Preparation method of nano Fe3+-Bi2WO6 composite catalytic material

Abstract

The invention relates to a preparation method of a nano Fe < 3 + >-Bi2WO6 composite catalytic material, which comprises the following steps: dissolving bismuth salt and tungstate in water, doping ferric salt to prepare a precursor solution, adjusting the pH value to 1.0-5.0, carrying out hydrothermal reaction at 160-180 DEG C, and continuously calcining the hydrothermal reaction product at 200-400 DEG C to prepare the creamy white nano Fe < 3 + >-Bi2WO6 composite catalytic material. By means of Fe < 3 + > doping and calcination post-treatment, formation of oxygen vacancies is promoted, the service life of photon-generated carriers is prolonged, an energy band structure can be regulated and controlled, the visible light absorption range is widened, and separation of photo-generated electron-hole pairs and. O < 2-> activation are enhanced, so that the photocatalytic performance of the composite catalytic material is greatly improved; therefore, the catalyst shows extremely high catalytic degradation performance in the aspect of degrading antibiotics such as tetracycline and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor photocatalytic materials, and relates to a bismuth-based semiconductor photocatalytic material, and in particular to a method for preparing an iron-doped bismuth-based photocatalytic material. The iron-doped bismuth tungstate prepared by the method of the present invention has high photocatalytic performance. Background Art

[0002] Tetracycline is slightly soluble in water and difficult to degrade, which has become an important issue affecting ecological balance and human health. Among the various existing methods for tetracycline degradation, photocatalytic degradation technology has the most development prospects due to its high removal rate and the use of solar energy and environmental protection. Currently, photocatalytic technology based on semiconductor materials has attracted considerable attention, and researchers are committed to developing photocatalysts with higher photocatalytic activity and environmental protection and low cost.

[0003] In general, the degradation of tetracycline is relatively complicated because, as an antibiotic, it has a relatively stable chemical structure and low water solubility, which requires more energy and time in the photocatalytic degradation process. In addition, the degradation of tetracycline may also be affected by factors such as pH value, catalyst type and concentration. Overall, the degradation of tetracycline may be more challenging than that of general organic dyes.

[0004] Bi2WO6 is a typical semiconductor photocatalytic material based on visible light response. Due to its excellent layered structure and physical and chemical properties, it is used in the degradation of tetracycline hydrochloride. However, its further application is limited by its narrow light response range and low efficiency of separation of photogenerated electron-hole pairs. Therefore, how to improve its visible light utilization and separation efficiency of photogenerated carriers to further improve its photocatalytic activity is the current main research direction.

[0005] It is known that the generation of defects such as oxygen vacancies is an effective way to enhance the visible light response activity of semiconductors, especially in the photooxidation process. Oxygen vacancies can not only extend the photoresponse of semiconductors to the visible light region, but also serve as active sites for O2 adsorption and activation; in addition, an appropriate amount of vacancies is also conducive to the separation of charge carriers. It can be foreseen that the construction of oxygen vacancies is a feasible strategy to improve the photooxidation ability of Bi2WO6, and doping with heteroatoms is a common method to generate oxygen vacancies.

[0006] Inorganic Chemistry Communications (Preparation of La-doped Bi2WO6 with rich oxygen vacancies and enhanced photocatalytic performance for removal of Rhodamine B, 2022, 146, 110239) discloses a La-doped Bi2WO6 photocatalyst prepared by a hydrothermal method using glacial acetic acid as solvent, indicating that La doping enhances the visible light absorption associated with oxygen vacancies. The experimental results show that Bi2WO6 doped with 0.6% (molar fraction) La has the highest photocatalytic activity within 4 hours, and the degradation rate of Rhodamine B reaches 71.7%.

[0007] Arabian Journal of Chemistry (Tuning the morphological structure, light absorption, and photocatalytic activity of Bi2WO6 and Bi2WO6-BiOCl through cerium doping, 2020, 13(1): 2844-2857) discloses a Ce-doped Bi2WO6 and Bi2WO6-BiOCl nanocomposite prepared by a hydrothermal method, and studies the effect of Ce doping on the photocatalytic performance and stability of Bi2WO6 and Bi2WO6-BiOCl. The results show that Ce doping can greatly promote the effective separation and transfer of photogenerated carriers, improve the photocatalytic performance, and the sample also shows good stability. The photocatalytic activity for salicylic acid is the highest within 5 hours, reaching 91.6%.

