A three-phase coexisting monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5.3H2O nanosheet material and a preparation method thereof

Abstract

A kind of triclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3] (NO3) 5·3H2O nanosheet material and its preparation method, comprising: bismuth nitrate pentahydrate and cetyltrimethylammonium bromide are dissolved in distilled water, after stirring, solution A is obtained by reaction in microwave reactor at 100 DEG C;Ammonium metavanadate is dissolved in distilled water, stirring until completely dissolved to obtain solution B;Solution A is added dropwise to the flask containing solution B and stirred to obtain solution C;Solution C is obtained by reaction at 100 DEG C using microwave irradiation method, after suspension is obtained by centrifugation, washing, drying to obtain triclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3] (NO3) 5·3H2O three-phase coexistence material.

Description

Technical Field

[0001] The target products of this invention patent are mainly applied in the field of photocatalytic materials, and in particular, they relate to a three-phase coexisting monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O nanosheet materials and their preparation methods. Background Technology

[0002] Bismuth vanadate (BiVO4) is a typical n-type semiconductor material with a band gap of 2.4 eV. Due to its small band gap, excellent redox properties and photocatalytic properties, it has attracted widespread attention from researchers (Tücks A, Beck HP. The photochromic effect of bismuth vanadate pigments: Investigations on the photochromic mechanism[J]. Dyes and pigments, 2007, 72(2): 163-177). BiVO4 materials have important applications in the fields of photocatalytic degradation of pollutants, pigments, solar energy conversion, and ferroelastic materials (Zhang Z, Wang W, Shang M, et al. Photocatalytic degradation of rhodamine B and phenol by solution combustion synthesized BiVO4photocatalyst[J]. Catalysis communications, 2010, 11(11): 982-986). BiVO4 mainly has three crystal structures: monoclinic, tetragonal scheelite, and tetragonal zircon. In the crystal structure of BiVO4, the empty 3d orbitals of vanadium are coupled with the 2p orbitals of oxygen and the 6p orbitals of bismuth, resulting in the smallest conduction band at the Brillouin zone boundary, which is conducive to the direct transition of low-energy electrons. Among them, the tetragonal BiVO4 has a band gap of 2.9 eV and has a good response to ultraviolet light, while the monoclinic BiVO4 has a band gap of 2.4 eV and has a good response to both ultraviolet and visible light, thus exhibiting higher photocatalytic activity. Monoclinic and tetragonal scheelite BiVO4 can interconvert at 255℃, while tetragonal zircon BiVO4 can be transformed into monoclinic BiVO4 after being heated to 400-500℃ and cooled to room temperature (Zhang X, Ai Z, Jia F, et al. Selective synthesis and visible-light photocatalytic activities of BiVO4 with different crystalline phases[J].Materials Chemistry and Physics, 2007, 103(1): 162-167; M, S,Ivanda M,et al.Synthesis and characterisation of bismuth(III)vanadate[J].Journal ofMolecular Structure,2005,744:535-540)。

[0003] Although monoclinic BiVO4 exhibits superior photocatalytic activity, issues such as the easy recombination of photogenerated electrons and holes remain the main factors restricting the improvement of BiVO4 photocatalytic performance (Guo Xiaoyu. Preparation and performance of bismuth vanadate and bismuth molybdate-based heterostructure photocatalysts [D]. Jilin Normal University, 2016). To address this, doping (Pilli SK, Furtak TE, Brown LD, et al. Cobalt-phosphate (Co-Pi) catalyst modified Mo-doped BiVO4 photoelectrodes for solar water oxidation[J]. Energy & Environmental Science, 2011, 4: 5028-5034), co-catalyst loading (Zhang A, Zhang J. Synthesis and characterization of Ag / BiVO4 composite photocatalyst[J]. Applied Surface Science, 2010, 256: 3224-3227) and heterostructure formation (Wang W, Huang X, Wu S, et al. Preparation of pn junction Cu2O / BiVO4 heterogeneous nanostructures with enhanced visible-light photocatalytic activity[J]. Applied Catalysis Several strategies, such as B: Environmental, 2013, 134: 293-301, provide feasible solutions for improving the performance of these photocatalysts. Among them, forming heterojunctions between different phases of the same material is a promising application method. The presence of mixed phases can lead to higher photocatalytic activity because the different valence band and conduction band potentials between the heterogeneous phases improve the separation efficiency of electrons and holes (Fan H, Jiang T, Li H, et al. Effect of BiVO4 crystalline phases on the photoinduced carriers behavior and photocatalytic activity[J]. Journal of Physical Chemistry C, 2012, 116: 2425-2430).

[0004] According to literature review, preparing BiVO4 materials with different structures and phase compositions using different methods is beneficial for improving the catalytic and redox performance of photocatalytic materials. Currently, methods for synthesizing BiVO4 materials include co-precipitation, sonochemical methods, solution-gel methods, and hydrothermal methods (Ravidhas C, Juliat Josephine A, Sudhagar P, et al. Facile synthesis of nanostructured monoclinic bismuth vanadate by a co-precipitation method: structural, optical and photocatalytic properties[J]. Materials Science in Semiconductor Processing, 2015, 30: 343-351.). However, these methods typically require high temperatures and pH control to regulate the morphology of the BiVO4 product, resulting in complex processes, high energy consumption, long processing times, and instability. Summary of the Invention

[0005] The purpose of this invention is to propose a method for preparing three-phase coexisting monoclinic BiVO4, tetragonal scheelite BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheets, which is expected to solve the problem of easy electron-hole recombination in single-phase photocatalytic materials. The method is simple to operate, does not require the use of acids or alkalis, has low energy consumption, short processing time, and is mild and controllable for application in the field of photocatalysis.

