A cofe2o4-based composite catalyst and a preparation method thereof

Abstract

The application discloses a CoFe2O4-based composite catalyst and a preparation method thereof. A cobalt source, an iron source, a surfactant and an alkali source are dissolved in a solvent to obtain a mixed solution; carbon material is added into the mixed solution to obtain a suspension; finally, the suspension is post-treated to prepare the CoFe2O4-based composite catalyst. CoFe2O4 in the prepared CoFe2O4-based composite catalyst is CoFe2O4 quantum dots, and the CoFe2O4 quantum dots are loaded on the carbon material, so that CoFe2O4 aggregation is prevented, and the catalytic performance is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanomaterial preparation, in particular to a CoFe2O4 quantum dot material and a preparation method thereof, and relates to a CoFe2O4-based composite catalyst and a preparation method thereof. BACKGROUND

[0002] The mainstream technologies for VOCs treatment include traditional technologies such as adsorption recovery method, catalytic combustion method, photocatalytic decomposition method and biological method. The above traditional technologies greatly improve the situation of chemical waste gas pollution, but have the disadvantages of high treatment cost, short service life of equipment and catalyst, long catalyst regeneration cycle and possible secondary pollution. Free radical induced AOPs not only can produce highly active free radicals with strong oxidation ability, but also can degrade most gaseous pollutants, and its reaction process is environmentally friendly, and is considered as one of the most promising technologies.

[0003] Studies have shown that binary transition metal spinel oxides have higher catalytic activity than single metal oxides when used as activators for peroxymonosulfate (PMS). This improvement is usually attributed to factors such as synergistic redox coupling between the two metals, morphology adjustment and improvement of specific surface area. Among Co-based binary metal oxide catalysts, magnetic CoFe2O4 has received extensive attention. However, large cobalt ferrite has the disadvantages of easy aggregation, which reduces the availability of catalytic active sites and significantly reduces the catalytic performance. Quantum dots (QDs) have attracted more and more attention in the fields of electronic devices, solar cells, catalytic processes, etc. due to their special properties such as ultra-small size, quantum confinement effect and surface effect. Since spinel quantum dots contain a large number of defects, the catalytic performance can be improved. Unfortunately, quantum dots are prone to self-aggregation during the preparation process, which leads to poor dispersion and reduces the catalytic performance. SUMMARY

[0004] In order to overcome the above problems, the present inventors have made intensive research and developed a CoFe2O4-based composite catalyst and a preparation method thereof. A cobalt source, an iron source, a surfactant and an alkali source are dissolved in a solvent to obtain a mixed solution. A carbon material is added to the mixed solution to obtain a suspension. Finally, the suspension is post-treated to obtain the CoFe2O4-based composite catalyst. The CoFe2O4 in the prepared CoFe2O4-based composite catalyst is CoFe2O4 quantum dots, and the CoFe2O4 quantum dots are loaded on the carbon material to prevent CoFe2O4 aggregation and effectively improve the catalytic performance, thereby completing the present application.

[0005] Specifically, the present application aims to provide the following aspects:

[0006] In one aspect, a CoFe2O4-based composite catalyst is provided, wherein CoFe2O4 quantum dots with a particle size of 6-9 nm are loaded on the surface of a carbon carrier, and the carbon carrier is activated carbon.

[0007] In another aspect, a preparation method of the CoFe2O4-based composite catalyst is provided, and the method comprises:

[0008] Step 1, dissolving a cobalt source, an iron source, a surfactant and an alkali source in a solvent to obtain a mixed solution;

[0009] Step 2, adding a carbon material to the mixed solution to obtain a suspension;

[0010] Step 3, post-treating the suspension to obtain the CoFe2O4-based composite catalyst.

[0011] In yet another aspect, the CoFe2O4-based composite catalyst of the first aspect is applied to degradation of volatile organic compounds.

[0012] The present application has the following beneficial effects:

[0013] (1) The preparation method of the CoFe2O4-based composite catalyst provided by the present application is simple, mild in conditions, low in cost and easy to realize industrialization.

