A method for preparing and applying manganese dioxide composite coal-based porous carbon material

Abstract

This invention discloses a method for preparing manganese dioxide composite coal-based porous carbon material, comprising: using potassium hydroxide to activate Naomaohu lignite to obtain coal-based porous carbon material as a precursor, using manganese dioxide obtained by hydrothermal treatment with potassium permanganate solution as a loading material, and preparing manganese dioxide composite coal-based porous carbon material by hydrothermal-oxidative roasting method. 0.23 The MnO2 / CK-400 composite material, used as an adsorbent, exhibits excellent static batch adsorption performance for lead ions in water under certain conditions. This invention combines manganese dioxide with a coal-based porous carbon material rich in oxygen-containing functional groups on its surface, improving the utilization rate of manganese dioxide. Furthermore, the resulting composite material can selectively remove lead ions from water, is easy to operate, uses readily available materials, has a significant removal effect, and the adsorbent is regenerable and recyclable.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for preparing manganese dioxide composite coal-based porous carbon material. Background Technology

[0002] Lead ions are a major element of heavy metal pollution, primarily originating from industrial and agricultural wastewater and landfill leachate. They can indirectly enter the human body through water, soil, and plants. Due to their non-degradable nature and persistent toxicity, lead pollution is highly likely to accumulate in the human body, leading to neurological disorders, intellectual disability, and immune system diseases. Therefore, the treatment of lead pollution has always been a research hotspot, with the treatment of lead pollution in water bodies receiving the most attention.

[0003] Traditional heavy metal removal methods include precipitation, membrane separation, photocatalysis, electrochemical treatment, and adsorption. Compared to other processes, adsorption is the most widely used due to its simplicity and high efficiency. In practical applications, commonly used adsorbents for treating lead pollution in water include biological activated carbon, coal-based activated carbon, clay minerals (such as montmorillonite and kaolinite), metal-organic frameworks, and some metal oxides. Coal-based activated carbon, in particular, has a stable and reliable source of raw materials, is relatively inexpensive, easily regenerated, and wear-resistant, making it more suitable for wastewater treatment. Literature reports that the hydroxyl bonds in oxygen-containing functional groups (such as hydroxyl, carbonyl, and carboxyl groups) on the surface of lignite can exchange ions with lead ions in water, achieving lead ion adsorption. Manganese dioxide, a widely distributed metal oxide in the environment, has attracted considerable research attention due to its high density of adsorption active sites and its ability to catalytically degrade pollutants. The unique octahedral structure of different crystal phases of manganese dioxide gives it excellent adsorption selectivity for lead ions. However, due to its low specific surface area and tendency to agglomerate, manganese dioxide alone has a low adsorption capacity for lead ions.

[0004] By effectively combining coal-based activated carbon with manganese dioxide, and leveraging the advantages of coal-based activated carbon such as its large specific surface area and abundant oxygen-containing groups, a manganese dioxide composite coal-based porous carbon adsorbent material is obtained. This material achieves rapid, efficient, and selective adsorption of lead ions, showing promising application prospects in the field of water pollution treatment. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a method for preparing manganese dioxide composite coal-based porous carbon material.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for preparing manganese dioxide composite coal-based porous carbon material, comprising the following steps:

[0007] S1. Mix lignite powder with a strong alkaline activating solvent and calcine in an inert gas atmosphere to obtain a calcined product. Mix and stir the calcined product with an aqueous solution to obtain a first suspension. After filtration, washing with water and drying, coal-based activated carbon is obtained.

[0008] S2. Mix potassium permanganate solution with nitric acid to obtain a second suspension; oxidize the second suspension hydrothermally at 120-130℃ for 12-14 hours, filter and dry to obtain brownish-yellow manganese dioxide;

[0009] S3. Mix the coal-based activated carbon in S1 with manganese dioxide in S2 and carry out a hydrothermal reaction at 100-150℃. After cooling to room temperature, filter and dry to obtain the manganese dioxide composite coal-based activated carbon material precursor.

