A lanthanum-doped cobalt oxide catalyst and its preparation and application

Abstract

The present invention relates to a lanthanum-doped cobalt oxide catalyst and its preparation and application. The present invention proposes a preparation method of a lanthanum-doped cobalt oxide catalyst based on metal vacancy regulation. Cobalt glycerate is converted into cobalt oxide containing a large number of metal vacancies under high-temperature calcination. Lanthanum ions adsorbed between the layers of cobalt glycerate can fill the cobalt vacancies during the conversion process to form a highly dispersed lanthanum-doped cobalt oxide 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, increase the specific surface area of the catalyst, thereby enhancing the overall catalytic performance. The lanthanum-doped cobalt oxide catalyst of the present invention has a good PMS activation efficiency, especially excellent degradation performance for pollutants such as tetracycline, methyl orange, rhodamine B, oxytetracycline, and bisphenol A, and has good universality, anti-interference ability for different pollutants and different water environments, and good reusability.

Description

Technical Field

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

[0002] The refractory organic pollutants generated in the industrialization process, such as antibiotics, pesticides, and dyes, etc., due to their characteristics of wide existence, environmental persistence, and bioaccumulation, continuously threaten the ecological environment and human health. Therefore, developing efficient and sustainable pollutant treatment methods has become an urgent task to solve the water pollution problem. The Fenton-like technology based on peroxymonosulfate (PMS) shows good potential in the field of sewage treatment due to its advantages such as simple operation and high efficiency. Developing efficient PMS activation catalysts is of great value for the development of Fenton-like technology and promoting its engineering application in environmental pollution treatment.

[0003] Transition metal catalysts have been widely used in the field of Fenton-like technology due to their high activity and low cost. Research shows that among many transition metals, cobalt (Co) is particularly excellent in activating PMS, so cobalt-based catalysts have become the research focus in this field. Currently, the reported cobalt-based oxides used to activate PMS to degrade organic pollutants mainly include CoO, CoOOH, Co2O3, and Co3O4, etc. However, CoO x is prone to agglomeration when used alone, which severely limits the exposure of active sites, thereby weakening its catalytic activity and making it difficult to meet the requirements of actual wastewater treatment. To break through this bottleneck, researchers have explored doping other metal elements (such as Cu, Fe, W, Ru, etc.) to optimize the catalytic activity of Co3O4. Practice shows that the synergistic effect between different metals can greatly improve the activation efficiency of persulfate. In the redox reaction, cobalt species serve as the dominant active sites, and other metal elements directly or indirectly participate in the reaction, jointly accelerating the decomposition of persulfate to generate more reactive oxygen species, thereby enhancing the catalytic effect.

[0004] Currently, the doping modification of cobalt-based oxide catalysts mostly uses traditional methods such as coprecipitation and impregnation. Although the introduction of metal elements is achieved, there are problems such as poor doping uniformity and uncontrollable structure, and it is even more impossible to achieve atomic-level dispersion of doping elements, seriously affecting 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 the catalytic degradation of organic pollutants by Fenton-like, so as to solve the problems that the doping elements of current cobalt-based oxide catalysts mostly focus on transition metals and the synergistic effect of rare earth elements is insufficiently developed, etc.

[0006] A preparation method of a lanthanum-doped cobalt oxide catalyst includes the following steps:

[0007] (1) Using Co(CH3COO)2·4H2O as the cobalt source, Co(CH3COO)2·4H2O was added to glycerol, and after hydrothermal reaction, a cobalt glycerolate precursor was obtained.

[0008] (2) The cobalt glycerolate precursor was dispersed in ethanol.

[0009] (3) The lanthanum source was added to the cobalt glycerolate precursor ethanol dispersion obtained in step (2) for reaction to obtain cobalt glycerolate adsorbed with lanthanum ions.

[0010] (4) Then, it was calcined at a high temperature of 300 - 600 °C to obtain a lanthanum-doped cobalt oxide catalyst.

[0011] Further, the lanthanum source was lanthanum nitrate.

[0012] Further, in step (1), the temperature of the hydrothermal reaction was 180 °C and the time was 2 - 4 h.