[0008] Research on Chemical Intermediates (Visible-light-driven photocatalysis of heterostructure Ag / Bi2WO6 nanocomposites and their photocatalytic degradation of dye under visible light irradiation, 2016, 42:1651-1662) Ag-doped Bi2WO6 composite photocatalytic material was prepared by combining hydrothermal and ultrasonic vibration. The results showed that Bi2WO6 doped with 3% (molar fraction) Ag had the highest photocatalytic activity for Rhodamine B within 180 min, reaching 98.20%.

[0009] The above-mentioned literature has improved the performance of Bi2WO6 in photocatalytic degradation of organic dyes such as Rhodamine B and salicylic acid by doping with transition metals, but the photodegradation time is generally too long.

[0010] Journal of Sol-Gel Science and Technology (Novel La-doped Bi2WO6photocatalysts with enhanced visible-light photocatalytic activity, 2018, 86(3): 640-649) disclosed a hydrothermal method for preparing Tb ion-doped Bi2WO6. Although the photocatalytic activity was highest when the Tb ion molar fraction was 1.2%, the degradation rate of tetracycline hydrochloride after 240 minutes of reaction was only 60.1%, indicating a long photodegradation time and a low degradation rate.

[0011] Inorganic Salt Industry (Fe / Bi2WO6 Hydrothermal Synthesis and Photocatalytic Performance, 2016, 48(3): 72-76) discloses a flower ball-shaped iron-doped bismuth tungstate (Fe / Bi2WO6) nanomaterial prepared by hydrothermal synthesis. Under visible light irradiation for 1 h and in the presence of hydrogen peroxide as an auxiliary, the photocatalytic degradation rate of 10 mg / L rhodamine B solution can reach 99.5%. Compared with pure bismuth tungstate (Bi2WO6) catalyst, the photocatalytic degradation rate of rhodamine B solution is increased by nearly 30%.

[0012] Although the degradation rate of Rhodamine B in the photocatalytic degradation of flower-ball-shaped particles Fe / Bi2WO6 prepared by hydrothermal method by doping iron elements was improved, its small specific surface area and lack of oxygen vacancies make only photogenerated holes the main active substances, which increases the difficulty of photocatalytic degradation for tetracycline with stable chemical structure. Summary of the invention

[0013] The purpose of the present invention is to provide a nano-Fe 3+ -A method for preparing a Bi2WO6 composite catalytic material, which increases the lifetime of photogenerated carriers by enriching oxygen vacancies on the composite catalytic material, enhances the separation of photogenerated electron-hole pairs, and improves its photocatalytic degradation performance for tetracycline.

[0014] In order to achieve the above-mentioned purpose, the present invention adopts the following method to prepare nano-Fe 3+ -Bi2WO6 composite catalytic material:

[0015] 1) According to the stoichiometric ratio of Bi2WO6, weigh the required amount of bismuth salt and tungstate and dissolve them in water, and prepare the precursor solution by doping with a certain amount of iron salt. The amount of doped iron salt meets the requirement of Fe3+ : Bi2WO6 molar doping ratio is (0.10-0.78) / 100;

[0016] 2) Adjust the pH value of the precursor solution to 1.0-5.0, and perform a hydrothermal reaction at 160-180°C;

[0017] 3) The hydrothermal reaction product is calcined at 200-400°C to prepare off-white nano-Fe 3+ -Bi2WO6 composite catalytic material.

[0018] The present invention has no special restrictions on the bismuth salt, tungstate and iron salt used as the reaction raw materials. As long as it is a water-soluble salt that can provide the required ions, it can be used as the reaction raw material. Further, the present invention preferably uses water-soluble salts of bismuth nitrate, sodium tungstate and iron nitrate as the reaction raw materials for preparing the composite catalyst material.

[0019] Preferably, the present invention uses NaOH solution to adjust the pH value of the precursor solution. More preferably, the concentration of the NaOH solution is 1-2 mol / L.

