CN108067277B - Preparation method of high nitrogen-doped single crystal TiO2 mesoporous material - Google Patents

Abstract

The invention relates to a preparation method of a single crystal _TiO2 mesoporous material with a high nitrogen-doping amount, and belongs to the technical field of material preparation. In the present invention, tetrabutyl titanate and urea are used as titanium source and nitrogen source respectively, and TiO ₂ material precursor is prepared by hydrothermal treatment, and then the molten salt method is adopted, and the added mixed nitrate is used as synergistic dopant and morphology modifier , the preparation of high nitrogen-doped single-crystal _TiO2 mesoporous materials. The method has the advantages of strictly controllable preparation conditions, simple equipment and process, large output and low cost. The obtained product has high purity, uniform particle size distribution and high nitrogen doping; this material has broad application prospects in photovoltaic cell electrodes, photocatalytic hydrogen production and degradation.

Description

Preparation method of high nitrogen-doped single crystal TiO2 mesoporous material

technical field

The invention relates to a preparation method of a single crystal _TiO2 mesoporous material with high nitrogen doping amount, and belongs to the technical field of material preparation.

Background technique

_TiO2 is an n-type wide-bandgap semiconductor material, which has the advantages of good stability, low price, non-toxic, non-polluting, reusable, and photocorrosion resistance. Its optoelectronic and photocatalytic properties have received extensive attention and have been continuously expanded, becoming a research hotspot in both academia and industry. However, TiO ₂ has a large forbidden band width of 3.0eV~3.2eV, which can only absorb light in the near-ultraviolet region, while the ultraviolet light in the solar spectrum only accounts for about 5%, which greatly reduces the utilization rate of solar energy. How to widen the photoresponse range of _TiO2 to the visible light region has become one of the research hotspots worldwide.

At present, the main methods to realize the widening of the excitation and absorption spectrum of TiO ₂ from the ultraviolet region to the visible region include: ion implantation, photosensitization, catalytic reduction treatment, noble metal deposition or metal element doping, etc., all of which can improve the visible light activity of TiO ₂ to varying degrees. However, these methods have shortcomings such as short catalyst life, narrow light utilization range, and poor thermal stability. Non-metal doping can make up for the above deficiencies to a large extent.

In 2001, Asahi R calculated the density functions of C, N, F, P, and S, and pointed out that N doping has the best effect, and the p orbital of N can be hybridized with the 2p orbital of O, thereby reducing the forbidden band width of _TiO2 . . Although S has a similar role as N, they believe that it is impossible for S to be doped into _TiO crystals because the size of the S ions is too large, and the C and P orbitals are too deep to match the energies. He used N to dope _TiO2 , which significantly improved the visible light catalytic efficiency. It is analyzed that the principle is that the doped N enters the TiO ₂ lattice and replaces part of the oxygen atomic sites in the oxygen lattice, forming an intermediate band gap (N 2p) energy level above the O 2p valence band of TiO ₂ , The middle band gap energy level is slightly higher than the top of the O 2p valence band, so under visible light irradiation, electrons can directly transition from the middle band gap energy level to the conduction band, thus realizing the expansion of the photoresponse to the visible light region. In 2004, Sano first dissolved 2,2-dipyridine in pyrimidine by organic precursor pyrolysis method, then added _TiCl4 to the solution, stirred at room temperature and filtered to obtain a pale yellow precipitate, which was then dried in air and ground. , and finally calcined in air and nitrogen atmospheres to obtain nitrogen-doped _TiO2 powders, and the catalysts exhibited certain photocatalytic performance. In 2005, Silveyra et al. adopted a high-temperature roasting method, using P25 nano-TiO ₂ powder as raw material and ammonia water as nitrogen source, mixed P25 powder and water to form a suspension, and injected it into a quartz tube in the form of small droplets with a peristaltic pump. The atomized ammonia water was reacted to prepare nitrogen-doped TiO ₂ , which enhanced the absorption of visible light by TiO ₂ . In 2008, Sun et al. added ammonia water dropwise to Ti(OBu) ₄ solution by hydrothermal method to make it hydrolyzed, then dried the mixture and calcined in muffle furnace to obtain white nitrogen-doped _TiO2 powder, which showed good visible light catalysis. active. In 2008, Qin et al. added the ethanol solution of tetrabutyl titanate dropwise to the ethanol solution of glacial acetic acid by the sol-gel method, then added ammonia water, the suspension was vigorously stirred and then precipitated, and the obtained gel was dried. , grinding and calcining for 2h to obtain nitrogen-doped TiO ₂ , which enhances its adsorption capacity and visible light catalysis capacity. In 2012, Tang et al. used the mechanochemical method to mix and grind amorphous titanium dioxide with nitrogen source and water. The obtained moist powder was dried and calcined at high temperature to obtain titanium dioxide. The doped nitrogen and oxygen defects made it have better properties. Visible light absorption capacity and photocatalytic performance.

