A biochar-loaded ultrafine nano-magnesium oxide material, a preparation method and application thereof

Abstract

The present application relates to the technical field of biochar material, and relates to a biochar loaded superfine nano magnesium oxide material and a preparation method and application thereof.The biochar loaded superfine nano magnesium oxide material is prepared by the following steps: dipping cellulose biomass in a magnesium salt solution to obtain a solid;mixing the solid with an alkali solution and stirring to obtain a stirred product; washing and drying the stirred product to obtain a precursor; and pyrolyzing the precursor in an inert atmosphere to obtain the biochar loaded superfine nano magnesium oxide material.In the present application, the cellulose biomass is used as a raw material, and the nano magnesium oxide is loaded on the biochar, and by using different types of magnesium salt, a precipitation process, a limited oxygen environment and a large number of pores in the biochar, the material loaded with a large amount of superfine nano magnesium oxide on the surface is obtained.The adsorbent in the present application can realize efficient adsorption of heavy metal ions such as lead, chromium, copper, cadmium and arsenic in water, and the adsorbent can also adsorb phosphate and realize nitrogen-phosphorus co-adsorption.The material has a large adsorption capacity, which is conducive to effective treatment of wastewater.

Description

Technical Field

[0001] This invention relates to the field of biochar materials technology, and in particular to a biochar-supported ultrafine nano-magnesium oxide material, its preparation method, and its application. Background Technology

[0002] Water pollution has become one of the most serious environmental problems facing the world. Excessive levels of heavy metals and nutrients such as nitrogen and phosphorus are frequently found in natural water bodies, posing a serious threat to the ecological environment, economic development, and human health. Adsorption is considered a more promising method for wastewater treatment due to its flexibility and practicality. The key to adsorption lies in the adsorbent, but traditional adsorbents suffer from limited adsorption efficiency and high cost. Therefore, there is an urgent need to find a new, highly efficient adsorption material to improve the efficiency and environmental friendliness of wastewater treatment.

[0003] Nano-magnesium oxide, as an alkaline oxide, widely exists in the form of periclase and has attracted much research attention due to its high specific surface area, tunability, and active surface. However, pure nano-magnesium oxide still faces some challenges as an adsorbent in water treatment. Firstly, it is prone to leaching Mg. 2+ Firstly, the material may accidentally release metal ions into the water. Secondly, due to its tendency to aggregate, nano-magnesium oxide has poor dispersibility in water, reducing its adsorption efficiency. Furthermore, the adsorption performance of nano-magnesium oxide is largely affected by pH, limiting its application under different environmental conditions. These drawbacks significantly limit the feasibility of pure nano-magnesium oxide in practical water treatment. Therefore, loading nano-magnesium oxide onto inert biochar not only reduces the amount of metal used and leaked, but also provides numerous loading sites for nano-magnesium oxide and maximizes its dispersion and fixation, thereby obtaining a highly efficient water pollution adsorption material. The type and concentration of magnesium salts, solid-liquid ratio, precipitation method, anaerobic conditions, calcination temperature, and time are crucial factors in the preparation of this type of magnesium oxide-biochar material. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a biochar-supported ultrafine nano-magnesium oxide material, its preparation method, and its application, which improves the adsorption effect on heavy metals and nitrogen and phosphorus.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing biochar-supported ultrafine nano-magnesium oxide materials, comprising the following steps:

[0007] 1) Cellulose biomass was impregnated in a magnesium salt solution to obtain solids;

[0008] 2) Mix the solid obtained in step 1) with an alkaline solution at a solid-liquid ratio of 1g:20mL to 120mL and stir to obtain a stirred mixture. Wash and dry the stirred mixture to obtain a precursor.

[0009] 3) The precursor obtained in step 2) is pyrolyzed in an inert atmosphere to obtain biochar-supported ultrafine nano-magnesium oxide material.

[0010] Preferably, the cellulosic biomass in step 1) includes one or more of corn stalks, wheat stalks, sugarcane bagasse, and peanut shells;

[0011] The cellulosic biomass undergoes any one of the following treatments: acid treatment, alkali treatment, and steam explosion treatment.

