Adsorption-enhanced preparation method of biomass tar modified flash graphene

Abstract

The invention relates to the technical field of graphene, and discloses an adsorption-enhanced preparation method of biomass tar modified flash graphene, which comprises the following steps: mixing biomass tar with a nitrogen source and an iron source, and pretreating to obtain mixed slurry; freeze-drying the mixed slurry to obtain a dried sample; sequentially carrying out heating treatment on the dried sample in an inert gas atmosphere, heating to a set carbonization temperature at a specific heating rate, and carrying out heat preservation for a preset time, so as to obtain a tar carbon precursor; and carrying out flash Joule heat treatment on the tar carbon precursor. The modified flash evaporation graphene is prepared by taking the biomass tar as a raw material, and high-value utilization of the biomass tar is realized, so that the problem of environmental pollution caused by direct discharge or simple treatment of the biomass tar as a waste is solved, high-value utilization of the biomass tar is realized, and potential harm of a traditional treatment mode to the environment is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of graphene, in particular to an adsorption-enhanced preparation method of biomass tar modified flash vaporized graphene. Background Art

[0002] With the acceleration of global industrialization, heavy metal pollution has become one of the major environmental challenges. Heavy metal ions such as lead, cadmium, and mercury are widely present in industrial wastewater. They are highly toxic, easily accumulate, and are difficult to degrade naturally. Once they enter water bodies, they are transmitted through the food chain, ultimately causing serious harm to human health. Traditional methods for treating heavy metal wastewater mainly include chemical precipitation, ion exchange, membrane separation, and adsorption. Among them, adsorption has attracted widespread attention due to its ease of operation, low cost, high efficiency, and ability to achieve deep removal of heavy metal ions.

[0003] As a new type of two-dimensional nanomaterial, graphene possesses a high specific surface area, excellent mechanical properties, good thermal and chemical stability, and a rich array of surface functional groups, giving it enormous potential in the field of adsorption. However, most current graphene preparation methods suffer from high costs, complex processes, and severe environmental pollution. Common preparation methods include chemical vapor deposition (CVD), redox methods, and mechanical exfoliation. CVD requires harsh conditions such as high temperature and high vacuum, requiring high equipment requirements and high costs. While the redox method is relatively simple to operate, the strong oxidants and reducing agents used can pollute the environment. Mechanical exfoliation has an extremely low yield, making it difficult to apply on a large scale.

[0004] Biomass tar is a byproduct produced during the thermochemical conversion of biomass. It is mainly composed of various organic compounds, including aromatic hydrocarbons such as benzene, toluene, and naphthalene, as well as oxygen-containing organic compounds such as phenols, alcohols, and aldehydes. Traditional methods for processing biomass tar mainly separate it into light oil, heavy oil and other products through physical separation or simple chemical conversion. However, these methods often fail to fully utilize the high carbon resources in the tar and are prone to secondary pollution during the processing process. Biomass tar has the characteristics of high carbon content, high oxygen content, high calorific value, high encapsulation, high foaming properties and low impurities. It is a good carbon source and can be used to prepare high-value-added carbon materials.

[0005] The existing technology for preparing high value-added materials using biomass tar has the following deficiencies:

[0006] First, although studies have recognized that biomass tar contains rich carbon resources, due to the limitations of traditional process technology, the utilization of tar mostly remains at the level of simple physical separation or production of low-value-added chemical products, failing to fully utilize its high-carbon characteristics and renewable advantages. It is difficult to achieve high-value utilization of biomass tar and cannot meet the current requirements for resource recycling and sustainable development.

[0007] Secondly, traditional methods for preparing graphene have numerous limitations. Chemical vapor deposition relies on high temperatures and pressures, resulting in high costs; redox methods use large amounts of chemical reagents, causing environmental pollution; and mechanical exfoliation methods have extremely low yields, making them difficult to scale up. These limitations restrict the large-scale application of graphene, particularly in cost-sensitive environmental remediation applications.

