CN111790373B - Preparation device of bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation - Google Patents
Preparation device of bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation Download PDFInfo
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- CN111790373B CN111790373B CN202010759047.1A CN202010759047A CN111790373B CN 111790373 B CN111790373 B CN 111790373B CN 202010759047 A CN202010759047 A CN 202010759047A CN 111790373 B CN111790373 B CN 111790373B
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- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
- B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
- B01J37/343—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of ultrasonic wave energy
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Abstract
A bismuth tungstate photocatalyst preparation device based on hydrodynamic cavitation and ultrasonic cavitation comprises a stator, an ultrasonic cavitation transducer, a rotor and a rotating shaft; the stator is a closed cavity, and the inner wall of the stator is distributed with an ultrasonic transducer; the upper end of the stator is provided with a feeding pipe, and the bottom of the stator is provided with a discharging pipe; the rotor sets up in the stator and with pivot upper end fixed connection, the pivot is vertical to be installed in the stator and the lower extreme stretches out the stator, and it has the slot to distribute on the outer wall of rotor. The device strengthens the preparation reaction of the bismuth tungstate at room temperature by efficiently coupling hydrodynamic cavitation and ultrasonic cavitation, and accelerates the reaction of the raw materials under the conditions of extreme high temperature and high pressure generated by the cavitation effect. In addition, the phenomena of shock waves, micro-jet and the like generated by the cavitation effect can greatly change the surface appearance of the generated catalyst, and the specific surface area is improved, so that the catalytic performance is improved. The device has the advantages of large treatment capacity, continuous operation, low cost and wide application prospect in the field of nano catalyst preparation.
Description
Technical Field
The invention relates to a preparation device of a bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation, and belongs to the technical field of preparation of bismuth tungstate photocatalytic materials.
Background
Bismuth tungstate (Bi)2WO6) Is a photocatalyst and has the obvious characteristics of no toxicity, high efficiency, low price and the like, and has wide application prospect in the aspects of sterilization, dielectric, photocatalysis and the like. The current preparation methods comprise a solid-phase sintering method, a precipitation method, a sol-gel method, a hydrothermal method, a solvothermal method and the like.
1. Solid phase sintering process
The solid phase sintering method is a relatively early method for preparing powder, and previously prepared bismuth tungstate (Bi)2WO6) Powder is mostly prepared by this method. The method is that the oxide containing Bi element and W element or the salt thereof is directly mixed mechanically and then is subjected to high temperature oxidationSintering at room temperature. The method generally needs to react at a higher temperature, consumes larger energy and is not beneficial to saving energy, and the catalyst prepared by the method has larger particle size, smaller specific surface area and less pollutant adhesion on the surface of the catalyst, so that the activity of photocatalysis is not high. Therefore, in recent years, with the development and progress of science and technology, the solid-phase sintering method has been substantially eliminated.
2. Precipitation method
The precipitation method is to utilize a metal salt solution to react with a precipitator, and a finished product can be prepared by a series of processes of washing, filtering and the like of the generated precipitate. The method has the advantages of simple equipment and simple operation, and can be used in large scale in industrial production. However, the product obtained by the method generates a crystal material only by calcination, and a large amount of energy is consumed in the calcination process, and the product is easy to agglomerate in the other side, so that the particle size is increased, and the photocatalytic performance of the product is not improved.
3. Sol gel process
The sol-gel method is used as a method for synthesizing inorganic materials under mild conditions, and metal inorganic salts are subjected to a series of chemical reactions in an organic solvent to form a sol substance, and then the sol substance is dried and calcined to obtain the required powder material. As can be seen from practice, the method has certain advantages and disadvantages: the physical and chemical properties of the obtained sol are relatively uniform and stable, and the reaction can be generally carried out at normal temperature; however, the raw materials used by the traditional Chinese medicine composition are consumed more, the cost is high, and the health is influenced if people contact the traditional Chinese medicine composition for a long time; secondly, the preparation steps are more, and the reaction time is too long; finally, large shrinkage can occur during later processing. Therefore, this method is not recommended in view of the principle that the operation is simple.