[0010] S4. The manganese dioxide composite coal-based activated carbon material precursor in S3 is calcined at 300-350℃ for 8-12 hours to obtain manganese dioxide composite coal-based activated carbon.

[0011] In a preferred embodiment of the present invention, the lignite powder is Naomaohu lignite with a particle size of 100-200 mesh.

[0012] In a preferred embodiment of the present invention, the strongly alkaline activating solvent is one or more of potassium hydroxide or sodium hydroxide.

[0013] In a preferred embodiment of the present invention, the mass ratio of lignite powder to strongly alkaline activating solvent is 1:2-4.

[0014] In a preferred embodiment of the present invention, in step S1, the calcination temperature is 400-700℃, the calcination heating rate is 3-10℃ / min, and the holding time is 5-7h.

[0015] In a preferred embodiment of the present invention, in step S2, the mass concentration of the potassium permanganate solution is 1-3 wt%, the concentration of nitric acid is 14-20 mol / L, and the mass ratio of potassium permanganate solution to nitric acid is 1:0.01-0.015.

[0016] In a preferred embodiment of the present invention, in step S3, the mass ratio of manganese dioxide to coal-based activated carbon is 3:8-12.

[0017] An application of a manganese dioxide composite coal-based porous carbon material, wherein the manganese dioxide composite coal-based porous carbon material is prepared by the above-described method: the application of the manganese dioxide composite coal-based porous carbon material in the selective removal of lead ions from water.

[0018] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0019] (1) This invention provides a manganese dioxide coal-based composite porous carbon material. The coal-based porous carbon material obtained by activating Naomaohu lignite with potassium hydroxide is used as a precursor. Manganese dioxide obtained by hydrothermal treatment with potassium permanganate solution is used as a loading material. The manganese dioxide composite coal-based porous carbon material is prepared by hydrothermal-oxidative calcination method. Under certain conditions, it can perform static batch adsorption of lead ions in water and has excellent adsorption performance.

[0020] (2) This invention combines manganese dioxide with coal-based porous carbon material rich in oxygen-containing functional groups on the surface, which improves the utilization rate of manganese dioxide. The resulting composite material can selectively remove lead ions from water. The operation is simple, the material is readily available, the removal effect is significant, and the adsorbent can be regenerated and recycled.

[0021] (3) In this invention, coal-based activated carbon powder CK-400 obtained by calcination at 400℃ is combined with manganese dioxide composite coal-based porous carbon material to obtain a composite material with a high manganese dioxide loading (23%), so that the composite material has the maximum adsorption capacity for lead ions. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a graph showing the adsorption capacity of the CK-400 to CK-700 coal-based activated carbon of the present invention for lead ions at different pH values.

[0024] Figure 2 These are the infrared analysis diagrams of CK-400 to CK-700 coal-based activated carbon of the present invention;

[0025] Figure 3 This is the adsorption isotherm analysis diagram of lead ions by CK-400 of the present invention at 25-45℃;

[0026] Figure 4 This is the manganese dioxide composite coal-based porous carbon material of Example 5 of the present invention. 0.23 Transmission electron microscopy image of MnO2 / CK-400;

[0027] Figure 5 This is the manganese dioxide composite coal-based porous carbon material of Example 5 of the present invention. 0.23 High-resolution transmission electron microscopy image of MnO2 / CK-400;

[0028] Figure 6The present invention relates to a manganese dioxide composite coal-based porous carbon material ( 0.23 Adsorption isotherm analysis of lead ions by MnO2 / CK-400;

[0029] Figure 7 The present invention is a manganese dioxide composite coal-based porous carbon ( 0.23 Figure 1. Relationship between the saturated adsorption capacity of MnO2 / CK-400 material for lead ions, copper ions, and cadmium ions and the initial concentration;

[0030] Figure 8 This is a diagram showing the concentration of manganese ions leached from the manganese dioxide composite coal-based porous carbon material precursor of the present invention during adsorption in a solution. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Unless otherwise stated, endpoint values ​​are included when describing numerical ranges herein. When two or more preferred or exemplary numerical values ​​or ranges are given, it is self-evident that all ranges formed by combining different numerical values ​​or endpoints are also included within the scope of this invention.

