Preparation method of Co-N / C@CeO2 composite material and method for degrading plastic by using thermal effect activated PMS system

Abstract

This invention belongs to the field of environmental material preparation technology and application, and discloses a method for preparing Co-N / C@CeO2 composite materials and a method for thermally activating a PMS system to degrade plastics. Firstly, CeO2 microspheres are prepared by hydrothermal and calcination methods. Subsequently, a Co-N / C@CeO2 composite catalyst is prepared using in-situ growth and calcination methods. Under thermal effects, the Co-N / C@CeO2 composite material helps promote the degradation of HSO5. ‑ Efficient activation of molecules, and in Co and Ce(M n / M n+1 A large amount of O2 was generated under the synergistic effect of the multivalent redox cycle. ‑ ·OH and SO4 ·‑ Active free radicals and 1 O2 is a non-radical active species. Under optimal conditions of 55℃, the degradation rate of PET microplastics reached 52.3%. Furthermore, the study found that adding a small amount of H2O2 to the thermally activated PMS synergistic system further improved the degradation activity of PET microplastics to 92.3%, exhibiting excellent degradation activity. This invention achieves the goal of efficiently degrading PET microplastics in a thermally activated PMS system using Co-N / C@CeO2 composite materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environment, and relates to a preparation method of a Co-N / C@CeO2 composite material and a method for degrading plastic by using a thermal effect activated PMS system. BACKGROUND

[0002] Peroxymonosulfate (PMS) can be activated by various strategies, such as light, heat, ultrasound, metal ions or various transition metal catalyst materials. However, considering the energy consumption and cost problems in the degradation process, it is urgent to find a more simple and inexpensive system for the degradation and conversion of PET microplastics. Studies have shown that among the activation methods of PMS, the thermal effect activation strategy has been proved to be an attractive and relatively simple method. The process of thermal effect activated PMS makes PMS molecules decompose into SO4 ·- The active free radicals generated thereby have stronger oxidation ability under high temperature conditions, and can more rapidly and completely degrade organic matter. Secondly, the thermal effect activated PMS has a wide range of applications and can be used to treat various types of organic pollutants, including industrial wastewater, surface water, and organic pollutants in soil. Therefore, it has wide application potential in wastewater treatment and environmental cleaning. Based on this, we will first try to use the thermal effect activated PMS system for the degradation of PET microplastics. In addition, it is necessary to construct a high-efficiency catalyst material for the degradation of PET microplastics in the thermal effect activated PMS system.

[0003] CeO2 material has good redox performance, and can form Ce 3+ / Ce 4+ ions on the surface of the catalyst, promote the activation of PMS and generate active oxygen species SO4 ·- and ·OH free radicals. However, the activity of PMS activated only by the surface properties of CeO2 is low, and compared with the composite material composed of two or more materials, various catalytic properties can be combined to improve the catalytic degradation activity. Transition metal ions are more concerned due to their lower energy consumption. At present, a large number of transition ions (such as Co 2+ , Fe 2+ , Ni 2+The PMS activation characteristics of the Co-N / C@CeO2 composite material have been deeply studied. In recent years, the strategy of using MOFs as self-sacrifice templates to prepare transition metal oxides / carbon materials has attracted the interest of many researchers. ZIF-67 is a Co-based hotspot MOFs material. By pyrolysis of ZIF-67, a Co-N / C catalyst can be prepared for activation of PMS molecules in the degradation system. However, the agglomeration of MOFs-derived metal oxides in practical applications is still a challenge, and developing high-quality support materials is one of the ways to solve this problem. Therefore, the combination of Co-N / C material and CeO2 material will help PMS to occur chain reaction in the activation process and promote the system to generate SO4 ·- and·OH free radicals in the electron transfer reaction. At present, the preparation method of the Co-N / C@CeO2 composite material and its application in the thermal effect activated PMS synergistic system for the degradation of PET microplastics have not been reported. SUMMARY

[0004] Based on the above discussion, the present application uses a hydrothermal method, in-situ growth and calcination method to construct a series of Co-N / C@CeO2 composite materials. The adsorption ability of the composite material to PMS molecules improves the synergistic effect of the multi-valence redox cycle of Co and Ce(M n / M n+1 ) and improves the activation ability of PMS molecules. And the Co-N / C@CeO2 composite material is used in the thermal effect activated PMS synergistic system for the degradation of PET microplastics, which provides a way for the treatment of a large number of microplastics in the environment.

