High-efficiency titanium dioxide photocatalyst with controllable crystal form and preparation method thereof

Abstract

The preparation method comprises the following steps: dissolving titanium potassium oxalate in water, sequentially adding ammonium sulfate and sodium chlorite, uniformly stirring to obtain a homogeneous mixed solution, and dropwise adding concentrated sulfuric acid to obtain a precursor solution; and carrying out hydrothermal reaction on the precursor solution, alternately washing the obtained precipitate with water and ethanol, and drying to obtain the efficient titanium dioxide photocatalyst. By accurately regulating and controlling the use amount of sodium chlorite, accurate regulation and control on the crystal phase composition of the product are successfully realized, and the prepared powder is in a blocky particle shape and has excellent monodispersity. According to the preparation process, subsequent high-temperature calcination or complex modification steps are not needed, energy consumption is reduced, doped element loss is avoided, the preparation process is simple and economical, and meanwhile the photocatalytic performance of titanium dioxide is remarkably improved. Compared with a commercial P25 photocatalyst, the double-phase titanium dioxide photocatalyst prepared by the invention has efficient degradation performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalysts, and particularly relates to a high-efficiency titanium dioxide photocatalyst with controllable crystal form and a preparation method thereof. BACKGROUND

[0002] In recent years, photocatalytic technology has shown great potential in the field of environmental governance. Titanium dioxide (TiO2) has become one of the most promising photocatalysts due to its high stability, non-toxicity, and low cost. Among them, the dual-phase titanium dioxide (such as anatase / rutile mixed phase) has attracted much attention due to its synergistic effect which significantly improves photocatalytic activity.

[0003] Although the dual-phase TiO2 synthesized by traditional methods can inhibit carrier recombination, the bulk defects and low electron mobility limit the rapid separation and transmission of photo-generated charges, resulting in a quantum efficiency much lower than the theoretical value. In addition, although noble metal doping (such as Pt / Au modification) can partially improve the performance, it further increases the cost of the material. For example, Degussa P25 requires the preparation of titanium tetrachloride by gas-phase combustion, which has high energy consumption, dangerous operation, and extremely harsh control of reaction conditions (temperature, gas flow rate), significantly increasing production costs and restricting large-scale applications. In addition, existing technologies generally involve toxic precursors (such as TiCl4), strong acid etching or high-temperature calcination steps, producing harmful by-products (such as chlorine gas and fluorine-containing waste liquid), which do not meet the concept of environmentally friendly synthesis and do not solve the biological toxicity of nanoparticles.

[0004] Therefore, it is an urgent need to develop a simple and efficient synthesis method for dual-phase titanium dioxide and simultaneously improve its photocatalytic performance. SUMMARY

[0005] This section aims to summarize some aspects of the embodiments of the application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the application.

[0006] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0007] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art and provide a preparation method of a high-efficiency titanium dioxide photocatalyst with controllable crystal form.

[0008] To solve the above technical problems, the present application provides the following technical solutions:

[0009] Titanium potassium oxalate is dissolved in water, ammonium sulfate and sodium chlorite are added in sequence, and the mixture is stirred uniformly to obtain a homogeneous solution, and then concentrated sulfuric acid is added dropwise to obtain a precursor solution;

[0010] The precursor solution is subjected to hydrothermal reaction, and the obtained precipitate is washed with water and ethanol alternately and dried to obtain the high-efficiency titanium dioxide photocatalyst.

[0011] The molar ratio of the potassium titanium oxalate, the ammonium sulfate and the sodium chlorite is 5:9-11:13-17.

[0012] As a preferred scheme of the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the molar ratio of the potassium titanium oxalate, the ammonium sulfate and the sodium chlorite is 5:11:17.

[0013] As a preferred scheme of the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the concentration of the potassium titanium oxalate aqueous solution is 0.1-0.15 mol / L.

[0014] As a preferred scheme of the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the addition amount of the concentrated sulfuric acid is 21-25 mol% compared to the total molar amount of the potassium titanium oxalate, the ammonium sulfate and the sodium chlorite.

[0015] As a preferred scheme of the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the temperature of the hydrothermal reaction is 140-160 ℃.

[0016] As a preferred scheme of the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the temperature of the hydrothermal reaction is 150 ℃.

[0017] As a preferred scheme of the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the time of the hydrothermal reaction is 10-12 h.