[0012] Preferably, the acid treatment includes: immersing the cellulosic biomass in a 2 mol / L hydrochloric acid solution, washing until neutral, and then drying; the immersion temperature is 80°C, and the time is 3 hours.

[0013] The alkaline-acid treatment includes: soaking the cellulosic biomass in a 3 mol / L sodium carbonate solution, washing until neutral, and then drying; the soaking temperature is 80°C and the time is 3 hours.

[0014] The steam explosion treatment includes: treating the cellulosic biomass with steam explosion at 180°C for 60 minutes.

[0015] Preferably, in step 1), the mass ratio of cellulosic biomass to magnesium salt solution is 1g:5mL to 30mL;

[0016] The concentration of the magnesium salt solution is 0.1–20 mol / L;

[0017] The magnesium salt in the magnesium salt solution includes one or more of magnesium chloride, magnesium sulfate, magnesium oxalate, magnesium citrate, and magnesium nitrate.

[0018] Preferably, the concentration of the alkaline solution in step 2) is 0.5–40 mol / L, and the alkaline solution is a sodium hydroxide solution;

[0019] The stirring speed is 600 rpm, and the stirring time is 30 to 800 min;

[0020] The drying conditions include a temperature of 70°C and a time of 12 hours.

[0021] Preferably, the conditions for pyrolysis in step 3) include: a temperature of 400-800℃, a time of 0.5-4h, and a heating rate of 20℃ / min.

[0022] The present invention also provides a biochar-supported ultrafine nano-magnesium oxide material prepared by the preparation method described above, wherein the ultrafine nano-magnesium oxide has a diameter of 6-8 nm and a loading of 5-43% by mass.

[0023] This invention also provides the application of the biochar-supported ultrafine nano-magnesium oxide material described above in the adsorption of heavy metals.

[0024] Preferably, the heavy metal includes one or more of arsenic, cadmium, chromium, copper and lead.

[0025] The present invention also provides the application of the biochar-supported ultrafine nano magnesium oxide material described above in the adsorption of nitrogen and / or phosphorus.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. In this invention, cellulose biomass is used as raw material, and nano-magnesium oxide is loaded onto biochar. By utilizing different types of magnesium salts, precipitation process, oxygen-limited environment and the large number of pores in biochar, a material with a large amount of ultrafine nano-magnesium oxide loaded on the surface is obtained.

[0028] 2. The adsorbent in this invention can efficiently adsorb heavy metal ions in water, such as lead, chromium, copper, cadmium, and arsenic. Simultaneously, the adsorbent can also adsorb phosphate ions, achieving nitrogen and phosphorus co-adsorption. Furthermore, the material has a large adsorption capacity, which is beneficial for the effective treatment of wastewater.

[0029] 3. The preparation method of the material of the present invention adopts the steps of first impregnation, then precipitation and pyrolysis, which reduces the process of multiple high-temperature pyrolysis, and the raw materials used are widely available and inexpensive, resulting in low preparation cost. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0031] Figure 1 Scanning electron microscope images of biochar-supported magnesium oxide nanomaterials prepared in Example 5 at different magnifications;

[0032] Figure 2 Here is a high-resolution transmission electron microscope image of the biochar-supported magnesium oxide nanomaterial prepared in Example 5;

[0033] Figure 3 EDS elemental distribution image of the biochar-supported magnesium oxide nanomaterial prepared in Example 5;

[0034] Figure 4 Image showing the relative elemental content of the biochar-supported magnesium oxide nanomaterial prepared in Example 5. Detailed Implementation

[0035] This invention provides a method for preparing biochar-supported ultrafine nano-magnesium oxide materials, comprising the following steps:

[0036] 1) Cellulose biomass was impregnated in a magnesium salt solution to obtain solids;

[0037] 2) Mix the solid obtained in step 1) with an alkaline solution at a solid-liquid ratio of 1g:30mL to 120mL and stir to obtain a stirred mixture. Wash and dry the stirred mixture to obtain a precursor.

[0038] 3) The precursor obtained in step 2) is pyrolyzed in an inert atmosphere to obtain biochar-supported ultrafine nano-magnesium oxide material.