[0020] Preferably, the hydrothermal reaction time is 20 to 24 hours.

[0021] Preferably, the present invention is to heat the hydrothermal reaction product to 200-400° C. at a heating rate of 5° C. / min for constant temperature calcination.

[0022] More preferably, the constant temperature calcination time is 1 to 2 hours.

[0023] Furthermore, in the present invention, the hydrothermal reaction product is preferably dried and expanded at 60 to 80° C. for 8 to 12 hours and then heated to be calcined.

[0024] Nano Fe prepared by the method of the present invention 3+ -Bi2WO6 composite catalytic material can be used for efficient photocatalytic degradation of tetracycline in wastewater.

[0025] Compared with the existing iron-doped bismuth tungstate nanomaterials, the nano Fe 3+ -Bi2WO6 composite catalytic material has the following beneficial effects:

[0026] 1) The present invention adopts transition metal ion Fe 3+ By doping bismuth tungstate, nano-Fe with rich oxygen vacancies and large specific surface area was obtained. 3+ -Bi2WO6 composite catalytic material;

[0027] 2) The present invention uses Fe 3+ Doping and calcination post-treatment methods make Fe3+ -Bi2WO6 composite catalytic materials enrich oxygen vacancies, increase the lifetime of photogenerated carriers, enhance the separation of photogenerated electron-hole pairs, regulate the energy band structure, broaden the visible light absorption range, and greatly improve the photocatalytic performance of the prepared composite catalytic materials, making them show extremely high benefits in degrading antibiotics such as tetracycline;

[0028] 3) During the photocatalytic degradation of tetracycline by the composite catalytic material of the present invention, its Fe 3+ Doping improves the photocatalytic performance through three mechanisms. First, W 6+ Fe 3+ After substitution, the local electron cloud is distorted, and the introduction of impurity energy levels leads to a decrease in the bandgap width, which promotes visible light excitation (λ>480nm); secondly, Fe 3+ As an electron trap to capture conduction band electrons (Fe 3+ +e - →Fe 2+ ), inhibiting carrier recombination; finally, the surface-enriched oxygen vacancies act as O2 adsorption sites, accelerating the Fe 2+ Transfer electrons to O2 to generate O2 - ,h + With O2 - Synergistic effect, h + Directly oxidizes tetracycline molecules, and O2 - The benzene ring structure is destroyed by nucleophilic attack, thus achieving efficient degradation;

[0029] 4) The composite catalytic material of the present invention improves the defects of Bi2WO6 material, such as high carrier recombination rate and insufficient visible light response, and greatly improves its performance, thus opening up broad prospects for the application of Bi2WO6 in the field of photocatalytic degradation of antibiotics. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 These are the X-ray diffraction analysis patterns of different catalysts.

[0031] Figure 2 FT-IR spectra of different catalysts.

[0032] Figure 3 It is the XPS spectra of different catalysts.

[0033] Figure 4 These are scanning electron microscope images of different catalysts.

[0034] Figure 5 These are the N2 adsorption-desorption curves and pore size distribution diagrams of different catalysts.

[0035] Figure 6 It is the photocatalytic degradation curve of different catalysts.

[0036] Figure 7 It is Fe 3+ -Active species capture diagram of Bi2WO6 composite catalyst.

[0037] Figure 8 are the UV-Vis DRS spectra of different catalysts.

[0038] Fig. 9 These are the Mott-Schottky spectra of different catalysts.

[0039] Fig.10 It is Fe 3+ -Degradation mechanism diagram of BWO composite catalyst. Implementation

[0040] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solution of the present invention so that those skilled in the art can fully understand and utilize the present invention.

[0041] However, the present invention can be implemented in many other ways different from those described in the following embodiments, and those skilled in the art can also make similar improvements without violating the connotation of the present invention. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0042] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art. The terms used in the present invention specification are only for describing specific embodiments and are not intended to limit the present invention.

[0043] The term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0044] The terms "multiple", "multiple", "multiple times", "multiple groups", etc. used in the present invention, unless otherwise specified, refer to a quantity greater than or equal to 2; "above" includes the number itself, such as "more than two" includes two, three or more.

