Preparation method of diatomite-graphene composite sintered body, sintered body and application thereof

Abstract

The invention aims to provide a preparation method of a diatomite-graphene composite sintered body, which comprises the following steps: 1) preparing diatomite, and cleaning and calcining the diatomite for later use; 2) generating graphene on diatomite in situ to obtain a diatomite-graphene composite material; 3) mixing the diatomite-graphene composite material, sodium carbonate and a binder to prepare a green body, and 4) sintering the green body to obtain the diatomite-graphene composite sintered body, the sintered body has excellent mechanical strength and adsorption characteristics, and has wide application prospects in sewage treatment.

Description

Technical Field

[0001] The invention relates to a diatomite-graphene composite sintered body. The sintered body is a porous material with good adsorption performance and excellent mechanical strength, and can be used in the technical field of sewage treatment. Background Art

[0002] Diatomaceous earth is a biologically deposited siliceous sedimentary rock, the main component of which is amorphous silicon dioxide. It has a porous structure and a high specific surface area, and has been widely used in the fields of adsorption and filtration.

[0003] However, natural diatomaceous earth suffers from low mechanical strength, easy pulverization, and poor adsorption selectivity. High-temperature sintering restructures the diatomaceous earth's crystal structure, improving its mechanical strength. However, during the sintering process, a large amount of amorphous silica covers the diatomaceous earth surface, partially blocking the primary pores and significantly reducing its adsorption capacity. Furthermore, the sintered diatomaceous earth material also suffers from weak electrostatic adsorption of heavy metal ions. These shortcomings limit its large-scale application in wastewater adsorption treatment.

[0004] Therefore, the present invention provides a diatomaceous earth sintered material with excellent adsorption performance and outstanding mechanical strength. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a diatomite-graphene composite sintered body, the sintered body, and its application. The sintered body produced by the method not only exhibits excellent mechanical strength but also possesses abundant pores and a large adsorption specific surface area, enabling excellent adsorption of organic matter and heavy metal ions during wastewater treatment.

[0006] The present invention aims to provide a method for preparing a diatomite-graphene composite sintered body, comprising the following steps: 1) preparing diatomite, cleaning the diatomite, and calcining the diatomite for later use; 2) in-situ generating graphene on the diatomite to obtain a diatomite-graphene composite material; 3) mixing the diatomite-graphene composite material, sodium carbonate, and a binder to prepare a green body; and 4) sintering the green body to obtain the diatomite-graphene composite sintered body.

[0007] In general, the technical idea of the present invention is to first generate graphene in situ on the surface of diatomite, and then sinter the composite material with sodium carbonate and a binder to obtain a diatomite-graphene composite sintered body.

[0008] During the sintering process, traditional diatomaceous earth will generate an amorphous silica layer on the surface, causing the primary pores to be partially blocked and even facing the problem of structural collapse. The present invention pre-generates graphene in situ on the surface of diatomaceous earth, so that the graphene covers part of the diatomaceous earth surface and the pore surface of the diatomaceous earth. In the subsequent sintering process, the graphene can effectively support the pore structure, enhance the structural strength, and avoid structural collapse, while reducing the coverage of the diatomaceous earth surface by amorphous silica, preventing the primary pores from being blocked; in addition, graphene has excellent adsorption properties. By generating graphene in situ on part of the surface of diatomaceous earth and part of the surface of its pores, the adsorption capacity of diatomaceous earth for organic matter in sewage can be greatly improved, and the diatomaceous earth generated by graphene in situ also has excellent heavy metal ion adsorption capacity, which effectively expands the adsorption capacity and adsorption range of diatomaceous earth.

[0009] Not limited to the above description, the present invention also adds sodium carbonate during the sintering process. Since the in-situ generation of graphene is not sufficient to completely cover all diatomaceous earth surfaces and their pore surfaces, it is still inevitable to be accompanied by the appearance of silicon dioxide during the sintering process. By adding sodium carbonate, sodium carbonate will generate sodium silicate with silicon dioxide at high temperature, and sodium silicate has excellent strength and bonding ability. High-strength sodium silicate can form an effective support for the overall structure of the sintered body, and the excellent bonding force can tightly bond the diatomaceous earth to each other, so that the sintered body has excellent mechanical strength. In addition, the carbon dioxide generated by sodium carbonate during the heating process will overflow to the outside, and this overflow will have a cleaning effect on the pores, which will then help to form a network structure that is interlaced and connected with each other and crisscrossed between the pores, thereby improving the adsorption capacity of the sintered body.

