CN101327425A - A kind of preparation method of nitrogen-doped titanium dioxide photocatalyst - Google Patents

Abstract

The invention relates to a method for preparing a nitrogen-doped titanium dioxide photocatalyst, which comprises the following steps: (1) using nanotube titanic acid as a precursor to prepare a new type of titanium dioxide by heat treatment at a certain temperature; (2) preparing the The prepared new titanium dioxide is heat-treated in NH ₃ flow; (3) then cooled naturally under the protection of NH ₃ , the nitrogen-doped titanium dioxide photocatalyst can be prepared. The photocatalyst of the nitrogen-doped titanium dioxide prepared by the method of the present invention has stronger absorption in the visible light region, compared with the N-doped P25 catalyst prepared by the same _NH3 treatment condition with this commercial titanium dioxide (P25 type) , the specific rate constant for the elimination of trace propylene gas in air is increased by about 4 times under visible light. The nitrogen-doped titanium dioxide catalyst prepared by the method of the invention has broad application prospects as a visible light catalytic material, and has simple preparation process, convenient operation and low cost, and is suitable for mass production.

Description

A kind of preparation method of nitrogen-doped titanium dioxide photocatalyst

technical field

The invention relates to a preparation method of a nitrogen-doped titanium dioxide photocatalyst, belonging to the technical field of titanium dioxide photocatalysis.

Background technique

In recent years, in order to utilize solar energy, an inexhaustible and inexhaustible clean energy source, the development of highly efficient visible light-responsive photocatalysts has become a research hotspot. Titanium dioxide is considered to be one of the most promising photocatalysts because of its strong oxidizing ability, stability, non-toxicity, and low price. However, due to the large band gap of titanium dioxide, it can only use less than 5% of the ultraviolet light in solar energy, so people focus on the development of titanium dioxide photocatalysts with visible light response. In 2001, Asahi et al. [R.Asahi, T.Morikawa, T.Ohwaki, K.Aoki, Y.Taga, Science 293 (2001) 269-271] reported that a small amount (0.75%) of the lattice was replaced by non-metallic N The visible-light activity brought about by oxygen is undoubtedly a pioneering work, opening up a new way to construct visible-light-excited photocatalysts. Doping _TiO2 with non-metal element nitrogen is now considered to be one of the better methods to develop photocatalysts with visible light response.

At present, there are various methods for preparing N-doped titanium dioxide, such as: magnetron sputtering method, ion implantation method, chemical evaporation deposition method, sol-gel method, TiN oxidation method, direct ammoniation method and hydrolysis of nitrogen-containing metals. Organic precursor method and so on. The N-doped _TiO2 prepared by these methods all exhibited visible-light photocatalytic activity to varying degrees.

Contents of the invention

The object of the present invention is to provide a preparation method of a nitrogen-doped titanium dioxide photocatalyst using nanotube titanic acid as a precursor.

In order to achieve the above object, the technical solution of the present invention is to adopt a kind of preparation method of nitrogen-doped titanium dioxide photocatalyst, comprising the following steps:

(1) Using nanotube titanic acid as a precursor to prepare a new type of titanium dioxide by heat treatment at a certain temperature;

(2) the prepared novel titanium dioxide is heat-treated in _NH3 air flow;

(3) Then cool naturally under the protection of NH ₃ to prepare nitrogen-doped titanium dioxide photocatalyst.

The novel titanium dioxide in the step (1) is prepared by heat-treating nanotube titanic acid at a temperature of 400-700° C. for 0.5-24 hours in air.

Before the novel titanium dioxide in the step (1) is heat-treated in NH ₃ air flow, NH ₃ should be fed in advance to replace the air in the pipeline.

The heat treatment temperature in the step (2) is 400-700°C.

The heat treatment time in the step (2) is 0.5-24h.

The method of the present invention uses nanotube titanic acid (NTA) as a precursor, and undergoes heat treatment and dehydration to prepare novel titanium dioxide with special photoelectric properties. Its crystal form is anatase structure and the crystal lattice contains a large number of stable lattice defects: Binding single-electron-trapped oxygen vacancy (single-electron-trapped oxygenvacancy, SETOV) and Ti ³⁺ , due to the relatively active nature of the titanium dioxide, the nitrogen-doped titanium dioxide photocatalyst (N-TiO ₂ -1) prepared from it is comparable to commercial Compared with the nitrogen-doped P25 catalyst (N-TiO ₂ -2) prepared under the same NH ₃ treatment conditions, the general-purpose titanium dioxide (P25 type) has an improved specific rate constant for the elimination of trace propylene gas in the air under visible light. up about 4 times. The novel titanium dioxide with special photoelectric properties used in the present invention as a precursor can also be used to prepare a new type of non-metallic C, S, F doped titanium dioxide catalyst, and the novel nitrogen doped titanium dioxide of the present invention can be used as a catalyst carrier. The N-doped titanium dioxide prepared by the method of the invention has an anatase crystal structure, has visible light absorption performance, and has visible light photocatalytic activity. The nitrogen-doped titanium dioxide catalyst prepared by the method of the invention has broad application prospects as a visible light catalytic material.

