A citric acid modified bagasse biochar, a preparation method thereof and application thereof in removing malachite green in water

Abstract

The present application relates to the technical field of water treatment, in particular to a kind of lemon acid modified bagasse biochar and its preparation method and application in removing malachite green in water.The present application uses bagasse as raw material, uses lemon acid as modifier, prepares the alkali treated lemon acid modified bagasse biochar by high-temperature limited oxygen pyrolysis, and is used to absorb organic dye malachite green in water, and the adsorption capacity can reach 1139 mg·g ‑1 .

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a citric acid-modified sugarcane bagasse biochar, its preparation method, and its application in removing malachite green from water. Background Technology

[0002] Malachite green, an organic dye, is widely used. It is not only used as a dye in the textile industry but also as an antibacterial agent and pesticide. However, due to its difficulty in degradation, high toxicity, and tendency to pollute water bodies, it has been banned as a veterinary drug in my country. Furthermore, malachite green can cause teratogenicity, carcinogenicity, and mutagenicity, and can have destructive effects on the liver, kidneys, and other systems of the human body, posing a threat to human health.

[0003] In recent years, the preparation of biochar adsorbent materials and their application in pollutant treatment has become a research hotspot in water pollution control. Biomass resources are often prepared into biochar as adsorbents to remove pollutants from water. On the one hand, biochar has a well-developed pore structure, is resistant to acids and alkalis, has excellent electrical conductivity and chemical stability, and a large specific surface area, providing a large number of adsorption sites for pollutants; at the same time, its surface is rich in active functional groups, which is beneficial for its modification. On the other hand, preparing it as an adsorbent can not only solve water pollution problems and turn biomass waste into treasure, but also realize its resource utilization, reducing resource waste and environmental pollution.

[0004] The preparation method of bagasse char is simple and inexpensive. Utilizing bagasse, an agricultural waste, to prepare composite materials can realize the resource utilization of agricultural waste and help solve the problem of waste treatment and disposal. At the same time, research on bagasse char can help develop highly efficient adsorbents for removing organic dyes from wastewater, alleviating water pollution problems, and is of great significance for recycling and sustainable development. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing citric acid-modified bagasse biochar and its application in removing malachite green from water.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] The first objective of this invention is to provide a method for preparing citric acid-modified sugarcane bagasse biochar, comprising the following steps:

[0008] S1. Soak and wash the sugarcane bagasse in ultrapure water, air dry naturally, crush it into fine particles using a pulverizer, and store it in a sealed bag for later use.

[0009] S2. Grind the product obtained in step (1) and citric acid, mix them evenly, and perform high-temperature oxygen-limited pyrolysis. Grind the pyrolyzed sample and package it for later use.

[0010] S3. Place the product obtained in step (2) in NaOH solution, stir, wash with deionized water until neutral, dry, and obtain alkali-treated modified sugarcane bagasse biochar. Grind evenly and package and dry for storage.

[0011] Furthermore, the high-temperature calcination temperature in step (2) is 500-700℃. If the calcination temperature is too low (<500℃), the organic components and impurities in the precursor cannot be effectively decomposed, and biochar cannot be formed. If the calcination temperature is too high (>700℃), carbon loss may occur, reducing the doping effect, and may also affect the specific surface area and activity of the material. The optimized calcination temperature range of 500-700℃ enables the decomposition of the organic precursor and promotes the formation of biochar.

[0012] 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 pyrolyze to generate a biochar framework. Citric acid decomposes at high temperature, releasing gas to create pores and forming a hierarchical pore structure (micropores / mesoporous pores). 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, resulting in low surface charge and an inability to form effective adsorption sites with the cationic groups of malachite green. If the addition amount is too high, too many functional groups are introduced, reducing the exposure of active sites and causing a decrease in the adsorption performance of the material.

[0013] Furthermore, in step (3), the ratio of sample to NaOH added is 500 mg sample to 0.05 mol NaOH, and the concentration of the NaOH solution is 1 mol·L⁻¹. -1 ,

[0014] Furthermore, the alkali treatment stirring time is 6 hours.

[0015] The present invention also provides citric acid-modified bagasse biochar prepared by the method.

[0016] This invention also provides the application of citric acid-modified bagasse biochar prepared by the method as an adsorbent for the removal of malachite green from water.