[0010] The diatomite-graphene composite sintered body prepared by the process of the present invention has both macroporous and mesoporous characteristics, and a network structure in which the pores are interpenetrating and staggered with each other is formed. On the basis of ensuring that the sintered body has good strength, the ability of the sintered body to adsorb heavy metal ions and organic matter in sewage is improved.

[0011] To obtain diatomaceous earth with low impurity content, washing the diatomaceous earth with deionized water and ethanol in step 1) is essential. Diatomaceous earth also contains a large amount of bound water, volatile matter, and organic matter. Therefore, calcination is necessary after washing to remove these. The calcination temperature is preferably 500-750°C. Insulation is optional, or a short insulation period, such as 0-15 minutes at the single calcination temperature, can be used. The calcination process is best performed under a protective atmosphere, such as nitrogen or argon.

[0012] As a non-limiting example, the in-situ formation of graphene on diatomite in step 2) can be performed by an in-situ carbonization reaction. Specifically, this includes dissolving a solid carbon source in ethanol to obtain a mixed solution, adding diatomite to the mixed solution while stirring and ultrasonically dispersing the solution, and then evaporating the solution in a rotary evaporator to remove the ethanol to obtain a carbon source-diatomite blend. The carbon source-diatomite blend is then carbonized at 750-900°C for 5-30 minutes to obtain a diatomite-graphene composite material.

[0013] The graphene content of the diatomite-graphene composite material prepared by the method of the present invention is approximately 0.10% to 0.60% by weight. Too high a graphene content can affect the continuity of the matrix and prevent the mechanical strength of the sintered material from being guaranteed; too low a graphene content can prevent excellent strength and adsorption properties.

[0014] As a non-limiting description, a mixture of hydrogen and argon is introduced during the carbonization treatment in step 2). It is necessary to control the reducing atmosphere during the carbonization process to prevent carbon atoms from being oxidized during the carbonization process.

[0015] The carbon source used in the in-situ graphene generation process of the present invention is one or more of paraffin, naphthol, and naphthalene. To obtain the mass percentage of graphene in the aforementioned diatomite-graphene composite material, the carbon source is added at about 0.06-0.6 parts per 50-80 parts of diatomite.

[0016] The raw materials used in step 3) of the method of the present invention are, by weight, 50-80 parts of a diatomaceous earth-graphene composite material, 5-15 parts of sodium carbonate, and 2-8 parts of a binder. Using too little sodium carbonate will not form sufficient sodium silicate, thus failing to provide sufficient strength support, effectively bonding the diatomaceous earth, and ensuring good mechanical strength. Using too much sodium carbonate will result in excessive sodium silicate formation, which will cover the active surface of the diatomaceous earth and its pores or clog the pores, reducing the porosity of the sintered body and affecting adsorption performance.

[0017] The binder of the present invention may be a sintering binder well known in the art, but is not limited to a mixture of one or more of polyvinyl alcohol (PVA), polyethylene glycol (PEG), paraffin wax, and sodium carboxymethyl cellulose (CMC).

[0018] As a preferred technical solution, step 3) includes: adding 30-50% water by weight of the total mass of the mixture to the mixture of diatomaceous earth-graphene composite material, sodium carbonate, and binder, and stirring to form a uniform mud; and then pressing the mud into a green body of the desired shape.

[0019] The molding pressure can be selected to be 5-50 MPa, and the green body is preferably dried at 80-120°C for 12-24 hours before sintering.

[0020] As a preferred technical solution, the method of the present invention is sintering at 850-1100°C for 2-5 hours (one-stage sintering); if the sintering temperature or sintering time is too long, the possibility of collapse of the sintered body structure increases, and the coverage area of amorphous silica on the diatomaceous earth surface and pore surface will increase, which is not conducive to obtaining excellent adsorption capacity; if the sintering temperature is too low or the time is too short, it will lead to insufficient sintering and unsatisfactory strength of the sintered body.

