A method for optimizing pores of magnesium oxide modified biochar

Abstract

The application belongs to the field of environment and material technology, and discloses a method for optimizing pore channels of magnesium oxide modified biochar, which increases micropore volume in biochar through biomass degradation pretreatment, increases macropore volume in biochar through magnesium nitrate microwave foaming, increases mesopore volume in biochar through magnesium nitrate in-situ etching pyrolysis, realizes micropore, mesopore and macropore structure regulation in porous magnesium modified biochar through the synergistic effect of biomass degradation, in-situ etching and microwave foaming, and realizes hierarchical pore channel optimization. The application realizes the construction of porous structure magnesium modified biochar through the combined action of alkali solution, magnesium nitrate and magnesium acetate, wherein the magnesium nitrate microwave foaming and pyrolysis etching can respectively improve the macropore and mesopore structure of the material, and play a key role in the improvement of the pore structure and adsorption performance of the material. The method has the advantages of simplicity, easy industrialization, high control precision, excellent performance and the like.

Description

Technical Field

[0001] This invention belongs to the field of environmental and materials technology, and relates to a method for optimizing the pores of magnesium oxide-modified biochar. Background Technology

[0002] In recent years, water pollution caused by rapid industrial development has become increasingly serious. National standards such as the "Integrated Wastewater Discharge Standard" (GB8978-1996) have set forth clear requirements for industrial wastewater discharge. Therefore, achieving efficient removal and recovery of pollutants from wastewater is of great significance for ecological balance and human health. Currently, existing water pollutant treatment methods include biological methods, sedimentation methods, adsorption methods, and membrane separation technologies. Among these, adsorption methods and photocatalysis are widely used due to their advantages of easy separation and low cost. High adsorption rates and high adsorption capacity adsorbents are key factors in the development of wastewater adsorption materials.

[0003] Biochar, a carbon material prepared from biomass, has attracted widespread attention due to its wide availability and environmental friendliness. Biochar possesses abundant functional groups, excellent physicochemical stability, and a rich pore structure, making it a promising candidate for pollutant adsorption. However, the insufficient porosity of raw biochar results in low removal capacity for many pollutants, limiting its industrial application. To improve the pore structure and surface functional groups of biochar, researchers have developed modification techniques using solid alkalis, acids, metal oxides, and oxidants. Alkali-activated biochar can etch biochar and expand its pore channels, but during pyrolysis, the reaction between alkali and biochar is vigorous, forming numerous macropores and supermacropores, which are detrimental to improving adsorption performance. Magnesium oxide-modified biochar has been shown to have good phosphorus adsorption performance. A common preparation method involves impregnating biomass with magnesium chloride, followed by further pyrolysis to convert magnesium chloride into magnesium oxide and biomass into biochar, ultimately yielding magnesium oxide-modified biochar adsorbent material. The resulting magnesium oxide significantly enhances the adsorption active sites of biochar. However, when magnesium oxide particles are embedded in biochar, they cause pore blockage, hindering pollutant transport. Furthermore, the unreasonable stepwise pore structure of the modified biochar itself severely limits the improvement of the material's adsorption capacity. Modifying the pore structure and surface functional groups of biochar alone is insufficient to meet application requirements. Therefore, developing modified biochar with a micropore-mesopore-macropore gradient distribution, a porous structure, and abundant MgO active sites is of great significance. To construct porous modified biochar, Qiu et al. activated biochar using potassium bicarbonate pyrolysis. The resulting modified biochar possessed a porous structure and exhibited excellent p-chlorophenol adsorption performance (DOI:10.1016 / j.resconrec.2021.105953). In addition, the foaming strategy has been proven to be an effective method for synthesizing porous materials. For example, Han et al. synthesized porous carbon by combining in-situ gas foaming with a hard template method. By introducing silica into the polymer, further foaming and carbonizing, and removing the silica hard template, porous carbon materials were obtained (DOI:10.1016 / j.jcis.2023.05.055).

