CN113735163B - Porous titanium dioxide material containing oxygen vacancies and preparation method and application thereof - Google Patents

Porous titanium dioxide material containing oxygen vacancies and preparation method and application thereof Download PDF

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CN113735163B
CN113735163B CN202111144639.3A CN202111144639A CN113735163B CN 113735163 B CN113735163 B CN 113735163B CN 202111144639 A CN202111144639 A CN 202111144639A CN 113735163 B CN113735163 B CN 113735163B
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titanium dioxide
porous titanium
dioxide material
oxygen vacancies
hexavalent chromium
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CN113735163A (en
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翟茂林
李爽笑
石伟群
王琳
彭静
李久强
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Peking University
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Abstract

The invention discloses a porous titanium dioxide material containing oxygen vacancies, a preparation method and application thereof, and the porous titanium dioxide material is prepared by taking Ti-based MXene as a precursor and utilizing a radiation oxidation method to prepare lamellar porous titanium dioxide containing oxygen vacancies. The porous titanium dioxide material has the characteristics of high specific surface area and strong visible light absorption, and can be used as a photocatalyst to be applied to photocatalytic reduction reaction, for example, the photocatalytic high-efficiency reduction of hexavalent chromium is realized under visible light. The adopted preparation method of irradiation oxidation is simple, convenient and quick, has a pure system, overcomes the defects of high energy consumption, need of adding additional oxidant and the like of the existing method, and is easy for mass large-scale production.

Description

Porous titanium dioxide material containing oxygen vacancies and preparation method and application thereof
Technical Field
The invention relates to the technical field of inorganic nano materials and photocatalysts, in particular to a lamellar porous titanium dioxide material containing oxygen vacancies and taking Ti-based MXene as a precursor, and a preparation method and application of the material.
Background
Titanium dioxide is a widely studied transition metal oxide material, and is widely noticed due to its excellent stability, low cost, and environmentally friendly characteristics, and is considered to be one of the most promising photocatalyst materials. However, the forbidden band width of titanium dioxide is about 3.2eV, and the larger forbidden band width enables the titanium dioxide to only utilize ultraviolet light which accounts for 4% of the total energy of sunlight, so that the practical application of the titanium dioxide is limited; in addition, the titanium dioxide in the bulk phase has a small specific surface area and cannot be in sufficient contact with the reactants, which is also not favorable for the performance of the material.
Researches show that oxygen vacancies are introduced into the semiconductor titanium dioxide, so that the electronic structure of the semiconductor titanium dioxide can be regulated and controlled, and the visible light absorption performance of the semiconductor titanium dioxide is improved; in addition, the regulation and control of the morphology and the increase of the specific surface area of the material are effective strategies for improving the photocatalytic performance of the titanium dioxide material. MXene is a novel two-dimensional transition metal carbo/nitride, which is used in multiple fieldsThe domain shows huge potential, and the series of derivatives with MXene as a precursor also receives wide attention. MXene is used as a precursor, so that on one hand, the shape of the oxide is favorably regulated and controlled, and a material with large specific surface area is obtained; on the other hand, the MXene structure also makes the material obtained by oxidation conversion have more diverse structures, and defect vacancies are easy to generate. For example, Qian et al use Ti3C2TxMXene as precursor, carbon-doped titanium dioxide containing oxygen vacancy is obtained by calcining in air, and the performance of photocatalytic Nitrogen Reduction for ammonia production is studied (J.Qian et al3C2 MXene Derived Oxygen Vacancy-Rich C/TiO2Adv. susatinable syst.2021,5,2000282); ZHEN et al use the thermal ethanol method to remove some Ti3C2TxMXene is converted into titanium dioxide containing oxygen vacancies, and the resulting composite (V-TiO)2/Ti3C2Tx) Used as an electrocatalyst for lithium-Oxygen batteries (R.Zheng et al. in Situ Fabricating Oxygen Vacancy-Rich TiO)2 Nanoparticles via Utilizing Thermodynamically Metastable Ti Atoms on Ti3C2Tx MXene Nanosheet Surface To Boost Electrocatalytic Activity for High-Performance Li-O2Batteries, acs appl, material, interfaces 2019,11, 46696-; in addition, Chinese patent publication No. CN 113120958A discloses a Chinese patent publication No. V2CTxMXene is used as a precursor and is prepared into lamellar vanadium oxide by adopting a heat treatment method.