[0039] This invention involves impregnating cellulose biomass in a magnesium salt solution to obtain a solid product.

[0040] In this invention, the cellulosic biomass preferably includes one or more of corn stalks, wheat stalks, sugarcane bagasse, and peanut shells. In this invention, the cellulosic biomass preferably undergoes any one of acid treatment, alkali treatment, and steam explosion treatment. In this invention, the acid treatment preferably includes: immersing the cellulosic biomass in a 2 mol / L hydrochloric acid solution, washing until neutral, and then drying; the immersion temperature is preferably 80°C, and the time is 3 hours. In this invention, the acid treatment aims to degrade cellulose, improve the biomass's biodegradability, and improve the pore structure of the biomass material. In this invention, the alkali-acid treatment preferably includes: immersing the cellulosic biomass in a 3 mol / L sodium carbonate solution, washing until neutral, and then drying; the immersion temperature is 80°C, and the time is 3 hours. In this invention, the alkali treatment aims to degrade lignin, improve the biomass's biodegradability, and remove impurities. In this invention, the steam explosion treatment preferably includes: treating the cellulosic biomass with steam explosion at 180°C for 60 minutes. In this invention, the steam explosion treatment results in a more porous and looser structure in the cellulosic biomass, which facilitates the adsorption of magnesium ions on and within the biomass. In this invention, the preferred mass ratio of the cellulosic biomass to the magnesium salt solution is 1g:5mL to 30mL. In this invention, the preferred concentration of the magnesium salt solution is 0.1 to 20 mol / L. In this invention, the magnesium salt in the magnesium salt solution preferably includes one or more of magnesium chloride, magnesium sulfate, magnesium oxalate, magnesium citrate, and magnesium nitrate.

[0041] In this invention, the obtained solid is mixed with an alkaline solution at a solid-liquid ratio of 1g:20mL to 120mL and stirred to obtain a stirred mixture. The stirred mixture is then washed and dried to obtain a precursor.

[0042] In this invention, the concentration of the alkaline solution is preferably 0.5–40 mol / L, and the alkaline solution is preferably a sodium hydroxide solution. In this invention, the stirring speed is preferably 600 rpm, and the stirring time is preferably 30–800 min. In this invention, the drying conditions preferably include a temperature of 70°C and a time of 12 h. In this invention, the purpose of treating the solid with the alkaline solution is to precipitate a large amount of Mg present on the surface and in the pores of the solid. 2+ Mg(OH)2 precipitate is formed.

[0043] The present invention involves pyrolyzing the obtained precursor under an inert atmosphere to obtain biochar-supported ultrafine nano-magnesium oxide material.

[0044] In this invention, the preferred pyrolysis conditions include: a temperature of 400-800℃, a time of 0.5-4 h, and a heating rate of 20℃ / min. The main purpose of precursor pyrolysis in this invention is to convert biomass materials into biochar, thereby increasing the specific surface area and porosity of the material. Simultaneously, at high temperature, Mg(OH)₂ precipitate is converted into the desired magnesium oxide nanoparticles.

[0045] The present invention also provides a biochar-supported ultrafine nano-magnesium oxide material prepared by the preparation method described above, wherein the ultrafine nano-magnesium oxide has a diameter of 6-8 nm and a loading of 5-43% by mass.

[0046] This invention also provides the application of the biochar-supported ultrafine nano-magnesium oxide material described above in the adsorption of heavy metals. In this invention, the heavy metal preferably includes one or more of arsenic, cadmium, chromium, copper, and lead.

[0047] The present invention also provides the application of the biochar-supported ultrafine nano magnesium oxide material described above in the adsorption of nitrogen and / or phosphorus.

[0048] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0049] Example 1

[0050] A method for preparing biochar-supported nano-magnesium oxide materials:

[0051] (1) Soak 5g of crushed corn stalks (0.5-1cm) in 25mL of 5mol / L magnesium chloride solution for 1 hour, centrifuge, and retain the solids after solid-liquid separation;

[0052] (2) Add the solid obtained in (1) to a 40 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 20 mL, stir magnetically at 600 r / min for 600 minutes, then wash the obtained material with water until neutral, and dry at 70 °C for 12 hours to obtain the precursor for preparing biochar.

