Low-temperature preparation method of anatase phase nanocrystalline titanium dioxide with photocatalytic activity
Technical Field
The invention relates to a preparation method of titanium dioxide, in particular to a low-temperature preparation method of anatase phase nanocrystalline titanium dioxide with photocatalytic activity.
Background
Titanium dioxide has three crystal forms, namely anatase phase, rutile phase and brookite phase. Rutile and anatase have nearly the same valence band energy level, and their positions in the energy level diagram are very low, and both have strongly oxidizing valence band holes (and hydroxyl radicals). Compared with the prior art, the anatase phase nanocrystalline titanium dioxide has higher photocatalytic activity, and is a semiconductor metal oxide which is most widely and deeply researched in the aspect of photocatalytic application at present. When it absorbs photons with a wavelength of 387.5nm or less, it generates electrons in the conduction band and holes in the valence band, which (and hydroxyl radicals) oxidize most organic and some inorganic pollutants and eventually degrade to CO2、H2O and other harmless substances, and can reduce metal ions in water, so that the water treatment agent can be applied to the fields of water treatment, harmful gas purification, self-cleaning technology, antibacterial materials, antifouling and antifogging coatings, cancer cell killing, solar energy conversion and the like.
Industrial production of TiO2The powder is generally prepared by a sulfuric acid methodand a chlorination method, anatase-phase titanium dioxide is produced by calcining at 500-750 ℃, titanium dioxide crystal grains grow rapidly at the temperature, the obtained titanium dioxide crystal grains are oversized, the specific surface area is obviously reduced, the surface adsorption capacity is poor, and the photocatalytic activity is influenced. Titanium dioxide manufactured by Degussa, Germany, authorizing Japan Aerosil is very small in particle size and is generally used as a heat stabilizer for a heat-resistant silicone rubber belt, and as a photocatalyst, it is used only as a sample in development work, so that commercial titanium dioxide having high photocatalytic activity is urgently required to be developed.
At present, nano TiO2The main preparation methods include a liquid-phase precipitation method, a sol-gel method, a microemulsion reaction method, a gas phase method, a hydrothermal method, a peptization method and the like. The liquid phase precipitation method is easy to cause over-high local concentration of materials and uneven particle shape; sol-gel process and microemulsion reactionHigh cost of raw materials, reactionThe reaction time is long; the gas phase method has complex process, large investment and easy sintering of particles; in contrast, the peptization method has simple process, but the raw materials are reagent grade, the source is less, and the price is high; hydrothermal method for preparing high-purity TiO2But the grain size of the resulting product is larger. In view of the limitations of these methods, it is difficult to prepare anatase phase nano-crystalline titanium dioxide with high photocatalytic activity (the particle size is required to be small and uniform, the specific surface area is large, and the surface of the anatase phase nano-crystalline titanium dioxide has strong surface adsorption capacity without special treatment), and it is a problem to be solved at present that the preparation method can be industrially produced, has low cost, and can obtain anatase phase nano-crystalline titanium dioxide with good quality and high photocatalytic activity.
Disclosure of Invention
The invention aims to provide a low-temperature preparation method of anatase phase nanocrystalline titanium dioxide with large specific surface area, strong surface adsorption capacity and high photocatalytic activity, and the method is simple to operate and low in cost.
In order to obtain anatase phase nanocrystalline titanium dioxide with high photocatalytic activity and large specific surface area and strong surface adsorption capacity at low temperature, the original size of particles is controlled by adjusting hydrolysis conditions and adding a crystal nucleus promoter in the process of preparing the anatase phase nanocrystalline titanium dioxide with photocatalytic activity; in order to maintain the original size of the particles as much as possible, the nascent titanium dioxide is present in the form of an aqueous sol. The low temperature referred to in the present invention means a temperature ranging from room temperature to 120 ℃.
The invention provides a low-temperature preparation method of anatase phase nanocrystalline titanium dioxide with high photocatalytic activity, which is a liquid phase method and comprises the following steps:
(1) alkaline hydrolysis: taking hydrated titanium dioxide slurry containing 20-30 wt% of titanium dioxide, adding inorganic alkali solution with the concentration of 20-50 wt% when the temperature is adjusted to 60-70 ℃, and enabling OH to be in contact with the inorganic alkali solution-With TiO2The molar ratio is 1.9-2.3, the temperature is controlled at 80-90 ℃, and the temperature is constant, so that an orthotitanate solution is obtained; then cooling toRoom temperature;
(2) adding a crystal nucleus promoter: adding a crystal nucleus promoter into the orthotitanate solution obtained in the step (1) at room temperature, wherein the addition amount of the crystal nucleus promoter is 0.5-5 wt% of the total content of titanium dioxide in the system, and then stirring at constant temperature;
(3) washing with water: under room temperature or ice water bath, diluting the orthotitanate solution added with the crystal nucleus accelerant in the step (2) to 4-5 times of the volume of the original solution by using water while stirring, precipitating for 8-10 hours, and removing supernatant to obtain amorphous white precipitate;
(4) acid dissolution: heating the white precipitate obtained in the step (3) to 50-70 ℃, controlling the pH value of the white precipitate to be 3.3-4.0 by using inorganic acid with the concentration of 25-30 wt%, dissolving the precipitate to obtain titanium compound sol, and continuously stirring at constant temperature;
(5) and (3) cooling: cooling the titanium compound sol obtained after the acid dissolution in the step (4) to room temperature to obtain titanium dioxide slurry with photocatalytic activity;
(6) and (5) washing, filtering, drying and crushing the titanium dioxide slurry obtained in the step (5) to obtain anatase phase nanocrystalline titanium dioxide with photocatalytic activity.
