A carbon-doped cobalt trioxide and cerium dioxide ultra-long hollow nanotube composite catalyst, its preparation method, and its application in photocatalytic degradation of microplastics

Abstract

The present invention is a carbon-doped cobalt tetroxide and ceria ultra-long hollow nanotube composite catalyst, its preparation method and application in photocatalytic degradation of microplastics, belonging to the field of nanocomposite materials and photocatalytic technology. The composite catalyst uses polyvinylpyrrolidone (PVP) as a precursor, adds cobalt nitrate hexahydrate (Co(NO3)3·6H2O) and cerium nitrate hexahydrate (Ce(NO3)3·6H2O), and is synthesized in a one-step process using high-voltage electrospinning technology; the composite catalyst is formed by hollow nanotubes interwoven into a network structure, forming a heterogeneous interface of cobalt tetroxide and ceria. The catalyst of the present invention utilizes the mutual synergy of the heterogeneous interface of cobalt tetroxide and ceria to promote the separation and transfer of photogenerated electrons and holes. In the photocatalytic degradation reaction of polyethylene terephthalate microplastic waste, it has excellent catalytic performance and achieves efficient degradation.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanocomposite materials and photocatalysis, and particularly relates to a preparation method of a carbon-doped cobaltous oxide and cerium dioxide ultra-long hollow nanotube composite catalyst and its application in photocatalytic degradation of microplastics. Background Art

[0002] Polyethylene terephthalate (PET) plastic is widely used in the manufacture of food plastic film, beverage bottles, household appliances, and precision instruments, with a production volume of 70 million tons. Importantly, due to its chemical stability, PET plastic does not effectively degrade in the natural environment and can only be disposed of through centralized landfills and incineration. These methods result in a large amount of plastic resource waste, and the resulting microplastics enter water bodies, ultimately endangering biological health. Developing efficient recycling and processing technologies for PET plastics can reduce white pollution and carbon emissions. However, current PET plastic recycling technologies are immature, and recycling methods may not effectively balance the goals of environmental protection and economic benefits.

[0003] Photocatalysis is a promising green technology for plastic degradation. However, simple degradation techniques cannot achieve effective plastic degradation in a short period of time. Currently, persulfate (PMS)-based advanced oxidation processes offer promising solutions for the treatment of PET plastics in the environment due to their high redox properties. These processes disrupt the bonds between aromatic rings in PET through electrophilic substitution, promoting the degradation of PET plastics in the environment. For example, 3D layered H2-reduced Mn-doped CeO2 nanoflowers have been used as highly efficient Fenton-like photocatalysts activated by persulfate (PMS). However, due to their wide band gap, CeO2 photocatalysts are difficult to excite with visible light, which severely limits their widespread application. Therefore, alternative methods are needed to modify CeO2 to enhance the pollutant removal activity of PMS under visible light irradiation.

[0004] Recent studies have shown that constructing heterojunction composite catalysts can promote the separation of photogenerated electrons and holes. Cerium dioxide is a low-cost n-type semiconductor with excellent redox performance and stable properties. 3+ and Ce 4+ The valence state of the nanoparticles can be flexibly transformed, giving them good electronic and ionic conductivity and reversible surface oxygen ion exchange. Currently, there are no reports on the construction of carbon-doped cobalt tetroxide and ceria ultra-long hollow nanotube composite catalysts for the efficient degradation of polyethylene terephthalate microplastic waste. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a preparation method and application of a carbon-doped cobalt trioxide and cerium dioxide ultra-long hollow nanotube composite catalyst, which will be used for the photocatalytic degradation of polyethylene terephthalate microplastic waste.

[0006] The technical solution adopted in the present invention is as follows:

[0007] The invention provides a carbon-doped cobalt oxide and ceria ultra-long hollow nanotube composite catalyst. The composite catalyst is synthesized in a one-step method by high-voltage electrospinning technology using polyvinylpyrrolidone (PVP) as a precursor, adding cobalt nitrate hexahydrate (Co(NO3)3·6H2O) and cerium nitrate hexahydrate (Ce(NO3)3·6H2O). The hollow nanotubes in the composite catalyst are interwoven into a network structure, forming a heterogeneous interface between cobalt oxide and ceria.

