Citric acid modified bagasse biochar, preparation method thereof and application of citric acid modified bagasse biochar in removal of malachite green in water

Abstract

The invention relates to the technical field of water treatment, in particular to citric acid modified bagasse biochar, a preparation method of the citric acid modified bagasse biochar and application of the citric acid modified bagasse biochar in removal of malachite green in water. The alkali-treated citric acid modified bagasse biomass charcoal is prepared by taking bagasse as a raw material and citric acid as a modifier through high-temperature oxygen-limited pyrolysis, the alkali-treated citric acid modified bagasse biomass charcoal is used for adsorbing organic dye malachite green in water, and the adsorption capacity can reach 1139 mg.g <-1 >.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, in particular to a citric acid-modified bagasse biochar, a preparation method thereof, and an application thereof in removing malachite green from water. Background Art

[0002] Malachite green is a widely used organic dye. It's not only a dye in the textile industry, but also an antibacterial agent and pesticide. However, due to its difficulty in degradation, high toxicity, and potential for water pollution, it is currently banned as a fishery drug in my country. Malachite green can also cause cell teratogenesis, carcinogenesis, and mutagenesis, and can have detrimental effects on the liver, kidneys, and other human systems, posing a health hazard.

[0003] In recent years, the preparation of biochar adsorption materials and their application in pollutant treatment have become a research hotspot in water pollution control. Biomass resources are typically processed into biochar as an adsorbent to remove pollutants from water. On the one hand, biochar has a well-developed pore structure, acid and alkali resistance, excellent electrical conductivity and chemical stability, and a large specific surface area, providing a large number of adsorption sites for pollutants. Furthermore, its surface is rich in active functional groups, which facilitates its modification. On the other hand, its preparation into adsorbents can not only solve water pollution problems, turning biomass waste into valuable resources, but also realize its resource utilization, reducing resource waste and environmental pollution.

[0004] Bagasse charcoal is simple to prepare and inexpensive. Using this agricultural waste, bagasse, to create composite materials, can recycle agricultural waste and help address waste treatment and disposal issues. Research on bagasse charcoal also contributes to the development of highly effective adsorbents for removing organic dyes from wastewater, alleviating water pollution and contributing to recycling and sustainable development. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for preparing citric acid-modified bagasse biochar and its application in removing malachite green in water.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: The first object of the present invention is to provide a method for preparing citric acid-modified bagasse biochar, comprising the following steps: S1. Soak and wash the bagasse with ultrapure water, dry it naturally in the sun, crush it into fine particles with a grinder, and put it into a sealed bag for drying and storage; S2, grinding the product obtained in step (1) and citric acid, mixing them evenly, performing high-temperature oxygen-limited pyrolysis, grinding the pyrolyzed sample, and packaging it for later use; S3. Place the product obtained in step (2) in a NaOH solution, stir, wash with deionized water until neutral, and dry to obtain alkali-treated modified sugarcane bagasse biochar, grind it evenly, and package it for dry storage.

[0007] Furthermore, the high-temperature calcination temperature in step (2) is 500-700°C. Calcination temperatures that are too low (<500°C) cannot effectively decompose the organic components and impurities in the precursor and cannot form biochar. Calcination temperatures that are too high (>700°C) may cause carbon loss, reduce the doping effect, and may also affect the specific surface area and activity of the material. The optimized calcination temperature range of 500-700°C can achieve the decomposition of the organic precursor and promote the formation of biochar.

[0008] Furthermore, the mass ratio of the product obtained in step (1) to citric acid is 5:(1.5-10). The amount of citric acid added is 50-150 mg. Under oxygen-limited conditions, cellulose, hemicellulose and lignin in sugarcane bagasse are pyrolyzed to form a biochar skeleton. Citric acid decomposes at high temperatures, releasing gas to form pores and forming a multi-level pore structure (micropores / mesopores). Therefore, citric acid is a source of increasing the specific surface area of ​​biochar, and its addition amount directly determines the specific surface area and pore size of the final product. If the addition amount is too low, fewer effective active functional groups are introduced, the surface charge is low, and it is impossible to form an effective adsorption site with the cationic group of malachite green. If the addition amount is too high, too many functional groups can be introduced, reducing the exposure of active sites and resulting in a decrease in the adsorption performance of the material.

