Amino acid modified biochar as well as preparation method and application thereof

Abstract

The invention relates to amino acid modified biochar as well as a preparation method and application thereof, natural amino acid is taken as a modifier (arginine or lysine), and integration of amino acid to a carbon skeleton through a covalent bond is completed in one step by adopting a low-temperature hydrothermal reaction (160-200 DEG C); efficient removal of heavy metal ions is realized through ultralow dosage (the solid-to-liquid ratio is (1: 100)-(1: 2000).

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of environmental functional materials and water pollution control technology, specifically involving an amino acid-modified biochar, its low-temperature preparation method, and its application in the adsorption and remediation of heavy metals in water. Background Technology

[0002] With the acceleration of industrialization and urbanization, heavy metal pollution in water has become a global environmental crisis. Toxic ions such as lead, cadmium, and chromium pose a serious threat to ecosystems and human health due to their persistent degradation, bioaccumulation, and strong carcinogenicity. Current heavy metal wastewater treatment technologies mainly fall into three categories: chemical methods (such as chemical precipitation and ion exchange), which are costly and prone to secondary sludge pollution; bioremediation methods (such as microbial adsorption), which are inefficient and have poor environmental adaptability; and adsorption methods, which have become the mainstream technology due to their ease of operation and low cost. Among these, modified biochar has become a research hotspot due to its wide availability of raw materials (agricultural waste) and large specific surface area. The limitations of existing modified biochar technologies are as follows:

[0003] Despite the progress made by modified biochar in the field of heavy metal adsorption, its core shortcomings still limit its large-scale application: 1. High energy consumption in the preparation process: Traditional pyrolysis requires high-temperature cracking at 400–700℃, with energy consumption accounting for more than 60% of the production cost; although hydrothermal methods can lower the temperature, most studies still require reaction conditions above 200℃ (e.g., polydopamine modification requires UV irradiation + pyrolysis). 2. Risk of secondary pollution: residual chemical activators: Acid modification (e.g., nitric acid, sulfuric acid) introduces acidic groups, but leads to pH imbalance in the effluent; metal modification (e.g., Mg, ZnCl2) poses a risk of ion leaching. 3. Complex modification process: Aminoation requires multiple nitration-reduction reactions (e.g., concentrated sulfuric acid / ammonia water treatment), generating toxic waste liquid. 4. Insufficient adsorption efficiency: Unmodified biochar has limited adsorption capacity for Pb. 2 +Adsorption capacity is generally <50mg / g; acid-modified biochar can increase capacity (e.g., nitric acid-modified pine char for Cd). 2 +Adsorption capacity increased by 30%), but selectivity was poor and cycle stability was low (efficiency decayed by more than 40% after <5 cycles).

[0004] Recent research has attempted to introduce amino acids into adsorbent materials, with current technologies focusing on chitosan-based materials (such as arginine-modified chitosan for Cu). 2+ Chitosan can be adsorbed, but its low mechanical strength and poor water stability make it unsuitable for industrial water flow conditions. Raw materials such as corn stalks have high porosity (>200 μm). 2While biochar possesses a rigid structure, the composite mechanism of amino acids and biochar remains unresolved. Current biochar modification technologies are limited by high energy consumption, secondary pollution, and adsorption capacity bottlenecks, while research on amino acid-modified materials is still confined to chitosan carriers and complex processes. This invention proposes for the first time a hydrothermal simultaneous modification technology for biochar using amino acids, constructing a bifunctional adsorption interface through a low-temperature one-step method, providing a novel pathway for the industrial application of green and efficient heavy metal adsorption materials. Summary of the Invention

[0005] The purpose of this invention is to provide an amino acid-modified biochar that uses natural amino acids (arginine or lysine) as modifiers and completes the integration of amino acids into the carbon skeleton through covalent bonds in one step using a low-temperature hydrothermal reaction (160–200℃); and achieves efficient removal of heavy metal ions with ultra-low dosage (solid-liquid ratio 1:100–1:2000).