[0008] Third, in the development of adsorption materials, existing graphene-based adsorbents suffer from insufficient surface active sites, poor selectivity for heavy metal ion adsorption, and difficulty in recycling and reuse. This limits their adsorption efficiency and service life in practical applications, making it difficult to meet the demand for efficient, economical, and environmentally friendly removal of heavy metal wastewater.

[0009] In view of the above shortcomings of the existing technology, there is an urgent need for a method that can efficiently utilize biomass tar resources, is green and environmentally friendly, and can produce high-quality graphene adsorption materials on a large scale, so as to achieve high-value utilization of biomass tar and efficient treatment of heavy metal wastewater, and promote technological progress and sustainable development in related fields. Summary of the Invention

[0010] In view of the shortcomings of the existing technology, the present invention provides an adsorption-enhanced preparation method of biomass tar modified flash graphene, which solves the problems raised in the above background technology.

[0011] To achieve the above objectives, the present invention is implemented by the following technical solutions: a method for preparing biomass tar modified flash graphene by adsorption enhancement, comprising the following steps:

[0012] The biomass tar is mixed with a nitrogen source and an iron source, and pretreated to obtain a mixed slurry;

[0013] freeze-drying the mixed slurry to obtain a dry sample;

[0014] The dried sample is subjected to a heating treatment in sequence under an inert gas atmosphere, the temperature is raised to a set carbonization temperature at a specific heating rate and kept at the temperature for a predetermined time to obtain a tar carbon precursor;

[0015] The tar-carbon precursor is subjected to flash Joule heating treatment, and the tar-carbon precursor is instantly converted into modified flash graphene by adjusting the discharge voltage and discharge time.

[0016] Preferably, the biomass tar is a by-product produced during the thermochemical conversion of biomass, including tar produced during the gasification or pyrolysis of biomass.

[0017] Preferably, the nitrogen source is one or more of urea or disodium edetate, and the iron source is ferric chloride.

[0018] Preferably, the pretreatment comprises ultrasonically dispersing the biomass tar with the nitrogen source and the iron source at room temperature for 10-60 minutes, and then continuing to stir for 1-6 hours.

[0019] Preferably, the freeze-drying temperature is -40°C to -80°C, and the drying time is 12-48 hours.

[0020] Preferably, the heating rate is 5-10°C / min, the carbonization temperature is 700-900°C, and the predetermined insulation time is 1-3h.

[0021] Preferably, the flash Joule heat treatment is specifically as follows: placing the tar carbon precursor in a quartz tube, sealing both ends with graphite plugs, evacuating to a negative pressure state, connecting a DC power supply, charging through a capacitor bank to a set discharge voltage and then discharging instantly, the discharge voltage is 130-170V, and the discharge time is 0.1-1s.

[0022] Preferably, the method further comprises the step of testing the adsorption performance of the modified flash evaporated graphene, specifically, mixing the prepared modified flash evaporated graphene with a solution containing heavy metal ions to perform an adsorption reaction, and calculating the adsorption capacity and removal rate by measuring the concentration of heavy metal ions in the solution before and after adsorption.

[0023] Preferably, the heavy metal ions are one or more of lead ions, cadmium ions, copper ions or mercury ions.

[0024] The present invention provides a method for preparing biomass tar-modified flash-evaporated graphene by enhanced adsorption, which has the following beneficial effects:

[0025] 1. This invention utilizes biomass tar as a raw material to produce modified flash graphene, achieving high-value utilization of biomass tar. Converting it into high-value-added modified flash graphene not only solves the problem of biomass tar disposal but also avoids the environmental pollution of soil, water, and other areas caused by direct discharge or simple treatment of tar, thus providing significant environmental benefits. Furthermore, compared to traditional methods of producing graphene using fossil energy as raw material, this method utilizes renewable biomass resources, reducing dependence on non-renewable energy sources. This method is in line with the concept of sustainable development and helps promote the development of biomass energy resource technology and the construction of a low-carbon economy.

