Bi2wo6 / bi2mo6 photocatalyst, preparation method thereof and photoelectrocatalytic application thereof

Abstract

The application discloses a Bi2WO6 / Bi2MoO6 photocatalyst and a preparation method and photoelectrocatalytic application thereof, and belongs to the technical field of photoelectrocatalytic materials. The Bi2WO6 / Bi2MoO6 microspheres with high specific surface area are prepared by a solvothermal synthesis method, and the mixed photocatalyst has outstanding performance in terms of solar absorption, photoelectric conversion and photoelectrocatalysis. Photoelectric tests show that the photoelectrode of the sample has high instantaneous visible light photoelectric current and low interface impedance. The rate constants of photoelectrocatalytic degradation of rhodamine B and methylene blue are 1.65*10 ‑2 min ‑1 and 3.78*10 ‑2 min ‑1 respectively. In addition, the sample also has high reduction performance on Cr 6+ under visible light irradiation, and the photoelectrocatalytic efficiency reaches 68.57% after 160 minutes of irradiation. The excellent photoelectrochemical performance is mainly due to high photoelectron separation and transmission caused by the Z-type heterojunction structure.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of photoelectrocatalytic materials, and particularly relates to a Bi2WO6 / Bi2MoO6 photocatalyst, a preparation method thereof and photoelectrocatalytic application. BACKGROUND

[0002] With the rapid development of textile industry, a large amount of organic dyes and antibiotic wastewater is produced, and the proportion of which in industrial wastewater is increasing. These pollutants released into aquatic ecosystems seriously affect the growth and survival of organisms, and some dyes with high toxicity and stability cannot be decomposed by microorganisms, causing serious ecological and environmental disasters. Developing new dye pollutant degradation technology is of great significance to further promote industrial production, ecological balance and environmental protection. Photocatalytic technology based on the conversion of solar energy into chemical energy has high redox activity, which can achieve the purposes of wastewater purification, photoelectric conversion and chemical synthesis. Due to its high efficiency, safety and environmental friendliness, photocatalytic technology for treating wastewater has attracted strong attention and research worldwide.

[0003] Selecting and designing photocatalysts with high activity is the core part of photocatalytic technology, and efficient photocatalysts not only have high activity, but also have a wide range of solar response. With the rising research enthusiasm, bismuth-based semiconductors have become the focus of research materials, and bismuth-based photocatalysts such as BiOBr, Bi2O3, Bi2WO6, Bi2MoO6, etc. provide new vitality for photocatalytic wastewater purification due to their unique electron transfer and space confinement effect.

[0004] Bi2WO6 photocatalyst traditionally exhibits interlaced layered structure and high surface area, which can effectively adsorb dye molecules in wastewater, providing multiple sites for photocatalytic dye degradation reaction. In addition, the narrow band gap of Bi2WO6 shows outstanding visible light response, and long-wavelength, low-energy visible light can still excite photoelectrons, which eventually decomposes organic dye pollutants into CO2 and H2O. Shang's group revealed the excellent photocatalytic ability of Bi2WO6, and 91.5% of rhodamine B was decomposed under visible light irradiation for 150 minutes. However, the lower conduction band position of Bi2WO6 limits the formation of ·O2 - , so it is usually coupled with other semiconductors to form a heterojunction structure, and the new interface feature will produce a magical photocatalytic effect. The heterojunction composed of two semiconductors with suitable band gap, energy band position and lattice matching can further realize the rapid separation of photoelectrons.

[0005] Bi2MoO6 is another bismuth-based semiconductor with Aurivillius perovskite structure, which is also composed of layered structure. The narrow band gap (~2.6eV) can be easily induced by visible light to excite photoelectrons, and it shows attractive potential in photocatalytic wastewater treatment. For example, Bi2MoO6 with layered structure has obtained excellent photocatalytic performance, and the photocatalyst shows high activity in the degradation of several dyes. Bi2WO6 / Bi2MoO6 heterojunction structure will retain the high photocatalytic activity of each other, and due to the similar energy structure and lattice matching, further provide effective photoelectron transport at the heterojunction interface. Professor Salari prepared Bi2WO6 / Bi2MoO6 Z-type heterojunction photocatalyst by two-step hydrothermal method, which showed high acid blue 92 dye photodegradation performance and charge carrier transport capacity. However, the complex operation process of Bi2WO6 / Bi2MoO6 Z-type heterojunction and the study of Z-type mechanism still need to be further optimized. SUMMARY