[0045] The term "preferred" used in the present invention is only used to describe an implementation method or example with better effects, and does not constitute a limitation on the protection scope of the present invention.

[0046] The production processes, experimental methods or detection methods involved in the embodiments of the present invention, unless otherwise specified, are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, and are very clear and unambiguous in the relevant application fields. Technical personnel in the field can understand the conventional process steps and apply the corresponding equipment according to the names, and implement them according to conventional conditions or conditions recommended by the manufacturer, or refer to experimental methods known in the field.

[0047] The various instruments, equipment, raw materials or reagents used in the embodiments of the present invention are not particularly limited in terms of their sources, and are all conventional products that can be purchased through regular commercial channels, or can be prepared according to conventional methods well known to those skilled in the art. Example

[0048] Example 1

[0049] Weigh 8mmol Bi(NO3)3·5H2O and 4mmol Na2WO4·2H2O and dissolve them in 50ml deionized water. 3+ : The molar doping ratio of Bi2WO6 is 0.26 / 100, and a sufficient amount of Fe(NO3)3·9H2O is added, and ultrasonic dispersion is performed for 15 minutes to obtain a precursor solution.

[0050] The pH value of the precursor solution was adjusted to 1 with NaOH solution, and then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 180° C. for 24 h.

[0051] The reaction solution was cooled naturally and centrifuged to collect the precipitate, which was washed three times with anhydrous ethanol and deionized water, dried overnight in a 60°C oven, and calcined at 300°C in a tube furnace to obtain the final Fe 3+ Doped catalyst product Fe 3+ -Bi2WO6, denoted as Fe 3+ -BWO.

[0052] Example 2

[0053] Weigh 8mmol Bi(NO3)3·5H2O and 4mmol Na2WO4·2H2O and dissolve them in 50ml deionized water. 3+ : The molar doping ratio of Bi2WO6 is 0.10 / 100, and a sufficient amount of Fe(NO3)3·9H2O is added, and ultrasonic dispersion is performed for 15 minutes to obtain a precursor solution.

[0054] The pH value of the precursor solution was adjusted to 3 with NaOH solution, and the solution was transferred to a polytetrafluoroethylene-lined autoclave for continuous reaction at 180° C. for 24 h.

[0055] The reaction solution was cooled naturally and centrifuged to collect the precipitate, which was washed three times with anhydrous ethanol and deionized water, dried overnight in a 60°C oven, and calcined at 300°C in a tube furnace to obtain the final Fe 3+ Doped catalyst product Fe 3+ -Bi2WO6.

[0056] Example 3

[0057] Weigh 8mmol Bi(NO3)3·5H2O and 4mmol Na2WO4·2H2O and dissolve them in 50ml deionized water. 3+ : The molar doping ratio of Bi2WO6 is 0.78 / 100, and a sufficient amount of Fe(NO3)3·9H2O is added, and ultrasonic dispersion is performed for 15 minutes to obtain a precursor solution.

[0058] The pH value of the precursor solution was adjusted to 5 with NaOH solution, and the solution was transferred to a polytetrafluoroethylene-lined autoclave for continuous reaction at 180° C. for 24 h.

[0059] The reaction solution was cooled naturally and centrifuged to collect the precipitate, which was washed three times with anhydrous ethanol and deionized water, dried overnight in an oven at 60 °C, and calcined at 350 °C in a tube furnace to obtain the final Fe 3+ Doped catalyst product Fe 3+ -Bi2WO6.

[0060] Comparative Example 1

[0061] Weigh 8 mmol Bi(NO3)3·5H2O and 4 mmol Na2WO4·2H2O, dissolve in 50 ml deionized water, and disperse by ultrasonic for 15 min to obtain a precursor solution.

[0062] The pH value of the precursor solution was adjusted to 1 with NaOH solution, and then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 180° C. for 24 h.

[0063] The reaction solution was naturally cooled and centrifuged, and the precipitate was collected and washed three times with anhydrous ethanol and deionized water respectively, dried in an oven at 60°C overnight, and calcined in a tubular furnace at 300°C to obtain a Bi2WO6 catalyst, which was recorded as BWO.