[0004] Therefore, in the absence of literature reports on the preparation of porous carbon materials by in-situ foaming of biomass, this invention ingeniously utilizes in-situ microwave-enhanced foaming with magnesium nitrate impregnation in conjunction with in-situ etching, and successfully develops porous magnesium-modified biochar technology, which is challenging and has no literature reports. Summary of the Invention

[0005] To address the aforementioned issues, this invention develops a synergistic technology for optimizing the pore structure of porous magnesium-modified biochar, based on a strategy involving biomass alkaline degradation, high-temperature etching with magnesium nitrate, and magnesium nitrate foaming. This technology utilizes biomass degradation, in-situ etching, and microwave foaming to enhance the pore volume of the biochar. Pretreatment with biomass degradation increases the micropore volume; microwave foaming with magnesium nitrate partially increases the macropore volume; and in-situ etching and pyrolysis with magnesium nitrate increases the mesopore volume. The synergistic effect of biomass degradation, in-situ etching, and microwave foaming allows for the control of the micropore, mesopore, and macropore structures in the porous magnesium-modified biochar, achieving hierarchical pore optimization. The resulting porous magnesium oxide-modified biochar material exhibits a gradient distribution of micropores, mesopores, and macropores, providing scientific channels for pollutants in wastewater to migrate through the adsorbent, thus improving the adsorption rate and capacity of the biochar. Simultaneously, the alkaline solution promotes the formation of graphitized carbon in the biochar, increasing the material's conductivity and further enhancing the adsorption rate of the magnesium-modified biochar. Most importantly, magnesium nitrate plays multiple roles in the construction of porous materials: First, during microwave pretreatment, the magnesium nitrate impregnated inside the biomass interacts with the biomass, causing foaming and increasing the proportion of macroporous structures; second, during pyrolysis, magnesium nitrate etches the biomass, enhancing the microporous structure of the biochar. Therefore, microwave foaming of magnesium nitrate plays a crucial role in regulating the pore structure of porous biochar materials. This technology is simple and suitable for industrial production.

[0006] The technical solution of the present invention:

[0007] A method for optimizing the pore structure of magnesium oxide-modified biochar involves increasing the micropore volume of the biochar through biomass degradation pretreatment; increasing the macropore volume of the biochar through microwave foaming with magnesium nitrate; and increasing the mesopore volume of the biochar through in-situ etching and pyrolysis with magnesium nitrate. The synergistic effect of biomass degradation, in-situ etching, and microwave foaming enables the regulation of the micropore, mesopore, and macropore structures in the porous magnesium-modified biochar, achieving hierarchical pore optimization. The specific steps are as follows:

[0008] (1) Alkaline degradation of biomass: The biomass is washed, dried and pulverized into biomass powder; the biomass powder is added to an alkaline solution and stirred at 25-90℃ for 1-10h. The mixture is washed with water until neutral to obtain alkaline pretreated biomass powder, which increases the micropore volume of biochar.

[0009] (2) Microwave foaming of magnesium nitrate: The pre-treated biomass powder is mixed with an aqueous solution of magnesium nitrate and magnesium acetate to obtain a mixed slurry. The mixed slurry is dried to obtain a mixture. The mixture is microwaved for 1-60 minutes to obtain sponge-like biomass, which improves the macroporous structure of the biomass.

[0010] (3) In-situ etching and pyrolysis of magnesium nitrate: The spongy biomass is placed in a pyrolysis furnace at 500-900℃ and pyrolyzed at high temperature for 1-3 hours in an inert gas atmosphere. The biomass is etched with magnesium nitrate to increase the mesopore volume of magnesium-modified biochar and obtain porous magnesium-modified biochar.

[0011] In step (1), it is preferable to stir the reaction at 80-90℃ for 6-8 hours.

[0012] In step (2), microwave treatment is performed for 5-20 minutes, and the microwave power is 600-1000W.

[0013] In step (3), the sponge-like biomass is placed in a pyrolysis furnace at 700℃, and the heating rate is 2-30℃ / min.

[0014] The biomass is one or more of the following: plant shells, stems, bark, roots, kernels, leaves, and animal bones, skin, hair, and feces.

[0015] The alkaline solution is one or a mixture of two of sodium hydroxide, potassium hydroxide, potassium bicarbonate, sodium bicarbonate, potassium carbonate, and sodium carbonate, and the concentration of the alkaline solution is 0.1-2 mol / L.

[0016] The amount of magnesium nitrate and magnesium acetate aqueous solution used is controlled so that the mass ratio of magnesium atoms to biomass is 1 to 20:100, preferably 20:100.

