A MOF / TiO2 air purification material, a preparation method and application thereof

Abstract

The application discloses a MOF / TiO2 air purification material and a preparation method and application thereof. The MOF / TiO2 air purification material is a Fe-BDC / TiO2 photocatalyst with a Z-type heterojunction structure, and comprises a Fe-BDC framework and titanium dioxide particles loaded on the Fe-BDC framework, wherein the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst is 1-10%. The nano TiO2 and Fe-BDC are subjected to heterostructure construction, the light absorption range is expanded, the recombination rate of photo-generated carriers is reduced, the photocatalytic efficiency and service life are improved, and the research and development of the new TiO2-based composite material for indoor air treatment have important significance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of air purification materials, in particular to a MOF / TiO2 air purification material and a preparation method and application thereof. BACKGROUND

[0002] Volatile organic compounds (VOCs) are the main pollutants of indoor air, such as benzene series, aldehydes, alcohols and ketones, etc. Most of VOCs have toxic, irritating, teratogenic and carcinogenic effects, which seriously threaten human health. Photocatalysis technology, as a green and cost-effective technology, can completely oxidize and degrade typical VOCs under indoor mild light conditions. Titanium dioxide (TiO2) is considered to be the best indoor air treatment material due to its low cost, non-toxicity and good stability. However, TiO2 has a low photocatalytic degradation efficiency in actual use due to the easy recombination of photo-generated carriers and the narrow light absorption range, and has a short service life in indoor environments with high benzene series concentration.

[0003] Metal-Organic Frameworks (MOFs) is a kind of porous nanomaterial composed of metal ions or metal clusters and bridged organic ligands. MOFs have the advantages of high porosity, large specific surface area, adjustable structure and multiple active sites. Among them, gel-like Fe-BDC (terephthalic acid) is of great concern to the industry due to its low preparation cost, environmental protection and unique physical and chemical properties. However, Fe-BDC has no VOCs degradation function. SUMMARY

[0004] In view of the above problems, the present application provides a MOF / TiO2 air purification material and a preparation method and application thereof. By heterostructure construction of nano-TiO2 and Fe-BDC, the light absorption range is expanded, the recombination rate of photo-generated carriers is reduced, and the photocatalytic efficiency and service life are improved. The development of new TiO2-based composite materials for indoor air treatment is of great significance.

[0005] In the first aspect, the present application provides a MOF / TiO2 air purification material, which is a Fe-BDC / TiO2 photocatalyst with Z-type heterojunction structure, comprising a Fe-BDC framework and titanium dioxide particles loaded on the Fe-BDC framework, wherein the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst is 1-10%.

[0006] Preferably, the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst is 2-10%.

[0007] Preferably, the Fe-BDC framework is in a dry gel state, and the particle size is 1-5 μm.

[0008] Preferably, the size of the titanium dioxide nanoparticles is 5-50 nm, and the nanoparticles are aggregated to form aggregated particles with a size of 1-5 μm; preferably, the titanium dioxide nanoparticles are packed to form meso / macroporous packing holes.

[0009] In a second aspect, the present application provides a preparation method of the MOF / TiO2 air purification material according to any one of the above, wherein Fe-BDC and TiO2 are formed into a Fe-BDC / TiO2 photocatalyst with a Z-type heterojunction structure by electrostatic self-assembly.

[0010] Preferably, Fe-BDC and TiO2 are ultrasonically dispersed in water and stirred at room temperature for a period of time, and then dried to form a Fe-BDC / TiO2 photocatalyst with a Z-type heterojunction structure.

[0011] Preferably, the TiO2 is calcined at 300-400°C for 1-5 hours before use.

[0012] Preferably, the stirring time is 2-24 hours.

[0013] In a third aspect, the present application provides an application of the MOF / TiO2 air purification material according to any one of the above in photocatalysis. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is an XRD spectrum of TiO2, Fe-BDC, 2% Fe-BDC / TiO2, 5% Fe-BDC / TiO2 and 10% Fe-BDC / TiO2.