[0018] As a preferred scheme of the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the temperature of the drying is 45-50 ℃.

[0019] As a preferred scheme of the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the time of the drying is 8-9 h.

[0020] Another object of the present application is to provide a high-efficiency titanium dioxide photocatalyst with controllable crystal form prepared by the preparation method of the high-efficiency titanium dioxide photocatalyst with controllable crystal form.

[0021] As a preferred scheme of the high-efficiency titanium dioxide photocatalyst with controllable crystal form, the high-efficiency titanium dioxide photocatalyst has a dual-phase crystal structure.

[0022] Advantages of the present application:

[0023] (1) The present application uses a one-step hydrothermal method to prepare a photocatalyst powder with a dual-phase synergistic effect. By precisely controlling the amount of sodium chlorite, the composition of the product crystal phase is precisely controlled, and the powder is prepared in a blocky particle morphology with excellent monodispersity.

[0024] (2) The process does not require subsequent high-temperature calcination or complex modification steps, reducing energy consumption and avoiding the loss of doped elements. The preparation process is simple and economical, while significantly improving the photocatalytic performance of titanium dioxide.

[0025] (3) Compared with commercial P25 photocatalyst, the dual-phase titanium dioxide photocatalyst prepared by the present application has high degradation performance. Under simulated sunlight, the target pollutant methyl orange (MO) solution can be fully degraded within 10 minutes, with a degradation rate of 97.95%. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0027] Figure 1 The photocatalytic degradation effect of the titanium dioxide photocatalyst prepared in Examples 1-2 and Comparative Example 1 on MO solution under simulated sunlight is shown in the following figure.

[0028] Figure 2 The photocatalytic degradation effect of the titanium dioxide photocatalyst prepared in Examples 3 and Comparative Examples 2-3 on MO solution under simulated sunlight is shown in the following figure.

[0029] Figure 3 The XRD spectrum of the dual-phase TiO2 prepared in Examples 1, 3 and Comparative Example 2 without sodium chlorite is shown in the following figure.

[0030] Figure 4 The morphology comparison figure of the photocatalyst of Examples 1 and Comparative Example 3 is shown in the following figure.

[0031] Figure 5 The FTIR spectrum of the photocatalyst of Examples 1 and Comparative Example 3 is shown in the following figure.

[0032] Figure 6 The photocatalytic degradation rate of the high-efficiency TiO2 photocatalyst prepared in Example 1 on the target pollutant MO solution when different free radical trapping agents are added is shown in the following figure.

[0033] Figure 7 The effect diagram of the titanium dioxide catalyst prepared for the present application comparative example 4 on the photocatalytic degradation of MO solution under simulated sunlight. DETAILED DESCRIPTION

[0034] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the embodiments of the present application.

[0035] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0036] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is separate or alternative to other embodiments.

[0037] The potassium titanyl oxalate used in the present application is purchased from Shanghai Haohong Biomedical Technology Co., Ltd., the ammonium sulfate is purchased from Shanghai Yinn Chemical Technology Co., Ltd., the sodium chlorite is purchased from Shanghai Adamas Reagent Co., Ltd., and the concentrated sulfuric acid is purchased from Shanghai Titan Science and Technology Co., Ltd.

[0038] Example 1

[0039] The present embodiment provides a preparation method of a high-efficiency titanium dioxide photocatalyst with controllable crystal form, specifically:

[0040] 5mmol of potassium titanyl oxalate is dissolved in 50mL of water to obtain a 0.1mol / L potassium titanyl oxalate aqueous solution, 11mmol of ammonium sulfate and 17mmol of sodium chlorite are sequentially added, and the mixture is stirred uniformly to obtain a homogeneous mixed solution, then 0.5mL of concentrated sulfuric acid (concentration of 98%) is slowly added dropwise to obtain a precursor solution, wherein the molar ratio of potassium titanyl oxalate, ammonium sulfate and sodium chlorite is 5:11:17.

[0041] The precursor solution is placed in a high-pressure reaction kettle and hydrothermally reacted at 150℃ for 12h to obtain a precipitate, which is washed with deionized water and anhydrous ethanol three times and dried at 50℃ overnight, and finally a titanium dioxide photocatalyst powder is obtained.