[0006] This invention is implemented using the following scheme:

[0007] A three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheet material and its preparation method, comprising the following steps:

[0008] First, at room temperature, weigh 2.0615 g of analytical grade Bi(NO3)3·5H2O and 1.5490 g of hexadecyltrimethylammonium bromide (CTAB) into a 250 mL beaker, add 115 mL of distilled water, and stir the solution on a magnetic stirrer at 800 rpm for 15 min. Then, transfer the solution to a 250 mL round-bottom flask. Place the round-bottom flask in a reactor of the brand "Midea" PJ21C-AU. This device is a microwave reactor with temperature control, reflux condenser, and atmospheric pressure reaction system. Set the heating power to 200–2000 W, the frequency to 2450 MHz, and the heating temperature to 100 °C. After mixing for 60 min, the precursor solution A is obtained.

[0009] Second, weigh 0.7457g of NH4VO3 into a 100mL beaker, add 85mL of distilled water to the beaker, and stir at a constant speed of 800rpm for 15min to obtain the reaction precursor solution B.

[0010] Third, transfer the precursor solution B obtained in the second step to a 500mL round-bottom flask. Under vigorous stirring, add the precursor solution A obtained in the first step dropwise to the 500mL flask containing the precursor solution B. After the addition is complete, continue stirring for 10 minutes to obtain a mixed solution C.

[0011] Fourth, place the mixed solution C obtained in the third step into a Midea brand PJ21C-AU microwave reactor equipped with an atmospheric pressure reflux cooling device, and set the heating power to 200-2000W, the frequency to 2450MHz, the heating temperature to 100℃, and the reaction time to 30-130min.

[0012] Fifth, after the reaction is complete, allow the product obtained in the round-bottom flask to cool naturally, transfer the product to a centrifuge, centrifuge at 5000 rpm for 2 min, remove the supernatant and retain the lower layer product, wash the lower layer product with distilled water and ethanol 3 to 5 times respectively, then place the washed product in an oven, adjust the oven temperature to 70℃, and keep it at the temperature for 24 h to obtain the target three-phase coexisting nanosheet material.

[0013] When the reaction time t = 30 min, the strongest peak of the monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 35.4% of the total peak values. The strongest peak of tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 36.2% of the total peak value. In addition, the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 28.4% of the total peak value. The three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.20~1.89μm and a thickness of 20~130nm.

[0014] When the reaction time t = 50 min, the strongest peak of the monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 39.0% of the total peak values. The strongest peak of the tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 39.0% of the total peak value, and the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 22.0% of the total peak value; the three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.44~1.97μm and a thickness of 46~90nm.

[0015] When the reaction time t = 70 min, the strongest characteristic peak of monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 43.2% of the total peak values. The strongest peak of the tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 13.6% of the total peak value, and the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 43.2% of the total peak value; the three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.12~1.96μm and a thickness of 26~76nm.

[0016] When the reaction time t = 90 min, the strongest peak of the monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 39.5% of the total peak values. The strongest peak of the tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 39.5% of the total peak value, and the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 21.0% of the total peak value; the three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.40~2.01μm and a thickness of 43~141nm.

[0017] When the reaction time t = 130 min, the strongest peak of monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 38.5% of the total peak values. The strongest peak of the tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 38.5% of the total peak value, and the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 23.0% of the total peak value; the three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.59~3.21μm and a thickness of 64~198nm.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects:

[0019] (1)BiVO4 is an n-type semiconductor material with a narrow band gap, excellent redox properties and photocatalytic properties. It is widely used in the fields of degrading organic pollutants, photoelectrochemical water splitting and energy storage materials.

[0020] (2) The microwave radiation method used in this patent is simple to operate and has concentrated energy, which is conducive to improving the reaction rate and the synthesis efficiency of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O three-phase coexistence materials;

[0021] (3) The microwave radiation method involved in this invention patent can prepare three-phase coexisting monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O materials with regular morphology, small size and large specific surface area. The preparation method of this three-phase blend material is expected to be an effective strategy to solve the problem of the difficulty in improving photocatalytic efficiency caused by the easy recombination of electrons and holes in a single phase. Moreover, the efficient and stable process characteristics have the potential for large-scale production and commercialization.

[0022] The three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheet materials prepared by this patented method have large specific surface areas, regular morphologies, high purity, and small sizes. The patent's key features are that the products are three-phase coexisting materials, the process is simple to operate, requires no acid or alkali, has low energy consumption, short processing time, and is mild and controllable. This method is essential for addressing the problem of easy electron-hole recombination when using single-phase BiVO4 as a photocatalytic material and improving its catalytic performance. It has distinct scientific merit, practicality, and innovation, and is conducive to promoting the research progress of BiVO4 in photocatalysis and energy storage.

