Preparation method and application of sodium lignosulfonate-based porous carbon

Abstract

This invention discloses a method for preparing sodium lignin sulfonate-based porous carbon and its application, belonging to the field of efficient resource utilization of biomass and water treatment technology. The method selects sodium lignin sulfonate waste from pulp mills as a carbon source, and processes it to obtain sodium lignin sulfonate powder; the sodium lignin sulfonate powder is then blended with SiO2 and / or HCO2K and activated to obtain sodium lignin sulfonate-based porous carbon; this carbon is then applied to the removal of antibiotics from water. This invention fully utilizes the waste sodium lignin sulfonate from pulp mills, realizing the recycling of waste, increasing the added value of waste, and the preparation process is simple, pollution-free, environmentally friendly, and in line with green chemistry principles.

Description

Technical Field

[0001] This invention belongs to the field of efficient resource utilization of biomass and water treatment technology, specifically relating to a sodium lignosulfonate-based porous carbon and its preparation method, and its application in the removal of antibiotics in aquatic environments. Background Technology

[0002] Lignin is an aromatic polymer that accounts for one-third of non-fossil organic carbon and 20%-35% of the dry weight of wood. Unlike hemicellulose and cellulose, lignin currently lacks a clearly defined primary structure and is typically composed of three basic units (p-coumarol, coniferol, and sinapyl alcohol). Due to limitations in lignin stabilization methods, most waste lignin generated in the paper industry is used for internal energy recovery from low-value fuels. Therefore, developing low-cost, pollution-free processes to effectively convert lignin into functional materials is a key issue in current biorefining processes.

[0003] Biochar is widely available and diverse, and can be produced by pyrolyzing agricultural and forestry waste, sludge, and manure under anaerobic conditions. Biochar possesses advantages such as a well-developed porous structure, abundant functional groups, low cost, and strong sustainability, making it an effective alternative to commercial activated carbon and gradually attracting the interest of researchers. Lignin, as a biomass, is inexpensive, readily available, and has high aromaticity and carbon content (approximately 60%). Lignin sulfonate is a byproduct of papermaking black liquor, with an annual production of approximately 70 million tons. However, only 2% of lignin is used as an additive or dispersant, while the remainder is directly burned as fuel, resulting in low utilization value. Therefore, effectively utilizing lignin to convert it into high-value lignin-based porous carbon is crucial. One important approach to improving the adsorption performance of biomass porous carbon for organic pollutants is to develop easy-to-operate and low-cost pore structures. Micropores can provide more adsorption sites, facilitating pore filling, while mesopores are beneficial for the mass transfer of organic matter. However, the chemical activators currently in use are strong bases and strong acids, such as potassium hydroxide, sodium hydroxide, and phosphoric acid. These are corrosive and cause secondary pollution to the environment, making them difficult to apply in practice.

[0004] Currently, quinolone antibiotics are widely used as growth promoters in livestock and aquaculture, and for treating human and animal diseases, due to their advantages of high antibacterial activity, high bioavailability, and low cost. They account for 17% of global antibiotic consumption. However, oral or injected antibiotics are not completely absorbed by the body; approximately 3 / 10–9 / 10 of antibiotic prodrugs are released into the environment in feces. Meanwhile, large amounts of quinolone antibiotics have been detected in heavily polluted surface waters such as rivers, lakes, and bays, with concentrations ranging from 0.5 to 497.6 nanograms per liter, while norfloxacin (NOR) levels in chicken, pig, and cattle feces are as high as 1.886–225 mg / kg. Residual antibiotics can enter humans and farmland through the food chain and water cycle. The continuous accumulation of antibiotics can trigger toxic reactions and generate new antibiotic resistance genes, posing a threat to human health and the ecological environment. Therefore, the development of novel antibiotic adsorbents with low investment costs, large adsorption capacity, and good regeneration performance is imperative. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention aims to provide a method for preparing sodium lignosulfonate-based porous carbon. This method uses sodium lignosulfonate from papermaking black liquor as a carbon precursor, prepared through blending and activation. This method is characterized by its wide availability of raw materials, low cost, and simple operation. The resulting porous carbon exhibits abundant surface functional groups, a large specific surface area, and controllable pore size. Another technical problem addressed by this invention is the application of sodium lignosulfonate-based porous carbon in the adsorption of antibiotics in water. It demonstrates a good removal effect on antibiotics and is an excellent adsorbent with promising application prospects.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing sodium lignosulfonate-based porous carbon involves using sodium lignosulfonate as raw material and SiO2 and / or HCO2K as auxiliary pore-forming agents, through blending and activation.

