A Ce-W / TiO2-NS photocatalyst, its preparation method and application

Abstract

The present invention discloses a Ce-W / TiO2-NS photocatalyst and its preparation method and application, belonging to the technical field of material preparation and photocatalytic toluene oxidation. In the present invention, hydrothermal reaction is carried out by mixing HF and tetrabutyl titanate, and TiO2-NS is obtained after washing and drying. Then, TiO2-NS, ammonium metatungstate and cerium nitrate hexahydrate are mixed and subjected to hydrothermal reaction. After the reaction is completed, it is cooled, washed, dried and calcined to obtain the Ce-W / TiO2-NS photocatalyst. The Ce-W / TiO2-NS photocatalyst prepared by the two-step hydrothermal method in the present invention has excellent light absorption ability and photo-generated electron-hole transfer ability due to more oxygen defects and the synergistic effect between Ce and W atom pairs, resulting in significantly better toluene mineralization rate of Ce-W / TiO2 than that of Ce / TiO2 and W / TiO2, and is used for photocatalytic toluene oxidation.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation and photocatalytic toluene oxidation, and particularly relates to a Ce-W / TiO2-NS photocatalyst, a preparation method thereof and an application thereof. Background Art

[0002] Volatile organic compounds (VOCs) are a major type of indoor air pollutants. They have a wide range of sources and great harm, and thus have attracted much attention. As one of the most common VOCs, toluene widely exists in chemicals such as gasoline, paint, resin, adhesive, cosmetics and coatings. It is a highly toxic chemical substance that can cause serious harm to human health and the ecological environment. Therefore, effective measures need to be taken to control VOCs represented by toluene indoors.

[0003] The photocatalytic oxidation method has the characteristics of mild reaction conditions, low energy consumption required, harmless final products, etc., and its application in the treatment of toluene oxidation has attracted increasing attention. However, the photocatalytic toluene oxidation technology still has problems such as low toluene conversion rate and mineralization rate. Therefore, it is urgent to develop highly efficient and stable catalysts for photocatalytic oxidation of toluene to meet the actual needs.

[0004] For many years, TiO2 has been used as a classic photocatalyst and has been widely applied because of its high photocatalytic performance, high light corrosion resistance, chemical stability and non-toxicity, and at the same time has the characteristics of low cost, easy manufacture, easy composite modification, etc. However, the pure TiO2 semiconductor catalyst has a too wide band gap (3.2 eV), and can only absorb about 5% of the ultraviolet light in sunlight. In addition, there are few active sites available for reaction on its surface, and h + -e - pairs are easy to recombine, which ultimately leads to low photocatalytic toluene oxidation efficiency. Therefore, modification is needed to improve its reaction performance. Cerium (Ce) is an important rare earth metal. It has a low redox potential, a low oxygen vacancy formation energy and a unique 4f electron structure, which makes it easy to form a 4f-d structure with other metals and generate electron interaction. And W can be used as an independent photocatalyst in the form of WO3 and is also commonly used for the modification of TiO2. Due to the existence of various possible photoexcitation types, the band gap value range of WO3 is very wide (E g =2.6-3.3 eV), so it also has considerable photocatalytic activity under visible light. The WO x species formed on TiO2 can significantly increase the surface acidity of the catalyst; due to the increase in acidity, W / TiO2 can adsorb more hydroxyl groups and at the same time adsorb more organic reactants.

[0005] Therefore, it is necessary to provide a Ce-W / TiO2-NS photocatalyst. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the first technical problem to be solved by the present invention is to provide a Ce-W / TiO2-NS photocatalyst, which has excellent photocatalytic performance for toluene oxidation. The second technical problem to be solved by the present invention is to provide a preparation method of the Ce-W / TiO2-NS photocatalyst, which is simple and convenient, and the Ce-W / TiO2-NS photocatalyst can be prepared by using a two-step hydrothermal method. The third technical problem to be solved by the present invention is to provide the application of the Ce-W / TiO2-NS photocatalyst in photocatalytic toluene oxidation for photocatalytic toluene oxidation.

