CN105712397B - A kind of method that electrostatic spray prepares nano titanium oxide - Google Patents

Abstract

The invention relates to a method for preparing nano-titanium dioxide by electrostatic spraying. (1) dissolving tetrabutyl titanate in absolute ethanol and glacial acetic acid and fully stirring; (2) adjusting the pH of deionized water with acetic acid; (3) dissolving The solution obtained in step (1) is slowly added dropwise to the above-mentioned deionized water, stirred vigorously under heat preservation conditions, and then subjected to aging treatment; (4) A high-voltage electrostatic field is established between the propeller nozzle and the receiving device through a high-voltage electrostatic generating device and sealed Place; (5) Inject the aged solution into the propeller, control the device voltage, propulsion speed and temperature, and spray it out through the nozzle to prepare nano-titanium dioxide. The invention breaks through the traditional preparation process of nano- _TiO2 which requires high-temperature calcination and crystallization, and can prepare nano- _TiO2 at low temperature, avoids the agglomeration of particles caused by calcination, and greatly broadens the application range of nano- _TiO2 .

Description

A kind of method for preparing nano-titanium dioxide by electrostatic spraying

technical field

The invention belongs to the field of nano material preparation, in particular to a method for preparing nano titanium dioxide by electrostatic spraying.

Background technique

Electrostatic spraying is a method of preparing polymer solution into nanoparticles by using electrohydrodynamic jet technology. The induction of the polymer fluid causes a large amount of charge to accumulate inside the polymer fluid, and the polymer droplet is kept at the outlet of the nozzle by the surface tension. At the same time, the droplet is subjected to an electric field force opposite to the direction of the surface tension. As the electric field strength gradually increases, the droplet at the nozzle elongates from a spherical shape to a cone shape, which is called a Taylor cone. When the electric field strength reaches a critical value, that is, when the electrostatic force generated by the charge is sufficient to overcome the surface tension of the fluid, the droplet is ejected from the "Taylor cone". Due to the repulsion between the same charges, the jet oscillates and becomes unstable under the action of the electric field, producing irregular spiral motion with high frequency, the jet is rapidly thinned, and the solvent is also rapidly volatilized. When the fine stream splits to a certain extent, as the solvent volatilizes, it solidifies into nanoparticles and then falls onto the receiving device.

Photocatalyst material TiO ₂ has become the most promising green photocatalytic material due to its high photocatalytic activity, good stability and heat resistance, no secondary pollution, no irritation, non-toxic to human body and low price. .

At present, the methods for synthesizing nano-TiO ₂ at home and abroad mainly include metal alkoxide hydrolysis, hydrothermal crystallization and sol-gel method.

The preparation method of TiO ₂ nanoparticles by hydrolysis of metal alkoxide is simple and easy, with low energy consumption and good process repeatability, and the obtained TiO ₂ is close to monodisperse and high in purity. However, the process is long, the auxiliary materials are expensive, and ethanol, toluene, solvent oil, ammonia, etc. are all flammable or toxic substances, and the safety production problem is very prominent. The preparation of nanopowder by hydrothermal method mostly uses organic compounds of titanium or intermediate products that are difficult to obtain as precursors, which has high cost and complicated preparation process, and the two most important parameters in this method are temperature and pressure. It has a great influence on the nucleation rate and particle size. Theoretically speaking, the higher the temperature, the more conducive to the generation of small particle size particles, and the higher the pressure, the higher the nucleation rate, which is conducive to the generation of small particle size powders, which requires high energy consumption, high production costs, and difficult control of production conditions. The peptization-gel method to prepare nano-sized TiO ₂ has more significant advantages than the metal alkoxide hydrolysis method and hydrothermal method: low raw material cost, simple equipment process, high purity of the produced powder, small particle size, narrow particle size distribution range, particle size The composition is well controllable, but there is a factor that is difficult to control, which is the agglomeration of the powder, and the prepared powder needs to be aged, dried, and burned to obtain a finished product, which limits its application on substrates that are not resistant to high temperatures.