[0026] 2. The present invention modifies biomass tar by introducing nitrogen and iron sources during the preparation process, and combines this with flash Joule heating to produce modified flash-evaporated graphene with excellent adsorption properties. Nitrogen doping introduces abundant nitrogen-containing functional groups to the graphene surface, which can strongly coordinate with heavy metal ions, greatly enhancing the graphene's adsorption capacity for heavy metal ions. The addition of an iron source promotes the formation of magnetic nanoparticles, making the resulting graphene magnetic. This facilitates solid-liquid separation via an external magnetic field after adsorption, improving the adsorbent's recyclability and reuse rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of the present invention;

[0028] Figure 2 The tar carbon to Pb 2+ Isotherm adsorption curve;

[0029] Figure 3 The tar carbon to Pb 2+ Kinetic curve diagram;

[0030] Figure 4 1 is a Raman characterization image of flash graphene of different samples at different discharge times in an embodiment of the present invention;

[0031] Figure 5 This is the hysteresis loop diagram of the NFe10-800-0.2 sample in the embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] The embodiment of the present invention provides a method for preparing biomass tar modified flash graphene by adsorption enhancement, comprising the following steps:

[0034] Biomass tar is mixed with a nitrogen source and an iron source and pretreated to obtain a mixed slurry. Biomass tar is a byproduct produced during the thermochemical conversion of biomass, including tar produced during biomass gasification or pyrolysis. The nitrogen source is urea.

[0035] Specifically, biomass tar is a complex mixture produced during the thermochemical conversion of biomass (such as gasification or pyrolysis), containing a variety of organic compounds. Biomass tar is mixed with a nitrogen source (urea in this case) and an iron source, and pre-treated (such as ultrasonic dispersion and stirring) to allow the various components to fully contact and evenly disperse to form a mixed slurry. This mixing process facilitates subsequent reactions and processing steps, preparing for further conversion and modification of biomass tar.

[0036] The mixed slurry was freeze-dried to obtain a dry sample.

[0037] The dried sample is subjected to a heating treatment in sequence under an inert gas atmosphere, the temperature is raised to a set carbonization temperature at a specific heating rate and kept at this temperature for a predetermined time to obtain a tar carbon precursor;

[0038] Specifically, in an inert gas atmosphere (such as argon or nitrogen), the dried sample can be prevented from undergoing an oxidation reaction with oxygen during high-temperature treatment. By heating the dried sample to a set carbonization temperature at a specific heating rate and keeping it warm for a certain period of time, the dried sample can be carbonized to form a tar carbon precursor. This carbonization process is a key step in converting biomass tar into a carbon material with specific structure and properties, preparing for subsequent flash Joule heat treatment.

[0039] The tar-carbon precursor is subjected to flash Joule heating treatment, and the tar-carbon precursor is instantly converted into modified flash graphene by adjusting the discharge voltage and discharge time.

[0040] Specifically, flash Joule heating is a technology that uses high temperature and high pressure conditions generated by electric pulses to cause the material to undergo an instantaneous structural transformation. The tar carbon precursor is placed in a specific device (such as a quartz tube), sealed at both ends with graphite plugs, and evacuated to a negative pressure state. Then, a DC power supply is connected, and the capacitor bank is charged to a set discharge voltage and then discharged instantly. The tar carbon precursor is at high temperature and high pressure. By adjusting the discharge voltage and discharge time, the structure and properties of graphene can be controlled, thereby achieving modification and optimization of graphene.

[0041] The pretreatment process involved ultrasonically dispersing the biomass tar with a nitrogen source and an iron source at room temperature for 30 minutes, followed by stirring for 4 hours. Freeze-drying was performed at -60°C for 24 hours. The temperature was increased at a rate of 10°C / min, the carbonization temperature was 800°C, and the holding time was set to 3 hours.