[0006] The purpose of the present application is to provide a Bi2WO6 / Bi2MoO6 photocatalyst and its preparation method and photoelectrocatalytic application, the present application simply prepares Bi2WO6 / Bi2MoO6 Z-type heterojunction photocatalyst by one-pot hydrothermal method, and studies its photocatalytic activity by RhB / MB dye and Cr 6+ photodegradation, and the active substance quenching test provides strong evidence for the formation of energy band structure and Z-type heterojunction.

[0007] The purpose of the present application can be realized by the following technical solutions:

[0008] A Bi2WO6 / Bi2MoO6 photocatalyst is prepared by one-pot hydrothermal method, and the specific preparation process is as follows:

[0009] Firstly, under continuous stirring, CTAB (cetyltrimethylammonium bromide) and Bi(NO3)3·5H2O are dissolved in ethylene glycol methyl ether, Na2WO4·2H2O and Na2MoO4·2H2O are dispersed into ethylene glycol methyl ether, then the two solutions are mixed and transferred into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, and a hydrothermal reaction is carried out.

[0010] Secondly, after the reaction is completed, the obtained solid powder is washed with deionized water and ethanol for 5 times respectively, and then dried at 60℃ for 5 hours, finally, the prepared powder is annealed to improve the crystallinity, and the Bi2WO6 / Bi2MoO6 photocatalyst is obtained.

[0011] Further, the ratio of the amount of CTAB, Bi(NO3)3.5H2O, Na2WO4.2H2O and Na2MoO4.2H2O in the first step is 0.1g:0.97g:0.33g:0.242g.

[0012] Further, the hydrothermal reaction parameters in the first step are as follows: heating at 160℃ for 14 hours.

[0013] Further, the annealing parameters in the second step are as follows: annealing at 450℃ for 2 hours.

[0014] The Bi2WO6 / Bi2MoO6 photocatalyst prepared above can be applied in the field of photoelectrocatalysis, and specifically, can be applied in photocatalytic wastewater treatment.

[0015] The present application has the following beneficial effects:

[0016] The present application synthesizes Bi2WO6 / Bi2MoO6 photocatalyst with microsphere structure by one-pot hydrothermal method, and the photocatalyst shows strong solar absorption and effective charge transfer. The mixed photocatalyst with Z-type energy band structure shows high photocatalytic degradation effect on RhB and MB dyes, and the Bi2WO6 / Bi2MoO6 photocatalyst still maintains high photocatalytic activity after four photocatalytic cycles. The charge carrier transfer and active species are studied in detail, and ·O2 free radicals are the decisive active groups for dye photodegradation, which provides reference for constructing Z-type photocatalyst for treating dyeing wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0017] The present application will be further described below in combination with the drawings.

[0018] Figure 1 XRD patterns of the catalysts prepared for Example 1 and Comparative Examples 1-2;

[0019] Figure 2 Scanning images of the catalysts prepared for Example 1 and Comparative Examples 1-2, Bi2WO6(a), Bi2MoO6(b) and Bi2WO6 / Bi2MoO6(c);

[0020] Figure 3 TEM image (a) and EDS pattern (b) of the Bi2WO6 / Bi2MoO6 photocatalyst prepared for Example 1;

[0021] Figure 4 XPS of the Bi2WO6 / Bi2MoO6 photocatalyst: (a) general spectrum diagram; (b) Bi 4f; (c) W 4f; (d) Mo 3d and (e) O 1s;

[0022] Figure 5N2adsorption-desorption isotherm (a) and pore size distribution (b) of Bi2WO6 / Bi2MoO6 photocatalyst;

[0023] Figure 6 DRS (a), Kubelka-Munk plot (b) and PL spectra (c) of catalysts prepared for Example 1 and Comparative Examples 1-2;

[0024] Figure 7 Visible light-driven transient photocurrent (a), linear sweep curves (b) and EIS curves of photocatalysts for catalysts prepared for Example 1 and Comparative Examples 1-2;