4. Sonochemical process
The sonochemical method utilizes the principle of acoustic cavitation, and under the action of ultrasonic wave, the micro bubble nucleus in the liquid is formed, grown and collapsed to simultaneously cause a series of physical and chemical reactions. It quickly concentrates and releases the energy emitted by the sound field, which provides a solution for some chemical reactions that are impossible or difficult to occur under normal conditions. The reaction of the ultrasonic chemical synthesis method is not easy to control, side reaction occurs, the microwave reactor is expensive and can only be limited to be used in small-scale synthesis in a laboratory, and the large-scale industrial production of the ionic liquid is difficult.
5. Hydrothermal method
The hydrothermal method belongs to one of liquid phase chemical synthesis methods, and is a method for growing crystals in a closed environment by using high temperature and high pressure conditions to react substances which cannot be synthesized at normal temperature and reducing the activation energy of the reaction through an additional action. It has wide application in preparing superfine particle, inorganic film, microporous material, etc. The hydrothermal method can directly prepare powder with good crystallinity, avoids agglomeration generated by high-temperature sintering, has simple preparation process, and can control the grain size and the morphology of the generated product by changing the hydrothermal condition, thereby changing the performance of the product, and becoming a mature method for preparing nano/micron powder. The hydrothermal method has the advantages of low cost, simple process, low reaction temperature and the like, so that the hydrothermal method can be used for preparing bismuth tungstate (Bi)2WO6) The conventional method still has the defects of intermittent preparation process and low efficiency.
6. Solvothermal process
The solvothermal method is an extension of the conventional hydrothermal method, and differs from the hydrothermal method in that the solvent used is an organic solvent rather than water. One of the advantages of using organic solvent as reaction medium is that the dispersibility of the product is improved, and the boiling point of the organic solvent is generally lower, so that the activity of the reaction is improved, the temperature required by the reaction is lowered, and the energy is saved. The method is simple to operate, and a plurality of researchers prepare products with good appearance and performance by adopting the method. However, the organic solvent used in the solvothermal method is unstable due to the presence of donor ribbons, and is liable to cause dangerous accidents such as explosion, and some organic solvents are toxic and harmful to the body, so that the method is not recommended from the viewpoint of environmental protection and health.
CN105727932A discloses a bismuth tungstate nanometer photocatalyst and a preparation method thereof,comprises the bismuth tungstate nano photocatalyst prepared by the preparation method and the application of the catalyst in photocatalysis. CN107311232A discloses a solid-phase synthesis method of bismuth tungstate powder of photocatalyst, which is to weigh Bi in proportion2WO3And WO3Calcining and grinding to obtain the target product.
The method can not efficiently carry out the industrial production of the bismuth tungstate nano photocatalyst on a large scale.
Disclosure of Invention
Aiming at the existing bismuth tungstate (Bi)2WO6) The preparation method has the defects that the preparation device of the bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation can be efficiently produced in a large-scale industrialized mode.
The invention relates to a preparation device of a bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation, which adopts the following technical scheme:
the device comprises a stator, a rotor, ultrasonic transducers and a rotating shaft, wherein the stator is a closed cavity, the ultrasonic transducers are distributed on the inner wall of the stator, and each ultrasonic transducer is connected with an external ultrasonic generator; the upper end of the stator is provided with a feeding pipe, and the bottom of the stator is provided with a discharging pipe; the rotor sets up in the stator and with pivot upper end fixed connection, the pivot is vertical to be installed in the stator and the lower extreme stretches out the stator, and the equidistance distributes on the outer wall of rotor has a plurality of slots. One end of the rotating shaft, which extends out of the stator, is connected with the motor through a coupler, and the rotating shaft drives the rotor to rotate in the stator. The cavitation holes form a flow-limiting structure under the small gap between the stator and the rotor, so that the flow-limiting effect is generated, and the generation of the cavitation phenomenon is enhanced.
One end of the rotating shaft, which extends out of the stator, is connected with the motor through a coupler, and the rotating shaft drives the rotor to rotate in the stator.
The feeding pipeline is arranged at the top end of the stator, and the discharging pipeline is arranged at the bottom of the stator.