At present, the oxidation methods adopted by the related researches using MXene as a precursor mainly comprise a calcination method, a chemical oxidation method, a hydrothermal method, a solvothermal method and the like. These methods require high temperature and high pressure or require the addition of an additional oxidizing agent, and are not well controllable, and the resulting materials are easily stacked and have relatively small specific surface areas. Therefore, Ti-based MXene is used as a precursor, and a more green, environment-friendly and efficient method is developed for preparing the porous titanium dioxide material containing oxygen vacancies and having a high specific surface area, so that the method has important significance in meeting the requirements of mass production and practical application.
Disclosure of Invention
The invention aims to provide a porous titanium dioxide which takes Ti-based MXene as a precursor and is prepared into lamellar oxygen-containing vacancies by a radiation oxidation method, has the characteristics of high specific surface area and strong visible light absorption, and further provides a photocatalyst capable of realizing efficient reduction of hexavalent chromium under visible light. The irradiation oxidation method adopted by the invention is simple, convenient and rapid, has a pure system, and overcomes the defects of high energy consumption, the need of adding additional oxidant and the like of the existing method.
Specifically, the technical scheme of the invention is as follows:
a lamellar porous titanium dioxide material containing oxygen vacancies, which is prepared by a radiation oxidation method and takes Ti-based MXene as a precursor, and the synthesis method comprises the following steps: and introducing oxidizing gas into the aqueous dispersion of the Ti-based MXene nanosheets, sealing, irradiating by using gamma rays or electron beams, washing the irradiated product, dispersing in water, and freeze-drying to obtain the lamellar porous titanium dioxide material containing oxygen vacancies.
The Ti-based MXene nanosheet can be prepared by adding a Ti-based MAX parent material into a mixed solution of lithium fluoride and hydrochloric acid for reaction. Wherein the Ti-based MAX matrix material is selected from one of the following: ti3AlC2、Ti3AlCN、Ti2AlC, and Ti-based MXene nanosheets correspondingly obtained are respectively Ti3C2Tx、Ti3CNTx、Ti2CTxAnd T represents a surface group attached to the Ti atom, and mainly comprises one or more of the following groups: o, OH, Cl and F, x being the number of surface groups.
Specifically, the preparation steps of the lamellar porous titanium dioxide material containing oxygen vacancies are as follows:
1) mixing lithium fluoride and hydrochloric acid with a certain concentration, placing the mixture in a reaction container, adding a Ti-based MAX matrix material, reacting at a constant temperature for a period of time, centrifugally washing for multiple times after the reaction is finished, and obtaining aqueous dispersion of Ti-based MXene nanosheets through ultrasonic stripping delamination and centrifugal separation;
2) adjusting the pH value of aqueous dispersion of Ti-based MXene nanosheets with a certain concentration, vibrating to uniformly mix the aqueous dispersion, introducing oxidizing gas for a period of time, and sealing;
3) irradiating the dispersion sealed in the step 2) by using gamma rays or electron beams;
4) cleaning the product irradiated in the step 3) for many times, dispersing the product in water, and freeze-drying to obtain the lamellar porous titanium dioxide material containing oxygen vacancies.
In step 1) of the above method, the Ti-based MAX precursor material is selected from one of the following substances: ti3AlC2、Ti3AlCN、Ti2AlC, and Ti-based MXene nanosheets correspondingly obtained are respectively Ti3C2Tx、Ti3CNTx、Ti2CTx. The concentration of the hydrochloric acid is 6-12 mol/L, the concentration of the lithium fluoride in the mixed solution is 1-3 mol/L, the reaction temperature is 30-50 ℃, and the reaction time is 1-3 days. The solvent used in the centrifugal washing process is water, the pH value is 5-6 after washing, the power of ultrasonic stripping layering is 40-100W, and the ultrasonic time is 10-60 min; in the centrifugal separation step, the rotating speed of the centrifugal process is 2000-3500 rpm, the centrifugal time is 10-30 min, and the upper-layer dispersion liquid is the aqueous dispersion liquid of the Ti-based MXene nanosheets.