Chinese patent CN102586948A discloses an anatase titanium dioxide nanofiber photocatalyst and a preparation method thereof, belonging to the technical field of nanomaterials and photocatalysis. In the present invention, composite nanofibers are firstly prepared by electrospinning technology, and then the titanium dioxide nanofiber photocatalyst is obtained by calcining in the air, and no sol-gel technology is introduced in the middle, which makes the process parameters easier to control and eliminates the need to affect the final titanium dioxide nanofiber photocatalyst. Many factors such as fiber crystallinity, crystal form, and particle size distribution and size are more conducive to obtaining photocatalytic materials with high catalytic efficiency, but this patent still requires high-temperature sintering.

Contents of the invention

The purpose of the present invention is to provide a kind of breakthrough traditional nano-TiO ₂ need high-temperature calcination crystallization preparation process in order to overcome the defective that above-mentioned prior art exists, can prepare nano-TiO ₂ method at low temperature, has avoided the method that causes because of calcination. The agglomeration among particles greatly broadens the application range of nano-TiO ₂ .

The purpose of the present invention can be achieved through the following technical solutions:

A method for preparing nano-titanium dioxide by electrostatic spraying, adopting the following steps:

(1) tetrabutyl titanate is dissolved in absolute ethanol and glacial acetic acid and fully stirred;

(2) adjust the pH of deionized water to 2-4 with acetic acid;

(3) The solution obtained in step (1) is slowly added dropwise to the above-mentioned deionized water, vigorously stirred under heat preservation conditions, and then aged;

(4) A high-voltage electrostatic field is established between the propeller nozzle and the receiving device through the high-voltage electrostatic generating device, the metal diversion pipe on the nozzle is connected to the negative pole, the receiving device is grounded to form the positive pole, and the nozzle and the receiving device are sealed;

(5) Inject the aged solution into the propeller, control the voltage, propulsion speed and temperature of the device, and spray it out through the nozzle to prepare nano-titanium dioxide.

The molar ratio of tetrabutyl titanate, absolute ethanol and glacial acetic acid described in step (1) is 1:2-4:5-7.

In the solution obtained in step (3), the molar amount of deionized water is 70-220 times of the molar amount of tetrabutyl titanate, and it is kept under the condition of 30-40°C for 2.5-3.5h, and the aging time is 19 -24h.

The nozzle described in step (4) is a 14G-27G flat dispensing needle, and the receiving device is aluminum foil.

In step (5), the voltage of the device is 20-30KV, the advancing speed of the aging solution is 0.01-0.02mm/s, the temperature is 100°C-150°C, and the receiving distance between the nozzle and the receiving device is 15-20cm. Under the action of electrostatic field force, the ejected _TiO2 gel solution will explode unstable and form nano-scale droplets. At a temperature of about 150°C, the solvent will volatilize and solidify into nanoparticles. The droplets have the same charge, and the repulsion between the same charges makes the collected TiO ₂ particle size small, difficult to agglomerate and good in dispersibility. This preparation method breaks through the traditional preparation process of nano-TiO ₂ that requires high-temperature calcination and crystallization. Nano- _{TiO 2} can be prepared at a temperature of about 150°C, which simplifies the production process and saves energy. The application and industrial preparation provide technical guidance, and at the same time avoid the agglomeration of particles caused by calcination, which greatly broadens the application range of nano-TiO ₂ .

The preparation process parameters used in the present invention are unique to the present invention, and are also different from the prior art, and have certain technical points of creativity.

Under the condition that other conditions remain unchanged, the voltage gradually increases from 20k V to 30k V, and the prepared TiO ₂ particles will gradually decrease, which is consistent with Hartman's Scaling law. According to the Scaling law, formulas (1) and (2 ).

