Graded porous flower-shaped magnesium oxide modified coconut shell biochar composite material as well as preparation method and application thereof

Abstract

The invention discloses a graded porous flower-shaped magnesium oxide modified coconut shell biochar composite material and a preparation method and application thereof, and the preparation method of the composite material comprises the following steps: uniformly mixing coconut shell biochar, potassium hydroxide, a magnesium oxide precursor and water, and drying to obtain a mixed material; placing the mixed material in a tubular furnace, roasting in a nitrogen atmosphere, naturally cooling, washing and drying to prepare the graded porous flower-shaped magnesium oxide modified coconut shell biochar composite material. The preparation method of the magnesium oxide precursor comprises the following steps: dissolving magnesium sulfate heptahydrate and urea in water, stirring and mixing, pouring into a sealed container, and carrying out hydrothermal reaction to obtain the magnesium oxide precursor. The composite material obtained by the invention is loaded with graded porous flower-shaped magnesium oxide and active functional groups, has abundant surface active sites and electron capture capability, promotes the adsorption of the composite material on heavy metal ions in wastewater, and expands the adsorption capacity of the composite material on the heavy metal ions; the raw materials are wide in source and conform to the green and low-cost concept.

Description

Technical Field

[0001] The present invention relates to a novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material, its preparation method and application, belonging to the technical field of environmental materials. Background Art

[0002] In recent years, developing biochar based on the conversion of coconut shell resources to remove heavy metal ions from polluted water has always been an environmental issue that has attracted much attention. Among them, a large number of studies have proved that metal oxide composites supported on porous carriers have great potential for sequestering heavy metals from various polluted waters. However, most of the metal oxides supported by traditional methods are granular, with a single structure and a relatively low surface area, which limits the adsorption performance of cadmium ions. Therefore, optimizing the structure of metal oxides and finding modified biochars that can simultaneously adsorb cadmium ions efficiently and quickly have become the research focus. Summary of the Invention

[0003] The present invention provides a novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material, its preparation method and application. Using the natural biomass resource coconut shell as the raw material, through the synergy of precursor morphology innovation and KOH activation, the limitation of traditional flaky templates is broken through, and a friendly and inexpensive novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material is prepared, which has good ion adsorption and rapid adsorption performance at the same time. The biochar prepared therefrom meets the national standard NY / T 3672-2020.

[0004] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0005] A preparation method of a hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material includes the following steps: mixing coconut shell biochar, potassium hydroxide, magnesium oxide precursor and water evenly, drying to obtain a mixed material; placing the mixed material in a tube furnace, roasting in a nitrogen atmosphere and cooling naturally, washing and drying to obtain the hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material;

[0006] The preparation method of the magnesium oxide precursor is: dissolving magnesium sulfate heptahydrate and urea in water, stirring and mixing, and then pouring into a sealed container for hydrothermal reaction to obtain the magnesium oxide precursor.

[0007] The present invention breaks through the limitation of traditional flaky templates through the synergy of precursor morphology innovation and KOH activation, providing a new idea for the development of multifunctional carbon-based composite materials.

[0008] The obtained composite material is characterized by an electron scanning electron microscope and an infrared spectrometer, indicating that the surface of the biochar is a porous structure and the hierarchically porous flower-like magnesium oxide is successfully loaded, and it also has active functional groups.

[0009] The novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material of the present application breaks through the limitation of traditional flaky templates through the synergy of precursor morphology innovation and KOH activation. Using natural biomass resource coconut shell as raw material, the raw material source is green; at the same time, it has fast and efficient metal ion adsorption performance.

[0010] The above composite material has good ion adsorption and fast adsorption performance.

[0011] In the hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material prepared above, it includes amorphous carbon, hierarchically porous flower-like magnesium oxide and oxygen-containing functional groups. Among them, the oxygen-containing functional groups are carboxyl group, carbonyl group, hydroxyl group, etc.