[0009] Furthermore, in step (3), the addition ratio of sample to NaOH is 500 mg sample corresponding to 0.05 mol NaOH, and the concentration of NaOH solution is 1 mol·L -1 , Furthermore, the stirring time of the alkali treatment is 6 h.

[0010] The present invention also provides citric acid-modified bagasse biochar prepared by the method.

[0011] The present invention also provides the use of citric acid-modified bagasse biochar prepared by the method as an adsorbent in removing malachite green from water.

[0012] The present invention also provides a method for adsorbing malachite green on the citric acid-modified bagasse biochar, comprising the following steps: Take 20 mL of 20-200 mg·L -1 of malachite green solution in a beaker and add 0.2-0.4g∙L -1 The modified biochar was adjusted to a pH of 7.0–11.0 and incubated at a constant temperature of 25–40°C for 3 h. The filtrate was filtered and the absorbance was measured using a UV spectrophotometer. All experiments were performed three times under the same conditions, and the results were averaged.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses bagasse as raw material and citric acid as modifier, and conducts high-temperature oxygen-limited pyrolysis to obtain a new product with a bagasse / citric acid ratio of 1:1 and a concentration of 1 mol·L -1 Alkali-treated citric acid-modified bagasse biochar was prepared by NaOH treatment for 6 h and used to adsorb the organic dye malachite green in water with an adsorption capacity of 1139 mg·g -1 .

[0014] (1) Citric acid decomposes during high-temperature oxygen-limited pyrolysis to produce gases such as CO2, forming microporous / mesoporous hierarchical channels within the sugarcane bagasse charcoal skeleton. The modified pore size is increased, making it more suitable for the diffusion and mass transfer of macromolecular malachite green and preventing micropore blockage. Citric acid provides carboxyl groups, which are converted into oxygen-rich functional groups after high-temperature pyrolysis, enhancing surface polarity. NaOH solution removes ash and organic impurities, exposing more active sites and potentially generating a negatively charged surface.

[0015] (2) Under alkaline conditions, the modified carbon surface deprotonates to form —COO⁻ groups, which generate strong electrostatic attraction with the positively charged malachite green, and the adsorption capacity reaches a peak of 1139 mg / g. In an acidic environment (pH < 5), although the adsorption capacity drops sharply due to electrostatic repulsion between the protonated surface and the dye cation, the π-π stacking effect between the aromatic carbon structure of the biochar and the benzene ring of the dye (the adsorption capacity is still maintained at 995 mg / g at pH = 2) and the hydrogen bonding between the oxygen-containing functional groups (—OH) and the amino groups (—NH2) of the dye together ensure wide pH adaptability. The enlarged mesopores also provide a spatial confinement effect, enhancing the adsorption stability.

[0016] (3) The amount of citric acid added achieves a structure-function balance through the mass ratio: too low a ratio (5:1.5) results in insufficient functional groups, while too high a ratio (5:10) results in pore blockage. A pyrolysis temperature of 500°C ensures that the organic matter is fully carbonized and retains active functional groups, while temperatures too high (e.g., 800°C) induce pore collapse. A 6-hour alkaline treatment fully activates the surface, resulting in a 10.6% increase in adsorption compared to the untreated sample (CA-C).

[0017] This patented method overcomes the adsorption bottleneck of traditional biochar through dual modification: pore formation by citric acid pyrolysis and surface activation by alkaline treatment. 1) Large pores (67.09 nm) address mass transfer limitations for large molecules; 2) Oxygen-rich functional groups enhance electrostatic attraction, while π-π interactions broaden the pH range; 3) Synergistic optimization of the mass ratio (5:5), temperature (500°C), and alkaline treatment (6 hours) significantly increases the adsorption capacity (1139 mg / g) compared to unmodified biochar (930 mg / g). This design provides a cost-effective solution for malachite green removal that combines structural efficiency with engineering feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a picture of the modified bagasse charcoal prepared in Example 1; Figure 2 This is a scanning electron microscope image of the modified bagasse charcoal prepared in Example 1; Figure 3 This is the general spectrum of element distribution of the modified bagasse charcoal prepared in Example 1; Figure 4 is the N2 adsorption-desorption curve of Example 1; Figure 5 is the pore size distribution diagram of Example 1; Figure 6 is the N2 adsorption-desorption curve of Comparative Example 1; Figure 7 This is the pore size distribution diagram of Comparative Example 1; Figure 8 is the standard curve of malachite green; Figure 9 Comparison of adsorption performance among Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3; Figure 10 The effect of calcination temperature on the adsorption performance of Example 1; Figure 11 The effect of the amount of citric acid added on the adsorption performance of Example 1; Figure 12 The effect of adsorption time on the adsorption performance of Example 1; Figure 13 The effect of adsorbent dosage on the adsorption performance of Example 1; Figure 14 The effect of pH on the adsorption performance of Example 1; Figure 15 is the effect of adsorption temperature and initial adsorbate concentration on the adsorption performance of Example 1; Figure 16 The effect of the concentration and type of coexisting anions on the adsorption performance of Example 1; Figure 17 The effect of the concentration and type of coexisting cations on the adsorption performance of Example 1. DETAILED DESCRIPTION