[0017] In the aforementioned aqueous solution of magnesium nitrate and magnesium acetate, the mass ratio of magnesium nitrate and magnesium acetate is 1:0.1 to 10, and the degree of foaming and pore structure are adjusted by microwave-assisted regulation through the synergistic effect of magnesium nitrate and magnesium acetate.

[0018] Application of porous magnesium oxide-modified biochar in pollutant adsorption.

[0019] The beneficial effects of this invention are as follows: This invention provides a method for optimizing the pore structure of porous magnesium-modified biochar by synergistically promoting biomass degradation / in-situ etching / microwave foaming, achieving separate control over the macropores, mesopores, and micropores of the porous magnesium-modified biochar. Through the combined action of alkaline solution-magnesium nitrate-magnesium acetate, the porous magnesium-modified biochar is constructed. Specifically, microwave foaming and pyrolytic etching of magnesium nitrate can respectively enhance the macropore and mesopore structures of the material, playing a crucial role in improving the pore structure and adsorption performance. This method has the advantages of simplicity, ease of industrialization, high control precision, and excellent performance. Attached Figure Description

[0020] Figure 1 This is a SEM image of the product in Embodiment 1 of the present invention;

[0021] Figure 2The image shown is a SEM-mapping image of the product in Embodiment 1 of the present invention, wherein (a) is a SEM image, (b) is a C element, (c) is a Mg element, (d) is an O element, and (e) is a N element;

[0022] Figure 3 This is the XRD pattern of the product in Embodiment 1 of the present invention;

[0023] Figure 4 This is a SEM image of the product from Embodiment 2 of the present invention;

[0024] Figure 5 This is a SEM image of the product from Embodiment 3 of the present invention;

[0025] Figure 6 This is a SEM image of the product from Embodiment 4 of the present invention;

[0026] Figure 7 This is a SEM image of the product in Comparative Example 1 of this invention;

[0027] Figure 8 This is a SEM image of the product in Comparative Example 2 of this invention;

[0028] Figure 9 This is a SEM image of the product in Comparative Example 3 of this invention;

[0029] Figure 10 This is a SEM image of the product in Comparative Example 4 of this invention;

[0030] Figure 11 This is a SEM image of the product in Comparative Example 5 of this invention. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0032] Example 1

[0033] Biomass was pretreated with sodium carbonate, and biochar was activated with magnesium nitrate and magnesium acetate, followed by microwave treatment. The operation steps are as follows:

[0034] (1) Biomass alkaline degradation: Peanut shells were washed, dried and crushed into powder for later use; 2g of peanut shell powder was added to 30mL of 0.5mol / L sodium carbonate solution, stirred at 80℃ for 6 hours, washed with water until neutral, and dried to obtain alkaline pretreated biomass powder;

[0035] (2) Microwave foaming: Dissolve 2.13g magnesium nitrate and 1.8g magnesium acetate in 10mL of water to obtain magnesium nitrate / magnesium acetate aqueous solution, m(Mg):m(biomass)=20:100. Mix peanut shell powder pretreated with mixed alkali with magnesium nitrate / magnesium acetate aqueous solution to obtain mixed slurry. Dry the mixed slurry to obtain a mixture. Microwave treat the mixture for 10 minutes with microwave power of 800W to obtain sponge biomass.

[0036] (3) In-situ oxidation pyrolysis of magnesium nitrate: The obtained sponge biomass was placed in a pyrolysis furnace at 650℃ and pyrolyzed at high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain porous magnesium oxide modified biochar. SEM images are shown below. Figure 1 See the scanned image Figure 2 XRD results are shown in Figure 3 .

[0037] Pore ​​structure analysis and SEM results showed that the sample possessed a rich pore structure, exhibiting a porous structure with a gradient distribution of macropores, mesopores, and micropores. SEM surface scanning results revealed that the main elements in the sample included carbon, magnesium, oxygen, and a small amount of nitrogen. XRD results showed that the 24° diffraction peak was the amorphous peak of the biochar, while the 36.7°, 42.8°, 62.2°, 74.4°, and 78.4° diffraction peaks were magnesium oxide (PDF-45-0946), confirming that magnesium oxide was loaded on the biochar surface. The obtained porous magnesium oxide-modified biochar was used for the adsorption of acid fuchsin in wastewater. Isothermal adsorption results showed that its maximum adsorption capacity reached 659.27 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of porous magnesium oxide-modified biochar added was 1 g / L, the removal rate of acid fuchsin reached 99.9%.