[0014] (2) The CoFe2O4-based composite catalyst provided by the present application has magnetic anisotropy, which makes it convenient to recycle in the actual application process of catalytic degradation of VOCs. s

[0015] (3) The CoFe2O4 in the CoFe2O4-based composite catalyst provided by the present application is CoFe2O4 quantum dots, and the CoFe2O4 quantum dots are loaded on a carbon material, which prevents CoFe2O4 from gathering and improves the catalytic performance in a multiplier effect. BRIEF DESCRIPTION OF DRAWINGS

[0016] Various other advantages and benefits of the present application will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a better understanding of the preferred embodiments, and are not to be considered as limitations of the present application. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained from these drawings by those of ordinary skill in the art without creative labor.

[0017] In the drawings:

[0018] Figure 1 The transmission electron microscope image of the CoFe2O4-based composite catalyst prepared in Example 1 is shown; ​

[0019] Figure 2 Figure 6 shows a particle size distribution diagram of the CoFe2O4-based composite catalyst prepared in Example 1;

[0020] Figure 3 Figure 7 shows a comparison diagram of the CoFe2O4-based composite catalyst prepared in Example 1 and the CoFe2O4 catalyst prepared in Comparative Example 1 in activating PMS to degrade toluene;

[0021] Figure 4 Figure 8 shows a VSM characterization diagram of the CoFe2O4-based composite catalyst prepared in Example 1;

[0022] Figure 5 Figure 9 shows a magnetic diagram of the CoFe2O4-based composite catalyst prepared in Example 1. DETAILED DESCRIPTION

[0023] Reference will now be made to the drawings, in which Figures 1 to 5 Specific embodiments of the present application will now be described in more detail. While these descriptions go into specific aspects of the application, it is to be understood that many variations and modifications will be apparent to those skilled in the art, which do not depart from the spirit and scope of the application. As such, the specific embodiments are to be understood only in a demonstrative context and are not intended to limit the scope of the application in any manner. Rather, the scope of the present application is to be understood only by reference to the claims.

[0024] It should be noted that certain terms have been used throughout the description and the claims that have particular meanings. Those skilled in the art will understand that the same component can be referred to by different names and that the names given are not intended to limit the scope of the component. The description and claims should not be construed as limited to the specific examples given, but understood to include all changes, modifications and equivalents that are within the scope of the present application. The description and the claims are to be construed as embracing all such changes, modifications and equivalents within the scope of the present application.

[0025] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "back", and the like, indicate relative positions or orientations based on the working state of the present application, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third", "fourth" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0026] For the purpose of facilitating the understanding of the embodiments of the present application, further explanation and description will be made below with specific examples as examples combined with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation to the embodiments of the present application.

[0027] In one aspect, a preparation method of a CoFe2O4-based composite catalyst is provided according to the present application, and the method comprises:

[0028] Step 1, dissolving a cobalt source, an iron source, a surfactant and an alkali source in a solvent to obtain a mixed solution;

[0029] Step 2, adding a carbon material into the mixed solution to obtain a suspension;

[0030] Step 3, post-treating the suspension to prepare the CoFe2O4-based composite catalyst.

[0031] The preparation method of the CoFe2O4-based composite catalyst is described in detail below.

[0032] Step 1, dissolving a cobalt source, an iron source, a surfactant and an alkali source in a solvent to obtain a mixed solution.

[0033] In Step 1, the cobalt source is a soluble cobalt salt, which is preferably selected from any one or several of cobalt nitrate, cobalt chloride, cobalt sulfate and cobalt acetate; the iron source is a soluble iron source, which is preferably selected from any one or several of iron nitrate, iron chloride or iron sulfate.

[0034] In the present application, the molar ratio of the cobalt source to the iron source is only 1:2.

[0035] Further, the amount of the cobalt source and the iron source is determined according to the crystal structure of CoFe2O4, and greater or smaller than the above-mentioned ratio cannot form the crystal structure of magnetic CoFe2O4.