[0012] Compared with directly using magnesium oxide, the use of magnesium oxide precursor in the above avoids the agglomeration of materials, significantly improves the uniformity and dispersibility, refines the particle size, obtains a hierarchically porous flower-like structure, and significantly improves the adsorption performance. In this process, MgSO4·H2O is used as the magnesium source, and urea (CO(NH2)2) hydrolyzes to generate NH3 and CO3 under high-temperature hydrothermal conditions 2- , gradually increasing the solution pH value to form an alkaline environment, generating a magnesium oxide precursor ((MgCO3·Mg(OH)2·xH2O)). The long-term hydrothermal reaction promotes the crystallization and morphology regulation of the precursor, forming a nanosphere structure, and its microscopic morphology provides a template for the "flower-like" structure of subsequent MgO. After the microsphere structure breaks at the initial stage of pyrolysis, its fragments act as "seeds" to guide the nucleation and growth of MgO nanosheets, and the collapse of the microsphere shell forms a macroporous framework to provide space support for the flower-like structure; compared with traditional flaky precursors, the rupture of the microspheres is more likely to form dispersed nanosheets to avoid interlayer stacking; the adsorption of SO4 2- in the preparation of the precursor inhibits two-dimensional flaky growth and promotes the formation of microspheres; the residual sulfate radical (SO4 2- ) in the precursor reacts with KOH to generate K2SO4, and part of the sulfur enters the MgO lattice in a doped form, forming oxygen vacancies or surface defects, enhancing the surface activity of the material.

[0013] When using potassium hydroxide in combination with a magnesium oxide precursor as described above, compared with using potassium hydroxide or the magnesium oxide precursor alone, when the microsphere precursor is pyrolyzed, CO2 and H2O are released, which synergistically acts with the H2 generated by KOH to form hierarchical pores on the surface of the biochar (macropores come from the collapse of microspheres, and mesopores / micropores are formed by gas etching), and the specific surface area increases several times compared to the original biochar; the precursor microspheres decompose into MgO nanoparticles in the initial stage of pyrolysis (300 - 500 °C), and at the same time, the rapid release of internal CO2 and H2O causes the microsphere shell to rupture. After rupture, the fragments undergo epitaxial growth in the alkaline molten environment of KOH (KOH is in a molten state at high temperatures), and MgO grows along specific crystal planes (such as the (200) plane) to form nanosheets; the molten KOH wraps the MgO nanoparticles, reducing particle agglomeration at high temperatures and promoting the uniform anchoring of nanosheets on the biochar surface; K in the molten KOH + is adsorbed on the MgO crystal plane, inhibiting isotropic growth and promoting the formation of two-dimensional nanosheets.

[0014] To further enhance the adsorption of heavy metals, the mass ratio of the magnesium oxide precursor to the coconut shell biochar is (1 - 3):10. The inventors found in the experiment that when the usage amount of the magnesium oxide precursor exceeds 30% of the coconut shell biochar, it will affect the synergistic effect with potassium hydroxide, thereby reducing the adsorption of heavy metals. Further preferably, the mass ratio of the magnesium oxide precursor to the coconut shell biochar is 1:5.

[0015] To further enhance the synergistic promotion effect, the mass ratio of the magnesium oxide precursor to potassium hydroxide is (1 - 3):30. Further preferably, the mass ratio of the magnesium oxide precursor to potassium hydroxide is 1:15.

[0016] To further improve the synergistic promotion effect with potassium hydroxide, when preparing the magnesium oxide precursor, the mass ratio of magnesium sulfate heptahydrate to urea is 1:3, the hydrothermal reaction temperature is 90 - 100 °C, and the reaction time is 8 - 12 h.

[0017] To improve the adsorption effect of the obtained composite material on heavy metals, when roasting the mixed material, the heating rate of the tube furnace is 8 - 10 °C / min, the roasting temperature is 800 °C, and the roasting time is 1.5 - 2 h.

[0018] The above washing is carried out by washing with ethanol and water in sequence, and the drying is carried out at 50 - 60 °C for 5 - 6 h.

[0019] The above method for preparing coconut shell biochar is: crushing the coconut shell, passing it through a 60 - 70 mesh sieve, placing it in a tube furnace, roasting it in a nitrogen atmosphere and naturally cooling to obtain the coconut shell biochar.

[0020] To improve the adsorption performance of the obtained composite material for heavy metals, when preparing coconut shell biochar, the heating rate of the tubular furnace is 3 - 5 °C / min, the calcination temperature is 500 - 550 °C, and the calcination time is 60 - 90 min.

[0021] The hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material of the present application can be used for water pollution treatment and can effectively adsorb heavy metals in sewage, etc.

[0022] The hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material of the present application is preferably used for the adsorption of cadmium and / or lead.