[0013] Further, the mass ratio of Co(CH3COO)2·4H2O to glycerol added in step (1) was 0.5 - 2:39. Cobalt ions coordinate with glycerol to form cobalt glycerolate. Adding too little glycerol results in some cobalt being unable to coordinate and being washed away in subsequent washing operations; adding too much glycerol will also produce a large amount of uncoordinated glycerol, and the excess glycerol will be washed away in the washing operation.

[0014] Further, the mass ratio of the lanthanum source to the added cobalt glycerolate in step (3) was (0.09 - 26):1; more preferably, the mass ratio of the lanthanum source to the added cobalt glycerolate was 26:1.

[0015] The lanthanum-doped cobalt oxide catalyst prepared by the above preparation method.

[0016] The application of the above lanthanum-doped cobalt oxide catalyst for catalytic degradation of organic pollutants by Fenton-like reaction.

[0017] Further, the organic pollutants include tetracycline, methyl orange, rhodamine B, oxytetracycline, and bisphenol A.

[0018] The present invention discovers that rare earth elements exhibit excellent electron regulation ability in the modification of catalytic materials due to their unique 4f electron structure and variable valence states.

[0019] Using cobalt glycerolate as the precursor, lanthanum ions were adsorbed between its layers, and then after heat treatment, a cobalt oxide catalyst with lanthanum filling cobalt vacancies was prepared. Cobalt glycerolate will be converted into cobalt oxide with metal vacancies under high-temperature calcination. At the same time, due to the strong interaction between cobalt glycerolate and lanthanum species, it can induce the doping of lanthanum elements in the metal vacancies of cobalt oxide to form a La-Co3O4 composite material.

[0020] The La-Co3O4 composite material of the present invention 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 shows good universality and anti-interference ability for different pollutants and complex water environments, and has excellent reusability.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1) The La-doped cobalt oxide catalyst of the present invention based on metal vacancy regulation. Cobalt glycerate will be converted into cobalt oxide containing a large number of metal vacancies under high-temperature calcination, and the lanthanum ions adsorbed between the layers of cobalt glycerate can be filled in the cobalt vacancies during the conversion process to form a highly dispersed La-doped cobalt oxide composite material.

[0023] (2) There is a synergistic effect between La and Co in the La-Co3O4 catalyst of the present invention. 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 lanthanum, the surface state of the catalyst can be adjusted, making the distribution of catalytic active sites more uniform and exposing more metal active sites. The doping of lanthanum 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 single-metal catalysts through a fine electronic structure regulation, exposing more active sites and an adsorption-activation synergistic cascade mechanism, and showing more excellent catalytic performance.

[0024] (3) The metal vacancy-regulated La-doped Co3O4 catalyst prepared by the present invention shows good PMS activation efficiency, especially excellent degradation performance for pollutants such as tetracycline, methyl orange, rhodamine B, oxytetracycline, and bisphenol A, and shows good universality and anti-interference ability for different pollutants and different water environments, and has good reusability at the same time. Brief Description of the Drawings

[0025] Figure 1 It is the N2 adsorption-desorption curve of the La-Co3O4 catalyst of the present invention.

[0026] Figure 2 It is the X-ray diffraction (XRD) pattern of the La-Co3O4 catalyst of the present invention.

[0027] Figure 3 It is a scanning electron microscope (SEM) image; wherein, (a) La-Co3O4; (b) Co 3-x O4.

[0028] Figure 4This is the transmission electron microscope (TEM) image of the La-Co3O4 catalyst of the present invention.

[0029] Figure 5 is Co 3-x O4, and the electron paramagnetic resonance (EPR) images of Co3O4 and La-Co3O4 catalysts.

[0030] Figure 6 This is the TC catalytic degradation and PMS activation effect test of the La-Co3O4 catalyst of the present invention; among them, (a) degradation performance test; (b) PMS consumption.

[0031] Figure 7 is the TC catalytic degradation test of La-Co3O4 catalysts with different lanthanum doping amounts and their X-ray diffraction (XRD) patterns; among them, (a) degradation performance test; (b) catalyst XRD patterns.