[0036] In Step 1, the surfactant is selected from any one or several of polyethylene glycol, polyvinylpyrrolidone and sodium citrate, and is preferably sodium citrate.

[0037] The surfactant not only plays a role of surface activation, but also plays a role of dispersant, which can effectively improve the dispersibility of the cobalt source and the iron source in the solvent.

[0038] In the present application, the concentration of the surfactant in the mixed solution is 0.001-0.01 mmol / ml, preferably 0.002-0.005 mmol / ml, for example 0.004 mmol / ml; and the molar ratio of the amount of the surfactant to the sum of the amounts of the iron source and the cobalt source is 1:(3-5), preferably 1:(3.5-4.5), for example 1:4.

[0039] According to the present application, the adsorption amount of the surfactant on the surface of the cobalt source and the iron source increases with the increase of the amount of the surfactant, and the excessive surfactant does not increase the adsorption amount, and these excessive surfactant molecules are disordered in the solvent or form micelles, which is not conducive to the synthesis of the CoFe2O4-based composite catalyst.

[0040] In step 1, the alkali source can be a strong base, can also be a weak base, preferably a weak base such as acetic acid, chlorous acid, ammonium hydroxide, ammonia, etc., more preferably ammonium hydroxide or ammonia.

[0041] In the present application, the alkali source is used to regulate the pH value of the solvent, and the pH value affects the growth of the crystals in the CoFe2O4-based composite catalyst. Generally, the pH value of the solvent is best when the alkali source is added to 12.

[0042] In the present application, the concentration of the alkali source is not strictly required, and its concentration can easily regulate the pH value of the solvent. When the alkali source is ammonia, its mass fraction is (10-20) %, preferably (13-16) %, for example 15 %.

[0043] In step 1, the solvent can dissolve the cobalt source, the iron source and the surfactant, and is selected from one or more of water, ethylene glycol and ethanol, preferably ultrapure water which is highly soluble and cheap and easy to obtain.

[0044] In step 1, in order to quickly dissolve the cobalt source, the iron source, the surfactant and the alkali source, it is preferred to dissolve the cobalt source, the iron source, the surfactant and the alkali source under heating conditions, and the heating temperature is 40-90℃, preferably 45-85℃, more preferably 50-80℃; the heating time is 0.5-4h, preferably 1-3h, more preferably 1.5-2.5h.

[0045] The heating temperature does not need to be too high to avoid causing side chemical reactions; but if the heating temperature is too low, the required heating time will be prolonged; as the heating temperature increases, the required heating time is correspondingly shortened, and under the above heating temperature and heating time conditions, the cobalt source, the iron source, the surfactant and the alkali source can be dissolved as soon as possible. According to the preferred embodiment, the heating includes the following steps, which can also be understood as step 1 including the following steps:

[0046] Step 1-1, dissolve the cobalt source, the iron source and the surfactant in the solvent, and stir under heating conditions to obtain solution I;

[0047] Step 1-2, add the alkali source to the solution I and stand under heating conditions to obtain a mixed solution.

[0048] In step 1-1, the heating temperature is 40-60℃, preferably 45-55℃, for example 50℃; and the heating time is 10-90min, preferably 20-40min, for example 30min.

[0049] According to the present application, the heating time is too short and / or the time is too short to obtain a uniform solution I; when the heating temperature is too high and / or the time is too long, it is unnecessary. Within the above parameter range, the effect is best.

[0050] In step 1-2, the heating temperature is slightly higher than that in step 1-1, preferably 61-90℃, more preferably 65-85℃, most preferably 70-80℃, for example 70℃; and the standing time is 1-3h, preferably 1.5-2.5h, for example 2h.

[0051] In step 1-2, standing under heating conditions can achieve sufficient reaction of the source, iron source, surfactant and alkali source in the solvent.

[0052] Step 2, adding carbon material to the mixed solution to obtain a suspension.