[0008] In the above technical solution, further, the diameter of the hollow nanotube is 300-400 nm and the length is 50-60 µm.

[0009] In the above technical solution, further, the molar mass ratio of cobalt oxide and cerium dioxide in the composite catalyst is 1:1-8, and the calculated theoretical mass of cobalt oxide and cerium dioxide is the actual mass of the calcined nanotubes after grinding.

[0010] In the above technical solution, further, the preparation method of the composite catalyst comprises the following steps:

[0011] (1) PVP, Ce(NO3)3·6H2O and Co(NO3)2·6H2O were added to distilled water and anhydrous ethanol, and stirred at room temperature to obtain a uniform and transparent composite sol; the amount ratio of PVP, Ce(NO3)3·6H2O, Co(NO3)3·6H2O, distilled water and anhydrous ethanol was 1g:0.1-0.3g:0.7-0.9g:4-7ml:4-7ml;

[0012] (2) electrospinning the prepared composite sol at room temperature to obtain composite micron fibers;

[0013] The electrospinning parameters are as follows: the needle diameter is 1 mm, the inclination angle with the horizontal plane is about 15-30 degrees, the DC voltage is 17-18 kV, the curing distance is 20-25 cm, and the injection speed is 0.7-1 mm·min -1 , drum speed is 300-350 r·min -1 ;

[0014] (3) Drying, calcining, and cooling the prepared composite micron fibers.

[0015] In the above technical solution, further, the stirring time of step (1) is 24-26 hours.

[0016] In the above technical solution, further, the drying temperature in step (3) is 40-60°C, and the drying time is 10-14 hours; the roasting temperature is 500-550°C, the roasting time is 2-4 hours, and the heating rate is 5-10°C / min.

[0017] The present invention also provides the use of the aforementioned carbon-doped cobalt tetroxide and ceria ultra-long hollow nanotube composite catalyst for the photocatalytic degradation of polyethylene terephthalate microplastic waste. The composite catalyst of the present invention utilizes its fine fibers, large specific surface area, and wide band gap, resulting in a large contact area with microplastics. This facilitates carrier migration to the catalyst surface, where redox reactions occur with adsorbed substances, thereby enhancing photocatalytic activity.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention employs a simple method to add cobalt nitrate hexahydrate and cerium nitrate hexahydrate to a polyvinylpyrrolidone precursor solution, and then prepares a carbon-doped cobalt oxide and ceria ultra-long hollow nanotube composite catalyst in a one-step electrospinning process. During the spinning process, the cobalt oxide and ceria hollow nanotubes align into uniform, thin, and long hollow tubes, interweaving into a network structure and forming a heterogeneous interface. This catalyst exhibits excellent catalytic performance in the photocatalytic degradation of polyethylene terephthalate (PET) microplastic waste. At 20°C, under 6 hours of illumination and in the presence of 3 mM PMS, the PET microplastic weight loss was 93.725 ± 4.32%. This result demonstrates that the synergistic interaction between cobalt oxide and ceria promotes the separation and transfer of photogenerated electrons and holes, achieving efficient photocatalytic degradation of PET microplastic waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the electron microscopy characterization of the cobalt oxide and cerium dioxide composite catalyst in different proportions.

[0021] Figure 2 It is the XRD characterization of carbon-doped cobalt tetroxide, carbon-doped ceria, and carbon-doped cobalt tetroxide and ceria composite catalysts.

[0022] Figure 3 This is the electron microscopy characterization of carbon-doped cobalt oxide and cerium dioxide composite catalyst.

[0023] Figure 4It is a characterization of the specific surface area of ​​carbon-doped cobalt tetroxide, carbon-doped ceria, and carbon-doped cobalt tetroxide and ceria composite catalysts.

