CN101289223B - Method for preparing titanic oxide nano powder with visual light catalytic activity - Google Patents

Abstract

The invention relates to a preparation method of titanium dioxide nano powder with visible light catalytic activity, which is characterized in that it has the following steps: _TiCl4 hydrolysis, neutralization, drying, and grinding to obtain nano- _TiO2 powder, nano _-TiO2 in vacuum or _H2 or _N2 Titanium dioxide nano powder with visible light catalytic activity is obtained by heat treatment in the atmosphere. The present invention can control the relative content of anatase type and rutile type nano- _TiO2 in the powder and the O/Ti atomic ratio of nano- _TiO2 by changing the heat treatment atmosphere and temperature, so as to meet the requirements of different uses.

Description

Preparation method of titanium dioxide nanopowder with visible light catalytic activity

technical field

The present invention relates to a preparation method of nano titanium dioxide, in particular to a method of modifying nano TiO ₂ prepared by hydrolysis of TiCl ₄ through heat treatment in different atmospheres and different temperatures, so as to control its crystal form composition and obtain oxygen vacancy defects to expand its Preparation method of titanium dioxide nanopowder with photocatalytic activity threshold.

Background technique

The many special properties of nano-TiO ₂ , especially the photocatalytic properties, make it widely used in the control of environmental pollution and the development of new energy, which are manifested in the following aspects:

① Purify the air Nano-TiO ₂ photocatalyst directly uses the oxygen in the air as an oxidant under the condition of light, so that the oxygen and water vapor in the air can be converted into free radicals such as OH, O, HO ₂ and so on with strong oxidizing ability , these free radicals can convert most indoor air pollutants into harmless substances. Therefore, nano TiO ₂ is a very convenient air purifier, which can be used repeatedly at normal temperature and pressure without causing secondary pollution.

② In sewage treatment, it has been found that more than 3000 kinds of refractory organic compounds can be rapidly degraded by TiO ₂ under the irradiation of ultraviolet rays. The photocatalytic reaction of nano-TiO ₂ can effectively convert many organic pollutants into harmless small molecules to achieve the purpose of complete inorganic; especially when the concentration of organic pollutants in water is high or it is difficult to degrade by other methods, nano-TiO TiO ₂ has more obvious advantages. When used to purify drinking water, the removal rate of the total organic pollutants is above 60%.

③Self-cleaning ceramics Ceramic materials coated with titanium dioxide nano-films can catalyze under the excitation of weak ultraviolet light contained in sunlight and lights, which can kill bacteria, prevent mold growth, decompose organic matter and eliminate odors, so as to achieve self-cleaning effect. Self-cleaning ceramics have broad application prospects, such as the interior walls and floors of operating rooms and wards in hospitals with high sanitary requirements, sanitary ceramic sanitary ware in wet rooms and toilets where bacteria are easy to breed, and high-rise buildings. Glazed bricks for exterior wall decoration of buildings, etc.

④ Sterilization material Nano-TiO ₂ has a strong ability to kill Pseudomonas aeruginosa, Escherichia coli, Gluconobacter aureus, Salmonella, Mycobacterium and Aspergillus. Since the 1990s, the research on nano-TiO ₂ in anti-tumor has also begun.

⑤ Photoelectric conversion The existing nano TiO ₂ solar cells sensitized by organic dyes can achieve a photoelectric conversion efficiency of more than 10%, and can be used repeatedly, which has great application value.

However, as a semiconductor material, nano-TiO ₂ photocatalyst has a wide band gap, can only absorb ultraviolet light, and has a low utilization rate of solar energy, thus limiting its application. In addition, photogenerated carriers are easy to recombine, which also affects the quantum efficiency of photocatalysis. In order to obtain the photocatalytic activity of nano-TiO ₂ in the visible light region and make full use of the cheap and clean solar energy in nature, it must be modified. The main methods currently used are: metal ion doping and non-metal ion doping , combined with other compounds to make artificially prepared nano-TiO ₂ such as compound semiconductor, noble metal deposition, dye sensitization, etc.

The common crystal forms of artificially prepared nano-TiO ₂ are anatase and rutile. The photocatalytic activity of anatase is better than that of rutile, which is the desired structure for photocatalytic nano-TiO ₂ . Currently, the main method for controlling the crystal form is The method is heat treatment, and in heat treatment, the relative content of anatase and rutile nano- _TiO2 cannot be controlled, and the use is limited.