[0017] The present invention also provides a method for adsorbing malachite green using citric acid-modified sugarcane bagasse biochar, comprising the following steps:

[0018] Take 20 mL of 20~200 mg·L -1Add 0.2-0.4 g∙L to a beaker of malachite green solution. -1 Modified biochar was prepared, and the pH was adjusted to 7.0–11.0. The mixture was then kept at 25–40°C with shaking for 3 hours. After filtration, the absorbance of the filtrate was measured using a UV spectrophotometer. All experiments were performed three times under the same conditions, and the average value was taken.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention uses sugarcane bagasse as raw material and citric acid as a modifier. Through high-temperature, oxygen-limited pyrolysis, at a sugarcane bagasse / citric acid ratio of 1:1, 1 mol·L⁻¹ -1 Alkali-treated citric acid-modified sugarcane bagasse biochar was prepared under NaOH alkali treatment for 6 h. This biochar was then used to adsorb the organic dye malachite green from water, achieving an adsorption capacity of 1139 mg·g⁻¹. -1 .

[0021] (1) Citric acid decomposes into CO2 and other gases during high-temperature oxygen-limited pyrolysis, forming microporous / mesoporous hierarchical channels within the bagasse carbon skeleton. After modification, the average pore size is increased, making it more suitable for the diffusion and mass transfer of macromolecular malachite green and avoiding 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 negatively charged surfaces.

[0022] (2) Under alkaline conditions, the modified carbon surface undergoes deprotonation to form -COO⁻ groups, which generate strong electrostatic attraction with positively charged malachite green, resulting in a peak adsorption capacity of 1139 mg / g. In acidic environments (pH < 5), although the adsorption capacity drops sharply due to electrostatic repulsion between the protonated surface and the dye cations, the aromatic carbon structure of the biochar and the π-π stacking effect of the dye benzene ring (maintaining an adsorption capacity of 995 mg / g at pH = 2), as well as the hydrogen bonding between the oxygen-containing functional group (-OH) and the dye amino group (-NH2), jointly ensure wide pH adaptability. The enlarged mesopores also provide a spatial confinement effect, enhancing adsorption stability.

[0023] (3) The amount of citric acid added achieves a structure-function balance through the mass ratio: too low (5:1.5) leads to insufficient functional groups, while too high (5:10) clogs the pores. A pyrolysis temperature of 500℃ ensures that the organic matter is fully carbonized and retains active functional groups, while excessively high temperatures (such as 800℃) cause pore collapse. A 6-hour alkali treatment fully activates the surface, increasing the adsorption capacity by 10.6% compared to the untreated sample (CA-C).

[0024] This patented technology overcomes the adsorption bottlenecks of traditional biochar through dual modification: citric acid pyrolysis for pore formation and alkali treatment for surface activation. 1) Large pore size (67.09 nm) overcomes the limitations of macromolecular mass transfer; 2) oxygen-rich functional groups enhance electrostatic attraction, and combined with π-π interactions, broaden the applicable pH range; 3) synergistic optimization of mass ratio (5:5), temperature (500℃), and alkali treatment (6 h) results in an adsorption capacity (1139 mg / g) significantly higher than unmodified char (930 mg / g). This design provides a cost-effective solution for removing malachite green that combines structural performance and engineering feasibility. Attached Figure Description

[0025] Figure 1 Image of the modified bagasse char prepared in Example 1;

[0026] Figure 2 This is a scanning electron microscope image of the modified bagasse char prepared in Example 1;

[0027] Figure 3 The elemental distribution spectrum of the modified bagasse char prepared in Example 1 is shown in the overall spectrum.

[0028] Figure 4 The N2 adsorption-desorption curve is shown in Example 1.

[0029] Figure 5 This is a pore size distribution diagram for Example 1;

[0030] Figure 6 The N2 adsorption-desorption curve is shown in Comparative Example 1.

