Carbon aerogel catalysts for activating persulfates and methods of making and using the same

Abstract

The application discloses a carbon aerogel catalyst for activating persulfate and a preparation method and application thereof. The preparation method comprises the following steps: dropping a carrageenan aqueous solution into a cobalt ion solution to prepare a cobalt-carrageenan hydrogel; washing the cobalt-carrageenan hydrogel, freezing, and then performing freeze drying to prepare a cobalt-carrageenan aerogel; and calcining the cobalt-carrageenan aerogel to obtain a cobalt-carrageenan carbon aerogel. By introducing metal Co to form Co9S8, the cobalt-carrageenan carbon aerogel can be used as a persulfate catalyst with excellent performance, and has high catalytic activity and good stability.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalyst technology, specifically relating to a carbon aerogel catalyst for activating persulfate, its preparation method, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Advanced oxidation processes (AOPs) are widely used in wastewater treatment due to their high reactivity and non-specific, broad-spectrum effectiveness against organic pollutants. Given their advantages such as fast reaction rates and low secondary pollution, persulfate (PMS)-based AOPs are increasingly being applied to wastewater treatment. Common PMS activation methods include photoactivation, thermal activation, and activation with transition metal ions to generate sulfate radicals. Cobalt is considered the most effective transition metal for activating PMS to degrade organic pollutants. However, these methods suffer from high energy consumption, high cost, metal ion leaching, and difficulty in recovery, limiting their practical engineering applications.

[0004] Given that the use of heterogeneous catalysts for PMS activation is environmentally friendly, cost-effective, and has excellent performance, many researchers have found that transition metal sulfides can effectively activate PMS and have higher conductivity, excellent optical properties, outstanding mechanical properties and thermal stability, as well as high catalytic efficiency for PMS, especially for recalcitrant organic matter.

[0005] Currently, the preparation of transition metal sulfide catalytic materials mostly adopts the in-situ solvothermal growth method (one-step hydrothermal method). During the preparation process, thiourea, ammonium sulfide, thioacetamide and other sulfur sources are added, which will cause harm and pollution to the health of workers and the ambient air. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a carbon aerogel catalyst for activating persulfate, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a carbon aerogel catalyst for activating persulfate, comprising the following steps:

[0009] Cobalt-carrageenan hydrogels were prepared by adding an aqueous carrageenan solution to a cobalt ion solution.

[0010] Cobalt-carrageenan hydrogel was washed, frozen, and then freeze-dried to prepare cobalt-carrageenan aerogel.

[0011] Cobalt-carrageenan aerogel was calcined to obtain cobalt-carrageenan carbon aerogel Co9S8 / CA.

[0012] Carrageenan is a hydrophilic colloid extracted from red algae, specifically seaweed. It is white or milky white in color and possesses hydrophilic, gelling, and thickening properties. Carrageenan is composed of alternating galactose or dehydrated galactose and sulfonic acid groups. Based on the different bonding morphologies of the sulfonic acid groups, it is classified into different configurations such as k-type, t-type, and l-type. K-type and t-type carrageenan exhibit thermally reversible gelation properties in aqueous solutions; that is, under heating conditions, the double helix structure of the carrageenan molecule unwinds, allowing the outer sulfonic acid groups to react with Co. 2+ Ion interactions form a new double-helix structure. Utilizing this property, cobalt metal can be composited with sulfonic acid groups to form transition metal sulfides supported on a carrageenan carbon substrate. This composite catalyst not only retains the catalytic performance of transition metal sulfides but also possesses a more stable structure, effectively avoiding secondary contamination and deactivation problems caused by metal ion loss.

[0013] In some embodiments, the cobalt ion concentration in the cobalt ion solution is 0.05-2 mol / L.

[0014] Preferably, the cobalt source in the cobalt ion solution is C4H6CoO4·4H2O, CoCl2·6H2O, or Co(NO3)2·6H2O.

[0015] Preferably, the method for preparing the carrageenan aqueous solution includes the following steps: adding carrageenan to water in a certain proportion and heating to dissolve it; the mass fraction of carrageenan in the carrageenan aqueous solution is 1%-3%.

[0016] More preferably, the volume ratio of carrageenan aqueous solution to cobalt ion solution is 1:1-2.

[0017] In some embodiments, after cleaning the cobalt-carrageenan hydrogel, the freezing temperature is -40°C to -20°C, and the freezing time is 10-15 hours.

