CN108906107A - A kind of preparation method of sulfur and nitrogen co-doped titanium dioxide - Google Patents

Abstract

The invention relates to the field of synthesis methods of photocatalytic materials, and discloses a preparation method of sulfur and nitrogen co-doped titanium dioxide, which comprises fully dissolving thiourea containing sulfur sources and nitrogen sources in absolute ethanol, adding butyl titanate to fully react, and carry out decompression evaporation treatment to obtain a slurry containing titanium dioxide precipitation, air-dried, ground into powder, and finally calcining the powder to obtain powdered sulfur and nitrogen co-doped titanium dioxide. The present invention provides sulfur and nitrogen sources through thiourea, fully reacts dissolved thiourea and butyl titanate in absolute ethanol, adopts a series of heat treatment processes to generate sulfur and nitrogen co-doped titanium dioxide, and mixes sulfur and nitrogen Mixed in the crystal lattice of titanium dioxide, the visible light photocatalytic activity of titanium dioxide is improved, and the wavelength of visible light absorbed can reach 700nm; the preparation method requires few types of raw materials, wide reaction temperature range, and simple process, easy to realize, and easy to scale up. mass production.

Description

A kind of preparation method of sulfur nitrogen co-doped titanium dioxide

technical field

The invention relates to the field of synthesis methods of photocatalytic materials, more specifically, to a preparation method of sulfur and nitrogen co-doped titanium dioxide.

Background technique

Since Fujishima and Honda ^[1] in Japan discovered that TiO ₂ single crystal electrode photo-splitting water in 1972, heterogeneous photocatalytic reactions have aroused people's strong interest, and scientists have conducted a lot of research on it. The semiconductors currently used for photocatalysis are mainly N-type semiconductors with wide bandgap. Including TiO ₂ , ZnO, CdS, WO ₃ , Fe ₂ O ₃ , SnO ₂ , ZnS, SiO ₂ and so on, it has been proved that TiO ₂ and ZnO have the best catalytic activity, and CdS also has good activity, but CdS and ZnO are very unstable when illuminated, so that photocorrosion and photocatalysis proceed simultaneously, and the stability is poor. However, TiO ₂ can be reused at least 12 times to keep the photodecomposition efficiency basically unchanged, and maintain its smoothness under continuous 580min light. In addition, some photocatalytic semiconductors are also poisonous, such as CdS. Therefore, TiO ₂ has become the most commonly used photocatalyst because of its non-toxicity, good stability, high catalytic activity, and reusability. It has broad application prospects in the fields of environmental pollution control, biomedicine, and solar energy utilization.

However, TiO ₂ has a wide band gap and requires high-energy light to excite. At present, most of the photocatalytic systems in research use artificial light sources such as high-pressure mercury lamps, black light lamps, and ultraviolet germicidal lamps, which consume a lot of energy. Sunlight is a free energy source, but the energy of its ultraviolet light only accounts for 3% to 5% of the total energy. If the light absorption of TiO ₂ is improved to absorb visible light and catalyzed by visible light, solar energy can be fully utilized. Therefore, from an economic point of view, how to improve the photocatalytic efficiency of nano-TiO ₂ , expand its available spectral range, shorten the time required for reaction, and achieve mass production are the current research focus, difficulty and development direction.

Contents of the invention

In order to overcome at least one defect described in the above-mentioned prior art, the present invention provides a method for preparing sulfur and nitrogen co-doped titanium dioxide, using thiourea and butyl titanate to directly react sulfur and nitrogen to titanium dioxide at room temperature In the crystal lattice, powdery sulfur and nitrogen co-doped titanium dioxide is obtained through a series of processes, which improves the visible light photocatalytic activity of titanium dioxide, broadens the wavelength of visible light absorbed by titanium dioxide, requires low preparation temperature and simple process.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A preparation method of sulfur and nitrogen co-doped titanium dioxide, comprising the following steps:

S1 adds thiourea to absolute ethanol and stirs until thiourea is fully dissolved; at room temperature, in order to facilitate the dissolution of thiourea solids in absolute ethanol, grind the thiourea solids before putting them into absolute ethanol. After adding absolute ethanol, stir for 1-1.5h to fully dissolve the thiourea solid.