[0031] Figure 7 This is a diagram showing the aperture distribution of Comparative Example 1;

[0032] Figure 8 The standard curve for malachite green;

[0033] Figure 9 This is a comparison of the adsorption performance of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0034] Figure 10 The effect of calcination temperature on the adsorption performance of Example 1;

[0035] Figure 11 The effect of citric acid addition on the adsorption performance of Example 1;

[0036] Figure 12 The effect of adsorption time on the adsorption performance of Example 1;

[0037] Figure 13 The effect of adsorbent dosage on the adsorption performance of Example 1;

[0038] Figure 14The effect of pH on the adsorption performance of Example 1;

[0039] Figure 15 The effect of adsorption temperature and initial adsorbate concentration on the adsorption performance of Example 1;

[0040] Figure 16 The effect of coexisting anion concentration and type on the adsorption performance of Example 1;

[0041] Figure 17 The effect of coexisting cation concentration and type on the adsorption performance of Example 1. Detailed Implementation

[0042] Example 1

[0043] S1. After the collected sugarcane bagasse raw material is pretreated to remove surface impurities, it is washed thoroughly three times with deionized water. The washed material is then placed under natural ventilation to dry to constant weight, crushed by a pulverizer, and sieved to obtain uniform particles. It is then sealed and stored in a desiccator for later use.

[0044] S2. Weigh 5g of sugarcane bagasse and 5g of citric acid separately and grind them in an agate mortar until they are evenly mixed. Place the ground mixture into a crucible. Then place it in a muffle furnace and heat it to 500℃ and maintain it for 3 hours. Grind the pyrolysis sample appropriately and package it for later use.

[0045] S3. Take 500 mg of sample into 50 mL of 1 mol·L⁻¹ solution. -1 The mixture was stirred in NaOH solution with a magnetic stirrer for 6 hours, then washed multiple times with deionized water until neutral. It was then dried in an 80℃ forced-air drying oven to constant weight to obtain alkali-treated modified sugarcane bagasse biochar. Finally, it was ground uniformly, packaged, dried, and stored for later use, labeled CA-C. NaOH .

[0046] Comparative Example 1

[0047] Preparation of sugarcane bagasse charcoal:

[0048] (1) Weigh 5g of sugarcane bagasse into a crucible.

[0049] (2) Then put it into a muffle furnace and heat it to 500°C and keep it for 3 hours. The pyrolysis sample is then ground appropriately to obtain the product, which is labeled as C.

[0050] Comparative Example 2 (without alkali treatment)

[0051] Preparation of citric acid-modified bagasse char

[0052] (1) Weigh 5g of sugarcane bagasse and 5g of citric acid into an agate mortar and grind them until they are evenly mixed. Then put the ground mixture into a crucible.

[0053] (2) Then put it into a muffle furnace and heat it to 500°C and keep it for 3 hours. The pyrolysis sample is then ground appropriately to obtain the product, which is labeled as CA-C.

[0054] Comparative Example 3 (without citric acid)

[0055] Preparation of alkali-treated bagasse char

[0056] (1) Weigh 5g of sugarcane residue and put it into a crucible.

[0057] (2) Then put it into a muffle furnace and heat it to 500°C and keep it for 3 hours. Then grind the pyrolysis sample appropriately.

[0058] (3) Take 500 mg of sample into 50 mL of 1 mol·L⁻¹ -1 The mixture was stirred in NaOH solution with a magnetic stirrer for 6 hours, then washed multiple times with deionized water until neutral. It was then dried in an 80℃ forced-air drying oven to constant weight to obtain alkali-treated modified sugarcane bagasse biochar. Finally, it was ground uniformly, packaged, dried, and stored for later use, labeled C. NaOH .

[0059] The CA-C obtained in Example 1 NaOH Characterization:

[0060] Figure 2 Here is a scanning electron microscope image of the prepared modified bagasse char; it can be seen that CA-C NaOH It is composed of stacked layered structures, but its surface is rougher and has more porous structures. This is because the pyrolysis of citric acid produces gases such as CO2, which destroys the original structure of biochar, increases the number of pores and the pore size, and exposes more active sites on the material surface.

[0061] Figure 3 The elemental distribution spectrum of the prepared modified bagasse char is shown in the diagram; it can be seen that CA-C NaOH It contains carbon and oxygen elements. Carbon and oxygen are in the CA-C... NaOH The internal distribution is uniform.