[0038] Example 2

[0039] Biomass was pretreated with sodium carbonate, and biochar was activated with magnesium nitrate and magnesium acetate. Microwave treatment was then applied to increase microwave power and regulate the pore structure of the biochar. The operation steps are as follows:

[0040] (1) Biomass alkaline degradation: Peanut shells were washed, dried and crushed into powder for later use; 2g of peanut shell powder was added to 30mL of 0.5mol / L sodium carbonate solution, stirred and reacted at 80℃ for 6 hours, washed with water until neutral, and dried to obtain alkaline pretreated biomass powder;

[0041] (2) Microwave foaming: Dissolve 2.13g magnesium nitrate and 1.8g magnesium acetate in 10mL of water to obtain magnesium nitrate / magnesium acetate aqueous solution, m(Mg):m(biomass)=20:100. Mix peanut shell powder pretreated with mixed alkali with magnesium nitrate aqueous solution to obtain mixed slurry. Dry the mixed slurry to obtain a mixture. Microwave treat the mixture for 10 minutes with microwave power of 1000W to obtain sponge biomass.

[0042] (3) In-situ oxidation pyrolysis of magnesium nitrate: The obtained sponge biomass was placed in a pyrolysis furnace at 650℃ and pyrolyzed at high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain porous magnesium oxide modified biochar. (SEM image shown) Figure 4 .

[0043] Pore ​​structure analysis and SEM results showed that the sample exhibited a gradient distribution structure of macropores, mesopores, and micropores, with an improved macropore structure compared to Example 1, demonstrating that microwave pretreatment can enhance the macropore structure. The obtained porous magnesium oxide-modified biochar was used for the adsorption of acid fuchsin in wastewater, and isothermal adsorption results showed that its maximum adsorption capacity reached 613.1 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of porous magnesium oxide-modified biochar added was 1 g / L, the removal rate of acid fuchsin reached 99.4%.

[0044] Example 3

[0045] Biomass was pretreated with sodium carbonate, and biochar was activated with magnesium nitrate and magnesium acetate. Compared with Example 1, the amount of magnesium nitrate added was increased, and microwave treatment was further implemented. The operation steps are as follows:

[0046] (1) Biomass alkaline degradation: Peanut shells were washed, dried and crushed into powder for later use; 2g of peanut shell powder was added to 30mL of 0.5mol / L sodium carbonate solution, stirred at 80℃ for 6 hours, washed with water until neutral, and dried to obtain alkaline pretreated biomass powder;

[0047] (2) Microwave foaming: Dissolve 3.195g magnesium nitrate and 0.9g magnesium acetate in 10mL of water to obtain magnesium nitrate / magnesium acetate aqueous solution, m(Mg):m(biomass)=20:100. Mix peanut shell powder pretreated with mixed alkali with magnesium nitrate aqueous solution to obtain mixed slurry. Dry the mixed slurry to obtain a mixture. Microwave treat the mixture for 10 minutes with microwave power of 800W to obtain sponge biomass.

[0048] (3) In-situ oxidation pyrolysis of magnesium nitrate: The obtained sponge biomass was placed in a pyrolysis furnace at 650℃ and pyrolyzed at high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain porous magnesium oxide modified biochar. SEM images are shown below. Figure 5 .

[0049] Pore ​​structure analysis and SEM results showed that the sample had a rich pore structure, exhibiting a porous structure with a gradient distribution of macropores, mesopores, and micropores. Compared with Example 1, the micropore content of the product decreased, while the mesopore content increased. This was attributed to the increased addition of magnesium nitrate, which enhanced the microwave foaming effect and thus increased the mesopore content. The obtained porous magnesium oxide-modified biochar was used for the adsorption of acid fuchsin in wastewater. Isothermal adsorption results showed that its maximum adsorption capacity reached 632.5 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of porous magnesium oxide-modified biochar added was 1 g / L, the removal rate of acid fuchsin reached 99.8%.