The ultrasonic transducers are embedded into the inner wall of the stator along the axial direction and the circumferential direction in an equidistant mode of 2-8 ultrasonic transducers in each row and 2-6 ultrasonic transducers in total.
The number of the ultrasonic generators is 1-4, the frequency is more than 20kHz, and the single-machine power is 1500-3000W.
The rotor and the stator are conical, the cone angle is 30-60 degrees, materials are uniformly distributed in the stator, the cavitation effect is gradually improved from the conical top to the conical bottom, and the reaction preparation effect is enhanced. Furthermore, the diameter of the rotor cone bottom is 20-200 mm, and the cone height is 20-200 mm.
The rotating speed of the rotor is 4000-5000 r/min.
Gaps between the outer wall of the rotor and the inner wall of the stator are 4-6 mm, a flow limiting structure is formed, and the cavitation phenomenon is guaranteed.
The groove is an isosceles trapezoid with a narrow upper part and a wide lower part, the length of the upper bottom edge of the isosceles trapezoid is 0.1-10 mm, and the length of the lower bottom edge of the isosceles trapezoid is 0.2-20 mm. The vertical distance from the upper bottom edge to the top end of the rotor is 0.5-20 mm, and the vertical distance from the lower bottom edge to the bottom end of the rotor is 0.5-20 mm. The distance between the middle points of the upper bottom edges of the adjacent grooves is 0.5-15 mm. The depth of the groove is 0.1-5 mm. The number of the grooves is 8-20, and the grooves are uniformly distributed on the rotor in a radial shape at equal intervals.
The device can accelerate bismuth tungstate (Bi) by coupling hydrodynamic cavitation and ultrasonic cavitation2WO6) The reaction rate of the preparation method enhances the catalytic performance of the catalyst. The cavitation phenomenon is a very complex physical phenomenon, can generate extremely high temperature and instantaneous high pressure, releases huge energy and has a promoting and strengthening effect on chemical and physical reactions. The process of formation, development and collapse of gas cavities in the liquid or at the liquid-solid interface when the local pressure in the liquid drops. When the liquid pressure drops to or below the liquid saturation vapor pressure, a large number of cavitation bubbles are generated due to the vigorous vaporization of the liquid. The cavitation bubbles expand and grow along with the flow of the liquid. When the liquid pressure recovers, the cavitation bubbles are instantaneously collapsed to form micro jet and shock waves, and instantaneous local high temperature and instantaneous high pressure are generated. Bismuth tungstate (Bi)2WO6) Preparation liquid (Bi (NO)3)3With Na2WO4The mixed aqueous solution and a certain amount of modifier) enters the stator, and the rotor is driven by the rotating shaft to rotate relative to the preparation liquid in the stator. The rotor is driven by the motor to rotate at high speed to make the grooves on the rotor shear the solution at high speed and make the parts localThe static pressure is lower than the saturated vapor pressure, and the hydrodynamic cavitation phenomenon is induced. Meanwhile, an external ultrasonic generator converts electricity into a high-frequency alternating current signal matched with the ultrasonic transducer and transmits the high-frequency alternating current signal to the ultrasonic transducer, and the ultrasonic transducer converts electric energy into sound energy to generate high-frequency ultrasonic waves. The ultrasonic wave acts on the fluid to induce the ultrasonic cavitation phenomenon, thereby greatly strengthening the number of cavitation bubbles generated by the hydraulic cavitation and the collapse intensity thereof. Under the coupling of hydrodynamic cavitation and ultrasonic cavitation, extremely high temperature and extremely high pressure are created to lead bismuth tungstate (Bi)2WO6) The preparation solution is fully mixed and the reaction rate is greatly increased. Moreover, the phenomena of shock waves, microjets and the like generated by the cavitation effect can greatly change the surface appearance of the generated catalyst and improve the specific surface area, thereby improving the catalytic performance and realizing the bismuth tungstate (Bi)2WO6) High-efficiency preparation at room temperature.