[0033] These and other aspects, features, and advantages of the invention will become apparent to those skilled in the art from the following detailed description. In this context, any feature or embodiment derived from one aspect of the invention may be used in any other aspect of the invention. Furthermore, it is self-evident that the embodiments contained herein are intended to describe and illustrate the invention, and not to limit it, and in particular, the invention is not limited to these embodiments.

[0034] The following will combine Figure 1 A method for preparing a manganese dioxide composite coal-based porous carbon material according to the present invention includes the following steps:

[0035] S1, lignite powder, and a strongly alkaline activating solvent are mixed and calcined in an inert gas atmosphere to obtain a calcined product. The calcined product is mixed with an aqueous solution and stirred to obtain a first suspension. After filtration, washing with water and drying, coal-based activated carbon is obtained.

[0036] S2. Mix potassium permanganate solution with nitric acid to obtain a second suspension; oxidize the second suspension hydrothermally at 120-130℃ for 12-14 hours, filter and dry to obtain brownish-yellow manganese dioxide;

[0037] S3. Mix the coal-based activated carbon in S1 with manganese dioxide in S2 and carry out a hydrothermal reaction at 100-150℃. After cooling to room temperature, filter and dry to obtain the manganese dioxide composite coal-based activated carbon material precursor.

[0038] S4. The manganese dioxide composite coal-based activated carbon material precursor in S3 is calcined at 300-350℃ for 8-12 hours to obtain manganese dioxide composite coal-based activated carbon.

[0039] The lignite powder used in this invention is preferably Naomaohu lignite with a particle size of 100-200 mesh; the strongly alkaline activating solvent can be one or more of potassium hydroxide or sodium hydroxide, preferably KOH. The mass ratio of lignite powder to strongly alkaline activating solvent is 1:2-4, preferably 1:3.

[0040] In this invention, the inert gas can be one or more of nitrogen, helium or argon, preferably nitrogen.

[0041] During the calcination process in step S1, the calcination temperature is 400-700℃, the calcination heating rate is 3-10℃ / min, and the holding time is 5-7h.

[0042] In step S1, the first suspension is filtered, washed with water and circulated 15 to 20 times, and then dried to obtain coal-based activated carbon.

[0043] Step S2 of this invention is the preparation process of manganese dioxide. After mixing potassium permanganate solution of a certain concentration with nitric acid, potassium permanganate is reduced to manganese dioxide under acidic conditions.

[0044] Here, the mass concentration of potassium permanganate solution is 1-3 wt%, preferably 2.2 wt%; the concentration of nitric acid is 14-20 mol / L, preferably 16 mol / L; wherein the mass ratio of potassium permanganate solution to nitric acid is 1:0.01-0.015, and the mixture is stirred for 4-5 hours to obtain a second suspension.

[0045] The manganese dioxide composite coal-based activated carbon material of the present invention is characterized by the preparation method: hydrothermal-oxidative calcination method; step S3 is the mixing and hydrothermal reaction of coal-based activated carbon and manganese dioxide, specifically, the mass ratio of manganese dioxide to coal-based activated carbon is 3:8-12, preferably 3:10.

[0046] Step S4 is the oxidation and calcination process of the precursor of manganese dioxide composite coal-based activated carbon material. Specifically, it is calcined at 300-350℃ for 8-12 hours to obtain manganese dioxide composite coal-based activated carbon.

[0047] Example 1

[0048] This embodiment provides a method for preparing coal-based activated carbon powder, comprising: mixing 200-mesh Naomohu lignite powder and KOH solution, wherein the mass ratio of Naomohu lignite powder to KOH solution is 1:3; after uniform mixing, placing the mixture in a tube furnace, continuously introducing nitrogen gas into the tube furnace for 74 min, heating to 400℃ and calcining for 5 h, washing with deionized water for 12-24 h, and then drying in an oven at 105℃ to obtain coal-based activated carbon powder, thereby obtaining coal-based activated carbon powder CK-400;

[0049] Example 2

[0050] The only difference between this embodiment and Example 1 is that the calcination process in Example 1 is carried out at 500°C for 5 hours to obtain coal-based activated carbon powder CK-500.