[0023] The synthesis mechanism of this invention is as follows: Microwave radiation is a type of electromagnetic radiation between infrared waves and radio waves. Unlike traditional conductive heating from the surface to the interior, microwave radiation heating is volume heating generated by the dielectric loss of the material in the electromagnetic field, which has the characteristics of high thermal efficiency and no hysteresis. Under microwave disturbance, a large number of small bubbles can be generated, providing a nucleation medium for the growth units of BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O. CTAB is a cationic surfactant with a long-chain structure. The macromolecular chain can adsorb and entangle with the crystal nuclei of the product, forming a micelle structure and inhibiting particle aggregation. The subsequent crystal growth process is based on this micelle template, growing and assembling three-phase coexisting monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O products with regular morphology, small size and large specific surface area. Attached Figure Description

[0024] Figure 1 The X-ray diffraction (XRD) patterns of the three-phase coexisting monoclinic BiVO4, tetragonal scheelite BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples are shown.

[0025] Figure 2 This is a diagram showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 30 min.

[0026] Figure 3 This is a table showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 30 min.

[0027] Figure 4 The crystal structure diagram of sample 14-0133 is a tetragonal scheelite-type BiVO4.

[0028] Figure 5 The crystal structure diagram of monoclinic BiVO4 in sample 14-0688 is shown.

[0029] Figure 6 The crystal structure diagram of phase [Bi6O5(OH)3](NO3)5·3H2O in samples 48-575 is shown.

[0030] Figure 7 The images are 30kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 30 min.

[0031] Figure 8The images are 100kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 30 min.

[0032] Figure 9 Schematic diagram of the synthetic morphology of three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples;

[0033] Figure 10 The X-ray diffraction (XRD) patterns of monoclinic BiVO4, tetragonal scheelite BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 50 min are shown.

[0034] Figure 11 This is a diagram showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 50 min.

[0035] Figure 12 This is a table showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 50 min.

[0036] Figure 13 The images are 13kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 50 min.

[0037] Figure 14 The images are 25kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 50 min.

[0038] Figure 15 The X-ray diffraction (XRD) patterns of the three-phase coexisting monoclinic BiVO4, tetragonal scheelite BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples are shown.

[0039] Figure 16 This is a diagram showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 70 min.

[0040] Figure 17 This is a table showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 70 min.

[0041] Figure 18The images are 25kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 70 min.

[0042] Figure 19 The images are 60kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 70 min.

[0043] Figure 20 The X-ray diffraction (XRD) patterns of monoclinic BiVO4, tetragonal scheelite BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 90 min are shown.

[0044] Figure 21 This is a diagram showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 90 min.

[0045] Figure 22 This is a table showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 90 min.

[0046] Figure 23 The images are 25kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 90 min.

[0047] Figure 24 The images are 30kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 90 min.

[0048] Figure 25 The X-ray diffraction (XRD) patterns of the three-phase coexisting monoclinic BiVO4, tetragonal scheelite BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples at a reaction time of 130 min are shown.

[0049] Figure 26 This is a diagram showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 130 min.

[0050] Figure 27 This is a table showing the proportion of each phase in the XRD pattern of the sample when the reaction time is 130 min;

[0051] Figure 28The images are 50kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 130 min.

[0052] Figure 29 The images are 100kx scanning electron microscope (SEM) images of monoclinic BiVO4, tetragonal scheelite BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with three phases coexisting at a reaction time of 130 min. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0054] Example 1: Preparation of three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples using microwave radiation technology.

[0055] At room temperature, 2.0615 g of analytical grade Bi(NO3)3·5H2O and 1.5490 g of hexadecyltrimethylammonium bromide (CTAB) were weighed into a 250 mL beaker, and 115 mL of distilled water was added. The solution was stirred on a magnetic stirrer at 800 rpm for 15 min, and then transferred to a 250 mL round-bottom flask. This round-bottom flask was placed in a microwave reactor (brand name "Midea" PJ21C-AU) equipped with temperature control, reflux condenser, and atmospheric pressure reaction system. The heating power was set to 1000 W, the frequency to 2450 MHz, and the heating temperature to 100 °C. After mixing for 60 min, the precursor solution A was obtained. Then, 0.7457 g of... NH4VO3 was added to a 100mL beaker with 85mL of distilled water. The mixture was stirred at 800rpm for 15min to obtain precursor solution B. Precursor solution B was then transferred to a 500mL round-bottom flask. Under vigorous stirring, precursor solution A from the first step was added dropwise to the flask containing precursor solution B. After the addition was complete, stirring was continued for 10min to obtain mixed solution C. Mixed solution C from the third step was then placed in a container equipped with a reflux reflux cooling system. In the PJ21C-AU microwave reactor, the heating power was set to 1000W, the frequency to 2450MHz, the heating temperature to 100℃, and the reaction time to 30min. After the reaction was completed, the product obtained in the round-bottom flask was allowed to cool naturally. The product was then transferred to a centrifuge and centrifuged at 5000rpm for 2min. The supernatant was removed and the lower layer of product was retained. The lower layer of product was washed 3-5 times with distilled water and ethanol, respectively. The washed product was then placed in an oven and the oven temperature was adjusted to 70℃. After 24h of heat treatment, the target three-phase coexisting nanosheet material was obtained.

