Lanthanum-doped cobalt oxide catalyst and preparation and application thereof

Abstract

The invention relates to a lanthanum-doped cobalt oxide catalyst as well as preparation and application thereof, and provides a preparation method of the lanthanum-doped cobalt oxide catalyst based on metal vacancy regulation and control, and the preparation method comprises the following steps: converting glycerol cobalt into cobalt oxide containing a large number of metal vacancies under high-temperature calcination; lanthanum ions adsorbed between glycerol cobalt layers can be filled in cobalt vacancies in the conversion process to form a highly dispersed lanthanum-doped cobalt oxide catalyst. The introduction of lanthanum not only can optimize the electronic structure of cobalt, but also can greatly improve the efficiency of the catalyst in the aspect of electron transport and increase the specific surface area of the catalyst, thereby improving the overall catalytic performance. The lanthanum-doped cobalt oxide catalyst has good PMS activation efficiency, especially has excellent degradation performance on pollutants such as tetracycline, methyl orange, rhodamine B, oxytetracycline and bisphenol A, has good universality and anti-interference capability on different pollutants and different water environments, and has good reusability.

Description

Technical Field

[0001] The invention belongs to the field of biotechnology, and specifically relates to a lanthanum-doped cobalt oxide catalyst and a preparation and application thereof. Background Art

[0002] Refractory organic pollutants such as antibiotics, pesticides and dyes produced during the industrialization process continue to threaten the ecological environment and human health due to their widespread existence, environmental persistence and bioaccumulation. Therefore, developing efficient and sustainable pollutant treatment methods has become a top priority for solving water pollution problems. Fenton-like technology based on peroxymonosulfate (PMS) has shown great potential in the field of sewage treatment due to its simple operation and high efficiency. The development of efficient PMS activation catalysts is of great value to the development of Fenton-like technology and its application in environmental pollution control engineering.

[0003] Transition metal catalysts are widely used in the field of Fenton-like technologies due to their high activity and low cost. Studies have shown that among many transition metals, cobalt (Co) has an excellent ability to activate PMS, so cobalt-based catalysts have become the research focus in this field. At present, the cobalt-based oxides reported for activating PMS to degrade organic pollutants mainly include CoO, CoOOH, Co 2 O 3 and Co 3 O 4 However, CoO x When used alone, it is easy to agglomerate, which severely limits the exposure of active sites, thereby weakening its catalytic activity and making it difficult to meet the needs of actual wastewater treatment. To break through this bottleneck, researchers have explored optimizing Co by doping with other metal elements (such as Cu, Fe, W, Ru, etc.). 3 O 4 The catalytic activity of persulfate. Practice has shown that the synergistic effect between different metals can greatly improve the activation efficiency of persulfate. In the redox reaction, cobalt species act as the dominant active site, and other metal elements directly or indirectly participate in the reaction, jointly accelerating the decomposition of persulfate and generating more active oxygen species, thereby enhancing the catalytic effect.

[0004] At present, the doping modification of cobalt-based oxide catalysts mostly adopts traditional co-precipitation, impregnation and other methods. Although the introduction of metal elements is achieved, there are problems such as poor doping uniformity and uncontrollable structure. It is even more impossible to achieve atomic-level dispersion of doping elements, which seriously affects the further improvement of catalytic activity. Summary of the invention

[0005] The purpose of the present invention is to provide a lanthanum-doped cobalt oxide catalyst and its preparation, and further expand its application in Fenton-like catalytic degradation of organic pollutants, so as to solve the problems that the doping elements of current cobalt-based oxide catalysts are mostly concentrated on transition metals and the synergistic effect of rare earth elements is underdeveloped.

[0006] A method for preparing a lanthanum-doped cobalt oxide catalyst comprises the following steps: (1) Co(CH 3 COO 2 ·4H 2 O is a cobalt source, Co(CH 3 COO 2 ·4H 2 O is added to glycerol, and after a hydrothermal reaction, a glycerol cobalt precursor is obtained; (2) dispersing the glycerol cobalt precursor in ethanol; (3) adding a lanthanum source to the ethanol dispersion of the glycerol cobalt precursor obtained in step (2) to react and obtain glycerol cobalt adsorbed with lanthanum ions; (4) The catalyst is then calcined at 300-600 °C to obtain a lanthanum-doped cobalt oxide catalyst. Furthermore, the lanthanum source is lanthanum nitrate.

[0007] Furthermore, the temperature of the hydrothermal reaction in step (1) is 180°C and the time is 2-4h.

