A highly ordered micron flower material with three phases coexisting: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, and its control method.

Abstract

This invention discloses a highly ordered micron-shaped flower material with three phases coexisting: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, and its control method. The method includes: preparing a mixed solution A of bismuth nitrate and hexadecyltrimethylammonium bromide and a solution B of ammonium metavanadate using deionized water as a solvent; adding mixed solution A dropwise to solution B under vigorous stirring to obtain a reaction precursor solution C; placing solution C in a microwave reactor and performing a microwave radiation reaction at 100°C without pH adjustment to obtain a solid-liquid suspension sample; and centrifuging, washing, and drying the sample to obtain the three-phase coexisting product. This invention utilizes microwave radiation technology to control the morphology and composition of the product without the need for acid or alkali conditions. The method is simple, efficient, and energy-saving.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic functional materials, and specifically relates to a highly ordered micron flower material with three phases coexisting: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, and its control method. Background Technology

[0002] With the rapid development of industry, environmental pollution and energy depletion are two major problems that urgently need to be solved. In recent years, semiconductor photocatalysts have received widespread attention due to their advantages such as high efficiency, low cost, and energy saving. They are mainly used in photocatalytic water splitting, sewage treatment, drinking water purification, and sterilization (Guo Xiaoyu. Preparation and Performance of Bismuth Vanadate and Bismuth Molybdate-based Heterostructure Photocatalysts [D]. Jilin Normal University, 2016). Although TiO2 is currently the most widely used photocatalytic material, certain inherent defects limit the improvement of its catalytic efficiency. Due to its high band gap of 3.2 eV, TiO2 can only be excited by ultraviolet light with high photon energy, resulting in a low quantum generation efficiency. Ultraviolet light accounts for only about 4% of the total sunlight, which greatly limits the utilization and efficiency improvement of such materials (Xiang Z, Wang Y, Zhang D, et al. BiOI / BiVO4 pn heterojunction with enhanced photocatalytic activity under visible-light irradiation[J]. Journal of Industrial and Engineering Chemistry, 2016, 40: 83-92). Therefore, it is essential to develop novel photocatalytic materials that can be excited by visible light and are both highly efficient and environmentally friendly. BiVO4, as a photocatalyst with visible light response, has broad application prospects due to its good stability, non-toxicity, and environmental friendliness (Wang Guilin. Morphology regulation and photocatalytic performance of bismuth vanadate[D]. Harbin University of Science and Technology, 2016).

[0003] BiVO4 mainly exists in three crystal forms: tetragonal zircon (ZT), monoclinic scheelite (SM), and tetragonal scheelite (ST). Different crystal structures can affect the band gap of the photocatalyst and the separation and migration efficiency of photogenerated carriers, thus affecting the photocatalytic activity and effect of the material. Among them, BiVO4 with monoclinic scheelite-type structure and tetragonal zircon structure have certain photocatalytic properties, but tetragonal zircon BiVO4 only responds in the ultraviolet region due to its large band gap (about 2.9 eV); while the monoclinic BiVO4 has a band gap of about 2.4 eV and responds in both the ultraviolet and visible regions (phase vibration wave). BiVO4-based composite material preparation and its photocatalytic antifouling performance study [D]. University of Chinese Academy of Sciences, 2017. The monoclinic phase, due to its smaller band gap, can be regarded as the optimal crystal form for photocatalysis (Oshikiri M, Boero M, Ye J, et al. Electronic structures of promising photocatalysts InMO4(M=V,Nb,Ta)andBiVO4 for water decomposition in the visible wavelength region[J]. Journal of Chemical Physics, 2002, 117(15): 7313-7318; Tokunaga S, Kato H, Kudo A. Selective preparation of monoclinic and tetragonal BiVO4 with scheelite structure and their photocatalytic properties [J]. Chemistry of Materials, 2001, 13(12): 4624-4628).However, due to its poor charge transport properties (Hong SJ, Lee S, Jang JS, et al. Heterojunction BiVO4 / WO3 electrons for enhanced photoactivity of water oxidation[J]. Energy Environ. Sci., 2011, 4(5): 1781-1787) and weak surface adsorption properties, the single monoclinic phase BiVO4 still exhibits insufficient photocatalytic activity (Yao W, Iwai H, Ye J. Effects of molybdenum substitution on the photocatalytic behavior of BiVO4[J]. Dalton Trans., 2008, 11: 1426-1430).