[0007] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0008] A Ce-W / TiO2-NS photocatalyst, the preparation method of the Ce-W / TiO2-NS photocatalyst is: mixing HF and tetrabutyl titanate for hydrothermal reaction, washing and drying to obtain TiO2-NS, then mixing TiO2-NS, ammonium metatungstate and cerium nitrate hexahydrate, and carrying out hydrothermal reaction. After the reaction is completed, cool, wash, dry and calcine to obtain the Ce-W / TiO2-NS photocatalyst.

[0009] Further, the loading ratio of Ce and W in the Ce-W / TiO2-NS photocatalyst is 1:1.

[0010] A preparation method of a Ce-W / TiO2-NS photocatalyst, the specific steps are as follows:

[0011] 1) Mix HF and tetrabutyl titanate, stir magnetically to obtain a suspension, put it into an oven for hydrothermal reaction. After the reaction is completed, cool, collect the precipitate, wash, and dry to obtain TiO2-NS;

[0012] 2) Disperse TiO2-NS in water to form a suspension; dissolve ammonium metatungstate in deionized water, adjust the pH by dropping concentrated nitric acid, add cerium nitrate hexahydrate and stir evenly, then mix with the TiO2-NS suspension, ultrasonicate and then carry out hydrothermal reaction. After the reaction is completed, cool, centrifuge to collect the precipitate, wash with distilled water, dry and calcine to obtain the Ce-W / TiO2-NS photocatalyst.

[0013] Further, in step 1), the volume ratio of HF to tetrabutyl titanate is 3:25.

[0014] Further, in step 1), when washing, first wash with acetone once, and then wash with deionized water three times.

[0015] Further, in step 2), the pH value is 1-2.

[0016] Further, in step 2), the concentration of the TiO2-NS suspension is 1 g / 30 mL.

[0017] Further, in step 2), the mass ratio of cerium nitrate hexahydrate, TiO2-NS and ammonium metatungstate is 0.0372:1:0.0214.

[0018] Application of the Ce-W / TiO2-NS photocatalyst in photocatalytic oxidation of toluene.

[0019] Further, the catalytic conditions are as follows: the light source is a 300 W xenon lamp, the concentration of toluene in the mixed gas is 20 ppm, and dark adsorption is carried out for 40 min before the photocatalytic reaction.

[0020] Beneficial effects: Compared with the prior art, the advantages of the present invention are as follows:

[0021] (1) The present invention uses a two-step hydrothermal method to prepare a Ce, W co-modified Ce-W / TiO2-NS photocatalyst material. Compared with TiO2, the prepared Ce-W / TiO2-NS photocatalyst material has a higher toluene conversion rate and mineralization rate.

[0022] (2) For the Ce-W / TiO2-NS photocatalyst material prepared in the present invention, there is a synergistic effect between Ce and W, and it has better photocatalytic toluene oxidation performance than the Ce / TiO2-NS and W / TiO2-NS catalyst materials loaded with Ce and W alone.

[0023] (3) The Ce-W / TiO2-NS photocatalyst material prepared in the present invention has more oxygen vacancies, which is more conducive to light absorption and the separation and transfer ability of photo-generated electron-hole pairs, so it has excellent photocatalytic toluene oxidation ability.

[0024] (4) The present invention utilizes the unique energy band structure of the TiO2 semiconductor material and its good catalytic oxidation performance for toluene. Coupled with the redox potential and acid sites generated by Ce and W, it provides the toluene adsorption and activation sites required for the reaction. The oxygen defects and the synergistic effect between Ce and W improve the light absorption and the separation and transfer ability of photo-generated electron-hole pairs, further enhancing the photocatalytic toluene oxidation reaction performance of the Ce-W / TiO2-NS photocatalyst. Description of the drawings

[0025] Figure 1 It is the XRD spectrum of the sample prepared in the present invention;

[0026] Figure 2 It is the TEM diagram of TiO2-NS and Ce-W / TiO2-NS prepared in the present invention;

[0027] Figure 3N2 adsorption - desorption result graph of the sample prepared according to the present invention;

[0028] Figure 4 FTIR spectrum of the sample prepared according to the present invention;

[0029] Figure 5 Raman spectrum of the sample prepared according to the present invention;

[0030] Figure 6 EPR graph of the sample prepared according to the present invention;

[0031] Figure 7 UV - vis DRS spectrum of the sample prepared according to the present invention;

[0032] Figure 8 Photocurrent response graph and impedance spectrum of the sample prepared according to the present invention;

[0033] Figure 9 Photocatalytic toluene oxidation performance comparison graph of the sample prepared according to the present invention. Detailed implementation manners

[0034] The present invention will be further described below in conjunction with specific embodiments.