The starting material used in the present invention is a hydrated titanium dioxide which may be metatitanic acid (TiO)2·H2O), orthotitanic acid (TiO)2·2H2O) or mixtures thereof, and all titanium-containing inorganic compounds, e.g. titanium chloride (Ti (Cl)4) Titanium sulfate (Ti (SO))4) Or titanyl sulfate (TiOSO)4) Hydrolyzing the resultant hydrated titanium dioxide. The hydrous titanium dioxide slurry containing 20-30 wt% of titanium dioxide can be prepared from a dry material of hydrous titanium dioxide, or an inorganic compound containing titanium is generated in a reaction.
The inorganic alkali comprises sodium hydroxide, potassium hydroxide and ammonia water sodium carbonate. And when the inorganic base is added into the hydrated titanium dioxide slurry, controlling the temperature to be 80-90 ℃.
The crystal nucleus accelerator used in the present invention may be potassium carbonate, potassium sulfate, potassium chlorate, antimony trioxide, antimony trichloride, phosphoric acid, ammonium phosphate, diammonium hydrogen phosphate or ammonium hydrogen carbonate.
The step (3) of washing by water also comprises immersion washing. The water used for water washing comprises distilled water, deionized water, ultrapure water or mixed water of any ratio of the distilled water, the deionized water and the ultrapure water.
The inorganic acid used in step (4) of the present invention may be hydrochloric acid, nitric acid or phosphoric acid.
The cooling in the step (5) of the invention can be rapid indirect cooling or direct cooling by using distilled water, deionized water, ultrapure water or mixed water of any ratio of the distilled water, the deionized water and the ultrapure water, wherein the addition amount of the water is 4-5 times of the volume of the stock solution during direct cooling.
In the low-temperature preparation method provided by the invention, the titanium dioxide slurry obtained in the step (5) can be further subjected to washing, filtering, drying and crushing, wherein the washing and filtering is carried out by rinsing with distilled water, deionized water, ultrapure water or mixed water of any ratio of distilled water, deionized water and ultrapure water, and vacuum filtration is carried out simultaneously, and the washing and filtering is carried out for not less than 3 times; drying, namely treating the filter cake after washing and filtering into a filter cake with the thickness within 20-40 mm, and drying for 3-4 h under normal pressure at the temperature of 40-120 ℃ or drying for 1-2 h under vacuum at the temperature of 40-120 ℃; crushing generally without special crushing equipment, the TiO obtained2Sieving the dry powder with 200 mesh sieve, and lightly brushing with brush to obtain high dispersibility nanoparticles, optionally using special pulverizing equipment such as jet mill.
The process flow chart of the low-temperature preparation method of anatase phase nanocrystalline titanium dioxide with photocatalytic activity provided by the invention is shown in figure 1.
In the invention, if the inorganic base is sodium hydroxide and the inorganic acid is hydrochloric acid, the chemical reaction process is as follows: the hydrated titanium dioxide reacts with sodium hydroxide to generate sodium orthotitanate solution, the sodium orthotitanate is hydrolyzed at low temperature under the action of a crystal nucleus promoter to obtain white amorphous orthotitanate, and further crystallization and peptization of hydrochloric acid are carried out to form a large amount of tiny titanium sol (TiO) with two positive charges2+) Crystallites which, when rinsed, are further hydrolysed to give titanyl hydroxide (TiO (OH)2) I.e. fresh waterTitanium oxide (TiO)2·H2O), drying and dehydrating the titanium dioxide to obtain anatase phase nanocrystalline, wherein the nanocrystalline has fine particles, narrow particle size distribution, large specific surface area, strong surface adsorption capacity and high photocatalytic activity.
Themain chemical reaction formula is:
the average particle size of the titanium dioxide aggregate prepared by the method is in a nano-scale range, the average particle size range is 10-80 nm, and the particle size is uniform; the specific surface area is 150-300 m2Within/g; the surface adsorption capacity is strong; the titanium dioxide has high photocatalytic activity.