[0021] As a preferred technical solution, the sintering process involves first holding at 450-550°C for 0.5-1.5 hours for debinding, followed by sintering at 850-1100°C for 2-5 hours. By adopting a two-stage sintering process, with the initial holding time at a lower temperature, the binder can be removed pre-emptively, preventing the gases generated during high-temperature sintering from causing cracking in the sintered body and affecting its strength, thereby improving the yield rate.

[0022] Alternatively, a separate debinding step can be omitted. Instead, the debinding step can be performed during the gradual heating process to the sintering temperature, using the previously described one-stage sintering method. This can effectively prevent cracking of the sintered body by maintaining a relatively low heating rate (e.g., 1-3°C / min). Furthermore, the gases generated by binder decomposition contribute to a more developed pore structure, thereby improving the adsorption capacity of the sintered body.

[0023] The present invention also provides a diatomite-graphene composite sintered body prepared by the above-mentioned method for preparing the diatomite-graphene composite sintered body. The sintered body has excellent mechanical strength and adsorption properties.

[0024] A third aspect of the present invention provides the use of the aforementioned diatomite-graphene composite sintered body in wastewater treatment. Due to its excellent mechanical strength and adsorption properties, the sintered body can effectively adsorb heavy metal ions and organic matter from wastewater. Its excellent mechanical strength also makes it well-suited for industrial applications.

[0025] The present invention pre-generates graphene in situ on the diatomite surface, so that the graphene covers a portion of the diatomite surface and the pore surfaces of the diatomite. During the subsequent sintering process, the graphene can effectively support the pore structure, enhance structural strength, and prevent structural collapse. It also reduces the coverage of amorphous silica on the diatomite surface, preventing the original pores from becoming clogged. Furthermore, graphene has excellent adsorption properties. By in situ generating graphene on a portion of the diatomite surface and a portion of the pore surfaces, the diatomite's adsorption capacity for organic matter in wastewater can be greatly improved. Furthermore, the diatomite generated with graphene in situ also has excellent adsorption capacity for heavy metal ions, effectively expanding the diatomite's adsorption capacity and adsorption range.

[0026] The present invention adds sodium carbonate during the sintering process. Since the in-situ generation of graphene is not sufficient to completely cover all the diatomite surfaces and the pore surfaces thereof, the appearance of silicon dioxide is still inevitable during the sintering process. By adding sodium carbonate, sodium carbonate will generate sodium silicate with silicon dioxide at high temperature, and sodium silicate has excellent strength and bonding ability. High-strength sodium silicate can form an effective support for the overall structure of the sintered body, and the excellent bonding force can tightly bond the diatomite to each other, so that the sintered body has excellent mechanical strength. In addition, the carbon dioxide generated by sodium carbonate during the heating process will overflow to the outside, and this overflow will have a cleaning effect on the pores, which is conducive to forming a network structure that is interlaced and connected with each other and crisscrossed between the pores. The adsorption capacity of the sintered body is improved.

[0027] In summary, the diatomite-graphene composite sintered body prepared by the present invention has a large specific surface area, rich pore structure and good mechanical strength. The specific surface area is 30-60m² / g, the pore volume is 0.4-0.8cm³ / g, and it has a high adsorption capacity and adsorption efficiency for heavy metal ions and organic pollutants in sewage, which can effectively purify sewage. The compressive strength is 17-40MPa, and it can be flexibly used in various working conditions. It has good application prospects in sewage treatment. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, further explanation is given below in conjunction with specific test examples.

[0029] 1. Preparation of diatomite-graphene composite materials.

[0030] Diatomaceous earth with a particle size of 25-45 μm is washed three times with ethanol and then rinsed with deionized water. The washed diatomaceous earth is heated to 700°C without insulation and then cooled to room temperature in the furnace to obtain calcined diatomaceous earth. This operation is performed under argon protection. The purpose of this operation is to remove impurities such as bound water, volatile matter, and organic matter from the diatomaceous earth. Of course, the heating process also naturally removes free water remaining from the washing step.