S2 Add butyl titanate to the absolute ethanol solution of thiourea, the molar ratio of thiourea to butyl titanate ranges from 6 to 3, and the thiourea and butyl titanate fully react; The thiourea in the water ethanol undergoes a chemical reaction to produce titanium dioxide containing sulfur, nitrogen and some other ions.

S3 performs decompression evaporation on the solution obtained from S2 to form a light yellow slurry; during the decompression evaporation process, the pressure should not be too low, if it is too low, it will cause bumping, and if necessary, it can be properly heated to increase the speed of evaporation and reaction speed.

S4 put the slurry obtained in S3 to air-dry at room temperature, and fully grind to obtain a light yellow powder;

S5 Calcining the powder obtained in S3 in the air to obtain powdery sulfur and nitrogen co-doped titanium dioxide.

Preferably, the reaction temperature in S2 is 18°C-40°C. The temperature in the early dissolving and reaction stages can be carried out within the range of 18°C-40°C. With a wider temperature range, the process is easier to realize and large-scale production is easy.

Preferably, the air-drying time in S4 is 24-48h.

Preferably, the optimal calcination temperature in S5 is 400-700°C.

Preferably, the optimal calcination temperature in S5 is 500-600°C.

Preferably, the calcination process of S5 adopts gradual temperature rise at room temperature, the temperature rise rate is 4-8°C/min, and the calcination time is 0.5-6h. Maintain a stable heating rate to avoid unbalanced local reactions caused by too fast heating rate, and carbonization of unreacted thiourea.

Compared with the prior art, the beneficial effect of the present invention is: the present invention provides sulfur source and nitrogen source through thiourea, fully reacts dissolved thiourea and butyl titanate in absolute ethanol, and adopts a series of heat treatment processes Generate sulfur-nitrogen co-doped titanium dioxide, doping sulfur and nitrogen into the titanium dioxide crystal lattice, improving the visible light photocatalytic activity of titanium dioxide, and absorbing visible light wavelengths up to 700nm; the preparation method requires fewer types of raw materials, The reaction temperature range is wide, and the process is simple, easy to realize, and easy to produce on a large scale; using the sulfur and nitrogen co-doped titanium dioxide prepared by the preparation method to carry out photocatalytic degradation of methyl orange experiments, in 500ml concentration of 0.02g/L methyl orange solution Add 0.5g of sulfur and nitrogen co-doped titanium dioxide into the mixture, irradiate with visible light with a wavelength ranging from 400nm to 430nm and a peak at 412nm, and keep stirring during the photocatalysis process. After 3 hours, by analyzing the ultraviolet-visible spectrum of the methyl orange solution, it was found that 90% of the methyl orange was decomposed, which is of great significance to the degradation of a class of pollutants such as methyl orange.

Description of drawings

Figure 1 is the XPS analysis full spectrum of sulfur and nitrogen co-doped titanium dioxide (TL501).

Figure 2 is a N1s high-resolution scan of sulfur and nitrogen co-doped titanium dioxide (TL501).

Fig. 3 is a S2p high-resolution scanning image of sulfur and nitrogen co-doped titanium dioxide (TL501).

Fig. 4 is a transmission electron microscope image of sulfur and nitrogen co-doped titanium dioxide (TL501).

Fig. 5 is an XRD analysis chart of sulfur and nitrogen co-doped titanium dioxide (TL501).

Figure 6 is a comparison chart of UV-Vis spectra of TL501 and Sol401.

Figure 7 is a comparison chart of the band gap between TL501 and Sol401.

Figure 8 is a schematic diagram of the energy bands of TL501 and Sol401.

Figure 9 is a diagram of the reaction device for the photocatalytic degradation experiment.

Figure 10 is a comparative analysis of the degradation efficiency of methyl orange by TL501, Sol401 and blank.

Detailed ways

The accompanying drawings are for illustrative purposes only, and should not be construed as limitations on this patent; in order to better illustrate this embodiment, certain components in the accompanying drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art It is understandable that some well-known structures and descriptions thereof may be omitted in the drawings. The positional relationship described in the drawings is for illustrative purposes only, and should not be construed as a limitation on this patent.