[0035] Example 1

[0036] The method for preparing Ce - W / TiO2 - NS is as follows:

[0037] (1) Slowly add 3.6 mL of hydrofluoric acid (HF, 40%) dropwise to 30 mL of tetrabutyl titanate (C 16 H 36 O4Ti), stir magnetically for 40 min, then transfer the suspension to a 50 - mL reaction kettle with a polytetrafluoroethylene inner liner, and keep it in an oven at 200 °C for 24 h. After the reaction kettle cools down, centrifuge to collect the precipitate. Wash the precipitate once with acetone, then wash it three times with deionized water, and dry it overnight in an oven at 80 °C to prepare TiO2 - NS (TiO2 nanosheets).

[0038] (2) Weigh 1.0 g of the TiO2 - NS prepared in step (1), disperse it in 30 mL of deionized water, and stir it on a magnetic stirrer for 2 h to obtain a TiO2 - NS suspension. Add 0.0214 g of ammonium metatungstate (H 28 N6O 41 W 12) It was dissolved in 20 mL of deionized water, and concentrated nitric acid was added dropwise to adjust the pH to 1 - 2. After dilution to 50 mL, 0.0372 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) was added and stirred evenly, then added to the TiO2-NS suspension. After ultrasonic treatment for 30 min, it was transferred to a 100 mL reaction kettle with a polytetrafluoroethylene liner, and then heated at 180 °C for 12 h. After cooling, the sample was collected by centrifugation, washed three times with distilled water, dried at 80 °C for 12 h, and calcined in a muffle furnace at 300 °C for 3 h to obtain Ce-W / TiO2-NS (the loading amounts of Ce and W are both 0.3% molar fraction, and the loading ratio of Ce and W is 1:1). The results are as Figures 1 to 8 shown.

[0039] Example 2

[0040] The preparation method of Ce / TiO2-NS is as follows:

[0041] Weighed 1.0 g of TiO2-NS prepared in step (1) of Example 1, dispersed it in 30 mL of deionized water, and stirred it on a magnetic stirrer for 2 h to obtain a TiO2-NS suspension. 0.0372 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) was dissolved in 20 mL of deionized water, concentrated nitric acid was added dropwise to adjust the pH to 1 - 2, diluted to 50 mL and stirred evenly, then added to the TiO2-NS suspension. After ultrasonic treatment for 30 min, it was transferred to a 100 mL reaction kettle with a polytetrafluoroethylene liner, and then heated at 180 °C for 12 h. After cooling, the sample was collected by centrifugation, washed three times with distilled water, dried at 80 °C for 12 h, and calcined in a muffle furnace at 300 °C for 3 h to obtain Ce / TiO2-NS (the loading amount of Ce is 0.3% molar fraction). The results are as Figures 1 to 8 shown.

[0042] Example 3

[0043] The preparation method of W / TiO2-NS is as follows:

[0044] Weighed 1.0 g of TiO2-NS prepared in step (1) of Example 1, dispersed it in 30 mL of deionized water, and stirred it on a magnetic stirrer for 2 h to obtain a TiO2-NS suspension. 0.0214 g of ammonium metatungstate (H 28 N6O 41 W 12) It was dissolved in 20 mL of deionized water, and concentrated nitric acid was added dropwise to adjust the pH to 1 - 2. After dilution to 50 mL, it was stirred evenly and added to the TiO2-NS suspension. After ultrasonic treatment for 30 min, it was transferred to a 100 mL reaction kettle with a polytetrafluoroethylene inner lining, and then heated at 180 °C for 12 h. After cooling, the sample was collected by centrifugation, washed three times with distilled water, dried at 80 °C for 12 h, and calcined in a muffle furnace at 300 °C for 3 h to obtain W / TiO2-NS (the loading amount of W was 0.3% molar fraction). The results are as Figures 1 to 8 shown.