[0042] Example 2

[0043] The difference between the present example and Example 1 is that the amount of ammonium sulfate is adjusted to 9 mmol, i.e. the molar ratio of potassium titanium oxalate, ammonium sulfate, sodium chlorite is adjusted to 5:9:17, and the rest of the preparation process is the same as that of Example 1, to obtain the titanium dioxide photocatalyst of the present example.

[0044] Comparative Example 1

[0045] The difference between the present example and Example 1 is that the amount of ammonium sulfate is adjusted to 9 mmol, i.e. the molar ratio of potassium titanium oxalate, ammonium sulfate, sodium chlorite is adjusted to 5:9:17, and the rest of the preparation process is the same as that of Example 1, to obtain the titanium dioxide photocatalyst of the present example.

[0046] The titanium dioxide photocatalysts prepared in Examples 1-2 and Comparative Example 1 are tested for photocatalytic degradation effect on MO solution under simulated sunlight, and the results are shown in Figure 1 (a) is the photocatalytic degradation rate of the catalyst prepared with different amounts of ammonium sulfate, and (b) is the change curve of the photocatalytic degradation rate constant K of the catalyst prepared with different amounts of ammonium sulfate with light irradiation time.

[0047] As can be seen from Figure 1 , under the condition of a certain amount of sodium chlorite, the degradation rate of the titanium dioxide photocatalyst first increases and then decreases with the increase of the amount of ammonium sulfate when the hydrothermal reaction temperature is controlled to be constant, and the degradation rate reaches about 100% and the photocatalytic degradation rate is the highest when the amount of ammonium sulfate is 11 mmol, i.e. the molar ratio of potassium titanium oxalate, ammonium sulfate, sodium chlorite is 5:11:17, and the degradation rate and degradation rate are also higher when the amount of ammonium sulfate is 9 mmol.

[0048] Example 3

[0049] The difference between the present example and Example 1 is that the amount of ammonium sulfate is adjusted to 9 mmol, i.e. the molar ratio of potassium titanium oxalate, ammonium sulfate, sodium chlorite is adjusted to 5:9:17, and the rest of the preparation process is the same as that of Example 1, to obtain the titanium dioxide photocatalyst of the present example.

[0050] Comparative Example 2

[0051] The difference between the present example and Example 1 is that the amount of ammonium sulfate is adjusted to 9 mmol, i.e. the molar ratio of potassium titanium oxalate, ammonium sulfate, sodium chlorite is adjusted to 5:9:17, and the rest of the preparation process is the same as that of Example 1, to obtain the titanium dioxide photocatalyst of the present example.

[0052] Comparative Example 3

[0053] The comparative example is a commercial P25 photocatalyst from De Gussa, a company of the Winnovia Industrial Group, Germany.

[0054] The photocatalytic degradation effect of the titanium dioxide catalyst prepared in Test Example 3 and Comparative Examples 2-3 on MO solution under simulated sunlight was tested, and the results are shown in Figure 2 . Among them, (a) is the photocatalytic degradation rate of the catalyst prepared with different amounts of sodium chlorite; (b) is the change curve of the photocatalytic degradation rate constant K of the catalyst prepared with different amounts of sodium chlorite with light irradiation time.

[0055] As can be seen from Figure 2 , with the increase of the amount of sodium chlorite, the degradation rate of the titanium dioxide photocatalyst first increases and then decreases, and the amount of sodium chlorite is 17 mmol, i.e. the molar ratio of potassium titanium oxalate, ammonium sulfate, and sodium chlorite is 5:11:17, which has the best effect, and has a higher degradation rate and reaction rate than the commercial P25 photocatalyst, while too high amount of sodium chlorite leads to poorer performance of the catalyst than the commercial P25.

[0056] The XRD spectrum of the dual-phase TiO2 prepared in Test Examples 1, 3 and Comparative Example 2 without sodium chlorite is shown in Figure 3 .

[0057] As can be seen from Figure 3 , the dual-phase TiO2 prepared without sodium chlorite has obvious diffraction peaks at 2θ of 25.28°, 37.8°, 48.05°, 55.06°, 62.69°, 68.76° and 75.03°, which correspond to the crystal faces (101), (004), (200), (211), (204), (116) and (215) in the XRD standard card (PDF #21-1272), and these diffraction peaks are characteristic peaks of anatase. Obvious diffraction peaks appear at 2θ of 27.45°, 36.09°, 41.23°, 44.05°, 54.32°, 56.64° and 69.79, which correspond to the crystal faces (110), (101), (111), (210), (211), (220) and (112) in the XRD standard card (PDF #21-1276), and these diffraction peaks are characteristic peaks of rutile, i.e. the prepared sample has a mixed crystal phenomenon, indicating that the prepared titanium dioxide has a dual-phase structure. In addition, with the increase of the amount of sodium chlorite from 9 mmol to 25 mmol, the intensity and position of each diffraction peak change to some extent.