[0032] Figure 8 This is the anti-interference and stability test of the La-Co3O4 catalyst of the present invention; among them, (a) the influence of various water body environments on the degradation of TC by the La-Co3O4 catalyst; (b) the degradation effect of the catalyst on different pollutants (20 mg / L); (c) the stability test of the La-Co3O4 catalyst. Detailed implementation manners

[0033] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0034] Example 1

[0035] A synthesis method of a lanthanum-doped cobalt oxide catalyst La-Co3O4 includes the following steps:

[0036] (1) Preparation of cobalt glycerolate: Add 1 g of cobalt acetate tetrahydrate to 39 g of glycerol, stir to completely dissolve and mix evenly, transfer the mixed solution to a polytetrafluoroethylene reaction kettle, react at 180 °C for 2 - 4 h, cool to room temperature, wash several times, and obtain a pink-purple solid and place it in an oven to dry to obtain a cobalt glycerolate precursor.

[0037] (2) Disperse the cobalt glycerolate precursor in ethanol;

[0038] (3) Preparation of the La-Co3O4 catalyst: Stir and mix 3 mmol of lanthanum nitrate and 50 mg of cobalt glycerolate solution evenly, wash several times with ethanol, and then dry under vacuum to obtain a solid powder;

[0039] (4) Calcinate the above solid powder in a muffle furnace (300 - 600 °C) for 2 - 4 h to obtain the La-Co3O4 catalyst.

[0040] Example 2

[0041] In step (3) of Example 1, 3 mmol of lanthanum nitrate was replaced with 0.01 mmol and 0.1 mmol respectively, and other conditions and steps remained unchanged.

[0042] Example 3

[0043] In step (1) of Example 1, the mass of cobalt acetate tetrahydrate was replaced with 0.1, 0.5, 1, and 3 g respectively, and 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 finally obtained catalyst was inferior to that of Example 1; when it was 0.1 g, a large amount of uncoordinated glycerol was produced, and when it was 3 g, part of the cobalt could not be coordinated, and the performance of the finally obtained catalyst was inferior to that of Example 1.

[0044] Comparative Example 1

[0045] Co 3-x Preparation of Co3O4 Catalyst

[0046] The cobalt glycerol precursor obtained in step (1) of Example 1 was directly heated to 300 °C in a muffle furnace and kept for 2 - 4 h to obtain Co3O4 with metal vacancies. 3-x O4.

[0047] Comparative Example 2

[0048] Preparation of Ce-Co3O4 Catalyst

[0049] In step (3) of Example 1, lanthanum nitrate was replaced with 3 mmol of cerium nitrate, and the others were similar to Example 1.

[0050] Comparative Example 3

[0051] Preparation of ads-La-Co3O4 Catalyst

[0052] The cobalt glycerol precursor obtained in step (1) of Example 1 was directly heated to 700 °C in a muffle furnace and kept for 4 h to obtain highly crystalline Co3O4, and then it was directly mixed with 0.01 mmol of lanthanum nitrate, washed, dried, and calcined in a muffle furnace (300 - 600 °C) for 2 - 4 h to obtain ads-La-Co3O4 (the cobalt vacancies were almost negligible).

[0053] Comparative Example 4

[0054] Exploration of Calcination Temperature

[0055] 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-Co3O4-200 and La-Co3O4-700 catalysts. It was found that, as Figure 2 shown, the Co3O4 phase could not be formed when the calcination temperature of the catalyst was 200 °C. When the calcination temperature was 700 °C, in addition to the diffraction peaks of Co3O4, the LaCoO3 phase was also detected. This indicates that the crystal structure and composition of the catalyst will change significantly at different calcination temperatures.

[0056] Comparative Example 5

[0057] Step (2) of Example 1 was replaced by dispersing cobalt glycerate precursor in an aqueous solution, and it was found that the dispersibility was very poor.

[0058] Comparative Example 6

[0059] Lanthanum nitrate in step (3) of Example 1 was replaced by LaCl3, and the others were the same as in Example 1. The performance of the obtained catalyst was not good, and the degradation efficiency of TC was less than 50%.

