Sludge-based composite hydrophobic material as well as preparation method and application thereof

Abstract

The invention discloses a sludge-based composite hydrophobic material and a preparation method and application thereof, and relates to the technical field of solid waste resource utilization and electrocatalysis, the sludge-based composite hydrophobic material comprises modified sludge-based SiO2 and PFAS loaded on the modified sludge-based SiO2; according to the preparation method, the sludge-based silicon-aluminum oxide is modified through hydrothermal treatment and acid leaching treatment, and the sludge-based silicon-aluminum oxide is endowed with high surface roughness and a 3D linear array micro-nano structure, so that the physical hydrophobicity of sludge-based SiO2 is remarkably improved; the chemical hydrophobicity of the PFAS is utilized, and the chemical hydrophobicity and the physical hydrophobicity are combined, so that the prepared composite material not only retains high stability of SiO2, but also shows excellent hydrophobicity.

Description

Technical Field

[0001] The present invention relates to the field of solid waste resource utilization and electrocatalysis technology, and in particular to a sludge-based composite hydrophobic material and a preparation method and application thereof. Background Art

[0002] With the vigorous development of social economy, environmental pollution problems have become increasingly prominent, especially the impact of industrial emissions on the global climate cannot be ignored. In the cement production process, carbonate decomposition reaction is an inevitable link, which will lead to large amounts of carbon dioxide (CO2) emissions. It is estimated that for every ton of cement clinker produced, approximately 0.8 tons of CO2 will be emitted, which has a significant impact on the global climate. As a cutting-edge CO2 conversion method, electroreduction technology can not only convert the CO2 generated in the cement production process into valuable chemicals or fuels, but also realize the recycling of resources and reduce carbon footprint. It plays a vital role in promoting low-carbon or zero-carbon cement production and achieving the ambitious goals of the cement industry.

[0003] However, the successful application of electrocatalytic CO2 reduction technology requires not only the development of catalytic materials but also the interfacial microenvironment, which plays a crucial role in the catalytic process and kinetics. In electrocatalytic devices, the gas diffusion electrode (GDE) is a key component, and its performance directly determines the efficiency and quality of CO2 reduction. The hydrophobic microenvironment of the GDE has a significant impact on the diffusion of reactants and products, the regulation of local pH, and the stability of active sites.

[0004] Sludge-based extracted-modified silica (SiO2) as an innovative material not only realizes the resource utilization of waste, but also shows great potential in hydrophobicity due to its unique physical and chemical properties, such as high surface roughness and 3D micro-nano structure. Polyfluoroalkyl substances (PFAS) occupy an important position in material modification due to their excellent hydrophobicity and chemical stability, and are widely used in coatings, textiles, leather and other industries. The present invention explores the use of sludge-based composite hydrophobic materials for optimizing the surface hydrophobicity of cement kiln flue gas CO2 electroreduction electrodes based on modified sludge-based SiO2 and PFAS. It is not only of great significance to promote the green transformation of the cement industry, but also provides a new idea for the development of CO2 resource utilization technology. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a sludge-based composite hydrophobic material and a preparation method thereof. The composite material combines the physical hydrophobicity of modified sludge-based SiO2 and the chemical hydrophobicity of PFAS, has excellent hydrophobic properties, and at the same time has the advantages of low cost and environmental friendliness of sludge-based materials.

[0006] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0007] The first object of the present invention is to provide a sludge-based composite hydrophobic material, comprising modified sludge-based SiO2 and PFAS loaded on the modified sludge-based SiO2.

[0008] A second object of the present invention is to provide a method for preparing a sludge-based composite hydrophobic material, comprising the following steps:

[0009] S1. calcining the sludge, acid leaching, and alkali leaching to obtain sludge-based silicon-aluminum composite oxide;

[0010] S2, hydrothermally reacting the sludge-based silicon-aluminum composite oxide prepared in step S1 with a surfactant, calcining, and etching to obtain modified sludge-based SiO2;

[0011] S3. The modified sludge-based SiO2 prepared in step S2 is subjected to a hydrothermal reaction with PFAS to obtain a sludge-based composite hydrophobic material.

[0012] In step S1, calcination is performed in air or oxygen at a temperature of 600-800°C for 3-5 hours. The purpose of calcining the sludge is to remove organic matter and obtain sludge ash, while also ensuring that the active components in the sludge remain relatively stable during use.

[0013] In step S1, the acid leaching is performed using a hydrochloric acid or sulfuric acid solution with a concentration of 0.1 to 0.3 mol / L at a temperature of 40 to 60°C for 2 to 4 hours. The purpose of low-concentration acid leaching is to remove metal oxides and impurities such as iron oxide, calcium oxide, and magnesium oxide from the sludge ash to obtain a silicon-aluminum composite oxide.