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A low-temperature preparation method for amino acid-modified biochar includes the following steps:

[0008] (1) The biomass raw material is crushed to below 80 mesh to obtain biomass powder;

[0009] (2) The biomass powder and amino acid solution are mixed at a solid-liquid ratio of 1:20 to 1:60 g / mL, wherein the concentration of the amino acid solution is 0.05 to 0.5 mol / L;

[0010] (3) Stir magnetically at 25℃ for 0.5–24 h to form a mixed slurry;

[0011] (4) The mixed slurry is subjected to hydrothermal reaction at 100-200°C for 1-5 hours;

[0012] (5) After the reaction is complete, centrifuge and wash 15 to 20 times, dry at 60°C and pass through an 80-mesh sieve to obtain amino acid modified biochar.

[0013] As a preferred technical solution of the present invention, the amino acid is selected from monomeric amino acids such as arginine or lysine.

[0014] As a preferred technical solution of the present invention, the biomass raw material is corn stalk, coconut shell, chicken manure or microalgae.

[0015] As a preferred technical solution of the present invention, the hydrothermal reaction is carried out in a high-pressure reactor lined with polytetrafluoroethylene.

[0016] The present invention provides an amino acid-modified biochar, wherein the amino acids are covalently integrated into the carbon skeleton.

[0017] The amino acid-modified biochar provided by this invention is used to adsorb heavy metal ions in water, including Pb. 2+ Cd 2+ Cu 2+ Zn 2+ or Cr 6+ .

[0018] This invention provides a method for removing heavy metal ions from water, comprising:

[0019] The amino acid-modified biochar was added to water containing heavy metal ions at a solid-liquid ratio of 1:100 to 1:2000, and the treatment time was 10 to 120 minutes.

[0020] As a preferred technical solution of the present invention, the pH value of the treatment is 5-7 and the temperature is 25-40℃.

[0021] Beneficial effects

[0022] This invention uses monomeric amino acids (such as arginine) for direct modification. The amino acids are covalently integrated into the carbon skeleton through a one-step low-temperature hydrothermal method. Monomeric amino acid modification is a molecular-level modification, which is simpler and lower in cost. Moreover, the adsorption mechanism focuses on the synergistic effect of bifunctional groups.

[0023] This invention uses a low-temperature hydrothermal process to directly treat wet biomass without pre-drying, reducing energy consumption by more than 50% compared to traditional pyrolysis (>400℃).

[0024] The present invention can treat 50 mg / L Pb with a biological dosage of only 1:2000 (solid-liquid ratio). 2 + Wastewater removal rate >95%, cost reduction of 60% compared to commercial activated carbon (dosage 1:500). Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope image of corn stalk powder.

[0026] Figure 2 Scanning electron microscope image of arginine-modified corn stalk biochar.

[0027] Figure 3 The effect of dosage on lead ion removal rate.

[0028] Figure 4 The effect of temperature on lead ion removal rate.

[0029] Figure 5 The effect of pH on lead ion removal rate.

[0030] Figure 6 The effect of initial concentration on lead ion removal rate.

[0031] Figure 7 For cyclic stability experiments.

[0032] Figure 8 This is an XRD pattern.

[0033] Figure 9 This is an FTIR spectrum. Detailed Implementation

[0034] The present invention will be further described below through specific embodiments, and the beneficial effects of the present invention will be illustrated in conjunction with practice. However, these embodiments are only used to illustrate the features and advantages of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials, reagents and instruments used are conventional materials, reagents and instruments in the art, which can be obtained by those skilled in the art through commercial channels.

[0036] Example 1: Preparation of arginine-modified corn straw biochar.

[0037] Raw material pretreatment: Weigh 5.00 g of corn stalk powder and place it in a 2500 mL Erlenmeyer flask. Add 200 mL of 0.100 mol / L L-arginine solution. Stir continuously at 25 °C for 30 minutes using a constant temperature magnetic stirrer (500 rpm) until a homogeneous suspension is formed.