[0064] Comparative Example 2

[0065] Weigh 8mmol Bi(NO3)3·5H2O and 4mmol Na2WO4·2H2O and dissolve them in 50ml deionized water. 3+ : The molar doping ratio of Bi2WO6 is 0.26 / 100, and a sufficient amount of Fe(NO3)3·9H2O is added, and ultrasonic dispersion is performed for 15 minutes to obtain a precursor solution.

[0066] The pH value of the precursor solution was adjusted to 1 with NaOH solution, and then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 180° C. for 24 h.

[0067] The reaction solution was cooled naturally and centrifuged to collect the precipitate, which was washed three times with anhydrous ethanol and deionized water respectively, and dried in an oven at 60°C overnight to obtain uncalcined Fe 3+ Doped catalyst product Fe 3+ -Bi2WO6.

[0068] Application Example 1

[0069] Figure 1 The above Example 1 is given to prepare Fe 3+ -BWO catalyst XRD spectrum, and compared with the pure BWO catalyst prepared in Comparative Example 1. 3+ -XRD patterns of BWO and BWO, (b) is a local comparison of the two.

[0070] From Figure (a), we can see that pure BWO and Fe 3+ -BWO all belong to the orthorhombic Bi2WO6 phase, and have very significant similar diffraction peaks at 2θ of 28.299°, 32.790°, 47.138°, 55.990°, 58.538°, 69.037°, 76.075°, and 78.534°, which correspond to the (131), (200), (202), (133), (262), (083), (2102), and (204) crystal planes of orthorhombic Bi2WO6 (PDF#39-0256), respectively. No other impurity peaks were found in the spectrum, indicating that the synthesized substance has a high purity.

[0071] In Fe 3+ -No iron metal peak was detected in the BWO catalyst, which is due to the Fe 3+ It has successfully entered the Bi2WO6 lattice. Figure 1 From the local comparison of (b), we can observe that the (131) crystal plane diffraction peak is at Fe 3+ After doping, a small angle shift occurs and the lattice constant becomes larger, indicating that the doped ions have a larger radius than the original ions. 3+ The radius is smaller than Fe 3+ , so it is speculated that Fe 3+ Successfully entered the Bi2WO6 lattice and replaced W 6+ result.

[0072] Figure 2 The infrared spectra of the catalysts prepared in Example 1 and Comparative Example 2 are provided. -1The left and right peaks are attributed to the stretching vibration of Bi-O and Fe-O bonds, 728 cm -1 The left and right peaks correspond to the stretching vibration of the WO bond, 1380cm -1 The left and right peaks are caused by the WOW bridge bond stretching vibration. It can be clearly seen that compared with the uncalcined Fe 3+ Doped catalyst product Fe 3+ Compared with -Bi2WO6, Fe 3+ The peak intensities of these peaks for the BWO catalyst are reduced, especially at 1380 cm -1 The peak intensity at is significantly reduced, which is closely related to the breaking of WO bonds and the formation of oxygen vacancies. This phenomenon is consistent with the result of increased oxygen vacancy concentration in XPS characterization.

[0073] Figure 3 The X-ray photoelectron spectroscopy (XPS) of the catalysts prepared in Example 1 and Comparative Example 1 is provided. As shown in (a), the Bi 4f orbital presents a typical double peak structure. 5 / 2 and Bi 4f 7 / 2 The binding energies of Bi 3+ Stable existence of Fe 3+ After doping, the Bi 4f double peaks shifted synchronously toward the high binding energy direction by 0.10 eV (158.86 eV / 164.14 eV), indicating that Fe 3+ The introduction of changed the local coordination environment of Bi-OW, resulting in Fe 3+ The surrounding electron cloud density decreases.

[0074] Figure 3 (b), pure BWO at 35.00 eV (W 4f 7 / 2 ) and 37.09 eV (W 4f 5 / 2 ) corresponds to the characteristic peak at W 6+ Typical chemical state of Fe 3+ After doping, the W 4f peak shifted by about +0.10 eV, and W appeared at 34.46 eV and 36.58 eV. 5 + Characteristic peak (area accounting for 12.7%), confirming that Fe 3+ In the W 6+ In the process of substitution, oxygen vacancies are generated to maintain charge balance. 3+ Change to Fe 2+ , Fe 2+ Then part W 6+ Restore to W 5+ .