[0005] The present application uses a hydrothermal method, in-situ growth and calcination method to construct a series of Co-N / C@CeO2 composite materials, and is used in the thermal effect activated PMS synergistic system for the degradation of PET microplastics.

[0006] To achieve the above technical purpose, the technical scheme adopted by the present application includes the following steps:

[0007] A preparation method of a Co-N / C@CeO2 composite material, comprising the following steps:

[0008] (1) Preparation of CeO2 three-dimensional flower balls

[0009] A mixed solution of cerium nitrate hexahydrate, glucose, acrylamide and water is added to a reaction kettle, stirred for a certain time, then ammonia solution is added dropwise, then placed in an oven for hydrothermal reaction, washed with deionized water several times after the reaction is completed, dried in a vacuum drying oven, and then sequentially calcined in an inert atmosphere tube furnace and in an air tube furnace to obtain CeO2 three-dimensional flower balls.

[0010] (2) Preparation of Co-N / C@CeO2 composite material

[0011] Cobalt nitrate hexahydrate is added to the methanol mixed solution containing the CeO2 three-dimensional flower balls prepared in step (1), and then 2-methyl imidazole methanol solution is added dropwise, Co ions will gradually grow into ZIF-67 dodecahedron on the surface of the CeO2 three-dimensional flower balls, after a certain time of reaction, centrifugation, washing, drying, and calcining in an inert atmosphere to obtain the Co-N / C@CeO2 composite material.

[0012] In step (1), the amount ratio of cerium nitrate hexahydrate, glucose, acrylamide and ammonia solution is 1 mmol:2 mmol:3 mmol:0.4-0.8 mL; the concentration of the ammonia solution is 30 wt%.

[0013] The temperature of the hydrothermal reaction is 160-200 DEG C, and the reaction time is 60-84 h;

[0014] The temperature of the first calcination is 500-700 DEG C, and the time is 4-8 h; the inert atmosphere is argon;

[0015] The temperature of the second calcination is 400-500 DEG C, and the time is 2-6 h;

[0016] In step (2), the amount ratio of cobalt nitrate hexahydrate, 2-methyl imidazole and CeO2 three-dimensional flower balls is 5 mmol:10 mmol:100-400 mg;

[0017] The time for growing ZIF-67 dodecahedron on the surface of the CeO2 three-dimensional flower balls is 30-120 min;

[0018] The temperature of the calcination is 400-600 DEG C, and the time is 1-4 h.

[0019] The application of the Co-N / C@CeO2 composite material prepared by the application to the thermal effect activated PMS synergistic system for degrading PET microplastics, the specific steps are as follows:

[0020] Co-N / C@CeO2 composite material and PET microplastics are taken into a glass reactor, deionized water, PMS and H2O2 are added, and constant temperature water bath heating reaction is carried out to realize the degradation rate of PET microplastics.

[0021] The amount ratio of Co-N / C@CeO2 composite material, PET microplastics, deionized water, PMS and H2O2 is 0.05 g:0.05 g:100 mL:5 mmol:1 mL; the temperature of the water bath heating reaction is 25-65 DEG C, and the time is 4-8 h. The concentration of H2O2 is 30 wt%.

[0022] The beneficial effects of the application are as follows:

[0023] (1) The application constructs a series of Co-N / C-n@CeO2 composite materials (n represents the growth time (min) of ZIF-67 on the surface of CeO2 three-dimensional flower ball) by hydrothermal method, in-situ growth and calcination method. With CeO2 three-dimensional flower ball as the carrier, it is helpful for the loading and dispersion of ZIF-67, and also helpful for the adsorption of a large number of PMS molecules of the Co-N / C@CeO2 composite material obtained after calcination, thereby improving the activation efficiency. The Co-N / C-90@CeO2 composite material is used for the degradation of PET microplastics in the PMS system activated by thermal effect, and when the reaction time reaches 6h, the degradation rate of PET microplastics reaches 52.3%. In addition, when 1mL H2O2 is added, the degradation rate is increased to 92.3%.