[0018] Freezing and drying are not performed simultaneously. First, the sample is fully frozen, then the frozen sample is subjected to vacuum treatment, maintaining its frozen state during vacuum treatment. In other words, the first "freezing" step simply brings the sample to a frozen state; it does not need to be performed under vacuum conditions, and liquid nitrogen can be used to achieve instantaneous freezing. The second "freeze-drying" step involves vacuum drying while the sample is frozen, i.e., performing a vacuum operation while maintaining a low temperature.

[0019] Preferably, the freeze-drying time is 48-72 hours.

[0020] In some embodiments, the cobalt-carrageenan aerogel is calcined in an inert atmosphere at a temperature of 600-800°C for 1-2 hours.

[0021] Preferably, the calcination temperature is 650-750℃.

[0022] Preferably, the heating rate of the calcination is 2-5℃ / min.

[0023] Secondly, the present invention provides a carbon aerogel catalyst for activating persulfate, which is prepared by the aforementioned preparation method.

[0024] Thirdly, the present invention provides the application of the carbon aerogel catalyst for activating persulfate in the activation of persulfate.

[0025] In some embodiments, the persulfate is used to catalytically degrade sulfamethoxazole (SMX) in wastewater.

[0026] Preferably, the persulfate is potassium persulfate (PMS, KHSO5·0.5KHSO4·0.5K2SO4), and the concentration of potassium persulfate in the catalytic degradation system is 0.3-0.9 mM.

[0027] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0028] The method for preparing Co9S8 carbon aerogel of the present invention introduces metallic Co to form Co9S8, which can be used as a high-performance persulfate catalyst with high catalytic activity and good stability. Compared with the traditional hydrothermal method that introduces a sulfur source, the carrageenan used in this method serves as a clean sulfur source and also provides a carbon substrate for Co9S8, allowing Co9S8 to be uniformly distributed on the carbon substrate to form Co9S8 carbon aerogel.

[0029] The preparation process of the Co9S8 carbon aerogel of the present invention is more environmentally friendly and safer; and carrageenan, as an extract of red algae, is widely available, inexpensive and readily available, has industrialization potential and is suitable for practical industrial applications. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 The XRD pattern of Co9S8 / CA prepared in Example 1 of this invention;

[0032] Figure 2The diagram shows the effect of the Co9S8 / CA catalyst prepared in Example 1 of the present invention and other materials prepared in Comparative Example 1 on the activation of PMS to degrade SMX in water.

[0033] Figure 3 This is a diagram illustrating the effect of the Co9S8 / CA catalyst on the activation of PMS and degradation of SMX in different concentration persulfate systems in this invention embodiment;

[0034] Figure 4 This is a diagram illustrating the effect of the Co9S8 / CA catalyst on the activation of PMS and degradation of SMX in 5 cycles in an embodiment of the present invention. Detailed Implementation

[0035] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] The present invention will be further described below with reference to the embodiments.

[0037] Example 1

[0038] The preparation method of Co9S8 / CA includes the following steps:

[0039] (1) Accurately weigh 1.2454g of C4H6CoO4·4H2O into 50mL of deionized water, stir and dissolve to obtain a 0.1mol / L cobalt metal solution.

[0040] (2) Accurately weigh 1g of τ-carrageenan solid powder, set the water bath temperature to 80℃, and dissolve τ-carrageenan in 49g of deionized water under stirring and heating conditions to obtain a 2% carrageenan aqueous solution.

[0041] (3) The completely dissolved carrageenan aqueous solution was added dropwise to the cobalt metal solution at a volume ratio of 1:1 to obtain a cobalt metal-carrageenan hydrogel.

[0042] (4) Rinse the cobalt-carrageenan hydrogel obtained in step (3) with deionized water, place the cleaned hydrogel in the cold trap of a freeze dryer (-40℃) and freeze for 12 hours. After freezing, place it in the freeze dryer and dry for 50 hours to obtain cobalt-carrageenan aerogel.

[0043] (5) The cobalt-carrageenan aerogel obtained in step (4) is placed in a tube furnace and heated to 700°C at a heating rate of 2°C / min under an argon (Ar) atmosphere and held for 1 hour. Then it is naturally cooled to room temperature to obtain the Co9S8 / CA catalyst.

[0044] Example 2

[0045] The preparation method of Co9S8 / CA includes the following steps:

[0046] (1) Accurately weigh C4H6CoO4·4H2O into 50mL of deionized water, stir and dissolve to obtain a 0.15mol / L cobalt metal solution.