In formulas (1) and (2), d is the droplet diameter, α is a constant, Q is the flow velocity, ρ is the solution density, I is the current, ε is the vacuum permittivity, and γ is the surface of the liquid in air Tension, K is the conductivity of the liquid. Formulas (1) and (2) indicate that the diameter of EFI particles is inversely proportional to the current I, the larger the current, the smaller the diameter of EFI particles, and the smaller the current, the larger the diameter. The current is proportional to the voltage applied between the injector and the collecting plate, that is, the larger the voltage, the smaller the diameter of the electrospray particles. This is because when the voltage reaches a certain value, after overcoming the surface tension of the liquid to form a jet, as the voltage increases, the more Coulomb splitting occurs in the electrospray process, and the _TiO2 particle size collected on the collecting plate becomes smaller. Small. However, when the voltage exceeds 30kV, the Coulomb split of the liquid during the EFI process is severe, it is difficult to collect on the receiving plate, and the loss is large; if the voltage is less than 20kV, the Coulomb split of the liquid during the EFI process is not obvious, The collected _TiO2 particle size is larger.

Under the condition that other conditions remain unchanged, the TiO ₂ particles prepared by electrostatic spraying will gradually increase when the flow rate of electrostatic spraying increases from 0.01mm/s to 0.02mm/s, which is consistent with Hartman's formulas (1) and (2) It is consistent, that is, according to the formulas (1) and (2), with the increase of the electrospray flow rate, the particle size of the obtained electrospray _TiO2 particles will increase. When the flow rate exceeds 0.02mm/s, the liquid at the EFI nozzle outlet flows out vertically, and the atomization effect cannot be produced. If the flow rate is less than 0.01mm/s, the atomization effect of the liquid sprayed from the EFI nozzle is not obvious.

When other conditions remain the same, as the receiving distance increases from 15cm to 20cm, the particle size of TiO ₂ decreases continuously. This is related to the Coulomb splitting in the electrospray process: during the movement of the electrospray liquid from the needle to the collecting plate, the jet first splits into charged droplets, and as the solvent volatilizes, the density of the charged droplets increases and the surface charge increases. Density also increases, and charge repulsion increases, causing Coulomb splitting to form smaller charged droplets. If the receiving distance is less than 15cm, the solvent volatilization on the surface of TiO ₂ particles is not complete. With the increase of the receiving distance, the solvent is completely volatilized, and the number of Coulomb splitting increases, which reduces the particle size. When the receiving distance exceeds 20cm, continue to increase the receiving distance, and the obtained _TiO2 particle size remains basically unchanged.

Compared with the prior art, the present invention has the following advantages:

1. The present invention aims at the shortcomings of powder agglomeration in the preparation of _TiO2 by the sol-gel method and the need for aging, drying and burning to prepare the powder. The electrostatic spraying technology is used to spray the titanium dioxide sol in a closed oven at about 150°C. Form into nano-scale droplets, the solvent volatilizes, and finally directly collects well-crystallized TiO ₂ , which avoids defects such as agglomeration caused by high-temperature calcination of the titanium dioxide sol as a whole. The production process is simple, excellent in stability, short in time, easy to operate, and easy to carry out Large-scale production, and the distribution of TiO ₂ particles is uniform, and the average particle size is less than about 40nm.

2. The nano- _TiO2 prepared by the present invention has strong absorption to visible light, which improves the utilization rate of light energy. At the same time, it breaks through the traditional sol-gel method to prepare nano-TiO ₂ that requires high-temperature calcination and crystallization, and provides guidance for its application on substrates that are not resistant to high temperatures.

3. The present invention adopts the hydrosol method using water as solvent under low temperature conditions to prepare _TiO sol, the main reaction step is that the precursor is dissolved in the water solvent to form a uniform solution, and the solute produces hydrolysis reaction and polycondensation reaction in the water solvent , the reaction products aggregate into particles and form a sol. Since the amount of water in the reaction process is much higher than the theoretical amount, when the amount of water is large, the precursor butyl titanate will be fully hydrolyzed to form inorganic substances, and the inorganic substances will spontaneously crystallize. Anatase TiO ₂ particles with good dispersibility, small particle size and excellent photocatalytic performance can be obtained by drying at low temperature.

Description of drawings

Fig. 1 is _TiO sol particle size figure;

Fig. ₂ is TiO The XRD figure of powder;

Fig. 3 is TiO ₂ powder transmission electron microscope is photographed;

Fig. 4 is TiO ₂ powder ultraviolet-visible diffuse reflectance spectrum;

Fig. 5 is the photocatalytic degradation rate of _TiO powder to methylene blue;

Fig. 6 is a schematic structural diagram of an electrostatic spraying system.