The precursor used in the present invention—nanotube titanic acid (NTA) is a new type of one-dimensional tubular material. After heat treatment, nanotube titanic acid is converted into TiO ₂ (anatase) by dehydration reaction. The lattice of the novel TiO ₂ (anatase) contains a large number of stable single-electron-trapped oxygen vacancies (single-electron-trapped oxygen vacancy, SETOV) and Ti ³⁺ [SL Zhang, W. Li, ZS Jin, JJ Yang, JW Zhang, ZLDu, ZJ Zhang, Journal of Solid State Chemistry 177 (2004) 1365-1371. QY, Li, XD Wang, ZS Jin, D. G Yang, SL Zhang, XY Guo, JJ Yang and ZJ Zhang, J. nanoparticle. rese]. It is precisely because of the stable SETOV and Ti ³⁺ lattice defects that the novel TiO ₂ (anatase) shows some special optoelectronic properties.

The preparation method of the invention has simple technological process, convenient operation, low cost, good social value and economic value, and is easy to popularize and apply.

Description of drawings

Fig. 1 is the XRD spectrum of the nitrogen-doped titanium dioxide photocatalyst prepared by the present invention;

Fig. 2 is the DRS spectrum of the nitrogen-doped titanium dioxide photocatalyst prepared by the present invention;

Fig. 3 is the curve of nitrogen-doped titanium dioxide photocatalyst of the present invention and nitrogen-doped P25 catalyst of the present invention under the same condition under the same condition that visible light eliminates propylene (the raw material gas is composed of air+600ppm propylene, the light source is a 500W xenon lamp, after λ ≥420nm cut-off filter filter, light intensity is 1.9mw/cm ² , catalyst coating amount is 31mg ± 1mg. Use Shimadzu GC-9A gas chromatograph to detect _the concentration of CO in the propylene and product before and after the reaction);

Fig. 4 is that the nitrogen-doped titania photocatalyst of the present invention and the nitrogen-doped P25 photocatalyst eliminate _the CO produced by propylene under visible light at different feed gas flow rates;

Fig. 5 shows the visible light photocatalytic activity test results of the nitrogen-doped titanium dioxide photocatalyst and the nitrogen-doped P25 catalyst of the present invention on methylene blue.

Wherein, the instrument used for X-ray diffraction (XRD) analysis is X'pert pro type X-ray diffractometer (XRD, Netherlands Philips company), adopts CuKα line excitation source, λ=0.15418366nm, voltage 40kV, electric current 40mA, sample can The powder is placed in the groove of the sample table to be flattened, or the sample is dispersed in acetone and dropped on the glass slide. After drying, a thin film is formed for direct detection.

The ultraviolet-visible diffuse reflectance spectrum (DRS) was measured on a Shimadzu U3010 ultraviolet-visible diffuse reflectometer.

Absorbance was measured with a 722 visible spectrophotometer produced by Shanghai Precision Instrument Factory.

Detailed ways

Example 1

The preparation method of the present invention is as follows:

(1) Preparation of nanotube titanic acid

Slowly add 3.0g of titanium dioxide into a polytetrafluoroethylene container containing 300ml of 40% NaOH solution, place it in an oil bath and raise the temperature to 118°C, heat to reflux for 24h, cool and settle, pour out the supernatant, and use distilled water Wash until pH = 8.0, filter, soak in 0.1 mol/L hydrochloric acid for 5 hours, filter, wash, and dry to obtain the precursor nanotube titanic acid.

(2) Preparation of new titanium dioxide

Put 1.5 g of the prepared nanotube titanic acid as a precursor in a tube furnace, program the temperature up to 600 °C at a rate of 20 °C/min at room temperature, keep it for 2 h, and then naturally cool to room temperature, that is A new type of titanium dioxide with special photoelectric properties was prepared, and the titanium dioxide prepared in this example was confirmed to have an anatase structure by X-ray diffraction analysis.