The system for preparing the bismuth tungstate by using the device further comprises a separation tank and a concentration drying tank, wherein the device, the separation tank and the concentration drying tank are sequentially connected. The bismuth tungstate (Bi) is subjected to the cavitation action of the bismuth tungstate preparation liquid through the hydrodynamic cavitation and ultrasonic cavitation generating device2WO6) The preparation reaction is strengthened, then the precipitate flows into a separation tank to separate out precipitate particles, and then the precipitate enters a drying tank to be evaporated and dried to obtain the bismuth tungstate.
The device of the invention has simple integral structure and achieves the aim of treating bismuth tungstate (Bi)2WO6) The preparation reaction has the advantages of enhanced acceleration effect, high reaction rate and capability of efficiently carrying out large-scale industrialized production of bismuth tungstate (Bi)2WO6). Meanwhile, the maintenance and the disassembly are convenient, the energy consumption is low, the large-scale operation can be realized, the sizes of the rotor and the stator are only required to be changed, the gap (4-6 mm, the occurrence of cavitation) between the stator and the rotor is ensured, and the requirement for larger treatment capacity can be met by replacing a high-power variable frequency motor.
The invention has the following characteristics:
1. the device for preparing the bismuth tungstate photocatalyst can react at room temperature, has high reaction rate, good product performance and large production capacity, can be operated continuously, and has high efficiency;
2. the device forms a flow-limiting structure through a small gap (4-6 mm) between the stator and the rotor, generates a flow-limiting effect, enhances the generation of a cavitation phenomenon, and is higher than the cavitation efficiency of the conventional common shear type cavitator;
3. the ultrasonic transducer in the device can be made into any shape according to different containers, and the device is built in, so that the generated noise is small, and the energy attenuation is small;
4. the electric energy is adopted as the energy source, so that the pollution is avoided, and the environment-friendly performance is good; the device is safe and stable in operation, simple in structure and convenient to clean, overhaul and disassemble;
5. the device of the invention efficiently couples hydrodynamic cavitation and ultrasonic cavitation technologies, and the integrated equipment greatly simplifies the whole process flow;
6. the device can be large-sized, the distances between the stator and the rotor and between cavitation holes in the reaction cavity are ensured to be 4-6 mm only by changing the sizes of the rotor and the stator, and the large preparation requirement can be met by replacing a high-power variable frequency motor;
7. in the running process of the device, the inner surface is periodically cavitated and cleaned, so that the device has a self-cleaning function;
8. the device is not limited to the preparation of bismuth tungstate, and is expected to have good preparation effect on other types of catalysts;
9. the structure and technological parameters of the device are obtained by actual preparation experiments.
Drawings
FIG. 1 is a schematic structural diagram of a bismuth tungstate photocatalyst preparation device based on hydrodynamic cavitation and ultrasonic cavitation.
Fig. 2 is a schematic view of a rotor structure in the present invention.
FIG. 3 is a schematic diagram of the structural principle of the system for preparing bismuth tungstate in the present invention.
In the figure: 1. the device comprises a feeding pipe, a stator, an ultrasonic transducer, an ultrasonic generator, a rotor, a groove, a sealing ring, a cover, a discharging pipe, a coupler, a rotating shaft, a motor, a base, a flow valve, a hydraulic cavitation and ultrasonic cavitation generating device, a separation tank and a drying tank, wherein the feeding pipe comprises 2, the stator, 3, the ultrasonic transducer, 4, the ultrasonic generator, 5, the rotor, 6, the groove, 7, the sealing ring, 8, the end cover, 9, the discharging pipe, 10, the coupler, 11, the rotating shaft, 12, the motor, 13, the base, 14, the flow valve, 15, the hydraulic cavitation and ultrasonic cavitation generating device, 16, the separation tank and 17.