At present, the preparation methods of nitrogen-doped TiO ₂ are mainly: organic precursor pyrolysis method, high temperature calcination method, hydrothermal method, sol-gel method, mechanochemical method and so on. Among them, the hydrothermal method is simple in process, abundant in raw materials, and relatively easy to control the particle size of the material, so as to prepare a pure and uniform product. However, when the sample is calcined by the above method, the nitrogen element doped by TiO ₂ will be lost and the specific surface area of TiO ₂ will be reduced, which will eventually reduce the catalytic performance and adsorption performance of the product. In the present invention, tetrabutyl titanate and urea are used as titanium source and nitrogen source respectively, TiO ₂ material precursor is prepared by hydrothermal method, and single crystal TiO ₂ with high nitrogen-doped content is prepared by molten salt method for the first time. Nitrate was introduced to modify the morphology of TiO2 single crystal, and at the same time, the doping nitrogen source was supplemented. The single-crystal TiO ₂ mesoporous material with high nitrogen doping amount is prepared, the one-time yield is large, the purity is high, and the morphology is uniform, and the preparation method is economical and environmentally friendly.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a method for preparing a single crystal TiO ₂ mesoporous material with high nitrogen doping content; the method uses tetrabutyl titanate and urea as the titanium source and the nitrogen source respectively, and hydrothermally prepares the TiO ₂ material precursor, Then through the molten salt method, mixed nitrate is used as a synergistic dopant and morphology modifier to prepare a high nitrogen-doped single crystal mesoporous TiO ₂ material; this method has the advantages of strictly controllable preparation conditions, simple equipment and process, and product yield. The obtained TiO ₂ has a single crystal mesoporous structure with a diameter of about 5-10 nm, high product purity, uniform particle size distribution, clear and complete shape, and high nitrogen doping.

A method for preparing a single crystal TiO ₂ mesoporous material with a high nitrogen doping amount, characterized in that the method obtains a high nitrogen doping amount single crystal TiO ₂ mesoporous material by hydrolysis of tetrabutyl titanate and nitrate molten salt, comprising: The following steps:

(1) slowly mix tetrabutyl titanate solution and urea solution, carry out hydrothermal reaction after stirring, then carry out centrifugation and drying;

(2) After fully grinding the prepared TiO ₂ precursor and NaNO ₃ -KNO ₃ mixed salt, calcining, cooling down to room temperature naturally, fully washing with deionized water and drying, the high nitrogen-doped monolayer can be prepared Crystalline _TiO2 mesoporous material.

In the above preparation method, the titanium source and nitrogen source in the step (1) are commercially available tetrabutyl titanate and urea, respectively.

In the above preparation method, the operation in the step (1) is carried out under stirring.

In the above preparation method, in the step (1), in the preparation of the TiO ₂ precursor by the hydrothermal method, the tetrabutyl titanate solution is firstly added slowly, and then 5 ml of 2-8M urea solution is added.

In the above preparation method, the temperature of the hydrothermal reaction in the step (1) is 80-200°C.

In the above preparation method, the holding time at the hydrothermal reaction temperature in the step (1) is 12-48 hours.

In the above preparation method, the drying method in the steps (1) and (2) adopts vacuum drying at 50-100°C.

In the above preparation method, the mixed salts in the step (2) are commercially available NaNO ₃ and KNO ₃ .

In the above preparation method, the mass ratio of NaNO ₃ and KNO ₃ in the step (2) is controlled between 5:1 and 1:5.

In the above preparation method, the mass ratio of the TiO ₂ precursor and the NaNO ₃ -KNO ₃ mixed salt in the step (2) is controlled between 5:1 and 1:5.

In the above preparation method, the calcination temperature in the step (2) is 300-600°C.

In the above preparation method, the holding time at the calcination temperature in the step (2) is 2-6 hours.

The high nitrogen-doped single crystal _TiO2 mesoporous material prepared by this technology has the characteristics of simple equipment and process, strictly controllable preparation conditions, high product yield, low cost, etc. The prepared high nitrogen-doped single crystal _TiO2 shape Uniform and neat, high purity, high nitrogen doping.

Description of drawings

Fig. 1 is the XRD pattern of the high nitrogen-doped single crystal _TiO2 mesoporous material prepared in Example 1 of the present invention

Fig. 2 is a transmission electron microscope photograph of the high nitrogen-doped single crystal _TiO2 mesoporous material prepared in Example 1 of the present invention, and the inset is its particle size distribution

Figure 3 shows the single-crystal TiO ₂ material (NS-TiO ₂ ) with high nitrogen-doped content prepared in Example 1 of the present invention, the nitrogen-doped TiO ₂ material (N-TiO ₂ ) prepared by the conventional method, and the non-doped TiO ₂ material ( Comparison of N 1s spectra of XPS test of Pure TiO ₂ )

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the embodiments.