[0024] Figure 5 These are the UV-vis DRS characterization and Tauc diagram of carbon-doped cobalt tetroxide, carbon-doped ceria, and carbon-doped cobalt tetroxide and ceria composite catalysts; a. UV-vis DRS characterization, b. Tauc diagram of carbon-doped ceria, c. Tauc diagram of carbon-doped cobalt tetroxide.

[0025] Figure 6 The photoelectric properties of carbon-doped cobalt tetroxide, carbon-doped ceria, and carbon-doped cobalt tetroxide and ceria composite catalysts; a. Mott-Schottky curve of carbon-doped ceria, b. Mott-Schottky curve of carbon-doped cobalt tetroxide, c. transient photocurrent response curve of carbon-doped cobalt tetroxide and ceria composite catalyst, d. EIS spectrum.

[0026] Figure 7 The photocatalytic degradation performance of polyethylene terephthalate microplastic waste by carbon-doped cobalt tetroxide, carbon-doped ceria, and carbon-doped cobalt tetroxide and ceria composite catalysts; a. Performance of different catalysts, b. Performance in different time periods, c. Kinetic fitting curve. DETAILED DESCRIPTION

[0027] The present invention is further described below with reference to specific examples, but is not intended to limit the present invention in any way.

[0028] To facilitate a better understanding of the technical solutions of the present invention by those skilled in the art, the following detailed description, combined with examples, describes a method for preparing and applying a carbon-doped cobalt oxide and ceria ultra-long hollow nanotube composite catalyst. The following examples are intended only to illustrate the present invention and are not intended to limit its scope.

[0029] Example 1 Preparation of Carbon-Doped Cobalt Tetroxide and Cerium Dioxide Ultra-Long Hollow Nanotube Composite Catalyst

[0030] 1g PVP, 0.1628g Ce(NO3)3·6H2O, and 0.8731g Co(NO3)2·6H2O were added to 6ml distilled water and 7ml anhydrous ethanol and stirred at room temperature for 24 hours to obtain a uniform and transparent composite sol. The prepared composite sol was injected into a syringe with a needle of 1 mm in diameter. The positive copper wire of a high-voltage DC power supply was inserted into the solution in the syringe. The inclination angle of the needle to the horizontal plane was adjusted to approximately 15°. The applied DC voltage was appropriately adjusted to 17 kV. The curing distance (the distance between the syringe needle tip and the collecting aluminum film) was 20 cm, and the injection speed was 0.7 cm·min.-1 , the drum speed is 300 r·min -1 Electrospinning was performed at room temperature, and composite micron fibers were collected on aluminum foil connected to the negative electrode of a high-voltage power supply. The prepared composite fibers were dried in a 60°C oven for 12 hours, then placed in a crucible and calcined in a programmed temperature furnace at 500°C for 4 hours at a heating rate of 5°C / min. After heating, the sample was naturally cooled to room temperature in the furnace, resulting in a carbon-doped cobalt tetroxide and ceria ultra-long hollow nanotube composite catalyst with a molar ratio of Co₃O₄ to CeO₂ of 1:8.

[0031] Meanwhile, according to the above preparation method, the only difference is that no cerium nitrate hexahydrate or no cobalt nitrate hexahydrate is added to prepare a carbon-doped cobalt oxide catalyst or a carbon-doped ceria catalyst.

[0032] According to the above preparation method, the addition amount of distilled water and anhydrous ethanol was changed. 1g PVP, 0.1628g Ce(NO3)3·6H2O and 0.8731g Co(NO3)2·6H2O were added to 8ml distilled water and 9ml anhydrous ethanol, and electrospinning was performed at room temperature. It was found that the solution was too viscous and the structure could not be formed. Figure 1 a. Add 1g PVP, 0.1628g Ce(NO3)3·6H2O and 0.8731g Co(NO3)2·6H2O to 3ml distilled water and 8ml anhydrous ethanol. The solution is too dilute and the structure is not formed. Figure 1 b; 1g PVP, 0.1628g Ce(NO3)3·6H2O and 0.8731g Co(NO3)2·6H2O were added to 9ml distilled water and 10ml anhydrous ethanol. During the spinning process, a large number of droplets fell, resulting in an unformed structure, such as Figure 1 c.

