CN111530445A - Composite photocatalyst La2O3/TiO2And preparation method and application thereof - Google Patents

Abstract

The invention uses La₂O₃And TiO₂Prepare La₂O₃/TiO₂Photocatalyst, and La₂O₃/TiO₂And performing characterization of a scanning electron microscope, X-ray diffraction, photoluminescence spectrum, ultraviolet-visible diffuse reflection and infrared spectrum. Methylene blue is taken as a model compound for photocatalytic degradation, and La is investigated₂O₃Content, calcination temperature, catalyst amount vs. La₂O₃/TiO₂Influence of photocatalytic properties. The results show that between 0.040-0.150g, the degradation rate of the degradation substrate is increased along with the increase of the dosage of the catalyst.

Description

Composite photocatalyst La2O3/TiO2And preparation method and application thereof

Technical Field

The invention relates to a novel composite photocatalyst for treating dye wastewater pollution, and a preparation method and application thereof, and belongs to the field of environmental material chemistry.

Background

The coupling between the semiconductors mainly enables the photocatalytic quantum efficiency of the semiconductors to be effectively improved. Due to the coupling of the semiconductors, a heterojunction can be formed between the two interfaces, so that the complementarity of the energy level structures of the two semiconductors can be fully utilized, namely the energy level difference between the two semiconductors is utilized to effectively separate electrons from holes, and the aims of promoting the separation, transfer and transfer of photo-generated electron and hole pairs are fulfilled, so that the recombination of the photo-generated electrons and the holes is inhibited.

However, the technical problem of titanium dioxide in the application of the photocatalysis technology can be solved well by compounding other semiconductor materials with the titanium dioxide. By compounding with other materials, the spectral response range of the titanium dioxide can be widened, visible light can be fully utilized, and photo-generated electron-hole pairs can be effectively separated, so that the quantum efficiency of the titanium dioxide is improved; on the other hand, by compounding with different semiconductor materials, not only can the advantages of each composite element be fully exerted, but also a synergistic effect can be generated, and a common catalysis effect can be realized. The rare earth element composite modification provides an important way for obtaining higher catalytic activity of titanium dioxide. In order to improve the photocatalytic performance of titanium dioxide and the utilization efficiency of titanium dioxide to visible light, at present, domestic and foreign research focuses on three fields of catalyst fixation, visible light wavelength response range expansion, photocatalytic quantum yield improvement, industrial application and the like (see: Liequua, rare earth Ce doped nano TiO)₂Preparation and photocatalytic Performance Studies [ J]Journal of the Jilin chemical academy of chemical engineering 2015,32(4) 8-11; high-navigation, high-plum, plum-pine field, etc. rare earth metal Dy doped TiO₂Preparation of photocatalyst and study of degradation property of photocatalyst on malachite green [ J]Application chemical industry, 2015,44(10): 1889-; research on rare earth-doped titanium dioxide photocatalysts [ J]Material report a, 2013, 27 (1): 38-44).

Because the rare earth element has special spectral properties and electronic structure, the rare earth element can be used for TiO in the aspects of light absorption performance, surface adsorption performance, crystal structure, energy band structure and the like₂The photocatalyst is modified, and simultaneously, a plurality of novel photocatalyst systems can be constructed, thereby having great application prospect (see: Zhang civilization, Li Ling, Zhang Hua Yan, and the like. preparation and photocatalytic performance of lanthanum-doped nano titanium dioxide transparent photocatalyst emulsion [ J]Atmospheric and environmental optics, 2013,8(6): 428-.

Disclosure of Invention

To overcome the above problems, the present inventors have set La₂O₃And TiO₂For precursor, La is prepared₂O₃/TiO₂Photocatalyst, and La₂O₃/TiO₂And performing characterization of a scanning electron microscope, X-ray diffraction, photoluminescence spectrum, ultraviolet-visible diffuse reflection and infrared spectrum. Methylene blue is taken as a model compound for photocatalytic degradation, and La is investigated₂O₃Content, calcination temperature, catalyst amount vs. La₂O₃/TiO₂Influence of photocatalytic Properties La was evaluated by photocatalytic degradation of methylene blue dye₂O₃/TiO₂The photocatalytic activity of the above compounds has led to the development of a photocatalytic material having excellent properties for treating dye-containing wastewater, and thus the present invention has been completed.