[0058] The morphology of the photocatalysts of Test Example 1 and Comparative Example 3 was tested, and the results are shown in Figure 4 . Among them, (a) and (b) are commercial P25 photocatalysts; (c) and (d) are titanium dioxide photocatalysts prepared in Example 1.

[0059] As can be seen from Figure 4 , the P25 photocatalyst presents a state of particle aggregation, the particle size is relatively small and the distribution is relatively concentrated, and the particle surface is relatively rough, while the titanium dioxide photocatalyst presents an irregular blocky particle morphology, the particle size distribution range is wider, the size difference is obvious, indicating that it has good dispersibility, and the particle surface has certain undulations and concaves and convexes. Compared with P25, the particle morphology and size distribution of the titanium dioxide photocatalyst have obvious differences. This may be due to the biphase structure of titanium dioxide, which may break the original crystal growth rule, promote the formation of larger and more irregular particles, and thus have higher photodegradation rate and faster reaction rate.

[0060] The FTIR spectra of the photocatalysts of Test Example 1 and Comparative Example 3 were tested, and the results are shown in Figure 5 .

[0061] As can be seen from Figure 5 , P25 has an absorption peak at 3422 cm -1 , and TiO2 has an absorption peak at 3385 cm -1 , which is attributed to the O-H stretching vibration of the surface adsorbed water. P25 has absorption peaks at 2926 cm -1 and 3061 cm -1 , which correspond to C-H stretching vibration. TiO2 does not have obvious absorption peaks in this interval, which means that the prepared biphase titanium dioxide reduces the residual organic impurities. P25 has a strong absorption peak at 449 cm -1 , which corresponds to Ti-O bond vibration, and the Ti-O bond vibration peak of TiO2 shifts to 530 cm -1 , which is a red shift phenomenon due to the different crystal structure and phase ratio of the prepared biphase titanium dioxide from P25.

[0062] Further, in order to study the importance of each free radical in the reaction process of the efficient TiO2 photocatalyst, the photocatalytic degradation rate of TiO2 on the target pollutant MO solution was tested under simulated sunlight irradiation when different free radical trapping agents were added, and the results are shown in Figure 6 .

[0063] As can be seen from Figure 6 , with the addition of isopropyl alcohol, p-benzoquinone and disodium ethylenediaminetetraacetate, the photocatalytic degradation rate of TiO2 on the MO solution is reduced to different extents. With the addition of p-benzoquinone, the degradation rate of the MO solution decreases sharply, indicating that ·O 2- is the main active component in the system. At the same time, the addition of isopropyl alcohol and disodium ethylenediaminetetraacetate also reduces the degradation rate of the prepared catalyst on the MO solution to different extents, indicating that ·OH and h +Also play a role in the degradation of MO system by TiO2 photocatalyst. According to the inhibition degree of different free radical trapping agents on the photocatalytic degradation activity, the importance of each free radical in the reaction process of the high-efficiency TiO2 photocatalyst is in the order of:·O 2- >·OH>h + 。

[0064] Comparative Example 4

[0065] The difference between the present comparative example and Example 1 is that the temperature of the hydrothermal reaction is adjusted to 140℃, 160℃ and 180℃ respectively, and the rest of the preparation process is the same as that of Example 1, thereby obtaining the titanium dioxide photocatalyst of the present comparative example.

[0066] The photocatalytic degradation effect of the titanium dioxide catalyst prepared in Comparative Example 4 on MO solution under simulated sunlight is tested, and the results are shown in Figure 7 , wherein (a) is the photocatalytic degradation rate of the catalyst prepared at different hydrothermal temperatures; and (b) is the change curve of the photocatalytic degradation rate constant K of the catalyst prepared at different hydrothermal temperatures with light irradiation time.

[0067] As can be seen from Figure 7 , when the molar ratio of potassium titanium oxalate, ammonium sulfate and sodium chlorite is 5:11:17, the catalyst prepared by hydrothermal reaction at 150℃ has the best performance, and the degradation rate can reach 100%, and the reaction rate is fast. However, if the hydrothermal temperature is too high, the photocatalytic activity of titanium dioxide will be reduced or even deactivated.