[0062] Figure 4 The N2 adsorption-desorption curve is shown in Example 1. Figure 5 This is a pore size distribution diagram for Example 1; Figure 6 The N2 adsorption-desorption curve is shown in Comparative Example 1. Figure 7 Pore ​​size distribution diagram of Comparative Example 1; Sugarcane bagasse char has abundant mesoporous structure, isotherm type I, average pore size of 20.62 nm, and specific surface area of ​​449.68 m². 2 ·g -1 The pore volume is 0.2131 cm³.3 / g. And CA-C NaOH It conforms to the adsorption characteristics of non-porous or macroporous materials, and is compatible with CA-C. NaOH The scanning electron microscopy characterization results are consistent with those of CA-C. NaOH The isotherm type is III, and the specific surface area is 5.97 m². 2 ·g -1 The average pore size is 67.09 nm, and the pore volume is 0.0125 cm³. 3 / g. The material's pore structure changes, resulting in a decrease in specific surface area, but the increased pore size is more conducive to the adsorption and mass transfer of organic macromolecules (such as malachite green molecules).

[0063] Prepare 300 mg·L -1 Malachite green standard stock solutions were used in experimental systems to prepare solutions of 60, 80, 100, 120, 140, 160, 180, 200, and 300 mg·L. -1 A gradient concentration of malachite green standard solution system was prepared, and an appropriate amount of solution was transferred to a quartz cuvette. A full-wavelength scan was performed using a UV spectrophotometer to obtain the absorbance at 615 nm, and the absorbance values ​​at the characteristic absorption wavelength were recorded. A standard curve fitting equation was established through linear regression analysis, as shown below. Figure 8 As shown in the figure. Experimental data indicate that the linear correlation coefficient R² of the standard curve is greater than 0.99, which meets the applicable conditions of Lambert-Beer's law and satisfies the requirements for quantitative analysis. Using this standard curve, the concentration of malachite green after biochar adsorption can be calculated, and then the adsorption capacity and removal rate can be calculated.

[0064] The adsorption performance of malachite green in Examples 1, 1, 2, and 3 was tested. The test experiments are as follows:

[0065] S1. Transfer 15 mL of solution with a concentration gradient of 180-300 mg·L⁻¹. -1 Malachite green working solution was placed in Erlenmeyer flasks, and 0.10–0.40 g·L⁻¹ was added to each flask. -1 The modified biochar adsorbent was prepared by adjusting the pH of the solution to within the range of 2.0-12.0 using an acid-base method, and then subjected to constant temperature shaking at 150 r·min in a 25-40℃ constant temperature shaker. -1 The reaction rate was 180 min.

[0066] S2. After the reaction system is filtered and separated, the concentration of residual pollutants in the filtrate is determined by ultraviolet spectrophotometry.

[0067] The results are as follows Figure 9 As shown, the adsorption capacity of bagasse char obtained in Comparative Example 1 for malachite green was 930 mg·g⁻¹. -1When sugarcane bagasse is treated with alkali and then pyrolyzed, the adsorption capacity of the resulting biochar decreases to 686 mg·g⁻¹. -1 (Comparative Example 3) This may be because the sugarcane bagasse, after being treated with a mild alkali, had some lignin removed, resulting in a decrease in its carbon content and thus reducing its adsorption capacity. When the sugarcane bagasse was treated with citric acid, its adsorption capacity increased to 1030 mg·g⁻¹. -1 (Comparative Example 2) This may be because the addition of citric acid altered the pore structure and specific surface area of ​​the bagasse biochar, effectively enhancing its adsorption capacity. Furthermore, the biochar prepared from bagasse after citric acid treatment followed by alkali treatment exhibited an adsorption capacity of 1139 mg·g⁻¹ for malachite green. -1 The addition of citric acid improves its pore size and specific surface area. In addition, alkali treatment not only removes organic matter and ash impurities from the surface of biochar, but also adjusts the chemical properties of the biochar surface, further increasing its adsorption performance for malachite green.

[0068] Example 2

[0069] The difference between Example 2 and Example 1 is that the calcination temperature is 600℃, while the other conditions are exactly the same.

[0070] Example 3

[0071] The difference between Example 3 and Example 1 is that the calcination temperature is 700℃, while the other conditions are exactly the same.

[0072] Comparative Example 4

[0073] The difference between Comparative Example 4 and Example 1 is that the calcination temperature is 800°C, while the other conditions are exactly the same.

[0074] Comparative Example 5

[0075] The difference between Comparative Example 5 and Example 1 is that the calcination temperature is 400°C, while the other conditions are exactly the same.