Example 1

A preparation method of sulfur and nitrogen co-doped titanium dioxide, thiourea solid 53.2g, 0.7mol is ground, then put into 500ml of absolute ethanol, at room temperature 25 ℃, the solution is stirred for 1 hour to 1.5 hours, let the sulfur Urea is fully dissolved, and then 59.5 g of butyl titanate, about 0.175 mol, is slowly dropped into the ethanol solution of thiourea. The molar ratio of thiourea to butyl titanate is 4, so that thiourea and butyl titanate fully react. Afterwards, it was evaporated under reduced pressure to obtain a light yellow slurry, which was left at room temperature for 48 hours and air-dried to obtain a light yellow powder, which was then fully ground. Finally, calcination is carried out in an air-circulating environment. The calcination temperature is 500°C, and the temperature is gradually raised at room temperature. The heating rate is 5°C/min, and the calcination is performed for 1 hour to obtain the target product. This sample is marked as TL501, and 50 means that the calcination temperature is 500°C. , 1 means the calcination time is 1h. The quantitative analysis results of TL501 are as follows:

Quantitative analysis results of TL501

It can be seen from the table that the atomic content of S and N co-doped TiO ₂ TL501 nitrogen is 0.762% (composed of N content in N 1s_b, N 1s_c, N 1s_d), and the atomic content of S is 1.085% (composed of S 2p3, S 2p1 S content composition), the ratio of O/Ti is 2.28. After S and N are mixed into TiO ₂ , it will affect the band gap of TiO ₂ and make it smaller, which can absorb visible light, generate photogenerated electrons and holes, have strong reducing and oxidizing properties for pollutants, and degrade pollutants. .

As shown in Figure 1, the full spectrum of XPS analysis of sulfur and nitrogen co-doped TiO ₂ (TL501), the peak with binding energy around 458.5eV is the characteristic peak of Ti2p, and the peak around 529eV is the characteristic peak of O1s, For the characteristic peak of C1s at 284.eV, it is impossible to judge whether it is the characteristic peak of contaminated C or the characteristic peak of doped C, because thiourea contains C element in the reacting elements, and it is likely that C is also mixed in during the reaction. TiO ₂ . The peak corresponding to the binding energy of 168eV is the characteristic peak of S2p, which indicates that S element also exists in some form in TiO ₂ . The main function of the XPS spectrum is to explain the valence state of the elements, and more recently, what form the elements exist in. The XPS of N1s and S2p here only shows the state of S and N in TiO ₂ , which can reduce the band gap. The characteristic of TL501 is that it has a high absorption rate of visible light, so that it can use visible light for photocatalysis (no ultraviolet light is required).

Figures 2 and 3 show the N1s high-resolution scans and S2p high-resolution scans of sulfur and nitrogen co-doped titanium dioxide (TL501), in which the characteristic peaks of N1s appear at the binding energies of 398.1eV, 400.0eV, and 402.1eV. , where 400eV is the characteristic peak of Ti-N bond, the peak at 402eV is the characteristic peak of NO bond, the peak at 398eV is the characteristic peak of NN; the two peaks of S element are at 168.6eV and 169.8eV respectively , these two outer peaks indicate the incorporation of S element into _TiO2 . The peak at 169.8eV is the characteristic peak of S ⁶⁺ , while the peak at 168.6eV is the characteristic peak of S ⁴⁺ . This indicates that sulfur element is incorporated into the TiO ₂ lattice in the manner of S ⁶⁺ and S ⁴⁺ . Compared with nitrogen-doped TiO ₂ , the nitrogen element in co-doped TiO ₂ not only increases in content, but also presents multivalent states. This may be due to the fact that S element was doped into TiO ₂ first, and N replaced the doped S ⁴⁺ and S ⁶⁺ in TiO ₂ during the subsequent heating process, forming a multivalent state.

Figure 4 shows the transmission electron microscope image of sulfur and nitrogen co-doped titanium dioxide (TL501). It can be seen from the figure that the particle size of co-doped _TiO2 is about 19nm, regular in shape, basically spherical, and uniform in size. This shows that the sample crystallization under this preparation condition is more complete.