[0014] In step S1, the alkaline leaching is performed using a sodium hydroxide or potassium hydroxide solution with a concentration of 2 to 3 mol / L, at a temperature of 25 to 30°C, for 2 to 4 hours. The purpose of the alkaline leaching is to further chemically treat the silicon-aluminum composite oxide in the acid-leached solid in a strong alkaline environment, thereby forming a gelled precursor.

[0015] In step S2, the surfactant is a polyaddition polymer of polypropylene glycol and ethylene oxide (F127 or P123). During the hydrothermal reaction, the addition of F127 or P123 as a surfactant affects the material's microstructure and surface properties. F127 or P123 interacts with the components of the gelled silica-alumina composite oxide through electrostatic and hydrogen bonding reactions, guiding the hydrolysis and condensation reactions of the silicon and aluminum sources, thereby promoting the formation of a 3D linear array micro-nanostructure of the silica-alumina composite oxide.

[0016] In step S2, the mass ratio of the surfactant to the sludge-based silicon-aluminum composite oxide is (1-2):(10-15).

[0017] In step S2, the reaction temperature of the hydrothermal reaction is 100-180° C., and the reaction time is 18-24 hours.

[0018] In step S2, the calcination is carried out in air or oxygen atmosphere at a temperature of 550-800°C for 2-4 hours. The purpose of calcining the hydrothermal reaction product is to remove surfactants, optimize the material structure, enhance the material stability, and promote the improvement of the material's hydrophobicity.

[0019] In step S2, the etching is performed using a hydrofluoric acid solution with a concentration of 0.5 to 1 mol / L, at a temperature of 30 to 60°C, for 5 to 10 minutes. The purpose of the acid etch is to dissolve some of the aluminum oxide on the surface of the SiO2 and increase the surface roughness of the SiO2, making it more hydrophobic.

[0020] In step S3, the mass ratio of the modified sludge-based SiO2 to PFAS is (2-3):(0.5-1).

[0021] In step S3, the temperature of the hydrothermal reaction is 130-180° C., and the time is 3-6 hours.

[0022] The third object of the present invention is to provide the use of the sludge-based composite hydrophobic material in electrocatalytic CO2 reduction.

[0023] The beneficial effects of the present invention are:

[0024] 1. The main gain component of the sludge-based composite hydrophobic material provided by the present invention comes from the sludge by-product of sewage treatment plants, which belongs to the resource utilization of solid waste. It has a wide source, low cost, and is environmentally friendly, achieving the dual goals of rational utilization of waste resources and environmental protection.

[0025] 2. Coating the sludge-based composite hydrophobic material provided by the present invention on the surface of the CO2 electrocatalytic reduction electrode can effectively improve the hydrophobic microenvironment on the electrode surface and enhance the mass transfer at the gas-liquid-solid three-phase interface, thereby helping to improve the CO2 electrocatalytic reduction activity.

[0026] 3. The present invention modifies sludge-based silicon aluminum oxide through hydrothermal and acid leaching treatments, giving it high surface roughness and 3D linear array micro-nano structure, thereby significantly improving the physical hydrophobicity of sludge-based SiO2; and utilizing the chemical hydrophobicity of PFAS, combining chemical hydrophobicity with physical hydrophobicity, so that the prepared composite material not only retains the high stability of SiO2, but also exhibits excellent hydrophobic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1The SEM image (a) of the modified sludge-based SiO2 prepared in Example 1 of the present invention and the SEM image (b) of the modified sludge-based SiO2 prepared in Comparative Example 1;

[0028] Figure 2 The water contact angle test results (a) of the sludge-based composite hydrophobic material prepared in Example 1 of the present invention and the water contact angle test results (b) of the sludge-based composite hydrophobic material prepared in Comparative Example 1 are shown. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to specific embodiments and illustrations.

[0030] The F127 in the following examples and comparative examples was purchased from Shanghai Xinfan Biotechnology Co., Ltd.; PFAS is perfluorooctanoic acid, purchased from Shanghai Hengyuan Biotechnology Co., Ltd.; the electrochemical workstation was purchased from Shanghai Chenhua Instrument Co., Ltd., model CHI706E; and the contact angle tester was purchased from Dataphysics, Germany, model OCA25.

[0031] Example 1

[0032] Preparation of sludge-based composite hydrophobic materials:

[0033] (1) The sludge was calcined at 800°C for 5 h, and after cooling, it was ground into powder to obtain sludge ash; the sludge ash was stirred with a 0.1 mol / L hydrochloric acid solution at a solid-liquid ratio of 1:10 at 60°C for 2.5 h, filtered, and the filter residue was collected; the filter residue was then stirred with a 2.0 mol / L sodium hydroxide solution at a solid-liquid ratio of 1:20 at 25°C for 2 h to obtain a suspension.

