Carbon-based electrocatalyst for in-situ sludge loading and preparation method thereof

Abstract

The application discloses a preparation method of a carbon-based electrocatalyst loaded with sludge in situ, which comprises the following steps: mixing a nanocellulose dispersion liquid and sludge particles, adding a cationic guar gum dispersion liquid into the mixed liquid to prepare a hydrogel, and performing a freeze-drying treatment and a pyrolysis treatment on the hydrogel. The carbon-based (biochar) electrocatalyst with a high specific surface area, rich multi-level pore structure and excellent electrochemical performance and electrocatalytic activity is successfully prepared by taking the nanocellulose / cationic guar gum hydrogel as a base material and taking papermaking sludge as a functional component. The hydrogel combined by the nanocellulose and the cationic guar gum can effectively disperse the sludge particles and prevent the sludge particles from flocculating. Moreover, the presence of the nanocellulose can improve the conductivity of the material after the pyrolysis treatment. In addition, the hydrogen bond effect between the nanocellulose, the cationic guar gum and the sludge particles can effectively combine the sludge particles and improve the stability of the sludge particles.

Description

Technical Field

[0001] This invention relates to the field of biochar, specifically to a carbon-based electrocatalyst for in-situ supported sludge and its preparation method. Background Technology

[0002] In recent years, with the rapid development of urbanization and industrialization, environmental pollution, especially water pollution, has attracted widespread attention globally. The large-scale discharge of dyeing and printing wastewater has led to severe water pollution. Among many dyes, azo dyes are widely used in daily life due to their good light absorption and stability. However, azo dyes can easily produce carcinogens (aromatic amines, etc.) in the aquatic environment, making pre-discharge treatment essential. Currently, the main methods for removing azo dyes are traditional methods such as coagulation, adsorption, and membrane technology. However, these methods are gradually fading from researchers' attention due to their incomplete treatment.

[0003] Electro-Fenton technology and Fenton-like technologies can efficiently and thoroughly treat recalcitrant dyeing and printing wastewater. Essentially, they combine the advantages of electrochemical and Fenton technologies, and are widely used in practice due to their low cost, high efficiency, and ease of control. However, currently known Fenton wastewater treatment methods have significant drawbacks, including easy material passivation, sludge production, and toxic intermediate products. Therefore, developing novel electrocatalysts to improve the performance of electrocatalytic materials and prevent the generation of byproducts during the catalytic process has become a key research focus.

[0004] In recent years, to improve the catalytic activity of electrocatalysts, some researchers have chosen to use wastewater sludge to prepare electrocatalysts. For example, existing technology reports a technical scheme for preparing electrocatalysts by loading carbonized sewage sludge onto glassy carbon electrodes. This catalyst can achieve a degradation rate of 95% for 10 mg / L methyl orange solution under a constant current of 50 mA (Zhang, C., et al., Characterization of electrodes modified with sludge-derived biochar and its performance of electrocatalytic oxidation of azo dyes. Journal of Environmental Management, 2022, 324). Furthermore, patent CN 107335435B describes an electro-Fenton catalyst, cathode, and wastewater treatment method, using municipal sludge as a precursor and employing a thermal pyrolysis method to prepare the electro-Fenton catalyst material. While existing technologies disclose that sewage sludge can be pyrolyzed to prepare electrocatalysts for degrading organic wastewater, the electrocatalysts prepared from sludge are in powder form and need to be loaded onto the surface of other substrates (such as glassy carbon electrodes and carbon paper) before they can be used. However, glassy carbon electrodes and carbon paper materials have limited contact sites and a limited potential tolerance range, which severely limits the practical application of the relevant electrocatalysts. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a carbon-based electrocatalyst for in-situ supported sludge and its preparation method, thereby solving the problems of poor catalytic activity and incomplete degradation of azo dyes by existing electrocatalysts.

[0006] To achieve the above objectives, the present invention first provides a method for preparing a carbon-based electrocatalyst for in-situ supported sludge, comprising the following steps:

[0007] (1) Mix the nanocellulose dispersion and sludge particles to obtain a mixed solution;

[0008] (2) Add cationic guar gum dispersion to the mixed solution of step (1) to obtain nanocellulose-based hydrogel loaded with sludge particles.

[0009] (3) The hydrogel obtained in step (2) is freeze-dried to obtain nanocellulose aerogel loaded with sludge particles.

[0010] (4) The aerogel obtained in step (3) is subjected to pyrolysis under a protective gas atmosphere to obtain a carbon-based electrocatalyst material for in-situ supported sludge.