[0008] Furthermore, the Co(CH 3 COO 2 ·4H 2 The mass ratio of O to glycerol is 0.5-2:39. Cobalt ions and glycerol coordinate to form glycerol cobalt. If too little glycerol is added, part of the cobalt cannot be coordinated and will be washed away in the subsequent washing operation; if too much glycerol is added, a large amount of glycerol that cannot be coordinated will also be produced, and the excess glycerol will be washed away in the washing operation.

[0009] Furthermore, in step (3), the mass ratio of the lanthanum source to the glycerol cobalt added is (0.09-26):1; more preferably, the mass ratio of the lanthanum source to the glycerol cobalt added is 26:1.

[0010] The lanthanum-doped cobalt oxide catalyst prepared by the above preparation method.

[0011] The above-mentioned lanthanum-doped cobalt oxide catalyst is used for Fenton-like catalytic degradation of organic pollutants.

[0012] Furthermore, the organic pollutants include tetracycline, methyl orange, rhodamine B, oxytetracycline and bisphenol A.

[0013] The present invention finds that rare earth elements have excellent electronic regulation capabilities in catalytic material modification due to their unique 4f electronic structure and variable valence state.

[0014] Glycerol cobalt is used as a precursor, and lanthanum ions are adsorbed between its layers. Then, after heat treatment, a cobalt oxide catalyst with lanthanum filling cobalt vacancies is prepared. Glycerol cobalt will be converted into cobalt oxide containing metal vacancies under high-temperature calcination. At the same time, due to the strong interaction between glycerol cobalt and lanthanum species, lanthanum elements can be induced to be doped in the metal vacancies of cobalt oxide to form La-Co 3 O 4 Composite materials.

[0015] The La-Co 3 O 4 The composite material exhibits excellent catalytic performance in the Fenton-like reaction of activating PMS, and can efficiently degrade the organic pollutant tetracycline (TC). In addition, the catalyst of the present invention exhibits good universality and anti-drying ability for different pollutants and complex water environments, and has excellent reusability.

[0016] Compared with the prior art, the present invention has the following advantages: 1) The present invention is based on a La-doped cobalt oxide catalyst regulated by metal vacancies. Glycerol cobalt is converted into cobalt oxide containing a large number of metal vacancies under high-temperature calcination, and the lanthanum ions adsorbed between the glycerol cobalt layers can fill in the cobalt vacancies during the conversion process to form a highly dispersed La-doped cobalt oxide composite material.

[0017] (2) La-Co of the present invention 3 O 4 There is a synergistic effect between La and Co in the catalyst. The introduction of lanthanum can not only optimize the electronic structure of cobalt, but also greatly improve the efficiency of the catalyst in electron transport and accelerate the activation of PMS. Moreover, by doping with lanthanum, the surface state of the catalyst can also be adjusted, making the catalytic active sites more evenly distributed and exposing more metal active sites. Lanthanum doping can also increase the specific surface area of ​​the catalyst, thereby improving the overall catalytic performance. This synergistic effect between La-Co metals can break through the performance bottleneck of a single metal catalyst and show better catalytic performance through fine electronic structure regulation, exposure of more active sites and synergistic cascade mechanism of adsorption activation.

[0018] (3) La-doped Co prepared by metal vacancy regulation 3 O 4 The catalyst exhibits good PMS activation efficiency, especially excellent degradation performance for pollutants such as tetracycline, methyl orange, rhodamine B, oxytetracycline and bisphenol A. It also shows good universality and anti-interference ability for different pollutants and different water environments, and has good reusability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The La-Co 3 O 4 Catalyst N 2 Adsorption–desorption curves.

[0020] Figure 2 The La-Co 3 O 4 X-ray diffraction (XRD) patterns of the catalysts.

[0021] Figure 3 Scanning electron microscope (SEM) images; (a) La-Co 3 O 4 ; (b) Co 3-x O 4 .

[0022] Figure 4 The La-Co 3 O 4 Transmission electron microscopy (TEM) image of the catalyst.

[0023] Figure 5 For Co 3-x O 4 、La-Co 3 O 4 Electron paramagnetic resonance (EPR) image of the catalyst.

[0024] Figure 6 The La-Co 3 O 4 TC catalytic degradation and PMS activation effect test of the catalyst; including: (a) degradation performance test; (b) PMS consumption.

[0025] Figure 7 La-Co with different lanthanum doping amounts 3 O 4 TC catalytic degradation test of the catalyst and its X-ray diffraction (XRD) spectrum; (a) degradation performance test; (b) catalyst XRD spectrum.