[0015] Figure 2 is an SEM spectrum (a-c) and an EDS spectrum (d) of TiO2, Fe-BDC and 5% Fe-BDC / TiO2.

[0016] Figure 3 is an ultraviolet-visible light diffuse reflection spectrum of TiO2, Fe-BDC, 2% Fe-BDC / TiO2, 5% Fe-BDC / TiO2 and 10% Fe-BDC / TiO2.

[0017] Figure 4 is an acetaldehyde adsorption curve of TiO2 and 5% Fe-BDC / TiO2 in dark reaction.

[0018] Figure 5 is an acetaldehyde adsorption amount of TiO2 and 5% Fe-BDC / TiO2 in dark reaction.

[0019] Figure 6 is an acetaldehyde degradation curve of TiO2, 2% Fe-BDC / TiO2, 5% Fe-BDC / TiO2 and 10% Fe-BDC / TiO2.

[0020] Figure 7 is the acetaldehyde degradation rate model of TiO2, 2% Fe-BDC / TiO2, 5% Fe-BDC / TiO2, 10% Fe-BDC / TiO2.

[0021] Figure 8 is the degradation efficiency curve of Fe-BDC on acetaldehyde.

[0022] Figure 9 is the PL spectrum (a), photocurrent response spectrum (b) and electrochemical impedance spectrum (c) of 5% Fe-BDC / TiO2 and TiO2.

[0023] Figure 10 is the superoxide radical spectrum (a) and hydroxyl radical spectrum (b) of 5% Fe-BDC / TiO2 and TiO2. DETAILED DESCRIPTION

[0024] The present application is further illustrated by the following embodiments, which should be understood as merely illustrative of the present application, but not limiting the present application. Unless otherwise specified, each percentage refers to mass percentage.

[0025] The MOF / TiO2 air purification material described in the present application comprises Fe-BDC framework and titanium dioxide particles loaded on the Fe-BDC framework. In the present application, the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst is 1-10%. Controlling the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst in the above range can ensure that the composite material has optimized light utilization capacity on the basis of maintaining good gas adsorption capacity. When the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst is less than 1%, the light absorption range and photocatalytic performance of the TiO2 photocatalyst are not significantly improved. When the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst is higher than 10%, it will have an adverse effect on the specific surface area and gas adsorption capacity of the composite material. In the preferred technical solution, the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst is 5%.

[0026] The MOF / TiO2 air purification material described in the present application is a Fe-BDC / TiO2 photocatalyst with Z-type heterojunction structure. The formation of Z-type heterojunction structure can effectively promote the separation of photo-generated electrons and holes in TiO2, so that the photo-generated electrons and holes can successfully migrate to the surface of the catalyst without recombination, and react with adsorbed water / oxygen to produce highly active hydroxyl / superoxide radicals, thereby facilitating the occurrence of photocatalytic reaction.

[0027] The Fe-BDC framework is in a xerogel state, has a flat surface, and has a small amount of small pores. In some embodiments, the particle size of the Fe-BDC framework can reach 1-5 μm.

[0028] The size of the titanium dioxide nanoparticles is about 5-50 nm, the nanoparticles form agglomerated particles with a size of about 1-5 μm, and the nanoparticles are stacked to form meso / macroporous stacking holes.

[0029] The preparation method of the MOF / TiO2 air purification material is described below.

[0030] The Fe-BDC and TiO2 are ultrasonically dispersed in water to obtain a mixed solution.

[0031] The TiO2 can be calcined at 300-400 ℃ for 1-5 hours before use. This can effectively remove the organic matter on the surface of the TiO2 and ensure that the material has good crystallinity. For example, the TiO2 can be calcined at 350 ℃ for 2 hours.