[0019] Example 1

[0020] S1. After pre-treating the collected bagasse to remove surface impurities, the bagasse was washed three times with deionized water. The washed bagasse was air-dried under natural ventilation until constant weight was achieved. The washed bagasse was crushed with a pulverizer and sieved to obtain uniform particles. The particles were then sealed and stored in a desiccator for later use.

[0021] S2. Weigh 5 g of bagasse and 5 g of citric acid, grind them in an agate mortar and mix them evenly. Place the ground mixture in a crucible. Then, heat the crucible to 500°C in a muffle furnace and hold for 3 hours. Grind the sample obtained by pyrolysis appropriately and package it for later use.

[0022] S3, take 500mg of sample and add it to 50mL 1mol·L -1 The alkali-treated modified bagasse biochar was obtained by stirring it in a NaOH solution with a magnetic stirrer for 6 h, then washing it with deionized water several times until it was neutral and drying it in a blast drying oven at 80 ° C to constant weight. Finally, it was ground evenly and packaged for drying and storage, and was marked as CA-C. NaOH .

[0023] Comparative Example 1 Preparation of bagasse charcoal: (1) Weigh 5 g of bagasse into a crucible.

[0024] (2) Then, it was placed in a muffle furnace and heated to 500 °C and maintained for 3 h. The sample obtained by pyrolysis was properly ground to obtain the product, which was marked as C.

[0025] Comparative Example 2 (without alkali treatment) Preparation of citric acid modified bagasse charcoal (1) Weigh 5 g of bagasse and 5 g of citric acid respectively, grind them in an agate mortar and mix them evenly, and put the ground mixture into a crucible.

[0026] (2) Then it was placed in a muffle furnace and heated to 500 °C and maintained for 3 h. The sample obtained by pyrolysis was properly ground to obtain the product, which was labeled CA-C.

[0027] Comparative Example 3 (no citric acid added) Preparation of alkali-treated bagasse charcoal (1) Weigh 5 g of sugarcane bagasse and place it in a crucible.

[0028] (2) Then put it into a muffle furnace and heat it to 500 °C and keep it for 3 h. The sample obtained by pyrolysis is properly ground.

[0029] (3) Take 500 mg of sample and dissolve it in 50 mL of 1 mol·L -1 The alkali-treated modified bagasse biochar was obtained by stirring it in a NaOH solution with a magnetic stirrer for 6 h, then washing it with deionized water several times until it was neutral and drying it in a blast drying oven at 80 °C until it was constant weight. Finally, it was ground evenly and packaged for drying and storage, which was marked as C. NaOH .

[0030] The CA-C obtained in Example 1 NaOHCharacterization: Figure 2 The scanning electron micrograph of the prepared modified bagasse charcoal is shown in Figure 2. NaOH It is stacked in a layered structure, but its surface is rougher and has more porous structures. This is because the thermal decomposition of citric acid produces gases such as CO2, which destroys the original structure of biochar, increases the pores and pore diameter, and exposes more active sites on the surface of the material.

[0031] Figure 3 The element distribution spectrum of the prepared modified bagasse charcoal is shown in Figure 2. NaOH Contains carbon and oxygen. Carbon and oxygen are in CA-C NaOH Evenly distributed inside.

