CN104897655A - Method for rapidly detecting oxygen vacancy in titanium oxide - Google Patents

Abstract

The invention discloses a method for rapidly detecting oxygen vacancies in titanium oxide. In this method, the gas molecule ether and oxygen are first diffused onto the surface of titanium oxide; since the oxygen vacancies on the surface of titanium oxide have a strong ability to adsorb oxygen molecules, the oxygen adsorbed to the oxygen vacancies forms superoxide with strong oxidative properties by capturing a free electron. species (O ₂ ^- ), and then, the chemically adsorbed ether molecules react with O ₂ ^- to generate excited acetaldehyde molecules (CH ₃ CHO ^* ), and the process of returning the excited acetaldehyde molecules to the ground state will generate a certain amount of energy , the energy is released in the form of optics, and the luminescence signal value is detected by a chemiluminescence analyzer. According to the relationship between the amount of oxygen vacancies and the luminescence signal, the value of oxygen vacancies in titanium oxide is obtained. The method has the advantages of simple equipment, rapidity and easy operation. It has broad application prospects for the evaluation of oxygen vacancies, which are widely studied in defect oxides.

Description

A method for rapid detection of oxygen vacancies in titanium oxide

technical field

The invention belongs to the research field of titanium oxide catalysts, and in particular relates to a method for rapidly detecting oxygen vacancies in titanium oxide by utilizing the correlation between oxygen vacancies of titanium oxide and ether-catalyzed luminescent reactions, and using ether as a molecular probe.

Background technique

Titanium oxide has excellent optical properties, high chemical stability, thermal stability, non-toxicity and large storage capacity in nature, and has shown good development prospects in many fields. The study found that the properties of titanium oxide are not only dependent on its geometry and electronic structure, but also affected by its defect structure. At present, many scientific workers have devoted themselves to the research on the chemical, electrical and optical properties of titanium oxide defects in order to better control the concentration of oxygen vacancies to promote catalytic reactions. Among these TiO defects, oxygen vacancies are considered to be of outstanding research significance. Theoretical calculations and experimental characterization show that the oxygen vacancies in TiO2 can act as photogenerated electron traps, thereby effectively enhancing its photocatalytic activity. Therefore, it is of great significance to effectively evaluate the concentration of oxygen vacancies in titania to regulate the properties of titania by appropriate means.

However, oxygen vacancies are difficult to detect due to their unstable and low-concentration nature. The methods currently used for oxygen vacancy detection mainly include surface titration, electron paramagnetic spectroscopy (ESR), and X-ray photoelectron spectroscopy (XPS). For example: AN Petrov, Solid State Ionics 1995, 80, _189-199 This document uses the surface titration method, which is a traditional qualitative and quantitative analysis method for oxygen vacancies. A certain error occurs. Literature Xu, X.Inorg.Chem.2015, 54, 1556-1562 used electron paramagnetic spectroscopy (ESR) to effectively characterize oxygen vacancies, but usually this method has relatively high system requirements and requires professional technology Personnel operation; Literature Murray, CBJAm.Chem.Soc.2012, 134, 6751-6761 uses X-ray photoelectron spectroscopy (XPS), and uses the XPS binding energy of O 1s to characterize the oxygen vacancies on the surface of TiO ₂ well, However, this method is relatively expensive and time-consuming, which limits the wide applicability of this technology. It is very important to develop a quick and easy method to evaluate oxygen vacancies in titanium oxide.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, and provide a method for rapidly detecting oxygen vacancies in titanium oxide, which is simple and quick, and has high practical application prospects.

In this method, ether molecules are used as probes, and the correlation between the catalytic activity of TiO ₂ doped with metal ions and hydrogen heat-treated TiO ₂ and its oxygen vacancy content is used, combined with gas catalytic luminescence to quickly detect the oxygen vacancies of titanium oxide, and then to The catalytic activity of titanium oxide was screened and evaluated. In the gaseous state, firstly, the gas molecules ether and oxygen diffuse to the surface of titanium oxide; the oxygen vacancies on the surface of titanium oxide have a strong ability to adsorb oxygen molecules, and the oxygen adsorbed to the oxygen vacancies can be formed by capturing a free electron. Oxidative superoxide species (O ₂ ^- ), then, chemically adsorbed ether molecules react with O ₂ ^- to generate excited acetaldehyde molecules (CH ₃ CHO ^* ), the process of excited acetaldehyde molecules returning to the ground state A certain amount of energy will be generated, which is released in the form of optics and detected by the amplified signal of the photomultiplier tube. According to the amount of oxygen vacancies in titanium oxide is directly proportional to the luminescent signal, the rapid detection of oxygen vacancies in titanium oxide can be realized by measuring the strength of the luminescent signal, and a suitable titanium oxide catalyst can be screened at the same time.

The device for detecting oxygen vacancies in titanium oxide is shown in Figure 1, in which the air pump, vaporization chamber, and quartz tube are connected by a silicone tube, and the quartz tube is placed in a chemiluminescence analyzer; there is a detachable ceramic rod in the quartz tube, and a contact A transformer heats the ceramic rod; a chemiluminescence analyzer is connected to a computer.