In the figure, 1-propeller, 2-nozzle, 3-receiving device, 4-high voltage electrostatic generating device

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

After the nano-TiO ₂ sol was centrifuged at a high speed under the condition of 7000r/min, the supernatant was taken and diluted a thousand times, and the particle size and particle size distribution of the sol were tested with a dynamic light scattering laser particle size analyzer, and the results are shown in Figure 1 .

It can be seen from the curve in the figure that the particle size of the sol colloidal particles is below 100nm, the average particle size of the TiO ₂ sol is 31.23nm, and the dispersion coefficient pdi is below 0.3, indicating good dispersion.

Example 2

The nano- _TiO2 sol was sprayed on the collector by electrostatic spraying method, and at the same time, it was thermally crystallized in a blast drying oven at 150 ° C for 6 hours to obtain nano- _TiO2 powder, and then X-ray diffractometer (X'pert Powder ) to characterize its crystal form, and the results are shown in Figure 2.

In Figure 2, nano-TiO ₂ has strong diffraction peaks around 2θ of 25.3, 37.8, and 48.0, which correspond to (101), (004), and (200) crystal planes of anatase, respectively, and have better crystallization properties. The average grain size of _TiO2 was estimated to be 9.1 nm according to the Scherrer formula.

Example 3

Ultrasonic dispersion of nano-TiO ₂ powder, diluted to 0.5g/L, and then Japanese JEM-2100F transmission electron microscope to observe the morphology and particle size of nano-TiO ₂ .

It can be seen from Figure 3 that the prepared nano-TiO ₂ powder has good crystallinity, perfect crystal form, particle size between 5-10nm, and good dispersion.

Example 4

The nano-TiO ₂ sol was sprayed on the collector by electrostatic spraying method, and at the same time, it was thermally crystallized in a blast drying oven at 150°C for 6 hours to obtain nano-TiO ₂ powder, and then the UV-3600 UV-visible spectrophotometer of Shimadzu, Japan Analyze their UV-Vis spectral features.

It can be seen from Figure 4 that nano-TiO ₂ has strong ultraviolet absorption in the ultraviolet region (200-400nm), and begins to respond to visible light at 406nm. Using formula (1), it can be calculated that the band gap energy of nano-TiO ₂ is 3.05eV. Compared with the band gap energy of standard anatase TiO ₂ which is 3.2eV, the experimentally prepared anatase TiO ₂ has a red shift , may be due to the influence of the lattice structure to reduce the bandgap energy and redshift.

Example 5

The nano-TiO ₂ sol is sprayed on the collector by electrostatic spraying method, and at the same time, it is thermally crystallized in a blast drying oven at 150°C for 6 hours to obtain nano-TiO ₂ powder, and then the degradation rate of methylene blue is used to reflect its photocatalytic activity. According to the requirements of the GB 23762-2009-T photocatalytic material aqueous solution system purification test method, the photocatalytic performance of the powder was characterized in the photocatalytic reaction device built by ourselves, and the ultraviolet lamp was used as the light source.

Fig. 5 is the photocatalytic degradation curve of nanometer _TiO2 powder to methylene blue solution. It can be seen from the figure that the degradation rate of methylene blue by nano-TiO ₂ powder within 90 minutes is 82.3%, and the methylene blue blank solution without nano-TiO ₂ powder hardly degrades under ultraviolet light.

Example 6

A method for preparing nano-titanium dioxide by electrostatic spraying, adopting the following steps:

(1) Dissolve tetrabutyl titanate in absolute ethanol and glacial acetic acid and fully stir the molar ratio of tetrabutyl titanate, absolute ethanol and glacial acetic acid to be 1:2:5;

(2) adjust the pH of deionized water to 2 with acetic acid;

(3) Slowly add the solution obtained in step (1) dropwise to the above-mentioned deionized water. In the obtained solution, the molar weight of deionized water is 70 times the molar weight of tetrabutyl titanate, and keep warm at 30°C Stir for 3.5h, then age for 19h;