[0011] The sludge particles used in this invention are obtained by sedimentation of wastewater collected from a paper mill.

[0012] The nanocellulose involved in this invention is anionic nanocellulose, including TEMPO oxidized nanocellulose, etc.

[0013] In one embodiment of the present invention, in step (1), the nanocellulose dispersion is obtained by dispersing nanocellulose in water, and the mass concentration of the nanocellulose dispersion is 0.1-2.0%.

[0014] In one embodiment of the present invention, in step (1), the mass ratio of the sludge particles to the nanocellulose is 1 to 4:1.

[0015] In one embodiment of the present invention, in step (2), the mass concentration of the cationic guar gum dispersion is 0.1-2%, and the cationic guar gum dispersion is prepared by dispersing cationic guar gum in water.

[0016] In one embodiment of the present invention, in step (2), the mass ratio of the cationic guar gum dispersion to the mixed solution is 1:0.1 to 10.

[0017] In one embodiment of the present invention, in step (3), the freeze-drying is vacuum freeze-drying, the freeze-drying temperature is -40 to -50°C, and the drying time is 12 to 48 hours.

[0018] In one embodiment of the present invention, in step (4), the protective atmosphere includes at least one of argon, nitrogen or helium.

[0019] In one embodiment of the present invention, in step (4), the pyrolysis temperature is 600-1000°C and the pyrolysis time is 1-3 hours.

[0020] The present invention also provides a carbon-based electrocatalyst for in-situ supported sludge prepared according to the above method.

[0021] The present invention also provides an application of the above-mentioned in-situ supported sludge carbon-based electrocatalyst in the field of wastewater degradation.

[0022] In one embodiment of the invention, the application includes the degradation of azo dye wastewater.

[0023] The beneficial effects of this invention are:

[0024] (1) This invention uses nanocellulose combined with sludge particles, utilizing the functional groups in nanocellulose to effectively anchor functional ions (such as Fe) in the sludge particles. 3+This promotes the efficient dispersion of sludge particles and functional ions, thereby improving the catalytic activity of the prepared electrocatalyst.

[0025] (2) This invention successfully prepared a carbon-based (biochar) electrocatalyst with high specific surface area, abundant hierarchical pore structure, and excellent electrochemical performance and electrocatalytic activity by using nanocellulose / cationic guar gum hydrogel as the substrate and papermaking sludge as the functional component. The conductivity of the material can be improved after pyrolysis of nanocellulose. Furthermore, cationic guar gum can provide nitrogen to the final carbon-based electrocatalyst, improving its electrocatalytic performance.

[0026] (3) The carbon-based electrocatalyst prepared by the method of the present invention has a good degradation effect on wastewater, especially azo wastewater. This is mainly due to the synergistic effect between nanocellulose, sludge particles and cationic guar gum. The carbon-based electrocatalyst of the present invention can achieve a degradation rate of up to 95.06% for methyl orange, which is much higher than that of electrocatalysts prepared by using nanocellulose or sludge particles alone. Attached Figure Description

[0027] Figure 1 This is a photograph of the carbon-based electrocatalyst obtained in Example 1 of the present invention.

[0028] Figure 2 The images shown are scanning electron microscope (SEM) images of the carbon-based electrocatalyst obtained in Example 1 of this invention, where a represents the morphology at low magnification and b represents the morphology at high magnification.

[0029] Figure 3 The images are scanning electron microscope (SEM) images of the sludge particle electrocatalyst before and after carbonization obtained in Comparative Example 1 of this invention, where a represents before carbonization and b represents after carbonization.

[0030] Figure 4 This is a scanning electron microscope image of the carbonized aerogel electrocatalyst obtained in Comparative Example 2 of the present invention.

[0031] Figure 5 This is a photograph of the carbon-based electrocatalyst obtained in Example 1 of the present invention degrading methyl orange;

[0032] Figure 6 The electrocatalysts obtained in Examples 1, 1, and 2 of this invention reduce the degradation rate of methyl orange.

[0033] Figure 7 The image shows the UV-Vis spectrum of the carbon-based electrocatalyst obtained in Example 1 of this invention for the degradation of methyl orange. Detailed Implementation

[0034] To better understand the technical solutions of the present invention, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0035] The nanocellulose used in this embodiment of the invention is TEMPO-oxidized nanocellulose prepared in the laboratory. The preparation method of TEMPO-oxidized nanocellulose includes the following steps: modifying nanocellulose using a tetramethylpiperidine oxide (TEMPO) / sodium bromide / sodium hypochlorite catalytic oxidation system. For every 1g of nanocellulose, use 0.01g of tetramethylpiperidine oxide, 0.1g of sodium bromide, and 10mL of sodium hypochlorite solution with a concentration of 0.1g / mL. Add the nanocellulose to the catalytic oxidation system and stir at room temperature for 2h to complete the anionization modification, obtaining an initial nanocellulose solution. Dilute with water as needed to obtain a 0.1-2.0wt.% TEMPO-oxidized nanocellulose aqueous solution.