[0075] Figure 3 (c) O 1s fine spectrum analysis further verifies the change in oxygen vacancy concentration. The O 1s of BWO is divided into three components: lattice oxygen (OL, 529.71 eV, 62.3%), oxygen vacancies (OV, 530.31 eV, 24.1%), and adsorbed oxygen (OA, 531.70 eV, 13.6%). 3+ After doping, the oxygen vacancy ratio increased significantly to 38.5% (Δ+14.4%), and its Fe 3+ -BWO:BWO relative strength ratio is 1.6:1, which is comparable to W 5+ The content increased in a consistent trend, confirming that Fe 3+ The doping effectively promotes the formation of oxygen vacancies.

[0076] Figure 3 In the Fe 2p fine spectrum in (d), 711.08 eV (Fe 2p 3 / 2 ) and 724.36 eV (Fe 2p 1 / 2 ) confirmed that Fe 3+ Successful doping.

[0077] Figure 4 The SEM images of the catalysts prepared in Comparative Example 1 and Example 1, where (a, b, c) are BWO at different magnifications, and (d, e, f) are Fe at different magnifications. 3+ -BWO. From the figure, we can see that the morphology of pure nano-BWO is a flake structure. 3+ Although the doped BWO is still a sheet-like nanostructure, its thickness can be clearly observed to have increased. 3+ The interplanar spacing after doping also increases, which is consistent with the results of XRD, further proving that Fe 3+ It has successfully entered the Bi2WO6 lattice and replaced W 6+ .

[0078] Figure 5 Further, the preparation of BWO (a) in Comparative Example 1 and the preparation of Fe in Example 1 are given. 3+ -BWO catalyst (b) pore size distribution curve and N2 adsorption-desorption isotherm. It can be clearly observed from the figure that BWO and Fe 3+ The N2 adsorption-desorption isotherm of -BWO is a type IV isotherm with an H3 hysteresis loop, and the H3 hysteresis loop appears in the range of P / P0=0.45~0.95, indicating that the material has a slit-like mesoporous structure formed by stacking nanosheets.

[0079] The total specific surface area of ​​the material was obtained by the BET method, and the pore size and pore volume of the catalyst were calculated using the BJH method equation, which are listed in Table 1. 3+-The specific surface area of ​​BWO catalyst is 29.82m 2 / g, higher than BWO's 24.00m 2 / g. Compared with BWO, with the increase of Fe 3+ With the addition of ions, the pore size of the nanocomposite material decreases and the specific surface area increases.

[0080]

[0081] Application Example 2

[0082] After grinding the prepared composite catalytic material, a certain amount was weighed for degradation experiment. A 10 mg / L tetracycline solution was used to simulate domestic antibiotic wastewater, and a 250W metal halide lamp was used to simulate sunlight. Degradation was carried out at room temperature to simulate the photocatalytic performance of the catalyst for degrading wastewater.

[0083] Add 100 mL of tetracycline solution and 75 mg of catalyst powder into a beaker, mix and stir for 30 minutes in the dark, and then irradiate the solution with a metal halide lamp as the excitation light source. Take samples every 15 minutes and measure their absorbance.

[0084] Figure 6 (a) shows the change of Fe under the condition of keeping other experimental conditions unchanged. 3+ Fe prepared with different molar doping ratios with Bi2WO6 3+ -BWO(Fe 3+ :Bi2WO6=0~0.78 / 100) catalyst degradation curve of tetracycline under simulated sunlight conditions. It can be seen from the figure that after 60 minutes of simulated sunlight irradiation, the degradation rate of Fe-doped 3+ The degradation rates of the catalysts were increased to 72.14%, 85.97%, 73.57% and 74.67% respectively, especially when the doping ratio was 0.26 / 100. 3+ The doped BWO catalyst has the highest tetracycline degradation rate. It can be seen that with the increase of the doping molar ratio, the degradation rate of the catalyst for tetracycline generally shows a trend of first increasing and then decreasing.