[0042] Specifically, the purpose of ultrasonic dispersion and stirring is to thoroughly mix the biomass tar with the nitrogen source (urea) and iron source, ensuring uniform dispersion of the components and providing good contact conditions for subsequent reactions. Ultrasonic dispersion utilizes the cavitation effect of ultrasound to refine the particles in the mixture, improve mixing uniformity, and create a more uniform reaction environment for subsequent chemical reactions.

[0043] The purpose of freeze drying is to remove moisture from the mixed slurry to obtain a dry sample. Choosing a low temperature of -60°C to freeze dry the biomass tar prevents the organic components in the biomass tar from oxidizing or decomposing at high temperatures. It also prevents adverse reactions between the nitrogen and iron sources at high temperatures, ensuring the stability and activity of the precursor.

[0044] The flash Joule heat treatment is specifically as follows: the tar carbon precursor is placed in a quartz tube, both ends are sealed with graphite plugs, vacuumed to a negative pressure state, connected to a DC power supply, charged to a set discharge voltage through a capacitor bank, and then discharged instantly. The discharge voltage is 160 V and the discharge time is 0.2 s.

[0045] Specifically, flash Joule heating uses high temperature and high pressure conditions generated by electric pulses to instantly convert a tar-carbon precursor into modified flash graphene. This method can restructure the precursor in a very short time, forming graphene with a two-dimensional layered structure.

[0046] Parameter Selection: The quartz tube and graphite plug are chosen to provide a closed, high-temperature, and stable reaction environment. The graphite plug also serves as an electrode, facilitating electrical conduction. Evacuating to a negative pressure prevents interference from atmospheric oxygen and nitrogen, ensuring reaction stability and safety. The discharge voltage is 160V, and the discharge time is 0.2 seconds. This provides sufficient energy within a short period of time to rapidly heat the tar-carbon precursor to a high temperature and achieve structural transformation, while preventing excessive discharge that could lead to excessive growth or structural damage of graphene.

[0047] The method also includes testing the adsorption performance of the modified flash-evaporated graphene. Specifically, the modified flash-evaporated graphene is mixed with a solution containing heavy metal ions to perform an adsorption reaction. The adsorption capacity and removal rate are calculated by measuring the concentration of the heavy metal ions in the solution before and after adsorption. The heavy metal ions are lead ions.

[0048] Specifically, modified flash graphene with excellent adsorption properties was prepared by mixing biomass tar with nitrogen and iron sources, followed by pretreatment, freeze-drying, carbonization, and flash Joule heating. This method not only achieves high-value utilization of biomass tar but also reduces environmental pollution.

[0049] Graphene adsorbent Pb 2+ Adsorption experiments

[0050] The effects of initial lead concentration, adsorption contact time, adsorption temperature, initial pH, adsorbent dosage, and Na+ on adsorption capacity and lead removal efficiency were primarily investigated. The initial lead concentration ranged from 10 mg / L to 5000 mg / L, the adsorption contact time ranged from 1 min to 60 min, the adsorption ambient temperature ranged from 25°C to 45°C, the initial solution pH ranged from 2 to 7, and the adsorbent dosage ranged from 0.33 g / L to 1.67 g / L.

[0051] All experiments were repeated three times, and the average value of the three repeated measurements was used for data analysis. The measured concentration was calculated by the following formula to obtain the lead adsorption amount (q e , mg / g) and removal rate (η,%):

[0052] q e =V(C0-C e ) / m

[0053] η=(C0-C e ) / C0

[0054] Where: q e is the equilibrium adsorption capacity of lead, mg / g; η is the removal efficiency of lead, %; V is the volume of the initial solution, mL; C0 is the initial concentration of the lead solution, mg / L; C e is the equilibrium concentration of lead solution, mg / L; m is the mass of dry adsorbent, g.