[0047] (2) Accurately weigh τ-carrageenan solid powder, set the water bath temperature to 75℃, and dissolve τ-carrageenan in deionized water under stirring and heating conditions to obtain a 1% carrageenan aqueous solution.

[0048] (3) The completely dissolved carrageenan aqueous solution was added dropwise to the cobalt metal solution at a volume ratio of 1:2 to obtain a cobalt metal-carrageenan hydrogel.

[0049] (4) Rinse the cobalt-carrageenan hydrogel obtained in step (3) with deionized water, place the cleaned hydrogel in the cold trap of a freeze dryer (-40℃) and freeze for 15 hours. After freezing, place it in the freeze dryer and dry for 70 hours to obtain cobalt-carrageenan aerogel.

[0050] (5) The cobalt-carrageenan aerogel obtained in step (4) is placed in a tube furnace and heated to 650°C at a heating rate of 2°C / min under an argon (Ar) atmosphere and held for 2 hours. Then it is naturally cooled to room temperature to obtain the Co9S8 / CA catalyst.

[0051] Example 3

[0052] The preparation method of Co9S8 / CA includes the following steps:

[0053] (1) Accurately weigh C4H6CoO4·4H2O into 50mL of deionized water, stir and dissolve to obtain a 0.05mol / L cobalt metal solution.

[0054] (2) Accurately weigh τ-carrageenan solid powder, set the water bath temperature to 75℃, and dissolve τ-carrageenan in deionized water under stirring and heating conditions to obtain a 3% carrageenan aqueous solution.

[0055] (3) The completely dissolved carrageenan aqueous solution was added dropwise to the cobalt metal solution at a volume ratio of 1:2 to obtain a cobalt metal-carrageenan hydrogel.

[0056] (4) Rinse the cobalt-carrageenan hydrogel obtained in step (3) with deionized water, place the cleaned hydrogel in the cold trap of a freeze dryer (-40℃) and freeze for 10h. After freezing, place it in the freeze dryer and dry for 60h to obtain cobalt-carrageenan aerogel.

[0057] (5) The cobalt-carrageenan aerogel obtained in step (4) is placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under an argon (Ar) atmosphere and held for 2 hours. Then it is naturally cooled to room temperature to obtain the Co9S8 / CA catalyst.

[0058] Comparative Example 1

[0059] Preparation of carrageenan carbon aerogel (CA):

[0060] The preparation steps of CA in Comparative Example 1 were the same as those in Example 1, except that cobalt acetate tetrahydrate was not added.

[0061] The Co9S8 / CA prepared in Example 1 and the CA prepared in Comparative Example 1 were characterized, and the results are as follows:

[0062] Figure 1 The XRD patterns of the Co9S8 / CA catalyst prepared in Example 1 and the CA catalyst obtained in Comparative Example 1 are shown. The diffraction peaks of Co9S8 / CA are highly consistent with those of Co9S8 in the XRD standard card. As can be seen from the XRD patterns, Example 1 of this invention successfully supported metallic Co on a carbon substrate with carrageenan as a precursor, and generated a cobalt-carrageenan carbon aerogel, namely Co9S8 / CA.

[0063] Comparative Example 2

[0064] Preparation of copper-carrageenan carbon aerogel:

[0065] The preparation steps of the copper-carrageenan carbon aerogel in Comparative Example 2 were the same as those in Example 1, except that cobalt acetate tetrahydrate was replaced with copper acetate monohydrate.

[0066] Comparative Example 3

[0067] Preparation of iron-carrageenan carbon aerogel:

[0068] The preparation steps of the iron-carrageenan carbon aerogel in Comparative Example 3 were the same as those in Example 1, except that cobalt acetate tetrahydrate was replaced with ferric chloride hexahydrate.

[0069] Comparative Example 4

[0070] Preparation of manganese-carrageenan carbon aerogel:

[0071] The preparation steps of the manganese-carrageenan carbon aerogel in Comparative Example 4 were the same as those in Example 1, except that cobalt acetate tetrahydrate was replaced with anhydrous manganese chloride.