[0050] Example 4

[0051] Biomass was pretreated with sodium carbonate, and biochar was activated with magnesium nitrate and magnesium acetate. Compared with Example 1, the alkali pretreatment time was increased, and microwave treatment was further implemented. The operation steps are as follows:

[0052] (1) Biomass alkaline degradation: Peanut shells were washed, dried and crushed into powder for later use; 2g of peanut shell powder was added to 30mL of 0.5mol / L sodium carbonate solution, stirred and reacted at 80℃ for 10 hours, washed with water until neutral, and dried to obtain alkaline pretreated biomass powder;

[0053] (2) Microwave foaming: Dissolve 2.13g magnesium nitrate and 1.8g magnesium acetate in 10mL of water to obtain magnesium nitrate / magnesium acetate aqueous solution, m(Mg):m(biomass)=20:100. Mix peanut shell powder pretreated with mixed alkali with magnesium nitrate aqueous solution to obtain mixed slurry. Dry the mixed slurry to obtain a mixture. Microwave treat the mixture for 2 minutes with microwave power of 800W to obtain micro-foamed sponge biomass.

[0054] (3) In-situ oxidation pyrolysis of magnesium nitrate: The obtained sponge biomass was placed in a pyrolysis furnace at 650℃ and pyrolyzed at high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain porous magnesium oxide modified biochar. SEM images are shown below. Figure 6 .

[0055] Pore ​​structure analysis and SEM results showed that the sample had a rich pore structure, exhibiting a porous structure with a gradient distribution of macropores, mesopores, and micropores. Compared with Example 1, the increased alkali pretreatment time in this example led to greater biomass degradation and a higher micropore content in the product, demonstrating that alkali pretreatment can control the micropore content of the material. The obtained porous magnesium oxide-modified biochar was used for the adsorption of acid fuchsin in wastewater, and isothermal adsorption results showed that its maximum adsorption capacity reached 648.6 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of porous magnesium oxide-modified biochar added was 1 g / L, the removal rate of acid fuchsin reached 99.8%.

[0056] Comparative Example 1

[0057] Biomass was directly placed in a 650℃ pyrolysis furnace and pyrolyzed at a high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain unmodified biochar. Its SEM image is shown below. Figure 7 .

[0058] Compared with Comparative Example 2, SEM results showed that the sample of Comparative Example 2 had less mesopore and micropore content, indicating that the pore structure of the original biochar was underdeveloped. The obtained biochar was used for the adsorption of acid fuchsin in wastewater, and isothermal adsorption results showed that its maximum adsorption capacity was 3.84 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of porous magnesium oxide-modified biochar added was 1 g / L, the removal rate of acid fuchsin was 0.15%.

[0059] Comparative Example 2

[0060] Biochar was prepared by microwave pretreatment and pyrolysis of biomass. The operation steps are as follows:

[0061] (1) Biomass alkaline degradation: Peanut shells were washed, dried and crushed into powder for later use; 2g of peanut shell powder was added to 30mL of 0.5mol / L sodium carbonate solution, stirred at 80℃ for 6 hours, washed with water until neutral, and dried to obtain alkaline pretreated biomass powder;

[0062] (2) The biomass was pretreated with microwaves for 10 minutes at a power of 800W. No foaming was observed. It was then placed in a pyrolysis furnace at 650℃ and pyrolyzed at a high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain biochar. Its SEM image is shown below. Figure 8 .

[0063] Pore ​​structure analysis and SEM results showed no foaming or etching effect from magnesium nitrate. Although the biomass underwent microwave pretreatment, no foaming occurred, resulting in an underdeveloped pore structure in the obtained samples. However, alkaline degradation pretreatment increased the microporous structure in the biochar. The sample in Comparative Example 1 had a relatively high micropore content, indicating that alkaline degradation can increase the micropore content. The obtained biochar was used for the adsorption of acid fuchsin in wastewater. Isothermal adsorption results showed that its maximum adsorption capacity was 6.22 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of porous magnesium oxide-modified biochar added was 1 g / L, the removal rate of acid fuchsin was 3.5%.