[0008] The method for preparing sodium lignin sulfonate-based porous carbon involves first removing water-insoluble impurities and cellulose from sodium lignin sulfonate obtained from papermaking black liquor, then filtering out low molecular weight reducing sugars and inorganic salts, drying in an oven at 90–105°C for 8–16 hours, grinding, and sieving to obtain uniformly sized raw sodium lignin sulfonate.

[0009] In the method for preparing sodium lignosulfonate-based porous carbon, when SiO2 is used as an auxiliary pore-forming agent, the mass ratio of sodium lignosulfonate to SiO2 is 1:1 to 1:3; when HCO2K is used as an auxiliary pore-forming agent, the mass ratio of sodium lignosulfonate to SiO2 is 1:0.5 to 1:3; and when SiO2 and HCO2K are used as auxiliary pore-forming agents, the mass ratio of sodium lignosulfonate, HCO2K, and SiO2 is 1:0.5 to 3:1 to 3.

[0010] The method for preparing the sodium lignosulfonate-based porous carbon involves activation under a nitrogen atmosphere, with a nitrogen flow rate of 150–350 mL / min, a heating rate of 1–5 °C / min, an activation temperature of 600–800 °C, and an activation time of 1–3 h.

[0011] The method for preparing the sodium lignosulfonate-based porous carbon includes the following steps:

[0012] (1) Sodium lignosulfonate was washed with deionized water, ultrafiltered, dried, ground and sieved to obtain sodium lignosulfonate powder with uniform size.

[0013] (2) Mix the sodium lignin sulfonate powder obtained in step (1) with SiO2 and / or HCO2K, then add water and mix until homogeneous;

[0014] (3) After stirring, the blend was concentrated and vacuum dried to obtain a brown powder.

[0015] (4) Place the brown powder obtained in step (3) in a tube furnace and heat it to activate it;

[0016] (5) The substance obtained after the reaction was washed with sodium hydroxide solution, dilute hydrochloric acid and deionized water until the pH remained unchanged, and then dried to obtain sodium lignosulfonate-based porous carbon with different pore size distribution.

[0017] In the preparation method of sodium lignosulfonate-based porous carbon, in step (4), the concentration of sodium hydroxide is 3-6 mol / L, the concentration of dilute hydrochloric acid is 0.1-1 mol / L, the temperature of the drying oven is 90-105℃, and the drying time is 8-16 h.

[0018] Sodium lignosulfonate-based porous carbon was prepared by the above method.

[0019] The above-mentioned sodium lignosulfonate-based porous carbon is used in the adsorption and removal of antibiotics from aqueous solutions.

[0020] The application involves diluting an aqueous solution containing antibiotics into a background solution containing NaCl, and then adding the sodium lignosulfonate-based porous carbon to the diluted solution; the sodium chloride concentration in the background aqueous solution is 0.02–0.04 mol / L, and the pH value of the aqueous solution is 3–10.

[0021] In the aforementioned application, the concentration of antibiotics in the aqueous solution is 20–60 mg / L; the mass ratio of sodium lignosulfonate-based porous carbon to antibiotics is 1:0.1–1:1; the water bath temperature is 15–35 °C; and the reaction speed is 120–180 rpm.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The raw material for preparation is waste from papermaking black liquor, which is widely available and low in cost, fully utilizing the concept of waste reuse and greatly increasing its added value. This preparation method can effectively control the pore size distribution of lignin-based porous carbon, increase or decrease the micropore volume occupancy rate, and improve its adsorption and mass transfer performance. The use of organic salt activators is pollution-free, increases the specific surface area, increases the oxygen content of lignin-based porous carbon, and increases the number of surface defect sites, which can effectively adsorb antibiotics in the aquatic environment. Attached Figure Description

[0024] Figure 1 N2 adsorption-desorption isotherms (a) and pore size distribution (b) of sodium lignosulfonate-based porous carbon obtained by carbonization alone;

[0025] Figure 2 The N2 adsorption-desorption isotherms and pore size distribution diagrams for LBCs-2, LBCs-3, and LBCs-4 are shown.

[0026] Figure 3 Scanning electron microscope image of sodium lignosulfonate-based porous carbon obtained by carbonization alone;

[0027] Figure 4 Scanning electron microscope images of LBCs-2, LBCs-3, and LBCs-4;

[0028] Figure 5 Raman spectroscopy for sodium lignosulfonate-based porous carbon obtained by carbonization alone;

[0029] Figure 6 Raman plots for LBCs-2, LBCs-3, and LBCs-4;

[0030] Figure 7 The adsorption kinetics of norfloxacin on LBCs-1, LBCs-2, LBCs-3, and LBCs-4 are shown.