[0045] Figure 1 This is the XRD pattern of the samples prepared in the present invention. As can be seen from the figure, all the samples are anatase TiO2 (JCPDS#21 - 1272), and no diffraction peaks attributed to Ce and W appear, indicating that Ce and W are uniformly dispersed on the surface of the nanosheets.

[0046] Figure 2 This is the TEM image of TiO2-NS and Ce-W / TiO2-NS prepared in the present invention. Among them, (a) is TiO2-NS and (b) is Ce-W / TiO2-NS. As can be seen from the figure, both samples show the characteristics of nanosheets and have uniform sizes, about 55 - 65 nm, indicating that the secondary hydrothermal treatment did not change the morphology of the samples.

[0047] Figure 3 This is the N2 adsorption - desorption result graph of the samples prepared in the present invention. As can be seen from the figure, the pore size of the W / TiO2-NS sample is smaller than that of other samples, and the average pore size is 20.85 nm, which is the reason for its low adsorption capacity. And according to the BET formula, the specific surface areas of TiO2-NS, Ce / TiO2-NS, W / TiO2-NS and Ce-W / TiO2-NS are 56.48, 54.00, 52.10, 50.50 m 2 ·g -1 -1. The specific surface area of the Ce-W / TiO2-NS sample is smaller than that of the pure nanosheets, while the pore volume and pore size change little, because the Ce and W atoms block some of the pores of the TiO2 nanosheets.

[0048] Figure 4 This is the FTIR spectrum of the samples prepared in the present invention. As can be seen from the figure, the broad peaks at 1000 - 1100 cm -1 and 520 - 800 cm -1 represent the vibrations of Ti - O bonds and Ti - O - Ti bonds on the surface of TiO2. The peaks at 3400 cm -1 and 1650 cm -1There is an obvious vibration peak attributed to surface hydroxyl groups at this position, which does not appear in the other samples. The reason for this phenomenon is that the samples loaded with Ce and W are calcined at high temperature during the preparation process, resulting in the dehydroxylation of the catalyst surface. In addition, overlapping vibration peaks attributed to Ti-O, Ce-O, and W-O appear at 600 - 400 cm -1 There are overlapping vibration peaks attributed to Ti-O, Ce-O, and W-O at this position.

[0049] Figure 5 Figure is the Raman spectrum of the samples prepared in this invention. As can be seen from the figure, the A1g peak is caused by the asymmetric bending vibration of O-Ti-O. Magnifying the range of 100 - 200 cm -1 It can be seen that the Raman vibration peak of the Ce / W-loaded sample undergoes a blue shift at 145 cm -1 The displacement of the high-frequency Raman vibration peak is related to the formation of more oxygen vacancies, and the formation of oxygen vacancies is more conducive to the generation of surface reactive oxygen species, which is beneficial to the activation of oxygen.

[0050] Figure 6 Figure is the EPR diagram of the samples prepared in this invention. As can be seen from the figure, compared with TiO2-NS, more oxygen vacancies are generated in Ce / TiO2-NS, W / TiO2-NS, and Ce-W / TiO2-NS, which is beneficial to the generation of reactive oxygen species such as hydroxyl radicals and oxygen radicals, consistent with the Raman spectroscopy results.

[0051] Figure 7 Figure is the UV-vis DRS spectrum of the samples prepared in this invention. As can be seen from the figure, the light absorption ability of the catalyst is improved after loading Ce and W, and when Ce and W are loaded simultaneously, the light absorption ability of Ce-W / TiO2-NS is further improved, indicating that the synergistic effect of Ce and W is beneficial to light absorption.

[0052] Figure 8 Figure is the photocurrent response diagram and impedance spectrum of the samples prepared in this invention. As can be seen from the figure, the photocurrent intensity of Ce-W / TiO2-NS is much higher than that of other samples and it has the smallest EIS curve radius, indicating that it has the strongest ability to separate photo-generated electron-hole pairs. Moreover, the photocurrent response intensity of the single-metal-loaded samples is only slightly higher than that of the unloaded pure TiO2-NS, and at the same time, the EIS curve radius is slightly smaller than that of pure TiO2-NS, indicating that the synergistic effect of Ce and W is an important factor leading to the enhanced ability to separate photo-generated carriers.