[0025] Figure 8 Photocatalytic decomposition curves and kinetic curves of RhB (a) and MB (b) under visible light irradiation;

[0026] Figure 9 Photocatalytic performance (a) and ESR signal (b) of Bi2WO6 / Bi2MoO6 photocatalyst after adding quencher;

[0027] Figure 10 Visible light-driven photocatalytic Cr 6+ Reduction (a) and stability of photocatalyst (b);

[0028] Figure 11 Schematic diagram of preparation mechanism of Bi2WO6 / Bi2MoO6 photocatalyst;

[0029] Figure 12 Schematic diagram of charge carrier transfer and free radical formation. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0031] Example 1

[0032] The Bi2WO6 / Bi2MoO6 photocatalyst is prepared as follows:

[0033] First step, 0.1000 g of CTAB and 0.9700 g of Bi (NO3) 3·5H2O were dissolved in 20 mL of ethylene glycol methyl ether under continuous stirring, 0.3300 g of Na2WO4·2H2O and 0.2420 g of Na2MoO4·2H2O were dispersed in 10 mL of ethylene glycol methyl ether, and then the two solutions were mixed and transferred to a hydrothermal reactor with a 50 mL polytetrafluoroethylene liner. The hydrothermal reaction was heated at 160℃ for 14 hours;

[0034] Second step, the obtained solid powder was washed with deionized water and ethanol for 5 times respectively, and then dried at 60℃ for 5 hours, finally, the prepared powder was annealed at 450℃ for 2 hours to improve the crystallinity, and the Bi2WO6 / Bi2MoO6 photocatalyst was obtained.

[0035] Comparative example 1

[0036] Bi2WO6 photocatalyst, the specific preparation process is as follows:

[0037] First step, 0.1000 g of CTAB and 0.9700 g of Bi (NO3) 3·5H2O were dissolved in 20 mL of ethylene glycol methyl ether under continuous stirring, 0.3300 g of Na2WO4·2H2O and 0.2420 g of Na2MoO4·2H2O were dispersed in 10 mL of ethylene glycol methyl ether, and then the two solutions were mixed and transferred to a hydrothermal reactor with a 50 mL polytetrafluoroethylene liner. The hydrothermal reaction was heated at 160℃ for 14 hours;

[0038] Second step, the obtained solid powder was washed with deionized water and ethanol for 5 times respectively, and then dried at 60℃ for 5 hours, finally, the prepared powder was annealed at 450℃ for 2 hours to improve the crystallinity, and the Bi2WO6Bi2MoO6 photocatalyst was obtained.

[0039] Comparative example 2

[0040] Bi2MoO6 photocatalyst, the specific preparation process is as follows:

[0041] First step, 0.1000 g of CTAB and 0.9700 g of Bi (NO3) 3·5H2O were dissolved in 20 mL of ethylene glycol methyl ether under continuous stirring, 0.3300 g of Na2WO4·2H2O and 0.2420 g of Na2MoO4·2H2O were dispersed in 10 mL of ethylene glycol methyl ether, and then the two solutions were mixed and transferred to a hydrothermal reactor with a 50 mL polytetrafluoroethylene liner. The hydrothermal reaction was heated at 160℃ for 14 hours;

[0042] Second step, the obtained solid powder was washed with deionized water and ethanol for 5 times respectively, and then dried at 60℃ for 5 hours, finally, the prepared powder was annealed at 450℃ for 2 hours to improve the crystallinity, and the Bi2WO6Bi2MoO6 photocatalyst was obtained.

[0043] Performance characterization:

[0044] SEM (SU 8010), TEM (FEI Tecnai F20), XRD (X'Pert PRO MPD), DRS (PE lambda 750) and PL (F4600) were used to study the physical and chemical properties of the powder samples.