[0031] Figure 8 The figure shows the test results of the effect of solution pH on the adsorption capacity of LBCs-2 for norfloxacin. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] Example 1

[0034] A method for preparing porous carbon by carbonizing sodium lignin sulfonate alone includes the following steps:

[0035] (1) Sodium lignin sulfonate was washed with deionized water to remove insoluble impurities and cellulose. Then, it was subjected to ultrafiltration to remove small molecule inorganic salts and reducing sugars. It was then dried in an oven at 102°C for 24 hours. After being pulverized by a pulverizer, it was passed through a 20-mesh sieve to obtain sodium lignin sulfonate powder with uniform size.

[0036] (2) Place about 6g of sodium lignosulfonate powder into a porcelain boat and place it in a tube furnace. The atmosphere of the tube furnace is nitrogen, the flow rate is 150mL / min, the heating rate is 3℃ / min, first reach 120℃ and hold for 60min, then heat to 700℃ and react for 60min, and then cool to room temperature after the reaction.

[0037] (3) The obtained sample was washed with 0.1 mol / L dilute hydrochloric acid and deionized water in sequence to remove ash and other impurities; at the same time, it was washed repeatedly with deionized water until the pH value of the rinsing water remained unchanged; finally, it was dried in a 102℃ forced-air drying oven for 24 hours to remove residual moisture and obtain porous carbon (LBCs-1), and its performance was tested.

[0038] Figure 1 These are the isotherms and pore size distribution diagram of LBCs-1, with a specific surface area of ​​249 m². 2 / g, with a micropore volume ratio of 27.33%.

[0039] Figure 3 This is a scanning electron microscope image of LBCs-1. The surface is relatively smooth with a few pores.

[0040] Figure 5 Raman plot of LBCs-1, I D / I G =1.026.

[0041] Example 2

[0042] A method for preparing porous carbon from sodium lignin sulfonate with pore size control includes the following steps:

[0043] (1) The sodium lignosulfonate powder obtained in step (1) of Example 1 is mixed with potassium formate at a mass ratio of 1:2 to obtain a mixture of sodium lignosulfonate powder and potassium formate;

[0044] (2) Prepare an aqueous solution with a mass fraction of 82% from the mixture in step (1), shake the mixture evenly with a vortex mixer, concentrate it, and dry it in a 102℃ forced-air drying oven for 12 hours.

[0045] (3) The dried blend is crushed evenly and placed in a tube furnace. The atmosphere is nitrogen, the flow rate is 150 mL / min, the heating rate is 3℃ / min, first reach 120℃ and hold for 60 min, then heat to 700℃ and react for 60 min, and then cool to room temperature after the reaction.

[0046] (4) The obtained sample was washed with 0.1 mol / L dilute hydrochloric acid and deionized water in sequence to remove ash and other impurities; the blend was washed repeatedly with deionized water until the pH value of the rinsing water remained unchanged; finally, it was dried in a 102℃ forced-air drying oven for 24 h to remove residual moisture and obtain product LBCs-2.

[0047] Example 3

[0048] A method for preparing porous carbon from sodium lignin sulfonate with pore size control includes the following steps:

[0049] (1) The sodium lignosulfonate powder obtained in step (1) of Example 1 is mixed with silicon dioxide at a mass ratio of 1:1 to obtain a mixture of sodium lignosulfonate powder and silicon dioxide;

[0050] (2) Prepare an aqueous solution with a mass fraction of 82% from the mixture in step (1), shake the mixture evenly with a vortex mixer, concentrate it, and dry it in a 102℃ forced-air drying oven for 12 hours.

[0051] (3) The dried blend is crushed evenly and placed in a tube furnace. The atmosphere is nitrogen, the flow rate is 150 mL / min, the heating rate is 3℃ / min, first reach 120℃ and hold for 60 min, then heat to 700℃ and react for 60 min, and then cool to room temperature after the reaction.

[0052] (4) The obtained sample was washed with 0.1 mol / L dilute hydrochloric acid and deionized water in sequence to remove ash and other impurities; in addition, it was etched with 5M NaOH to remove SiO2; the blend was repeatedly washed with deionized water until the pH value of the rinsing water remained unchanged; finally, it was dried in a 102℃ forced-air drying oven for 24 h to remove residual moisture, and the product LBCs-3 was obtained.