[0053] (3) The precursor obtained in (2) was placed in a tube furnace with N2 and pyrolyzed at 400°C for 4 hours in an oxygen-deficient environment with a heating rate of 20°C / min to obtain biochar loaded with nano-magnesium oxide.

[0054] Comparative Example 1

[0055] A method for preparing biochar:

[0056] (1) Soak 5g of crushed corn stalks (0.5-1cm) in 25mL of aqueous solution for 1 hour, centrifuge, and retain the solids after solid-liquid separation;

[0057] (2) Add the solid obtained in (1) to a 40 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 20 mL, stir magnetically at 600 r / min for 600 minutes, then wash the obtained material with water until neutral, and dry at 70 °C for 12 hours to obtain the precursor for preparing biochar.

[0058] (3) The precursor obtained in (2) was placed in a tube furnace with N2 and pyrolyzed at 400°C for 4 hours in an oxygen-deficient environment with a heating rate of 20°C / min to obtain biochar.

[0059] Example 2

[0060] A method for preparing biochar-supported nano-magnesium oxide materials:

[0061] (1) Soak 5g of crushed sugarcane bagasse (0.5-1cm) in 150mL of 0.1mol / L magnesium sulfate solution for 1 hour, centrifuge, and retain the solids after solid-liquid separation;

[0062] (2) The solid obtained in (1) was added to a 0.5 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 120 mL and stirred magnetically at 600 r / min for 600 minutes. The resulting material was then washed with water until neutral and dried at 70 °C for 12 hours to obtain the precursor for preparing biochar.

[0063] (3) The precursor obtained in (2) was placed in a tube furnace with N2 and pyrolyzed at 800°C for 0.5 hours in anoxic conditions with a heating rate of 20°C / min to obtain biochar loaded with nano-magnesium oxide.

[0064] Example 3

[0065] A method for preparing biochar-supported nano-magnesium oxide materials:

[0066] (1) Immerse 10g of crushed wheat straw (0.5-1cm) completely in a 2mol / L hydrochloric acid solution at a temperature of 80℃ for 3 hours;

[0067] (2) Wash the product obtained in (1) until neutral, dry and grind it to obtain acid-treated wheat straw;

[0068] (3) Weigh 5g of the acid-treated wheat straw obtained in (2) and soak it in 50mL of 20mol / L magnesium oxalate solution for 1 hour. After centrifugation and solid-liquid separation, retain the solids.

[0069] (4) Add the solid obtained in (3) to a 40 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 40 mL, stir magnetically at 600 r / min for 30 minutes, then wash the obtained material with water until neutral, and dry at 70 °C for 12 hours to obtain the precursor for preparing biochar.

[0070] (5) The precursor obtained in (4) was placed in a tube furnace with N2 and pyrolyzed at 800°C for 0.5 hours in an oxygen-deficient environment with a heating rate of 20°C / min to obtain biochar loaded with nano-magnesium oxide.

[0071] Example 4

[0072] A method for preparing biochar-supported nano-magnesium oxide materials:

[0073] (1) Crush 10g of peanut shells (0.5-1cm) and immerse them completely in a 3mol / L sodium carbonate solution at a temperature of 80℃ for 3 hours.

[0074] (2) Wash the product obtained in (1) until neutral, dry and grind it to obtain corn stalks treated with alkali.

[0075] (3) Weigh 5g of the alkali-treated corn stalks obtained in (2) and soak them in 50mL of 5mol / L magnesium citrate solution for 1 hour. After centrifugation and solid-liquid separation, retain the solids.

[0076] (4) Add the solid obtained in (3) to a 0.5 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 40 mL, stir magnetically at 600 r / min for 600 minutes, then wash the obtained material with water until neutral, and dry at 70°C for 12 hours to obtain the precursor for preparing biochar.

[0077] (5) The precursor obtained in (4) was placed in a tube furnace with N2 and pyrolyzed at 600°C for 2 hours in an oxygen-deficient environment with a heating rate of 20°C / min to obtain biochar loaded with nano-magnesium oxide.