[0023] The novel hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material of the present application for heavy metal ions Cd 2+ 、Pb 2 + shows good adsorption performance. Among them, the maximum adsorption capacity for Cd 2+ is 379.5 mg / L, and the maximum adsorption capacity for Pb 2+ is 579.5 mg / L.

[0024] Technologies not mentioned in the present invention shall refer to the prior art.

[0025] The novel hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material of the present invention is loaded with hierarchical porous flower-like magnesium oxide and active functional groups, has rich surface active sites and electron capture ability, promotes the adsorption of heavy metal ions in wastewater by the composite material, and expands the adsorption capacity of the composite material for heavy metal ions; the present invention uses natural biomass resource coconut shell as raw material, not only develops a biochar with fast and efficient adsorption, but also through the synergy of precursor morphology innovation and KOH activation, breaks through the limitation of traditional flaky templates, provides a new idea for the development of multifunctional carbon-based composite materials, and also provides a new way for the high-value utilization of coconut shell resources. The synthesis process is simple and conforms to the current concept of green and low-cost. Description of the Drawings

[0026] Figure 1 is the SEM / EDS diagram of coconut shell biochar (BC) and the novel hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material (2-MBC) in the embodiments of the present invention.

[0027] Figure 2 is the nitrogen adsorption-desorption isotherm diagram of coconut shell biochar (BC) and the novel hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material (2-MBC) in the embodiments of the present invention.

[0028] Figure 3It is the infrared spectrum diagram of coconut shell biochar (BC) and the novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material (2-MBC) in the embodiments of the present invention.

[0029] Figure 4 It is the adsorption kinetics diagram of coconut shell biochar and the novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material for heavy metal cadmium ions in Examples (1-3) of the present invention.

[0030] Figure 5 It is the adsorption kinetics diagram of coconut shell biochar and the novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material for heavy metal lead ions in Examples (1-3) of the present invention.

[0031] Figure 6 It is the isothermal adsorption diagram of the novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material (2-MBC) for cadmium ions in Example 4 of the present invention.

[0032] Figure 7 It is the isothermal adsorption diagram of the novel hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material (2-MBC) for lead ions in Example 4 of the present invention. Detailed implementation manners

[0033] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited only to the following embodiments.

[0034] In each example, if the temperature is not specifically stated, it is carried out at room temperature (15-25 °C). If the stirring speed is not specifically stated, it is carried out at 200 r / min.

[0035] Example 1

[0036] Step 1: Add 2 g of MgSO4·7H2O and 6 g of urea to 40 mL of deionized water, and stir vigorously for 10 min (500 rpm / min). Then transfer it to a 100 mL conical flask, seal it, and heat it at 100 °C for 720 min. Centrifuge to collect the white precipitate, wash the residual liquid on the surface of the precipitate with deionized water, and dry it at 60 °C to obtain the magnesium oxide precursor ((MgCO3·Mg(OH)2·xH2O)).

[0037] Step 2: Crush the coconut shell, pass it through a 70-mesh sieve, place it in a tube furnace, heat it to 550 °C at a rate of 5 °C / min, calcine it in a nitrogen atmosphere for 2 h, and then cool it naturally to prepare the coconut shell biochar, denoted as BC.

[0038] Step 3: Take 10 g of coconut shell biochar and 30 g of KOH and add them to 50 mL of deionized water. Stir vigorously (500 rpm / min) and simultaneously add 1 g of magnesium oxide precursor. After continuously stirring (500 rpm / min) for 30 min, transfer the obtained material into a beaker and heat it at a constant temperature of 90 °C until it is dried to a constant weight to obtain a mixed material. Place the mixed material in a tubular furnace under a nitrogen atmosphere and heat it to 800 °C at a rate of 10 °C / min, and then keep it at a constant temperature of 800 °C for 2 h, and naturally cool it to room temperature in the nitrogen atmosphere. Finally, wash and filter it successively with 500 mL of ethanol and 500 mL of water, and dry it at 60 °C for 6 h to prepare a hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material, denoted as 1-MBC.

[0039] Step 4: Test the adsorption kinetics performance of the hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material:

[0040] Use the composite material to remove heavy metal ions in wastewater. Add 25 mL of heavy metal solution (aqueous CdCl2 solution and aqueous Pb(NO3)2 solution) to a test tube containing 25 mg of 1-MBC. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removed 85.2% of heavy metal cadmium ions (the initial concentration of cadmium ions is 16 mg / L), and the adsorption equilibrium time is 15 min. After adsorption equilibrium, 98.9% of heavy metal lead ions (the initial concentration of lead ions is 80 mg / L) were removed, and the adsorption equilibrium time is 10 min.