[0045] The photoelectric properties of the samples of Example 1, Comparative Examples 1-2 were studied using a three-electrode system under visible light irradiation, in which a platinum wire was used as a counter electrode, an Ag / AgCl electrode as a reference electrode, and the sample photoelectrode as a working electrode. The working electrode was prepared as follows. 0.2 grams of sample powder and 50 μL of Nafion were dispersed in 2 mL of ethanol under ultrasonic for 5 minutes, and then 100 μL of the suspension was stuck on the surface of the ITO glass. After drying under infrared lamp irradiation, 100 μL of the suspension was again applied to the ITO surface, and after the above-mentioned 3 times of filming process, the working electrode was obtained. In a 0.2 mol / L Na2SO4 electrolyte, the transient photocurrent, photocurrent-voltage curve and EIS were tested by an electrochemical workstation (CHI 660E).

[0046] Photocatalytic test

[0047] The photocatalytic activity of the samples of Example 1 and Comparative Examples 1, 2 was studied by visible light photodegradation of dyes and Cr 6+ . In the photocatalytic degradation test, the absorbance of RhB and MB dyes was tested by a 721 spectrophotometer, and the maximum absorption wavelengths were 552 nm and 664 nm, respectively. The photoreduction of Cr 6+ was carried out under similar operation as the degradation of dyes, and the concentration of Cr 6+ was tested by diphenyl carbazide spectrometry with diphenyl carbazide as a chromogenic agent. The photocatalytic efficiency was calculated and evaluated according to the following formula (1):

[0048] η = (A0- A t ) / A0x 100% (1)

[0049] The active groups of dye photodegradation were studied by adding quenching agents (BQ vs·O2 - , t-BuOH vs·OH, EDTA-2Na vs hole), and the changes in photocatalytic performance reflected the role of active groups in the photocatalytic process. In addition, the formation of·O2 - and·OH free radicals was studied by ESR technology with DMPO as a quenching agent.

[0050] Results and discussion

[0051] Figure 1 The XRD patterns of the Bi₂WO₆ / Bi₂MoO₆ photocatalyst were investigated. All the strong diffraction peaks in the Bi₂WO₆ sample were attributed to cubic Bi₂WO₆ (PDF: 39-0256), with the 28.30°, 32.67°, 32.79°, 32.91°, 46.97°, 47.14°, 55.99°, and 58.54° diffraction peaks originating from the (1 3 1), (0 0 6), (2 0 0), (0 0 2), (2 6 0), (2 0 2), (1 3 3), and (2 6 2) crystal planes. Similar diffraction peaks were also observed in the XRD patterns of Bi₂MoO₆ due to its similar lattice structure. Specifically, the diffraction peaks at 27.33°, 28.31°, 32.53°, 32.64°, 33.14°, 46.74°, 47.12°, 47.18°, 55.44°, 55.59°, 56.25°, and 58.48° originate from the (1 4 0), (1 3 1), (2 0 0), (0 0 2), (0 6 0), (2 0 2), (2 60), (0 6 2), (3 3 1), (1 33), (1 9 1), and (2 6 2) crystal planes of the cubic phase Bi₂WO₆ (PDF:21-0102). The presence of these diffraction peaks confirms the formation of Bi₂WO₆ / Bi₂MoO₆; however, due to the similar lattice spacing, the diffraction peaks are difficult to distinguish definitively. Therefore, XPS, TEM, and EDS spectra were used to further demonstrate the formation of heterojunctions.

[0052] Morphology and microstructure are crucial to the adsorption of contaminants and photocatalytic performance of catalysts. Specific morphologies of the powder samples are detailed in [link to sample description]. Figure 2 As shown, Bi₂WO₆ microspheres with an average diameter of 3 μm are composed of thin nanosheets, while Bi₂MoO₆ microspheres have a diameter of approximately 4 μm, larger than the Bi₂WO₆ microspheres. Unlike the Bi₂WO₆ microspheres, the Bi₂MoO₆ microspheres are assembled from thick nanosheets. The morphology of the Bi₂WO₆ / Bi₂MoO₆ composite photocatalyst is still microspheres, with a diameter of approximately 3 μm, and the surface is covered by thin Bi₂WO₆ nanosheets and thick Bi₂MoO₆ nanosheets.