Contents of the invention

The purpose of the present invention is to provide a preparation method of titanium dioxide nano powder with visible light catalytic activity. The method of the invention can control the relative content of the anatase type and rutile type nano _TiO2 in the powder by changing the heat treatment temperature, so as to meet the requirements of different uses.

Realize the technical scheme of the present invention is:

TiCl ₄ is hydrolyzed, and the pH value of the solution is adjusted to 6 with ammonia water. After hydrolysis, the resulting precipitate is aged for 8 to 12 hours, dried, and ground to obtain nano-TiO ₂ powder. Nano-TiO ₂ is vacuum or H ₂ or N ₂ heat-treated to obtain visible light catalytic activity. Titanium dioxide nanopowder.

The method for hydrolyzing TiCl ₄ is: adding (NH ₄ ) ₂ SO ₄ crystals to 20-50ml of TiCl ₄ to make the SO ₄ ^2- /Ti ⁴⁺ ion concentration ratio 10-20, and hydrolyzing at 95°C.

Nano TiO ₂ powder with an O/Ti atomic ratio of 2.0 is prepared by hydrolysis of TiCl ₄ , and heat treatment is carried out in different atmospheres, such as vacuum or nitrogen or hydrogen, at different temperatures. The heat treatment temperature is 350-750 ° C, and the time is 0.5-2h. Titanium dioxide nanopowders with oxygen vacancy defects to extend their photocatalytic activity threshold.

The inventive method has the following advantages:

1) The heat treatment process provided by the present invention can improve the crystallinity of nano- _TiO2 , and the relative content of anatase type and rutile type nano- _TiO2 in the powder can be regulated by changing the heat treatment temperature to meet the needs of different uses.

2) The heat treatment atmosphere used in the present invention is easy to control. After treatment, different O/Ti atomic ratios can be obtained, that is, different amounts of O vacancy defects can be formed, so that nano- _TiO has different visible light absorption thresholds.

3) Through different combinations of heat treatment temperature and atmosphere, the crystal form composition and O vacancy concentration of nano-TiO ₂ powder can be adjusted in a wide range, thereby changing the visible light absorption threshold and absorptivity of nano-TiO ₂ .

Description of drawings

Fig. 1 hydrolysis method prepares nanometer TiO ₂ technological process of powder;

The anatase nanometer TiO that Fig. ₂ hydrolysis obtains Diffraction spectrum;

The TEM morphology of Fig. 3 nanometer TiO ₂ ;

Fig. 4 Diffraction spectrum of nano-TiO ₂ after vacuum calcination at 400°C for 1 h;

Fig. 5 Diffraction spectrum of nano-TiO ₂ after vacuum calcination at 1000°C for 0.5h;

Fig. 6 Diffraction spectrum of nanometer TiO ₂ calcined in hydrogen at 700°C for 1 hour.

Detailed ways

Preparation of 1 nm _TiO2 (see Figure 1)

In the fume hood, measure 20-50ml of TiCl ₄ with a dry clean measuring cylinder, slowly pour it into a clean beaker filled with ice cubes, and keep stirring at the same time, be careful not to let the TiCl ₄ liquid drip into the beaker during the pouring process Otherwise, the TiCl ₄ liquid will form a yellow precipitate on the beaker wall when it meets the water vapor on the beaker wall, which will affect the purity of the TiCl ₄ aqueous solution. After the ice cubes are completely dissolved, a clear, colorless and transparent TiCl ₄ aqueous solution is obtained with a solution concentration of 1.5-3.0M.