[0041] Example 2

[0042] The preparation of the magnesium oxide precursor and coconut shell biochar refers to Example 1.

[0043] Take 10 g of coconut shell biochar and 30 g of KOH and add them to 50 mL of deionized water. Stir vigorously (500 rpm / min) and simultaneously add 2 g of magnesium oxide precursor. After continuously stirring (500 rpm / min) for 30 min, transfer the above solution into a beaker and heat it at a constant temperature of 90 °C until it is dried to a constant weight to obtain a mixed material. Place the mixed material in a tubular furnace under a nitrogen atmosphere and heat it to 800 °C at a rate of 10 °C / min, and then keep it at a constant temperature of 800 °C for 2 h, and naturally cool it to room temperature in the nitrogen atmosphere. Finally, wash and filter it successively with 500 mL of ethanol and 500 mL of water, and dry it at 60 °C for 6 h to prepare a hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material, denoted as 2-MBC. The scanning electron microscope image, nitrogen adsorption-desorption curve graph and infrared spectrum graph are as Figures 1-3 shown. It can be seen from Figure 1 this that a porous hierarchical flower-like layered nanostructure formed by the self-assembly of numerous MgO nanosheets is formed on the surface of 2-MBC, and from Figure 2It can be seen that the nitrogen adsorption / desorption isotherm of 2-MBC shows a typical type-IV isotherm in the relative pressure range of 0.2 to 1.0, indicating the presence of mesopores on the surface of 2-MBC. The pore size distribution ( Figure 2 Illustration) further confirms the mesoporous characteristics. The BET specific surface area of 2-MBC is as high as 975.3600 m 2 / g. The above results are due to the combined use of potassium hydroxide and magnesium oxide precursor. When the microsphere precursor is pyrolyzed, CO2 and H2O are released, which synergistically act with H2 generated by KOH, resulting in the formation of hierarchical pores on the surface of the biochar (macropores come from the collapse of microspheres, and mesopores / micropores are formed by gas etching), and the specific surface area increases several times compared with the original biochar. From Figure 3 it can be seen that the stretching vibration of MgO is around 730 cm -1 , indicating that magnesium oxide has been loaded onto the biochar, which is also confirmed by the SEM / EDS data.

[0044] Adsorption kinetic performance test of hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite:

[0045] The composite material was used to remove heavy metal ions from wastewater. 25 mL of heavy metal solution was added to a test tube containing 25 mg of 1-MBC. Under the condition that the adsorption time was 0 - 720 min, 88.8% of heavy metal cadmium ions (the initial concentration of cadmium ions was 16 mg / L) were removed after adsorption equilibrium, and the adsorption equilibrium time was 15 min. 99.5% of heavy metal lead ions (the initial concentration of lead ions was 80 mg / L) were removed after adsorption equilibrium, and the adsorption equilibrium time was 10 min.

[0046] Example 3

[0047] The preparation of magnesium oxide precursor and coconut shell biochar was referred to Example 1.

[0048] 10 g of coconut shell biochar and 30 g of KOH were added to 50 mL of deionized water, and stirred vigorously (500 rpm / min). At the same time, 3 g of magnesium oxide precursor was added. After continuous stirring (500 rpm / min) for 30 min, the above solution was transferred to a beaker and heated at a constant temperature of 90 °C until dry and constant weight to obtain a mixed material. The mixed material was placed in a tubular furnace under a nitrogen atmosphere and heated to 800 °C at a rate of 10 °C / min, and then heated at 800 °C for 2 h, and naturally cooled to room temperature in a nitrogen atmosphere. Hierarchical porous flower-like magnesium oxide modified coconut shell biochar was obtained. Finally, it was washed and filtered successively with 500 mL of ethanol and 500 mL of water, and dried at 60 °C for 6 h to prepare a hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite, denoted as 3-MBC.

[0049] Adsorption kinetic test of hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite:

[0050] The composite material is used to remove heavy metal ions from wastewater. 25 mL of heavy metal solution is added to a test tube containing 25 mg of 1-MBC. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removes 85.2% of cadmium ions (the initial concentration of cadmium ions is 16 mg / L), the adsorption equilibrium time is 15 min, and after adsorption equilibrium, it removes 90% of lead ions (the initial concentration of lead ions is 80 mg / L), and the adsorption equilibrium time is 10 min.