[0033] The cobalt nitrate hexahydrate used in the present invention is analytically pure with a purity of ≥99.0%, the cerium nitrate hexahydrate is analytically pure with a purity of ≥99.0%, and the anhydrous ethanol is analytically pure with a purity of ≥99.7%. The carbon-doped cobalt tetroxide and ceria ultra-long hollow nanotube composite catalyst, the carbon-doped ceria catalyst, and the carbon-doped cobalt tetroxide catalyst prepared in the present invention are labeled C / Co3O4 / CeO2, C / CeO2, and C / Co3O4, respectively.

[0034] Figure 2The XRD spectrum of the synthesized catalyst is shown in Figure 2. The carbon-doped cobalt oxide sample shows diffraction peaks at 31.27°, 36.85°, 59.35° and 65.23°, which correspond to the (220), (311), (511) and (440) crystal planes of cobalt oxide, respectively, indicating that the synthesized sample is pure cobalt oxide. The carbon-doped ceria sample shows diffraction peaks at 28.55°, 33.07°, 47.48° and 56.34°, which correspond to the (111), (200), (220) and (311) crystal planes of ceria, respectively, indicating that the synthesized sample is pure ceria. The carbon-doped cobalt oxide and ceria composite catalyst spectrum only shows the diffraction peaks corresponding to the single-phase cobalt oxide and ceria samples, and no other diffraction peaks appear, indicating that a composite catalyst of cobalt oxide and ceria is formed.

[0035] Figure 3 The morphological characterization of the carbon-doped cobalt oxide and cerium dioxide composite catalyst is given. From the figure, we can clearly see that the cobalt oxide and cerium dioxide composite catalyst is composed of uniform, thin and long hollow tubes with a diameter of 300-400nm and a length of 50-60µm, which are interwoven into a network structure.

[0036] Figure 4 Figure 3 shows the specific surface area of ​​carbon-doped cobalt tetroxide, carbon-doped ceria, and a carbon-doped cobalt tetroxide / ceria composite catalyst. The figure shows that the adsorption capacity of ceria increases with increasing relative pressure, and the growth rate is significantly faster at higher relative pressures. This indicates that ceria has stronger adsorption capacity at high relative pressures, possibly due to the presence of a larger number of mesopores or macropores, which facilitates gas adsorption at high pressures. The adsorption capacity of the cobalt tetroxide / ceria composite catalyst increases with increasing relative pressure, with the overall adsorption capacity trend falling between cobalt tetroxide and ceria. Its adsorption characteristics are similar to those of ceria, but its adsorption capacity is slightly weaker, possibly due to differences in the number or nature of its pore structure. The adsorption capacity of cobalt tetroxide is low across the entire relative pressure range, with minimal change with increasing relative pressure. This may be due to its smaller pore structure or pore size distribution, which is unfavorable for the adsorption process, with a predominantly micropore structure and small pore volume.

[0037] Example 2 Energy band structure of the synthesized catalyst

[0038] The energy band structures of the synthesized catalysts were determined by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and Mott-Schottky curve (MS curve) using Lambda 355 and CHI760D, respectively.

[0039] Figure 5a is the UV-Vis DRS of the synthesized catalyst. The absorption edge of ceria is located at 450 nm, indicating that ceria can only absorb ultraviolet light, has a wide band gap, and has a band structure. In CC-8, the absorption edge extends to 800 nm, which is the effect of the heterojunction. The band gaps of ceria and cobalt oxide were then determined using the Tauc plot method ( Figure 5 b), where the band gap values ​​of ceria and cobalt oxide are determined to be 3.01 eV and 2.08 eV, respectively.