[0053] Example 4

[0054] The photocatalysts prepared in Examples 1 - 3 were applied to the toluene oxidation reaction. The photocatalytic toluene oxidation reaction test was carried out in a flowing-phase reactor. The specific steps are as follows:

[0055] The reactor of the device is a stainless-steel reactor with a quartz transparent window on the top and capable of performing mobile-phase reactions. 50 mg of the catalyst was evenly spread on a 304 stainless-steel mesh, and there was a support below for support. After sealing the reaction vessel, a continuous mixed gas containing 50 ppm (the mixed gas is a mixture of toluene, air, and water vapor generated by air bubbling) was introduced into it, and the toluene concentration in the mixed gas was maintained at 20 ppm. The mixed gas entered the reactor through a stainless-steel pipe, and the outside of the stainless-steel pipe was wrapped with a heating tape to keep the temperature at 65 °C. Before the photocatalytic reaction, dark adsorption was carried out for 40 min, and then it was irradiated with a 300 W xenon lamp for 3 h. The gaseous products flowing out were on-line detected by gas chromatography (model GC-7920), and the detection time interval was 10 min. The reaction performance was evaluated through the following two formulas:

[0056]

[0057] Among them, C0 and Cx represent the toluene concentrations (ppm) at the inlet and outlet respectively, and C(CO2) is the CO2 concentration (ppm) at the outlet. The results are as Figure 9 shown.

[0058] Figure 9 is a comparative graph of the photocatalytic toluene oxidation performance of the samples prepared by the present invention. It can be seen from the figure that compared with TiO2-NS, Ce / TiO2-NS, W / TiO2-NS, and Ce-W / TiO2-NS have more excellent photocatalytic toluene oxidation performance, with a toluene conversion rate of 93.5% and a maximum mineralization rate of up to 48%. Moreover, due to having more oxygen defects and the synergistic effect between Ce and W, Ce-W / TiO2-NS has better photocatalytic toluene oxidation performance than Ce / TiO2-NS and W / TiO2-NS with single loading of Ce and W.

Claims

1. Application of Ce-W / TiO2-NS photocatalyst in photocatalytic toluene oxidation, characterized in that: The catalytic conditions were as follows: the light source was a 300 W xenon lamp, the concentration of toluene in the mixed gas was 20 ppm, and dark adsorption was performed for 40 min before the photocatalytic reaction; The preparation method of the photocatalyst comprises the following specific steps: (1) Slowly add 3.6 mL of 40% HF hydrofluoric acid to 30 mL of tetrabutyl titanate C. 16 H 36 After magnetic stirring in O4Ti for 40 min, the suspension was transferred to a 50 mL polytetrafluoroethylene-lined reactor and kept in an oven at 200 °C for 24 h. After the reactor was cooled, the precipitate was collected by centrifugation, washed once with acetone, then washed three times with deionized water, and dried in an oven at 80 °C overnight to prepare TiO2 nanosheets TiO2-NS. (2) Weigh 1.0 g of the TiO2-NS prepared in step (1), disperse it in 30 mL of deionized water, and stir on a magnetic stirrer for 2 h to obtain a TiO2-NS suspension; 0.0214 g ammonium metatungstate H 28 N6O 41 W 12 Dissolved in 20 mL of deionized water, concentrated nitric acid was added dropwise to adjust the pH to 1-2, diluted to 50 mL, 0.0372 g of cerium nitrate hexahydrate Ce(NO3)3·6H2O was added and stirred evenly, then added to the TiO2-NS suspension, ultrasonically treated for 30 min, transferred to a 100 mL polytetrafluoroethylene-lined reactor, and then heated at 180 ℃ for 12 h; after cooling, the sample was collected by centrifugation and washed three times with distilled water, dried at 80 ℃ for 12 h, and calcined in a muffle furnace at 300 ℃ for 3 h to obtain Ce-W / TiO2-NS, with the loading amounts of Ce and W being 0.3% molar fraction and the loading ratio of Ce to W being 1:1.

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