[0053] Example 4

[0054] A method for preparing porous carbon from pore-size controlled lignin sulfonates includes the following steps:

[0055] (1) The lignin sulfonate powder obtained in step (1) of Example 1 is mixed with potassium formate and silicon dioxide in a mass ratio of 1:2:1 to obtain a mixture of lignin sulfonate powder, potassium formate and silicon dioxide;

[0056] (2) Prepare an aqueous solution with a mass fraction of 82% from the mixture in step (1), shake the mixture evenly with a vortex mixer, concentrate it, and dry it in a 102℃ forced-air drying oven for 12 hours.

[0057] (3) The dried blend is crushed evenly and placed in a tube furnace. The atmosphere is nitrogen, the flow rate is 150 mL / min, the heating rate is 3℃ / min, first reach 120℃ and hold for 60 min, then heat to 700℃ and react for 60 min, and then cool to room temperature after the reaction.

[0058] (4) The obtained sample was washed with 0.1 mol / L dilute hydrochloric acid and deionized water in sequence to remove ash and other impurities. In addition, it was etched with 5M NaOH to remove SiO2. All blends were washed repeatedly with deionized water until the pH value of the rinsing water remained unchanged. Finally, the product LBCs-4 was dried in a 102℃ drying oven for 24 hours to remove residual moisture.

[0059] Figure 2 The figures show the N2 adsorption-desorption isotherms and pore size distributions of LBCs-2, LBCs-3, and LBCs-4, with specific surface areas of 1916, 762, and 1077 m², respectively. 2 / g, the micropore volume percentages were 64.10%, 3.36% and 15.70%, respectively. Compared with LBCs-1, this indicates that potassium formate-assisted activation helps increase micropores, while the introduction of SiO2 generates more mesopores and macropores. This method can effectively regulate the pore size distribution of LBCs. The presence of micropores is conducive to the adsorption of organic matter and provides more active sites, while mesopores help accelerate the mass transfer of organic matter.

[0060] Figure 4 The images show scanning electron microscope (SEM) images of LBCs-2, LBCs-3, and LBCs-4. LBCs-2 has more pore structures, LBCs-3 has a rougher surface and shows irregular blocky structures, and LBCs-4 has a large number of regular pore structures. Compared with the surface morphology of LBCs-1, it can be seen that these three porous carbons are more conducive to the adsorption of organic matter due to the presence of more pore structures and defect sites.

[0061] Figure 6 Raman plots for LBCs-2, LBCs-3, and LBCs-4, I D / I G =1.06, 0.99 and 1.05.

[0062] Example 5

[0063] A method for preparing porous carbon from pore-size controlled lignin sulfonates includes the following steps:

[0064] (1) The sodium lignin sulfonate powder obtained in step (1) of Example 1 is mixed with silicon dioxide at a mass ratio of 1:3 to obtain a mixture of lignin sulfonate powder and silicon dioxide;

[0065] (2) Prepare an aqueous solution with a mass fraction of 82% from the mixture in step (1), shake the mixture evenly with a vortex mixer, concentrate it, and dry it in a 102℃ forced-air drying oven for 12 hours.

[0066] (3) The dried blend is crushed evenly and placed in a tube furnace. The atmosphere is nitrogen, the flow rate is 150 mL / min, the heating rate is 3℃ / min, first reach 120℃ and hold for 60 min, then heat to 700℃ and react for 60 min, and then cool to room temperature after the reaction.

[0067] (4) The obtained sample was washed sequentially with 0.1 mol / L dilute hydrochloric acid and deionized water to remove ash and other impurities; in addition, it was etched with 5M NaOH to remove SiO2; the blend was repeatedly washed with deionized water until the pH of the rinsing water remained unchanged; finally, it was dried in a 102℃ forced-air drying oven for 24 h to remove residual moisture, yielding the product sodium lignin sulfonate porous carbon. The porous carbon obtained by mixing sodium lignin sulfonate powder and silica at a mass ratio of 1:3 had specific surface areas of 639 and 513 m², respectively. 2 / g, all are less than the specific surface area of ​​LBCs-3.

[0068] Example 6

[0069] Adsorption experiment of LBCs on norfloxacin

[0070] Norfloxacin was dissolved in deionized water as a stock solution, and then diluted to a background solution containing 0.02 M NaCl (to maintain a constant ionic strength) (pH = 7.0 ± 1). All adsorption experiments were conducted in stoppered conical glass flasks.

[0071] A certain amount of LBCs (20 mg each for LBCs-1, LBCs-3, and LBCs-4; 10 mg for LBCs-2) and 200 mL of NOR solution were placed in a 250 mL stoppered glass conical flask and shaken at 180 rpm at 25 °C. Specifically, LBCs-1 was mixed with NOR at a concentration of 10 mg / L, LBCs-2 was mixed with NOR at a concentration of 50 mg / L, LBCs-3 was mixed with NOR at a concentration of 45 mg / L, and LBCs-4 was mixed with NOR at a concentration of 40 mg / L.

