Lanthanum ferrite-based photocatalytic material with oxygen vacancy as well as preparation method and application of lanthanum ferrite-based photocatalytic material

Abstract

The invention discloses a lanthanum ferrite-based photocatalytic material with oxygen vacancies and a preparation method and application thereof, and relates to the technical field of photocatalytic materials, the photocatalytic material is prepared by the following method: S1, preparing LaFeO3 powder; s2, the LaFeO3 powder is sequentially subjected to the following treatment including acid etching, wherein the LaFeO3 powder is dispersed in a 0.18 mol / L to 0.22 mol / L HNO3 solution, stirring is conducted for 0.8 h to 1.2 h, and centrifugal washing and drying are conducted; alkali etching is conducted, specifically, the LaFeO3 powder obtained after acid etching is dispersed in a NaOH solution with the concentration being 0.48-0.52 mol / L to be stirred for 0.8-1.2 h, centrifugal washing and drying are conducted, and the LaFeO3 powder obtained after acid etching and alkali etching is obtained; and plasma treatment: putting the LaFeO3 powder material subjected to acid etching and alkali etching into a 90-110V radio frequency electric field, and carrying out plasma bombardment for 4-6 minutes in an N2 atmosphere with the flow rate of 250-350ml / min to obtain a final material OV2-LFO, namely the lanthanum ferrite-based photocatalytic material with oxygen vacancies. LaFeO3 is modified through a three-step method of acid etching, alkali etching and a plasma technology, lanthanum ferrite rich in surface oxygen vacancies is prepared, and the photocatalytic degradation performance of the lanthanum ferrite can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and particularly to a lanthanum ferrite-based photocatalytic material with oxygen vacancies, a preparation method thereof, and an application thereof. Background Art

[0002] Lanthanum ferrite-based perovskite photocatalytic materials (LaFeO3) are a class of composite oxide materials with an ABO3-type perovskite structure. Due to their unique optoelectronic properties, high chemical stability, and environmental friendliness, they have attracted much attention in the field of photocatalysis in recent years. In its crystal structure, La 3+ occupies the A site, Fe 3+ occupies the B site, and oxygen atoms form an octahedral coordination framework. This structure endows the material with excellent carrier migration ability and a tunable energy band structure. The narrow bandgap (about 2.1 eV) of LaFeO3 enables it to have a significant response to visible light. At the same time, the hybridization of the d-orbital electrons of Fe 3+ with the p-orbitals of O2 can promote the separation of photo-generated electron-hole pairs, thereby enhancing the photocatalytic activity. This material shows potential in the fields of photocatalytic water splitting for hydrogen production, degradation of organic pollutants (such as dyes, antibiotics), and CO2 reduction. Researchers have further optimized its performance by means of element doping (such as Sr 2+ , Co 3+ ), morphology regulation (nanoparticles, porous structures), and construction of heterojunctions (such as composite with g-C3N4, TiO2), etc., to solve the problems of low visible light utilization rate and high carrier recombination rate of traditional photocatalysts. Its low cost, high stability, and non-toxicity make it an important candidate material in the fields of green energy and environmental remediation.

[0003] Although lanthanum ferrite-based perovskite (LaFeO3) photocatalytic materials perform excellently in terms of visible light response, environmental friendliness, etc., they still face multiple limitations: their photo-generated electron-hole pairs are prone to rapid recombination due to internal defects (such as oxygen vacancies), resulting in low quantum efficiency; the characteristic of a bandgap of about 2.1 eV can absorb some visible light, but the utilization of long-wavelength light is insufficient, which limits the overall solar energy conversion efficiency; traditional synthesis methods are prone to cause particle aggregation, with a low specific surface area and few active sites, affecting the adsorption and catalytic efficiency of reactants; in addition, there are problems such as low product selectivity and insufficient long-term cycle stability (such as Fe 3+ dissolution or structural distortion) in complex reaction systems, and processes such as element doping and heterostructure construction required for optimizing performance face challenges such as high cost and difficult precise regulation; at the same time, the basic research on the charge transfer mechanism and surface reaction kinetics during the photocatalytic process is not deep enough, which restricts the further design and performance breakthrough of the material. These limitations urgently need to be solved through strategies such as structural design, energy band regulation, and mechanism exploration. Summary of the Invention

[0004] The object of the present invention is to overcome the deficiencies of the prior art, and to provide a lanthanum ferrite-based photocatalytic material with oxygen vacancies, a preparation method and an application thereof. By means of a three-step method of acid etching, alkali etching and plasma technology, LaFeO3 is modified to prepare lanthanum ferrite rich in surface oxygen vacancies, which can significantly improve its photocatalytic degradation performance.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A preparation method of a lanthanum ferrite-based photocatalytic material with oxygen vacancies, comprising the following steps:

[0007] S1, preparing LaFeO3 powder;

[0008] S2, successively processing the LaFeO3 powder as follows:

[0009] Acid etching: dispersing the LaFeO3 powder in a 0.18 - 0.22 mol / L HNO3 solution and stirring for 0.8 - 1.2 h, centrifuging, washing and drying;

[0010] Alkali etching: dispersing the acid-etched LaFeO3 powder in a 0.48 - 0.52 mol / L NaOH solution and stirring for 0.8 - 1.2 h, centrifuging, washing and drying to obtain the acid-etched and alkali-etched product;

[0011] Plasma treatment: placing the acid-etched and alkali-etched LaFeO3 powder material in a 90 - 110 V radio frequency electric field, and performing plasma bombardment for 4 - 6 min under an N2 atmosphere with a flow rate of 250 - 350 ml / min to obtain the final material OV2-LFO, that is, a lanthanum ferrite-based photocatalytic material with oxygen vacancies.

[0012] Further, in step S1, the sol-gel method is used to prepare LaFeO3 powder. The specific operation method is as follows: dissolving La(NO3)·6H2O in ultrapure water to obtain solution A; dissolving Fe(NO3)·9H2O and citric acid in ultrapure water to obtain solution B; slowly adding solution A to solution B, magnetically stirring for 4 - 6 h, performing ultrasonic treatment for 28 - 35 min, and then heating to an orange-red gel at 75 - 85 °C; drying the gel in an oven, grinding it, and calcining it in a muffle furnace at a heating rate of 2.2 - 2.8 °C / min to 580 - 620 °C for 3.5 - 4.5 h to obtain LaFeO3 powder.

[0013] Further, when preparing LaFeO3 powder, La(NO3)·6H2O and Fe(NO3)·9H2O are added in equimolar amounts, and the addition amount of citric acid is 2 times the molar amount of Fe(NO3)3·9H2O.

[0014] Further, when preparing LaFeO3 powder, the gel is dried in an oven at 95 - 105 °C for 10 - 14 h.

[0015] Further, in step S2, 0.4 g of LaFeO3 powder is dispersed in 20 mL of HNO3 solution, the concentration of the HNO3 solution is 0.2 mol / L, and the number of centrifugal washing times is 2 - 3 times.

[0016] Further, in step S2, the acid-etched LaFeO3 powder is dispersed in 20 mL of NaOH solution, the concentration of the NaOH solution is 0.5 mol / L, and the number of centrifugal washing times is 2 - 3 times.

[0017] Further, in step S2, the plasma bombardment time is 5 min, the N2 flow rate is 300 ml / min, and the voltage of the radio frequency electric field is 100 V.

[0018] Furthermore, the present invention also provides a lanthanum ferrite-based photocatalytic material with oxygen vacancies prepared as described above, and the surface of the lanthanum ferrite-based photocatalytic material is rich in oxygen vacancies.

[0019] Furthermore, the present invention also provides the application of the lanthanum ferrite-based photocatalytic material with oxygen vacancies prepared as described above in the degradation of tetracycline antibiotics. The lanthanum ferrite-based photocatalytic material generates e - and H + , and through reduction-oxidation, active free radicals ·O2 - and ·OH are generated, realizing the efficient mineralization of tetracycline.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention uses the sol-gel method to prepare a lanthanum ferrite-based photocatalytic powder material. By acid etching, alkali etching, and the dielectric barrier discharge (DBD) excited microplasma technology, oxygen atoms on the surface of the lanthanum ferrite-based photocatalytic powder are selectively removed, and lanthanum ferrite rich in surface oxygen vacancies is prepared. After testing, the modified lanthanum ferrite-based photocatalytic powder significantly improves the degradation effect of tetracycline hydrochloride. Compared with the unmodified lanthanum ferrite, the degradation rate is increased by 35%. Description of the Drawings

[0022] Figure 1 is the unmodified LaFeO3 powder (LFO);

[0023] Figure 2 is the acid-etched LaFeO3 powder (AL-LFO);

[0024] Figure 3 is the LaFeO3 powder after acid etching and alkali etching (OV1-LFO);

[0025] Figure 4 is LaFeO3 powder (OV2-LFO) after acid etching, alkali etching, and plasma treatment;

[0026] Figure 5 is the microplasma discharge treatment process;

[0027] Figure 6 is the standard curve for TCH degradation;

[0028] Figure 7 is the graph of the degradation rate of TCH by LFO, AL-LFO, OV1-LFO, and OV2-LFO. Detailed implementation manners

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. The implementation manners of the present invention include but are not limited to the following embodiments.