[0056] X-ray diffraction results indicate that the product consists of three phases: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O. The XRD pattern of the product obtained at a reaction time of t = 30 min is shown below. Figure 1 As shown, characteristic peaks corresponding to tetragonal scheelite-type BiVO4 are present at 2θ = 18.319°, 24.373°, 30.677°, 32.679°, 39.527°, and 48.402°, which are consistent with standard JCPDS card number 14-0133 and correspond to the (101), (200), (211), (112), (301), and (312) crystal planes, respectively. The strongest peak corresponds to the hkl crystal plane index (200). Its crystal structure diagram is shown below. Figure 4 As shown, the lattice spacing is 0.365 nm, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the corresponding peak value accounts for 36.2% of the total peak value. Figure 2 , 3 Meanwhile, characteristic peaks corresponding to monoclinic BiVO4 are present at 2θ = 18.988°, 28.586°, 28.822°, 28.947°, 30.548°, 42.464° and 53.310°, which are consistent with standard JCPDS card number 14-0688, and are respectively consistent with (011), The (121), (040), (051), and (161) crystal planes correspond to the strongest peak, which corresponds to the hkl crystal plane index. Its crystal structure diagram is as follows Figure 5 As shown, the lattice spacing is 0.309 nm, the space group is I² / a, and the cell parameters are... and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​accounted for 35.4% of the total peak values. Figure 2 , 3 Furthermore, characteristic peaks corresponding to [Bi6O5(OH)3](NO3)5·3H2O are also present at 2θ = 6.596°, 10.995°, 13.184°, 19.756°, and 42.823°, which correspond to standard JCPDS card number 48-575. Its crystal structure diagram is shown below. Figure 6 As shown, the corresponding peak value of this substance accounts for 28.4% of the total peak value. Figure 2 , 3 ).

[0057] Scanning electron microscope image ( Figure 7 , 8 The three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.20–1.89 μm and a thickness of 20–130 nm, as shown in the schematic diagram below. Figure 9 As shown, these nanosheets have uniform structures, are evenly distributed, and have good dispersion.

[0058] Example 2: Preparation of three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples using microwave radiation technology.

[0059] At room temperature, 2.0615 g of analytical grade Bi(NO3)3·5H2O and 1.5490 g of hexadecyltrimethylammonium bromide (CTAB) were weighed into a 250 mL beaker, and 115 mL of distilled water was added. The solution was stirred on a magnetic stirrer at 800 rpm for 15 min, and then transferred to a 250 mL round-bottom flask. This round-bottom flask was placed in a microwave reactor (brand name "Midea" PJ21C-AU) equipped with temperature control, reflux condenser, and atmospheric pressure reaction system. The heating power was set to 1000 W, the frequency to 2450 MHz, and the heating temperature to 100 °C. After mixing for 60 min, the precursor solution A was obtained. Then, 0.7457 g of... NH4VO3 was added to a 100mL beaker with 85mL of distilled water. The mixture was stirred at 800rpm for 15min to obtain precursor solution B. Precursor solution B was then transferred to a 500mL round-bottom flask. Under vigorous stirring, precursor solution A from the first step was added dropwise to the flask containing precursor solution B. After the addition was complete, stirring was continued for 10min to obtain mixed solution C. Mixed solution C from the third step was then placed in a container equipped with a reflux reflux cooling system. In the PJ21C-AU microwave reactor, the heating power was set to 1000W, the frequency to 2450MHz, the heating temperature to 100℃, and the reaction time to 50min. After the reaction was completed, the product obtained in the round-bottom flask was allowed to cool naturally. The product was then transferred to a centrifuge and centrifuged at 5000rpm for 2min. The supernatant was removed and the lower layer product was retained. The lower layer product was washed 3-5 times with distilled water and ethanol, respectively. The washed product was then placed in an oven and the oven temperature was adjusted to 70℃. After 24h of heat treatment, the target three-phase coexisting nanosheet material was obtained.

[0060] X-ray diffraction results indicate that the product consists of three phases: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O. The XRD pattern of the product obtained at a reaction time of t = 50 min is shown below. Figure 10 As shown, characteristic peaks corresponding to tetragonal scheelite-type BiVO4 are present at 2θ = 18.319°, 24.373°, 32.679°, 34.714°, 39.527°, and 46.993°, which are consistent with standard JCPDS card number 14-0133 and correspond to the (101), (200), (112), (220), (301), and (321) crystal planes, respectively. The strongest peak corresponds to the hkl crystal plane index (200). Its crystal structure diagram is shown below. Figure 4 As shown, the lattice spacing is 0.365 nm, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the corresponding peak value accounts for 39.0% of the total peak value. Figure 11 , 12 Meanwhile, characteristic peaks corresponding to monoclinic BiVO4 are present at 2θ = 18.669°, 28.586°, 28.822°, 34.494°, 39.782° and 46.711°, which are consistent with standard JCPDS card number 14-0688, and are respectively consistent with (110), The (200), (211), and (240) crystal planes correspond to the strongest peak, which corresponds to the hkl crystal plane index. Its crystal structure diagram is as follows Figure 5 As shown, the lattice spacing is 0.309 nm, the space group is I² / a, and the cell parameters are... and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​accounted for 39.0% of the total peak values. Figure 11 , 12 Furthermore, characteristic peaks corresponding to [Bi6O5(OH)3](NO3)5·3H2O are also present at 2θ = 6.596°, 10.995°, 11.790°, 13.184°, and 42.823°, which correspond to standard JCPDS card number 48-575. Its crystal structure diagram is shown below. Figure 6 As shown, the corresponding peak value of this substance accounts for 22.0% of the total peak value. Figure 11 , 12 ).