[0024] (2) With Co-N / C@CeO2 composite material as active material, improving the reaction temperature is helpful to improve the ability of thermal effect activated PMS and improve the degradation efficiency of PET microplastics. Co-N / C@CeO2 composite material is helpful to promote the efficient activation of HSO5 - molecule under the action of thermal effect, and a large number of ·O2 n , ·OH and SO4 n+1 active free radicals and - O2 non-radical active species are produced under the synergistic action of the multivalent redox cycle of Co and Ce (M ·- / M 1 ).

[0025] (3) The application selects Co-N / C@CeO2 composite material as the catalyst of thermal effect activated PMS, and gradually degrades PET microplastics into CO2 and H2O under low temperature heating condition, which is a green and environmentally friendly plastic waste treatment technology. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 SEM images of CeO2 three-dimensional flower ball (a), ZIF-67 (b), Co-N / C (c) obtained after calcination and Co-N / C-90@CeO2 composite material (d);

[0027] Figure 2 XRD images of CeO2 three-dimensional flower ball, ZIF-67, ZIF-67-90@CeO2 composite material, Co-N / C obtained after calcination and Co-N / C-90@CeO2 composite material;

[0028] Figure 3ESR free radical and non-free radical active oxygen detection chart of CeO2 three-dimensional flower ball, Co-N / C and Co-N / C-90@CeO2 composite material obtained after calcination: (a) hydroxyl radical and sulfate radical, (b) superoxide radical and (c) singlet oxygen;

[0029] Figure 4 Thermal effect activated PMS synergistic system (a) different materials (* represents the addition of 1 mL H2O2 in the system) and (b) Co-N / C-90@CeO2 composite material under different temperature conditions for the degradation efficiency of PET microplastics. DETAILED DESCRIPTION

[0030] The application will be further described below in conjunction with the accompanying drawings and specific examples, but the scope of protection of the application is not limited thereto.

[0031] Example 1:

[0032] (1) Preparation of CeO2 three-dimensional flower ball:

[0033] A mixed solution of 5 mmol cerium nitrate hexahydrate, 10 mmol glucose, 15 mmol acrylamide and 60 mL deionized water was added to a 100 mL reaction kettle, stirred for 1 h, then 3.2 mL of ammonia was added, and stirring was continued for 5 h. The reaction was then placed in a 180°C oven for hydrothermal reaction for 72 h, then washed with deionized water and ethanol for 3 times respectively, dried in a 60°C vacuum drying oven, and calcined in a 600°C tube furnace in an inert atmosphere and a 400°C tube furnace in air atmosphere to obtain CeO2 three-dimensional flower ball;

[0034] (2) 200 mg of CeO2 three-dimensional flower ball in (1) was placed in 100 mL of methanol, stirred and dispersed uniformly, then 5 mmol of cobalt nitrate hexahydrate was added to the above methanol mixed solution, stirred for 1 h to obtain methanol mixed solution A, 10 mmol of 2-methyl imidazole was dissolved in 30 mL of methanol to obtain solution B, then B solution was added dropwise to methanol mixed solution A, and stirring was continued for 30 min, then centrifuged, washed, dried and calcined at 500°C in an inert gas for 2 h to obtain Co-N / C-30@CeO2 composite material;

[0035] (3) 0.05 g of Co-N / C-30@CeO2 composite material and 0.05 g of PET microplastics were added to a glass reactor, 100 mL of deionized water and 5 mmol of PMS were added, and the reaction was carried out in a constant temperature water bath at 55°C for 6 h, achieving a PET microplastics degradation rate of 35.5%.

[0036] (4) Take 0.05g Co-N / C-30@CeO2 composite material and 0.05g PET microplastic into the glass reactor, add 100mL deionized water, 5mmol PMS and 1mL H2O2(30wt%), heat in constant temperature water bath pot at 55℃ for 6h, and achieve 70.6% PET microplastic degradation rate.