[0055] Isothermal adsorption experiment:

[0056] Weigh 50 mg of the adsorbent into a centrifuge tube, and add 50 mL of lead solution of 10 mg / L, 40 mg / L, 70 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 300 mg / L, 500 mg / L, 750 mg / L, 1000 mg / L, 2000 mg / L, 3000 mg / L, 4000 mg / L, and 5000 mg / L, respectively. Cover the centrifuge tube and mark it. Place the centrifuge tube in a constant temperature oscillator set at 25°C and a speed of 150 rad / min. React for 60 minutes. Take the filtrate after filtering through a 0.22 μm pore size membrane, and measure the lead content in the filtrate using an ICP-OES tester.

[0057] The Langmuir isotherm adsorption model is as follows:

[0058]

[0059] The Freundlich isotherm adsorption model is as follows:

[0060] q e=k f C e 1 / n

[0061] Where: q e is the equilibrium adsorption capacity of lead, mg / g; q m is the maximum adsorption capacity, mg / g; C e is the equilibrium concentration, mg / L; k l is the Langmuir adsorption constant, L / mg; k f The unit of Freundlich adsorption constant is mg 1-n ·L n / g; n is the Freundlich index.

[0062] Adsorption kinetics experiments

[0063] 80 mg of the adsorbent was weighed into a centrifuge tube, and 80 mL of a 2000 mg / L lead solution was added. The tube was capped and labeled, and the tube was placed in a thermostatted oscillator set at 25°C and oscillated at 150 rad / min. Samples were taken at 2, 5, 10, 20, 40, 80, 120, 180, 280, 400, 580, 720, and 1440 minutes. The filtrate was filtered through a 0.22 μm pore size membrane, and the lead content in the filtrate was measured using an ICP-OES analyzer. The most common pseudo-first-order and pseudo-second-order kinetic models were selected to fit the adsorption data.

[0064] Pseudo-first-order kinetic model:

[0065] Adsorbent diffusion model: q t =k id t 1 / 2 +C

[0066] Pseudo-second-order kinetic model:

[0067] Where: q t is the unit lead adsorption capacity at contact time t (min), μg / g; q e is the equilibrium unit lead adsorption capacity, μg / g; k1 is the rate constant of the pseudo-first-order kinetic model, min -1 ;k id is the diffusion rate constant in the adsorbent, g·μg -1 min -1 ; C is a constant related to the thickness at the boundary, μg / g; k2 is the rate constant of the pseudo-second-order kinetic model, g·μg -1min -1 ; h0 is the initial adsorption rate, μg·g -1 min -1 .

[0068] Adsorption thermodynamics experiments

[0069] Weigh 80 mg of the adsorbent into a centrifuge tube, add 80 mL of a 2000 mg / L lead solution, cover the centrifuge tube and mark it, place the centrifuge tube in a constant temperature oscillator set at 25°C, 35°C, and 45°C, respectively, and oscillate at a speed of 150 rad / min. Samples were taken after 60 minutes, and the filtrate after filtering through a 0.22 μm pore size membrane was used to measure the lead content in the filtrate using an ICP-OES tester.

[0070] Arrhenius equation: lnk2 = lnA-E a / (RT)

[0071] Gibbs free energy change formula: ΔG 0 =-RTlnK D

[0072] Adsorption equilibrium constant formula: K D =q e / C e

[0073] Van't Hoff equation: lnK D =-ΔH 0 / (RT)+ΔS 0 / R

[0074] Where k2 is the rate constant of the pseudo-second-order kinetic model, g·μg -1 min -1 ; A is the pre-exponential factor of the Arrhenius formula; R is the universal gas constant, 8.314 J·mol -1 ·K -1 ; T is the reaction temperature, K; E a Adsorption reaction activation energy, kJ·mol -1 ;K D is the distribution coefficient of the adsorbent; C e is the outlet concentration of the reactor at adsorption equilibrium, μg / m 3 ; ΔH 0 is the enthalpy change, kJ·mol -1 ;ΔS 0 is the entropy change, J·mol -1 K -1 .