The specific test method for oxygen vacancies in titanium oxide is as follows:

A. Add titanium oxide powder into deionized water to make a slurry of 0.50-0.55g/mL, and evenly coat it on the ceramic rod with a thickness of 0.45-0.50mm.

The titanium oxide is doped with M metal ions, M is one of Cu, Fe, Co, Cr ions, the doping amount of M accounts for 0.5%-2.0% of the mass percentage of TiO ₂ and after 250 ° C Titanium oxide calcined for 30-60 minutes under hydrogen atmosphere at -400°C.

B. When the slurry on the ceramic rod in step A is slightly dry, put the ceramic rod into the quartz tube inside the chemiluminescence analysis instrument; remove the water in the air pump, use the air filtered by activated carbon as the carrier gas for the reaction, and control the flow rate At 200-300mL/min, make the gas flow rate evenly pass through the surface of the ceramic rod in the quartz tube; use a contact transformer to apply a voltage of 100-110V to the ceramic rod, and raise the temperature of the ceramic rod to the detected temperature of 150-200°C;

C. Turn on the temperature raising device in the vaporization chamber to raise the temperature to 150-200°C, inject 0.1 mole ether solution into the vaporization chamber, the air in the air pump flows through the vaporization chamber and bring the vaporized ether into the quartz tube, ether and ceramics The titanium oxide on the rod reacts and produces luminescence, and the data is collected, recorded and analyzed by a chemiluminescence analyzer. According to the phenomenon that the amount of oxygen vacancies in titanium oxide is directly proportional to the luminescent signal generated by the reaction, the content of oxygen vacancies in titanium oxide catalysts can be compared.

The vaporization chamber is a metal container with a volume of 1-2 mL with a heating jacket outside.

Figure 2 shows the catalytic luminescence signals of Cu-doped titania with different mass fractions. With the increase of Cu-doped content, the chemiluminescence signal values show a trend of first increasing and then decreasing. This trend is consistent with that of Cu in Table 1. The change trend of the content of oxygen vacancies in doped titanium oxide samples is consistent; Fig. 3 shows the catalytic luminescence signals of titanium oxide doped with Cu, Fe, Co and Cr four metal ions, in which Cu/TiO ₂ luminescence signal The highest, followed by Co/TiO ₂ , Fe/TiO ₂ , Cr/TiO ₂ ; Figure 4 shows the chemiluminescence signals of titanium oxide samples calcined at different temperatures under hydrogen atmosphere, the chemiluminescence signal intensity varies with the calcining temperature There is an increasing trend.

The beneficial effects of the present invention are: using ether as a molecular probe to quickly evaluate the oxygen vacancy method in titanium oxide. Evaluation of the vacancy.

Description of drawings

Figure 1 Schematic diagram of the reaction setup for the evaluation of oxygen vacancies in titania catalysts.

1 is an air pump, 2 is a gasification chamber, 3 is a chemiluminescence analyzer, 4 is a computer, 5 is a quartz tube, 6 is a ceramic heating rod, and 7 is a transformer.

Fig. 2 is a graph corresponding to Cu doping amount in titanium oxide and catalytic luminescence signal in Example 1.

Fig. 3 is a corresponding graph of metal ions doped in titanium oxide and catalytic luminescence signals in Example 2.

Fig. 4 is a graph corresponding to the calcination temperature of titanium oxide in hydrogen and the catalytic luminescent signal in Example 3.

Detailed ways

Example 1

The experimental setup described in Figure 1 was used.

A. Take undoped TiO ₂ and 1.0%, 1.5%, 2.0% Cu-doped TiO ₂ powder and add them into deionized water and stir evenly to make a 0.50g/mL slurry; apply it on the ceramic rod and The thickness is about 0.50mm, insert the ceramic rod into the quartz tube, apply a voltage of 105V to the ceramic rod, and then use the air treated with silica gel and activated carbon in the air pump as the carrier gas for reaction for 30min, and the gas flow rate is 250mL/min , when the temperature of the ceramic rod reaches 170°C, start the heating device of the vaporization chamber until the temperature of the vaporization chamber is 170°C. Ensure the stable operation of the chemiluminescence analyzer.

B. Inject 25 μL of 0.1mol/L ether solution into the vaporization chamber, the air from the air pump is loaded into the quartz tube and reacts with the oxygen chemisorbed on the catalyst on the Cu/ _TiO2 on the ceramic rod to produce luminescence, Data were collected by a chemiluminescence analyzer. The results are shown in Figure 2. The strength of the chemiluminescence signal is: TiO ₂ <1.0%Cu/TiO ₂ <1.5%Cu/TiO ₂ >2.0%Cu/TiO ₂ , and the luminescent signal increases with the increase of Cu doping amount , when the doping amount is 1.5%, the chemiluminescence signal reaches the maximum; continue to increase the doping amount to 2.0%, and the chemiluminescence signal decreases. It shows that the change trend of the luminescence signal intensity with the amount of Cu doping is consistent with the change trend of the content of oxygen vacancies in titanium oxide with the amount of Cu doping, so it is concluded that the intensity of the luminescence signal is positively correlated with the content of oxygen vacancies .