[0004] To enhance the photocatalytic activity of monoclinic BiVO4, various methods have been proposed, including heterojunction formation, co-catalyst loading, and impurity doping. Among these methods, heterostructures with coexisting phases are a novel approach worth considering. Tan et al. reported a feasible scheme to obtain monoclinic and monoclinic-tetragonal mixtures by controlling the pH of the precursor (Tan G, Zhang L, Ren H, et al. Effects of pH on the hierarchical structures and photocatalytic performance of BiVO4 powders prepared via the microwave hydrothermal method[J].ACS Appl. Mater. Interfaces, 2013, 5(11): 5186-5193), demonstrating that the presence of mixed-phase BiVO4 exhibits higher photocatalytic activity than that of a single phase. Monoclinic structures are typically obtained through high-temperature methods, while tetragonal structures are usually achieved through a water-medium method at low temperatures (S. Obregón, A. Caballero, G. Colón, et al. Hydrothermal synthesis of BiVO4: Structural and morphological influence on the photocatalytic activity[J]. Applied Catalysis B: Environmental, 2012, 117: 59-66).

[0005] Currently, commonly used techniques for preparing BiVO4 include high-temperature solid-phase methods, sol-gel methods, sonicochemical methods, hydrothermal methods, and liquid-phase synthesis methods. However, these preparation methods usually require long reaction times and high-temperature, high-pressure reaction conditions. The processes often use acids or bases to control pH and morphology, resulting in significant secondary contamination problems, and the reproducibility of the samples is not stable enough. Summary of the Invention

[0006] The purpose of this invention is to propose a high-order micron flower material with three phases coexisting, namely tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, and its control method, which is simple to use, has low and readily available raw materials, mild and controllable reaction conditions, is fast, efficient, green and environmentally friendly.

[0007] This invention is implemented using the following scheme:

[0008] Step 1: Analytical grade Bi(NO3)3·5H2O and hexadecyltrimethylammonium bromide (CTAB) were added to 115 mL of deionized water and thoroughly dissolved on a magnetic stirrer at 800 rpm for 15 min. The solution was then transferred to a 250 mL round-bottom flask. The mixture was placed in a microwave reactor (model "Midea PJ21C-AU") with a frequency of 2450 MHz and a normal pressure reflux cooling device. The heating temperature was set to 100℃ and the power to 1000 W. After heating and mixing for 60 min, a bismuth nitrate mixed solution A was obtained. NH4VO3 was dissolved in 85 mL of deionized water and thoroughly stirred on a magnetic stirrer at 800 rpm for 15 min to obtain ammonium metavanadate solution B. The molar ratio of Bi:CTAB:V was 2:2:3 or 2:3:3.

[0009] Step 2: While vigorously stirring the ammonium metavanadate solution B, add the bismuth nitrate mixed solution A prepared in Step 1. After the addition is completed, continue stirring for 10 minutes to obtain a homogeneous reaction precursor solution C and transfer it to a 500mL round-bottom flask.

[0010] Step 3: Place the reaction precursor solution C obtained in Step 2 into a microwave reactor with the same model and parameters as in Step 1, and set the heating temperature to 100℃ and the power to 1000W for reaction. After the reaction is completed and cooled to room temperature, centrifuge the obtained solid-liquid suspension at 5000rpm for 2min, discard the supernatant and retain the lower suspension solid sample. Wash the solid sample with distilled water and ethanol 3-5 times respectively and dry it in an oven at 70℃ for 24h to obtain a highly regular micron flower with three phases of tetragonal scheelite type BiVO4, monoclinic type BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O.

[0011] Furthermore, in step 1, when the molar ratio of Bi:CTAB:V is 2:2:3, the weighed raw materials are 2.0615g Bi(NO3)3·5H2O, 1.5490g hexadecyltrimethylammonium bromide (CTAB), and 0.7457g NH4VO3, respectively; when the molar ratio of Bi:CTAB:V is 2:3:3, the weighed raw materials are 2.0615g Bi(NO3)3·5H2O, 2.3234g hexadecyltrimethylammonium bromide (CTAB), and 0.7457g NH4VO3, respectively.