[0037] Example 2:

[0038] (1) Preparation of CeO2 three-dimensional flower ball:

[0039] 5mmol cerium nitrate hexahydrate, 10mmol glucose, 15mmol acrylamide and 60mL deionized water mixed solution, added into 100mL reactor, stirred for 1h, then added 3.2mL ammonia water, continue to stir for 5h, put into 180℃ oven for hydrothermal reaction for 72h, then washed with deionized water and ethanol for 3 times respectively, dried in 60℃ vacuum drying oven, and calcined by 600℃ in inert atmosphere and 400℃ in air atmosphere respectively to obtain CeO2 three-dimensional flower ball;

[0040] (2) Take 200mg CeO2 three-dimensional flower ball in (1) into 100mL methanol, stir and disperse uniformly, then add 5mmol cobalt nitrate hexahydrate into the above methanol mixed solution, stir for 1h to obtain methanol mixed solution A, dissolve 10mmol 2-methyl imidazole in 30mL methanol to obtain solution B, then add B solution dropwise into methanol mixed solution A, and continue to stir for 60min, then centrifuge, wash, dry and calcine at 500℃ in inert gas to obtain Co-N / C-60@CeO2 composite material;

[0041] (3) Take 0.05g Co-N / C-60@CeO2 composite material and 0.05g PET microplastic into the glass reactor, add 100mL deionized water and 5mmol PMS, heat in constant temperature water bath pot at 55℃ for 6h, and achieve 44.2% PET microplastic degradation rate.

[0042] (4) Take 0.05g Co-N / C-60@CeO2 composite material and 0.05g PET microplastic into the glass reactor, add 100mL deionized water, 5mmol PMS and 1mL H2O2(30wt%), heat in constant temperature water bath pot at 55℃ for 6h, and achieve 81.7% PET microplastic degradation rate.

[0043] Example 3:

[0044] (1) Preparation of CeO2 three-dimensional flower ball:

[0045] 5 mmol cerium nitrate hexahydrate, 10 mmol glucose, 15 mmol acrylamide and 60 mL deionized water were added into a 100 mL reactor, stirred for 1 h, then 3.2 mL ammonia was added, continued to stir for 5 h, placed in a 180 °C oven for hydrothermal reaction for 72 h, then washed with deionized water and ethanol for 3 times respectively, dried in a vacuum drying oven at 60 °C, and calcined in a tube furnace at 600 °C in an inert atmosphere and 400 °C in air atmosphere respectively to obtain CeO2 three-dimensional flower balls;

[0046] (2) 200 mg of CeO2 three-dimensional flower balls in (1) were taken into 100 mL of methanol, stirred and dispersed uniformly, then 5 mmol of cobalt nitrate hexahydrate was added into the above methanol mixed solution, stirred for 1 h to obtain a methanol mixed solution A, 10 mmol of 2-methylimidazole was dissolved in 30 mL of methanol to obtain a solution B, then the B solution was added dropwise into the methanol mixed solution A, and continued to stir for 90 min, then centrifuged, washed, dried and calcined at 500 °C in an inert gas for 2 h to obtain a Co-N / C-90@CeO2 composite material;

[0047] (3) 0.05 g of Co-N / C-90@CeO2 composite material and 0.05 g of PET microplastics were taken into a glass reactor, 100 mL of deionized water and 5 mmol of PMS were added, and the reaction was carried out at 55 °C in a constant temperature water bath for 6 h, achieving a PET microplastics degradation rate of 52.3%.

[0048] (4) 0.05 g of Co-N / C-90@CeO2 composite material and 0.05 g of PET microplastics were taken into a glass reactor, 100 mL of deionized water, 5 mmol of PMS and 1 mL of H2O2 (30 wt%) were added, and the reaction was carried out at 55 °C in a constant temperature water bath for 6 h, achieving a PET microplastics degradation rate of 92.3%.