In the step 2) of the method, the mass concentration of the aqueous dispersion of the Ti-based MXene nanosheets is preferably 0.1-2 mg/mL, and the oxidizing gas may be any one of the following gases: laughing gas, oxygen and oxidizing gas are introduced for 10-20 min. Adjusting the pH value to 5-9 by using an alkali solution, wherein the alkali solution can be selected from one or more of the following substances: sodium hydroxide, potassium hydroxide and ammonia water.
In the step 3) of the method, the irradiation dose rate can be 10-500 Gy/min, the absorbed dose can be 100-600 kGy, and the gamma rays can be selected from60Co or137Cs and other radiation sources, and electron beams are generated by an electron accelerator (the energy is 0.15-10 MeV).
In step 4), the solvent used for washing may be selected from any one or more of the following: deionized water, methanol and ethanol. A centrifugal cleaning method can be adopted, the rotating speed in the centrifugal process can be 3000-10000 rpm, the centrifugal time is 5-15 min, and the centrifugal times are 3-6.
The invention also provides application of the prepared lamellar porous titanium dioxide material containing oxygen vacancies as a photocatalyst in photocatalytic reduction reaction, such as application in photocatalytic reduction of hexavalent chromium, hexavalent uranium and perrhenate, photocatalytic reduction of water to produce hydrogen and photocatalytic reduction of nitrogen to produce ammonia.
Adding the laminar porous titanium dioxide material containing oxygen vacancy, which is obtained by the invention, into an aqueous solution containing hexavalent chromium, stirring the mixture for a period of time in a dark box of photocatalytic reaction at a certain temperature by using citric acid as a sacrificial agent, and after adsorption equilibrium is reached, realizing the photocatalytic reduction of the hexavalent chromium under the illumination condition of a xenon lamp (provided with a UVCUT 400nm long-wavelength pass filter).
The specific test method is as follows: preparing a hexavalent chromium solution by using potassium dichromate, adding the hexavalent chromium solution with a certain initial concentration into a quartz reactor, using citric acid as a sacrificial agent, wherein the concentration of the citric acid is 0.1-1 mmol/L, adding a certain amount of lamellar porous titanium dioxide material containing oxygen vacancies prepared by the invention, adjusting the solid-to-liquid ratio of a photocatalytic system to be 0.1-1 mg/mL, adjusting the pH value to be 1-7 by using sulfuric acid and sodium hydroxide, placing the quartz reactor into a dark box for photocatalytic reaction, stirring at the temperature of about 25 ℃ for 30-60 min, and determining the concentration of hexavalent chromium to be C0(ii) a Then, a xenon lamp (provided with a UVCUT 400nm long-wavelength pass filter) is turned on, samples are taken at intervals and filtered, diphenylcarbazide is taken as a color developing agent, and the concentration C of hexavalent chromium is measured by an ultraviolet spectrophotometryt. By calculating Ct/C0And evaluating the performance of the material in the aspect of photocatalytic reduction of hexavalent chromium along with the change of the illumination time t.
The invention has the following advantages:
1) the invention adopts oxidative free radicals generated by a gamma ray or electron beam radiation method to realize the room-temperature oxidation of Ti-based MXene, provides a new oxidation method of Ti-based MXene, obtains the lamellar porous titanium dioxide material containing oxygen vacancies, has excellent performance of reducing hexavalent chromium by visible light catalysis, and has obvious effect on the conversion of toxic and harmful hexavalent chromium.