[0012] Furthermore, when the molar ratio of Bi:CTAB:V in step 1 is 2:2:3, the reaction time in step 3 is 10 min; when the molar ratio of Bi:CTAB:V in step 1 is 2:3:3, the reaction time in step 3 is 90 min.

[0013] When the molar ratio of Bi:CTAB:V is 2:2:3 and the reaction time is 10 min, the proportion of the characteristic peak of tetragonal scheelite-type BiVO4 in the product is 48.22%, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the strongest peak corresponds to the crystal plane index (200); the characteristic peak ratio of monoclinic BiVO4 is 31.58%, the space group is I2 / a, and the cell parameters are... and α=γ=90.0° and β=90.38°, the strongest peak corresponds to the crystal plane indices of The characteristic peak percentage of [Bi6O5(OH)3](NO3)5·3H2O was 20.20%.

[0014] Furthermore, the morphology of the product is micron flowers with a width of 2.58–3.40 μm and a thickness of 2.24–3.23 μm, composed of nanosheets with a particle size of 0.81–2.63 μm and a thickness of 46–178 nm.

[0015] When the molar ratio of Bi:CTAB:V is 2:3:3 and the reaction time is 90 min, the proportion of the characteristic peak of tetragonal scheelite-type BiVO4 in the product is 19.34%, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the strongest peak corresponds to the crystal plane index (200); the characteristic peak ratio of monoclinic BiVO4 is 32.68%, the space group is I2 / a, and the cell parameters are... and α=γ=90.0° and β=90.38°, the strongest peak corresponds to the crystal plane indices of The characteristic peak of [Bi6O5(OH)3](NO3)5·3H2O accounted for 47.98%.

[0016] Furthermore, the morphology of the product is micron flowers with a width of 3.04–6.58 μm and a thickness of 2.13–4.38 μm, composed of nanosheets with a particle size of 0.42–2.72 μm and a thickness of 45–177 nm.

[0017] This invention addresses the problems of existing BiVO4 preparation processes requiring long reaction times and high-temperature, high-pressure conditions, the frequent use of acids or bases for pH and morphology control, significant secondary pollution, and unstable sample reproducibility. It proposes a highly ordered micron-flower material with three phases coexisting: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, along with their control methods. The method of this invention does not require acid or alkali intervention for regulation, has a simple preparation process, is green and environmentally friendly, economical and efficient, and is stable and controllable. It can achieve regulation of product morphology and phase through rapid microwave radiation. The obtained products are three-dimensional network structures of tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O three-phase coexisting highly regular micron flower materials. The samples have high specific surface area, regular morphology, and good crystallinity, and are expected to become an effective way to improve the photocatalytic performance of BiVO4 materials. It has obvious scientific, practical and innovative characteristics, and has important application value in solving environmental pollution and new energy development.

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

[0019] (1) Currently, most research and preparation of bismuth vanadate focuses on monoclinic bismuth vanadate with a single phase or the doping and composite of monoclinic bismuth vanadate with other ions or substances, and heterostructures are usually constructed between two phases or two substances. This invention prepares highly ordered micron flowers with three phases coexisting: monoclinic BiVO4, tetragonal scheelite-type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, using microwave radiation. The products have high specific surface area and highly ordered morphology and size, and are expected to become a new approach to solve the problems of poor electron-hole separation efficiency and few active sites in photocatalytic materials.

[0020] (2) This method overcomes the shortcomings of commonly used hydrothermal and solid-phase methods, such as high equipment requirements, complex operation, high temperature and high pressure and poor repeatability. Unlike microwave hydrothermal methods, this patented method does not require the use of acid or alkali and hydrothermal reactors, and the reaction does not require high temperature and high pressure. It has the advantages of simple process equipment, energy saving and high efficiency, stability and controllability, and compliance with environmental requirements.

[0021] This invention patent provides a highly ordered micron-flower material with three phases coexisting: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, and its control method. The product obtained by this method is a multi-layered micron-flower composite of three phases assembled from nanosheets. The positional relationship between the nanosheets is not one of stacking and aggregation, but rather a three-dimensional flower-like structure formed by sharing edges. This structure not only inhibits the stacking and aggregation of nanosheets and creates a large surface area, but also utilizes the multi-layered structure to repeatedly scatter light, thereby increasing the optical path and improving light absorption and catalytic activity.