[0026] Figure 8 The La-Co 3 O 4 Anti-interference and stability test of the catalyst; (a) the effects of various water environments on La-Co 3 O 4 Effect of catalyst on TC degradation; (b) Catalyst degradation effect on different pollutants (20 mg / L); (c) La-Co 3 O4 Stability testing of catalysts. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] Example 1 A lanthanum-doped cobalt oxide catalyst La-Co 3 O 4 The synthesis method comprises the following steps: (1) Preparation of glycerol cobalt: Add 1 g of cobalt acetate tetrahydrate to 39 g of glycerol and stir to dissolve it completely and mix it thoroughly. Transfer the mixed solution to a polytetrafluoroethylene reactor and react it at 180 °C for 2-4 h. After cooling to room temperature, wash it several times to obtain a pink-purple solid and dry it in an oven to obtain a glycerol cobalt precursor.

[0029] (2) dispersing the glycerol cobalt precursor in ethanol; (3) La-Co 3 O 4 Preparation of catalyst: 3 mmol of lanthanum nitrate and 50 mg of glycerol cobalt solution were stirred and mixed evenly, washed with ethanol several times, and then vacuum dried to obtain solid powder; (4) The solid powder is calcined in a muffle furnace (300-600 °C) for 2-4 h to obtain La-Co 3 O 4 catalyst.

[0030] Example 2 The 3 mmol lanthanum nitrate in step (3) of Example 1 was replaced with 0.01 mmol and 0.1 mmol respectively, while other conditions and steps remained unchanged.

[0031] Example 3 The mass of cobalt acetate tetrahydrate in step (1) of Example 1 was changed to 0.1, 0.5, 1 and 3 g respectively, and the other conditions and steps remained unchanged. It was found that when the mass of cobalt acetate tetrahydrate was 0.5 g and 1 g, the performance of the catalyst finally obtained was not as good as that of Example 1; when the mass of cobalt acetate tetrahydrate was 0.1 g, a large amount of glycerol that could not be coordinated was produced, and when the mass of cobalt acetate tetrahydrate was 3 g, part of the cobalt could not be coordinated, and the performance of the catalyst finally obtained was not as good as that of Example 1.

[0032] Comparative Example 1 Co 3-x O 4 Catalyst preparation The glycerol cobalt precursor obtained in step (1) of Example 1 was directly heated to 300 °C in a muffle furnace and maintained for 2-4 h to obtain a Co with metal vacancies.3-x O 4 .

[0033] Comparative Example 2 Ce-Co 3 O 4 Catalyst preparation The lanthanum nitrate in step (3) of Example 1 was replaced with 3 mmol of cerium nitrate, and the rest was similar to Example 1.

[0034] Comparative Example 3 ads-La-Co 3 O 4 Catalyst preparation The glycerol cobalt precursor obtained in step (1) of Example 1 was directly heated to 700 °C in a muffle furnace and maintained for 4 h to obtain a highly crystalline Co 3 O 4 , and then directly mixed it with 0.01 mmol of lanthanum nitrate, washed and dried, and calcined in a muffle furnace (300-600 ° C) for 2-4 h to obtain ads-La-Co 3 O 4 (Cobalt vacancies are almost negligible).

[0035] Comparative Example 4 Exploration of calcination temperature The solid powder obtained in step (3) of Example 1 was calcined in a muffle furnace at 200 and 700 °C for 2-4 h to obtain La-Co 3 O 4 -200, and La-Co 3 O 4 -700 catalyst. Figure 2 As shown in Figure 2, the catalyst cannot form Co under the calcination temperature of 200 °C. 3 O 4 When the calcination temperature is 700℃, in addition to the Co 3 O 4 The diffraction peaks of LaCoO were also detected. 3 This indicates that the crystal structure and composition of the catalyst will change significantly at different calcination temperatures.

[0036] Comparative Example 5 When step (2) of Example 1 was replaced by dispersing the glycerol cobalt precursor in an aqueous solution, it was found that the dispersibility was very poor.

[0037] Comparative Example 6 The lanthanum nitrate in step (3) of Example 1 was replaced with LaCl 3 , and the rest is the same as Example 1. The performance of the obtained catalyst is not good, and the degradation efficiency of TC is less than 50%.