2) Compared with materials obtained by other oxidation methods, the lamellar titanium dioxide material derived from Ti-based MXene obtained by the invention has a porous structure and oxygen vacancies, and the porous structure endows the lamellar titanium dioxide material with a large specific surface area, so that the lamellar titanium dioxide material can be in full contact with hexavalent chromium ions, and the reaction rate of photocatalytic reduction of hexavalent chromium can be increased; in addition, the abundant oxygen vacancies improve the utilization efficiency of visible light, and the hexavalent chromium has excellent photocatalytic reduction performance under the visible light (lambda is more than 400 nm).
3) According to the method for radiating and oxidizing the Ti-based MXene, provided by the invention, the strong-oxidizing free radicals are uniformly and continuously generated in the whole system, so that the Ti-based MXene can be converted into the titanium dioxide material containing oxygen vacancies in situ, and meanwhile, the lamellar structure of the Ti-based MXene is maintained in the oxidation process. In addition, the etching of the Ti-based MXene C or N layer in the radiation oxidation process is beneficial to generating holes on the sheet layer, and high specific surface area is obtained. Compared with the traditional chemical oxidation method, the radiation method can be carried out at room temperature, is simple to operate and easy to regulate and control, and is easy for mass production.
Drawings
FIG. 1 shows that the invention utilizes a radiation oxidation method to prepare laminar porous titanium dioxide (OV-porous TiO) containing oxygen vacancy by using Ti-based MXene as a precursor2) Schematic process diagram of (1).
FIG. 2 shows Ti in example 13AlCN and Ti3CNTxX-ray diffraction (XRD) pattern of the nanoplatelets.
Fig. 3 is an XRD spectrum of the lamellar oxygen vacancy-containing porous titania prepared in example 1.
FIG. 4 is an electron spin resonance (EPR) diagram of the lamellar oxygen vacancy-containing porous titania prepared in example 1.
FIG. 5 is a high resolution X-ray photoelectron spectroscopy (XPS) of oxygen element of the lamellar oxygen vacancy-containing porous titania prepared in example 1.
FIG. 6 is a Transmission Electron Microscope (TEM) image of the lamellar oxygen vacancy-containing porous titania prepared in example 1.
FIG. 7 is a nitrogen adsorption and desorption curve of the lamellar oxygen vacancy-containing porous titania prepared in example 1.
FIG. 8 is a graph showing the effect of visible light photocatalytic reduction of hexavalent chromium for the lamellar porous titania containing oxygen vacancies prepared in example 1 and the material obtained in comparative example 1.
FIG. 9 is a nitrogen adsorption/desorption curve of the material obtained in comparative example 1.
Detailed Description
The present invention will be described in detail below by referring to examples, but the present invention is not limited thereto. The following examples are given without specific reference to the conventional conditions, and the reagents and materials are commercially available.
Example 1
With Ti3CNTxMXene is a lamellar porous titanium dioxide material containing oxygen vacancies of a precursor, the preparation process of which is shown in figure 1 and comprises the following steps:
1) adding 3.20g LiF and 40mL of 9mol/L hydrochloric acid into a plastic bottle with a gas-guide tube at the bottle opening, uniformly stirring, and slowly adding 2.00g of Ti3AlCN, reacting in 35 deg.C water bath for 2 days, and absorbing tail gas with 5% NaOH water solution. After the reaction is finished, the lower-layer precipitate is separated out through centrifugation, the supernatant is discarded, and deionized water is added for multiple times of centrifugal washing until the pH value of the dispersion liquid is 6. Treating with 40W ultrasonic wave in an ultrasonic instrument for 60min, and centrifuging at 2500rpm for 30min to obtain upper layer dispersion liquid as Ti3CNTxAqueous dispersion of MXene nanosheets.