(3) Preparation of nitrogen-doped titania photocatalyst

Put 1.0g of the prepared new-type titanium dioxide powder with special photoelectric properties in a tube furnace, and at the same time pass through _NH3 to replace the air in the tube furnace, and then at room temperature at 20 °C/min The heating rate was programmed to 600°C, kept for 4 hours, and then naturally cooled to room temperature under the protection of NH ₃ flow, and a new nitrogen-doped titanium dioxide photocatalyst with high visible light activity could be prepared.

The XRD spectrum in Fig. 1 shows that the crystal form of the nitrogen-doped titanium dioxide prepared in the present invention is an anatase structure.

Figure 2 DRS shows that the nitrogen-doped titanium dioxide prepared by the present invention has obvious absorption performance in the visible light region.

Application Example 1

Nitrogen-doped titanium dioxide photocatalyst of the present invention is coated on ground glass sheet, under visible light (λ≥420nm) trace propylene gas in air is eliminated, and the elimination rate of propylene is shown in Fig. 3 under different feed gas flow rates, from It can be seen from Fig. 3 that when the feed gas flow rate is 100ml/h, the elimination rate of propylene is as high as 58%. The elimination rate of propylene is significantly higher than that of the N-doped P25 catalyst prepared under the same conditions, and the specific rate constant is about 5 times that of the N-doped P25 catalyst (see Figure 3). When propylene is fully oxidized, 1mol propylene (C ₃ H ₆ ) should generate 3mol CO ₂ . Fig. 4 is the variation of the generation amount of _CO with the feed gas flow rate, thus obtained _CO The generation selectivity is 73% (nitrogen-doped titania of the present invention) and 43% (N-doped P25), indicating that propylene (C The visible light catalytic oxidation of ₃ H ₆ ) is incomplete, but compared with the N-doped P25 catalyst, the mineralization ability of the nitrogen-doped titanium dioxide photocatalyst of the present invention to propylene (C ₃ H ₆ ) is obviously improved.

Application Example 2

Measure 80mL of methylene blue solution with a concentration of 10mg/L and add it into the quartz reactor, then add 80mg of the nitrogen-doped titanium dioxide photocatalyst and nitrogen-doped P25 catalyst prepared by the present invention respectively, ultrasonically disperse each for 30min, and magnetically stir in the dark state Next, after the adsorption of methylene blue reaches equilibrium, add visible light, pour out a certain amount of solution at regular intervals for centrifugation, and measure the absorbance of the supernatant at 662nm (the maximum absorption wavelength of methylene blue). The visible light source is a 500W xenon lamp. The beam absorbs infrared light through the water pool and then passes through a λ≥420nm cut-off filter to obtain visible light. The light intensity irradiated on the reaction container is 1.2mw/cm ² . Both catalysts showed high activity for the photocatalytic decolorization of methylene blue, and the specific rate constants were k ₁ =1.5×10 ^-2 (N-TiO ₂ -1), k ₂ =1.1×10 ^-2 (N- TiO ₂ -2), the former is 1.4 times of the latter. (See Figure 5)

Finally, it should be noted that the above embodiments are only used to illustrate and not limit the technical solutions of the present invention, although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be modified Or an equivalent replacement, any modification or partial replacement without departing from the spirit and scope of the present invention shall fall within the scope of the claims of the present invention.

Claims (5)

1, a kind of preparation method of nitrogen-doped titanium dioxide photocatalyst is characterized in that: may further comprise the steps:

(1) is presoma with the nanotube metatitanic acid,, prepares a kind of Novel Titanium dioxide by heat-treating at a certain temperature;

(2) with prepared Novel Titanium dioxide at NH ₃Heat-treat in the air-flow;

(3) then at NH ₃Protection under naturally the cooling, can make nitrogen-doped titanium dioxide photocatalyst.

2, the preparation method of nitrogen-doped titanium dioxide photocatalyst according to claim 1, it is characterized in that: the Novel Titanium dioxide in the described step (1) be by the nanotube metatitanic acid in air, heat-treat 0.5-24h under 400-700 ℃ the temperature and prepare.

3, the preparation method of nitrogen-doped titanium dioxide photocatalyst according to claim 1 and 2 is characterized in that: the Novel Titanium dioxide in the described step (1) is at NH ₃Before heat-treating in the air-flow, should feed NH in advance ₃Clean the air displacement in the pipeline.

4, the preparation method of nitrogen-doped titanium dioxide photocatalyst according to claim 1 is characterized in that: the heat treatment temperature in the described step (2) is 400-700 ℃.

5, the preparation method of nitrogen-doped titanium dioxide photocatalyst according to claim 4 is characterized in that: the heat treatment time in the described step (2) is 0.5-24h.

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