[0053] Figure 3 The microstructure of the Bi₂WO₆ / Bi₂MoO₆ photocatalyst was further investigated using TEM images, clearly revealing a microsphere structure composed of nanosheets. HRTEM images showed lattice fringes in the nanosheets, with interplanar spacings of 2.72 Å and 3.16 Å corresponding to the (1 0 1) and (1 3 1) planes of Bi₂WO₆, respectively. An interplanar spacing of 3.15 Å corresponds to the (1 3 1) plane of Bi₂MoO₆. Figure 3The b energy spectrum clearly shows that the Bi, O, W and Mo elements are uniformly distributed, indicating the formation of the Bi2WO6 / Bi2MoO6 heterojunction photocatalyst. In addition, the formation mechanism of the Bi2WO6 / Bi2MoO6 microspheres is described in Figure 11 . First, a large number of Bi2WO6 / Bi2MoO6 crystal nuclei are generated under solvothermal conditions, and CTAB, as a morphology control agent, is adsorbed on the high-energy crystal faces of the catalyst, inducing directional growth and producing Bi2WO6 / Bi2MoO6 nanosheets. Finally, Bi2WO6 / Bi2MoO6 microspheres are obtained by assembly of the nanosheets.

[0054] Figure 4 The XPS spectrum in Table 1 further confirms the synthesis of the Bi2WO6 / Bi2MoO6 heterojunction photocatalyst. In the XPS spectrum, Figure 4 a, Bi, O, W, Mo and C elements are observed, and all element peaks are corrected by C1s at 284.5 eV. As shown in Figure 4 b, the Bi 4f XPS spectrum has two sharp peaks at 164.5 eV (Bi 4f 5 / 2 ) and 159.1 eV (Bi 4f 7 / 2 ), which is consistent with previous reports on Bi2WO6 and Bi2MoO6. Figure 4 c, the XPS peaks at 37.3 eV and 35.2 eV are attributed to W 4f 5 / 2 and W 4f 7 / 2 , indicating the hexavalent oxidation state of W 6+ in Bi2WO6. Figure 4 d, the Mo 3d XPS spectrum shows two characteristic peaks of Mo 3d 5 / 2 at 232.3 eV and Mo 3d 7 / 2 at 235.5 eV. Figure 4 e, the O1s XPS peak is divided into three peaks at 532.9 eV, 530.2 eV and 529.8 eV, because the photocatalyst surface in Bi2WO6 and Bi2MoO6 adsorbs oxygen from H2O or other hydroxyl contaminants, Mo-O and W-O bonds.

[0055] Table 1 Specific surface parameters of the photocatalysts.

[0056] Photocatalyst S BET (m 2 / g)]]> Pore volume (cm3 / g) 3 / g) Aperture (nm) Bi2WO6 11.26 0.054 15.91 Bi2MoO6 8.02 0.0334 15.05 Bi2WO6 / Bi2MoO6 12.16 0.094 22.26

[0057] The specific surface area determines the adsorption of pollutants and active sites, and is an important factor affecting the photocatalytic performance. Figure 5 The adsorption-desorption isotherms of N2 and specific surface parameters are described in Table 1. As shown in Figure 5a. The N2 adsorption isotherm of the photocatalyst was classified as a type IV isotherm. The sample exhibited high adsorption performance under high relative pressure (P / P0 = 0.9-1), indicating the presence of accumulation pores. Figure 5 The pore size distribution curve in section b was calculated using the adsorption branch of the isotherm using the Barrett-Joyner-Halenda (BJH) method, and the pore size distribution contains mesopores with a size of 15–25 nm. Data in Table 1 show that the Bi₂WO₆ / Bi₂MoO₆ photocatalyst has the largest surface area (12.16 m²). 2 / g), higher than Bi2WO6 (11.26m 2 / g) and Bi2MoO6 (8.02m) 2 The large surface area and pore size will help improve the photodegradation of dye pollutants.

[0058] The optical properties of the sample are obtained through Figure 6 The UV-Vis DRS and PL spectra were used to study the photocatalysts. Bi2WO6, Bi2MoO6, and Bi2WO6 / Bi2MoO6 photocatalysts showed similar visible light absorption regions and intensities, absorbing visible light with wavelengths shorter than 450 nm. Figure 6 The band gap and conduction / valence band positions were calculated from the Kubelka-Munk diagram in b. The band gaps of Bi2WO6, Bi2MoO6, and Bi2WO6 / Bi2MoO6 photocatalysts were 2.66 eV, 2.72 eV, and 2.63 eV, respectively, and the formation of the heterojunction was beneficial to the absorption of visible light. The conduction / valence band positions of Bi2WO6 and Bi2MoO6 were calculated according to the following formulas (2) and (3).