[0038] Hydrothermal carbonization: The mixture is transferred to a closed high-pressure reactor (material: SUS316L stainless steel, PTFE lining, 300mL volume) and reacted at a constant temperature of 160℃ for 120 minutes.

[0039] Product purification: After naturally cooling to room temperature, the reaction product was transferred to a 300 mL centrifuge tube and centrifuged at 7000 rpm and 25°C for 3 minutes using a high-speed refrigerated centrifuge (model CR22GIII, rotor angle type S100A3). The supernatant was discarded. Deionized water was added to the precipitate to the initial liquid level, and the above centrifugation operation was repeated 15 times, with fresh deionized water used each time.

[0040] Post-processing: The washed precipitate was transferred to a glass petri dish (150 mm in diameter) and placed in a vacuum drying oven at 60°C for 12 hours. The powder was then ground in an agate mortar until the particle size was ≤75 μm (corresponding to a 200-mesh standard sieve). The resulting powder was placed in a sealed sample bottle and stored in a drying oven at room temperature for subsequent experiments.

[0041] Example 2: Adsorption experiment of lead ions on arginine-modified corn straw biochar.

[0042] Measure 200 mL of a 20 mg / L lead ion solution into an Erlenmeyer flask. Adjust the pH of the solution to 6 using 1 mol / L HNO3 and NaOH solutions. Quickly add 0.2 g of arginine-modified hydrothermal corn straw charcoal. Simultaneously, immediately use a syringe to extract 3 mL of the reaction mixture and filter it through a 0.22 μm pore size filter membrane. Mix the filtered solution with 1 mL of 1 mol / L HNO3, transfer it to a test tube, clearly label it, and store it properly as the initial sample. Place the remaining mixture in a constant temperature shaker at 20 °C and a shaking rate of 150 rpm / min for 5 hours to ensure the adsorption reaction proceeds fully. After the reaction is complete, take another 3 mL of the sample, filter it through a 0.22 μm pore size filter membrane, mix it with 1 mL of HNO3, place it in a test tube, clearly label it, and store it. The obtained sample was placed in a digester and digested at a constant temperature of 110℃ for 2 hours. After digestion, the sample was transferred back to a test tube, and the sample solution was diluted to 3 mL with 1 mol / L HNO3. Finally, the lead ion content in the sample was accurately determined using inductively coupled plasma atomic absorption spectrometry (ICP-AES). The measured and compared results showed that the lead ion concentration before adsorption was 19.85 mg / L, and the lead ion content after adsorption was 2.93 mg / L. The adsorption capacity was calculated to be 16.93 mg / g using the adsorption capacity calculation formula, resulting in a removal rate of 85.26%, indicating that arginine-modified biochar has a certain adsorption efficiency for lead ions.

[0043] Analysis of Example 2 shows that the adsorption performance of corn stalks modified with amino acids for lead is improved to some extent compared with unmodified corn stalks. Among them, the corn stalk char modified with arginine shows a significant improvement in lead ion adsorption performance, with an adsorption capacity increase of 39.95% and a lead ion removal rate of 85.26%. This indicates that amino acid-modified pyrolysis treatment can effectively improve the adsorption capacity of corn stalk char for lead ions, which has positive significance in the application of heavy metal pollution control. The pores of this invention are more intact, as shown in SEM images. Figure 2 As shown.

[0044] Example 3: Effect of Arginine-Modified Corn Stalk Biochar Dosage on Lead Ion Adsorption

[0045] like Figure 3As shown, in a solution system with an initial lead ion concentration of 20 mg / L, when the dosage of arginine-modified corn straw biochar increased from 1 g / L to 3 g / L, the lead ion removal rate significantly increased from 85.26% to 95.67%. The biochar material of this invention exhibits a clear dose-response relationship. Its mechanism of action is as follows: with the increase of adsorbent dosage, the number of effective active sites increases exponentially. Under fixed initial concentration conditions, the increased abundance of active sites significantly enhances the mass transfer efficiency at the solid-liquid interface, allowing lead ions to be captured more fully.

[0046] Example 4: Adsorption patterns of lead ions on arginine-modified corn straw biochar at different temperatures.