[0064] Comparative Example 3

[0065] Biochar was activated using magnesium acetate alone, followed by microwave treatment. The operating steps are as follows:

[0066] (1) Biomass alkaline degradation: Peanut shells were washed, dried and crushed into powder for later use; 2g of peanut shell powder was added to 30mL of 0.5mol / L sodium carbonate solution, stirred at 80℃ for 6 hours, washed with water until neutral, and dried to obtain alkaline pretreated biomass powder;

[0067] (2) Microwave foaming: Dissolve 3.6g of magnesium acetate in 10mL of water to obtain magnesium acetate aqueous solution, m(Mg):m(biomass)=20:100. Mix peanut shell powder pretreated with mixed alkali with magnesium acetate aqueous solution to obtain mixed slurry. Dry the mixed slurry to obtain a mixture. Microwave treat the mixture for 10 minutes with microwave power of 800W to obtain biomass pellets without foaming.

[0068] (3) Pyrolysis: The obtained biomass was placed in a pyrolysis furnace at 650℃ and pyrolyzed at high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain magnesium oxide modified biochar. SEM images are shown below. Figure 9 .

[0069] Pore ​​structure analysis and SEM results showed that although magnesium acetate was added for activation, there was no foaming or etching effect from magnesium nitrate. Although the biomass underwent microwave pretreatment, no foaming occurred, resulting in an underdeveloped pore structure in the obtained samples. However, alkaline degradation pretreatment increased the micropore structure in the biochar. The obtained biochar was used for the adsorption of acid fuchsin in wastewater, and isothermal adsorption results showed a maximum adsorption capacity of 214.6 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of magnesium oxide-modified biochar added was 1 g / L, the acid fuchsin removal rate was 83.6%. Surface modification with magnesium oxide could achieve partial adsorption of the dye, but due to the underdeveloped pore structure, the dye removal rate and adsorption capacity were insufficient.

[0070] Comparative Example 4

[0071] Biochar was activated using magnesium nitrate alone; microwave treatment was not performed. The operating steps are as follows:

[0072] (1) Biomass alkaline degradation: Peanut shells were washed, dried and crushed into powder for later use; 2g of peanut shell powder was added to 30mL of 0.5mol / L sodium carbonate solution, stirred and reacted at 80℃ for 6 hours, washed with water until neutral, and dried to obtain alkaline pretreated biomass powder;

[0073] (2) Drying: Dissolve 4.27g of magnesium nitrate in 10mL of water to obtain magnesium nitrate aqueous solution, m(Mg):m(biomass)=20:100. Mix peanut shell powder pretreated with mixed alkali with magnesium nitrate aqueous solution to obtain mixed slurry. Dry the mixed slurry to obtain a mixture. Further dry at 80℃ to obtain biomass. The biomass pellets obtained do not exhibit foaming phenomenon.

[0074] (3) In-situ oxidation pyrolysis of magnesium nitrate: The obtained biomass was placed in a pyrolysis furnace at 650℃ and pyrolyzed at high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain magnesium oxide modified biochar. SEM results are shown in […]. Figure 10 .

[0075] Pore ​​structure analysis and SEM results showed that the sample had a porous structure. The etching effect of magnesium nitrate enhanced the mesoporous structure of the biochar, but due to the lack of microwave pretreatment, the macropore content of the material was relatively low. The obtained porous magnesium oxide-modified biochar was used for the adsorption of acid fuchsin in wastewater. Isothermal adsorption results showed that its maximum adsorption capacity reached 384.38 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of porous magnesium oxide-modified biochar added was 1 g / L, the removal rate of acid fuchsin reached 93.4%.

[0076] Comparative Example 5

[0077] Magnesium nitrate and magnesium acetate were used to activate the biochar; microwave treatment was not performed. The operating steps are as follows:

[0078] (1) Biomass alkaline degradation: Peanut shells were washed, dried and crushed into powder for later use; 2g of peanut shell powder was added to 30mL of 0.5mol / L sodium carbonate solution, stirred and reacted at 80℃ for 6 hours, washed with water until neutral, and dried to obtain alkaline pretreated biomass powder;

[0079] (2) Drying: Dissolve 2.13g magnesium nitrate and 1.8g magnesium acetate in 10mL of water to obtain magnesium nitrate aqueous solution, m(Mg):m(biomass)=20:100. Mix peanut shell powder pretreated with mixed alkali with magnesium nitrate aqueous solution to obtain mixed slurry. Further dry at 80℃ to obtain mixture. The resulting biomass pellets do not exhibit foaming phenomenon.