[0032] Figure 4 is the N2 adsorption-desorption curve of Example 1; Figure 5 is the pore size distribution diagram of Example 1; Figure 6 is the N2 adsorption-desorption curve of Comparative Example 1; Figure 7 Pore ​​size distribution diagram of comparative example 1; bagasse charcoal has rich mesoporous structure, the isotherm type belongs to type I, the average pore size is 20.62nm, and the specific surface area is 449.68m 2 ·g -1 , the pore volume is 0.2131cm 3 / g. And CA-C NaOH It is consistent with the adsorption characteristics of non-porous or macroporous materials and is similar to CA-C NaOH The results of scanning electron microscopy characterization of CA-C are consistent. NaOH The isotherm type is type III, and the specific surface area is 5.97m 2 ·g -1 The average pore size is 67.09 nm and the pore volume is 0.0125 cm 3 / g. The pore structure of the material changes, the specific surface area decreases, but the increase in pore size is more conducive to the adsorption and mass transfer of organic macromolecules (such as malachite green molecules).

[0033] Prepare 300 mg·L -1 Malachite green standard stock solution was used in the experimental system to prepare 60, 80, 100, 120, 140, 160, 180, 200, and 300 mg∙L -1 A gradient concentration of malachite green standard solution system was prepared. An appropriate amount of solution was transferred to a quartz cuvette. The full wavelength was scanned by UV spectrophotometer to obtain the absorbance value at the characteristic absorption wavelength at 615 nm. The standard curve fitting equation was established by linear regression analysis as follows: Figure 8As shown in Figure 2 , experimental data show that the standard curve has a linear correlation coefficient R² > 0.99, which conforms to the Lambert-Beer law and meets the requirements for quantitative analysis. Using this standard curve, the concentration of malachite green after biochar adsorption can be calculated, and thus the adsorption capacity and removal rate.

[0034] Test Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were tested for the adsorption performance of malachite green. The test experiments were as follows: S1, pipette 15 mL of the solution with a concentration gradient of 180-300 mg·L -1 The malachite green working solution was added into a conical flask, and 0.10-0.40 g·L -1 The modified biochar adsorbent was used to control the pH value of the solution in the range of 2.0-12.0 by acid-base adjustment method, and the solution was stirred in a constant temperature oscillator at 25-40℃ at 150 r·min -1 The reaction rate was 180 min.

[0035] S2. After the reaction system is separated by filtration, the concentration of residual pollutants in the filtrate is determined by ultraviolet spectrophotometry.

[0036] The result is as follows Figure 9 As shown in Figure 2, the adsorption capacity of malachite green by the bagasse charcoal obtained in Comparative Example 1 is 930 mg·g -1 When sugarcane bagasse was treated with alkali and then pyrolyzed, the adsorption capacity of the biochar prepared was reduced to 686 mg·g -1 (Comparative Example 3) This may be because the sugarcane bagasse removed part of the lignin after the alkali treatment, resulting in a decrease in its carbon content, thereby reducing its adsorption performance. When the sugarcane bagasse was treated with citric acid, its adsorption capacity increased to 1030 mg·g -1 (Comparative Example 2) This may be because the addition of citric acid changes the pore structure and specific surface area of ​​the sugarcane bagasse charcoal, effectively improving its adsorption capacity. In addition, when the sugarcane bagasse is treated with citric acid and then with alkali, the adsorption capacity of the biochar prepared for malachite green reaches 1139 mg·g -1 The addition of citric acid improves its pore size and specific surface area. In addition, alkaline treatment can not only remove impurities such as organic matter and ash on the surface of biochar, but also adjust the chemical properties of the biochar surface, further increasing its adsorption performance for malachite green.

[0037] Example 2

[0038] The difference between Example 2 and Example 1 is that the calcination temperature is 600° C., and the other conditions are exactly the same.

[0039] Example 3

[0040] The difference between Example 3 and Example 1 is that the calcination temperature is 700° C., and the other conditions are exactly the same.

[0041] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the calcination temperature is 800° C., and the other conditions are exactly the same.

[0042] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the calcination temperature is 400° C., and the other conditions are exactly the same.