[0051] Example 3

[0052] The only difference between this embodiment and Example 1 is that the calcination process in Example 1 is carried out at 600℃ for 5 hours to obtain coal-based activated carbon powder CK-600.

[0053] Example 4

[0054] The only difference between this embodiment and Example 1 is that the calcination process in Example 1 is carried out at 700℃ for 5 hours to obtain coal-based activated carbon powder CK-700.

[0055] To verify the adsorption behavior of CK-400, CK-500, CK-600, and CK-700 coal-based activated carbons for lead ions at different pH values ​​in Examples 1-4, the following experiment was designed:

[0056] Experiment 1: Static batch adsorption experiments were conducted on lead ion-containing solutions using the coal-based activated carbon prepared in Examples 1-4 as adsorbents. The mass ratio of adsorbent to adsorption solution was 1:1000, pH was 2-7, the adsorption temperature was 25℃, and the adsorption time was 6 hours. The adsorption capacity and the content of functional groups on the activated carbon surface were also measured. Figure 1 The adsorption capacity of CK-400 to CK-700 coal-based activated carbon for lead ions at different pH values ​​is shown. Figure 2 Infrared spectroscopy results for CK-400 to CK-700 coal-based activated carbon.

[0057] As shown in the figure, the adsorption of lead ions by coal-based activated carbon is affected by the oxygen-containing functional groups on the surface, and CK-400 has the largest adsorption capacity for lead ions.

[0058] This invention further investigates the adsorption capacity of CK-400 coal-based activated carbon for lead ions at 25-45℃, and designs Experiment 2.

[0059] Experiment 2: Using CK-400 coal-based activated carbon prepared in Example 1 as the adsorbent, a static batch adsorption experiment was conducted on a lead ion-containing solution, such as... Figure 3 The figure shows the adsorption isotherm analysis of lead ions by CK-400 at 25-45℃.

[0060] The adsorbent-to-adsorption solution mass ratio was 1:1000, pH was 4.8–5.4, adsorption temperature was 25–45℃, and adsorption time was 6 hours. The lead ion concentration was 20–300 mg / L. The maximum adsorption capacity of CK-400 is shown in [reference needed]. Figure 5 The concentration was 139.02 mg / L.

[0061] Example 5

[0062] This embodiment selects CK-400, the coal-based activated carbon with the highest lead ion adsorption capacity among the CK-400 to CK-700 types, to prepare manganese dioxide composite coal-based porous carbon materials. The specific steps include:

[0063] 200-mesh Naomohu lignite powder and KOH solution were mixed, with a mass ratio of Naomohu lignite powder to KOH solution of 1:3. After uniform mixing, the mixture was placed in a tube furnace, and nitrogen gas was continuously introduced into the tube furnace for 74 minutes. The temperature was raised to 400℃ and calcined for 5 hours. The mixture was washed with deionized water for 12-24 hours and then dried in an oven at 105℃ to obtain coal-based activated carbon powder, which is CK-400 coal-based activated carbon powder.

[0064] 22.5 g of potassium permanganate solid powder was dissolved in 1 L of deionized water to obtain a potassium permanganate solution with a mass concentration of 22 wt%. 150 mL of the potassium permanganate solution was taken, and 2 mL of 16 mol / L nitric acid was added dropwise with stirring. Stirring was continued for 4 h. The well-stirred potassium permanganate solution was poured into a hydrothermal reactor and reacted at 130 °C for 14 h to obtain a brownish-black liquid. After filtration and drying, a brownish-black powder was obtained, which was manganese dioxide solid powder.