The invention provides a method for preparing a high nitrogen-doped single crystal _TiO2 mesoporous material, which is characterized in that the method obtains a high nitrogen-doped single crystal _TiO2 by hydrolysis of tetrabutyl titanate and nitrate molten salt mesoporous material, and includes the following steps and content:

(1) The titanium source and nitrogen source used are commercially available tetrabutyl titanate and urea, respectively.

(2) The preparation operation is carried out under stirring.

(3) In the preparation process, the tetrabutyl titanate and the urea solution are slowly mixed first, and then subjected to a hydrothermal reaction, followed by centrifugation and drying.

(4) In the preparation process, the hydrothermal reaction temperature is 80-200° C., and the holding time is 12-48 hours.

(5) In the preparation process, the drying method adopts vacuum drying at 50-100°C.

(6) The prepared TiO ₂ precursor and NaNO ₃ -KNO ₃ mixed salt are fully ground, then calcined, and then naturally cooled to room temperature, and the product is fully washed with deionized water and dried to obtain a high nitrogen-doped single crystal _TiO2 mesoporous material.

(7) The mixing mass ratio of NaNO ₃ and KNO ₃ is controlled between 5:1 and 1:5 in the preparation process.

(8) During the preparation process, the mixing mass ratio of TiO ₂ precursor sample and NaNO ₃ -KNO ₃ mixed salt is controlled between 5:1 and 1:5

(9) In the preparation process, the calcination temperature is 300-600° C., and the holding time is 2-6 hours.

The prepared high nitrogen-doped single crystal _TiO2 mesoporous material is white powder in appearance.

Under the transmission electron microscope, a large number of nanoparticles can be observed, and the obtained product particles are about 5-10 nm according to the particle size distribution statistics. XRD testing showed that the nanoparticles were anatase phase _TiO2 . From the N 1s spectrum of XPS, it can be seen that N element is successfully incorporated into TiO ₂ , and the doping amount of nitrogen can be significantly increased by adding nitrate.

In conclusion, single-crystal _TiO2 mesoporous materials with high nitrogen doping can be prepared by this technique.

Example: Slowly mix 2ml of tetrabutyl titanate with 5ml of 2M urea solution under stirring, continue to stir for 30min, carry out hydrothermal reaction at 150°C for 24h, centrifuge and vacuum dry at 60°C to obtain TiO ₂ precursor .

Then, the TiO ₂ precursor, NaNO ₃ and KNO ₃ were uniformly mixed in a mass ratio of 5:1:1, calcined at 350 °C for 4 h, fully washed with deionized water, and dried to obtain high nitrogen-doped single crystal TiO ₂ mesoporous materials.

The prepared product is nanoparticulate TiO ₂ (see Fig. 1), with large yield, uniform diameter, and particle size of 5-10 nm (see Fig. 2). Nitrogen was successfully incorporated into _TiO2 , and the amount of nitrogen doping was significantly increased (see Figure 3).

Claims (2)

1. A method for preparing a single crystal TiO ₂ mesoporous material with high nitrogen doping amount, characterized in that: the material is TiO ₂ with a single crystal structure; the doping amount of nitrogen is increased; The single-crystal _TiO2 mesoporous material with high nitrogen doping was prepared by hydrolysis and molten salt of nitrate, including the following steps: (1) Slowly mix tetrabutyl titanate and urea solution, stir evenly, carry out hydrothermal reaction, then carry out centrifugation and drying to obtain TiO ₂ precursor; (2) The prepared TiO ₂ precursor and NaNO ₃ -KNO ₃ mixed salt are stirred evenly, calcined and cooled to room temperature naturally, washed with deionized water, and dried to obtain a single crystal with high nitrogen content _TiO2 mesoporous material. 2. according to the described preparation method of claim 1, it is characterized in that: described step (1) hydrothermal method prepares in TiO ₂ precursor, first slowly adds tetrabutyl titanate under stirring, then adds 5ml 2- 8M urea solution; the temperature of the hydrothermal reaction in the step (1) is 80-200°C, and the holding time is 12-48 hours; the drying method in the step (1) adopts 50-100°C vacuum drying; the In step (2), the mass ratio of NaNO ₃ and KNO ₃ is controlled between 5: 1 and 1: 5, and the grinding and mixing are uniform; in the step (2), the TiO ₂ precursor and the NaNO ₃ -KNO ₃ mixed salt The mixing mass ratio is also controlled between 5:1 and 1:5, and the grinding and mixing are uniform; in the step (2), the calcination temperature is 300-600° C., and the holding time is 2-6 hours.

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