[0040] Figure 6 a and Figure 6 b shows the MS curves for ceria and cobalt oxide, respectively. The slope of the MS curve represents the semiconductor type, indicating that ceria is an n-type semiconductor and cobalt oxide is a p-type semiconductor, both of which conduct electrons. The intersection of the tangents to the MS curves on the x-axis represents the flat-band potential (Ef) of the materials. Therefore, Ef(CeO2) = -0.72 V vs. SSC, and Ef(Co3O4) = 0.82 V vs. SSC. The saturated silver chloride electrode (SSC) potential is converted to the standard hydrogen electrode (NHE) potential, i.e., Ef(CeO2) = -0.52 V vs. NHE, and Ef(Co3O4) = 1.02 V vs. NHE. Since the conduction band potential of an n-type semiconductor is generally 0.2 V less than the flat band potential, and the conduction band potential of a p-type semiconductor is generally 0.2 V greater than the flat band potential, ECB(CeO2) = -0.72 V vs. SSC, and ECB(Co3O4) = 1.22 V vs. SSC. Finally, the valence band potential of CeO2 is calculated based on the band gap value of CeO2, i.e., EVB(CeO2) = 2.29 V vs. NHE, and the valence band potential of Co3O4 is calculated based on the band gap value of Co3O4, i.e., EVB(Co3O4) = -0.86 V vs. NHE.

[0041] Example 3 Photoelectric performance of the synthesized catalyst

[0042] The photoelectric performance of the synthesized catalyst was tested on an electrochemical workstation (CHI760D). This test involved the assembly of a three-electrode system, with a Pt counter electrode and a silver chloride reference electrode. The working electrode was prepared as follows: 50 mg of the catalyst was evenly dispersed in 2 mL of ethanol and 30 μL of a perfluorinated resin aqueous solution and ground in a mortar until the solution thickened. The viscous liquid was then evenly coated onto the conductive side of a FTO conductive glass sheet using a pipette. The catalyst-coated glass was further dried in an infrared oven for 20 minutes to prevent the catalyst coating from detaching during testing. The electrolyte solution was a 0.5 M Na₂SO₄ solution. For the photocurrent measurements, a 300 W xenon lamp was used as the light source.

[0043] The catalysts used were the carbon-doped cobalt tetroxide, carbon-doped ceria, and carbon-doped cobalt tetroxide and ceria composite catalyst prepared in Example 1, respectively. Figure 6 c is the transient photocurrent response curve of carbon-doped cobalt tetroxide, carbon-doped ceria, and carbon-doped cobalt tetroxide and ceria composite catalysts. The transient photocurrent intensity of the cobalt tetroxide and ceria composite catalyst is higher than that of cobalt tetroxide and ceria, indicating that after the photogenerated carrier separation effect of the cobalt tetroxide and ceria composite catalyst is enhanced, more photoelectrons are transferred to the photocatalytic surface to participate in the activation of PMS. Figure 6 Figure d shows the EIS spectrum of the synthesized catalysts. The cobalt oxide / cerium dioxide composite catalyst has the smallest Nyquist radius, indicating the best conductivity. The cobalt oxide / cerium dioxide composite catalyst has the largest Nyquist radius, indicating that photogenerated carriers in cobalt oxide and ceria are most easily recombined. The composite catalyst exhibits a significantly reduced Nyquist radius, which may improve the separation of photogenerated carriers.

[0044] Example 4 Photocatalytic Degradation of Polyethylene Terephthalate Microplastic Waste Reaction

[0045] Photocatalytic degradation of polyethylene terephthalate microplastic waste was reacted in a 200 ml reactor. 30 mg of the C / Co3O4 / CeO2 catalyst prepared in Example 1, single-phase carbon-doped cobalt tetroxide, single-phase carbon-doped cerium dioxide, 20 mg of microplastics, 3 mM PMS and 100 mL of water were added, mixed evenly and the reactor was sealed. A 300 W xenon lamp was used to simulate sunlight. The xenon lamp was turned on for illumination, and condensed water was passed into the reactor to maintain room temperature to avoid excessive temperature. The photodegradation experiment lasted for 6 h. The solid product was filtered using a dried and weighed 0.1 μm organic system filter. The filter was kept dry in an oven for 72 hours until the mass did not change. The liquid product was filtered through the filter head, collected and detected by GC-MS. All tests were repeated more than 3 times and the average value was taken. The degradation efficiency was calculated as follows: t ) / w0×100%.