[0032] The mixed solution is stirred at room temperature for a period of time. In some embodiments, the stirring time is 2-24 hours. For example, the stirring time is 6 hours.

[0033] The Fe-BDC is preferably in a gel phase. The gel phase Fe-BDC can form a large number of small crystals after ultrasonic dispersion in water, and then form a uniform sol. After mixing with the TiO2 nanoparticles, the small crystals adhere to the surface of the TiO2 nanoparticles to form a uniform and stable Z-type heterojunction structure.

[0034] Then, the Fe-BDC / TiO2 photocatalyst with a Z-type heterojunction structure is dried. After drying, the Fe-BDC small crystals in the Fe-BDC / TiO2 and the TiO2 are in close contact, and the band structures of the two are matched to form the Fe-BDC / TiO2 photocatalyst with a Z-type heterojunction structure.

[0035] The Fe-BDC and TiO2 are combined by electrostatic self-assembly to form the Fe-BDC / TiO2 photocatalyst with a Z-type heterojunction structure. The electrostatic self-assembly method is a fast and efficient method for preparing MOF / TiO2-based composite photocatalyst materials. In the synthesis process, the gel phase Fe-BDC is ultrasonically dispersed in water to obtain a sol formed by a large number of small crystals uniformly dispersed. These small crystals are uniformly attached to the surface of the TiO2 nanoparticles. After drying, the Fe-BDC small crystals in the Fe-BDC / TiO2 and the TiO2 are in close contact, and the band structures of the two are matched to form the Fe-BDC / TiO2 photocatalyst with a Z-type heterojunction structure.

[0036] The MOF / TiO2 air purification material has higher photocatalytic activity, is suitable for the field of indoor air purification, and has good application prospect. Moreover, the electrostatic self-assembly preparation method is simple in process, convenient to operate, does not need complex and expensive equipment, and is easy to realize industrial production.

[0037] The application further provides application of the MOF / TiO2 air purification material in photocatalysis. By constructing a heterostructure of nano-TiO2 and Fe-BDC, the light absorption range is expanded, the recombination rate of photo-generated carriers is reduced, the photocatalytic efficiency and service life are improved, and the development of a new TiO2-based composite material for indoor air treatment has important significance.

[0038] The following further illustrates the embodiments to further illustrate the application. It should also be understood that the following embodiments are only used to further illustrate the application, and cannot be understood as limiting the protection scope of the application. Some non-essential improvements and adjustments made by those skilled in the art according to the above content of the application all belong to the protection scope of the application. The specific process parameters in the following examples are only one example in the appropriate range, that is, those skilled in the art can select within the appropriate range through the description herein, and are not limited to the specific values in the following examples.

[0039] Example 1

[0040] 1 mmol of FeCl3·6H2O was added in 50 mL of DMF, and after stirring at room temperature for 30 minutes, 1 mmol of terephthalic acid (H2BDC), 4 mL of ethanol, 4 mL of deionized water and 1.5 mL of triethanolamine were sequentially added. After continuing to stir for 12 hours, centrifugal washing was performed, the colloids were collected, and freeze-drying was performed to obtain a gel phase Fe-BDC. Nano-TiO2 was calcined at 350 DEG C for 2 hours. 5 mg of Fe-BDC and 95 mg of calcined TiO2 were ultrasonically dispersed in 50 mL of deionized water, respectively, and were mixed and stirred at room temperature for 6 hours. After centrifugal washing and drying, 5% Fe-BDC / TiO2 was obtained.

[0041] Example 2

[0042] Except that the mass ratio of Fe-BDC and TiO2 added was changed to 2 mg and 98 mg, 2% Fe-BDC / TiO2 was prepared in the same manner as in Example 1.

[0043] Example 3

[0044] Except that the mass ratio of Fe-BDC and TiO2 added was changed to 10 mg and 90 mg, 10% Fe-BDC / TiO2 was prepared in the same manner as in Example 1.