[0036] Example 1:

[0037] 10g of a 1wt.% nanocellulose dispersion and 0.1g of sludge particles were placed in a beaker. Then, 5g of a 2wt.% cationic guar gum was added to the beaker and mixed uniformly with the nanocellulose dispersion and sludge particles to prepare a sludge particle-loaded nanocellulose hydrogel. The hydrogel was then subjected to vacuum freeze-drying at -40℃ for 48h to obtain a sludge particle-loaded nanocellulose aerogel. The aerogel was then carbonized at 1000℃ under an argon atmosphere to obtain an in-situ sludge-loaded carbon-based electrocatalyst.

[0038] Figure 1 and Figure 2 The images shown are physical photos and SEM images of the carbon-based electrocatalyst prepared in Example 1. Figure 1 It can be seen that the prepared carbon-based electrocatalyst can be adsorbed by a magnet, indicating that the catalyst possesses a certain degree of magnetism. From... Figure 2 It can be seen that the sludge particles are uniformly dispersed on the surface of the carbon aerogel, indicating the successful preparation of the electrocatalyst.

[0039] Figure 5 The image shows the carbon-based electrocatalyst used to degrade methyl orange. It can be seen that the color of methyl orange gradually lightens with increasing degradation time, indicating that the catalyst plays a catalytic role in the degradation of methyl orange.

[0040] An experiment was conducted on the electrocatalytic degradation of methyl orange using a carbon-based electrocatalyst supported on in-situ sludge. 3 mL samples of methyl orange were taken every 20 minutes, and their absorbance was measured using a UV-Vis spectrophotometer to determine the electrocatalytic performance of the catalyst. Figure 6 As shown, the results indicate that after applying a constant current of 10 mA for 120 min, the degradation rate of methyl orange solution with a concentration of 30 mg / L reached 92.91%.

[0041] Figure 7 The UV spectrum of the carbon-based electrocatalyst for the degradation of methyl orange was obtained. The UV spectrum of the degradation of methyl orange more clearly shows that the carbon-based electrocatalyst with in-situ grown sludge particles has excellent electrocatalytic degradation performance.

[0042] Example 2:

[0043] 10g of a 2wt.% nanocellulose dispersion and 0.4g of sludge particles were placed in a beaker. Then, 100g of a 0.1wt.% cationic guar gum was added to the beaker and mixed uniformly with the nanocellulose dispersion and sludge particles to prepare a sludge particle-loaded nanocellulose hydrogel. The hydrogel was then subjected to vacuum freeze-drying at -40℃ for 24h to obtain a sludge particle-loaded nanocellulose aerogel. The aerogel was then carbonized at 1000℃ for 2h under an argon atmosphere to obtain an in-situ sludge-loaded carbon-based electrocatalyst.

[0044] The electrocatalytic performance of the carbon-based electrocatalyst with in-situ supported sludge was tested using the same method as in Example 1. The results showed that after applying a constant current of 10 mA for 120 min, the degradation rate of methyl orange solution with a concentration of 30 mg / L reached 95.06%.

[0045] Example 3:

[0046] 10g of a 0.1wt.% nanocellulose dispersion and 0.1g of sludge particles were placed in a beaker. Then, 1g of a 2wt.% cationic guar gum was added to the beaker and mixed uniformly with the nanocellulose dispersion and sludge particles to prepare a sludge particle-loaded nanocellulose hydrogel. The hydrogel was subjected to vacuum freeze-drying at -40℃ for 48h to obtain a sludge particle-loaded nanocellulose aerogel. The aerogel was carbonized at 1000℃ for 1h under an argon atmosphere to obtain an in-situ sludge-loaded carbon-based electrocatalyst.

[0047] The electrocatalytic performance of the carbon-based electrocatalyst with in-situ supported sludge was tested using the same method as in Example 1. The results showed that after applying a constant current of 10 mA for 120 min, the degradation rate of methyl orange solution with a concentration of 30 mg / L reached 90.85%.

[0048] Comparative Example 1

[0049] Take 0.1g of sludge particles into a beaker, add 5mL of deionized water and sonicate for 5min. The resulting dispersion is then freeze-dried under vacuum at -40℃ for 48h. Subsequently, it is carbonized at 1000℃ for 3h to obtain the carbonized sludge particle electrocatalyst.