[0085] Among the numerous transition metal elements, Fe is cheap and abundant, and has gradually become the best choice to replace precious metal doping elements such as Au and Ag. The present invention adopts a simple hydrothermal calcination method to dope iron ions in the flaky Bi2WO6 to generate oxygen vacancies. 3+ Partially replace W 6+ , the enrichment of oxygen vacancies promotes the adsorption and activation of O2. Compared with BWO, Fe 3+ The doped BWO exhibits higher photocatalytic activity and stability.

[0086] Figure 6 (b) shows the uncalcined Fe 3+ -Bi2WO6 and Fe after calcination in Example 1 3+ -BWO photocatalytic degradation performance comparison. After 60 minutes of simulated sunlight irradiation, the degradation rate of tetracycline by the composite material was 67.88% before calcination, and increased to 85.97% after calcination. It can be seen that calcination treatment can further improve the tetracycline degradation performance of the catalyst, because the holes show higher activity in the oxidation reaction, thus greatly improving its degradation effect.

[0087] Application Example 3

[0088] In order to explore the main active substances and degradation mechanism of catalyst materials during degradation, the present invention selects ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), isopropyl alcohol (IPA) and benzoquinone (BQ) as holes (h + ), hydroxyl radicals (·OH) and superoxide radicals (·O2 - ) active scavenger, and carried out free radical active scavenging experiments to study and determine the effective active substances in the photocatalytic degradation process and the degradation mechanism occurring on the catalyst.

[0089] from Figure 7 Fe 3+ -BWO catalyst active material capture diagram shows that without adding any capture agent, Fe 3 + The degradation efficiency of tetracycline by the doped BWO catalyst reached 85.97%. When isopropyl alcohol (IPA) was added as a scavenger for ·OH, the degradation rate dropped to 55.56%, which was only less than 15% lower than that of the blank, indicating that ·OH was not the main active group of the catalyst.

[0090] However, under the same experimental conditions, when benzoquinone (BQ) and ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) were introduced as ·O2 - and h + After the capture agent was added, the degradation rate dropped sharply to 27.16% and 27.31%, which is a significant change that highlights the - and h + It plays a key role in the photocatalytic degradation process. It can be seen that in the catalyst prepared by the present invention, O2 - and h + Together they become Fe 3+ The main active species of doped BWO catalyst in the photocatalytic degradation of tetracycline.

[0091] Figure 8 (a) BWO and Fe 3+The UV-visible diffuse reflectance spectrum of the -BWO catalyst was analyzed to explore the absorption characteristics of the catalyst. Pure BWO exhibits a steep absorption edge at 450nm, corresponding to a direct band gap of 2.90eV, which is consistent with the typical optical properties of orthorhombic BWO. 3+ After doping, the absorption edge significantly red-shifted to 467nm (Δλ=17nm), and the tail of the absorption band extended to the 550nm visible light region, indicating that Fe 3+ The introduction of 2D photoresponse effectively expands the photoresponse range of the material.

[0092] As can be seen from (b), according to the Kubelka-Munk equation, the direct band gap of the doped catalyst is reduced to 2.58 eV (ΔEg=0.32 eV), which is lower than the 2.90 eV of pure BWO, confirming that Fe 3+ Doping induces significant band structure adjustments.

[0093] Fig. 9 By BWO and Fe 3+ -Mott-Schottky curve of BWO catalyst, analyzing the relationship between BWO and Fe 3+ -BWO band structure. According to the n-type semiconductor characteristics, the positive slope of the curve confirms that both are n-type semiconductors. Relative to the Ag / AgCl reference electrode, pure BWO and Fe 3+ The flat band potentials of -BWO are -0.78V and -0.63V respectively, and the standard hydrogen electrode conversion formula E NHE =E Ag / AgCl After correction of +0.197V, the corresponding conduction band position (E CB ) are -0.58 V and -0.43 V. Combined with the band gap (Eg) data obtained by UV-Vis DRS (2.90 eV vs 2.58 eV), the formula E VB =E CB +Eg calculated valence band position (E VB ) are 2.32V and 2.15V respectively. It is worth noting that Fe 3+ Doping shifts the conduction band negatively by 0.15 V, providing a thermodynamic basis for enhancing O2 adsorption and activation.