[0076] The adsorption performance of biochar prepared in Examples 1-3, Comparative Examples 4 and 5 on malachite green was tested:

[0077] Test results: The adsorption performance of biochar prepared in Examples 1-3 on malachite green was tested as follows: Figure 9 As shown, the adsorption capacity of bagasse char increased from 400℃ to 800℃, with values ​​of 650 mg·g⁻¹. -1 730 mg·g -1 951 mg·g -1 1102 mg·g -1 and 1053 mg·g -1The modified carbon obtained by adding 1.5g of citric acid at 500℃ has an adsorption capacity of 853mg·g. -1 The adsorption capacity of the modified carbon obtained by adding 1.5 g of citric acid at the same temperature is higher than that of the modified carbon in Comparative Example 1 (bagasse char) at the same temperature. The modified carbon obtained by adding 1.5 g of citric acid at temperatures of 400℃, 600℃, 700℃, and 800℃ has an adsorption capacity of 789 mg·g⁻¹. -1 780 mg·g -1 772mg·g -1 and 706 mg·g -1 The adsorption capacity of modified char is lower than that of bagasse char at the same temperature. This indicates that increasing the temperature can increase the microporous structure and improve the 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℃ is selected as the preferred condition for calcining modified char.

[0078] Example 4

[0079] The difference between Example 4 and Example 1 is that the amount of citric acid added is 1.5g, and the mass ratio of sugarcane bagasse to citric acid is 5:1.5. All other conditions are exactly the same.

[0080] Example 5

[0081] The difference between Example 5 and Example 1 is that the amount of citric acid added is 3g, and the mass ratio of sugarcane bagasse to citric acid is 5:3. All other conditions are exactly the same.

[0082] Example 6

[0083] The difference between Example 6 and Example 1 is that the amount of citric acid added is 7g, and the mass ratio of sugarcane bagasse to citric acid is 5:7. All other conditions are exactly the same.

[0084] Example 7

[0085] The difference between Example 7 and Example 1 is that the amount of citric acid added is 10g, and the mass ratio of sugarcane bagasse to citric acid is 5:10. All other conditions are exactly the same.

[0086] Comparative Example 4

[0087] The difference between Comparative Example 4 and Example 1 is that the amount of citric acid added is 0g, and the mass ratio of sugarcane bagasse to citric acid is 5:10. All other conditions are exactly the same.

[0088] The effect of citric acid addition on the adsorption performance of biochar:

[0089] The adsorption performance test results of biochar prepared in Examples 1, 4, 5, 6, 7, and 8 for malachite green are as follows: Figure 11As shown, when the dosage of citric acid increased from 0g to 3g, the adsorption capacity of modified bagasse char for malachite green increased from 684mg·L⁻¹. -1 Rising to 1139 mg·L -1 However, when the dosage of citric acid increased from 3g to 10g, the adsorption capacity of modified bagasse char for malachite green increased from 1139mg·L⁻¹. -1 Decreased to 885 mg·L -1 It is evident that both excessively high and low citric acid dosages lead to a decrease in the adsorption performance of the material. Insufficient citric acid dosage introduces fewer effective active functional groups, resulting in low surface charge and an inability to form effective adsorption sites with the cationic groups of malachite green. Excessive citric acid dosage may introduce too many functional groups, reducing the exposure of active sites. The modified bagasse char exhibits the best adsorption performance when the citric acid dosage is 5g. Therefore, this patent uses a citric acid dosage of 5g to prepare modified bagasse biochar and further investigates its adsorption performance.

[0090] Effect of adsorption time on adsorption performance

[0091] The effect of adsorption time on the adsorption performance of biochar for malachite green was investigated. The experimental results are as follows: Figure 12 As shown. Experimental results indicate that the adsorption capacity of modified bagasse char for malachite green increased from 684 mg·L⁻¹ in the first 60 minutes. -1 Rising to 1139 mg·L -1 The adsorption capacity showed a rapid upward trend; the adsorption capacity of modified bagasse char for malachite green increased from 684 mg·L⁻¹ in the 60-180 min range. -1 Rising to 1122 mg·L -1 The adsorption capacity increased significantly, and after 180 min, the adsorption capacity tended to stabilize, with the equilibrium adsorption capacity reaching 1139.03 mg·g⁻¹. -1 This phenomenon indicates that the adsorbent surface is rich in active sites in the initial stage, leading to rapid binding of pollutants; as the adsorption sites gradually become saturated, the diffusion mass transfer resistance increases, causing the adsorption rate to decrease. Based on kinetic equilibrium characteristics and energy consumption optimization considerations, 180 min was determined to be the optimal adsorption contact time.