Figure 5 shows the XRD analysis diagram of sulfur and nitrogen co-doped titanium dioxide (TL501). It can be seen from the figure that the co-doped TiO ₂ sample TL501 is an anatase phase. According to the XRD experimental results, Scherrer formula:

(where D _hkl is the grain size of the vertical plane hkl, λ is the X-ray wavelength, θ is the diffraction angle, K is a constant (usually 0.89), B _M is the broadening degree of the diffraction line at half intensity, and B _S is instrument broadening) to estimate the average particle size of _TiO2 particles. Calculation can be obtained: the particle size of TL501 is 18nm.

Comparative example 1

The sol-gel method was used to prepare undoped titanium dioxide, and the content, ratio and reaction temperature of the reactants were controlled in the same manner as in Example 1. Firstly, butyl titanate (Ti(OBu) ₄ ) and absolute ethanol (C ₂ H ₅ OH) were mixed according to a certain volume ratio, and ultrasonically oscillated for 5 minutes; then 5% HNO3 solution prepared with deionized high-purity water was added dropwise to adjust the pH value to about 4, and ultrasonic oscillation was continued for 5 minutes. Then use magnetic force (heating at a constant temperature of 60°C) to vibrate for 30 minutes, and obtain a stable, uniform, clear and transparent yellow-orange sol after aging for 4 hours; then, dry the sol in a drying oven at 100°C to obtain xerogel powder. A _TiO2 precursor prepared by the sol-gel method was obtained.

The reaction equation is: hydrolysis reaction: Ti(OR) ₄ +4H ₂ O→Ti(OH) ₄ +4ROH

Polymerization reaction: Ti(OH) ₄ +Ti(OR) ₄ →2TiO ₂ +4ROH

Ti(OH) ₄ +Ti(OH) ₄ →2TiO ₂ +4H ₂ O

As shown in Figure 6, the position of the absorption edge of Sol401 is 390nm, while the position of the absorption edge of TL501 is at 510nm, which is about 100nm red shifted from the sample Sol401. As shown in Figure 7-8, the band gap of the energy band of TL501 is reduced from 3.2eV to 2.92eV , the minimum excitation photon energy is 2.2eV. Due to the smaller band gap, photogenerated electrons and holes can be generated under the excitation of visible light (without ultraviolet light), which expands the light absorption range of TiO ₂ , makes better use of energy, and expands the use range of TiO ₂ , which can be used in visible light under photocatalysis.

Photocatalytic degradation experiment: Methyl orange is a colored compound that is difficult to degrade. The azo and quinone structures under acidic and alkaline conditions are the main structures of dye compounds. Therefore, using it as a dye model compound has certain representative.

As shown in Figure 9-10, blank represents the degradation curve of methyl orange without adding titanium dioxide. The prepared TL501 and Sol401 were respectively put into 0.02g/L methyl orange solution at a ratio of 2g/L, and the light source irradiated It is a high-pressure mercury lamp, and it is filtered by a 412nm filter, and the wavelength of the filtered light is around 412nm. During the catalysis, the solution was stirred continuously. The degree of degradation was expressed by the decolorization rate of methyl orange.

Take a sample every 20 minutes to check the methyl orange decolorization rate.

From Figure 10, we can see that the sol401 prepared by the sol-gel method has a degradation rate of methyl orange of 60% after 160 minutes, while the degradation rate of the titanium dioxide-doped sample TL501 reaches 93%, indicating that TL501 has visible light activity and is superior to undoped titanium dioxide under the same conditions, which is of great significance for the degradation of a class of pollutants such as methyl orange.

Doped titanium dioxide has a small band gap of only 2.92eV, which can absorb visible light and perform photocatalytic reactions, while undoped titanium dioxide has a large band gap of 3.15eV, weak absorption of visible light, and low catalytic efficiency.