[0061] Scanning electron microscope image ( Figure 13 , 14 The three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.44–1.97 μm and a thickness of 46–90 nm, as shown in the schematic diagram below. Figure 9 As shown, these nanosheets have uniform structures, are evenly distributed, and have good dispersion.

[0062] Example 3: Preparation of three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples using microwave radiation technology.

[0063] At room temperature, 2.0615 g of analytical grade Bi(NO3)3·5H2O and 1.5490 g of hexadecyltrimethylammonium bromide (CTAB) were weighed into a 250 mL beaker, and 115 mL of distilled water was added. The solution was stirred on a magnetic stirrer at 800 rpm for 15 min, and then transferred to a 250 mL round-bottom flask. This round-bottom flask was placed in a microwave reactor (brand name "Midea" PJ21C-AU) equipped with temperature control, reflux condenser, and atmospheric pressure reaction system. The heating power was set to 1000 W, the frequency to 2450 MHz, and the heating temperature to 100 °C. After mixing for 60 min, the precursor solution A was obtained. Then, 0.7457 g of... NH4VO3 was added to a 100mL beaker with 85mL of distilled water. The mixture was stirred at 800rpm for 15min to obtain precursor solution B. Precursor solution B was then transferred to a 500mL round-bottom flask. Under vigorous stirring, precursor solution A from the first step was added dropwise to the flask containing precursor solution B. After the addition was complete, stirring was continued for 10min to obtain mixed solution C. Mixed solution C from the third step was then placed in a container equipped with a reflux reflux cooling system. In the PJ21C-AU microwave reactor, the heating power was set to 1000W, the frequency to 2450MHz, the heating temperature to 100℃, and the reaction time to 70min. After the reaction was completed, the product obtained in the round-bottom flask was allowed to cool naturally. The product was then transferred to a centrifuge and centrifuged at 5000rpm for 2min. The supernatant was removed and the lower layer product was retained. The lower layer product was washed 3-5 times with distilled water and ethanol, respectively. The washed product was then placed in an oven and the oven temperature was adjusted to 70℃. After 24h of heat treatment, the target three-phase coexisting nanosheet material was obtained.

[0064] X-ray diffraction results indicate that the product consists of three phases: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O. The XRD pattern of the product obtained at a reaction time of t = 70 min is shown below. Figure 15 As shown, characteristic peaks corresponding to tetragonal scheelite-type BiVO4 are present at 2θ = 18.319°, 24.373°, 30.677°, 32.679°, 39.527°, 46.993°, and 48.402°, which are consistent with standard JCPDS card number 14-0133 and correspond to the (101), (200), (211), (112), (301), (321), and (312) crystal planes, respectively. The strongest peak corresponds to the hkl crystal plane index (200). Its crystal structure diagram is shown below. Figure 4 As shown, the lattice spacing is 0.365 nm, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the corresponding peak value accounts for 13.6% of the total peak value. Figure 16 , 17 Meanwhile, characteristic peaks corresponding to monoclinic BiVO4 are present at 2θ = 18.669°, 18.988°, 28.822°, 28.947°, 30.548°, 35.221°, 39.782° and 47.305°, which are consistent with standard JCPDS card number 14-0688, and are respectively consistent with (110), (011), The strongest peak corresponds to the hkl crystal plane indices corresponding to the crystal planes (121), (040), (002), (211), and (042). Its crystal structure diagram is as follows Figure 5 As shown, the lattice spacing is 0.309 nm, the space group is I² / a, and the cell parameters are... and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​accounted for 43.2% of the total peak values. Figure 16 , 17 Furthermore, characteristic peaks corresponding to [Bi6O5(OH)3](NO3)5·3H2O are also present at 2θ = 6.596°, 10.995°, 13.184°, 19.756°, and 42.823°, which correspond to standard JCPDS card number 48-575. Its crystal structure diagram is shown below. Figure 6 As shown, the corresponding peak value of this substance accounts for 43.2% of the total peak value. Figure 16 , 17 ).

[0065] Scanning electron microscope image ( Figure 18 , 19 The three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.12–1.96 μm and a thickness of 26–76 nm, as shown in the schematic diagram below. Figure 9 As shown, these nanosheets have uniform structures, are evenly distributed, and have good dispersion.

[0066] Example 4: Preparation of three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples using microwave radiation technology.