[0065] 0.5g of coal-based activated carbon was uniformly dispersed in 15-20mL of deionized water and sonicated for 1h to make the activated carbon more uniformly dispersed. 0.150g of manganese dioxide was added and sonicated for 1h to make the manganese dioxide uniformly dispersed in the coal-based activated carbon aqueous solution. The mixture was then transferred to a hydrothermal reactor and reacted at 120℃ for 8h. After filtration and drying, a brown-black manganese dioxide composite coal-based porous carbon material precursor was obtained. The precursor was then placed in a muffle furnace and calcined at 350℃ for 12h to obtain the manganese dioxide composite coal-based porous carbon material.

[0066] This embodiment presents a transmission electron microscope (TEM) image of the prepared manganese dioxide composite coal-based porous carbon material, as shown below. Figure 4 and Figure 5 As shown, the manganese dioxide loading in the manganese dioxide composite coal-based porous carbon material was measured to be 23%, which yielded...0.23 MnO2 / CK-400.

[0067] In order to verify the invention in Example 5 0.23 To investigate the adsorption capacity of MnO2 / CK-400 for lead ions, the following experiment was designed.

[0068] Experiment 3: Using the manganese dioxide composite coal-based porous carbon material prepared in Example 5 ( 0.23 Static batch adsorption experiments were conducted on lead ion-containing solutions using MnO2 / CK-400 as the adsorbent. The mass ratio of adsorbent to adsorption solution was 1:1000, the pH was 4.8–5.4, the initial lead ion concentration was 20–300 mg / L, the adsorption temperature was 25℃, and the adsorption time was 6 hours.

[0069] like Figure 6 As shown, this is a manganese dioxide composite coal-based porous carbon material. 0.23 The adsorption isotherm analysis of MnO2 / CK-400 for lead ions shows that the maximum adsorption capacity of lead ions is 202 mg / L. This indicates that the composite material (MnO2 / CK-400) exhibits [adsorption capacity]. 0.23 The adsorption of lead ions by MnO2 / CK-400 conforms to the Langmuir model, and the maximum adsorption capacity of lead ions by this adsorbent was calculated to be 202 mg / L.

[0070] This invention is for further verification 0.23 To investigate whether MnO2 / CK-400 can rapidly and efficiently adsorb lead ions, and whether it exhibits high selectivity for lead ion adsorption within a certain concentration range, Experiment 4 was designed as follows:

[0071] Experiment 4: Similar to Experiment 3, the initial concentrations of lead ions, copper ions, and cadmium ions were set to 50 mg / L, 70 mg / L, 100 mg / L, and 150 mg / L, respectively, with other conditions remaining unchanged. The experimental results are shown in the table below. Figure 7 As shown, this is a manganese dioxide composite coal-based porous carbon ( 0.23 The relationship between the saturated adsorption capacity of MnO2 / CK-400 material for lead ions, copper ions, and cadmium ions and the initial concentration.

[0072]

[0073] As shown in the table above, manganese dioxide composite materials ( 0.23 MnO2 / CK-400 adsorbs lead ions rapidly and efficiently, and exhibits high selectivity for lead ion adsorption within a certain concentration range.

[0074] This invention is for verification 0.23 Experiment 5 was designed to assess the adsorption stability and cycling performance of MnO2 / CK-400.

[0075] Experiment 5: Using the manganese dioxide composite coal-based porous carbon material prepared in Example 5 ( 0.23 MnO2 / CK-400 was used as the adsorbent for static batch adsorption experiments on lead ion-containing solutions. The adsorbent-to-adsorbent solution mass ratio was 1:1000, pH was 4.8–5.4, the initial lead ion concentration was 20–300 mg / L, the adsorption temperature was 25°C, and the adsorption time was 6 hours. After adsorption saturation, a second desorption and regeneration process was performed using 1 mol / L hydrochloric acid solution for 10–12 hours. After washing with deionized water until neutral, adsorption was carried out according to Example 2, with an initial lead ion concentration of 50 mg / L and other conditions remaining unchanged.

[0076] Experimental results: The saturation capacity of lead ion adsorption was measured to be 40.64 mg / g. This indicates that the adsorption capacity of the adsorbent remained high even after two regenerations, demonstrating the stable adsorption performance of the composite material and its recyclability.