[0045] Comparative Example 1

[0046] In 50 mL DMF, 1 mmol FeCl3·6H2O was added, stirred at room temperature for 30 minutes, then 1 mmol of terephthalic acid (H2BDC), 4 mL of ethanol, 4 mL of deionized water, 1.5 mL of triethanolamine were added in turn, and the stirring was continued for 12 hours. After centrifugal washing, the gel was collected, freeze-dried to obtain the gel phase Fe-BDC.

[0047] Figure 1 The XRD spectra of TiO2, Fe-BDC and 2% Fe-BDC / TiO2, 5% Fe-BDC / TiO2, 10% Fe-BDC / TiO2 obtained in Examples 1-3. It can be seen that the crystal structure of TiO2 in the composite material has not changed significantly. No characteristic peaks of Fe-BDC were observed in the three composite systems, which is due to the low doping amount of Fe-BDC and the small grain size and low crystallinity of the gel phase Fe-BDC.

[0048] Figure 2 The SEM spectra (a-c) and EDS spectra (d) of TiO2, Fe-BDC and 5% Fe-BDC / TiO2 obtained in Example 1. It can be seen that in the 5% Fe-BDC / TiO2 composite material, Fe-BDC is successfully compounded on the surface of TiO2 nanoparticles, and the microstructure of TiO2 has not changed significantly.

[0049] Figure 3 The UV-Vis diffuse reflectance spectra of TiO2, Fe-BDC and 2% Fe-BDC / TiO2, 5% Fe-BDC / TiO2, 10% Fe-BDC / TiO2 obtained in Examples 1-3. It can be seen that compared with single TiO2, the light absorption edge of the composite material has a significant red shift, indicating that the introduction of gel phase Fe-BDC effectively expands the light absorption range of the composite material. And with the increase of the amount of gel phase Fe-BDC introduced, the visible light absorption capacity of the composite material is significantly improved.

[0050] Acetaldehyde adsorption capacity and photocatalytic degradation efficiency test: 0.1 g of the powder to be tested was added to 3 g of anhydrous ethanol, ultrasonicated for 0.5 h, and then dropped on a 7.5 cm x 15 cm glass plate and dried. The dark reaction adsorption and photocatalytic performance test were carried out by flowing phase acetaldehyde gas. The initial concentration of acetaldehyde gas was 500 ppm, the flow rate was 20 sccm, the light irradiation condition was 250 W xenon lamp, the distance from the sample was 30 cm, and the acetaldehyde adsorption capacity and photocatalytic degradation efficiency were calculated.

[0051] The degradation efficiency of 5% Fe-BDC / TiO2 coating of Example 1 is 44.6%. The degradation efficiency of 2% Fe-BDC / TiO2 coating of Example 2 is 32.4%. The degradation efficiency of 10% Fe-BDC / TiO2 coating of Example 3 is 35.5%. The degradation efficiency of Examples 1-3 is improved compared to the degradation efficiency of pure TiO2 powder, which is 19.1%.

[0052] Figure 4 The dark reaction acetaldehyde adsorption curves of TiO2 and 5% Fe-BDC / TiO2 are shown in FIG. 2. It can be seen that both TiO2 and the composite material can effectively adsorb low concentration acetaldehyde molecules in the flow phase.

[0053] Figure 5 The acetaldehyde adsorption capacities of TiO2 and 5% Fe-BDC / TiO2 are shown in FIG. 3. It can be seen that the acetaldehyde adsorption capacity of the composite material is lower than that of TiO2, which may be due to the fact that the introduction of the gel phase Fe-BDC during the synthesis process aggravates the agglomeration of TiO2 nanoparticles to some extent. Compared to TiO2, the pore size and specific surface area of the composite material are reduced. On the other hand, the active sites of Fe-BDC are limited in type and cannot effectively adsorb acetaldehyde molecules, resulting in a decrease in the number of acetaldehyde adsorption sites in the composite material with the addition of Fe-BDC.