[0030] Example 1

[0031] This example provides a preparation method for a lanthanum ferrite-based photocatalytic material with oxygen vacancies. The raw materials used are: ferric nitrate nonahydrate (Fe(NO3)3·9H2O, ≥98.5%), lanthanum nitrate hexahydrate (La(NO3)3·6H2O, 99.99%), citric acid (C6H8O7·H2O, ≥99.8%), and ultrapure water.

[0032] The LaFeO3 powder is prepared by the sol-gel method:

[0033] Dissolve 5 mmol of La(NO3)·6H2O in 30 mL of ultrapure water to obtain an aqueous solution of La(NO3)·6H2O. At the same time, dissolve 5 mmol of Fe(NO3)·9H2O and 10 mmol of citric acid in another 30 mL of ultrapure water to prepare a mixed solution. Then, slowly add the aqueous solution of La(NO3)·6H2O to the mixed solution and perform vigorous magnetic stirring for 5 h. After ultrasonic treatment for 30 min, heat it at 80 °C on a constant temperature heater for 2 h while maintaining continuous stirring to obtain an orange-red gel. Then, dry the gel in an oven at 100 °C for 12 h to obtain the LaFeO3 precursor. After grinding, calcine it in a muffle furnace at a heating rate of 2.5 °C / min at 600 °C for 4 h to obtain the LaFeO3 powder material, as Figure 1 shown.

[0034] Modify LaFeO3:

[0035] Disperse 0.4 g of LaFeO3 powder material in 20 mL of 0.2 mol / L HNO3 solution and continuously stir for 1 h. Subsequently, centrifuge and wash 3 times using a centrifuge, and place the washed material in an oven at 100 °C for drying for 3 h to obtain the acid-etched LaFeO3 powder, as shown in Figure 2. Next, disperse the dried material in 20 mL of 0.5 mol / L NaOH solution, continue to stir continuously for 1 h, and again centrifuge and wash 3 times using a centrifuge. Then, dry the treated material in an oven at 100 °C for 3 h and grind it to obtain the acid-etched and alkali-etched LaFeO3 material, as Figure 3 shown. Prepare OV2-LFO by the N2 radio frequency plasma method. The specific operation is as follows: Place the acid-etched and alkali-etched LaFeO3 material in a 100 V radio frequency electric field and bombard it with high-energy N2 (flow rate of 300 ml·min -1 ) plasma for 5 min to obtain the final modified material OV2-LFO, that is, a lanthanum ferrite-based photocatalytic material with oxygen vacancies, as Figure 4 shown, that is, a lanthanum ferrite-based photocatalytic material with oxygen vacancies; Figure 5 is the micro-plasma discharge treatment process.

[0036] The degradation mechanism of OV2-LFO is as follows: Visible light excites OV2-LFO to generate electrons (e-) and holes (H + ), where e - reduces O2 to generate ·O2 - , and H + oxidizes H2O to form ·OH or directly attacks TCH (tetracycline hydrochloride); subsequently, H + , ·OH, and ·O2 - synergistically act on the active sites of TCH and gradually decompose TCH through reactions such as demethylation, hydroxylation, and ring opening, and finally mineralize it into CO2 and H2O; oxygen vacancies in OV2-LFO enhance the adsorption of O2 and TCH, broaden the band gap and optimize the energy level, promote the separation of photo-generated carriers, improve the generation efficiency of ·O2 - and ·OH, accelerate electron transfer, and provide more active sites, significantly improving its photocatalytic degradation performance. These effects jointly promote the decomposition process of TCH, making OV2-LFO an efficient perovskite-based photocatalytic material.