[0022] The mechanism involved in this patented method is as follows: When electromagnetic waves encounter the reaction system medium, the high energy of the microwaves can be absorbed by the sample, thereby accelerating the movement and collision of particles within the system, increasing the activity and temperature of the reaction system. Compared with traditional heating methods, microwave heating technology has advantages such as non-contact heating, selective heating, rapid start-up and shutdown, and high yield and efficiency. Under the action of a microwave field, adding a mixed solution of Bi(NO3)3·5H2O and CTAB to a stirred NH4VO3 solution in a dropwise manner is beneficial to obtaining a product with small particle size and uniform dispersion at a lower temperature. The micromicelles formed by CTAB in the solution act as soft templates, restricting the growth direction of the product crystals. Crystal nuclei attach to CTAB and grow along the direction of the template arrangement. In the initial stage of the reaction, the system concentration is high, and the crystals grow rapidly along the petals of the crystal nuclei; as the reactant concentration decreases, the growth rate slows down, and the petal width narrows. At the same time, the amount of CTAB also significantly affects the morphology of the product. If the CTAB concentration is less than the CMC, the surfactant cannot form micelles. At this time, the interaction between CTAB and the initial BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O nuclei is small and unstable. If CTAB is added in excess and the concentration exceeds the CMC, supersaturated adsorption will occur, and the long-chain macromolecules in the solution system tend to become entangled with each other, increasing the system viscosity and causing particle aggregation. Therefore, under microwave radiation and specific parameters such as CTAB dosage, reactant concentration, and temperature, the method of this invention can controllably synthesize tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O three-phase coexistence materials with high-order micron flower-like structures. Attached Figure Description

[0023] Figure 1 X-ray diffraction (XRD) patterns of tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with a Bi:CTAB:V molar ratio of 2:2:3 and a reaction time of 10 min.

[0024] Figure 2The proportion of each phase in the XRD pattern of the sample when the molar ratio of Bi:CTAB:V is 2:2:3 and the reaction time is 10 min;

[0025] Table 1 shows the proportion of each phase in the XRD pattern of the sample when the molar ratio of Bi:CTAB:V is 2:2:3 and the reaction time is 10 min.

[0026] Figure 3 The crystal structure diagram of sample 14-0133 is a tetragonal scheelite-type BiVO4.

[0027] Figure 4 The crystal structure diagram of monoclinic BiVO4 in sample 14-0688 is shown.

[0028] Figure 5 The crystal structure diagram of phase [Bi6O5(OH)3](NO3)5·3H2O of sample 48-575 is shown.

[0029] Figure 6 13kx scanning electron microscope (SEM) images of tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with a Bi:CTAB:V molar ratio of 2:2:3 and a reaction time of 10 min.

[0030] Figure 7 60kx scanning electron microscope (SEM) images of tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with a Bi:CTAB:V molar ratio of 2:2:3 and a reaction time of 10 min.

[0031] Figure 8 Schematic diagram of the synthetic morphology of three-phase coexisting tetragonal scheelite-type BiVO4, monoclinic BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O samples;

[0032] Figure 9 X-ray diffraction (XRD) patterns of tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with a Bi:CTAB:V molar ratio of 2:3:3 and a reaction time of 90 min.

[0033] Figure 10 The proportion of each phase in the XRD pattern of the sample when the molar ratio of Bi:CTAB:V is 2:3:3 and the reaction time is 90 min;

[0034] Table 2 shows the proportion of each phase in the XRD pattern of the sample when the molar ratio of Bi:CTAB:V is 2:3:3 and the reaction time is 90 min.

[0035] Figure 11 7kx scanning electron microscope (SEM) images of tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with a Bi:CTAB:V molar ratio of 2:3:3 and a reaction time of 90 min.

[0036] Figure 12 The images are 25kx scanning electron microscope (SEM) images of tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O samples with a Bi:CTAB:V molar ratio of 2:3:3 and a reaction time of 90 min. Detailed Implementation

[0037] 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.

[0038] Example 1: Sample 1 synthesized using microwave radiation technology to synthesize a highly ordered micron-shaped flower-like structure with three phases coexisting: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O.