2) Ti obtained in the above3CNTxDiluting the aqueous dispersion of MXene nanosheets to 2mg/mL, adding a small amount of 5mol/L sodium hydroxide solution into 75mL of the obtained dispersion to adjust the pH value to 6, shaking to uniformly mix the dispersion, and introducing laughing gas for 20 min; and sealing the container, and then sending the container to a cobalt source chamber for gamma-ray irradiation, wherein the dose rate is 120Gy/min, and the absorbed dose is 450 kGy. Centrifuging the irradiated product (6000rpm,15min), discarding the supernatant, adding 30mL deionized water, centrifuging again, repeating the process for cleaning for 3 times, centrifuging for the last time, discarding the supernatant, dispersing in 10mL deionized water, and freeze-drying in a freeze-dryer for 48 h. Drying to obtain lamellar porous titanium dioxide material containing oxygen vacanciesThe specific surface area of the material is 401m2The oxygen vacancy proportion was 13.3%.
3) The obtained lamellar porous titanium dioxide material containing oxygen vacancies is used for the photocatalytic reduction of hexavalent chromium. In a photocatalysis experiment, 30mL of hexavalent chromium solution with the initial concentration of 20ppm is added into a quartz reactor, the solid-to-liquid ratio of a photocatalysis system is 1mg/mL, the concentration of citric acid is 1mmol/L, the pH value is adjusted to 3 by using 1mol/L sulfuric acid and 1mol/L sodium hydroxide, after stirring for 60min in a dark box of a photocatalysis reaction, a xenon lamp (provided with a UVCUT 400nm long-wave pass filter) is turned on, and after irradiation of visible light for 120 min, the removal rate of hexavalent chromium of the material serving as a photocatalyst is 100%.
FIG. 2 is Ti3AlCN raw material and Ti prepared in step 1)3CNTxXRD pattern of MXene nanosheet. As can be seen from FIG. 2, Ti3CNTxOccurrence of diffraction peak corresponding to (002) crystal face of MXene located at about 7.3 degrees and Ti3The disappearance of diffraction peaks corresponding to AlCN parent material proves that Ti with high purity and nano lamellar structure3CNTxSuccessful synthesis of MXene.
Fig. 3 is an XRD chart of the prepared lamellar oxygen vacancy-containing porous titanium dioxide, and it can be seen that distinct anatase characteristic peaks appear at 25.4 ° and the like, indicating that the prepared titanium dioxide material is mainly in anatase crystal form, and the broadening of the peaks further indicates the existence of oxygen vacancies.
Fig. 4 is an EPR chart of the porous titania material produced in a lamellar state containing oxygen vacancies, and it can be seen that the signal peak g ═ 2.009 in which oxygen vacancies are clearly present. In the course of room-temperature radiation oxidation, Ti3CNTxThe existence of the surface fluorine-containing group in MXene is beneficial to forming abundant oxygen vacancies on the surface of MXene, so that the titanium dioxide containing the oxygen vacancies is successfully prepared.
Fig. 5 is an XPS high resolution plot of oxygen element in the prepared lamellar porous titania material containing oxygen vacancies, which can further demonstrate the existence of oxygen vacancies, and the proportion of oxygen vacancies formed is 13.3%.
The TEM image of FIG. 6 shows that, after radiation oxidation, Ti3CNTxNano meterConversion of flakes into porous TiO2Nanosheets, due to the tendency of oxidation of Ti at the surface to convert in situ to lamellar TiO during irradiation2And Ti3CNTxThe oxidation of C and N in the nanosheets will create pores in the lamellae.
FIG. 7 is a nitrogen adsorption and desorption curve of the prepared lamellar porous titanium dioxide material containing oxygen vacancies, and the specific surface area of the porous titanium dioxide material is 401m2The high specific surface area is due to its porous lamellar structure.
Fig. 8 shows the reduction effect of the lamellar porous titanium dioxide material containing oxygen vacancies on hexavalent chromium, and it can be seen from the figure that the lamellar porous titanium dioxide material containing oxygen vacancies obtained under the condition can completely remove hexavalent chromium within 120 minutes, which shows that the lamellar porous titanium dioxide containing oxygen vacancies obtained by radiating oxidation of Ti-based MXene has good reduction effect on hexavalent chromium under visible light.