[0051] Comparative Example 1

[0052] Coconut shell biochar is denoted as BC and used as Comparative Example 1.

[0053] From Figures 4-5 It can be seen that when the composite material is used to remove heavy metal ions from wastewater, 25 mL of heavy metal solution is added to a test tube containing 25 mg of BC. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removes 48% of cadmium ions (the initial concentration of cadmium ions is 16 mg / L), the adsorption equilibrium time is 15 min, and after adsorption equilibrium, it removes 47.5% of lead ions (the initial concentration of lead ions is 80 mg / L), and the adsorption equilibrium time is 10 min.

[0054] Comparative Example 2

[0055] The difference from Example 2 is that the magnesium oxide precursor is replaced with magnesium hydroxide, and the rest are referred to Example 2.

[0056] The composite material is used to remove heavy metal ions from wastewater. 25 mL of heavy metal solution is added to a test tube containing 25 mg of the composite material. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removes 58% of cadmium ions (the initial concentration of cadmium ions is 16 mg / L), the adsorption equilibrium time is 20 min, and after adsorption equilibrium, it removes 59.8% of lead ions (the initial concentration of lead ions is mg / L), and the adsorption equilibrium time is 30 min.

[0057] Comparative Example 3

[0058] The difference from Example 2 is that the magnesium oxide precursor is replaced with magnesium oxide, and the rest are referred to Example 2.

[0059] The composite material is used to remove heavy metal ions from wastewater. 25 mL of heavy metal solution is added to a test tube containing 25 mg of the composite material. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removes 51% of cadmium ions (the initial concentration of cadmium ions is 16 mg / L), the adsorption equilibrium time is 20 min, and after adsorption equilibrium, it removes 56.8% of lead ions (the initial concentration of lead ions is 80 mg / L), and the adsorption equilibrium time is 20 min.

[0060] Comparative Example 4

[0061] The difference from Example 2 is that the magnesium oxide precursor is omitted, and the rest are referred to Example 2.

[0062] The composite material is used to remove heavy metal ions from wastewater. 25 mL of heavy metal solution is added to a test tube containing 25 mg of the composite material. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removes 50.1% of cadmium ions (the initial concentration of cadmium ions is 16 mg / L), the adsorption equilibrium time is 15 min, and after adsorption equilibrium, it removes 55.6% of lead ions (the initial concentration of lead ions is 80 mg / L), and the adsorption equilibrium time is 20 min.

[0063] Comparative Example 5

[0064] The difference from Example 2 is that 30 g of KOH is replaced by 30 g of Mg(OH)2, and at the same time the magnesium oxide precursor is omitted, and the rest are referred to Example 2.

[0065] The composite material is used to remove heavy metal ions from wastewater. 25 mL of heavy metal solution is added to a test tube containing 25 mg of the composite material. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removes 49.1% of cadmium ions (the initial concentration of cadmium ions is 16 mg / L), the adsorption equilibrium time is 15 min, and after adsorption equilibrium, it removes 50.3% of lead ions (the initial concentration of lead ions is 80 mg / L), and the adsorption equilibrium time is 10 min.

[0066] Comparative Example 6

[0067] The difference from Example 2 is that 30 g of KOH is replaced by 30 g of Mg(OH)2, and the rest are referred to Example 2.

[0068] The composite material is used to remove heavy metal ions from wastewater. 25 mL of heavy metal solution is added to a test tube containing 25 mg of the composite material. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removes 60.2% of cadmium ions (the initial concentration of cadmium ions is 16 mg / L), the adsorption equilibrium time is 15 min, and after adsorption equilibrium, it removes 65.9% of lead ions (the initial concentration of lead ions is 80 mg / L), and the adsorption equilibrium time is 10 min.