Example 2

A method for preparing sulfur and nitrogen co-doped titanium dioxide. Grind 79.8 g of thiourea solid, 1.05 mol, then put it into 1500 ml of absolute ethanol, and stir the solution for 1 hour to 1.5 hours at a room temperature of 30° C. Urea is fully dissolved, and then 59.5 g of butyl titanate, about 0.175 mol, is slowly dropped into the ethanol solution of thiourea. The molar ratio of thiourea to butyl titanate is 6, so that thiourea and butyl titanate can fully react. Afterwards, it was evaporated under reduced pressure to obtain a light yellow slurry, which was left at room temperature for 48 hours and air-dried to obtain a light yellow powder, which was then fully ground. Finally, the calcination was carried out in an air-circulating environment, the calcination temperature was 500° C., and the temperature was gradually raised at room temperature at a heating rate of 5° C./min, and the calcination was carried out for 3 hours to obtain the target product.

Example 3

A preparation method of sulfur and nitrogen co-doped titanium dioxide, thiourea solid 39.9g, 0.525mol is ground, then put into 1000ml of absolute ethanol, at room temperature 40 ℃, the solution is stirred for 1 hour to 1.5 hours, let the sulfur The urea was fully dissolved, and then 59.5 g of butyl titanate, about 0.175 mol, was slowly dropped into the ethanol solution of thiourea. The molar ratio of thiourea to butyl titanate was 3, so that the thiourea and butyl titanate fully reacted. Afterwards, it was evaporated under reduced pressure to obtain a light yellow slurry, which was left at room temperature for 48 hours and air-dried to obtain a light yellow powder, which was then fully ground. Finally, calcining was carried out in an air-circulating environment, the calcining temperature was 600° C., and the temperature was gradually raised at room temperature at a heating rate of 5° C./min, and calcined for 3 hours to obtain the target product.

Example 4

A preparation method of sulfur and nitrogen co-doped titanium dioxide, thiourea solid 39.9g, 0.525mol is ground, then put into 500ml of absolute ethanol, at room temperature 40 ℃, the solution is stirred for 1 hour to 1.5 hours, let the sulfur Urea is fully dissolved, and then 59.5 g of butyl titanate, about 0.175 mol, is slowly dropped into the ethanol solution of thiourea. The molar ratio of thiourea to butyl titanate is 4, so that thiourea and butyl titanate fully react. Afterwards, it was evaporated under reduced pressure to obtain a light yellow slurry, which was left at room temperature for 24 hours and air-dried to obtain a light yellow powder, which was then fully ground. Finally, the calcination was carried out in an air-circulating environment, the calcination temperature was 700° C., the temperature was gradually raised at room temperature, and the temperature increase rate was 8° C./min, and the calcination was carried out for 3 hours to obtain the target product.

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the implementation of the present invention. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. All modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (6)

1. a preparation method of sulfur nitrogen co-doped titanium dioxide, is characterized in that: comprise the following steps: S1 joins thiourea in absolute ethanol, stirs until thiourea is fully dissolved; S2 adding butyl titanate to the absolute ethanol solution of thiourea, the molar ratio of thiourea to butyl titanate ranges from 6 to 3, and the thiourea and butyl titanate fully react; S3 evaporates the solution obtained in S2 under reduced pressure to form a light yellow slurry; S4 put the slurry obtained in S3 to air-dry at room temperature, and fully grind to obtain a light yellow powder; S5 Calcining the powder obtained in S3 in the air to obtain powdery sulfur and nitrogen co-doped titanium dioxide. 2. A method for preparing sulfur and nitrogen co-doped titanium dioxide according to claim 1, characterized in that: the reaction temperature in S2 is 18°C-40°C. 3 . The method for preparing sulfur and nitrogen co-doped titanium dioxide according to claim 1 , characterized in that: the air-drying time in S4 is 24-48 hours. 4. A method for preparing sulfur and nitrogen co-doped titanium dioxide according to claim 1, characterized in that: the optimum calcination temperature in S5 is 400-700°C. 5 . The method for preparing sulfur and nitrogen co-doped titanium dioxide according to claim 4 , characterized in that: the optimal calcination temperature in S5 is 500-600° C. 6. A method for preparing sulfur and nitrogen co-doped titanium dioxide according to claim 1, characterized in that: the calcination process of S5 adopts gradual temperature rise at room temperature, the temperature rise rate is 4-8°C/min, and the calcination time is 0.5-6h.