[0060] Performance Test

[0061] 1. X-ray Diffraction Analysis

[0062] The prepared catalysts were subjected to X-ray diffraction analysis, and the results were as Figure 2 shown. Except for the sample La-Co3O4-200, diffraction peaks attributed to Co3O4 (PDF#43-1003) appeared in other samples. At 31.26 o , 36.82 o , 44.78 o , 59.36 o and 65.22 o corresponded to the (220), (311), (400), (511) and (440) crystal planes of Co3O4, respectively.

[0063] 2. Morphology Analysis

[0064] The morphology of the La-Co3O4 catalyst of Example 1 was analyzed by scanning electron microscopy. As shown in (a) of Figure 3 , La-Co3O4 was composed of uniformly sized nanoparticles with an average diameter of about 7 - 8 nm. Moreover, the morphological structure of La-Co3O4 was similar to that of Co3O4, indicating that the doping of lanthanum did not change the basic morphology of the material. Transmission electron microscopy ( Figure 4Similarly, La-Co3O4 is shown to be in a nanoparticle structure, which is consistent with the SEM results. High-resolution transmission electron microscopy shows that the lattice fringe spacings of the nanoparticles are 0.25 nm and 0.15 nm, which can be attributed to the (311) and (440) crystal planes of Co3O4, respectively, further indicating that the cobalt species exist in the form of Co3O4, which is consistent with the XRD results.

[0065] It can be seen from Figure 1 that doping lanthanum can also regulate the surface state of the catalyst, making the distribution of catalytic active sites more uniform and exposing more metal active sites. The doping of lanthanum can also increase the specific surface area of the catalyst.

[0066] 3. Electron paramagnetic resonance analysis

[0067] The La-Co3O4 catalyst prepared in Example 1 was subjected to electron paramagnetic resonance analysis, as Figure 5 shown. The La-Co3O4 catalyst has a symmetric signal at g = 2.004, confirming the existence of cobalt vacancies. Compared with Co 3-x O4, the EPR signal intensity of La-Co3O4 is significantly weakened, proving that lanthanum has been successfully doped into the cation vacancies, thereby reducing the concentration of cation vacancies.

[0068] It should be noted that compared with pure Co3O4, the EPR signal intensity of the La-Co3O4 catalyst is significantly weakened, which strongly proves that lanthanum has been successfully doped into the cation vacancies, thereby effectively reducing the concentration of cation vacancies.

[0069] 4. Performance evaluation of La-Co3O4 catalyst-activated PMS-like Fenton degradation of TC

[0070] 7.5 mg of the La-Co3O4 catalyst and a certain amount of PMS were weighed and added to the TC solution (50 mL, 20 mg / L). During the reaction, 2 mL of the suspension was taken out at given time intervals, the catalyst was filtered off, and 1 mL of methanol solution was immediately added to quench the reaction. The absorbance was measured at 356 nm with a UV-visible spectrophotometer to analyze the residual concentration of TC. The experimental results are as Figure 6 shown in (a) below. Alone, PMS cannot effectively degrade TC, and the ability of Co 3-x O4 alone to activate PMS is also relatively limited. However, the doped catalyst La-Co3O4 exhibits significantly enhanced degradation performance, and the degradation efficiency of TC reaches 97.9% within 10 min of the reaction (degradation rate constant k = 0.4874 min -1 ). In contrast, under the same conditions, Co 3- xO4 could only achieve a TC degradation rate of 48.6% after 20 min (degradation rate constant k = 0.0293 min -1 ). The degradation rate constant of La-Co3O4 is 16.6 times that of Co 3-x O4. In addition, the degradation efficiency and rate of ads-La-Co3O4 for TC are similar to those of Co 3-x O4, which are 53.5% and 0.0354 min -1 respectively. This indicates that La doping based on metal vacancy regulation can significantly improve the efficiency of cobalt oxide-activated PMS for pollutant degradation. Figure 6 (b) in shows the consumption of PMS under different catalytic systems, where La-Co3O4 has the largest consumption of PMS, indicating that La-Co3O4 has the highest activation efficiency for PMS.

[0071] Under the same conditions, the catalytic performance of cerium-doped cobalt oxide (Ce-Co3O4) was evaluated and compared with that of lanthanum-cobalt catalyst (La-Co3O4). As Figure 6 shown, the Ce-Co3O4 catalyst is far inferior to the La-Co3O4 catalyst in terms of degradation performance, which further proves the significant advantage of lanthanum metal in the Fenton-like catalytic reaction.