[0054] Figure 6 The acetaldehyde degradation curves of TiO2 and 2% Fe-BDC / TiO2, 5% Fe-BDC / TiO2, 10% Fe-BDC / TiO2 obtained in Examples 1-3 are shown in FIG. 4. It can be seen that the acetaldehyde degradation efficiency of the composite material is improved from about 19.1% to about 44.6% (5% Fe-BDC / TiO2) compared to TiO2. This is mainly due to the fact that the introduction of Fe-BDC expands the light utilization range of the composite material, improves the separation efficiency of photo-generated carriers, and is conducive to the generation of highly active oxidative free radicals.

[0055] Figure 7 The acetaldehyde degradation rate models of TiO2, 2% Fe-BDC / TiO2, 5% Fe-BDC / TiO2, 10% Fe-BDC / TiO2 are shown in FIG. 5. It can be seen that the acetaldehyde degradation rate of the composite material is improved by nearly 1.5 times (5% Fe-BDC / TiO2) compared to TiO2. This is mainly due to the fact that the introduction of Fe-BDC promotes the generation of highly active oxidative free radicals, thereby accelerating the occurrence of the catalytic oxidation reaction of acetaldehyde.

[0056] Figure 8 The acetaldehyde degradation efficiency curve of Fe-BDC is shown in FIG. 6. It can be seen that single Fe-BDC has no photocatalytic degradation ability for acetaldehyde, indicating that the improvement in the acetaldehyde degradation efficiency of the composite material is mainly due to the formation of Z-type heterojunction between the two.

[0057] The TiO2 and the 5% Fe-BDC / TiO2 sample powder obtained in Example 1 were characterized by fluorescence spectroscopy (PL spectrum). The above powder was dispersed in an alcohol solution and spin-coated on FTO glass as a working electrode, a platinum sheet as a counter electrode, a saturated Ag / AgCl as a reference electrode, and a xenon lamp as a light source to characterize the photocurrent response spectrum and electrochemical impedance spectrum of the sample.

[0058] Figure 9 Fig. 5 is the PL spectrum (a), photocurrent response spectrum (b) and electrochemical impedance spectrum (c) of 5% Fe-BDC / TiO2 and TiO2. It can be seen that compared with single TiO2, the PL spectrum peak intensity of the composite material is significantly reduced, the photocurrent response intensity is improved, and the impedance is reduced, indicating that the conductivity of the composite material is effectively improved, and the photo-generated carrier recombination is effectively inhibited, which is due to the formation of Z-type heterojunction to realize the spatial separation of photo-generated electrons and holes.

[0059] The TiO2 and the 5% Fe-BDC / TiO2 sample obtained in Example 1 were characterized by free radicals. The above sample powder was dispersed in an ethanol solution, DMPO was added as a free radical trapping agent, and the solution was irradiated under a xenon lamp after mixing. Finally, a certain amount of mixed solution was sucked by a capillary, and after being covered with a quartz tube, it was placed in an EPR sample cavity for testing of hydroxyl radicals and superoxide radicals.

[0060] Figure 10 Fig. 6 is the (a) superoxide radical spectrum and (b) hydroxyl radical spectrum of 5% Fe-BDC / TiO2 and TiO2. It can be seen that compared with single TiO2, the introduction of Fe-BDC effectively promotes the generation of hydroxyl radicals and superoxide radicals, which is due to the formation of heterojunction to expand the light utilization range of the composite material, while avoiding the recombination of photo-generated carriers, so that more photoexcited electrons / holes migrate to the surface of the catalyst, and hydroxyl radicals / superoxide radicals are generated with adsorbed water / oxygen.