[0034] (2) Add 3% (w / v) F127 aqueous solution to the suspension prepared in step (1) at a mass ratio of 10:1, stir at 40°C until clear, then hydrothermally react at 120°C for 24 hours, filter after the reaction, and calcine the filter residue at 550°C for 4 hours; the calcined product and 0.5 mol / L hydrofluoric acid solution at a solid-liquid ratio of 1:15 are stirred at 30°C for 10 minutes, filtered, the filter residue is washed with water, and dried to obtain modified sludge-based SiO2.

[0035] (3) PFAS and ethanol were mixed evenly at a solid-liquid ratio of 1:5 to obtain a PFAS solution.

[0036] (4) The modified sludge-based SiO2 prepared in step (2) is evenly mixed with the PFAS solution prepared in step (3) and ethanol, wherein the mass ratio of the modified sludge-based SiO2 to PFAS is 3:1, and the amount of ethanol is 5 times the mass of the PFAS solution. The mixture is hydrothermally reacted at 150°C for 4 hours. After the reaction is completed, the mixture is naturally cooled to room temperature, centrifuged, and the precipitate is alternately washed with ethanol and water, and dried to obtain a sludge-based composite hydrophobic material.

[0037] Application of sludge-based composite hydrophobic materials:

[0038] 5 mg of sludge-based composite hydrophobic material and 20 mg of tin oxide obtained in Example 1 were ultrasonically dispersed in 1 mL of ethanol, and 100 μL of Nafion solution was added and ultrasonically dispersed to obtain a mixed solution. Use a pipette to evenly apply the mixed solution on carbon paper in small amounts and multiple times, dry it, and obtain a gas diffusion electrode. A flow electrolysis cell was built using the gas diffusion electrode, CO2 was introduced, an electrochemical workstation was used to perform an electrolysis test for 30 minutes, and an ion chromatography was used to detect the product of the electrolyte after electrolysis. The test results showed that the Faraday efficiency of formic acid was 79.6%, and the current density was 230 mA / cm 2 , which shows that the gas diffusion electrode has good current conduction capability and catalytic activity during the electrolysis process.

[0039] The sludge-based composite hydrophobic material obtained in Example 1 was fabricated into a gas diffusion electrode using the aforementioned method. The gas diffusion electrode was then placed on a glass slide and its hydrophobicity was tested using a contact angle meter. The test results showed a water contact angle of 144.66°, demonstrating that the sludge-based composite hydrophobic material exhibited excellent hydrophobic properties.

[0040] Example 2

[0041] The sludge-based composite hydrophobic material was prepared according to the method of Example 1, except that the hydrothermal reaction temperature of the PFAS solution and the modified sludge-based SiO2 was adjusted to 130°C, and the hydrothermal reaction time was adjusted to 5 hours.

[0042] The performance test of the sludge-based composite hydrophobic material was carried out according to the method of Example 1. The test results showed that the Faradaic efficiency of formic acid was 77.9% and the current density was 228 mA / cm 2 , the water contact angle is 141.67°.

[0043] Example 3

[0044] The sludge-based composite hydrophobic material was prepared according to the method of Example 1, except that the surfactant was replaced by P123, a 3% (w / v) P123 aqueous solution was added to the suspension prepared in step (1) at a mass ratio of 15:2, and the hydrothermal temperature was adjusted to 160°C and the hydrothermal reaction time was adjusted to 20 h.

[0045] The performance test of the sludge-based composite hydrophobic material was carried out according to the method of Example 1. The test results showed that the Faradaic efficiency of formic acid was 78.5% and the current density was 219 mA / cm 2 , the water contact angle is 142.02°.

[0046] Example 4

[0047] The sludge-based composite hydrophobic material was prepared according to the method of Example 1, except that the 0.1 mol / L hydrochloric acid solution used in the acid leaching was replaced with a 0.1 mol / L sulfuric acid solution, and the acid leaching temperature was adjusted to 40°C, the acid leaching time was adjusted to 4 h, and the alkali leaching time was adjusted to 4 h.

[0048] The performance test of the sludge-based composite hydrophobic material was carried out according to the method of Example 1. The test results showed that the Faradaic efficiency of formic acid was 75.3% and the current density was 224 mA / cm 2 , the water contact angle is 139.86°.

[0049] Example 5

[0050] The sludge-based composite hydrophobic material was prepared according to the method of Example 1, except that the mass ratio of modified sludge-based SiO2 to PFAS was adjusted to 2:0.5.

[0051] The performance test of the sludge-based composite hydrophobic material was carried out according to the method of Example 1. The test results showed that the Faradaic efficiency of formic acid was 76.3% and the current density was 216 mA / cm 2 , the water contact angle is 140.75°.