Accordingly, the present invention provides a La₂O₃/TiO₂A composite photocatalyst consisting of La₂O₃And TiO₂Is prepared by compounding.

The invention also provides a method for preparing La₂O₃/TiO₂A method of compounding a photocatalyst, comprising:

step 1, preparing TiO₂And La₂O₃,

Step 2, adding La₂O₃And TiO₂Mixing together, and treating to obtain La₂O₃/TiO₂A composite photocatalyst is provided.

In step 1, La was used₂O₃In an amount less than TiO₂Preferably, La in parts by weight₂O₃Is used in an amount of 0.5% to 20%, preferably 1% to 10%, of both materials.

In step 2, the treatment comprises drying, grinding, preferably drying without calcination.

According to the photocatalyst provided by the invention, in an ultraviolet-visible diffuse reflection spectrogram, La₂O₃/TiO₂Characteristic absorption wavelength of (D) compared to TiO₂A blue shift occurred, and the characteristic (101), (004), (200), (105), (211), (204) reflections were shown in the X-ray diffraction pattern, indicating that TiO₂The shape of the crystal exists in the anatase phase crystal, and in the scanning electron microscope image, the crystal is a spheroid with particles gathered together, La₂O₃Partially or fully attached to TiO₂On the surface.

The composite photocatalyst can be used for degrading dye wastewater, for example, the dye wastewater contains methylene blue.

Drawings

FIG. 1 is an X-ray diffraction pattern of a catalyst sample. TiO2₂，1％La₂O₃/TiO₂，3％La₂O₃/TiO₂，9％La₂O₃/TiO₂；

FIG. 2 is a graph of the ultraviolet-visible diffuse reflectance spectrum. TiO2₂，1％La₂O₃/TiO₂，3％La₂O₃/TiO₂，9％La₂O₃/TiO₂；

FIG. 3 is a photoluminescence spectrum of a catalyst. TiO2₂，1％La₂O₃/TiO₂，3％La₂O₃/TiO₂，9％La₂O₃/TiO₂；

FIG. 4 is an infrared spectrum of the catalyst. TiO2₂，1％La₂O₃/TiO₂，3％La₂O₃/TiO₂，9％La₂O₃/TiO₂；

Fig. 5 is a scanning electron micrograph of the catalyst. (a) La₂O₃，(b)TiO₂，(c)3％La₂O₃/TiO₂；

FIG. 6 is a graph showing the effect of catalyst composition on its photocatalytic activity. 0: TiO2₂，1：1％La₂O₃/TiO₂，3：3％La₂O₃/TiO₂，9：9％La₂O₃/TiO₂；

FIG. 7 is calcination temperature vs. La₂O₃/TiO₂Graph of catalytic activity effect. Room temperature, 550 ℃, 850 ℃;

FIG. 8 shows the amount of catalyst used vs. La₂O₃/TiO₂Influence of the catalytic activity. 0.04,0.08,0.10,0.15.

Detailed Description

According to the invention, firstly, La is provided₂O₃/TiO₂A composite photocatalyst consisting of La₂O₃And TiO₂Is prepared by compounding.

In order to prepare the composite photocatalyst, the preparation method comprises the following steps:

step 1, preparing La₂O₃And TiO₂。

In step 1, in order to prepare the composite photocatalyst, La is prepared₂O₃And TiO₂Both of them may be commercially available products or may be obtained by converting the respective salt compounds, for example, from La₂CO₃Calcining to obtain La₂O₃。

According to the present invention, it is preferable to use La for cost and efficiency₂O₃In an amount less than TiO₂The amount of (c). For example, La in parts by weight₂O₃Is used in an amount of 0.5 to 20% of the two materials, preferably La₂O₃In an amount of 1 to 10% of the two materials, e.g. La₂O₃When the amount of (A) is 1% of the amount of the two materials, it is recorded as 1% of La₂O₃/TiO₂，La₂O₃When the amount of (A) is 10% of the amount of the two materials, it is recorded as 10% La₂O₃/TiO₂。

Step 2, adding La₂O₃And TiO₂Mixing together, and treating to obtain La₂O₃/TiO₂A composite photocatalyst is provided.