[0039] At room temperature, with a Bi:CTAB:V molar ratio of 2:2:3, 2.0615 g of analytical grade Bi(NO3)3·5H2O and 1.5490 g of hexadecyltrimethylammonium bromide (CTAB) were added to 115 mL of deionized water. The mixture was thoroughly dissolved for 15 min on a magnetic stirrer at 800 rpm, then transferred to a 250 mL round-bottom flask. This mixture was placed in a microwave reactor (model "Midea PJ21C-AU") with a frequency of 2450 MHz and equipped with a normal pressure reflux cooling device. The heating temperature was set to 100℃, the power to 1000 W, and the mixture was heated and mixed for 60 min to obtain bismuth nitrate mixed solution A. 0.7457 g of analytical grade NH4VO3 was dissolved in 85 mL of deionized water and thoroughly stirred for 15 min on a magnetic stirrer at 800 rpm to obtain ammonium metavanadate solution B. While stirring ammonium metavanadate solution B, a prepared bismuth nitrate mixed solution A was added. After the addition was completed, stirring was continued for 10 min to obtain a homogeneous reaction precursor solution C, which was then transferred to a 500 mL round-bottom flask. The reaction precursor solution C was placed in a microwave reactor of the same model and parameters as in the above steps, and the heating temperature was set to 100℃, the power to 1000W, and the reaction time to 10 min. After the reaction was completed and cooled to room temperature, the obtained solid-liquid suspension was centrifuged at 5000 rpm for 2 min. The supernatant was discarded, and the lower suspension solid sample was retained. The solid sample was washed 3 to 5 times with distilled water and ethanol, respectively, and dried in an oven at 70℃ for 24 h to obtain a highly regular micronized flower with three phases coexisting: tetragonal scheelite type BiVO4, monoclinic type BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O.

[0040] X-ray diffraction results showed that the product consisted of three phases: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O. The XRD pattern of sample 1 is shown below. Figure 1 As shown, characteristic peaks of tetragonal scheelite-type BiVO4, corresponding to standard JCPDS card number No. 14-0133, are observed at 2θ = 18.319°, 24.373°, 32.679°, 34.714°, 39.527°, 48.402°, and 49.931°, with a peak percentage of 48.22%. Figure 2 Table 1), and corresponding to the (101), (200), (112), (220), (301), (312) and (400) crystal planes respectively, with space group I41 / amd and cell parameters. and α=β=γ=90.0°, the strongest peak corresponds to the hk1 crystal plane index (200), and its crystal structure is as follows. Figure 3As shown, the lattice spacing is 0.365 nm; simultaneously, the XRD pattern of the product also shows characteristic peaks of monoclinic BiVO4 corresponding to standard JCPDS card number No. 14-0688 at 2θ = 18.669°, 28.586°, 28.822°, 28.947°, 39.782°, 46.711°, and 53.310°, with a peak percentage of 31.58%. Figure 2 Table 1), and respectively with (110), The (121), (211), (240), and (161) crystal planes correspond to each other, with a space group of 12 / a and cell parameters of [missing information]. and α=γ=90.0° and β=90.38°, the strongest peak corresponds to the hk1 crystal plane index. Its crystal structure is as follows Figure 4 As shown, the lattice spacing is 0.309 nm; in addition, there are characteristic peaks of [Bi6O5(OH)3](NO3)5·3H2O at 2θ = 6.596°, 10.995°, 11.790°, 13.184°, 19.756° and 24.992°, corresponding to standard JCPDS card number No. 48-575. Its crystal structure is as follows. Figure 5 As shown, the peak percentage of these characteristic peaks is 20.20% ( Figure 2 (Table 1).

[0041] Scanning electron microscope (SEM) image Figure 6 , 7 The morphology of the product is shown to be micron flowers with a width of 2.58–3.40 μm and a thickness of 2.24–3.23 μm, composed of nanosheets with a particle size of 0.81–2.63 μm and a thickness of 46–178 nm. A schematic diagram of the morphology is shown below. Figure 8 As shown.

[0042] Example 2: Sample 2 synthesized using microwave radiation technology to control the coexistence of three phases: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, exhibiting highly ordered micron-sized flowers.