[0031] Diatomaceous earth and a solid carbon source were weighed and dissolved in 400 mL of ethanol to obtain a mixed solution. The diatomaceous earth was added to the mixed solution with mechanical stirring (250 rpm) and ultrasonic dispersion for 20 minutes. The ethanol was evaporated in a rotary evaporator (120°C, 1 hour) to remove the ethanol. This carbon source-diatomaceous earth blend was obtained. The blend was then carbonized in a quartz tube furnace under an atmosphere of H2 (80 vol.%) + Ar (20 vol.%) to obtain a diatomaceous earth-graphene composite. The weight percentage of graphene was then calculated based on the weight of the weighed diatomaceous earth and the weight of the diatomaceous earth-graphene composite. The specific raw material amounts, carbonization parameters, and graphene weight percentage are listed in Table 1.

[0032] Table 1: Raw materials, carbonization parameters and percentage of graphene.

[0033]

[0034] 2. Preparation of diatomite-graphene composite sintered body.

[0035] The diatomite-graphene composite material, sodium carbonate (particle size 25-45 μm), and binder prepared above were weighed at a ratio of 1 part per gram. After mixing thoroughly, 50% of the total weight of water was added and stirred into a uniform slurry. The slurry was pressed into a 1 cm diameter preform at 35 MPa. The preform was then cut into several 1 cm high green bodies and dried at 100°C for 15 hours. The green bodies were then sintered in a vacuum sintering furnace at a heating rate of 1.5°C / min to 920°C for 3.5 hours to obtain sintered bodies. See Table 2 for the specific raw material ratios.

[0036] Table 2: Raw materials for preparing diatomite-graphene composite sintered bodies.

[0037]

[0038] As a control experiment for experiment numbered G, the raw materials and preparation process for experiment numbered M were as follows: calcined diatomaceous earth (particle size 25-45 μm) was mixed with commercially available single-layer graphene (diameter approximately 5 μm) to form a diatomaceous earth and single-layer graphene blend with a graphene content of 0.475%. 70 g of this blend was weighed, added with 6.6 g of sodium carbonate (particle size 25-45 μm) and 7.2 g of CMC. After mixing, 50% of the total weight of water was added and stirred into a uniform slurry. The slurry was pressed into a 1 cm diameter preform at 35 MPa. The preform was then cut into several 1 cm high preforms and dried at 100°C for 15 hours. The preforms were then sintered in a vacuum sintering furnace at a heating rate of 1.5°C / min to 920°C for 3.5 hours to obtain sintered bodies.

[0039] The sintered bodies numbered AL and M in Table 2 were tested for their adsorption capacity for heavy metal ions in sewage, adsorption capacity for organic pollutants, specific surface area and pore volume, and compressive strength.

[0040] Among them, Pb 2+ Simulate the adsorption capacity of heavy metal ions in sewage, use methyl orange to simulate the adsorption capacity of organic pollutants in sewage, configure Pb 2+ The concentration of test solution 1 is 300 mg / L, and the concentration of methyl orange in test solution 2 is 300 mg / L. 4 g of the sintered material of each number is added to each 1 L of test solution 1 and each 1 L of test solution 2. Stir once every 20 minutes. The adsorption time is 2 hours. After the adsorption is completed, the Pb content in the test solution is determined by atomic absorption spectrometry. 2+ The concentration of methyl orange in the test solution was determined by UV-visible spectrophotometer, and the Pb content was calculated based on the change in the concentration of pollutants before and after adsorption. 2+ adsorption rate and decolorization rate.

[0041] The specific surface area and pore volume of the sintered body were measured using a specific surface area and porosity analyzer.

[0042] The compression testing machine is used to test the compressive strength of the sintered body.

[0043] The results of the above tests are recorded in Table 3.

[0044] Table 3: Properties of various sintered bodies.

[0045]

[0046] A brief analysis is given below.

[0047] The graphene content in the diatomite-graphene composite material used in No. C is too high. Although the final diatomite-graphene composite sintered body has a good specific surface area and pore volume and exhibits excellent adsorption performance, the excessive graphene affects the continuity of the matrix and the compressive strength of the sintered body decreases; while the graphene content in the diatomite-graphene composite material used in No. I is too low. On the one hand, it cannot form an effective support for the matrix structure, and the strength of the sintered body is insufficient. On the other hand, it leads to poor adsorption performance of the sintered body.