The low-temperature preparation method of the anatase phase nanocrystalline titanium dioxide with high photocatalytic activity, provided by the invention, is simple, time-saving and low in cost. Anatase phase nanocrystalline titanium dioxide with high catalytic activity can be obtained at low temperature, and the slurry or powder of the anatase phase nanocrystalline titanium dioxide can be used for photocatalysis.
Drawings
FIG. 1 is a process flow diagram of the low temperature preparation method of anatase phase nanocrystalline titanium dioxide with high photocatalytic activity according to the present invention;
FIG. 2 is an X-ray diffraction (XRD) spectrum of the powdery anatase phase nanocrystalline titanium dioxide prepared in example 1 of the present invention;
FIG. 3 is a Scanning Electron Microscope (SEM) photograph of the anatase phase nano-crystalline titanium dioxide powder prepared in example 1 of the present invention;
FIG. 4 shows the comparison of the photocatalytic activity of the powdered anatase phase nanocrystalline titanium dioxide prepared in examples 1, 2 and 3 of the present invention with that of commercial product P-25.
Detailed Description
The following examples are intended to illustrate embodiments of the present invention in particular, and are not intended to limit the scope of the present invention.
Example 1
(1) Alkaline hydrolysis: 25Kg (125mol) of washed, clean, hydrated titanium dioxide slurry (containing 40 wt% TiO) was treated with an amount of deionized water2) Preparing a uniform suspension containing 25 wt% of titanium dioxide; slowly injecting the solution into a reaction kettle, adding a 50 wt% NaOH solution into the reaction kettle at a constant temperature of 65 ℃, controlling the total addition amount of NaOH to be 250mol and the temperature to be 80-90 ℃ (the dosing time is about 30min), and continuously stirring at the constant temperature for 60min to obtain a sodium orthotitanate solution; then rapidly cooling the solution in the kettle to room temperature at a cooling speed of about 8 ℃/min; (2) adding a crystal nucleus promoter: adding potassium sulfate with the titanium dioxide content of 2.0 wt% into the reaction kettle, and stirring at constant temperature; (3) washing with water: adding deionized water with the volume 4 times that of the stock solution into the reaction kettle for dilution, stirring, settling for 10 hours, and removing supernatant to obtain amorphous white precipitate; (4) acid dissolution: heating the precipitate in the reaction kettle to 65 ℃ at the heating rate of 2 ℃/min, adding 25 wt% of HCl to adjust the pH value to 3.5 at constant temperature, and continuously stirring at constanttemperature for 40 min; (5) and (3) cooling: and cooling to room temperature to obtain the titanium dioxide slurry. Washing and filtering the titanium dioxide powder by using deionized water for three times, and drying a filter cake for 3.5 hours at the temperature of 100 ℃ to obtain the anatase phase nanocrystalline titanium dioxide with high photocatalytic activity powder.
FIG. 2 shows an X-ray diffraction (XRD) pattern of the anatase-phase nano-crystalline titanium dioxide photocatalyst powder of this example using a Dmax/2400X-ray diffractometer (Nippon chemical Co., Ltd.). The diffraction peak is consistent with the standard map of anatase phase titanium dioxide provided by international diffraction data center (ICDD), which indicates that the obtained product is anatase phase titanium dioxide. The diffraction peak shows obvious broadening, which is caused by fine crystal grains. According to the half-value width, the average grain size was calculated to be 12.5nm by using the Scherrer equation.
FIG. 3 is a Scanning Electron Micrograph (SEM) of the powdery anatase phase nanocrystalline titanium dioxide of this example, using a JEOL JSM-6700F (Japanese Electron). It is further possible from the image to count that the average particle diameter of the produced titanium dioxide is 13.2 nm. The particle size is uniform. The specific surface area was measured by the BET method and found to be 286.74m2/g。
Line 1 in FIG. 4 shows the photocatalytic activity for decomposing methylene blue of product P-25, line 2 shows the photocatalytic activity for decomposing methylene blue of the powdery anatase phase nano-crystalline titanium dioxide of this example, and the apparatus used was a Model PCC-1 photocatalytic detector (Sinku-Riro, Inc., Japan vacuum chemical Co., Ltd.), and the results showed that the photocatalytic activity of the anatase phase nano-crystalline titanium dioxide prepared in this example was much higher than that of product P-25. The photocatalytic activity of the anatase phase nanocrystalline titanium dioxide prepared in this example was about 7 times that of commercial product P-25, depending on the degree of decomposition of methylene blue.