[0043] At room temperature, with a Bi:CTAB:V molar ratio of 2:3:3, 2.0615g of analytical grade Bi(NO3)3·5H2O and 2 .3234g of hexadecyltrimethylammonium bromide (CTAB) was added to 115mL of deionized water and thoroughly dissolved for 15 minutes on a magnetic stirrer at 800rpm. The solution was then transferred to a 250mL round-bottom flask. This mixture was placed in a microwave reactor (model "Midea PJ21C-AU") with a frequency of 2450MHz and a normal pressure reflux cooling device. The heating temperature was set to 100℃, the power to 1000W, and the mixture was heated and mixed for 60 minutes to obtain bismuth nitrate mixed solution A. 0.7457g of analytical grade NH4VO3 was dissolved in 85mL of deionized water and thoroughly stirred for 15 minutes on a magnetic stirrer at 800rpm to obtain ammonium metavanadate solution B. While vigorously stirring ammonium metavanadate solution B, the prepared bismuth nitrate mixed solution was added to it. Liquid A was added dropwise and stirred continuously for 10 minutes to obtain a homogeneous reaction precursor solution C, which was then transferred to a 500 mL round-bottom flask. The reaction precursor solution C was placed in a microwave reactor of the same model and parameters as the one described above, and the heating temperature was set to 100℃, the power to 1000W, and the reaction time to 90 minutes. After the reaction was completed and cooled to room temperature, the resulting solid-liquid suspension was centrifuged at 5000 rpm for 2 minutes. The supernatant was discarded, and the lower suspension solid sample was retained. The solid sample was washed 3 to 5 times with distilled water and ethanol, respectively, and dried in an oven at 70℃ for 24 hours to obtain a highly regular micronized flower with three phases coexisting: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O.

[0044] X-ray diffraction results showed that the product consisted of three phases: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O. The XRD pattern of sample 2 is shown below. Figure 9 As shown, characteristic peaks of tetragonal scheelite-type BiVO4, corresponding to standard JCPDS card number No. 14-0133, are observed at 2θ = 18.319°, 24.373°, 30.677°, 32.679°, 39.527°, 46.993°, 48.402°, and 49.931°, with a peak percentage of 19.34%. Figure 10 Table 2), and corresponding to the (101), (200), (211), (112), (301), (321), (312) and (400) crystal planes respectively, with space group I41 / amd and cell parameters. and α=β=γ=90.0°, the strongest peak corresponds to the hk1 crystal plane index (200), and its crystal structure is as follows. Figure 3As shown, the lattice spacing is 0.365 nm; simultaneously, the XRD pattern of the product also shows characteristic peaks of monoclinic BiVO4 corresponding to standard JCPDS card number No. 14-0688 at 2θ = 18.988°, 28.586°, 28.822°, 28.947°, 30.548°, 35.221°, 42.464°, and 47.305°, with a peak percentage of 32.68%. Figure 10 Table 2), and respectively with (011), The crystal planes (121), (040), (002), (051), and (042) correspond to each other, with space group I2 / a and cell parameters [missing information]. and α=γ=90.0° and β=90.38°, the strongest peak corresponds to the hk1 crystal plane index. Its crystal structure is as follows Figure 4 As shown, the lattice spacing is 0.309 nm; furthermore, characteristic peaks of [Bi6O5(OH)3](NO3)5·3H2O corresponding to standard JCPDS card number No. 48-575 are present at 2θ = 6.596°, 10.995°, 13.184°, 14.877°, 19.756°, 24.992°, and 29.454°, respectively. Its crystal structure is as follows: Figure 5 As shown, the peak percentage of these characteristic peaks is 47.98%. Figure 10 (Table 2).

[0045] Scanning electron microscope (SEM) image Figure 11 , 12 The morphology of the product is shown to be micron flowers with a width of 3.04–6.58 μm and a thickness of 2.13–4.38 μm, composed of nanosheets with a particle size of 0.42–2.72 μm and a thickness of 45–177 nm. A schematic diagram of the morphology is shown below. Figure 8 As shown.