[0049] Example 4:

[0050] (1) Preparation of CeO2 three-dimensional flower balls:

[0051] 5 mmol cerium nitrate hexahydrate, 10 mmol glucose, 15 mmol acrylamide and 60 mL deionized water were added into a 100 mL reactor, stirred for 1 h, then 3.2 mL ammonia was added, continued to stir for 5 h, placed in a 180 °C oven for hydrothermal reaction for 72 h, then washed with deionized water and ethanol for 3 times respectively, dried in a vacuum drying oven at 60 °C, and calcined in a tube furnace at 600 °C in an inert atmosphere and 400 °C in air atmosphere respectively to obtain CeO2 three-dimensional flower balls;

[0052] (2) Take 200 mg of CeO2 three-dimensional flower balls in (1) into 100 mL of methanol, stir and disperse uniformly, then add 5 mmol of cobalt nitrate hexahydrate to the above methanol mixed solution, stir for 1 h to obtain methanol mixed solution A, dissolve 10 mmol of 2-methylimidazole in 30 mL of methanol to obtain solution B, then add the B solution dropwise to the methanol mixed solution A, and continue to stir for 120 min, then centrifuge, wash, dry and calcine at 500°C in an inert gas for 2 h to obtain a Co-N / C-120@CeO2 composite material;

[0053] (3) Take 0.05 g of Co-N / C-120@CeO2 composite material and 0.05 g of PET microplastics into a glass reactor, add 100 mL of deionized water and 5 mmol of PMS, and react at 55°C in a constant temperature water bath for 6 h, achieving a PET microplastic degradation rate of 53.6%.

[0054] (4) Take 0.05 g of Co-N / C-120@CeO2 composite material and 0.05 g of PET microplastics into a glass reactor, add 100 mL of deionized water, 5 mmol of PMS and 1 mL of H2O2 (30 wt%), and react at 55°C in a constant temperature water bath for 6 h, achieving a PET microplastic degradation rate of 93.4%.

[0055] Figure 1 SEM images of the prepared CeO2 three-dimensional flower balls (a), ZIF-67 dodecahedron (b), Co-N / C obtained after calcination (c) and Co-N / C-90@CeO2 composite material (d). From Figure 1 (a) can be seen, the CeO2 three-dimensional flower balls have uniform morphology. From Figure 1 (b) and (c) can be seen, ZIF-67 (b) and Co-N / C obtained after calcination both have dodecahedron structure. In addition, from Figure 1 (d) can be seen, Co-N / C is uniformly dispersed on the surface of CeO2 three-dimensional flower balls, which is conducive to the uniform distribution of active sites and improves the adsorption and activation ability of PMS.

[0056] Figure 2For all the XRD patterns of the samples, it can be seen that all the diffraction peaks of the synthesized Ce02 three-dimensional flower balls are in good agreement with the corresponding crystal faces of cubic Ce02 (JCPDS No. 89-8436). The XRD characteristic peaks of the ZIF-67 dodecahedron have good crystal form, which proves the successful synthesis of Co-MOF. In addition, the XRD characteristic peaks of cubic Ce02 and ZIF-67 dodecahedron can be clearly seen in the ZIF-67-90@Ce02 composite material. After calcination, ZIF-67 is converted into Co-N / C, and an obvious Co elemental peak can be seen at 44.23°. However, there is no obvious characteristic peak of Co in the Co-N / C@Ce02 composite material. This also shows that Co-N / C is uniformly dispersed on the surface of the Ce02 flower ball.

[0057] Figure 3 ESR free radical and non-free radical active oxygen detection chart of Ce02 three-dimensional flower ball, Co-N / C obtained after calcination and Co-N / C-90@Ce02 composite material. Figure 3 The ESR spectra of (a) hydroxyl radical and sulfate radical, (b) superoxide radical and (c) singlet oxygen active species show that four kinds of active species can be generated simultaneously under heating conditions. Moreover, the concentration of various active species gradually increases with increasing temperature.