[0072] The above experimental results illustrate the existence of a synergistic effect between La and Co. The introduction of lanthanum can not only optimize the electronic structure of cobalt but also greatly enhance the efficiency of the catalyst in electron transfer, accelerating the activation of PMS. Moreover, by doping lanthanum, the surface state of the catalyst can be adjusted, making the distribution of catalytic active sites more uniform and exposing more sites, thus improving the overall catalytic performance. This La-Co metal synergistic effect, through a fine electronic structure regulation, exposing more active sites, and an adsorption-activation synergistic cascade mechanism, can break through the performance bottleneck of single-metal catalysts and exhibit more excellent catalytic performance.

[0073] 5. Influence of Lanthanum Doping Concentration on Degradation Performance

[0074] To deeply explore the influence of lanthanum doping concentration on degradation performance, 0.01 mmol, 0.1 mmol, and 3 mmol of lanthanum were added respectively in this invention to investigate its influence. As Figure 7 can be seen from (a) in, when the amount of lanthanum added is 0.01 mmol, the degradation rate of TC is 82% at 20 minutes. When the amount of lanthanum is further increased to 0.1 mmol, the degradation rate of TC increases to 90%. When the amount of lanthanum is increased to 3 mmol, although the degradation rate in the first 10 minutes increases significantly, the degradation efficiency of TC does not increase significantly.

[0075] XRD patterns of catalysts with different lanthanum doping amounts, asFigure 7 As shown in Fig. (b), it can be clearly seen that as the La concentration increases, the diffraction peak intensity of the composite material weakens and the peak width broadens. This may be due to the doping of lanthanum causing a slight distortion in the crystal structure of cobalt oxide, which further confirms that lanthanum 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 diffraction peaks consistent with Co3O4, indicating that the increase in lanthanum doping does not introduce new phases.

[0076] 6. Analysis of Application Potential in Actual Water Treatment

[0077] To further verify the application potential of the La-Co3O4 catalyst in actual water treatment, the present invention systematically investigated its anti-interference ability, broad-spectrum degradation ability and cycle stability, as Figure 8 shown. In a simulated complex water environment system, as Figure 8 shown in Fig. (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 the potential to operate in actual water environments. In addition, Figure 8 Fig. (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 min, and the degradation rate is as high as 98%, which fully demonstrates its excellent efficiency and wide applicability in degrading a variety of pollutants. As can be seen from Figure 8 Fig. (c), after five cycles, the degradation rate of the catalyst can still remain above 90%. The results fully show that the catalyst has excellent reusability and stability, providing a solid foundation for its practical application in water treatment.

Claims

1. A preparation method of a lanthanum-doped cobalt oxide catalyst, characterized in that, It includes the following steps: (1) Using Co(CH3COO)2·4H2O as the cobalt source, add Co(CH3COO)2·4H2O to glycerol, and after hydrothermal reaction, obtain a cobalt glycerol precursor; (2) Disperse the cobalt glycerol precursor in ethanol; (3) Add the lanthanum source to the cobalt glycerol precursor ethanol dispersion obtained in step (2) for reaction to obtain cobalt glycerol adsorbed with lanthanum ions; (4) Then calcine at a high temperature of 300 - 600 °C to obtain a lanthanum-doped cobalt oxide catalyst; In step (1), the mass ratio of Co(CH3COO)2·4H2O to glycerol added is (0.5 - 2):39; In step (3), the mass ratio of the lanthanum source to the added cobalt glycerol is (0.09 - 26):1; the lanthanum source is lanthanum nitrate.

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

3. A lanthanum-doped cobalt oxide catalyst prepared by the preparation method according to claim 1 or 2.

4. Use of the lanthanum-doped cobalt oxide catalyst according to claim 3, characterized in that, It is used for activating peroxymonosulfate PMS for Fenton-like catalytic degradation of organic pollutants.

5. The application according to claim 4, characterized in that The organic pollutants include tetracycline, methyl orange, rhodamine B, oxytetracycline or bisphenol A.

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