[0046] from Figure 7 a As can be seen from the graph, the carbon-doped cobalt tetroxide and ceria ultra-long hollow nanotube composite catalyst C / Co3O4 / CeO2 showed enhanced reaction activity compared to single-phase carbon-doped cobalt tetroxide and carbon-doped ceria. When the reaction time was 6 h and 3 mM PMS was present, the weight loss of polyethylene terephthalate microplastics was 95.987±4.32%. Figure 7 b It can be seen that with the increase of reaction time, the degradation efficiency of C / Co3O4 / CeO2 gradually increases. Figure 7 c It can be seen that the degradation rate of C / Co3O4 / CeO2 under the conditions of reaction time 6 h and 3 mM PMS is (0.40308 h -1 ).

[0047] By constructing a heterojunction between semiconductors, not only can the inherent defects of individual semiconductors be compensated, facilitating the preparation of advanced catalysts for targeted reactions, but it also provides a deeper understanding of the structure-activity relationship between catalyst structure and reaction performance. This invention uses a one-step electrospinning process to prepare a carbon-doped cobalt tetroxide and ceria ultra-long hollow nanotube composite catalyst. These nanotubes have fine fibers, a large specific surface area, and a wide band gap, creating a large contact area with microplastics. This facilitates carrier migration to the catalyst surface, allowing adsorbed substances to undergo redox reactions, thereby enhancing photocatalytic activity.

[0048] The examples of the present invention are described in detail above in conjunction with the embodiments, but the present invention is not limited to the above examples. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of the present invention, and should also be regarded as the scope of protection of the present invention.

Claims

1. Application of a carbon-doped cobalt trioxide and ceria composite catalyst in the photocatalytic degradation of polyethylene terephthalate microplastic waste, characterized in that: At 20 °C, 6 h of light exposure, and the presence of 3 mM PMS, the weight loss of polyethylene terephthalate microplastics was 93.725 ± 4.32%; The composite catalyst uses polyvinyl pyrrolidone (PVP) as a precursor, adds cobalt nitrate hexahydrate (Co(NO3)3·6H2O) and cerium nitrate hexahydrate (Ce(NO3)3·6H2O), adds PVP, Ce(NO3)3·6H2O and Co(NO3)2·6H2O to distilled water and anhydrous ethanol, and is stirred at room temperature to obtain a uniform and transparent composite sol, which is synthesized in a one-step process using high-voltage electrospinning technology. The composite catalyst is composed of hollow nanotubes interwoven into a network structure, forming a heterogeneous interface between cobalt oxide and cerium dioxide. The preparation method of the composite catalyst comprises the following steps: (1) PVP, Ce(NO3)3·6H2O and Co(NO3)2·6H2O were added to distilled water and anhydrous ethanol, and stirred at room temperature to obtain a uniform and transparent composite sol; the amount ratio of PVP, Ce(NO3)3·6H2O, Co(NO3)3·6H2O, distilled water and anhydrous ethanol was 1g:0.1-0.3g:0.7-0.9g:4-7mL:4-7mL; (2) electrospinning the prepared composite sol at room temperature to obtain composite micron fibers; The electrospinning parameters are: needle diameter of 1 mm, inclination angle with the horizontal plane of 15-30 degrees, DC voltage of 17-18 kV, curing distance of 20-25 cm, and injection speed of 0.7-1 mm·min -1 , drum speed is 300-350r·min -1 ; (3) Drying, calcining, and cooling the prepared composite micron fibers.

2. The use according to claim 1, wherein the hollow nanotube has a diameter of 300-400 nm and a length of 50-60 μm.

3. The use according to claim 1, wherein the stirring time in step (1) is 24-26 hours.

4. The use according to claim 1, characterized in that The drying temperature in step (3) is 40-60°C, and the drying time is 10-14h; the roasting temperature is 500-550°C, the roasting time is 2-4h, and the heating rate is 5-10°C / min.

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