[0058] Figure 4 Degradation performance chart of PET microplastics in various conditions in the heat-activated PMS synergistic system. From 4 (a), it can be seen that in the aqueous solution of 5 mM PMS, the mass loss rate of 0.5 g L -1 of PET microplastics is only 12.4%. When the usage amount of catalyst and PET microplastics is 0.5 g L -1 , the degradation rate of PET microplastics gradually increases with the increase of Co-N / C loading amount, and the highest performance of Co-N / C-120@Ce02 composite material is 53.6%, which is only about 2.4% higher than that of Co-N / C-90@Ce02 composite material, therefore, the following experiments are all taken as reference with Co-N / C-90@Ce02 composite material. In addition, when 1 mL of H2O2 is added in the heat-activated PMS synergistic system, the degradation rate of PET microplastics shows a great improvement and reaches 92.3%, which shows that H2O2 helps to further improve the activity of Co-N / C-90@Ce02 composite material, and the following experiments are all carried out under the condition of adding 1 mL of H2O2. Figure 4 (b) shows that the degradation efficiency of PET microplastics gradually increases with the increase of temperature, and reaches 92.3% and 94.5% at 55°C and 65°C, respectively. Therefore, 55°C is the best degradation temperature in terms of effect and cost.

Claims

1. A preparation method of a Co-N / C@CeO2 composite material, characterized in that, It comprises the following steps: (1) Preparation of CeO2 three-dimensional flower balls A mixed solution of cerium nitrate hexahydrate, glucose, acrylamide and water is added to a reaction kettle, stirred for a certain period of time, then ammonia solution is added dropwise, and then placed in an oven for hydrothermal reaction. After the reaction is completed, the product is washed several times with deionized water, dried in a vacuum drying oven, and then calcined in a tubular furnace under inert atmosphere for the first time and in a tubular furnace in air for the second time to obtain CeO2 three-dimensional flower balls. (2) Preparation of Co-N / C@CeO2 composite material Cobalt nitrate hexahydrate is added to a methanol mixed solution containing the CeO2 three-dimensional flower balls prepared in step (1), followed by dropwise addition of 2-methylimidazole methanol solution. The Co ions will gradually grow into ZIF-67 dodecahedrons on the surface of the CeO2 three-dimensional flower balls. After a certain period of reaction, centrifugation, washing, drying, and calcination in an inert atmosphere at 400-600℃ for 1-4h, the Co-N / C@CeO2 composite material is obtained.

2. The production method according to claim 1, wherein In step (1), the ratio of the amounts of cerium nitrate hexahydrate, glucose, acrylamide and ammonia solution is 1mmol:2mmol:3mmol:0.4-0.8mL; the concentration of the ammonia solution is 30wt%.

3. The production method according to claim 1, wherein In step (1), the temperature of the hydrothermal reaction is 160-200℃, and the reaction time is 60-84h.

4. The production method according to claim 1, wherein In step (1), the temperature of the first calcination is 500-700℃, and the time is 4-8h; the inert atmosphere is argon; The temperature of the second calcination is 400-500℃, and the time is 2-6h.

5. The production method according to claim 1, wherein In step (2), the ratio of the amounts of cobalt nitrate hexahydrate, 2-methylimidazole and CeO2 three-dimensional flower balls is 5mmol:10mmol:100-400mg.

6. The production method according to claim 1, wherein In step (2), the time for growing ZIF-67 dodecahedrons on the surface of the CeO2 three-dimensional flower balls is 30-120min.

7. Use of the Co-N / C@CeO2 composite material prepared by the preparation method of any one of claims 1-6 in a thermal effect activated PMS synergistic system for degrading PET microplastics.

8. Use according to claim 7, wherein the compound is ###0002### The specific steps are as follows: Co-N / C@CeO2 composite material and PET microplastics are taken and added to a glass reactor, deionized water, PMS and H2O2 are added, and constant temperature water bath heating reaction is carried out to achieve the degradation rate of PET microplastics.

9. Use according to claim 8, wherein the compound is ###0002### The ratio of the amounts of Co-N / C@CeO2 composite material, PET microplastics, deionized water, PMS and H2O2 is 0.05g:0.05g:100mL:5mmol:1mL; the temperature of the water bath heating reaction is 25-65℃, and the time is 4-8h.

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