[0053] In step 2, the carbon material is activated carbon.

[0054] In the present application, activated carbon is selected as the carbon carrier due to its high oxidation resistance, large specific surface area and economic feasibility; in addition, the activated carbon also has the advantages of good mechanical strength, low cost, easy preparation, large surface area, porous structure and diverse surface functional groups, etc. These characteristics not only help to accelerate the adsorption of target pollutants, but also play a key role in improving the dispersion of nano-catalysts and increasing the catalytic degradation efficiency. In particular, the present inventors have found that the addition of activated carbon not only enhances the adsorption of organic pollutants, but also accelerates electron transfer in cooperation with metal oxide CoFe2O4, so that the catalytic reaction rate will be significantly improved, thereby improving the activation performance of PMS.

[0055] In step 2, the concentration of the carbon material in the suspension is 0.5-3mg / ml, preferably 1.8-2.5mg / ml, more preferably 1-1.5mg / ml. Within the above parameter range, the CoFe2O4-based composite catalyst with the best magnetic performance and micro-morphology can be obtained.

[0056] Preferably, the activated carbon is added together with an organic solvent to achieve sufficient mixing.

[0057] Further, the organic solvent is preferably ethanol which is safe and non-toxic.

[0058] In step 2, the volume ratio of the organic solvent to the solvent is 1:(1.5-3), preferably 1:(1.8-2.5), more preferably 1:2, and in this parameter range, a uniform suspension can be obtained

[0059] In step 2, the carbon material is added to the mixed solution, and optional ultrasonic treatment is performed to obtain a suspension. The ultrasonic treatment time is 0.5-2 h, preferably 1-1.5 h, for example 1 h.

[0060] In step 2, the cavitation effect, mechanical effect and thermal effect specific to the ultrasonic treatment can form a local high temperature and high pressure in the suspension and are accompanied by a jet, can promote the renewal and disturbance of the phase interface and the cavitation effect of forming bubbles or cavities, and the ultrasonic treatment promotes the uniform dispersion of the activated carbon in the mixed solution, so that the CoFe2O4 quantum dots can be uniformly loaded on the surface of the activated carbon.

[0061] In step 3, the suspension is post-treated to obtain a CoFe2O4-based composite catalyst.

[0062] In step 3, the post-treatment includes heat treatment, drying and calcination.

[0063] In the present application, the heat treatment is a solvothermal reaction, and specifically includes incubation at 150-210°C for 15-25 h, followed by natural cooling to room temperature.

[0064] In the present application, the CoFe2O4-based composite catalyst prepared by heat treatment has controllable particle size, uniform morphology and good dispersibility. When the heat treatment temperature is lower than 150°C, the CoFe2O4-based composite catalyst cannot be self-assembled; when the heat treatment temperature is higher than 210°C, blocky impurities appear in the CoFe2O4-based composite catalyst, which may be due to the fact that the product is sintered together due to the excessively high reaction temperature; when the heat treatment temperature is between 150°C and 210°C, the product is uniformly distributed and has no impurities. When the heat treatment time is less than 15 h, the CoFe2O4-based composite catalyst cannot be self-assembled, which may be due to the fact that the reaction is not complete due to the insufficient time; when the heat treatment time is more than 25 h, the quantum dots in the CoFe2O4-based composite catalyst begin to grow larger and have poor morphology. When the heat treatment time is between 15 h and 25 h, the CoFe2O4-based composite catalyst with uniform morphology and good magnetic properties can be prepared.

[0065] In a further preferred embodiment, the heat treatment includes incubation at 170-190°C for 15-25 h, followed by natural cooling to room temperature.

[0066] In a further preferred embodiment, the heat treatment includes incubation at 170-190°C for 15-25 h, followed by natural cooling to room temperature.