[0092] Effect of adsorbent dosage on adsorption performance

[0093] The effect of adsorbent dosage on adsorption performance was investigated, and the experimental results are as follows: Figure 13 As shown. When the adsorbent concentration is increased from 0.10 g / L... -1 Increased to 0.40 g / L -1 At that time, the removal efficiency of malachite green increased from 75.9% to 91.2%, while the adsorption capacity per unit volume increased from 2277.6 mgg. -1 Significantly decreased to 684.2 mgg -1From the perspective of removal rate, the larger the adsorbent dosage, the greater the chance of pollutants adhering to the adsorbent surface, and the higher the removal rate. However, a larger adsorbent dosage also reduces the amount of pollutants adhering to the adsorbent per unit surface area. The surface site competition effect caused by excessive adsorbent leads to a decrease in the effective utilization rate of adsorbent per unit mass. Based on the surface chemisorption mechanism analysis, there is a nonlinear antagonistic relationship between adsorbent concentration and adsorption efficiency. The efficiency balance threshold needs to be determined through synergistic optimization of surface utilization efficiency and mass transfer kinetics. Experimental data show that 0.30 g / L... -1 Under the given dosage conditions, the system achieves both an 85% pollutant removal rate and 1139 mg·g⁻¹. -1 The adsorption capacity demonstrates the synergistic optimization effect between adsorbent surface utilization efficiency and mass transfer kinetics.

[0094] Effect of pH on adsorption performance

[0095] 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 solution is altered by the pH of its environment, thus affecting the adsorption process. Malachite green is colorless at pH 7.0 and 2.0, therefore the pH value should not be adjusted too high or too low. Figure 14 As shown, when pH is less than 5.0, the adsorption capacity of modified bagasse char for malachite green decreases from 995 mg·L⁻¹ to 995 mg·L⁻¹. -1 Decreased to 337 mg·L -1 When the solution pH was in the range of 5.0-6.0, the adsorption capacity of modified bagasse char for malachite green increased from 337 mg·L⁻¹. -1 Rise to 1060 mg·L -1 The adsorption capacity showed a significant increasing trend, reaching an adsorption saturation plateau of 1139 mg·L⁻¹ when pH ≥ 7.0. -1 The adsorption efficiency is limited under acidic conditions (pH < 5.0), mainly due to protonation, which causes the active sites on the adsorbent surface to interact with H+. + Competitive coordination occurs, and the positively charged malachite green cations generate electrostatic repulsion with the protonated surface. Notably, even in strongly acidic environments, the modified biochar 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 undergo deprotonation to form negatively charged centers, significantly enhancing the pollutant binding capacity through electrostatic attraction, π-π stacking, and the synergistic effect of hydrogen bonding. Simultaneously, H... + The competitive adsorption effect with pollutant cations gradually decreases with increasing pH, allowing the adsorption capacity to reach an equilibrium state. Based on the above adsorption characteristic analysis, subsequent experiments selected pH 7.0–12.0 as the optimal reaction condition range.

[0096] Effects of adsorption temperature and initial concentration on adsorption performance

[0097] The effects of adsorption temperature and initial concentration on the adsorption performance of biochar for malachite green were investigated. The experimental results are as follows: Figure 15 As shown. From Figure 15 As can be seen, the adsorption capacity of modified biochar for malachite green increases with the increase of the initial concentration of malachite green (from 577 mg·g at 25℃). -1 Rising to 1139 mg·g -1 The slopes of the adsorption isotherms were similar under different temperature conditions. Increased temperature slightly increased the overall adsorption capacity of the adsorbent. This was achieved with an initial malachite green concentration of 300 mg·L⁻¹. -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. -1 Rising to 1301 mg·g -1 This allows for a more complete diffusion process within the pores of the adsorbent. The adsorption capacity increases linearly with increasing initial adsorbate concentration, as the higher the malachite green concentration, the more malachite green molecules can be adsorbed at the adsorption sites. Considering that temperature has a relatively minor effect on the adsorption capacity of modified biochar and is not a dominant determining factor, subsequent adsorption operations were conducted at room temperature (25℃).

