⁻¹. -1 ·h -1 The maximum oxygen production rate can reach 20.4 μmol·g. -1 ·h -1This represents a 27.2-fold improvement over Mn₂V₂O₇, a level of improvement that would be difficult for someone skilled in the art to anticipate based on existing technology. Synchrotron radiation analysis indicates that Bi doping stabilizes Mn²⁺. + This process induces the formation of Mn-O / V bonds and establishes weak Bi-Mn interactions, constructing a unique Mn-V / O / Bi multi-component synergistic network. DFT calculations further confirm that this electronic reconstruction simultaneously achieves three key effects: ① bandgap engineering enhances light absorption; ② reduces the activation energy of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER); ③ creates dual active centers at Mn and Bi sites. These findings provide a paradigm for designing narrow-bandgap photocatalysts that utilize strategic doping to control electronic structure and construct hierarchical active sites, thus promoting the development of scalable solar fuel production systems.

[0065] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A bismuth-doped vanadate-based environmental functional material, characterized in that: The material is bismuth-doped manganese vanadate (Bi). x @Mn2V2O7, where x is 1~7.

2. The material according to claim 1, characterized in that: The value of x is 3 to 5.

3. The material according to claim 1, characterized in that: The bismuth-doped manganese vanadate has a nanosheet, layered, or porous structure.

4. The material according to claim 1, characterized in that: The material contains a multi-component synergistic bonding structure formed by the interaction of Mn-O bonds, VO bonds, and Bi-Mn bonds.

5. The material according to claim 1, characterized in that: The material can simultaneously catalyze the hydrogen evolution reaction and the oxygen evolution reaction under sacrificial agent-free conditions.

6. A method for preparing a bismuth-doped vanadate-based environmental functional material as described in claim 1, characterized in that, Includes the following steps: (1) Sacrificial template construction steps: A metal oxide nanosheet array is grown on a conductive substrate by hydrothermal method to form a sacrificial template; (2) Gas-phase ion exchange conversion step: Under an inert atmosphere, the sacrificial template reacts with the manganese source, vanadium source and bismuth source through a gas-phase ion exchange reaction to form bismuth-doped manganese vanadate Bi in situ. x @Mn2V2O7, where x is 1~7.

7. The preparation method according to claim 6, characterized in that: The temperature of the gas-phase ion exchange reaction is 425~550 ℃, the time of the gas-phase ion exchange reaction is 5~35 min, and x is 3~5.

8. The application of a bismuth-doped vanadate-based environmental functional material as described in claim 1 in the photocatalytic water splitting reaction.

9. The application according to claim 8, characterized in that: The photocatalytic water splitting reaction is carried out under conditions without sacrificial agents, and the photocatalytic water splitting reaction is carried out under visible light or simulated sunlight irradiation.

10. The application according to claim 8, characterized in that: The bismuth-doped vanadate-based environmental functional material is used to simultaneously catalyze the hydrogen evolution reaction and the oxygen evolution reaction.

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