[0037] Test the LaFeO3 powder material (LFO), acid-etched LaFeO3 powder (AL-LFO), acid-etched and alkali-etched LaFeO3 material (OV1-LFO), and acid-etched, alkali-etched, and plasma-treated LaFeO3 material (OV2-LFO) prepared in this example. By using a concentration of 40 mg·L -1TCH was used as the target pollutant to evaluate the catalytic effects of different treatment methods on LFO, AL-LFO, OV1-LFO, and OV2-LFO. The dosage of the four powder materials was 0.025 g each. 20 mL of TCH with a concentration of 40 mg·L -1 was placed in a transparent headspace bottle with a standard volume of 20 mL. Before the start of light irradiation, the pollutants were subjected to a 30-min dark reaction to establish the adsorption-desorption equilibrium, and then a 60-min photocatalytic degradation was carried out. The degraded solution was centrifuged by a centrifuge to obtain the supernatant. 4 mL of the supernatant was taken and placed in a quartz cuvette and then put into a UV spectrophotometer. The absorbance was measured at an absorption wavelength of 357 nm, and the concentration after degradation was calculated from the TCH degradation standard curve ( Figure 6 ). The degradation rate was calculated and the degradation rate curve was plotted (as shown in Figure 7 ). The ordinate represents the degradation rate of TCH, and the abscissa represents the degradation time (where -30 - 0 min represents the reaction under dark conditions, and 0 - 60 min represents the reaction under visible light). In the figure, the degradation rate of LFO was 31%, the degradation rate of AL-LFO was 45%, the degradation rate of OV1-LFO was 51%, and the degradation rate of OV2-LFO was 66%. It shows that after modifying the LaFeO3 powder material by the three-step method provided in this example, the photocatalytic degradation effect of the lanthanum ferrite-based photocatalytic powder on TCH was significantly improved.

[0038] Example 2

[0039] 5 mmol of La(NO3)·6H2O was dissolved in 30 mL of ultrapure water to obtain an aqueous solution of La(NO3)·6H2O. At the same time, 5 mmol of Fe(NO3)·9H2O and 10 mmol of citric acid were dissolved in another 30 mL of ultrapure water to prepare a mixed solution. Then, the aqueous solution of La(NO3)·6H2O was slowly added to the mixed solution, and intense magnetic stirring was carried out for 4 h. After ultrasonic treatment for 28 min, it was heated at 75 °C on a constant-temperature heater for 2 h while maintaining continuous stirring to obtain an orange-red gel. Then, the gel was dried in an oven at 95 °C for 10 h to obtain a LaFeO3 precursor. After grinding, it was calcined in a muffle furnace at a heating rate of 2.2 °C / min at 580 °C for 3.5 h to obtain a LaFeO3 powder material.

[0040] Modify LaFeO3:

[0041] Disperse 0.4 g of LaFeO3 powder material in 20 mL of 0.18 mol HNO3 solution, and continuously stir for 0.8 h. Subsequently, centrifuge and wash 3 times using a centrifuge. Place the washed material in an oven at 100 °C and dry for 3 h. Next, disperse the dried material in 20 mL of 0.48 mol NaOH solution, continue to continuously stir for 0.8 h, and again centrifuge and wash 2 times using a centrifuge. Then, dry the treated material in an oven at 100 °C for 3 h, and after grinding, obtain the acid-etched and alkali-etched LaFeO3 material. Prepare OV2-LFO using the N2 radio frequency plasma method. The specific operation is as follows: Place the acid-etched and alkali-etched LaFeO3 material in a 90 V radio frequency electric field and bombard it under high-energy N2 (flow rate: 250 ml·min -1 ) plasma for 4 min to obtain the final modified material OV2-LFO, that is, a lanthanum ferrite-based photocatalytic material with oxygen vacancies.

[0042] Test the photocatalytic material prepared in this example. The test method is the same as that in Example 1. After testing, the degradation rate of TCH reaches 57%.

[0043] Example 3

[0044] Dissolve 5 mmol of La(NO3)·6H2O in 30 mL of ultrapure water to obtain an aqueous solution of La(NO3)·6H2O. At the same time, dissolve 5 mmol of Fe(NO3)·9H2O and 10 mmol of citric acid in another 30 mL of ultrapure water to prepare a mixed solution. Then, slowly add the aqueous solution of La(NO3)·6H2O to the mixed solution and carry out vigorous magnetic stirring for 6 h. After ultrasonic treatment for 35 min, heat it on a constant temperature heater at 85 °C for 2.2 h while maintaining continuous stirring to obtain an orange-red gel. Then, dry the gel in an oven at 95 - 105 °C for 14 h to obtain the LaFeO3 precursor. After grinding, calcine it in a muffle furnace at a heating rate of 2.8 °C / min at 580 - 620 °C for 4.5 h to obtain the LaFeO3 powder material.

[0045] Modify LaFeO3:

[0046] Disperse 0.4 g of LaFeO3 powder material in 20 mL of 0.22 mol HNO3 solution, and continuously stir for 1.2 h. Subsequently, centrifuge and wash 3 times using a centrifuge, and place the washed material in an oven at 100 °C for drying for 3 h. Next, disperse the dried material in 20 mL of 0.52 mol NaOH solution, continue to continuously stir for 1.2 h, and again centrifuge and wash 3 times using a centrifuge. Then, dry the treated material in an oven at 100 °C for 3 h, and obtain the acid-etched and alkali-etched LaFeO3 material after grinding. Prepare OV2-LFO by the N2 radio frequency plasma method. The specific operation is as follows: Place the acid-etched and alkali-etched LaFeO3 material in a 110 V radio frequency electric field, and bombard it under high-energy N2 (flow rate of 350 ml·min -1 ) plasma for 6 min to obtain the final modified material OV2-LFO, that is, a lanthanum ferrite-based photocatalytic material with oxygen vacancies.