[0046] Comparative Example 1 of the Examples:

[0047] In (Ma L, Li WH, Luo J H. Solvothermal synthesis and characterization of well-dispersed monoclinic olive-like BiVO4 aggregates[J]. Materials Letters, 2013, 102: 65-67), Ma et al. synthesized the target monoclinic olive-like BiVO4 aggregate product using a solvothermal method as follows: 1 mmol Bi(NO3)3·5H2O was dissolved in 30 mL of ethylene glycol to form solution A, and 1 mmol... NH4VO3 was dissolved in 10 mL of deionized water to form solution B; then, solution B was slowly added dropwise to solution A under stirring to form a mixture; the pH was adjusted to 4.0 with 10% HCl solution, and after stirring for about 30 min, the mixture was transferred to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene, sealed, and reacted at 160 °C for 16 h; after that, the autoclave was allowed to cool naturally, the product was collected, washed three times with deionized water and anhydrous ethanol, and then vacuum dried at 60 °C for 12 h; this method requires acid and base adjustment and the reaction conditions are high temperature and high pressure, and the product obtained is a monoclinic olive-shaped BiVO4 aggregate with an average length of 1.21 μm and an average width of 610 nm.

[0048] This invention patent is fundamentally different from the comparative example; this invention patent has distinct innovation.

[0049] Comparative Example 2 of the Implementation Examples:

[0050] (Liu Y, Huang B, Dai Y, et al.Selective ethanol formation from photocatalytic reduction of carbon dioxide in water with BiVO4 photocatalyst[J].Catalysis In Communications, 2009, 11(3): 210-213, Liu et al. prepared monoclinic BiVO4 using a microwave-assisted hydrothermal method as follows: stoichiometric Bi(NO3)3·5H2O and NH4VO3 were dissolved in dilute HNO3 and NaOH aqueous solutions, respectively; then, the surfactant CTAB (hexadecyltrimethylammonium bromide) was added to the two solutions; after stirring for 0.5 h, the two solutions were mixed; the precursor solution was poured into a stainless steel autoclave lined with polytetrafluoroethylene, and then heated at 200 °C for 30 min under microwave irradiation; after the autoclave cooled to room temperature, the yellow precipitate was filtered to separate it, washed several times with distilled water to completely remove the surfactant, and then dried at 100 °C for 4 h; this method requires acid-base adjustment and the reaction conditions are high temperature and high pressure, and the obtained product is a sheet-like monoclinic BiVO4 with a length of 400 nm to 1 μm.

[0051] This invention patent is fundamentally different from the comparative example; this invention patent has distinct innovation.

[0052] Comparative Example 3 of the Examples:

[0053] In (Wang XJ, Liu HL, Wan XL, et al. Additive-free solvothermal synthesis of peanut-like BiVO4 powders with enhanced photocatalysis activity[J]. Cryst. Res. Technol., 2013, 48(12): 1066-1072), Wang et al. prepared peanut-like monoclinic BiVO4 by solvothermal method as follows: 1 mmol Bi(NO3)3·5H2O and 1 mmol NH4VO3 were dissolved in 5 mL glacial acetic acid and 55 mL 2 mol / L acetic acid, respectively. The mixture was stirred in NH3·H2O solution for 1 h at room temperature. When both solutions were clear, they were mixed together in a 1:1 molar ratio and stirred for about 1 h to obtain a stable pink homogeneous solution. The resulting suspension was then transferred to an 80 mL polytetrafluoroethylene-lined autoclave and kept at 180 °C for 12 h. After the autoclave cooled naturally to room temperature, the product was collected, washed several times with deionized water and anhydrous ethanol, and then dried at 70 °C for 12 h. This method uses acid and alkali to adjust the morphology of the product phase. The reaction requires high temperature and high pressure and is time-consuming. The product obtained is a monoclinic BiVO4 product with a peanut-shaped single phase with a width of about 3 μm and a length of about 1.5 μm.

[0054] This invention patent is fundamentally different from the comparative example; this invention patent has distinct innovation.