[0069] Comparative Example 7

[0070] Pretreat the biomass with sodium carbonate, activate the biochar with magnesium nitrate and magnesium acetate, and apply microwave action. The operation steps are as follows:

[0071] (1) Alkali degradation of biomass: Wash the coconut shell, dry it, and crush it into powder for standby; add 2 g of coconut shell powder to 30 mL of 0.5 mol / L sodium carbonate solution, stir and react at 80 °C for 6 hours, wash it to neutral, and dry it to obtain the biomass powder after alkali pretreatment;

[0072] (2) Microwave foaming: Dissolve 2.13 g of magnesium nitrate and 1.8 g of magnesium acetate in 10 mL of water to obtain a magnesium nitrate / magnesium acetate aqueous solution, m(Mg):m(biomass)=20:100. Mix the coconut shell powder after mixed alkali pretreatment with the magnesium nitrate / magnesium acetate aqueous solution to obtain a mixed slurry. Dry the mixed slurry to obtain a mixture, and microwave-treat the mixture for 10 minutes with a microwave power of 800 W to obtain sponge biomass;

[0073] (3) In-situ oxidation pyrolysis of magnesium nitrate: Put the obtained sponge biomass into a pyrolysis furnace at 650 °C, pyrolyze it at high temperature in an inert gas atmosphere for 1 hour, and the heating rate is 5 °C / minute to obtain porous magnesium oxide modified biochar.

[0074] Adsorption kinetics test of porous magnesium oxide modified biochar

[0075] The composite material is used to remove heavy metal ions from wastewater. 25 mL of heavy metal solution is added to a test tube containing 25 mg of the composite material. Under the condition that the adsorption time is 0 - 720 min, after adsorption equilibrium, the composite material removes 68.2% of cadmium ions (the initial concentration of cadmium ions is 16 mg / L), the adsorption equilibrium time is 25 min, and after adsorption equilibrium, it removes 70.4% of lead ions (the initial concentration of lead ions is 74 mg / L), and the adsorption equilibrium time is 20 min.

[0076] Example 4

[0077] The preparation of the hierarchical porous flower-like magnesium oxide modified coconut shell biochar composite material refers to Example 2.

[0078] Testing the isothermal adsorption performance of the composite material:

[0079] The composite material is used to remove heavy metal ions from wastewater. 50 mL of heavy metal solution is added to a test tube containing 25 mg of 2-MBC. As Figures 6-7 shown, under the condition that the adsorption time is 24 h, after adsorption equilibrium, the maximum adsorption capacity of the composite material for heavy metal cadmium ions (600 mg / L) is 397.5 mg / g, and the maximum adsorption capacity for heavy metal lead ions (600 mg / L) is 579.5 mg / g.

Claims

1. A preparation method of a hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite, characterized in that: It includes the following steps: uniformly mix coconut shell biochar, potassium hydroxide, magnesium oxide precursor and water, and dry to obtain a mixed material; place the mixed material in a tubular furnace, calcine in a nitrogen atmosphere and cool naturally, wash and dry to prepare a hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material; The preparation method of the magnesium oxide precursor is: dissolve magnesium sulfate heptahydrate and urea in water, stir and mix, then pour into a sealed container for hydrothermal reaction to prepare the magnesium oxide precursor.

2. The preparation method according to claim 1, wherein: The mass ratio of the magnesium oxide precursor to the coconut shell biochar is (1-3):

10.

3. The preparation method according to claim 1 or 2, characterized in that: The mass ratio of the magnesium oxide precursor to potassium hydroxide is (1-3):

30.

4. The preparation method according to claim 1 or 2, characterized in that: The mass ratio of magnesium sulfate heptahydrate to urea is 1:3, the hydrothermal reaction temperature is 90-100 °C, and the reaction time is 8-12 h.

5. The preparation method according to claim 1 or 2, characterized in that: When calcining the mixed material, the heating rate of the tubular furnace is 8-10 °C / min, the calcination temperature is 800 °C, and the calcination time is 1.5-2 h.

6. The preparation method according to claim 1 or 2, characterized in that: Washing is successively with ethanol and water, and drying is at 50-60 °C for 5-6 h.

7. The preparation method according to claim 1 or 2, characterized in that: The preparation method of the coconut shell biochar is: crush the coconut shell, pass through a 60-70 mesh sieve, place it in a tubular furnace, calcine in a nitrogen atmosphere and cool naturally to prepare the coconut shell biochar.

8. The preparation method according to claim 7, characterized in that: When preparing the coconut shell biochar, the heating rate of the tubular furnace is 3-5 °C / min, the calcination temperature is 500-550 °C, and the calcination time is 60-90 min.

9. A hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material prepared by the preparation method according to any one of claims 1-8.

10. Application of the hierarchically porous flower-like magnesium oxide modified coconut shell biochar composite material according to claim 9, characterized in that: It is used for water pollution treatment and / or for the adsorption of cadmium and / or lead.

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