Detailed Description
The structure of the bismuth tungstate photocatalyst preparation device 15 based on hydrodynamic cavitation and ultrasonic cavitation is shown in figure 1, and comprises a stator 2, an ultrasonic transducer 3, an ultrasonic generator 4, a rotor 5 and a rotating shaft 11. The stator 2 is a conical closed cavity, the bottom of the stator 2 is connected with the end cover 8 through a bolt, and the bottom of the end cover 8 is supported on the base 13. An ultrasonic transducer 3 is arranged on the inner wall of the stator 2. Each ultrasonic transducer 3 is connected to an ultrasonic generator 4. The ultrasonic transducers 3 are embedded into the inner wall of the stator along the axial direction and the circumferential direction in the form of 2-8 rows of ultrasonic transducers, 2-6 rows of ultrasonic transducers and equal intervals. The number of the ultrasonic generators 4 is 1-4, the frequency is more than 20kHz, and the single-machine power is 1500-3000W. After the ultrasonic wave is coupled, the energy generated when the cavitation bubbles collapse can be greatly enhanced, so that the physical and chemical effects of the cavitation phenomenon are enhanced, and the preparation efficiency (the reaction rate is accelerated) and the catalyst performance (the appearance is changed to a greater extent, and the specific surface area is improved) are finally improved. The top of the stator 2 is connected with a feed pipe 1 through a bolt, and the feed pipe 1 is connected with a flow valve 14 to control bismuth tungstate (Bi)2WO6) Preparation liquid (Bi (NO)3)3With Na2WO4And adding a certain amount of modifier), and a discharge pipe 9 is arranged on an end cover 8 at the bottom. Mechanical seals are arranged between the stator 2 and the end cover 8 and between the stator and the feed pipe 1. In order to prevent the short flow phenomenon, the feeding pipe 1 is arranged at the top end of the conical stator 2, and the discharging pipe 9 is arranged at the edge of the end cover 8 at the bottom of the conical stator 2 as close as possible. The rotor 5 is arranged in the stator 2 and is also a conical closed cavity, and a certain gap is reserved at each position between the outer wall of the rotor 5 and the inner wall of the stator 2, so that the cavitation phenomenon is guaranteed.
The structure of the stator 2 in the invention is shown as 2 in figure 1, the stator 2 is a conical closed cavity, the taper of the cavity is consistent with that of the rotor, and equidistant gaps are reserved at all positions of the cavity and the rotor, and the distances are 4-6 mm, so that the formation of a cavitation effect is ensured. The gap between the stator and the rotor needs to meet a range interval, when the gap is larger than 6 mm, the blind hole and the stator cannot form a flow-limiting structure, the rotor cannot rotate to initiate cavitation or generate obvious cavitation, and the cavitation efficiency can be reduced by more than 50%; when the size of the gap is smaller than 4 mm, cavitation is not obviously changed, and the phenomenon of instability can occur, so that energy consumption is increased, huge noise is generated, and the whole device is unstable and is easy to block. Therefore, in the design and manufacture process, the optimal gap size interval of the efficient treatment is 4-6 mm.
The structure of the rotor 5 is shown in figure 2, the integral structure of the rotor is a cone and is the same as the angle of the conical inner wall of the stator 2, the design that the vertex angle of the rotor is 30-60 degrees is obtained through a large amount of experimental simulation analysis, the angle can enable materials to be uniformly distributed in the gap between the stator and the rotor, and the cavitation effect of the device from the top of the cone to the bottom of the cone can be gradually enhanced. In addition, every two equi-spaced surrounding isosceles trapezoid-shaped grooves are formed in the outer wall of the rotor, the shapes, depths and intervals of the grooves are determined through a large number of experiments, the length of the upper bottom side is 0.1-10 mm, and the vertical distance from the upper bottom side to the conical top of the rotor is 0.5-20 mm; the length of the lower bottom edge is 0.2-20 mm, and the vertical distance from the lower bottom edge to the conical bottom of the rotor is 0.5-20 mm. The distance between the middle points of the upper bottom edges of the adjacent grooves is 0.5-15 mm. The number of the grooves is 8-20, and the grooves are uniformly distributed on the rotor. The basic idea that the groove is designed into an isosceles trapezoid is consistent with the conical gradual cavitation of the rotor, and through experimental tests, the groove design can promote the generation and collapse of cavitation bubbles, and the gradual cavitation effect of the rotor from the cone top to the cone bottom is enhanced to a certain extent, so that the reaction preparation effect is enhanced. The lower end of the rotor is fixed to the rotary shaft 11 so that the entire rotor is rotated integrally with the rotary shaft. Wherein the rotating speed of the rotor has a certain range of 4000-5000 r/min. The shaft power fluctuation of the rotor in the interval is stable, the energy consumption is moderate, and the high-efficiency preparation can be realized. The rotating speed in the range has good cavitation effect, and when the rotating speed of the rotor is lower than 4000 r/min, the rotating speed of the rotor is lower than the critical rotating speed, the cavitation effect is not obvious; when the rotating speed of the rotor is higher than 5000r/min, not only can great noise be generated, but also the rotor can generate unstable phenomenon, and the shaft power and the energy consumption are increased, so that the high-efficiency preparation is not facilitated.