[0047] In a 20 mg / L lead ion solution, this adsorption system exhibits a typical thermal enhancement effect in the temperature range of 10–40 °C. For example... Figure 4 The data show that the equilibrium removal rate increases monotonically with increasing temperature (10℃: 74.45% → 40℃: 92.55%, an increase of 24.3%). This confirms that the adsorption process is an endothermic controlled reaction. Increasing temperature not only promotes the diffusion of lead ions but also enhances the chemical bond strength between the active site and the target ion.

[0048] Example 5: Adsorption patterns of lead ions on arginine-modified corn straw biochar at different pH levels.

[0049] Figure 5 The study revealed the significant regulatory effect of solution pH on adsorption efficiency: the maximum removal rate of 85.26% was achieved at pH=6, while it plummeted to 4.55% and 14.39% under strong acid (pH=2) and strong alkaline (pH=10) conditions, respectively. This phenomenon can be attributed to: (1) the alkaline environment (pH>8) triggers the hydrolysis and precipitation of lead ions; (2) the protonation degree of biochar surface is intensified under acidic conditions (pH<4), resulting in electrostatic repulsion with lead ions; (3) under neutral conditions, the abundant oxygen-containing functional groups (-COOH, -OH) achieve efficient adsorption through ion exchange and surface complexation, and the pH range is broadened to 4-8 through carboxyl compensation.

[0050] Example 6. Adsorption pattern of lead ions on arginine-modified corn straw biochar at different initial concentrations.

[0051] like Figure 6 As shown, when the initial lead ion concentration increased from 10 mg / L to 200 mg / L, the removal rate exhibited a typical two-stage decline characteristic: a slow decrease in the low concentration range (10–50 mg / L) (from 89.82% to 45.73%), and a sharp decrease to 15.54% in the high concentration range (100–200 mg / L). This result confirms that the modification process effectively improved the density of active sites and binding energy.

[0052] Example 7: Cyclic stability experiment of arginine-modified corn straw biochar.

[0053] like Figure 7 As shown, by establishing an adsorption-desorption dynamic equilibrium system (adsorption conditions: 20℃, pH=6, 150rpm; desorbent: 1mol / L HNO3), and through low-temperature processing and small molecule modification, the material still retains 69.9% of its initial adsorption efficiency after 5 cycles, demonstrating its excellent mechanical stability and chemical reversibility.

[0054] Example 8: X-ray diffraction (XRD) analysis of arginine-modified corn straw biochar.

[0055] like Figure 8 As shown, XRD analysis of the materials before and after modification revealed the same (002) diffraction peak at 2θ = 23°, corresponding to the disordered glassy carbon polymer of cellulose. This indicates that the original state of the corn stalks was not destroyed after modification, but the increased crystal abundance means that more active sites are exposed on the surface, confirming that the modified material can improve the adsorption efficiency for lead ions.

[0056] Example 9: Fourier Transform Infrared (FTIR) Analysis of Arginine-Modified Corn Stalk Biochar

[0057] FTIR analysis ( Figure 9 The modified material was revealed to be at 1623 cm⁻¹ -1 A new characteristic absorption peak appears, attributed to the C=N stretching vibration of the arginine guanidine group; simultaneously, the antisymmetric stretching vibration peak of the carboxyl group (-COOH) is observed (1730 cm⁻¹). -1 The increased intensity indicates that arginine modification not only introduces specific functional groups, confirming that arginine is covalently integrated into the carbon skeleton, but also exposes more inherent oxygen-containing groups through oxidation, providing abundant coordination binding sites for lead ions.

[0058] Example 10

[0059] The difference between this embodiment and Embodiment 1 is that L-arginine is replaced with lysine.

[0060] Example 11

[0061] The difference between this embodiment and Embodiment 1 is that L-arginine is replaced with glutamic acid.

[0062] Example 12

[0063] The difference between this embodiment and Embodiment 1 is that the solid-liquid ratio of the biomass powder to the amino acid solution is 1:60 g / mL.