In the present invention, the treatment includes drying and grinding.

Drying may be carried out in a drying oven to remove moisture that may be present.

According to the invention, the drying is carried out at a temperature not higher than the calcination temperature, for example in a drying oven, or at a temperature lower than 100 ℃, or even at room temperature.

According to the present invention, drying is performed without calcination. The calcination may generally refer to being carried out at a temperature of 300 to 1000 ℃, preferably 500 to 900 ℃, more preferably 550 ℃ to 850 ℃.

Then grinding is carried out to obtain particles with smaller and uniform particle size, for example, grinding into powder, and finally La is obtained₂O₃/TiO₂A composite photocatalyst is provided.

La provided by the invention₂O₃/TiO₂The composite photocatalyst comprises:

in its ultraviolet-visible diffuse reflectance spectrogram, La₂O₃/TiO₂The characteristic absorption wavelength of (a) is blue-shifted compared with that of TiO 2;

in the photoluminescence spectrogram, the intensity sequence of the peaks of a sample at 390-440nm is TiO₂＞1％La₂O₃/TiO₂＞9％La₂O₃/TiO₂＞3％La₂O₃/TiO₂。

In its infrared spectrogram, La₂O₃/TiO₂Chemical structure of composite catalyst and TiO₂Essentially identical, indicating that the two types of samples are essentially similar in structure.

In its X-ray diffraction pattern, whether it is TiO₂Or La₂O₃/TiO₂The photocatalyst and the samples all show characteristic (101), (004), (200), (105), (211) and (204) reflection without other peaks, which indicates that TiO in the samples₂Exists in anatase phase crystal, and XRD diffraction peak thereofThe corresponding 2 theta values are substantially consistent, indicating that La₂O₃/TiO₂Doped body of (2) to TiO₂The crystal structure of (A) has no destructive effect. (101) Among diffraction peaks of crystal planes, along with La₂O₃The peak value increases and then decreases with increasing addition amount. The peak intensities of the samples of 1% and 3% are stronger, indicating that they are better in crystallinity. La was not observed₂O₃Due to a very small amount of La₂O₃Dispersed on the catalyst surface without forming a separate phase.

In the scanning electron microscope image, the morphology is an irregular spheroid with a plurality of particles gathered together. In particular, 3% La₂O₃/TiO₂The scanning electron micrograph of the composite catalyst shows that La is formed₂O₃Has been attached to TiO₂Surface, this is also La₂O₃To TiO2₂The modification of (2) can be smoothly expressed.

The photocatalytic activity shows that the degradation rate of organic waste (such as methylene blue) in the wastewater is dependent on La₂O₃The mass percentage content increases gradually, and when the mass percentage content exceeds 3%, the mass percentage content begins to decrease.

According to the invention with La₂O₃And TiO₂As a precursor, La is prepared₂O₃/TiO₂Composite photocatalyst for La₂O₃/TiO₂And performing characterization of a scanning electron microscope, X-ray diffraction, photoluminescence spectrum, ultraviolet-visible diffuse reflection and infrared spectrum. Methylene blue is taken as a model compound for photocatalytic degradation, and La is investigated₂O₃Content, calcination temperature, catalyst amount vs. La₂O₃/TiO₂Influence of photocatalytic properties. The results show that the beneficial effects are as follows:

between 0.040 and 0.150g, the degradation rate of the degradation substrate is increased along with the increase of the dosage of the catalyst. When the catalyst composition is 3% of La₂O₃/TiO₂When the dosage of the catalyst is 0.150g, the concentration of the methylene blue is 5mg/L, and the volume is 300mL, the illumination is 60min, and the degradation rate of the methylene blue can reach 90.1%.