[0050] Figure 3 (a) and (b) are scanning electron microscope images of the sludge particle electrocatalyst before and after carbonization obtained in Comparative Example 1 of the present invention, respectively. It can be seen from the figures that the size of the sludge particles is reduced after carbonization.

[0051] Since the carbonized sludge is in powder form, its electrocatalytic performance cannot be directly tested. In this comparative example, when analyzing the electrocatalytic performance of the sludge particles, the carbonized sludge was first compressed into tablets, and the electrocatalytic performance of the tableted sludge was tested using the same method as in Example 1. The results showed that after applying a constant current of 10 mA for 120 min, its degradation rate of a 30 mg / L methyl orange solution was only 1.04%.

[0052] Comparative Example 2

[0053] The difference between Comparative Example 2 and Example 1 is that no sludge particles were added.

[0054] Figure 4 The SEM image of the carbon-based electrocatalyst prepared in Comparative Example 2 is shown, and the results show that the catalyst has an excellent hierarchical porous structure.

[0055] The electrocatalytic performance of the obtained carbon-based electrocatalyst was analyzed using the same testing method as in Example 1. The results showed that after applying a constant current of 10 mA for 120 min, its degradation rate of a 30 mg / L methyl orange solution was 13.36%. This was mainly due to the adsorption generated by the rich porous structure of the carbon aerogel, while its own catalytic degradation performance was relatively weak.

[0056] Comparative Example 3

[0057] The difference between Comparative Example 3 and Example 1 is that the cationic guar gum dispersion was replaced with a cationic starch dispersion.

[0058] The electrocatalytic performance of the prepared in-situ supported carbon-based electrocatalyst was tested using the same method as in Example 1. The results showed that after applying a constant current of 10 mA for 120 min, the degradation rate of a 30 mg / L methyl orange solution reached 63.05%. Since the crosslinking effect between cationic starch and nanocellulose is weaker than that of cationic guar gum, the pore structure of the corresponding material is poor, resulting in weaker catalytic degradation performance.

[0059] Comparative Example 4:

[0060] The difference between Comparative Example 4 and Example 1 is that the mass of the added sludge particles is 0.8g.

[0061] Because an excessive amount of sludge particles were added in this embodiment, the hydrogen bonding and electrostatic interaction between nanocellulose and cationic guar gum were weakened, thus preventing the formation of a hydrogel and the preparation of a carbon-based electrocatalyst with in-situ supported sludge.

[0062] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a carbon-based electrocatalyst for in-situ supported sludge, characterized in that, Includes the following steps: (1) The nanocellulose dispersion and sludge particles are mixed to obtain a mixed solution, wherein the mass ratio of the sludge particles to the nanocellulose is 1 to 4:1; (2) Add a cationic guar gum dispersion to the mixed solution in step (1) to obtain a nanocellulose-based hydrogel loaded with sludge particles, wherein the mass ratio of the cationic guar gum dispersion to the mixed solution is 1:0.1 to 10. (3) The hydrogel obtained in step (2) is freeze-dried to obtain nanocellulose aerogel loaded with sludge particles. (4) The aerogel obtained in step (3) is subjected to pyrolysis under a protective gas atmosphere to obtain a carbon-based electrocatalyst material for in-situ supported sludge.

2. The preparation method according to claim 1, characterized in that, In step (1), the nanocellulose dispersion is obtained by dispersing nanocellulose in water, and the mass concentration of the nanocellulose dispersion is 0.1-2.0%.

3. The preparation method according to claim 1, characterized in that, In step (2), the mass concentration of the cationic guar gum dispersion is 0.1-2%, and the cationic guar gum dispersion is prepared by dispersing cationic guar gum in water.

4. The preparation method according to claim 1, characterized in that, In step (3), the freeze drying is vacuum freeze drying, the freeze drying temperature is -40 to -50℃, and the drying time is 12 to 48 hours.

5. The preparation method according to claim 1, characterized in that, In step (4), the protective atmosphere includes at least one of argon, nitrogen or helium, the pyrolysis temperature is 600 to 1000°C, and the pyrolysis time is 1 to 3 hours.

6. The carbon-based electrocatalyst for in-situ supported sludge prepared by the method according to any one of claims 1 to 5.

7. The application of the carbon-based electrocatalyst with in-situ supported sludge as described in claim 6 in the field of wastewater degradation.

8. The application according to claim 7, characterized in that, The application includes the degradation of azo dye wastewater.

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