[0059] E VB =χ-E e +0.5E g (2)

[0060] e CB =e VB -e g (3)

[0061] Where χ is the average electronegativity of all atoms, and E e E is the energy of a free electron on the hydrogen scale, typically a constant (4.5 V). VB E CB and E g These are the conduction band position, valence band position, and band gap, respectively. The χ² values ​​for Bi₂WO₆ and Bi₂MoO₆ are 6.39 and 6.31, respectively; therefore, the Et values ​​for Bi₂WO₆ and Bi₂MoO₆ are... VB / E CB The values ​​are 0.56 eV / 3.22 eV and 0.45 eV / 3.17 eV, respectively. Furthermore, inFigure 6 In section c, the photoluminescence (PL) spectrum of the photocatalyst was tested to study photoelectron recombination. The PL peak intensity of Bi2WO6 / Bi2MoO6 was much smaller than that of Bi2WO6 and Bi2MoO6 alone, indicating that the photoelectron transfer pathway was effective and the recombination probability was low, which is extremely important for improving photocatalytic activity.

[0062] Figure 7 The photoelectric properties of all electrodes were investigated, and significant changes in photocurrent were observed with the switching on and off of Xe lamp illumination. Photocurrent generation was observed under visible light irradiation; however, the photocurrent value gradually decreased due to the low powder adhesion on the electrode surface. The Bi₂WO₆ / Bi₂MoO₆ photoelectrode exhibited the highest photocurrent value (1.91 μA / cm) among the three samples. 2 ). Figure 7 The linear scan curve in b also demonstrates the excellent photoelectric activity of the Bi2WO6 / Bi2MoO6 photoelectrode. Furthermore, in Figure 7 The interfacial impedance of the sample under visible light irradiation was studied in section c. The narrow impedance radius revealed the high interfacial conductivity of the Bi2WO6 / Bi2MoO6 photoelectrode, confirming its optimal photoelectric activity.

[0063] Figure 8 The photocatalytic activity of the photocatalyst was evaluated by studying the degradation of the dye. After 30 minutes of magnetic stirring, the adsorption of the dye on the photocatalyst surface reached equilibrium. Bi₂WO₆ / Bi₂MoO₆ exhibited the most efficient photocatalytic activity, and the RhB dye was completely decomposed after 100 minutes of visible light irradiation. The kinetic process was calculated based on a first-order reaction, and the photocatalytic rate constant was 1.65 × 10⁻⁶. -2 min -1 Furthermore, in Figure 8 In section b, a similar procedure was used to study the photodegradation of MB. Due to its low molecular weight and simple chemical structure, the photodegradation of MB dyes is easier than that of RhB. Bi₂WO₆ and Bi₂WO₆ / Bi₂MoO₆ photocatalysts exhibited excellent photocatalytic performance and photocatalytic rate, with rate constants close to 3.78 × 10⁻⁶. -2 min -1 .

[0064] Figure 9 The active groups involved in the photodegradation of dyes were investigated. Changes in photocatalytic activity after the addition of a quencher indicated the photocatalytic effect of the active groups. The sharp decrease in photocatalytic performance after the addition of BQ revealed the influence of ·O2. - Its decisive role. Furthermore... Figure 9 b proved that O2 - The formation of DMPO-·O2 resulted in a strong six-ESR peak in the methanol solution under visible light irradiation, which is attributed to the formation of DMPO-·O2. -The formation of ·OH radicals was also confirmed by four ESR characteristic signal peaks with an intensity ratio of 1:2:2:1.