[0068] Comparative Example 5

[0069] The difference between the present comparative example and Example 1 is that 17mL of sodium chlorite is adjusted to 60mL of 7.5wt% sodium hypochlorite, and the rest of the preparation process is the same as that of Example 1, thereby obtaining the titanium dioxide photocatalyst of the present comparative example.

[0070] The photocatalytic degradation effect of the titanium dioxide catalyst prepared in Comparative Example 5 on MO solution under simulated sunlight is tested, and the degradation rate reaches 68%, which is much lower than that of the photocatalyst prepared in Example 1.

[0071] In summary, the present application uses potassium titanium oxalate as the titanium source, ammonium sulfate as the in-situ pH regulator, and sodium chlorite as the oxidant. Ammonium sulfate neutralizes the acidic environment by releasing ammonium ions (NH4 + ), thereby controlling the rate of hydrolysis reaction; sodium chlorite provides an oxidizing environment to ensure the stability of titanium ions (Ti 4+ ) and the synergy of crystal face regulation.

[0072] The application realizes accurate control of the amount of sodium chlorite and ammonium sulfate, and one-step hydrothermal method is used to prepare photocatalyst powder with double-phase synergistic effect, so that accurate control of the crystal phase composition of the product is successfully realized, the powder is prepared in block granular morphology, and has excellent monodisperse characteristics. The process does not need subsequent high-temperature calcination or complex modification steps, reduces energy consumption and avoids loss of doped elements, and the preparation method is simple and economical, while significantly improving the photocatalytic performance of titanium dioxide.

[0073] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a highly efficient titanium dioxide photocatalyst with controllable crystal form, characterized in that: The application relates to a preparation method of a high-efficiency titanium dioxide photocatalyst. Titanium potassium oxalate is dissolved in water, ammonium sulfate and sodium chlorite are added in sequence, stirring is carried out to obtain a homogeneous mixed solution, and concentrated sulfuric acid is added dropwise to obtain a precursor solution; The precursor solution is subjected to a hydrothermal reaction, the obtained precipitate is washed with water and ethanol alternately, and then dried to obtain the high-efficiency titanium dioxide photocatalyst. The molar ratio of the titanium potassium oxalate, the ammonium sulfate and the sodium chlorite is 5:9-11:13-17.

2. The method of claim 1, wherein the preparation of the crystalline form-controllable high-efficiency titanium dioxide photocatalyst is characterized by: The molar ratio of the titanium potassium oxalate, the ammonium sulfate and the sodium chlorite is 5:11:

17.

3. The method of claim 1, wherein the preparation of the crystalline form-controllable high-efficiency titanium dioxide photocatalyst is characterized by: The concentration of the titanium potassium oxalate aqueous solution is 0.1-0.15 mol / L.

4. The method of claim 1, wherein the preparation of the crystalline form-controllable high-efficiency titanium dioxide photocatalyst is characterized by: The addition amount of the concentrated sulfuric acid is 21-25 mol% compared to the total molar amount of the titanium potassium oxalate, the ammonium sulfate and the sodium chlorite.

5. The method of claim 1, wherein the preparation of the crystalline form-controllable high-efficiency titanium dioxide photocatalyst is characterized by: The temperature of the hydrothermal reaction is 140-160 DEG C.

6. The method of claim 5, wherein the preparation of the crystalline form-controllable high-efficiency titanium dioxide photocatalyst is characterized by: The temperature of the hydrothermal reaction is 150 DEG C.

7. The method of claim 5, wherein the preparation of the crystalline form-controllable high-efficiency titanium dioxide photocatalyst is characterized by: The time of the hydrothermal reaction is 10-12 h.

8. The method of claim 1, wherein the preparation of the crystalline form-controllable high-efficiency titanium dioxide photocatalyst is characterized by: The temperature of the drying is 45-50 DEG C.

9. The method of claim 8, wherein the preparation of the crystalline form-controllable high-efficiency titanium dioxide photocatalyst is characterized by: The time of the drying is 8-9 h.

10. The high-efficiency titanium dioxide photocatalyst prepared by the preparation method according to any one of claims 1-9, characterized in that: The high-efficiency titanium dioxide photocatalyst has a double-phase crystal structure.

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