Example 2
(1) Alkaline hydrolysis: using a certain amount of deionized water, 12.5Kg of hydrated titanium dioxide dry powder (containing TiO)280%) to prepare a uniform suspension containing 25 wt% of titanium dioxide, slowly injecting the uniform suspension into a reaction kettle, quickly and slowly adding a 40 wt% KOH solution containing 250mol of KOH into the uniform suspension at the constant temperature of 65 ℃, controlling the temperature to be 80-90 ℃, and continuously stirring for 80min at the constant temperature to obtain a potassium orthotitanate solution; then rapidly cooling the solution in the kettle to room temperature at a cooling speed of about 8 ℃/min; (2) adding a crystal nucleus promoter: adding antimony trichloride with the titanium dioxide content of 3.0 wt% into the reaction kettle, and stirring for 40min at constant temperature; (3) washing with water: adding deionized water with the volume 4 times that of the stock solution into the reaction kettle for dilution, stirring, settling for 10 hours, and removing supernatant to obtain amorphous white precipitate; (4) acid dissolution: heating the precipitate in the reaction kettle to 65 ℃ at a heating rate of 2 ℃/min, and adding 30 wt% of HNO at a constant temperature3Adjusting the pH value to 3.5, and continuously stirring for 40min at constant temperature; (5) and (3) cooling: and rapidly cooling to room temperature at a cooling speed of 6-10 ℃/min to obtain the titanium dioxide slurry. Is removed fromWashing and filtering the titanium dioxide powder by using sub water for three times, and drying a filter cake for 2 hours at the temperature of 110 ℃ to obtain the anatase phase nanocrystalline titanium dioxide with high photocatalytic activity. Line 3 of fig. 4 shows the photocatalytic activity of the powdered anatase phase nanocrystalline titania for decomposing methylene blue in this example.
Example 3
(1) Alkaline hydrolysis: 25Kg (125mol) of washed, clean, hydrated titanium dioxide slurry (containing 40 wt% TiO) was treated with an amount of deionized water2) Preparing a uniform suspension containing 30 wt% of titanium dioxide; slowly injecting into a reaction kettle, adding Na at 60 deg.C2CO3260mol of 30 wt% Na2CO3Controlling the temperature of the solution at 80-90 ℃ (adding the drug for about 30min), and continuously stirring at constant temperature for 60min to obtain a sodium orthotitanate solution; then cooling to room temperature; (2) adding a crystal nucleus promoter: adding potassium sulfate with the titanium dioxide content of 1.0 wt% into the reaction kettle, and stirring at constant temperature for about 30 min; (3) washing with water: adding deionized water 4 times the volume of the stock solution into the reaction kettle for dilution, stirring for about 30min, settling for 8h, and removingRemoving the supernatant to obtain an amorphous white precipitate; (4) acid dissolution: heating the precipitate in the reaction kettle to 65 ℃ at the heating rate of 2 ℃/min, adding 25 wt% of H at constant temperature3PO4Adjusting the pH value in the kettle to 3.5, and continuously stirring at constant temperature; (5) and (3) cooling: and cooling to room temperature to obtain the titanium dioxide slurry. Washing and filtering the titanium dioxide powder by using deionized water for three times, and drying a filter cake for 3 hours at the temperature of 100 ℃ to obtain the anatase phase nanocrystalline titanium dioxide with high photocatalytic activity. Line 4 of fig. 4 shows the photocatalytic activity of the powdered anatase phase nanocrystalline titania of this example in decomposing methylene blue.
Example 4
(1) Alkaline hydrolysis: 25Kg (125mol) of washed, clean, hydrated titanium dioxide slurry (containing 40 wt% TiO) was treated with an amount of deionized water2) Preparing a uniform suspension containing 25 wt% of titanium dioxide; slowly injecting the solution into a reaction kettle, adding a 50 wt% NaOH solution containing 250mol of NaOH at the constant temperature of 65 ℃, controlling the temperature to be 80-90 ℃, and continuously stirring at the constant temperature to obtain a sodium orthotitanate solution; cooling to room temperature; (2) adding crystal nucleus to promoteFeeding: adding ammonium phosphate with the titanium dioxide content of 3 wt% into the reaction kettle, and stirring at constant temperature; (3) washing with water: adding deionized water with 4 times of the volume of the stock solution into the reaction kettle for dilution, stirring, settling, and removing supernatant to obtain amorphous white precipitate; (4) acid dissolution: heating the precipitate in the reaction kettle to 65 ℃ at the heating rate of 2 ℃/min, adding 25 wt% of HCl to adjust the pH value to 3.5 at constant temperature, and continuously stirring at constant temperature for 40 min; (5) and (3) cooling: and rapidly cooling to room temperature at a cooling speed of 6-10 ℃/min to obtain the titanium dioxide slurry. Washing and filtering the titanium dioxide powder by using deionized water for three times, and drying a filter cake for 1 hour in vacuum at the temperature of 50 ℃ to obtain the anatase phase nanocrystalline titanium dioxide with high photocatalytic activity powder.