[0064] Example 13

[0065] The difference between this embodiment and Embodiment 1 is that the solid-liquid ratio of the biomass powder to the amino acid solution is 1:20 g / mL.

[0066] Example 14

[0067] The difference between this embodiment and Embodiment 1 is that the concentration of the amino acid solution is 0.05 mol / L.

[0068] Example 15

[0069] The difference between this embodiment and Embodiment 1 is that the concentration of the amino acid solution is 0.5 mol / L.

[0070] Example 16

[0071] The difference between this embodiment and Embodiment 1 is that the low-temperature hydrothermal temperature is 100℃.

[0072] Example 17

[0073] The difference between this embodiment and Embodiment 1 is that the low-temperature hydrothermal temperature is 200℃.

[0074] Example 18

[0075] The difference between this embodiment and Embodiment 1 is that the corn stalks are replaced with coconut shells.

[0076] Example 19

[0077] The difference between this embodiment and Embodiment 1 is that corn stalks are replaced with chicken manure.

[0078] Table 1 shows the adsorption capacity and removal rate of lead ions by different carbon materials.

[0079] Table 1

[0080]

[0081]

[0082] The preparation method of this invention uses monomeric amino acids (such as arginine) for direct modification. These amino acids have a small molecular weight (100–200 Da) and form physical-chemical grafts with biochar through functional groups such as amino (-NH2) and carboxyl (-COOH). Monomeric amino acid modification is a molecular-level modification, which is simpler and lower in cost. Moreover, the adsorption mechanism focuses on the synergistic effect of dual functional groups.

[0083] Existing methods involve modifying materials through chemical impregnation. This involves first preparing biochar materials to form a porous structure, and then using the impregnation and the already formed porous structure to adsorb some functional groups from amino acids, thus giving the resulting material certain functions. However, the prepared material is unstable, and the adsorbed functional groups are prone to detachment. In this invention, amino acids are reacted with corn stalks via a hydrothermal reaction, resulting in a more stable material. This is because of the hydrothermal oxidation process, and in this application, the arginine loading is not simply achieved through adsorption, but rather through a carbon skeleton linkage.

[0084] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A low-temperature preparation method for amino acid-modified biochar, characterized in that, Includes the following steps: (1) The biomass raw material is crushed to below 80 mesh to obtain biomass powder; (2) The biomass powder and amino acid solution are mixed at a solid-liquid ratio of 1:20 to 1:60 g / mL, wherein the concentration of the amino acid solution is 0.05 to 0.5 mol / L; (3) Stir magnetically at 25℃ for 0.5–24 h to form a mixed slurry; (4) The mixed slurry is subjected to hydrothermal reaction at 100-200°C for 1-5 hours; (5) After the reaction is complete, centrifuge and wash 15 to 20 times, dry at 60°C and pass through an 80-mesh sieve to obtain amino acid modified biochar.

2. The preparation method according to claim 1, characterized in that: The amino acid is selected from arginine or lysine.

3. The preparation method according to claim 1, characterized in that: The biomass raw materials are corn stalks, coconut shells, chicken manure, or microalgae.

4. The preparation method according to claim 1, characterized in that: The hydrothermal reaction is carried out in a high-pressure reactor lined with polytetrafluoroethylene.

5. An amino acid-modified biochar, characterized in that: The amino acid is prepared by the method described in any one of claims 1 to 4 and is covalently integrated into the biochar via a carbon skeleton.

6. The application of the amino acid-modified biochar according to claim 5, characterized in that: Used for adsorbing heavy metal ions in water, including Pb 2+ Cd 2+ Cu 2+ Zn 2+ or Cr 6+ .

7. A method for removing heavy metal ions from water, characterized in that, include: The amino acid-modified biochar according to claim 5 or 6 is added to water containing heavy metal ions at a solid-liquid ratio of 1:100 to 1:2000, and the treatment time is 10 to 120 minutes.

8. The method according to claim 7, characterized in that: The treatment involves a pH value of 5–7 and a temperature of 25–40°C.

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