[0067] In step 3, the water and / or solvent in the heat-treated substance is removed by drying, which is conducive to shortening the calcination time in the later stage, and the drying temperature is relatively low, and the drying can ensure the uniformity of the prepared CoFe2O4-based composite catalyst. The drying temperature only needs to be able to preliminarily remove the water and / or solvent in the heat-treated substance, and the drying time also does not need to be too long, and an excessively long drying time is unnecessary.

[0068] Further, the drying temperature is 50-80℃, preferably 55-70℃, for example 60℃; and the drying time is 8-24h, preferably 10-18h, for example 12h.

[0069] In step 3, the calcination temperature is 300-600℃, preferably 350-500℃, more preferably 400-500℃; the calcination time is 1-6h, preferably 2-4h, more preferably 2-3h; the calcination is started from room temperature, for example 25℃, and then heated to the required temperature, and the heating rate is 1-10℃ / min, preferably 3-8℃ / min, more preferably 5℃ / min.

[0070] In the present application, the uncalcined sample is not completely crystallized, and at the same time, the particle size is small, the proportion of surface atoms is large, and the coordination is unsaturated, which has a strong thermal disturbance characteristic, and the atomic magnetic moment is not easy to keep consistent with the external field, and calcination can improve this problem.

[0071] Further, as the calcination temperature increases, the crystallinity increases, the grain size increases, and the defects decrease, and the specific saturation magnetization, the remanence and the coercive force all increase, but the higher the calcination temperature, the more easily the CoFe2O4-based composite catalyst particles are aggregated, resulting in an increase in defects, and the specific saturation magnetization, the remanence and the coercive force all decrease; as the calcination time is prolonged, the crystallinity increases, and the specific saturation magnetization, the remanence and the coercive force all increase, but if the calcination time is too long, the activity of the finally prepared CoFe2O4-based composite catalyst decreases, which may be caused by the physical structure change of the CoFe2O4-based composite catalyst, for example, particle aggregation and reduced dispersity. The calcination temperature is 300-600℃, and the calcination time is 1-6h, and thus a CoFe2O4-based composite catalyst with excellent performance can be prepared.

[0072] Preferably, the calcination is carried out in a calcination atmosphere to improve the crystallinity. The calcination atmosphere uses inert gases such as argon, helium, etc., and nitrogen can also be used.

[0073] In the present application, after the heat treatment and before the drying, the heat-treated substance is preferably washed to remove excess solvent impurities, for example, the heat-treated substance is washed with ethanol and deionized water alternately until the supernatant is transparent, and usually the heat-treated substance is washed with ethanol and deionized water alternately for 3-5 times, i.e., the total washing times of ethanol are 3-5 times, and the washing times of deionized water are 3-5 times.

[0074] According to the application, the catalytic activity of the binary transition metal spinel oxide CoFe2O4 is higher than that of single metal cobalt or iron oxide, but the cobalt ferrite has the disadvantages of easy aggregation and the like, thereby reducing the availability of catalytic active sites and significantly reducing the catalytic performance. The CoFe2O4 in the CoFe2O4-based composite catalyst is a CoFe2O4 quantum dot, and the catalytic performance is improved by loading the quantum dot on the carbon material through a reasonable technical scheme, which is due to the properties of the quantum dot, such as super-small size, quantum confinement effect and surface effect.

[0075] According to the application, the mixed solution includes a metal source precursor (a cobalt source and an iron source), a surfactant, an alkali source and a solvent, and the morphology and performance of the synthesized material are controlled by the selection of the metal source precursor, the solvent and the surfactant, and the control of the reaction temperature, the reaction time and the raw material ratio. The finally obtained magnetic quantum dot CoFe2O4-based composite catalyst has the advantages of good crystallization performance, excellent magnetic response and adjustable morphology and size.

[0076] On the other hand, the CoFe2O4-based composite catalyst prepared by the method of the first aspect is provided, and the composite catalyst has unique magnetic anisotropy, which facilitates the recovery in the actual application process of catalytic degradation of VOCs.