Add (NH ₄ ) ₂ SO ₄ crystals to the prepared TiCl ₄ aqueous solution. The amount of (NH ₄ ) ₂ SO ₄ crystals added is such that the SO ₄ ^2- /Ti ⁴⁺ ion concentration ratio is 10-20, and fully stirred to ensure The uniformity of the solution, after mixing evenly, move the mixed solution into a constant temperature water bath for constant temperature hydrolysis, and control the hydrolysis temperature at about 95°C. In order to check whether the hydrolysis is complete, take the supernatant and add NH ₃ ·H ₂ O to it dropwise. If there is white precipitate, it means that the solution is not completely hydrolyzed and needs to continue hydrolysis. If there is no precipitate, it means that the hydrolysis is complete. After the hydrolysis is completed, the mixed solution containing the white precipitate of hydrated TiO ₂ is aged for 8-12 hours, so that the TiO ₂ is fully precipitated, and then ammonia water is added to adjust the pH value of the mixed solution to about 6 to control the precipitation of TiO ₂ into an anatase structure. Suction filtration is then carried out and powder is separated with liquid, until the white precipitation that obtains with distilled water washing repeatedly does not have Cl in the liquid that filters out ^- Ion exists (with 1% _AgNO solution inspection does not appear white precipitation), finally the white precipitation that obtains Put it into a vacuum drying oven for drying, and dry it at 100°C for 4 hours to ensure that the level is fully dried. After taking it out, it is ground to obtain anatase nano-TiO ₂ .

Heat treatment of 2 nm _TiO2

1) Vacuum heat treatment

The above-mentioned nano- _TiO2 powder was filled into a corundum crucible and placed in a vacuum furnace. Before heating, vacuumize first, and start heating when the vacuum degree of the furnace body reaches below 1.0×10 ^-1 Pa. During the subsequent heating and holding process, continue vacuuming to keep the vacuum degree of the furnace at about 1.0×10 ^-2 Pa, the heating rate is 30-50°C/h, the temperature is 350°C-1100°C, and the holding time is 0.5-2h After the heat preservation is completed, the heating power supply is cut off, and the vacuum condition is still maintained until the furnace temperature drops to room temperature, so as to obtain the titanium dioxide nanopowder of the present invention.

2) _H2 or _N2 gas heat treatment

Put the above-mentioned nano TiO ₂ powder into a corundum crucible, place it in an atmosphere furnace, and first pass H ₂ or N ₂ gas for 10-20 minutes to eliminate the influence of air in the furnace; 30-50°C/h, keep warm for 0.5-2h, keep feeding H ₂ or N ₂ gas during the whole heating and holding process; cut off the heating power after the holding is over, stop the ventilation when the temperature drops to about 100°C, when the furnace body When the temperature reaches room temperature, the sample is taken out to obtain the titanium dioxide nanopowder of the present invention.

Example 1

Prepare TiCl ₄ according to the above method, hydrolyze and age TiCl ₄ at about 95°C, add ammonia water to adjust the pH value of the mixture to 6.1, and obtain nano-TiO ₂ powder after suction filtration, washing and drying, and analyze by XRD ( See Figure 2), it is found that the 2θ of the characteristic diffraction peak of the (101) crystal plane is about 25.3°, which belongs to the anatase structure, and the spectral line broadening is obvious, indicating that its crystallinity is not good. TEM observation found that the particle diameter was 6-10nm (see Figure 3). The O/Ti atomic ratio was determined to be 2.0 by XPS. UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis shows that its light absorption threshold is less than 400nm, which is only limited to the ultraviolet region.

The anatase nano-TiO ₂ was calcined at 400° C. for 1 h under vacuum conditions, and the heating rate was 35° C./h. Its crystal structure was tested by XRD, and it was found that it was still anatase, but the spectral line was narrowed (Figure 4), indicating that its crystallinity increased. The O/Ti atomic ratio was determined to be 1.9337 by XPS. UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis showed that the light absorption threshold of the sample was red-shifted to 480nm after calcination.

Using methyl orange solution as a degradation model, the photocatalytic activity of the modified sample under visible light was studied. Add a filter to the photocatalytic degradation experimental device to remove ultraviolet light with a wavelength of <400nm, use 200ml of 0.02g/L methyl orange solution as a degradation reagent, add 0.2g of calcined nano-TiO ₂ , and the degradation rate after 3 hours of light Reached 81.233%.

Example 2

The difference from Example 1 is that the vacuum calcination temperature is 1000°C, the heating rate is 50°C/h, and the time is 0.5h. Its crystal structure was tested by XRD, and it was found that it had all transformed into rutile type (Fig. 5). The O/Ti atomic ratio was determined to be 1.9390 by XPS. UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis showed that the light absorption threshold of the sample was red-shifted to 600nm after calcination. Adding the methyl orange solution of calcined nano-TiO ₂ , the degradation rate was 40.055% after 3 hours of visible light irradiation.