The design of the stator 2 and the rotor 5 is determined by a large number of experiments, and the method has a better effect on the preparation reaction of the bismuth tungstate. The inventor carries out a large number of preparation experiments to obtain the optimal solution, and can realize the optimal cavitation intensity of the cavitation device.
The rotating shaft 11 is vertically installed on the stator 2 through a bearing in the end cover 8, a sealing ring 7 is arranged between the rotating shaft 11 and the end cover 8, and the upper end of the rotating shaft 11 is fixedly connected with the rotor 5. One end of the rotating shaft 11 extending out of the stator 2 is connected with a motor 12 through a coupling 10, and the motor 12 is fixed on a base 13. The motor 12 drives the rotating shaft 11 and the rotor 5 to rotate through the coupling 10.
The overall system for preparing the bismuth tungstate photocatalyst comprises a hydrodynamic cavitation generation device 15, a separation tank 16 and a concentration drying tank 17 which are connected in sequence as shown in figure 3. Bismuth tungstate (Bi)2WO6) Preparation liquid (Bi (NO)3)3With Na2WO4And a certain amount of modifier) is fed into the cavitation chamber of the stator 2 through the feed pipe 1. The rotor 5 is driven by the motor to rotate at a high speed by the rotating shaft 11, so that the groove 6 on the rotor 5 shears the solution at a high speed, the local static pressure is lower than the saturated vapor pressure, and the hydrodynamic cavitation phenomenon is induced. Meanwhile, the external ultrasonic generator 4 converts electricity into a high-frequency alternating current signal matched with the ultrasonic transducer 3, and transmits the high-frequency alternating current signal to the ultrasonic transducer 3, and the ultrasonic transducer 3 converts electric energy into sound energy to generate high-frequency ultrasonic waves. The ultrasonic wave acts on the fluid to induce the ultrasonic cavitation phenomenon, thereby greatly strengthening the number of cavitation bubbles generated by the hydraulic cavitation and the collapse intensity thereof. Under the coupling of hydrodynamic cavitation and ultrasonic cavitation, extremely high temperature and extremely high pressure are created to lead bismuth tungstate (Bi)2WO6) The preparation solution is fully mixed and the reaction rate is greatly increased. Moreover, the phenomena of shock waves, micro-jet and the like generated by the cavitation effect can greatly change the surface appearance of the generated catalyst, and the specific surface area is improved, so that the catalytic performance is improved. The solution after the reaction flows into a separation tank 16 through a discharge pipe 9 of a hydrodynamic cavitation generator 15 for separation, a bismuth tungstate precipitate is separated, and then the bismuth tungstate precipitate enters a drying tank 17 for evaporation and drying to obtain bismuth tungstate, so that the efficient preparation at room temperature is realized.
Through verification experiments, the device (structural parameters: the diameter of the rotor cone bottom is 100 mm, the cone height is 100 mm, the length of the upper bottom edge of an isosceles trapezoid is 2 mm, the length of the lower bottom edge is 3 mm, the vertical distance between the upper bottom edge and the top end of the rotor is 20mm, the vertical distance between the lower bottom edge and the bottom end of the rotor is 6 mm, the distance between the middle points of the upper bottom edges of adjacent grooves is 6 mm, the depth of each groove is 10mm, 4 ultrasonic transducers are arranged in each row and 3 rows in total in the stator) is used for synthesizing Bi with optimal photocatalytic activity under the conditions that the rotating speed is 4200 r/min and the reaction time is 1 h2WO6Compared with the conventional preparation method, the specific surface area of the sample can be improved by more than 100%. Then, the method is applied to degrading 10 mg/L rhodamine B solution, the reaction condition is 350W xenon lamp illumination and 1 h reaction time, and the degradation rate of rhodamine B reaches 93.6%.