(4) A high-voltage electrostatic field is established between the nozzle 2 of the propeller 1 and the receiving device 3 through the high-voltage electrostatic generating device 4, thereby forming an electrostatic spray system. As shown in Figure 6, the nozzle 2 used is a flat mouth of 14G The dispensing needle, its metal guide tube is connected to the negative pole, the receiving device 3 is grounded with aluminum foil to form the positive pole, and the nozzle 2 and the receiving device 3 are sealed and placed in a transparent oven;

(5) Inject the aged solution into the propeller, control the voltage of the device to 20kV, the propulsion speed of the aged solution to 0.01mm/s, control the temperature of the entire transparent oven to 100°C, and the receiving distance between the nozzle and the receiving device It is 15cm, and the nanometer titanium dioxide is prepared by spraying through the nozzle.

Example 7

A method for preparing nano-titanium dioxide by electrostatic spraying, adopting the following steps:

(1) Dissolve tetrabutyl titanate in absolute ethanol and glacial acetic acid and fully stir the molar ratio of tetrabutyl titanate, absolute ethanol and glacial acetic acid to be 1:4:7;

(2) adjust the pH of deionized water to 4 with acetic acid;

(3) Slowly add the solution obtained in step (1) dropwise to the above-mentioned deionized water. In the obtained solution, the molar weight of deionized water is 220 times the molar weight of tetrabutyl titanate, and keep warm at 40°C Stir for 2.5h, then age for 24h;

(4) A high-voltage electrostatic field is established between the nozzle of the propeller and the receiving device through a high-voltage electrostatic generating device. The nozzle used is a 27G flat-mouth dispensing needle, the metal diversion tube is connected to the negative electrode, and the receiving device is formed by grounding aluminum foil. The positive electrode, the nozzle and the receiving device are airtightly placed in a transparent oven;

(5) Inject the aged solution into the propeller, control the voltage of the device to 30kV, the advancing speed of the aged solution to 0.02mm/s, control the temperature of the entire transparent oven to 150°C, and the receiving distance between the nozzle and the receiving device It is 20cm, and the nanometer titanium dioxide is prepared by spraying through the nozzle.

Claims (5)

1. a method for preparing nanometer titanium dioxide by electrostatic spraying, is characterized in that, the method adopts the following steps: (1) tetrabutyl titanate is dissolved in absolute ethanol and glacial acetic acid and fully stirred; (2) adjust the pH of deionized water to 2-4 with acetic acid; (3) Slowly add the solution obtained in step (1) dropwise into the above-mentioned deionized water, the molar weight of the deionized water is 70-220 times of the molar weight of tetrabutyl titanate, stir vigorously under the condition of heat preservation, and then carry out aging deal with; (4) A high-voltage electrostatic field is established between the propeller nozzle and the receiving device through the high-voltage electrostatic generating device, the metal diversion pipe on the nozzle is connected to the negative pole, the receiving device is grounded to form the positive pole, and the nozzle and the receiving device are sealed; (5) Inject the aged solution into the propeller, the voltage of the control device is 20-30KV, the advancing speed of the aged solution is 0.01-0.02mm/s, the temperature is 100°C-150°C, the distance between the nozzle and the receiving device The receiving distance between them is 15-20cm, and the nano-titanium dioxide is prepared by spraying through the nozzle. 2. a kind of electrostatic spraying according to claim 1 prepares the method for nano-titanium dioxide, it is characterized in that, the molar ratio of tetrabutyl titanate, dehydrated alcohol and glacial acetic acid described in step (1) is 1:2 -4:5-7. 3 . The method for preparing nano-titanium dioxide by electrostatic spraying according to claim 1 , characterized in that, in step (3), heat preservation and stirring at 30-40° C. for 2.5-3.5 hours. 4 . 4. The method for preparing nano titanium dioxide by electrostatic spraying according to claim 1, characterized in that, the aging time of step (3) is 19-24h. 5. the method for preparing nano titanium dioxide by a kind of electrostatic spraying according to claim 1, is characterized in that, the nozzle described in step (4) is the flat dispensing needle head of 14G-27G, and described receiving device is aluminum foil paper .