[0038] Performance Testing 1. X-ray diffraction analysis The obtained catalyst was subjected to X-ray diffraction analysis. Figure 2 As shown, except for the sample La-Co 3 O 4 -200, and all other samples showed the presence of Co 3 O 4 (PDF#43-1003) has a diffraction peak at 31.26 o , 36.82 o ,44.78 o ,59.36 o and 65.22 o The corresponding positions are Co 3 O 4 (220), (311), (400), (511) and (440) crystal planes.

[0039] 2. Morphology analysis The La-Co 3 O 4 The catalyst was subjected to morphological analysis, such as Figure 3 As shown in (a), La-Co 3 O 4 It is composed of nanoparticles of uniform size, with an average diameter of about 7~8 nm. 3 O 4 The morphology and structure of Co 3 O 4 similar, indicating that lanthanum doping does not change the basic morphology of the material. Transmission electron microscopy ( Figure 4 ) also shows La-Co 3 O 4 The structure of nanoparticles is consistent with the SEM results. High-resolution transmission electron microscopy shows that the lattice fringe spacing of the nanoparticles is 0.25 nm and 0.15 nm, respectively, belonging to Co 3 O 4 The (311) and (440) crystal planes further indicate that the cobalt species is mainly Co 3 O 4 , which is consistent with the XRD results.

[0040] from Figure 1 It can be seen that doping with lanthanum can also adjust the surface state of the catalyst, making the catalytic active sites more evenly distributed and exposing more metal active sites. Lanthanum doping can also increase the specific surface area of ​​the catalyst.

[0041] 3. Electron paramagnetic resonance analysis The La-Co prepared in Example 1 3 O 4 The catalyst was subjected to electron paramagnetic resonance analysis, such as Figure 5 As shown. La-Co 3 O 4 The catalyst has a symmetric signal at g = 2.004, confirming the existence of cobalt vacancies. 3-x O 4 In comparison, La-Co 3 O 4 The EPR signal intensity is significantly weakened, proving that lanthanum is successfully doped into the cation vacancies, thereby reducing the concentration of cation vacancies.

[0042] It is worth noting that compared with the simple Co 3 O 4 In comparison, La-Co 3 O 4 The EPR signal intensity of the catalyst was significantly weakened, which strongly proved that the lanthanum element had been successfully doped into the cation vacancies, thereby effectively reducing the concentration of cation vacancies.

[0043] 4. La-Co 3 O 4 Performance evaluation of TC degradation by catalyst activated PMS-type Fenton Weigh 7.5 mg of La-Co 3 O 4 The catalyst and a certain amount of PMS were added to the TC solution (50 mL, 20 mg / L). During the reaction, 2 mL of the suspension was taken out at a given time interval, the catalyst was filtered out, and 1 mL of methanol solution was immediately added to quench the reaction. The absorbance was measured at 356 nm using a UV-visible spectrophotometer to analyze the residual concentration of TC. The experimental results are shown in Figure 2. Figure 6 As shown in (a), PMS alone cannot effectively degrade TC, while Co 3-x O 4 The ability to activate PMS is also limited. However, the lanthanum-doped catalyst La-Co 3 O 4 The degradation performance was significantly enhanced, and the degradation efficiency of TC reached 97.9% within 10 min (degradation rate constant k = 0.4874 min -1 ). In contrast, under the same conditions, Co 3- x O 4 After 20 min, only 48.6% of the TC degradation rate was achieved (degradation rate constant k = 0.0293 min -1 ). La-Co 3 O4 The degradation rate constant is Co 3-x O 4 In addition, ads-La-Co 3 O 4 The degradation efficiency and rate of TC are related to Co 3-x O 4 The results are similar, 53.5% and 0.0354 min respectively. -1 This indicates that La doping based on metal vacancy regulation can significantly improve the efficiency of PMS activated by cobalt oxide in degrading pollutants. Figure 6 (b) shows the consumption of PMS under different catalytic systems, among which La-Co 3 O 4 The consumption of PMS is the largest, indicating that La-Co 3 O 4 The activation efficiency of PMS is the highest.

[0044] Under the same conditions, cerium-doped cobalt oxide (Ce-Co 3 O 4 ) and compared with the lanthanum-cobalt catalyst (La-Co 3 O 4 ) for comparison. Figure 6 As shown, Ce-Co 3 O 4 The degradation performance of the catalyst is far inferior to that of La-Co 3 O 4 This further demonstrates the significant advantages of lanthanum metal in Fenton-like catalytic reactions.