Example 2
Will be as in example 160The Co gamma ray is changed into an electron beam generated by an electron accelerator, the absorption dose rate is 50kGy/pass, the absorption dose is 450kGy, and other conditions are the same as those in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 353m2/g-1The oxygen vacancy proportion is 18.1%, and the removal rate of hexavalent chromium is 100%.
Example 3
Ti in step 1) of example 13Conversion of AlCN to Ti3AlC2The concentration of hydrochloric acid is changed to 12mol/L, the temperature of water bath is changed to 40 ℃, and the obtained dispersion liquid is Ti3C2TxAqueous dispersion of MXene nanosheets. The other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 233m2The oxygen vacancy proportion is 12.1 percent, and the removal rate of hexavalent chromium is 85 percent.
Example 4
Ti in step 1) of example 13Conversion of AlCN to Ti2The concentration of AlC and hydrochloric acid is changed to 6mol/L, and the obtained dispersion liquid is Ti2CTxMXene nano-sheetAn aqueous dispersion of (1). The other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 343m2The oxygen vacancy proportion is 5.6 percent, and the removal rate of hexavalent chromium is 88 percent.
Example 5
The concentration of Ti-based MXene in step 2) of example 1 was changed to 1mg/mL, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 427m2The oxygen vacancy proportion is 13.0 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 6
The concentration of Ti-based MXene in step 2) of example 1 was changed to 0.5mg/mL, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 435m2The oxygen vacancy proportion is 12.6 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 7
The volume of Ti-based MXene in step 2) of example 1 was changed to 50mL, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 381m2The oxygen vacancy proportion is 11.6 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 8
The volume of Ti-based MXene in step 2) of example 1 was changed to 30mL, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 365m2The oxygen vacancy proportion is 10.9 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 9
The pH was changed to 9 in step 2) of example 1, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 451m2The oxygen vacancy proportion is 11.8 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 10
The pH was changed to 7 in step 2) of example 1, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 430m2The oxygen vacancy ratio is 12.8 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 11
The pH was changed to 5 in step 2) of example 1, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 390m2The oxygen vacancy proportion is 14.3 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 12
The absorption dose rate in example 1 was changed to 150Gy/min, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 446m2The oxygen vacancy proportion is 14.0 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 13
The absorption dose rate in example 1 was changed to 55Gy/min, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 366m2The oxygen vacancy proportion is 11.0 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 14
The absorption dose rate in example 1 was changed to 10Gy/min, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 243m2The oxygen vacancy proportion is 8.0 percent, and the removal rate of hexavalent chromium is 90 percent.
Example 15
The gas introduction in step 2) of example 1 was changed to oxygen, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 335m2The oxygen vacancy proportion is 15.4 percent, and the removal rate of hexavalent chromium is 97 percent.
Example 16
The absorbed dose in example 1 was changed to 100kGy, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 366m2 g-1The oxygen vacancy proportion is 14.3%, and the removal rate of hexavalent chromium is 100%.
Example 17
The absorbed dose in example 1 was changed to 200kGy, which isThe conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 391m2The oxygen vacancy proportion is 13.8 percent, and the removal rate of hexavalent chromium is 100 percent.
Example 18
The absorbed dose in example 1 was changed to 600kGy, and the other conditions were the same as in example 1. The specific surface area of the obtained lamellar porous titanium dioxide material containing oxygen vacancies is 401m2The oxygen vacancy proportion is 11.5 percent, and the removal rate of hexavalent chromium is 100 percent.
Comparative example 1
Based on H2O2Oxygen vacancy-containing TiO synthesized by chemical oxidation method2。
To Ti obtained in step 1) of example 13CNTxAdding 30 wt% of H into a certain volume of aqueous dispersion of MXene nanosheets2O2So that Ti in the system3CNTxThe concentration of MXene nano-sheet is 2mg/mL, H2O2Was 3 wt%, and was stirred until the reaction was complete. Washing with water, and freeze drying to obtain H2O2Oxidation process synthesized oxygen vacancy containing TiO2。
FIG. 9 is a nitrogen adsorption/desorption curve of the material obtained in comparative example 1, which was calculated to have a specific surface area of 53m2The volume ratio of the porous titanium dioxide material is far less than that of a lamellar oxygen vacancy-containing porous titanium dioxide material obtained by radiation oxidation (the specific surface area is 401 m)2As can be seen from fig. 8, the removal rate of hexavalent chromium of the material obtained in comparative example 1 under the same test conditions is 44%, which is much smaller than that of the lamellar oxygen vacancy-containing porous titanium dioxide material obtained by radiation oxidation.