Example 3

The difference from Example 1 is that the calcination atmosphere is H ₂ , the heating rate is 30° C./h, and the time is 1.5 h. Its crystal structure was tested by XRD, and the obtained pattern was the same as that in Figure 4, indicating that it was an anatase crystal with good crystallization. The O/Ti atomic ratio was determined to be 1.9037 by XPS. UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis shows that the light absorption threshold of the sample after calcination is red-shifted to 410nm; in the visible region with a wavelength of 400-500nm, the light absorption value of the sample is about 0.1. The treated nano TiO ₂ powder makes the degradation rate of the methyl orange solution reach 99.349% after 3 hours of visible light irradiation.

Example 4

The difference from Example 3 is that the calcination temperature is 700° C., the heating rate is 40° C./h, and the time is 1 h. The XRD test showed (see Fig. 6) that the structure of the powder changed to a mixed crystal form, in which 2.44% of the rutile phase appeared. The O/Ti atomic ratio was determined to be 1.7889 by XPS. UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis shows that the light absorption threshold of the sample after calcination is red-shifted to 450hm; in the visible region with a wavelength of 400-500nm, the light absorption value of the sample is about 0.4. The treated nano TiO ₂ powder makes the degradation rate of the methyl orange solution reach 67.393% after 3 hours of visible light irradiation.

Example 5

The difference from Example 1 is that the calcination atmosphere is N ₂ . The O/Ti atomic ratio was determined to be 1.9681 by XPS. UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis shows that the light absorption threshold of the sample is red-shifted to 420nm after calcination; in the visible region with a wavelength of 400-500nm, the light absorption value of the sample is 0.1-0.2. The treated nano- _TiO2 powder makes the degradation rate of the methyl orange solution reach 53.059% after 3 hours of visible light irradiation.

in conclusion:

The above facts show that the nano-TiO ₂ prepared by hydrolysis of TiCl ₄ has an anatase structure, its O/Ti atomic ratio is 2.0, the crystallinity is low, and the light absorption effect is limited to the ultraviolet region. After heat treatment in vacuum, nitrogen or hydrogen at different temperatures and times, the crystallinity is significantly improved, and as the heat treatment temperature increases, the crystal structure changes from anatase to rutile, and the O/Ti atomic ratio decreases. Below 2.0, the light absorption threshold also extends to the visible light region, and exhibits good photocatalytic activity.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some changes and improvements without departing from the spirit and scope of the present invention. Therefore The scope of protection of the present invention should be defined by the claims.

Claims (1)

1. a preparation method with visible light catalytic activity titanium dioxide nanopowder, it is characterized in that having the following steps: 1) TiCl ₄ is hydrolyzed, the condition is that (NH ₄ ) ₂ SO ₄ crystals are added to 20-50ml of TiCl ₄ to make the SO ₄ ^2- /Ti ⁴⁺ ion concentration ratio 10-20, and hydrolyze at 95°C; 2) Adjust the pH value of the solution to 6 with ammonia water, age the precipitate obtained after hydrolysis for 8-12 hours, and dry; 3) Grinding nano _TiO2 powder, nano _TiO2 vacuum or _H2 or _N2 heat treatment, cooling to room temperature with the furnace, to obtain titanium dioxide nanopowder with visible light catalytic activity, wherein 3.1) Nano TiO ₂ The method of vacuum heat treatment is: Put the nano _TiO2 powder into the crucible and put it into the vacuum furnace; Heating starts when the vacuum degree in the vacuum furnace reaches 1.0×10 ^-1 Pa; The vacuum degree is 1.0×10 ^-2 Pa, the temperature is 350℃～1100℃, the heating rate is 30～50℃/h, and the heat preservation is 0.5～2h; Cut off the heating power after keeping warm, but still keep the vacuum condition, and cool down to room temperature with the furnace, and then get titanium dioxide nanopowder with visible light catalytic activity; 3.2) The method of nano-TiO ₂ hydrogen or nitrogen heat treatment is: Put the nano _TiO2 powder into the crucible and place it in the atmosphere furnace; Introduce _H2 or _N2 gas for 10-20 minutes, then start to heat up to 350°C-750°C, the heating rate is 30-50°C/h, and keep warm for 0.5-2h; After keeping warm, cut off the heating power supply, and stop ventilation when the temperature drops to 100°C; cool down to room temperature with the furnace, and obtain titanium dioxide nanopowder with visible light catalytic activity. the

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