[0094] Fig.10 Further explanation of Fe 3+ -Degradation mechanism of Bi2WO6 catalyst. Under visible light irradiation, when the light energy exceeds the band gap width (Eg) of the photocatalyst, the electrons in the valence band gain energy and jump to the conduction band, leaving holes (h + ), electrons are generated in the conduction band (e - ), forming electron-hole pairs. Some of these electron-hole pairs will recombine immediately, while the other part will migrate to the catalyst surface.3+ , the band gap of Bi2WO6 is adjusted from Eg1 to Eg2. Given the negative charge of the conduction band of Bi2WO6, the electrons on it can migrate to the catalyst surface and react with Fe 3+ effect, leading to - Fe 3+ capture, effectively promoting the separation of photogenerated electron-hole pairs. 2+ Unstable, the captured electrons are easily captured by O2 on the catalyst surface to generate highly active ·O2 - . ·O2 - It has a strong oxidizing ability and can react with tetracycline. In turn, the photocatalytic activity of Bi2WO6 is enhanced. 3+ Doping Bi2WO6 catalyst can improve the photocatalytic performance of semiconductor materials by increasing the separation efficiency of photogenerated electron-hole pairs.

[0095] The technical features of the above embodiments of the present invention can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the description of the present invention.

[0096] The above embodiments express several more specific and detailed implementation methods of the present invention, but they should not be understood as limiting the scope of protection of the present invention. It should be pointed out that ordinary technicians in this field can also make several substitutions, deformations or improvements without departing from the principles and purpose of the present invention, which should all be included in the scope of protection of the present invention.

Claims

1. A nano-Fe 3+ -A method for preparing a Bi2WO6 composite catalytic material, comprising: 1) According to the stoichiometric ratio of Bi2WO6, weigh the required amount of bismuth salt and tungstate and dissolve them in water, and prepare the precursor solution by doping with a certain amount of iron salt. The amount of doped iron salt meets the requirement of Fe 3+ : Bi2WO6 molar doping ratio is (0.10-0.78) / 100; 2) Adjust the pH value of the precursor solution to 1.0-5.0, and perform a hydrothermal reaction at 160-180°C; 3) The hydrothermal reaction product is calcined at 200-400°C to prepare off-white nano-Fe 3+ -Bi2WO6 composite catalytic material.

2. Nano Fe according to claim 1 3+ -Bi2WO6 composite catalytic material preparation method, characterized in that The bismuth salt, tungstate and iron salt are bismuth nitrate, sodium tungstate and iron nitrate respectively.

3. Nano Fe according to claim 1 3+ -Bi2WO6 composite catalytic material preparation method, characterized in that The pH value of the precursor solution was adjusted using NaOH solution.

4. Nano Fe according to claim 3 3+ -Bi2WO6 composite catalytic material preparation method, characterized in that The concentration of NaOH solution is 1-2 mol / L.

5. The nano Fe according to claim 1 3+ -Bi2WO6 composite catalytic material preparation method, characterized in that The hydrothermal reaction time is 20 to 24 hours.

6. The nano Fe according to claim 1 3+ -Bi2WO6 composite catalytic material preparation method, characterized in that The hydrothermal reaction product is heated to 200-400°C at a heating rate of 5°C / min for constant temperature calcination.

7. The nano Fe according to claim 1 or 6 3+ -Bi2WO6 composite catalytic material preparation method, characterized in that Calcination time is 1 to 2 hours.

8. The nano Fe according to claim 1 3+ -Bi2WO6 composite catalytic material preparation method, characterized in that The method also includes performing a drying and expansion treatment at 60 to 80° C. for 8 to 12 hours before calcining the hydrothermal reaction product.

9. The nano-Fe prepared by the preparation method of claim 1 3+ -Bi2WO6 composite catalytic material.

10. The nano Fe according to claim 9 3+ -Application of Bi2WO6 composite catalytic material in photocatalytic degradation of tetracycline in wastewater.

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