[0080] (3) In-situ oxidation pyrolysis of magnesium nitrate: The obtained biomass was placed in a pyrolysis furnace at 700℃ and pyrolyzed at high temperature for 1 hour in an inert gas atmosphere with a heating rate of 5℃ / min to obtain porous magnesium oxide modified biochar. SEM results are shown in […]. Figure 11 .

[0081] Pore ​​structure analysis and SEM results showed that the sample had a porous structure. The etching effect of magnesium nitrate enhanced the mesoporous structure of the biochar, and the incorporation of magnesium acetate controlled the etching degree of magnesium nitrate, inhibiting its oxidation performance and reducing the mesoporous content compared to Comparative Example 4. However, due to the lack of microwave pretreatment, the macroporous content of the material was relatively low. The obtained porous magnesium oxide-modified biochar was used for the adsorption of acid fuchsin in wastewater. Isothermal adsorption results showed that its maximum adsorption capacity was as high as 328.53 mg / g. When the initial pollutant concentration was 50 mg / L and the amount of porous magnesium oxide-modified biochar added was 1 g / L, the removal rate of acid fuchsin reached 96.6%.

[0082] The above samples were subjected to adsorption performance tests for acid fuchsin dye. The test method involved adding 0.05 g of adsorbent to an acid fuchsin solution and inducing adsorption under isothermal shaking at 25℃ and 180 rpm. The removal rate of acid fuchsin was measured, and the adsorption experiment was conducted using the isothermal adsorption method. The maximum adsorption capacity of the material was calculated using the Langmuir model. The pore volume of the samples was measured using a specific surface area analyzer, and the proportions of micropores (<2 nm), mesopores (2-50 nm), and macropores (>50 nm) in the total pore volume were calculated based on the pore distribution data.

[0083] Table 1. Pore structure and acid fuchsin removal rate

[0084]

Claims

1. Use of a porous magnesium oxide modified biochar in the adsorption of pollutants, characterized in that, The method for optimizing the pore channel of the porous magnesium oxide modified biochar is as follows: (1) Alkaline degradation of biomass: the biomass is washed with water, dried, and crushed into biomass powder; the biomass powder is added into an alkaline solution, and stirred at 80-90°C for 6-8h; the alkaline pretreated biomass powder is obtained after washing to neutral, and the micropore volume in the biochar is increased; (2) Microwave foaming of magnesium nitrate: the alkaline pretreated biomass powder is mixed with a magnesium nitrate and magnesium acetate aqueous solution to obtain a mixed slurry; the mixed slurry is dried to obtain a mixture; the mixture is subjected to microwave treatment for 1-60min to obtain a sponge-like biomass, which improves the macropore structure of the biomass; (3) In-situ etching pyrolysis of magnesium nitrate: the sponge-like biomass is placed in a 500-900°C pyrolysis furnace and pyrolyzed at high temperature for 1-3h in an inert gas atmosphere; the magnesium nitrate etches the biomass to improve the mesopore volume of the magnesium modified biochar, and the porous magnesium oxide modified biochar is obtained; the biomass is peanut shell.

2. Use according to claim 1, characterized in that, In step (2), the microwave treatment is performed for 5-20min, and the power of the microwave is 600-1000W.

3. Use according to claim 1, characterized in that, In step (3), the sponge-like biomass is placed in a 700°C pyrolysis furnace, and the heating rate is 2-30°C / min.

4. Use according to claim 1, characterized in that, The alkali in the alkaline solution is one or a mixture of two of sodium hydroxide, potassium hydroxide, potassium bicarbonate, sodium bicarbonate, potassium carbonate, and sodium carbonate, and the concentration of the alkaline solution is 0.1-2 mol / L.

5. The use according to claim 1, characterized in that, The amount of the magnesium nitrate and magnesium acetate aqueous solution is controlled such that the mass ratio of magnesium atoms to biomass is 1-20:

100.

6. Use according to claim 1, characterized in that, In the magnesium nitrate and magnesium acetate aqueous solution, the mass ratio of magnesium nitrate to magnesium acetate is 1:0.1-10.

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