Examples

Examples 1 to 3

1％La₂O₃/TiO₂The preparation of (1): weighing 0.020g La on an analytical balance₂O₃1.980g of TiO were weighed₂Mixing, drying and grinding;

3％La₂O₃/TiO₂the preparation of (1): 0.060g of La are weighed out on an analytical balance₂O₃Weighing 1.940g TiO₂Mixing, drying and grinding;

9％La₂O₃/TiO₂the preparation of (1): 0.180g La was weighed on an analytical balance₂O₃Weighing 1.820g TiO₂Mixing, drying and grinding.

The four samples obtained above were designated as sample 1, sample 3 and sample 9, respectively, and sealed.

Comparative example 1:

pure TiO₂The preparation of (1): 2.000g of TiO are weighed on an analytical balance₂Drying and grinding. The sample obtained was designated as sample 0 and sealed.

Comparative example 2:

calcining La₂O₃/TiO₂ Catalyst sample preparation 3 parts by mass of 2.000g of 3% La were weighed₂O₃/TiO₂Mixing the catalyst, drying and grinding, wherein 2 parts of the catalyst are calcined for 1 hour at the temperature of 550 ℃ and 850 ℃, cooling to room temperature after calcination, and grinding into powder.

The sample obtained above was designated as sample 03 and sealed.

Examples of the experiments

Experimental example 1: characterization by X-ray diffraction

A small amount of TiO2 and 1% La are respectively taken by a key₂O₃/TiO₂、3％La₂O₃/TiO₂、9％La₂O₃/TiO₂Catalyst sample (powder), pressing the sample into thin pieces (only central covering), scanning with XD-3 diffractometer, wherein the parameters include Cu-K α radiation and tube voltage36KV, 20mA tube current, 10-80 degree scanning range and 8deg/min scanning speed.

FIG. 1 is an X-ray diffraction pattern of a catalyst sample. As can be seen from FIG. 1, it is either TiO₂Or La₂O₃/TiO₂The photocatalyst and the samples all show characteristic (101), (004), (200), (105), (211) and (204) reflection without other peaks, which indicates that TiO in the samples₂The crystals exist in anatase phase, and the 2 theta values corresponding to XRD diffraction peaks of the crystals are basically consistent, which indicates that La₂O₃/TiO₂Doped body of (2) to TiO₂The crystal structure of (A) has no destructive effect. (101) Among diffraction peaks of crystal planes, along with La₂O₃The peak value increases and then decreases with increasing addition amount. The peak intensities of the samples of 1% and 3% are stronger, indicating that they are better in crystallinity. La was not observed₂O₃Due to a very small amount of La₂O₃Dispersed on the catalyst surface without forming a separate phase.

Experimental example 2: ultraviolet-visible diffuse reflectance spectral characterization

Taking a small amount of TiO₂、1％La₂O₃/TiO₂、3％La₂O₃/TiO₂、9％La₂O₃/TiO₂Catalyst samples (powders) were tableted and each catalyst sample was characterized using an ultraviolet-visible diffuse reflectance spectrometer. The scanning wavelength is 200 and 800 nm.

FIG. 2 is a graph of the ultraviolet-visible diffuse reflectance spectrum. As can be seen from FIG. 2, La₂O₃/TiO₂Characteristic absorption wavelength of (D) compared to TiO₂Blue shift occurred to indicate that La₂O₃The introduction of (2) can increase the forbidden bandwidth of the semiconductor, enhance the oxidation-reduction capability of photoinduced holes and electrons, and easily generate oxidation groups in the reaction, thereby being beneficial to improving the photocatalytic activity. Wherein 3% of La₂O₃The blue shift phenomenon of the catalyst with the doping amount is most obvious, and the photocatalytic capability is strongest.