[0067] At room temperature, 2.0615 g of analytical grade Bi(NO3)3·5H2O and 1.5490 g of hexadecyltrimethylammonium bromide (CTAB) were weighed into a 25 mL beaker, and 115 mL of distilled water was added. The solution was stirred on a magnetic stirrer at 800 rpm for 15 min, and then transferred to a 250 mL round-bottom flask. This round-bottom flask was placed in a microwave reactor (brand name "Midea" PJ21C-AU) equipped with temperature control, reflux condenser, and atmospheric pressure reaction system. The reactor was set to a heating power of 1000 W, a frequency of 2450 MHz, and a heating temperature of 100 °C. After mixing for 60 min, the precursor solution A was obtained. Then, 0.7457 g of... NH4VO3 was added to a 100mL beaker with 85mL of distilled water. The mixture was stirred at 800rpm for 15min to obtain precursor solution B. Precursor solution B was then transferred to a 500mL round-bottom flask. Under vigorous stirring, precursor solution A from the first step was added dropwise to the flask containing precursor solution B. After the addition was complete, stirring was continued for 10min to obtain mixed solution C. Mixed solution C from the third step was then placed in a container equipped with a reflux reflux cooling system. In the PJ21C-AU microwave reactor, the heating power was set to 1000W, the frequency to 2450MHz, the heating temperature to 100℃, and the reaction time to 90min. After the reaction was completed, the product obtained in the round-bottom flask was allowed to cool naturally. The product was then transferred to a centrifuge and centrifuged at 5000rpm for 2min. The supernatant was removed and the lower layer product was retained. The lower layer product was washed 3-5 times with distilled water and ethanol, respectively. The washed product was then placed in an oven and the oven temperature was adjusted to 70℃. After 24h of heat treatment, the target three-phase coexisting nanosheet material was obtained.

[0068] X-ray diffraction results indicate that the product consists of three phases: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O. The XRD pattern of the product obtained at a reaction time of t = 90 min is shown below. Figure 20 As shown, characteristic peaks corresponding to tetragonal scheelite-type BiVO4 are present at 2θ = 18.319°, 24.373°, 30.677°, 32.679°, 39.527°, 46.993°, and 48.402°, which are consistent with standard JCPDS card number 14-0133 and correspond to the (101), (200), (211), (112), (301), (321), and (321) crystal planes, respectively. The strongest peak corresponds to the hkl crystal plane index (200). Its crystal structure diagram is shown below. Figure 4 As shown, the lattice spacing is 0.365 nm, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the corresponding peak value accounts for 39.5% of the total peak value. Figure 21 , 22 Meanwhile, characteristic peaks corresponding to monoclinic BiVO4 are present at 2θ = 18.988°, 28.822°, 28.947°, 30.548°, 39.782° and 42.464°, which are consistent with standard JCPDS card number 14-0688, and are respectively consistent with (011), The (121), (040), (211), and (051) crystal planes correspond to the strongest peak, which corresponds to the hkl crystal plane index. Its crystal structure diagram is as follows Figure 5 As shown, the lattice spacing is 0.309 nm, the space group is I² / a, and the cell parameters are... and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​accounted for 39.5% of the total peak values. Figure 21 , 22 Furthermore, characteristic peaks corresponding to [Bi6O5(OH)3](NO3)5·3H2O are also present at 2θ = 6.596°, 10.995°, 13.184°, 19.756°, and 42.823°, which correspond to standard JCPDS card number 48-575. Its crystal structure diagram is shown below. Figure 6 As shown, the corresponding peak value of this substance accounts for 21.0% of the total peak value. Figure 21 , 22 ).

[0069] Scanning electron microscope image ( Figure 23 , 24 The three-phase coexistence product is shown to be composed of stacked nanosheets with a particle size of 0.40–2.01 μm and a thickness of 43–141 nm, as illustrated in the schematic diagram below. Figure 9 As shown, these nanosheets have uniform structures, are evenly distributed, and have good dispersion.

[0070] Example 5: Preparation of three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples using microwave radiation technology.

[0071] At room temperature, 2.0615 g of analytical grade Bi(NO3)3·5H2O and 1.5490 g of hexadecyltrimethylammonium bromide (CTAB) were weighed into a 250 mL beaker, and 115 mL of distilled water was added. The solution was stirred on a magnetic stirrer at 800 rpm for 15 min, and then transferred to a 250 mL round-bottom flask. This round-bottom flask was placed in a microwave reactor (brand name "Midea" PJ21C-AU) equipped with temperature control, reflux condenser, and atmospheric pressure reaction system. The heating power was set to 1000 W, the frequency to 2450 MHz, and the heating temperature to 100 °C. After mixing for 60 min, the precursor solution A was obtained. Then, 0.7457 g of... NH4VO3 was added to a 100mL beaker, and 85mL of distilled water was added. The mixture was stirred at 800rpm for 15min to obtain precursor solution B. Then, precursor solution B obtained in the second step was transferred to a 500mL round-bottom flask. Under vigorous stirring, precursor solution A obtained in the first step was added dropwise to the 500mL flask containing precursor solution B. After the addition was complete, stirring was continued for 10min to obtain mixed solution C. Mixed solution C obtained in the third step was placed in a Midea container equipped with an atmospheric pressure reflux cooling device. In the PJ21C-AU microwave reactor, the heating power was set to 1000W, the frequency to 2450MHz, the heating temperature to 100℃, and the reaction time to 130min. After the reaction was completed, the product obtained in the round-bottom flask was allowed to cool naturally. The product was then transferred to a centrifuge and centrifuged at 5000rpm for 2min. The supernatant was removed and the lower layer product was retained. The lower layer product was washed 3-5 times with distilled water and ethanol, respectively. The washed product was then placed in an oven and the oven temperature was adjusted to 70℃. After 24h of heat treatment, the target three-phase coexisting nanosheet material was obtained.