Claims (5)
1. A bismuth tungstate photocatalyst preparation device based on hydrodynamic cavitation and ultrasonic cavitation is characterized in that: the ultrasonic generator comprises a stator, a rotor, ultrasonic transducers and a rotating shaft, wherein the stator is a closed cavity, the ultrasonic transducers are distributed on the inner wall of the stator, and each ultrasonic transducer is connected with an external ultrasonic generator; the rotor and the stator are conical, and the cone angle is 30-60 degrees; the upper end of the stator is provided with a feeding pipe, and the bottom of the stator is provided with a discharging pipe; the rotor is arranged in the stator and is fixedly connected with the upper end of the rotating shaft, the rotating shaft is vertically arranged in the stator, the lower end of the rotating shaft extends out of the stator, a plurality of grooves are distributed on the outer wall of the rotor at equal intervals, and cavitation holes form a flow limiting structure under a small gap of 4-6 mm between the stator and the rotor, so that the flow limiting effect is generated, and the generation of a cavitation phenomenon is enhanced; the groove is in an isosceles trapezoid shape with a narrow upper part and a wide lower part; the number of the grooves is 8-20, the depth of each groove is 0.1-5 mm, and the grooves are uniformly distributed on the rotor in a radial mode at equal intervals; the ultrasonic transducers are embedded in the inner wall of the stator along the axial direction and the circumferential direction in a mode that 2-8 ultrasonic transducers are arranged in each row, 2-6 ultrasonic transducers are arranged in total, and the ultrasonic transducers are arranged at equal intervals; the number of the ultrasonic generators is 1-4, the frequency is more than 20kHz, and the single-machine power is 1500-3000W;
the bismuth tungstate preparation liquid enters the stator, the rotor is driven by the rotating shaft to rotate relative to the preparation liquid in the stator, the groove on the rotor shears the solution at a high speed, the local static pressure is lower than the saturated vapor pressure, and the hydrodynamic cavitation phenomenon is induced; meanwhile, an external ultrasonic generator converts electricity into a high-frequency alternating current signal matched with the ultrasonic transducer and transmits the high-frequency alternating current signal to the ultrasonic transducer, and the ultrasonic transducer converts electric energy into sound energy to generate high-frequency ultrasonic waves; the ultrasonic wave acts on the fluid to induce an ultrasonic cavitation phenomenon, and the number of cavitation bubbles generated by hydraulic cavitation and the collapse intensity of the cavitation bubbles are enhanced; under the coupling of hydrodynamic cavitation and ultrasonic cavitation, extremely high temperature and extremely high pressure are created, so that the bismuth tungstate preparation liquid is fully mixed, and the reaction rate is increased; the phenomena of shock waves and micro-jet generated by cavitation effect change the surface appearance of the generated catalyst, and the specific surface area is increased, so that the catalytic performance is improved, and the efficient preparation of the bismuth tungstate at room temperature is realized.
2. The preparation device of the bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation as claimed in claim 1, wherein: the diameter of the rotor cone bottom is 20-200 mm, and the cone height is 20-200 mm.
3. The preparation device of the bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation as claimed in claim 1, wherein: the rotating speed of the rotor is 4000-5000 r/min.
4. The preparation device of the bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation as claimed in claim 1, wherein: the isosceles trapezoid is 0.1-10 mm long in the upper base side, 0.2-20 mm long in the lower base side, 0.5-20 mm long in the vertical distance from the upper base side to the top end of the rotor, and 0.5-20 mm long in the vertical distance from the lower base side to the bottom end of the rotor.
5. The preparation device of the bismuth tungstate photocatalyst based on hydrodynamic cavitation and ultrasonic cavitation as claimed in claim 1, wherein: the distance between the middle points of the upper bottom edges of the adjacent grooves is 0.5-15 mm.
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