Comparative example 1

Get the undoped TiO in embodiment ₁ and Cu doping mass fraction is respectively 1.0%, 1.5%, 2.0% powder adopts traditional XPS analytical method to carry out comparative test:

Using a Thermo ESCALAB 250 instrument, take 30-60 mg of the above powder, press them into tablets, and put them into the transition chamber. After evacuating and replenishing nitrogen three times, transfer the sample into the main body of the glove box, and then put it into the reactor for pretreatment; After the completion, take the flake sample out of the reactor, stick it on the sample stage with conductive adhesive, and transfer it to the vacuum chamber of the energy spectrometer under nitrogen atmosphere for vacuum treatment. After the vacuum degree is higher than 10 ^-4 Pa, then Transfer to the analysis room of the energy spectrometer for detection. According to the XPS data test results, the following formula (Vo: oxygen vacancies) is used to calculate the percentage of oxygen vacancies in Cu/TiO ₂ :

Percentage of oxygen vacancies = {[(Ti atomic percentage×4)–(lattice oxygen atomic percentage×2)]*sensitivity factor}/2×100.

(Wagner, C.D.; Moulder, J.F.; Davis, L.E.; Riggs, W.M. Perkin-Elmer Corporation: Eden Prairie, MN, 1979; You, M.; Kim, T.G.; Sung, Y.M. Growth Des. 2010, 10, 983-987)

The results are shown in Table 1:

Table 1

It can be seen from Table 1 that the change trend of oxygen vacancies in titanium oxide with different Cu doping amounts detected by XPS method is TiO ₂ <1.0%Cu/TiO ₂ <1.5%Cu/TiO ₂ >2.0%Cu/TiO ₂ , this result is the same as the change trend of the chemiluminescent signal measured in Figure 2. It can be seen that there is a positive correlation between the intensity of chemiluminescent signal and the content of oxygen vacancies. The method adopted in the present invention is consistent with the detection result of the traditional XPS method.

Example 2

TiO ₂ doped with Cu, Co, Fe, Cr four metal ions with a mass fraction of 1.0% was used. Other steps are the same as in Example 1. The test results are shown in FIG. 3 . The magnitude of the chemiluminescence signal is: Cu/TiO ₂ >Co/TiO ₂ >Fe/TiO ₂ >Cr/TiO ₂ .

Example 3

The undoped _TiO2 powders in Example 1 were calcined at 250°C, 300°C, 350°C, and 400°C for 2h under a hydrogen atmosphere, and the obtained samples were respectively designated as H-250, H-300, H-350, H-400. The other steps are the same as in Example 1. The test results are shown in Figure 4. The intensity of the chemiluminescent signal is: H-400>H-350>H-300>H-250.

Claims (3)

1. detect a method for Lacking oxygen in titanium dioxide fast, the concrete method of testing changing Lacking oxygen in titanium is as follows:

A. titanium dioxide powder is added in deionized water the slurries being made into 0.50-0.55g/mL, be evenly coated on ceramic rod, the thickness of coating is 0.45-0.50mm;

B. treat that the slurries on steps A ceramic rod are micro-dry, ceramic rod is loaded in the quartz ampoule of chemiluminescent analyzer device inside; Removing pneumatic pump in water, with the air after activated carbon filtration as reaction carrier gas, coutroi velocity, at 200-300mL/min, makes the surface by ceramic rod in quartz ampoule of Uniform gas flow velocity; Impose the voltage of 100-110V with contact transformer to ceramic rod, the temperature of ceramic rod is risen to the temperature 150-200 DEG C of detection;

C. rising temperature device in unlatching vaporizer makes temperature rise to 150-200 DEG C, 0.1 mole of diethyl ether solution is injected vaporizer, air in pneumatic pump flows through vaporizer and brings the ether of wherein vaporizing into quartz ampoule, titanium dioxide on ether and ceramic rod reacts and produces luminescence, detects its luminous signal value by chemiluminescent analyzer.

2. the method for Lacking oxygen in quick detection titanium dioxide according to claim 1, it is characterized in that the titanium dioxide described in steps A is doped with M metallic ion, M is one of Cu, Fe, Co, Cr ion, and the doping of M accounts for TiO ₂mass percentage be 0.5%-2.0%, this iron oxide is through the titanium dioxide of under 250 DEG C of-400 DEG C of hydrogen atmospheres calcination process 30-60 minute.

3. the method for Lacking oxygen in quick detection titanium dioxide according to claim 1, is characterized in that the relation be directly proportional to luminous signal according to the amount of Lacking oxygen, and the luminous signal value obtained from step C obtains the qualitative value of Lacking oxygen titanium dioxide indirectly.