[0072] Performance test of Co9S8 / CA catalytically activated PMS for removing organic matter from wastewater 1:

[0073] Five mg (0.1 g / L) of Co9S8 / CA prepared in Example 1, CA prepared in Comparative Example 1, copper-carrageenan carbon aerogel prepared in Comparative Example 2, iron-carrageenan carbon aerogel prepared in Comparative Example 3, and manganese-carrageenan carbon aerogel prepared in Comparative Example 4 were weighed out and dispersed in 50 mL of SMX solution (concentration 20 mg / L). Adsorption-desorption equilibrium was reached after 30 min. Then, 4.6 mg of PMS was added to bring the PMS concentration to 0.3 mM. At regular intervals, 0.5 mL of solution was taken to measure the SMX concentration. Under the action of Co9S8 / CA, PMS was activated to generate free radicals, thereby achieving the degradation of SMX.

[0074] The comparison graph of the degradation effects of the catalysts prepared in Example 1 and Comparative Examples 1-4 on SMX is shown in the figure. Figure 2 ,Depend on Figure 2 It can be seen that the Co9S8 / CA catalyst prepared in Example 1, when used as an activation catalyst, exhibits a significantly higher degradation effect than the catalysts prepared in Comparative Examples 1-4. This demonstrates that only the Co9S8 / CA catalyst can effectively activate PMS to degrade SMX.

[0075] Test 2:

[0076] The operating procedures for this test were the same as those for Test 1, except that the PMS dosage was adjusted (the activation catalyst for PMS was fixed at Co9S8 / CA).

[0077] The effect of Co9S8 / CA catalyst on the degradation of SMX by PMS under different PMS dosage conditions is shown in the figure. Figure 3 It is evident that, within a certain range, the degradation effect increases with increasing PMS concentration. This is because the increased PMS concentration leads to the generation of more free radicals. However, when the PMS concentration increases from 0.6 mM to 0.9 mM, the enhancement of the degradation effect becomes less significant. Considering factors such as economic cost, a suitable PMS concentration should be selected for practical applications.

[0078] Co9S8 / CA Cyclic Degradation Performance Test:

[0079] Weigh 5 mg of the Co9S8 / CA catalyst prepared in Example 1 and mix it with 50 mL of a 20 mg / L SMX solution. After 30 min, add 0.6 mM PMS and measure the SMX concentration at regular intervals. After 30 min, filter out the solid catalyst from the solution and dry it under vacuum. Repeat the above steps 4 times.

[0080] Figure 4 This is a graph showing the cyclic degradation effect of Co9S8 / CA prepared in Example 1 on a 20 mg / L SMX solution at a concentration of 0.6 mM PMS. Figure 4It can be seen that Co9S8 / CA has good stability and can still maintain high catalytic activity after multiple cycles. After 5 cycles, the removal rate of SMX can still reach 81.5%.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a carbon aerogel catalyst for activating persulfate in the activation of persulfate, characterized in that: The preparation method of carbon aerogel catalyst for activating persulfate includes the following steps: Cobalt-carrageenan hydrogels were prepared by adding an aqueous carrageenan solution to a cobalt ion solution. Cobalt-carrageenan hydrogel was washed, frozen, and then freeze-dried to prepare cobalt-carrageenan aerogel. Cobalt-carrageenan aerogel was calcined to obtain cobalt-carrageenan carbon aerogel; The freezing temperature is -40 ℃ to -20 ℃, the freezing time is 10-15 h, the freeze-drying time is 48-72 h, and the calcination heating rate is 2-5 ℃ / min. The persulfate is used to catalytically degrade sulfamethoxazole in wastewater.

2. The application according to claim 1, characterized in that: The cobalt ion solution has a cobalt ion concentration of 0.05-2 mol / L.

3. The application according to claim 1, characterized in that: The cobalt source in the cobalt ion solution is C4H6CoO4·4H2O, CoCl2·6H2O, or Co(NO3)2·6H2O.

4. The application according to claim 1, characterized in that: The method for preparing the carrageenan aqueous solution includes the following steps: adding carrageenan to water in a certain proportion and heating to dissolve it; the mass fraction of carrageenan in the carrageenan aqueous solution is 1%-3%.

5. The application according to claim 1, characterized in that: The volume ratio of carrageenan aqueous solution to cobalt ion solution is 1:1-2.

6. The application according to claim 1, characterized in that: The cobalt-carrageenan aerogel was calcined in an inert atmosphere at a temperature of 600-800℃ for 1-2 hours.

7. The application of the carbon aerogel catalyst for activating persulfate according to claim 6 in the activation of persulfate, characterized in that: The calcination temperature is 650-750℃.

8. The application according to claim 1, characterized in that: The persulfate is potassium persulfate, and the concentration of potassium persulfate in the catalytic degradation system is 0.3-0.9 mM.

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