Experimental example 3: photoluminescence spectral characterization

Taking a small amount of TiO₂、1％La₂O₃/TiO₂、3％La₂O₃/TiO₂、9％La₂O₃/TiO₂And (3) testing the photoluminescence performance of each composite catalyst sample by using a fluorescence spectrometer. In the experiment, the sample should be pressed as densely as possible with a glass slide to keep the surface of the sample flat after pressing into a sheet, and one sample should be tested at least twice in parallel to ensure the validity of the data.

FIG. 3 is a photoluminescence spectrum of a catalyst. As can be seen from FIG. 3, the intensity order of the peaks of the sample at 390-440nm is TiO₂＞1％La₂O₃/TiO₂＞9％La₂O₃/TiO₂＞3％La₂O₃/TiO₂. The intensity of the peak is proportional to the recombination rate of the photo-generated electron-hole pairs. Pure TiO₂The fluorescence signal of the sample is strongest, the recombination probability of the photo-generated electron-hole pair is highest, and the photocatalytic activity is lowest. Is doped with La₂O₃Due to La₂O₃To TiO2₂The modification effect of the particles reduces the recombination rate of photogenerated electron-hole pairs, wherein the La accounts for 3 percent₂O₃The recombination rate of the photoproduction electron-hole pairs of the content catalyst is the lowest, the separation efficiency is the highest, and the catalytic effect is the best.

Experimental example 4: fourier transform infrared spectroscopy characterization

Taking a small amount of TiO₂、1％La₂O₃/TiO₂、3％La₂O₃/TiO₂、9％La₂O₃/TiO₂Respectively adding a small amount of potassium bromide powder into a catalyst sample (powder), drying the potassium bromide powder, grinding the potassium bromide powder until the potassium bromide powder is uniformly mixed, pressing the mixture into a sheet, and performing infrared spectrum characterization on the catalyst by using a Fourier transform infrared spectrometer.

FIG. 4 is an infrared spectrum of the catalyst. As can be seen from FIG. 4, La₂O₃/TiO₂Chemical structure of composite catalyst and TiO₂Essentially identical, indicating that the two types of samples are essentially similar in structure. Wherein the absorption peak around 543cm-1 corresponds to the stretching vibration of Ti-O-Ti bonds; absorption at about 1622cm-1Peaks correspond to CO₂Stretching vibration of the middle C ═ O bond; the absorption peak around 3415cm-1 corresponds to the stretching vibration of the O-H bond of a trace amount of water contained in the sample. No absorption peak of La-O bond due to La₂O₃Too little content of (A) to be detected by an instrument.

Experimental example 5: characterization of scanning Electron microscope

The obtained La was subjected to a CM200-FEG type scanning electron microscope (TEM, acceleration voltage 200kV, Philips Co., Ltd.)₂O₃、TiO₂、3％La₂O₃/TiO₂The catalyst powder was subjected to morphology testing.

Fig. 5 is a scanning electron micrograph of the catalyst. (a) La₂O₃，(b)TiO₂，(c)3％La₂O₃/TiO₂。

As can be seen from FIG. 5, FIG. 5(a) La₂O₃The morphology of (A) is irregular block-shaped. FIG. 5(b) shows TiO₂The shape of the spherical particle can be seen by a scanning electron microscope, and the spherical particle is an irregular spheroid with a plurality of particles gathered together. FIG. 5(c) is 3% La₂O₃/TiO₂The scanning electron micrograph of the composite catalyst shows that La is formed₂O₃Has been attached to TiO₂Surface, this is also La₂O₃To TiO2₂The modification of (2) can be smoothly expressed.

Experimental example 6: la₂O₃/TiO₂Determination of the photocatalytic Activity of the catalyst

A certain amount of catalyst sample (powder) was accurately weighed into a column reactor (diameter 7cm, height 30cm), 300mL of methylene blue solution with a concentration of 5 mg. L-1 was added, and a small magneton was added. And installing a magnetic stirrer and cooling water. Stirring continuously, treating in dark for 30min, sampling, centrifuging for 20min, and measuring absorbance A0. Turning on a light source, carrying out ultraviolet irradiation treatment, sampling once every 20min, sampling 3 times in total (namely, sampling once every 20min, 40 min and 60 min), sampling, centrifuging for 20min, measuring the absorbance At, calculating the degradation rate W (%) (A0-At)/A0 x 100%, and drawing an ultraviolet light activity graph of different catalyst samples according to the obtained degradation rate.