Claims

1. A method for controlling the coexistence of tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O three-phase highly ordered micron flower material, characterized in that... Includes the following steps: Step 1: Analytical grade Bi(NO3)3·5H2O and hexadecyltrimethylammonium bromide (CTAB) were added to 115 mL of deionized water and thoroughly dissolved on a magnetic stirrer at 800 rpm for 15 min. The solution was then transferred to a 250 mL round-bottom flask. The mixed solution was placed in a microwave reactor (model "Midea PJ21C-AU") with a frequency of 2450 MHz and a normal pressure reflux cooling device. The heating temperature was set to 100℃ and the power to 1000 W. After heating and mixing for 60 min, a bismuth nitrate mixed solution A was obtained. NH4VO3 was dissolved in 85 mL of deionized water and thoroughly stirred on a magnetic stirrer at 800 rpm for 15 min to obtain ammonium metavanadate solution B. Where, Bi: The molar ratio of CTAB to V is 2:2:3 or 2:3:3; Step 2: While vigorously stirring the ammonium metavanadate solution B, add the bismuth nitrate mixed solution A prepared in Step 1. After the addition is completed, continue stirring for 10 minutes to obtain a homogeneous reaction precursor solution C and transfer it to a 500mL round-bottom flask. Step 3: Place the reaction precursor solution C obtained in Step 2 into a microwave reactor with the same model and parameters as in Step 1, set the heating temperature to 100℃ and the power to 1000W for reaction; after the reaction is completed and cooled to room temperature, centrifuge the obtained solid-liquid suspension at 5000rpm for 2min, discard the supernatant and retain the lower suspension solid sample, wash the solid sample with distilled water and ethanol 3-5 times respectively, and dry it in an oven at 70℃ for 24h to obtain a highly regular micron flower with three phases of tetragonal scheelite type BiVO4, monoclinic type BiVO4 and [Bi6O5(OH)3](NO3)5·3H2O; In step 1, when the molar ratio of Bi:CTAB:V is 2:2:3, the weighed raw materials are 2.0615g Bi(NO3)3·5H2O, 1.5490g hexadecyltrimethylammonium bromide (CTAB), and 0.7457g NH4VO3, respectively; when the molar ratio of Bi:CTAB:V is 2:3:3, the weighed raw materials are 2.0615g Bi(NO3)3·5H2O, 2.3234g hexadecyltrimethylammonium bromide (CTAB), and 0.7457g NH4VO3, respectively. When the molar ratio of Bi:CTAB:V in step 1 is 2:2:3, the reaction time in step 3 is 10 min; when the molar ratio of Bi:CTAB:V in step 1 is 2:3:3, the reaction time in step 3 is 90 min.

2. A highly ordered micron flower material with three phases coexisting: tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, prepared by the control method according to claim 1.

3. The highly ordered micron-flower material with three phases coexisting, namely tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, as described in claim 2, is characterized in that: When the molar ratio of Bi:CTAB:V is 2:2:3 and the reaction time is 10 min, the proportion of the characteristic peak of tetragonal scheelite-type BiVO4 in the product is 48.22%, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the strongest peak corresponds to the crystal plane index (200); the characteristic peak ratio of monoclinic BiVO4 is 31.58%, the space group is I2 / a, and the cell parameters are... and α=γ=90.0° and β=90.38°, the strongest peak corresponds to the crystal plane indices of The characteristic peak percentage of [Bi6O5(OH)3](NO3)5·3H2O was 20.20%; the morphology of the product was micron flowers with a width of 2.58–3.40 μm and a thickness of 2.24–3.23 μm, composed of nanosheets with a particle size of 0.81–2.63 μm and a thickness of 46–178 nm.

4. The highly ordered micron-flower material with three phases coexisting, including tetragonal scheelite-type BiVO4, monoclinic BiVO4, and [Bi6O5(OH)3](NO3)5·3H2O, as described in claim 2, is characterized in that: When the molar ratio of Bi:CTAB:V is 2:3:3 and the reaction time is 90 min, the proportion of the characteristic peak of tetragonal scheelite-type BiVO4 in the product is 19.34%, the space group is I41 / amd, and the cell parameters are... and α=β=γ=90.0°, the strongest peak corresponds to the crystal plane index (200); the characteristic peak ratio of monoclinic BiVO4 is 32.68%, the space group is I2 / a, and the cell parameters are... and α=γ=90.0° and β=90.38°, the strongest peak corresponds to the crystal plane indices of The characteristic peak percentage of [Bi6O5(OH)3](NO3)5·3H2O was 47.98%; the morphology of the product was micron flowers with a width of 3.04–6.58 μm and a thickness of 2.13–4.38 μm, composed of nanosheets with a particle size of 0.42–2.72 μm and a thickness of 45–177 nm.

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