[0077] Further, the CoFe2O4 quantum dots are uniformly loaded on the surface of the carbon carrier, the particle size of the CoFe2O4 quantum dots is 6-9 nm, and the carbon carrier is activated carbon; and the saturation magnetization of the CoFe2O4-based composite catalyst is 0.3-0.4 emu / g.

[0078] According to the application, when the CoFe2O4-based composite catalyst is used to activate PMS to catalytically degrade VOCs, the removal rate of VOCs reaches 95-99%.

[0079] On the other hand, the CoFe2O4-based composite catalyst prepared by the method of the first aspect is provided, and the composite catalyst has unique magnetic anisotropy, which facilitates the recovery in the actual application process of catalytic degradation of VOCs.

[0080] Embodiment

[0081] The application is further described below through specific examples, but these examples are merely exemplary and do not constitute any limitation on the protection scope of the application.

[0082] Example 1

[0083] Dissolve 1 mmol of cobalt nitrate, 2 mmol of ferric nitrate and 0.75 mmol of sodium citrate in 100 ml of deionized water, and magnetically stir at 50°C until the cobalt nitrate, ferric nitrate and sodium citrate are completely dissolved, then add 25 ml of 15% ammonia water, at this time the pH of the solvent is 12, and place at 70°C for 2 h to obtain a mixed solution;

[0084] Subsequently, add 50 ml of ethanol and 200 mg of activated carbon to the mixed solution, and ultrasonically mix at 25°C for 1 h to obtain a suspension;

[0085] Transfer the suspension to a reaction kettle lined with polytetrafluoroethylene for a solvothermal reaction, and incubate at 180°C for 20 h, then naturally cool to room temperature, then alternately wash the solvothermal reaction product with ethanol and deionized water three times (specifically: first ethanol wash, first deionized water wash, second ethanol wash, second deionized water wash, third ethanol wash, and third deionized water wash), and finally dry in a vacuum oven at 60°C for 12 h, and finally place the dried powder in a tube furnace, and heat from room temperature 25°C to 450°C at a heating rate of 5°C / min under nitrogen protection, and calcine for 2 h to obtain a CoFe2O4-based composite catalyst.

[0086] Disperse the CoFe2O4-based composite catalyst in a container containing an aqueous solution, so that the CoFe2O4-based composite catalyst is in a suspended state, then move the magnet outside the container wall, and it can be clearly observed that the CoFe2O4-based composite catalyst moves towards the magnet, and the results are shown in Figure 5 Thus, it is proved that the CoFe2O4-based composite catalyst has magnetism and is easy to recover.

[0087] Figure 1 The transmission electron microscope image of the prepared CoFe2O4-based composite catalyst is shown, and it can be seen that the CoFe2O4 quantum dots are uniformly loaded on the surface of the activated carbon; Figure 2 The particle size distribution graph of the prepared CoFe2O4-based composite catalyst is shown, and it can be seen that the average particle size of the CoFe2O4 is 7.64 nm; Figure 4 The VSM characterization graph of the prepared CoFe2O4-based composite catalyst is shown, and it can be seen that the saturation magnetization of the CoFe2O4-based composite catalyst is 0.38 emu / g.

[0088] Example 2

[0089] 1 mmol of cobalt chloride, 2 mmol of iron chloride and 0.75 mmol of sodium citrate were dissolved in 100 ml of deionized water, and magnetic stirring was performed at 50°C until the cobalt chloride, iron chloride and sodium citrate were completely dissolved, and then 25 ml of 15% ammonia water was added, at this time, the pH of the solvent was 12, and the mixture was placed at 70°C for 2 h to obtain a mixed solution;

[0090] Subsequently, 50 ml of ethanol and 200 mg of activated carbon were added to the mixed solution, and ultrasonic mixing was performed at 25°C for 1 h to obtain a suspension;

[0091] The suspension was transferred to a reaction kettle lined with polytetrafluoroethylene for solvothermal reaction, and the temperature was kept at 180°C for 20 h, and then naturally cooled to room temperature, and then the product of the solvothermal reaction was washed alternately with ethanol and deionized water for 3 times (specifically: ethanol washing for the first time, deionized water washing for the first time, ethanol washing for the second time, deionized water washing for the second time, ethanol washing for the third time, and deionized water washing for the third time), and finally dried in a vacuum oven at 60°C for 12 h, and finally the dried powder was placed in a tube furnace, and heated from room temperature 25°C to 400°C at a heating rate of 5°C / min under the protection of nitrogen, and calcined for 3 h to obtain a CoFe2O4-based composite catalyst.