Compared with the common chemical oxidation, the hydroxyl radical with strong oxidizing property generated by the radiation oxidation has stronger oxidizing capability, so that holes, cracks and the like are favorably generated on the sheet layer in the irradiation process; in addition, because the hydroxyl radicals are continuously and uniformly generated in the irradiation system, the hydroxyl radicals and Ti are generated in the radiation oxidation process3CNTxMXene nano-sheets are contacted more fully, the oxidation process is more uniform, and stacking in the oxidation process is reduced, so thatThe oxidation products have a higher specific surface area. While the high specific surface area facilitates the contact of the material with hexavalent chromium and the subsequent reduction removal.
The above description is only an example of the present invention and is not intended to limit the present invention. For a person skilled in the art, on the basis of the above description, various changes and modifications can be made to the technical solutions in the embodiments. And are neither required nor exhaustive of all embodiments. Any modification, variation, replacement, etc. based on the technical content disclosed in the present invention should be included in the protection scope of the present invention.

Claims (5)

1. A preparation method of a porous titanium dioxide material comprises the following steps:
1) mixing lithium fluoride and hydrochloric acid with the concentration of 6-12 mol/L, adding a Ti-based MAX matrix material, reacting at the constant temperature of 30-50 ℃ for 1-3 days, centrifuging and washing for multiple times by using water after the reaction is finished until the pH value is 5-6, and obtaining aqueous dispersion of the Ti-based MXene nanosheets through ultrasonic stripping layering and centrifugal separation, wherein the ultrasonic power of the ultrasonic stripping layering is 40-100W, the ultrasonic time is 10-60 min, the rotating speed of the centrifugal separation is 2000-3500 rpm, the centrifugal time is 10-30 min, and the upper-layer dispersion is the aqueous dispersion of the Ti-based MXene nanosheets;
2) adjusting the mass concentration of the aqueous dispersion of the Ti-based MXene nanosheets to 0.1-2 mg/mL, adjusting the pH value to 5-9, shaking to uniformly mix the dispersion, introducing oxidizing gas laughing gas or oxygen for a period of time, and sealing;
3) irradiating the dispersion liquid sealed in the step 2) by using gamma rays or electron beams, wherein the irradiation dose rate is 10-500 Gy/min, and the absorption dose is 100-600 kGy;
4) cleaning the product irradiated in the step 3) for many times, dispersing the product in water, and freeze-drying to obtain the lamellar porous titanium dioxide material containing oxygen vacancies.
2. The method of claim 1, wherein the step of preparing the composition comprisesIn step 1), the Ti-based MAX matrix material is selected from one of the following substances: ti3AlC2、Ti3AlCN、Ti2AlC, and Ti-based MXene nanosheets correspondingly obtained are respectively Ti3C2T x 、Ti3CNT x 、Ti2CT x Wherein T represents a surface group attached to the Ti atom, including one or more of the following groups: o, OH, Cl or F,xthe number of surface groups.
3. A porous titania material obtained by the production process according to claim 1 or 2.
4. Use of the porous titania material of claim 3 as a photocatalyst in a photocatalytic reduction reaction.
5. The use of claim 4, wherein the photocatalytic reduction reaction is a photocatalytic reduction of hexavalent chromium, the porous titanium dioxide material is added to an aqueous solution containing hexavalent chromium, citric acid is used as a sacrificial agent, and the porous titanium dioxide material is stirred for a period of time at a certain temperature in a dark box of the photocatalytic reaction, after reaching an adsorption equilibrium, the photocatalytic reduction of hexavalent chromium is achieved under light conditions.
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