[0098] Effect of coexisting ions on adsorption performance

[0099] In the treatment of industrial wastewater with modified biochar, the challenge of complex aquatic environments is often encountered. Multivalent anions / cations (such as Cl⁻, SO₄²⁻) are commonly found in actual wastewater. 2- K + Ions (such as Cl-, Cl-, etc.) may interfere with the directional adsorption of target pollutants by the adsorbent through charge competition and steric hindrance. This competitive adsorption effect leads to a decrease in the adsorption capacity of the material. Therefore, studying the influence 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 controlled variable method to construct a multi-ion competitive adsorption system, selecting six typical coexisting ions (Cl-, Cl-, Cl-, etc.). - CO3 2- SO4 2- K + Mg 2+ Na + ) was used as the research object. An equal concentration (0.1 mol·L⁻¹) was prepared. -1 A series of salt solutions (NaCl, KCl, MgCl2, K2CO3, K2SO4) were used to conduct comparative adsorption experiments under isothermal shaking conditions. Figure 16 and Figure 17 It can be seen that Cl - SO4 2- The adsorption capacity of modified bagasse char for malachite green dye after the addition of monovalent / polyvalent anions was 10-10 mg·g⁻¹. -1 926 mg·g -1 Compared with the blank control group, 1139 mg / g -1 Compared to other treatments, it exhibits a significant inhibitory effect. This may be because it competes with positively charged malachite green molecules for adsorption sites, and ion exchange weakens the π-π stacking effect. K... + Mg 2 + Na + After the addition of cations, the adsorption capacity of modified bagasse char for malachite green dye was 1055 mg·g. -1 718mg·g -1 1088mg·g -1 It inhibits the adsorption of malachite green. This may be because it binds to the positively charged malachite green molecules, hindering the adsorption of malachite green by the adsorbent. CO3 2- It promotes the adsorption of malachite green, with an adsorption capacity of 1301 mg·g. -1 Overall, the presence of these anions and cations has a limited impact on the adsorption capacity of the material, indicating that the material has certain application potential in actual wastewater treatment.

Claims

1. A method for preparing citric acid-modified sugarcane bagasse biochar for adsorbing malachite green, characterized in that: Includes the following steps: S1. After the collected sugarcane bagasse raw material is pretreated to remove surface impurities, it is washed thoroughly with deionized water three times. The washed material is placed under natural ventilation to dry to constant weight, crushed by a pulverizer and sieved to obtain uniform particles, and then sealed and stored in a desiccator for later use. S2. Weigh 5g of sugarcane bagasse and 5g of citric acid into an agate mortar and grind them until they are evenly mixed. Place the ground mixture into a crucible and then place it in a muffle furnace and heat it to 500°C for 3 hours. Grind the pyrolysis sample appropriately and package it for later use. S3. Take 500 mg of sample into 50 ml of 1 mol·L⁻¹ -1 The mixture was stirred in NaOH solution with a magnetic stirrer for 6 hours, followed by washing with deionized water multiple times until neutral. It was then dried in an 80°C oven to constant weight to obtain alkali-treated modified sugarcane bagasse biochar. Finally, it was ground uniformly, packaged, dried, and stored for later use, labeled CA-C. NaOH ; The citric acid-modified bagasse biochar used for adsorbing malachite green is composed of stacked layers with a rough surface and numerous pores, having a specific surface area of ​​5.97 m². 2 g -1 The average pore size is 67.09 nm, and the pore volume is 0.0125 cm³. 3 / g.

2. The application of citric acid-modified bagasse biochar prepared by the method described in claim 1 as an adsorbent for the removal of malachite green from water.

3. A method for adsorbing malachite green using citric acid-modified sugarcane bagasse biochar prepared according to claim 1, comprising the following steps: Take 20 mL of 20~200 mg·L -1 Add 0.2-0.4 g∙L to a beaker of malachite green solution. -1 Modified biochar was prepared, and the pH was adjusted to 7.0-11.

0. The mixture was kept at 25-40ºC and shaken for 3 hours. After filtration, the absorbance of the filtrate was measured using a UV spectrophotometer. All experiments were performed three times under the same conditions, and the average value was taken.

Images