[0043] The biochar prepared in Examples 1-3 and Comparative Examples 4 and 5 was tested for its adsorption performance on malachite green: Test results: The adsorption performance test results of malachite green by biochar prepared in Examples 1-3 are as follows: Figure 9 As shown in Figure 2, as the temperature increases from 400℃ to 800℃, the adsorption capacity of bagasse carbon increases from 650 mg·g -1 , 730 mg·g -1 , 951 mg·g -1 、1102 mg·g -1 and 1053 mg·g -1 The adsorption capacity of the modified carbon obtained by adding 1.5g citric acid at 500℃ is 853mg·g -1 The adsorption capacity of the modified carbon obtained by adding 1.5 g of citric acid at 400 °C, 600 °C, 700 °C and 800 °C is 789 mg·g -1 、780 mg·g -1 , 772mg·g -1 and 706 mg·g -1 , which is lower than the adsorption capacity of bagasse charcoal at the same temperature. This indicates that increasing temperature can increase the microporous structure and porosity, but sintering or pore collapse is very likely to occur under high temperature conditions, resulting in a decrease in the material's adsorption capacity. Therefore, 500-700°C is selected as the optimal firing temperature for modified charcoal.

[0044] Example 4

[0045] The difference between Example 4 and Example 1 is that the amount of citric acid added is 1.5 g, and the mass ratio of bagasse to citric acid is 5:1.5. The other conditions are exactly the same.

[0046] Example 5

[0047] The difference between Example 5 and Example 1 is that the amount of citric acid added is 3 g, and the mass ratio of bagasse to citric acid is 5:3. The other conditions are exactly the same.

[0048] Example 6

[0049] The difference between Example 6 and Example 1 is that the amount of citric acid added is 7 g, and the mass ratio of bagasse to citric acid is 5:7. The other conditions are exactly the same.

[0050] Example 7

[0051] The difference between Example 7 and Example 1 is that the amount of citric acid added is 10 g, and the mass ratio of bagasse to citric acid is 5:10, and the other conditions are exactly the same.

[0052] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the amount of citric acid added is 0 g, and the mass ratio of bagasse to citric acid is 5:10, and the other conditions are exactly the same.

[0053] Effect of citric acid addition on biochar adsorption performance: The adsorption performance test results of the biochar prepared in Example 1, Example 4, Example 5, Example 6, Example 7 and Example 8 on malachite green are as follows: Figure 11 As shown in the figure, when the dosage of citric acid increased from 0 g to 3 g, the adsorption capacity of modified bagasse carbon for malachite green increased from 684 mg·L -1 Rising to 1139 mg·L -1 When the dosage of citric acid increased from 3 g to 10 g, the adsorption capacity of modified bagasse charcoal for malachite green increased from 1139 mg·L -1 Dropped to 885 mg·L -1 . It can be seen that too high or too low a dosage of citric acid will lead to a decrease in the adsorption performance of the material. When the dosage of citric acid is too low, fewer effective active functional groups are introduced, the surface charge is low, and effective adsorption sites cannot be formed with the cationic groups of malachite green. When the dosage of citric acid is too high, too many functional groups may be introduced, reducing the exposure of active sites. When the dosage of citric acid is 5g, the adsorption performance of the modified sugarcane bagasse charcoal is the best. Therefore, this patent uses a citric acid dosage of 5g to prepare modified sugarcane bagasse biomass charcoal, and further explores its adsorption performance.

[0054] Effect of adsorption time on adsorption performance The effect of adsorption time on the adsorption performance of biochar on malachite green was investigated. The experimental results are as follows: Figure 12 The experimental results show that the adsorption capacity of modified bagasse charcoal for malachite green increased from 684 mg·L -1 Rising to 1139 mg·L -1 The adsorption capacity showed a rapid upward trend; the adsorption capacity of modified bagasse carbon for malachite green in the range of 60-180 min increased from 684 mg·L -1 Increased to 1122 mg·L -1The adsorption capacity increased significantly, and after 180 min, the adsorption capacity tended to be stable, and the equilibrium adsorption capacity reached 1139.03 mg·g -1 This phenomenon indicates that the adsorbent surface has abundant active sites in the initial stage, leading to rapid contaminant binding. As the adsorption sites gradually become saturated, the diffusion and mass transfer resistance increases, causing the adsorption rate to decrease. Based on kinetic equilibrium characteristics and energy consumption optimization considerations, 180 minutes was determined to be the optimal adsorption contact time.