[0061] Comparative Example 2

[0062] FeCl3·6H2O was used as the metal source, added into DMF and stirred to obtain a brown transparent solution. Then H2BDC was added as the ligand to the above solution under stirring. After stirring for ten minutes, a mixed solution of ethanol and deionized water was added to the above transparent solution. TEA was added to promote the deprotonation of the organic ligand. After stirring the above solution for a period of time, the obtained solid product was separated and washed, and a dry gel phase Fe-BDC was obtained by freeze-drying. 5 mg of the gel phase Fe-BDC and 95 mg of ZnO were respectively ultrasonically dispersed in 50 mL of deionized water, mixed at room temperature and stirred for 6 hours, then centrifuged, washed and dried to obtain 5% Fe-BDC / ZnO, and the acetaldehyde adsorption and photocatalytic degradation capacity thereof were characterized. Studies have shown that the 5% Fe-BDC / ZnO composite material has no photocatalytic degradation capacity for the flowing phase acetaldehyde under the same reaction conditions described in the application.

[0063] Comparative Example 3

[0064] 5 mg of the gel phase MIL-100(Fe) and 95 mg of calcined TiO2 were respectively ultrasonically dispersed in 50 mL of deionized water, mixed at room temperature and stirred for 6 hours, then centrifuged, washed and dried to obtain 5% MIL-100(Fe) / TiO2, and the acetaldehyde adsorption and photocatalytic degradation capacity thereof were characterized. Studies have shown that the 5% MIL-100(Fe) / TiO2 composite material has no obvious improvement in photocatalytic degradation capacity for the flowing phase acetaldehyde compared with single TiO2 under the same reaction conditions described in the application, because the band structure of the two cannot be matched to form a Z-type heterojunction.

[0065] Comparative Example 4

[0066] FeCl3·6H2O was used as the metal source, H2BDC was used as the ligand, and DMF was added and stirred. The above solution was moved into a reaction kettle, and a crystalline phase Fe-BDC was obtained by solvothermal reaction. Nano-TiO2 was calcined at 350°C for 2 hours. 5 mg of the crystalline phase Fe-BDC and 95 mg of calcined TiO2 were respectively ultrasonically dispersed in 50 mL of deionized water, mixed at room temperature and stirred for 6 hours, then centrifuged, washed and dried to obtain 5% Fe-BDC / TiO2-2, and the photocatalytic degradation acetaldehyde performance thereof was characterized. Compared with single TiO2, the performance of the composite material has no obvious improvement. This is due to the large crystal size of the crystalline phase Fe-BDC, which cannot be closely combined with TiO2 nanoparticles to form a Z-type heterojunction.

Claims

1. A method for preparing a MOF / TiO2 air purification material, characterized in that, The MOF / TiO2 air purification material is a Fe-BDC / TiO2 photocatalyst with Z-type heterojunction structure formed by electrostatic self-assembly of gel phase Fe-BDC and TiO2; wherein the gel phase Fe-BDC and the calcined TiO2 are ultrasonically dispersed in water and stirred at room temperature for 2-24 hours, and then dried to form the Fe-BDC / TiO2 photocatalyst, and the TiO2 is calcined at 300-400℃ for 1-5 hours before use to ensure that the TiO2 has good crystallinity; the MOF / TiO2 air purification material comprises a Fe-BDC framework in xerogel state and titanium dioxide nanoparticles loaded on the Fe-BDC framework, wherein the mass percentage of Fe-BDC in the Fe-BDC / TiO2 photocatalyst is 2%-10%.

2. The production method according to claim 1, characterized by, The particle size of the Fe-BDC framework is 1-5 μm.

3. The production method according to claim 1, characterized by, The size of the titanium dioxide nanoparticles is 5-50 nm, and the nanoparticles are aggregated to form aggregated particles with a size of 1-5 μm.

4. The production method according to claim 1, characterized by, The accumulation of titanium dioxide nanoparticles produces meso / macroporous accumulation pores.

5. Application of the MOF / TiO2 air purification material obtained by the preparation method of any one of claims 1 to 4 in photocatalysis.

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