[0045] The above experimental results show that there is a synergistic effect between La and Co. The introduction of lanthanum can not only optimize the electronic structure of cobalt, but also greatly improve the efficiency of the catalyst in electron transport and accelerate the activation of PMS. Moreover, by doping with lanthanum, the surface state of the catalyst can also be adjusted, making the catalytic active sites more evenly distributed and exposing more sites, thereby improving the overall catalytic performance. This synergistic effect between La-Co metals can break through the performance bottleneck of a single metal catalyst and show better catalytic performance through fine electronic structure regulation, exposure of more active sites and synergistic cascade mechanism of adsorption activation.

[0046] 5. Effect of lanthanum doping concentration on degradation performance In order to further explore the effect of lanthanum doping concentration on degradation performance, the present invention added 0.01 mmol, 0.1 mmol and 3 mmol of lanthanum respectively to explore its effect. Figure 7As shown in (a), when the amount of lanthanum added was 0.01 mmol, the degradation rate of TC was 82% in 20 minutes. When the amount of lanthanum was further increased to 0.1 mmol, the degradation rate of TC increased to 90%. When the amount of lanthanum was increased to 3 mmol, although the degradation rate in the first 10 minutes increased significantly, the degradation efficiency of TC did not increase significantly.

[0047] XRD patterns of catalysts with different lanthanum doping amounts, such as Figure 7 As shown in (b), it can be clearly seen that with the increase of La concentration, the diffraction peak intensity of the composite material becomes weaker and the peak width becomes wider. This may be due to the slight distortion of the cobalt oxide crystal structure caused by the doping of lanthanum. This further confirms that the lanthanum element effectively enters the lattice structure of the catalyst, thus affecting its physical and chemical properties. Nevertheless, the composite materials with different lanthanum contents still show the same 3 O 4 The consistent diffraction peaks indicate that increasing the lanthanum doping does not introduce new phases.

[0048] 6. Analysis of application potential in actual water treatment To further verify the La-Co 3 O 4 The application potential of the catalyst in actual water treatment, the present invention systematically investigated its anti-interference ability, broad-spectrum degradation and cyclic stability, such as Figure 8 In the simulation of complex water environment system, such as Figure 8 In (a), the catalyst showed excellent degradation performance for tetracycline (TC) in different water sources, including lake water, reservoir water, tap water, and primary sewage, indicating that the system has good anti-interference ability and has the potential to operate in actual water environments. In addition, Figure 8 Figure (b) shows that, in addition to tetracycline (TC), the catalyst also has significant oxidative degradation effects on a variety of pollutants, such as methyl orange, rhodamine B, oxytetracycline and bisphenol A. These pollutants can be effectively degraded within 20 minutes, with a degradation rate of up to 98%, which fully demonstrates its excellent performance and wide applicability in degrading a variety of pollutants. Figure 8 As can be seen in (c), after five cycles, the degradation rate of the catalyst can still be maintained above 90%. The results fully demonstrate that the catalyst has excellent reusability and stability, providing a solid foundation for its practical application in water treatment.

Claims

1. A method for preparing a lanthanum-doped cobalt oxide catalyst, characterized in that: The following steps are involved: (1) Using Co(CH3COO)2·4H2O as a cobalt source, Co(CH3COO)2·4H2O was added to glycerol and subjected to a hydrothermal reaction to obtain a glycerol cobalt precursor; (2) dispersing the glycerol cobalt precursor in ethanol; (3) adding a lanthanum source to the ethanol dispersion of the glycerol cobalt precursor obtained in step (2) to react and obtain glycerol cobalt adsorbed with lanthanum ions; (4) The catalyst is then calcined at 300-600 °C to obtain a lanthanum-doped cobalt oxide catalyst.

2. The preparation method according to claim 1, characterized in that: The lanthanum source is lanthanum nitrate.

3. The preparation method according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step (1) is 180°C and the time is 2-4 hours.

4. The preparation method according to claim 1, characterized in that: The mass ratio of Co(CH3COO)2·4H2O and glycerol added in step (1) is 0.5-2:

39.

5. The preparation method according to claim 1, characterized in that: In step (3), the mass ratio of the lanthanum source to the glycerol cobalt added is (0.09-26):

1.

6. The lanthanum-doped cobalt oxide catalyst prepared according to the preparation method according to any one of claims 1 to 5.

7. The use of the lanthanum-doped cobalt oxide catalyst according to claim 6, characterized in that: Used for Fenton-like catalytic degradation of organic pollutants.

8. The use according to claim 7, characterized in that: The organic pollutants include tetracycline, methyl orange, rhodamine B, oxytetracycline and bisphenol A.

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