[0092] Example 3

[0093] 1 mmol of cobalt chloride, 2 mmol of iron chloride and 0.75 mmol of sodium citrate were dissolved in 100 ml of deionized water, and magnetic stirring was performed at 50°C until the cobalt chloride, iron chloride and sodium citrate were completely dissolved, and then 25 ml of 15% ammonia water was added, at this time, the pH of the solvent was 12, and the mixture was placed at 70°C for 2 h to obtain a mixed solution;

[0094] Subsequently, 50 ml of ethanol and 200 mg of activated carbon were added to the mixed solution, and ultrasonic mixing was performed at 25°C for 1 h to obtain a suspension;

[0095] The suspension was transferred to a reaction kettle lined with polytetrafluoroethylene for solvothermal reaction, and the temperature was kept at 180°C for 20 h, and then naturally cooled to room temperature, and then the product of the solvothermal reaction was washed alternately with ethanol and deionized water for 3 times (specifically: ethanol washing for the first time, deionized water washing for the first time, ethanol washing for the second time, deionized water washing for the second time, ethanol washing for the third time, and deionized water washing for the third time), and finally dried in a vacuum oven at 60°C for 12 h, and finally the dried powder was placed in a tube furnace, and heated from room temperature 25°C to 400°C at a heating rate of 5°C / min under the protection of nitrogen, and calcined for 3 h to obtain a CoFe2O4-based composite catalyst.

[0096] Example 4

[0097] 1 mmol of cobalt nitrate, 2 mmol of ferric nitrate and 0.75 mmol of sodium citrate were dissolved in 100 ml of deionized water, and magnetic stirring was performed at 50°C until the cobalt nitrate, ferric nitrate and sodium citrate were completely dissolved. Then, 25 ml of 15% ammonia water was added, and the mixture was placed at 80°C for 2 h to obtain a mixed solution;

[0098] Subsequently, 50 ml of ethanol and 200 mg of activated carbon were added to the mixed solution, and ultrasonic mixing was performed at 25°C for 1 h to obtain a suspension.

[0099] The suspension was transferred to a reaction kettle lined with polytetrafluoroethylene for solvothermal reaction, and the temperature was kept at 180°C for 20 h. Then, the temperature was naturally cooled to room temperature. The product of the solvothermal reaction was washed with ethanol and deionized water alternately for 3 times (specifically, the first ethanol washing, the first deionized water washing, the second ethanol washing, the second deionized water washing, the third ethanol washing and the third deionized water washing). Finally, the dried powder was placed in a tube furnace, and the temperature was increased from room temperature 25°C to 450°C at a rate of 5°C / min under nitrogen protection, and calcination was performed for 2 h to obtain a CoFe2O4-based composite catalyst.

[0100] Comparative Example

[0101] Comparative Example 1

[0102] 1 mmol of cobalt nitrate, 2 mmol of ferric nitrate and 0.75 mmol of sodium citrate were dissolved in 100 ml of deionized water, and magnetic stirring was performed at 50°C until the cobalt nitrate, ferric nitrate and sodium citrate were completely dissolved. Then, 25 ml of 15% ammonia water was added, and the mixture was placed at 80°C for 2 h to obtain a mixed solution;

[0103] The suspension was transferred to a reaction kettle lined with polytetrafluoroethylene for solvothermal reaction, and the temperature was kept at 180°C for 20 h. Then, the temperature was naturally cooled to room temperature. The product of the solvothermal reaction was washed with ethanol and deionized water alternately for 3 times (specifically, the first ethanol washing, the first deionized water washing, the second ethanol washing, the second deionized water washing, the third ethanol washing and the third deionized water washing). Finally, the dried powder was placed in a tube furnace, and the temperature was increased from room temperature 25°C to 450°C at a rate of 5°C / min under nitrogen protection, and calcination was performed for 2 h to obtain a CoFe2O4-based composite catalyst.