[0072] X-ray diffraction results indicate that the product consists of three phases: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O. The XRD pattern of the product obtained at a reaction time of t = 130 min is shown below. Figure 25 As shown, characteristic peaks corresponding to tetragonal scheelite-type BiVO4 are present at 2θ = 18.319°, 24.373°, 30.677°, 32.679°, 34.714°, 48.402°, and 49.931°, which are consistent with standard JCPDS card number 14-0133 and correspond to the (101), (200), (211), (112), (220), (312), and (400) crystal planes, respectively. The strongest peak corresponds to the hkl crystal plane index (200). Its crystal structure diagram is shown below. Figure 4 As shown, the lattice spacing is 0.365 nm, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the corresponding peak value accounts for 38.5% of the total peak value. Figure 26 , 27 Meanwhile, characteristic peaks corresponding to monoclinic BiVO4 are present at 2θ = 18.669°, 18.988°, 28.586°, 28.822°, 28.947°, 35.221°, 39.782° and 42.464°, which are consistent with standard JCPDS card number 14-0688, and are respectively consistent with (110), (011), The (121), (002), (211), and (240) crystal planes correspond to the strongest peak, which corresponds to the hkl crystal plane index. Its crystal structure diagram is as follows Figure 5 As shown, the lattice spacing is 0.309 nm, the space group is I² / a, and the cell parameters are... and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​accounted for 38.5% of the total peak values. Figure 26 , 27 Furthermore, characteristic peaks corresponding to [Bi6O5(OH)3](NO3)5·3H2O are also present at 2θ = 6.596°, 10.995°, 11.790°, 19.756°, 24.992°, and 42.823°, which correspond to standard JCPDS card number 48-575. Its crystal structure diagram is shown below. Figure 6 As shown, the corresponding peak value of this substance accounts for 23.0% of the total peak value. Figure 26 , 27 ).

[0073] Scanning electron microscope image ( Figure 28 , 29 The three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.59–3.21 μm and a thickness of 64–198 nm, as shown in the schematic diagram below. Figure 9 As shown, these nanosheets have uniform structures, are evenly distributed, and have good dispersion.

[0074] To demonstrate the effects achieved by the experimental steps used in Examples 1-5 of this invention, the product cannot achieve the expected effects and innovation of Examples 1-5 of this invention if the operations of Examples 1-5 are not used.

[0075] Comparative example of Example 1:

[0076] In (Sun S, Wang W, Zhou L, et al. Efficient methylene blue removal overhydrothermally synthesized starlike BiVO4[J]. Industrial & Engineering Chemistry Research, 2009, 48(4): 1735-1739), Sun et al. synthesized the target product using a solvothermal method as follows: At room temperature, firstly, 0.2924 g of NH4VO3 and 0.731 g of EDTA were weighed and dissolved in 5 mL of 2 mol / L NaOH solution and 15 mL of 2 mol / L ammonia solution, respectively; secondly, 1.213 g of Bi(NO3)3·5H2O was weighed and added to 5 mL of... 2 mol / L nitric acid solution was added and stirred for 10 min. Then, the three solutions were mixed and 5 mL of ethanol was added. Finally, the mixed solution was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner and heated at 120 °C for 6 h. After the reaction was completed, the product was washed with deionized water and ethanol. The washed product was then dried at 80 °C for 12 h to obtain the target product. This method cannot prepare a product with three coexisting phases of BiVO4 (14-0133 and 14-0688) and [Bi6O5(OH)3](NO3)5·3H2O (48-575), and the obtained product is a micron sheet with a size of 1-2 μm.

[0077] This invention patent is fundamentally different from the comparative example, and this invention patent has distinct innovation.

[0078] Comparative example of Example 2:

[0079] In (Huo R, Yang XL, Liu YQ, et al. Visible-light photocatalytic degradation of glyphosate over BiVO4 prepared by different co-precipitation methods[J]. Materials Research Bulletin, 2017, 88: 56-61), Huo et al. synthesized the target product using the co-precipitation method as follows: At room temperature, firstly, 8.9850 g of Bi(NO3)3·5H2O was weighed and dissolved in 150 mL of 1.34 mol / L glacial acetic acid solution; secondly, 2.1660 g of NH4VO3 was weighed and added to 150 mL of glacial acetic acid solution. The solution was prepared in a 0.5 mol / L sodium hydroxide solution. Subsequently, the two solutions were rapidly mixed under ultrasound, and the suspension was filtered off. The yellow precipitate was washed with distilled water and anhydrous ethanol and then dried at 70°C. Finally, the dried product was calcined in air at 300–500°C for 2 hours to obtain the target product. This method cannot prepare a product with three coexisting phases of 14-0133, 14-0688 BiVO4 and 48-575 [Bi6O5(OH)3](NO3)5·3H2O, and the obtained product is a nanoparticle with a size of 45–235 nm.

[0080] This invention patent is fundamentally different from the comparative example, and this invention patent has distinct innovation.