[0047] Test the photocatalytic material prepared in this example. The test method is the same as that in Example 1. After testing, the degradation rate of TCH reaches 61%.

[0048] The above embodiments are only one of the preferred embodiments of the present invention and should not be used to limit the protection scope of the present invention. Any meaningless modifications or polishings made on the main design concept and spirit of the present invention, as long as the technical problems solved are still consistent with the present invention, should be included in the protection scope of the present invention.

Claims

1. A method for preparing a lanthanum ferrite-based photocatalytic material having oxygen vacancies, characterized in that: The following steps are involved: S1, preparing LaFeO3 powder; S2, LaFeO3 powder is sequentially treated as follows: Acid etching: Disperse LaFeO3 powder in 0.18-0.22mol / L HNO3 solution and stir for 0.8-1.2h, centrifuge, wash and dry; Alkali etching: disperse the acid-etched LaFeO3 powder in 0.48-0.52 mol / L NaOH solution and stir for 0.8-1.2 h, centrifuge, wash and dry to obtain acid-alkali etched LaFeO3 powder; Plasma treatment: The LaFeO3 powder material after acid etching and alkali etching is placed in a 90-110V radio frequency electric field and plasma bombarded for 4-6 minutes in a N2 atmosphere with a flow rate of 250-350ml / min to obtain the final material OV2-LFO, that is, a lanthanum ferrite-based photocatalytic material with oxygen vacancies.

2. The method for preparing the lanthanum ferrite-based photocatalytic material with oxygen vacancies according to claim 1, characterized in that: In step S1, LaFeO3 powder is prepared by a sol-gel method, and the specific operation method is as follows: dissolve La(NO3)·6H2O in ultrapure water to obtain solution A; dissolve Fe(NO3)·9H2O and citric acid in ultrapure water to obtain solution B; slowly add solution A to solution B, stir magnetically for 4-6 hours, ultrasonically treat for 28-35 minutes, and heat at 75-85°C to form an orange-red gel; dry the gel in an oven and then grind it, and heat it to 580-620°C in a muffle furnace at 2.2-2.8°C / min and calcine it for 3.5-4.5 hours to obtain LaFeO3 powder.

3. The method for preparing the lanthanum ferrite-based photocatalytic material with oxygen vacancies according to claim 2, characterized in that: When preparing LaFeO3 powder, La(NO3)·6H2O and Fe(NO3)·9H2O are added in equimolar amounts, and the amount of citric acid added is twice the molar amount of Fe(NO3)3·9H2O.

4. The method for preparing the lanthanum ferrite-based photocatalytic material with oxygen vacancies according to claim 3, characterized in that: When preparing LaFeO3 powder, the gel is dried in an oven at 95-105°C for 10-14h.

5. The method for preparing the lanthanum ferrite-based photocatalytic material with oxygen vacancies according to claim 1 or 4, characterized in that: In step S2, 0.4 g of LaFeO 3 powder is dispersed in 20 mL of HNO 3 solution, the concentration of the HNO 3 solution is 0.2 mol / L, and the number of centrifugal washings is 2-3 times.

6. The method for preparing the lanthanum ferrite-based photocatalytic material with oxygen vacancies according to claim 5, characterized in that: In step S2, the acid-etched LaFeO3 powder is dispersed in 20 mL of NaOH solution, the concentration of the NaOH solution is 0.5 mol / L, and the number of centrifugal washing times is 2-3 times.

7. The method for preparing the lanthanum ferrite-based photocatalytic material with oxygen vacancies according to claim 6, characterized in that: In step S2, the plasma bombardment time is 5 minutes, the N2 flow rate is 300 ml / min, and the voltage of the radio frequency electric field is 100V.

8. The lanthanum ferrite-based photocatalytic material having oxygen vacancies prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The surface of the lanthanum ferrite-based photocatalytic material is rich in oxygen vacancies.

9. The use of the lanthanum ferrite-based photocatalytic material with oxygen vacancies as claimed in claim 8 in the degradation of tetracycline antibiotics, characterized in that: The lanthanum ferrite-based photocatalytic material generates e- and H+ under visible light excitation, and generates active free radicals ·O2- and ·OH through reduction and oxidation, thereby achieving efficient mineralization of tetracycline.

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