[0048] The amount of sodium carbonate added in No. K is too low, resulting in an inability to form a sufficient amount of sodium silicate, which cannot fully and effectively bond the diatomaceous earth. The strength support for the matrix is insufficient, the compression resistance is poor, and due to insufficient bonding and support, many pores collapse during the sintering process, resulting in affected adsorption capacity; the amount of sodium carbonate added in No. L is too large, and the amount of sodium silicate generated is too much. Although the strength is improved, the excessive sodium silicate will cover the active surface of the diatomaceous earth and its pores or block the pores, causing the porosity of the sintered body to decrease, affecting the adsorption performance.

[0049] No. M uses a method of directly mixing single-layer graphene into sintering to prepare a diatomite-graphene composite sintered body. However, simple mixing and sintering cannot firmly attach the graphene to the surface of the diatomite and its pores, and cannot form a strong support for the matrix. The compressive strength of the sintered body is insufficient. At the same time, due to insufficient support, many pores collapsed during the sintering process, resulting in the adsorption capacity being affected.

[0050] The in-situ generation method can produce a synergistic effect on the adsorption capacity of graphene and diatomaceous earth. Comparing the direct mixing and in-situ generation methods, it can be seen that the adsorption capacity of the diatomaceous earth-graphene composite sintered body prepared by the direct mixing method is significantly lower than that of the diatomaceous earth-graphene composite sintered body prepared by the in-situ generation method.

[0051] It is not difficult to conclude from the other numbered tests in Table 3 that the diatomite-graphene composite sintered body prepared by the method of the present invention has a specific surface area between 30-60 m² / g, a pore volume between 0.4-0.8 cm³ / g, and a compressive strength between 17-40 MPa. It has good mechanical strength and excellent adsorption capacity and can be widely used in various sewage treatment conditions.

[0052] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a diatomite-graphene composite sintered body, characterized in that: The steps include: 1) Prepare diatomaceous earth, clean it, calcine it and set it aside; 2) In situ generation of graphene on diatomite to obtain diatomite-graphene composite materials; 3) mixing the diatomite-graphene composite material, sodium carbonate, and a binder to prepare a green body; 4) Sintering the green body to obtain a diatomite-graphene composite sintered body.

2. The method for preparing a diatomite-graphene composite sintered body according to claim 1, wherein: The step 2) comprises: dissolving a solid carbon source in ethanol to obtain a mixed solution, adding diatomaceous earth to the mixed solution, stirring and ultrasonically dispersing the mixture, and then evaporating the mixture in a rotary evaporator to remove the ethanol to obtain a carbon source-diatomaceous earth blend, and carbonizing the carbon source-diatomaceous earth blend at 750-900° C. for 5-30 minutes to obtain a diatomaceous earth-graphene composite material.

3. The method for preparing a diatomite-graphene composite sintered body according to any one of claims 1 to 2, characterized in that: The mass percentage of graphene in the diatomite-graphene composite material is approximately 0.10%-0.60%.

4. The method for preparing a diatomite-graphene composite sintered body according to any one of claims 1 to 3, characterized in that: The solid carbon source is one or more of paraffin, naphthol and naphthalene.

5. The method for preparing a diatomite-graphene composite sintered body according to any one of claims 1 to 4, characterized in that: In parts by weight, the amounts of the raw materials used in step 3) are: 50-80 parts of diatomaceous earth-graphene composite material, 5-15 parts of sodium carbonate, and 2-8 parts of binder.

6. The method for preparing a diatomite-graphene composite sintered body according to any one of claims 1 to 5, characterized in that: The step 3) comprises: adding 30-50% of the total mass of water to the mixture of the diatomite-graphene composite material, sodium carbonate and the binder, and stirring the mixture into a uniform slurry; and then pressing the slurry into a green body of a desired shape.

7. The method for preparing a diatomite-graphene composite sintered body according to any one of claims 1 to 6, characterized in that: The sintering is carried out at 850-1100° C. for 2-5 hours.

8. The method for preparing a diatomite-graphene composite sintered body according to any one of claims 1 to 7, characterized in that: The sintering is firstly carried out at 450-550° C. for 0.5-1.5 hours to perform degreasing, and then sintering at 850-1100° C. for 2-5 hours.

9. A diatomite-graphene composite sintered body prepared by the method for preparing a diatomite-graphene composite sintered body according to any one of claims 1 to 8.

10. Use of the diatomaceous earth-graphene composite sintered body according to any one of claims 1 to 9 in sewage treatment.

Images