[0078] Example 5

[0079] A method for preparing biochar-supported nano-magnesium oxide materials:

[0080] (1) After crushing the corn stalks (0.5-1cm), treat them in a steam explosion container at 180℃ for 60min and then quickly discharge them to obtain steam-exploded corn stalks;

[0081] (2) Soak 5g of steam-exploded corn stalks in 50mL of 5mol / L magnesium chloride solution for 1 hour, centrifuge, and retain the solids after solid-liquid separation;

[0082] (3) Add the solid obtained in (2) to a 10 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 40 mL, stir magnetically at 600 r / min for 800 minutes, then wash the obtained material with water until neutral, and dry at 70°C for 12 hours to obtain the precursor for preparing biochar.

[0083] (4) The precursor obtained in (3) was placed in a tube furnace with N2 and pyrolyzed at 600°C for 2 hours in an oxygen-deficient environment with a heating rate of 20°C / min to obtain biochar loaded with nano-magnesium oxide.

[0084] Scanning and high-resolution transmission electron microscopy images of the final product are shown below. Figure 1-2 The surface Mg content was determined using EDS mapping, and the results are shown in [Figure number missing]. Figure 3-4 .

[0085] Example 6

[0086] A method for preparing biochar-supported nano-magnesium oxide materials:

[0087] (1) After crushing the corn stalks (0.5-1cm), treat them in a steam explosion container at 180℃ for 60min and then quickly discharge them to obtain steam-exploded corn stalks;

[0088] (2) Soak 5g of steam-exploded corn stalks in 50mL of 5mol / L magnesium nitrate solution for 1 hour, centrifuge, and retain the solids after solid-liquid separation;

[0089] (3) Add the solid obtained in (2) to a 10 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 40 mL, stir magnetically at 600 r / min for 800 minutes, then wash the obtained material with water until neutral, and dry at 70°C for 12 hours to obtain the precursor for preparing biochar.

[0090] (4) The precursor obtained in (3) was placed in a tube furnace with N2 and pyrolyzed at 600°C for 2 hours in an oxygen-deficient environment with a heating rate of 20°C / min to obtain biochar loaded with nano-magnesium oxide.

[0091] Example 7

[0092] The MgO content on the surface of biochar-supported nano-magnesium oxide material was calculated using EDS, and heavy metal ions in water were adsorbed.

[0093] a. Experimental scheme

[0094] (1) Prepare Pb at different concentrations respectively. 2+ Cr 3+ Cu 2+ Cd 2+ and AsO4 3- The solution (10-500 mg / L) was used as the adsorption solution, and the pH of the adsorption solution was set to 2-6.

[0095] (2) Weigh 20 mg of the biochar obtained in Examples 1-6 and Comparative Example 1 respectively and add it to Pb in (1). 2+ Cr 3+ Cu 2+ Cd 2+ and AsO4 3- In the solution, the concentration of biochar was set at 0.2 g / L. -1 And shake in a constant temperature incubator for 12 hours;

[0096] (3) After adsorption is complete, centrifuge and use inductively coupled plasma spectrometry to determine the concentrations of Pb, Cr, Cu, Cd and As in the supernatant, and calculate the adsorption amount.

[0097] b. Experimental Results

[0098] Table 1. MgO content of biochar-supported magnesium oxide nanomaterials prepared in different embodiments

[0099]

[0100] c. Experimental Results

[0101] Table 2 Adsorption of heavy metal ions by biochar-supported magnesium oxide nanomaterials prepared in different embodiments

[0102]

[0103] Example 8

[0104] Example 5: Co-removal of binary, ternary, and multi-metal ions from water by biochar-supported magnesium oxide nanomaterials.

[0105] a. Experimental scheme

[0106] (1) Prepare wastewater containing metal ions, in which there are multiple combinations of metal ions, with a content of (10-500 mg / L), and adjust the pH of the solution to 2-6;

[0107] (2) Weigh 40 mg of biochar and add it to the mixed solution of binary / ternary / multi-metal ions in (1) to make the biochar concentration 0.2 g / L. -1 And shake in a constant temperature incubator for 12 hours;

[0108] (3) After adsorption is complete, centrifuge and use inductively coupled plasma spectrometry to determine the concentrations of Pb, Zn, Cr, Cu, Cd and As in the supernatant, and calculate the adsorption amount.