[0052] Comparative Example 1

[0053] The sludge-based composite hydrophobic material was prepared according to the method of Example 1, except that the calcined product in step (2) was not acid-leached with hydrofluoric acid solution.

[0054] The performance test of the sludge-based composite hydrophobic material was carried out according to the method of Example 1. The test results showed that the Faradaic efficiency of formic acid was 62.6% and the current density was 189 mA / cm 2 , the water contact angle is 127.31°.

[0055] Comparative Example 2

[0056] The sludge-based composite hydrophobic material was prepared according to the method of Example 1, except that the suspension prepared in step (1) was not modified using F127 solution.

[0057] The performance test of the sludge-based composite hydrophobic material was carried out according to the method of Example 1. The test results showed that the Faradaic efficiency of formic acid was 53.0% and the current density was 132 mA / cm 2 , the water contact angle is 121.32°.

[0058] Comparative Example 3

[0059] The sludge-based composite hydrophobic material was prepared according to the method of Example 1, except that steps (3) and (4) were not performed, and the modified sludge-based SiO2 prepared in step (2) was directly used as the hydrophobic material.

[0060] The performance test of the sludge-based composite hydrophobic material was carried out according to the method of Example 1. The test results showed that the Faradaic efficiency of formic acid was 45.9% and the current density was 105 mA / cm 2 , the water contact angle is 115.67°.

[0061] It can be seen from the above embodiments and comparative examples that the present invention improves the surface roughness of SiO2 by constructing a special micro-nano structure of modified sludge-based SiO2 and by acid etching sludge-based SiO2, so that its combination with PFAS is tighter and its hydrophobicity is significantly improved; and by using PFAS solution to modify SiO2, the hydrophobicity of the composite material is further improved, so that it is mixed with the catalyst and coated on the electrode surface, effectively inhibiting water flooding of the electrode surface, achieving excellent gas mass transfer effect, and thus improving the catalytic performance of the catalyst.

[0062] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A sludge-based composite hydrophobic material, characterized by: It includes modified sludge-based SiO2 and PFAS loaded on modified sludge-based SiO2.

2. A method for preparing a sludge-based composite hydrophobic material, characterized in that: The following steps are involved: S1. calcining the sludge, acid leaching, and alkali leaching to obtain sludge-based silicon-aluminum composite oxide; S2, hydrothermally reacting the sludge-based silicon-aluminum composite oxide prepared in step S1 with a surfactant, calcining, and etching to obtain modified sludge-based SiO2; S3. The modified sludge-based SiO2 prepared in step S2 is subjected to a hydrothermal reaction with PFAS to obtain a sludge-based composite hydrophobic material.

3. The preparation method according to claim 2, wherein: In step S1, the calcination is carried out in air or oxygen atmosphere, the calcination temperature is 600-800° C., and the calcination time is 3-5 hours.

4. The preparation method according to claim 2, wherein: In step S1, the acid leaching uses a hydrochloric acid or sulfuric acid solution with a concentration of 0.1 to 0.3 mol / L, the acid leaching temperature is 40 to 60° C., and the acid leaching time is 2 to 4 hours.

5. The preparation method according to claim 2, wherein: In step S1, the alkali leaching uses a sodium hydroxide or potassium hydroxide solution with a concentration of 2 to 3 mol / L, the alkali leaching temperature is 25 to 30° C., and the alkali leaching time is 2 to 4 hours.

6. The preparation method according to claim 2, wherein: In step S2, the surfactant is an addition polymer of polypropylene glycol and ethylene oxide; Preferably, the mass ratio of the surfactant to the sludge-based silicon-aluminum composite oxide is (1-2):(10-15); Preferably, the reaction temperature of the hydrothermal reaction is 100-180° C., and the reaction time is 18-24 hours.

7. The preparation method according to claim 2, characterized in that: In step S2, the calcination is carried out in air or oxygen atmosphere, the calcination temperature is 550-800° C., and the calcination time is 2-4 hours.

8. The preparation method according to claim 2, wherein: In step S2, the etching is performed using a hydrofluoric acid solution with a concentration of 0.5 to 1 mol / L, an etching temperature of 30 to 60°C, and an etching time of 5 to 10 minutes.

9. The preparation method according to claim 2, wherein: In step S3, the mass ratio of the modified sludge-based SiO2 to PFAS is (2-3):(0.5-1); Preferably, the temperature of the hydrothermal reaction is 130-180° C., and the time is 3-6 hours.

10. Use of the sludge-based composite hydrophobic material according to claim 1 or the sludge-based composite hydrophobic material prepared by the preparation method according to any one of claims 2 to 9 in electrocatalytic CO2 reduction.

Images