[0081] Comparative example of Example 3:

[0082] In (Khan I, Ali S, Mansha M, et al. Sonochemical assisted hydrothermal synthesis of pseudo-flower shaped Bismuth vanadate (BiVO4) and their solar-driven water splitting application[J]. Ultrasonics sonochemistry, 2017, 36: 386-392), Khan et al. synthesized the target product using a sonochemical method as follows: At room temperature, 4.85 g of Bi(NO3)3·5H2O and 1.82 g of V2O5 were weighed and dissolved in a 25 mL container. The product was first placed in a Teflon tube containing 1 wt% SDS; then, it was treated with a pulsed ultrasonic machine at an on / off cycle of 10 s, a power of 400 W, and a frequency of 20 kHz for 2 h; subsequently, the pale yellow precipitate in the Teflon tube was removed and washed with deionized water; finally, the washed precipitate was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and stored at 90 °C for 4 h; after the reaction, the product was dried at room temperature and calcined at 550 °C for 4 h to obtain the target product; this method cannot prepare a product with three coexisting phases of 14-0133, 14-0688 BiVO4 and 48-575 [Bi6O5(OH)3](NO3)5·3H2O, and the obtained product is a micron flower with a size of 7 μm.

[0083] This invention patent is fundamentally different from the comparative example, and this invention patent has distinct innovation.

Claims

1. A method for preparing three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheet materials, characterized in that... Includes the following steps: First, at room temperature, weigh 2.0615 g of analytical grade Bi(NO3)3·5H2O and 1.5490 g of hexadecyltrimethylammonium bromide (CTAB) into a 250 mL beaker, add 115 mL of distilled water, stir the solution on a magnetic stirrer at 800 rpm for 15 min, and then transfer it to a 250 mL round-bottom flask. Place the round-bottom flask in a microwave reactor. This device is a microwave reactor with temperature control, reflux condenser, and atmospheric pressure reaction system. Set the heating power to 200–2000 W, the frequency to 2450 MHz, and the heating temperature to 100 °C. After mixing for 60 min, the precursor solution A is obtained. Second, weigh 0.7457g of NH4VO3 into a 100mL beaker, add 85mL of distilled water to the beaker, and stir at a constant speed of 800rpm for 15min to obtain the reaction precursor solution B. Third, transfer the precursor solution B obtained in the second step to a 500mL round-bottom flask. Under vigorous stirring, add the precursor solution A obtained in the first step dropwise to the 500mL flask containing the precursor solution B. After the addition is complete, continue stirring for 10 minutes to obtain a mixed solution C. Fourth, place the mixed solution C obtained in the third step into a microwave reactor equipped with an atmospheric pressure reflux cooling device, and set the heating power to 200-2000W, the frequency to 2450MHz, the heating temperature to 100℃, and the reaction time to 30-130min. Fifth, after the reaction is complete, allow the product obtained in the round-bottom flask to cool naturally, transfer the product to a centrifuge, centrifuge at 5000 rpm for 2 min, remove the supernatant and retain the lower layer product, wash the lower layer product with distilled water and ethanol 3 to 5 times respectively, then place the washed product in an oven, adjust the oven temperature to 70℃, and keep it at the temperature for 24 h to obtain the target three-phase coexisting nanosheet material.

2. A three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheet material, characterized in that... It is prepared by the preparation method described in claim 1.

3. The three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheets according to claim 2, characterized in that: When the reaction time t = 30 min, the strongest peak of the monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 35.4% of the total peak values. The strongest peak of tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 36.2% of the total peak value. In addition, the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 28.4% of the total peak value. The three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.20~1.89μm and a thickness of 20~130nm.

4. The three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheets according to claim 2, characterized in that: When the reaction time t = 50 min, the strongest peak of the monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 39.0% of the total peak values. The strongest peak of the tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 39.0% of the total peak value, and the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 22.0% of the total peak value; the three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.44~1.97μm and a thickness of 46~90nm.

5. The three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheets according to claim 2, characterized in that: When the reaction time t = 70 min, the strongest characteristic peak of monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 43.2% of the total peak values. The strongest peak of the tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 13.6% of the total peak value, and the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 43.2% of the total peak value; the three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.12~1.96μm and a thickness of 26~76nm.

6. The three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheets according to claim 2, characterized in that: When the reaction time t = 90 min, the strongest peak of the monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 39.5% of the total peak values. The strongest peak of the tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 39.5% of the total peak value, and the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 21.0% of the total peak value; the three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.40~2.01μm and a thickness of 43~141nm.

7. The three-phase coexisting monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O nanosheets according to claim 2, characterized in that: When the reaction time t = 130 min, the strongest peak of monoclinic BiVO4 corresponds to the hkl crystal plane index. Space group I2 / a, cell parameters and With α = γ = 90.0° and β = 90.38°, the corresponding peak values ​​account for 38.5% of the total peak values. The strongest peak of the tetragonal scheelite-type BiVO4 corresponds to the hkl crystal plane index (200), space group I41 / amd, and cell parameters are... and α=β=γ=90.0°, the corresponding peak value of this product accounts for 38.5% of the total peak value, and the corresponding peak value of [Bi6O5(OH)3](NO3)5·3H2O accounts for 23.0% of the total peak value; the three-phase coexistence product is composed of stacked nanosheets with a particle size of 0.59~3.21μm and a thickness of 64~198nm.

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