[0055] Effect of adsorbent addition amount on adsorption performance The effect of adsorbent addition on adsorption performance was investigated. The experimental results are as follows: Figure 13 As shown. When the adsorbent concentration is increased from 0.10gL -1 Increased to 0.40 g / L -1 When the malachite green removal efficiency increased from 75.9% to 91.2%, the unit adsorption capacity increased from 2277.6 mg g -1 Significantly attenuated to 684.2 mgg -1 . From the perspective of removal rate, the greater the adsorbent dosage, the greater the chance of pollutants adhering to the adsorbent surface, and the higher the removal rate; however, the greater the adsorbent dosage, the fewer pollutants will be attached to the adsorbent per unit specific surface area, and the surface site competition effect caused by excessive adsorbent will lead to a decrease in the effective utilization rate of the adsorbent per unit mass. Based on the analysis of the surface chemical adsorption mechanism, there is a nonlinear antagonistic relationship between adsorbent concentration and adsorption efficiency, and the efficiency balance threshold needs to be determined through the coordinated optimization of surface utilization efficiency and mass transfer kinetics. Experimental data show that 0.30gL -1 Under the same dosage conditions, the system has a pollutant removal rate of 85% and a -1 The adsorption capacity of the adsorbent was 1.547 W·m-1, which showed the synergistic optimization effect of adsorbent surface utilization efficiency and mass transfer kinetics.

[0056] Effect of pH on adsorption performance The effect of solution pH on the adsorption performance of biochar on malachite green was investigated. The experimental results are as follows: Figure 14 As shown. The surface charge of the adsorbent in the solution will be changed by the pH of the environment in which it is located, thereby affecting the adsorption process. Malachite green is colorless at pH 7.0 and 2.0, so the pH value should not be adjusted too high or too low. Figure 14 As shown in the figure, when the pH is less than 5.0, the adsorption capacity of malachite green by the modified bagasse carbon increases from 995 mg·L -1 Dropped to 337 mg·L -1 When the pH value of the solution was in the range of 5.0-6.0, the adsorption capacity of modified bagasse carbon for malachite green increased from 337 mg·L -1 Increased to 1060 mg·L -1The adsorption capacity showed a significant upward trend. When pH ≥ 7.0, the system reached the adsorption saturation platform of 1139 mg·L -1 The limited adsorption efficiency under acidic conditions (pH < 5.0) is mainly attributed to the protonation effect, which causes the active sites on the adsorbent surface to bind to H + Competitive coordination occurs, and the positively charged malachite green cation produces an electrostatic repulsion effect with the protonated surface. It is worth noting that even in a strong acid environment, the modified biochar still maintains a certain adsorption capacity, revealing that non-electrostatic effects such as π-π electron donor-acceptor interactions and hydrogen bonding dominate its adsorption mechanism. When pH>5.0, the functional groups on the biochar surface are deprotonated to form negatively charged centers, which significantly enhance the pollutant binding capacity through electrostatic attraction, π-π stacking and hydrogen bonding synergistic effects. At the same time, H + The competitive adsorption effect with pollutant cations gradually decreases with increasing pH, allowing the adsorption capacity to reach equilibrium. Based on the above adsorption characteristics analysis, subsequent experiments selected pH 7.0-12.0 as the optimal reaction condition range.

[0057] Effects of adsorption temperature and initial concentration on adsorption performance The effects of adsorption temperature and initial concentration on the adsorption performance of biochar on malachite green were investigated. The experimental results are as follows: Figure 15 As shown. Figure 15 It can be seen that with the increase of the initial concentration of malachite green, the adsorption capacity of modified biochar for malachite green also increases (from 577 mg·g at 25 °C to -1 Increased to 1139 mg·g -1 The slopes of the adsorption isotherms under different temperature conditions are similar. The increase in temperature slightly increases the adsorption capacity of the adsorbent. When the initial concentration of malachite green is 300 mg∙L -1 For example, as the temperature increases, the migration rate of malachite green molecules increases, and the adsorption capacity of modified biochar for malachite green increases from 1139 mg·g -1 Increased to 1301 mg·g -1 , allowing for more complete diffusion within the adsorbent's pores. The adsorption capacity increased linearly with increasing initial adsorbate concentration. This is because the higher the malachite green concentration, the more malachite green molecules are available for adsorption on the adsorbent's adsorption sites. Considering that temperature has a minor influence on the adsorption capacity of the modified biochar and is not a dominant factor, subsequent adsorption operations were performed at room temperature (25°C).