[0075] Raman scattering occurs when light passing through a transparent medium is scattered by molecules within the medium, causing a change in frequency. Raman spectroscopy analyzes the change in the energy of the reflected light to indicate the rotational and vibrational modes of the lattice or molecules within the medium. When ions and electrons within a material interact with incident photons, an inelastic scattering phenomenon, known as Raman spectroscopy, occurs.

[0076] Transmission electron microscopy (TEM) analysis involves projecting an accelerated and focused electron beam onto a very thin sample. The electrons collide with atoms in the sample, changing their direction and producing a three-dimensional angular scattering effect. The scattering angle depends on the density and thickness of the sample, resulting in images of varying brightness and darkness.

[0077] Scanning electron microscope analysis. Scanning electron microscopy uses a scanning beam of electrons to scan and image the sample, further observing the sample's surface morphology. It obtains various physical information about the sample based on the interaction between electrons and matter. The observation method of the test sample's surface morphology can be simply described as receiving, amplifying, and displaying the image of the information.

[0078] X-ray photoelectron spectroscopy. X-ray photoelectron spectroscopy uses X-rays to irradiate samples, causing the inner electrons or valence electrons of atoms or molecules to be excited and emitted. The electrons excited by photons are called photoelectrons. The energy of photoelectrons can be measured as the kinetic energy / binding energy (E b =h v Light Energy-E k The photoelectron spectrum can be plotted with kinetic energy (w - work function) as the horizontal axis and relative intensity (pulse / s) as the vertical axis, thereby obtaining relevant information about the sample.

[0079] X-ray diffraction analysis. X-ray diffraction is done by emitting X-rays with a wavelength on the same order of magnitude as the interatomic distance between atoms towards the sample to be tested. The rays irradiate the sample to produce diffraction, and the spatial distribution and intensity of the diffraction reflect the unit cell structure of the sample.

[0080] Fourier transform infrared spectroscopy. FTIR is an instrument used to analyze the structure and composition of substances. It uses the Fourier transform to convert infrared radiation absorbed by a substance into visible light signals for analysis. Different functional groups correspond to different infrared radiation absorption. Using Fourier transform infrared spectroscopy, the types and distribution of functional groups on the surface of different samples can be determined.

[0081] Nitrogen adsorption-desorption testing. The pore structure of the prepared graphene was characterized using a nitrogen adsorption / desorption instrument. Based on the isothermal adsorption / desorption results, the specific surface area, total pore volume, and average pore diameter were determined using the BET method.

[0082] Vibrating Sample Magnetometer Analysis. VSM can measure the magnetic properties of modified graphene. When the sample particle size is reduced to the nanometer scale, it exhibits superparamagnetism. Superparamagnetism can be identified by its temperature dependence, the magnetization-temperature curve.

[0083] Pb 2+ Adsorption experiments were conducted, and adsorption kinetics and isothermal adsorption analysis were performed simultaneously. The results were as follows: Figure 2 and Figure 3 As shown, the Pb content of NFe10-800 and NFe20-800 is compared with that of NFe0-800. 2+ The adsorption capacity is significantly improved, indicating that the introduction of Fe element has a significant effect on the adsorption of Pb 2+ The adsorption performance is positively affected by ferric chloride, which is because ferric chloride can be a pore-forming agent in the carbonization of biomass tar, giving the tar carbon a pore structure that is beneficial to adsorption.

[0084] Flash graphene of different samples at different discharge times (0.1s, 0.2s, 0.3s, 0.4s, 0.5s) was prepared and Raman characterization was performed. The results are shown in Figure 4 .

[0085] Depend on Figure 4 It can be seen that as the discharge time decreases, graphene obtains a larger 2D peak intensity, which is beneficial to I 2D / I G At the same time, compared with Tar-800 and NFe0-800, NFe10-800 and NFe20-800 have lower D peak intensity, which is beneficial to I D / I G is reduced, and graphene with smaller defects is obtained.