FIG. 6 shows the composition of a catalyst to photocatalyze itGraph of activity impact. 0: TiO2₂，1：1％La₂O₃/TiO₂，3：3％La₂O₃/TiO₂，9：9％La₂O₃/TiO₂。

As can be seen from FIG. 6, the degradation rate of methylene blue is dependent on La₂O₃The mass percentage content increases gradually, and when the mass percentage content exceeds 3%, the mass percentage content begins to decrease. The main reason is 3% La₂O₃The doping proportion is beneficial to improving TiO₂The crystallinity of the anatase phase can reduce the recombination rate of photo-generated electron-hole pairs. If La is present₂O₃Too much addition will result in TiO₂The recombination probability of the photo-generated electron-hole pairs is improved. And, excessive La₂O₃The particles will be coated on the TiO₂The photocatalytic reaction is hindered by the molecular surface. Therefore, the optimum La₂O₃The doping ratio was 3%.

FIG. 7 is calcination temperature vs. La₂O₃/TiO₂Graph of catalytic activity effect. Room temperature, 550 ℃, 850 ℃.

As can be seen from FIG. 7, as the calcination temperature increased, the catalyst 3% La₂O₃/TiO₂The activity decreases rapidly because of the anatase TiO form being calcined at high temperature₂Conversion to rutile TiO with poor catalytic performance₂Resulting in 3% La₂O₃/TiO₂The photocatalytic efficiency is reduced.

FIG. 8 shows the amount of catalyst used vs. La₂O₃/TiO₂Influence of the catalytic activity. 0.04,0.08,0.10,0.15.

As can be seen from FIG. 8, when the amount of the mixed catalyst is between 0.040 and 0.150g, the degradation rate of methylene blue increases with the amount of the catalyst. When the catalyst composition is 3% of La₂O₃/TiO₂The dosage of the catalyst is 0.100g, the catalyst is not calcined, the concentration of the methylene blue solution is 5.00 mg.L < -1 >, the volume is 300mL, and the catalytic degradation rate of the methylene blue is 90.1% when the catalyst is illuminated for 1 h.

The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (10)

1. La₂O₃/TiO₂A composite photocatalyst consisting of La₂O₃And TiO₂Is prepared by compounding.

2. Preparation of La₂O₃/TiO₂The method for compounding the photocatalyst is characterized in that: comprises the following steps:

step 1, preparing TiO₂And La₂O₃,

Step 2, adding La₂O₃And TiO₂Mixing together, and treating to obtain La₂O₃/TiO₂A composite photocatalyst is provided.

3. The method of claim 1, wherein: in step 1, La was used₂O₃In an amount less than TiO₂The amount of (c).

4. The method of claim 3, wherein: in step 1, La is added in parts by weight₂O₃Is used in an amount of 0.5% to 20%, preferably 1% to 10%, of both materials.

5. Method according to one of claims 1 to 4, characterized in that: in step 2, the treatment comprises drying, grinding, preferably drying without calcination.

6. The photocatalyst according to any one of claims 1 to 5, wherein: in its ultraviolet-visible diffuse reflectance spectrogram, La₂O₃/TiO₂Characteristic absorption wavelength of (D) compared to TiO₂A blue shift occurs.

7. The photocatalyst according to any one of claims 1 to 6, wherein: the X-ray diffraction pattern thereof showed characteristic (101), (004), (200), (105), (211) and (204) reflections, indicating that TiO₂Exists in anatase phase crystal.

8. The photocatalyst according to any one of claims 1 to 7, wherein: in the scanning electron microscope image, the morphology is a spheroid with particles gathered together, La₂O₃Partially or fully attached to TiO₂On the surface.

9. Use of the composite photocatalyst according to any one of claims 1 to 8 for degrading dye waste water.

10. Use according to claim 9, characterized in that: the dye wastewater contains methylene blue.

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