[0104] The CoFe2O4 catalyst was used to activate PMS to degrade toluene, and the specific operation was as follows:

[0105] The initial toluene concentration was set at 30 ppm, and nitrogen was used as the carrier gas. A mass flow meter was used to control the gas flow rate at 200 mL / min. The incoming gas was bubbled through a bubbler at the bottom of the reactor, and magnetic stirring was applied to ensure effective contact between the CoFe₂O₄ catalyst and PMS. During the reaction, ultrapure water was used to maintain a constant temperature in a water bath, and all reactions were carried out at 30 °C. Before the degradation experiment, 0.1 g of CoFe₂O₄ catalyst and 2 g of PMS powder were added to 1 L of ultrapure water, and the reactor was sealed. Then, toluene standard gas was injected into the reactor to start the catalytic degradation process. Finally, the change in toluene concentration after degradation was monitored in real time using gas chromatography.

[0106] The CoFe2O4-based composite catalyst prepared in Example 1 was used to activate PMS to degrade toluene in the same manner as the steps described above.

[0107] A comparison of the activation of PMS for toluene degradation by CoFe2O4 catalyst and CoFe2O4-based composite catalyst is shown in the figure below. Figure 3 As shown, during the 2-hour continuous flow toluene degradation reaction, the toluene removal rate of the CoFe2O4-based composite catalyst activated by PMS remained stable at 95-98%; however, the toluene removal rate of the CoFe2O4 catalyst was less than 60% in the initial 10 minutes.

[0108] The present invention has been described in detail above with reference to preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are merely illustrative explanations of the invention and do not constitute any limitation on the scope of protection of the invention. Various improvements, equivalent substitutions, or modifications can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of protection of the invention, and all such modifications fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. Use of a CoFe2O4-based composite catalyst, characterized in that, the CoFe2O4-based composite catalyst is used for activating PMS to catalytically degrade VOCs, wherein the CoFe2O4-based composite catalyst is prepared by the following method: Step 1, dissolving a cobalt source, an iron source, a surfactant and a base source in a solvent to obtain a mixed solution; the concentration of the surfactant in the mixed solution is 0.002-0.005 m mol / ml; the cobalt source is cobalt nitrate, the iron source is ferric nitrate, the surfactant is sodium citrate, and the base source is ammonia; the solvent is ultrapure water; Step 2, adding a carbon material to the mixed solution to obtain a suspension, the carbon material is activated carbon; the concentration of the carbon material in the suspension is 1.8-2.5 mg / ml; Step 3, post-treating the suspension to obtain a CoFe2O4-based composite catalyst; the post-treatment includes heat treatment, drying and calcination; the heat treatment includes: heat preservation at 170-190℃ for 15-25h, and then natural cooling to room temperature; the drying temperature is 55-70℃, and the drying time is 10-18h; the calcination temperature is 400-500℃, and the calcination time is 2-4h, the calcination starts from room temperature to the required temperature, and the heating rate is 3-8℃ / min; In the prepared CoFe2O4-based composite catalyst, CoFe2O4 quantum dots are loaded on the surface of the carbon carrier, the particle size of the CoFe2O4 quantum dots is 6-9nm, and the carbon carrier is activated carbon.

2. Use according to claim 1, characterized in that, The saturation magnetic intensity of the CoFe2O4-based composite catalyst is 0.3-0.4emu / g.

3. The use according to claim 1 or 2, wherein the removal rate of the CoFe2O4-based composite catalyst for degrading VOCs reaches 95-99%.

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