[0109] b. Experimental Results

[0110] Table 3 shows the co-removal of binary, ternary, and multi-metal ions in water by the biochar-supported magnesium oxide nanomaterial prepared in Example 5.

[0111]

[0112] Example 9

[0113] Biochar-supported magnesium oxide nanomaterials prepared in different embodiments adsorb phosphorus in water and co-remove nitrogen and phosphorus from water.

[0114] a. Experimental Scheme 1

[0115] (1) Prepare solutions with different pH values ​​(pH 1-13) and different concentrations (1-1000 mg PL). -1 Phosphate solution was used as the adsorption liquid;

[0116] (2) Weigh 20 mg of biochar and add it to the phosphate solution in (1) to make the biochar concentration 0.2 g / L. -1 And shake in a constant temperature incubator for 24 hours;

[0117] (3) After adsorption was completed, centrifugation was performed, and the PO4 in the supernatant was determined by ammonium molybdate spectrophotometry. 3- The concentration was determined, and the adsorption amount was calculated.

[0118] b. Experimental Scheme 2

[0119] (4) Configure different pH values ​​(1-13), N / P molar ratios (1:10-10:1), and different NH4+ ratios. - and PO4 3- solution of content

[0120] (5) Weigh 40 mg of biochar and add it to NH4 in (1). - and PO4 3-In a mixed solution, the biochar concentration was adjusted to 0.2 g / L. -1 And shake in a constant temperature incubator for 4 hours;

[0121] (3) After adsorption is complete, centrifuge and determine the concentrations of N and P in the supernatant by Nessler's reagent spectrophotometry and ammonium molybdate spectrophotometry, respectively, and calculate the adsorption amount.

[0122] c. Experimental Results

[0123] Table 4. Phosphate adsorption capacity and nitrogen and phosphorus removal efficiency of different embodiments

[0124]

[0125] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. The application of biochar-supported ultrafine nano-magnesium oxide materials in the adsorption of heavy metals, characterized in that, The heavy metals include one or more of cadmium, chromium, copper and lead; The preparation method of the biochar-supported nano-magnesium oxide material is as follows: (1) After crushing the corn stalks, treat them in a steam explosion container at 180°C for 60 minutes and then quickly discharge them to obtain steam-exploded corn stalks. (2) Soak 5g of steam-exploded corn stalks in 50mL of 5mol / L magnesium chloride solution for 1 hour, centrifuge, and retain the solids after solid-liquid separation; (3) Add the solid obtained in (2) to a 10 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 40 mL, stir magnetically at 600 r / min for 800 minutes, then wash the obtained material with water until neutral, and dry at 70°C for 12 hours to obtain the precursor for preparing biochar. (4) The precursor obtained in (3) was placed in a tube furnace with N2 and pyrolyzed at 600°C for 2 hours in an oxygen-deficient environment with a heating rate of 20°C / min to obtain biochar loaded with nano-magnesium oxide.

2. The application of biochar-supported ultrafine nano-magnesium oxide materials in the adsorption of nitrogen and / or phosphorus, characterized in that, The preparation method of the biochar-supported nano-magnesium oxide material is as follows: (1) After crushing the corn stalks, treat them in a steam explosion container at 180°C for 60 minutes and then quickly discharge them to obtain steam-exploded corn stalks. (2) Soak 5g of steam-exploded corn stalks in 50mL of 5mol / L magnesium chloride solution for 1 hour, centrifuge, and retain the solids after solid-liquid separation; (3) Add the solid obtained in (2) to a 10 mol / L sodium hydroxide solution at a solid-liquid ratio of 1 g: 40 mL, stir magnetically at 600 r / min for 800 minutes, then wash the obtained material with water until neutral, and dry at 70°C for 12 hours to obtain the precursor for preparing biochar. (4) The precursor obtained in (3) was placed in a tube furnace with N2 and pyrolyzed at 600°C for 2 hours in an oxygen-deficient environment with a heating rate of 20°C / min to obtain biochar loaded with nano-magnesium oxide.

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