[0077] To verify the adsorption capacity of manganese dioxide composite coal-based activated carbon before and after calcination, the present invention designed the following experiment six.

[0078] Experimental group (calcined): Using the manganese dioxide composite coal-based porous carbon material prepared in Example 5 as the adsorbent, a static batch adsorption experiment was conducted on a lead ion-containing solution. The adsorbent dosage was 30 mg, the adsorption solution dosage was 30 mL, the adsorbent-to-adsorption solution mass ratio was 1:1000, the pH was 4.8–5.4, the initial lead ion concentration was 100 mg / L, the adsorption temperature was 25 °C, and the adsorption time was 6 hours.

[0079] Control group (without calcination): The manganese dioxide composite coal-based porous carbon material prepared in Example 5 was not calcined. The manganese dioxide composite coal-based porous carbon material precursor was directly used as an adsorbent to conduct static batch adsorption experiments on a lead ion-containing solution. The adsorbent dosage was 30 mg, the adsorption solution dosage was 30 mL, the adsorbent-to-adsorption solution mass ratio was 1:1000, the pH was 4.8–5.4, the initial lead ion concentration was 100 mg / L, the adsorption temperature was 25℃, and the adsorption time was 6 hours.

[0080] The experimental results showed that the highest leaching concentration of Mn2+ in the manganese dioxide composite coal-based porous carbon precursor in the adsorption solution was 31.3 mg / L in the experimental group (calcined); while the highest leaching concentration of Mn2+ in the adsorption solution of the manganese dioxide composite coal-based porous carbon precursor in the control group (not calcined) was 1.8 mg / L.

[0081] Comparison of Mn2+ leaching concentrations in adsorption solutions for the two materials Figure 8As shown, the leaching concentration of the composite material precursor before oxidation and calcination is 17 times that of the composite material after oxidation and calcination. Therefore, the hydrothermal-oxidation and calcination combined method can make manganese oxides tightly embedded on the surface of activated carbon, and it is not easy to cause secondary pollution.

[0082] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. An application of a manganese dioxide composite coal-based porous carbon material, characterized in that: The application of the manganese dioxide composite coal-based porous carbon material in selectively adsorbing lead ions in water; The preparation method of the manganese dioxide composite coal-based porous carbon material includes the following steps: S1. Mix lignite powder with a strong alkaline activating solvent and calcine in an inert gas atmosphere to obtain a calcined product. Mix and stir the calcined product with an aqueous solution to obtain a first suspension. After filtration, washing with water and drying, coal-based activated carbon is obtained. S2. Mix potassium permanganate solution with nitric acid to obtain a second suspension; oxidize the second suspension hydrothermally at 120-130℃ for 12-14 hours, filter and dry to obtain brownish-yellow manganese dioxide; S3. Mix the coal-based activated carbon in S1 with manganese dioxide in S2 and carry out a hydrothermal reaction at 100-150℃. After cooling to room temperature, filter and dry to obtain the manganese dioxide composite coal-based activated carbon material precursor. S4. The manganese dioxide composite coal-based activated carbon material precursor in S3 is calcined at 300-350℃ for 8-12 hours to obtain manganese dioxide composite coal-based activated carbon.

2. The application of the manganese dioxide composite coal-based porous carbon material according to claim 1, characterized in that: The lignite powder is Naomaohu lignite with a particle size of 100-200 mesh.

3. The application of the manganese dioxide composite coal-based porous carbon material according to claim 1, characterized in that: The strongly alkaline activating solvent is one or more of potassium hydroxide or sodium hydroxide.

4. The application of the manganese dioxide composite coal-based porous carbon material according to claim 1, characterized in that: The mass ratio of lignite powder to strongly alkaline activating solvent is 1:2-4.

5. The application of the manganese dioxide composite coal-based porous carbon material according to claim 1, characterized in that: In S1, the calcination temperature is 400-700℃, the calcination heating rate is 3-10℃ / min, and the holding time is 5-7h.

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