[0086] Depend on Figure 5 It can be seen that the hysteresis loop of NFe10-800-0.2 shows a typical S-shaped curve and exhibits superparamagnetism, with good recovery performance. The saturation magnetization intensity is about 90emu / g.

[0087] In summary, the preparation of modified flash graphene using biomass tar as a raw material achieves high-value utilization of biomass tar. Converting it into high-value-added modified flash graphene not only solves the problem of biomass tar disposal but also avoids the environmental pollution of soil and water bodies caused by direct discharge or simple treatment of tar, thus providing significant environmental benefits. Furthermore, compared to traditional methods of preparing graphene using fossil energy as raw materials, this method utilizes renewable biomass resources, reducing dependence on non-renewable energy sources. This is in line with the concept of sustainable development and will help promote the development of biomass energy resource technology and the construction of a low-carbon economy.

[0088] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing biomass tar modified flash graphene by adsorption enhancement, characterized in that: The following steps are involved: The biomass tar is mixed with a nitrogen source and an iron source, and pretreated to obtain a mixed slurry; freeze-drying the mixed slurry to obtain a dry sample; The dried sample is subjected to a heating treatment in sequence under an inert gas atmosphere, the temperature is raised to a set carbonization temperature at a specific heating rate and kept at the temperature for a predetermined time to obtain a tar carbon precursor; The tar-carbon precursor is subjected to flash Joule heating treatment, and the tar-carbon precursor is instantly converted into modified flash graphene by adjusting the discharge voltage and discharge time.

2. The adsorption-enhanced preparation method of biomass tar modified flash graphene according to claim 1, characterized in that: The biomass tar is a by-product produced during the thermochemical conversion of biomass, including tar produced during the gasification or pyrolysis of biomass.

3. The adsorption-enhanced preparation method of biomass tar modified flash graphene according to claim 1, characterized in that: The nitrogen source is one or more of urea and disodium edetate, and the iron source is ferric chloride.

4. The adsorption-enhanced preparation method of biomass tar modified flash graphene according to claim 1, characterized in that: The pretreatment comprises ultrasonically dispersing the biomass tar with the nitrogen source and the iron source at room temperature for 10-60 minutes, and then continuing to stir for 1-6 hours.

5. The adsorption-enhanced preparation method of biomass tar modified flash graphene according to claim 1, characterized in that: The freeze-drying temperature is -40°C to -80°C, and the drying time is 12-48 hours.

6. The adsorption-enhanced preparation method of biomass tar modified flash graphene according to claim 1, characterized in that: The heating rate is 5-10°C / min, the carbonization temperature is 700-900°C, and the predetermined insulation time is 1-3h.

7. The adsorption-enhanced preparation method of biomass tar modified flash graphene according to claim 1, characterized in that: The flash Joule heat treatment is specifically as follows: placing the tar carbon precursor in a quartz tube, sealing both ends with graphite plugs, evacuating to a negative pressure state, connecting a DC power supply, charging through a capacitor bank to a set discharge voltage and then discharging instantly, the discharge voltage is 130-170V, and the discharge time is 0.1-1s.

8. The adsorption-enhanced preparation method of biomass tar modified flash graphene according to claim 1, characterized in that: The method also includes the step of testing the adsorption performance of the modified flash-evaporated graphene, specifically, mixing the prepared modified flash-evaporated graphene with a solution containing heavy metal ions to perform an adsorption reaction, and calculating the adsorption capacity and removal rate by measuring the concentration of heavy metal ions in the solution before and after adsorption.

9. The adsorption-enhanced preparation method of biomass tar modified flash graphene according to claim 8, characterized in that: The heavy metal ions are one or more of lead ions, cadmium ions, copper ions or mercury ions.

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