[0058] Effect of coexisting ions on adsorption performance In the treatment of industrial wastewater by modified biochar, we often face the challenge of complex water environment. The multivalent anions / cations (such as Cl⁻, SO4 2- , K+ The competitive adsorption of target pollutants by adsorbents (such as ions) may interfere with the directional adsorption of target pollutants through charge competition, steric hindrance and other effects. This competitive adsorption effect will lead to a decrease in the adsorption capacity of the material. Therefore, studying the effect of different ion types on the adsorption performance of modified biochar is of great value for optimizing adsorbents and designing process parameters. Therefore, this study uses the control variable method to construct a multi-ion competitive adsorption system, and selects six typical coexisting ions (Cl - 、CO3 2- 、SO4 2- , K + Mg 2+ 、Na + ) was used as the research object. -1 ) series of salt solutions (NaCl, KCl, MgCl2, K2CO3, K2SO4), comparative adsorption experiments were carried out under constant temperature and oscillation conditions. Figure 16 and Figure 17 It can be seen that Cl - 、SO4 2- The adsorption capacity of modified bagasse carbon for malachite green dye after adding monovalent / polyvalent anions was 1010 mg·g -1 , 926mg·g -1 , compared with 1139 mg·g in the blank control group -1 The reason may be that it competes with the positively charged malachite green molecules for adsorption sites, and the ion exchange effect weakens the π-π stacking effect. + Mg 2 + 、Na + The adsorption capacity of malachite green dye on modified bagasse carbon after adding cations was 1055 mg·g -1 , 718mg·g -1 , 1088mg·g -1 It inhibits the adsorption of malachite green. The reason may be that it combines with the positively charged malachite green molecules, hindering the adsorption of malachite green by the adsorbent. 2- It promotes the adsorption of malachite green, with an adsorption capacity of 1301 mg·g -1 In general, the effects of the presence of these anions and cations on the adsorption capacity of the material are controlled within a certain range, indicating that the material has certain application potential in actual wastewater treatment.

Claims

1. A method for preparing citric acid-modified bagasse biochar, characterized by: The steps include: S1. Soak and wash the bagasse with ultrapure water, dry it naturally in the sun, crush it into fine particles with a grinder, and put it into a sealed bag for drying and storage; S2, grinding the product obtained in step (1) and citric acid, mixing them evenly, performing high-temperature oxygen-limited pyrolysis, grinding the pyrolyzed sample, and packaging it for later use; S3. Place the product obtained in step (2) in a NaOH solution, stir, wash with deionized water until neutral, and dry to obtain alkali-treated modified sugarcane bagasse biochar, grind it evenly, and package it for dry storage.

2. The method for preparing citric acid-modified bagasse biochar according to claim 1, wherein: The temperature of high temperature calcination in S2 is 500-700℃.

3. The method for preparing citric acid-modified bagasse biochar according to claim 1, wherein: The mass ratio of the product obtained in S1 to citric acid is 5:(1.5-10).

4. The method for preparing citric acid-modified bagasse biochar according to claim 1, wherein: The addition ratio of sample to NaOH in S3 is 500 mg sample corresponding to 0.05 mol NaOH, and the concentration of NaOH solution is 1 mol·L -1 .

5. The method for preparing citric acid-modified bagasse biochar according to claim 1, wherein: The stirring time for alkali treatment is 6h.

6. A citric acid-modified sugarcane bagasse biochar prepared by the method according to any one of claims 1 to 5.

7. Use of citric acid-modified bagasse biochar prepared by the method according to any one of claims 1 to 5 as an adsorbent for removing malachite green from water.

8. Use of citric acid-modified bagasse biochar prepared by the method according to any one of claims 1 to 5 as an adsorbent for removing malachite green from water.

9. A method for adsorbing malachite green on citric acid-modified bagasse biochar prepared by the method according to any one of claims 1 to 5, comprising the following steps: Take 20 mL of 20-200 mg·L -1 of malachite green solution in a beaker and add 0.2-0.4g∙L -1 The modified biochar was adjusted to pH 7.0-11.0, and the mixture was shaken at a constant temperature of 25-40°C for 3 h. After filtration, the filtrate was taken and the absorbance was measured by UV spectrophotometer. All experiments were performed three times under the same conditions, and the results were averaged.

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