[0065] Besides the photodegradation of dyes, Figure 10 Cr was carried out in a 6+ Photoreduction. After complete adsorption (16.07%) in the dark, the photoreduction performance of the photocatalysts was observed, especially the Bi2WO6 / Bi2MoO6 photocatalyst, which exhibited a high degree of Cr reduction. 6+ The optimal photocatalytic removal of Cr. Bi₂WO₆, Bi₂MoO₆, and Bi₂WO₆ / Bi₂MoO₆ photocatalysts for Cr removal. 6+ The photoreduction efficiencies were 36.75%, 25.32%, and 68.57%, respectively. Furthermore, Cr was removed through four consecutive photocatalytic processes. 6+ The photocatalytic stability of the photocatalyst was tested, and the main efficiency decrease occurred in the second photocatalytic cycle. The results showed that the photocatalytic performance degradation was minimal (9.95%). Its excellent photocatalytic activity and stability ensure its effective application in industrial wastewater purification.

[0066] ·O2 - The description of the ·OH active groups reflects the band structure of the Bi2WO6 / Bi2MoO6 photocatalyst, which is shown in [reference needed]. Figure 12 As is well known, neither Bi₂WO₆ nor Bi₂MoO₆ alone can produce ·O₂. - Free radicals, because their potential is higher than φ(O2 / ·O2). - Correction: After the formation of the heterojunction, a new band structure is constructed, and the band positions will shift significantly. Photoelectrons in the Bi2WO6 conduction band can transfer to the Bi2MoO6 valence band, while electron recombination, in turn, retains the high reduction activity of electrons in the Bi2MoO6 conduction band and the oxidation activity of holes in the Bi2WO6 valence band. Professor Salari reported a similar Z-type mechanism for the Bi2WO6 / Bi2MoO6 photocatalyst. The photodegradation process of the dye follows equations (4–10).

[0067] Bi2WO6 / Bi2MoO6+ hv → Bi2MoO6 ( e - ) +Bi2WO6( h + (4)

[0068] Bi2MoO6 (e) - ) + O2 → ·O2 (5)

[0069] O2 + H2O → OH - + ·OOH (6)

[0070] ·OH + H2O → ·OH + H2O2 (7)

[0071] H2O2 + e - → ·OH + OH - (8)

[0072] Bi2WO6( h + ) + H2O / OH - → 2·OH (9)

[0073] ·OH + RhB / MB → CO2 + H2O (10)

[0074] The above specific embodiment part specifically introduces the analysis method involved in the present application. It should be noted that the above introduction is only to help the person skilled in the art better understand the method and idea of the present application, and is not a limitation on the related content. Without departing from the principles of the present application, the person skilled in the art can also make appropriate adjustments or modifications to the present application, and the above adjustments and modifications should also belong to the protection scope of the present application.

Claims

1. A method for preparing a Bi₂WO₆ / Bi₂MoO₆ photocatalyst, characterized in that, The specific process of the preparation method is as follows: Step 1: Under continuous stirring, CTAB and Bi(NO3)3·5H2O are dissolved in ethylene glycol methyl ether, and Na2WO4·2H2O and Na2MoO4·2H2O are dispersed in ethylene glycol methyl ether. Then the two solutions are mixed and transferred to a hydrothermal reactor with a polytetrafluoroethylene liner for solvothermal reaction. In the second step, after the reaction is completed, the obtained solid powder is washed five times with deionized water and ethanol, then dried at 60°C for 5 hours. Finally, the prepared powder is annealed to improve the crystallinity, and the Bi2WO6 / Bi2MoO6 photocatalyst is obtained. The Bi2WO6 / Bi2MoO6 photocatalyst is a Z-type heterojunction catalyst and has a microsphere structure; In the first step, the ratio of the amounts of CTAB, Bi(NO3)3･5H2O, Na2WO4･2H2O, and Na2MoO4･2H2O is 0.1g:0.97g:0.33g:0.242g.

2. The method for preparing a Bi₂WO₆ / Bi₂MoO₆ photocatalyst according to claim 1, characterized in that, The solvothermal reaction parameters in the first step are: heating at 160℃ for 14 hours.

3. The method for preparing a Bi₂WO₆ / Bi₂MoO₆ photocatalyst according to claim 1, characterized in that, The annealing parameters in the second step are: annealing at 450℃ for 2 hours.

4. A Bi₂WO₆ / Bi₂MoO₆ photocatalyst, characterized in that, Prepared according to the method according to any one of claims 1-3.

5. The application of the Bi2WO6 / Bi2MoO6 photocatalyst according to claim 4 in photocatalytic wastewater treatment.

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