[0072] Subsequently, 2 mL samples were collected at intervals of 10, 30, 60, 120, 180, 240, 300, and 540 minutes. After centrifugation, the absorbance at 273 nm was measured using a UV-Vis spectrophotometer, and the adsorption kinetics were investigated.

[0073] The adsorption capacity of LBCs for norfloxacin was calculated using the following equation:

[0074]

[0075] Where: V(L) represents the volume of norfloxacin solution; C0(mg / L) and C t (mg / L) represent the initial and equilibrium concentrations of the norfloxacin solution, respectively. m(g) represents the mass of LBCs; Q t (mg / g) represents the amount of norfloxacin adsorbed by LBCs.

[0076] Figure 7 The graph shows the adsorption kinetics of norfloxacin by LBCs (the horizontal axis represents adsorption time (min), and the vertical axis represents the equilibrium adsorption amount (mg / g)). As time increases, the adsorption amount also increases. LBCs-3 and LBCs-4 reach equilibrium faster, while LBCs-2 has the best adsorption performance.

[0077] Example 7

[0078] Effect of pH on norfloxacin adsorption performance

[0079] Norfloxacin was dissolved in deionized water as a stock solution, and then diluted to a background solution containing 0.02 M NaCl (to maintain a constant ionic strength). The pH was adjusted to 5, 6, 7, 8, 9, and 10, respectively. All adsorption experiments were conducted in stoppered conical glass flasks.

[0080] A certain amount of LBCs-2 and 200 mL of NOR (50 mg / L) solution were placed in a 250 mL stoppered glass conical flask and shaken at 180 rpm at 25 °C. Subsequently, 2 mL of sample was collected after 24 h. After centrifugation, the absorbance at 273 nm was measured using a UV-Vis spectrophotometer, and the adsorption kinetics were studied.

[0081] The adsorption capacity of LBCs-2 for norfloxacin was calculated using the following equation:

[0082]

[0083] Where: V(L) represents the volume of norfloxacin solution; C0(mg / L) and C t (mg / L) represent the initial and equilibrium concentrations of the norfloxacin solution, respectively. m(g) represents the mass of LBCs; Q t(mg / g) represents the amount of norfloxacin adsorbed by LBCs.

[0084] Figure 8 The graph shows the effect of pH on the adsorption performance of norfloxacin (the horizontal axis represents pH value, and the vertical axis represents the equilibrium adsorption capacity (mg / g)). Although changes in pH value have a significant impact on the adsorption capacity, the adsorption capacity remains high. These results demonstrate that LBCs can adapt to different pH environments and exhibit excellent adsorption performance for NOR.

Claims

1. The application of sodium lignosulfonate-based porous carbon in the adsorption and removal of norfloxacin from aqueous solutions, characterized in that, Includes the following steps: (1) Sodium lignin sulfonate was washed with deionized water to remove insoluble impurities and cellulose. Then, it was subjected to ultrafiltration to remove small molecule inorganic salts and reducing sugars. It was then dried in an oven at 102 °C for 24 h. After pulverization, it was passed through a 20-mesh sieve to obtain sodium lignin sulfonate powder with uniform size. (2) Mix the sodium lignosulfonate powder obtained in step (1) with the pore-forming agent to obtain a mixture; (3) Prepare an aqueous solution with a mass fraction of 82% from the mixture in step (2), shake the mixture evenly with a vortex mixer, concentrate it, and dry it in a 102 ℃ forced-air drying oven for 12 h. (4) The dried blend is crushed evenly and placed in a tube furnace. The atmosphere is nitrogen, the flow rate is 150 mL / min, the heating rate is 3 ℃ / min, first reach 120 ℃ and hold for 60 min, then heat to 700 ℃ and react for 60 min. After the reaction, cool to room temperature. (5) The obtained sample was washed with 0.1 mol / L dilute hydrochloric acid and deionized water in sequence to remove ash and other impurities; in addition, when the pore-forming agent contained SiO2, it was etched with 5 M NaOH to remove SiO2; the blend was repeatedly washed with deionized water until the pH value of the rinsing water remained unchanged; finally, it was dried in a 102 ℃ forced-air drying oven for 24 h to remove residual moisture and obtain sodium lignosulfonate based porous carbon. Among them, when potassium formate is used as an auxiliary pore-forming agent, the mass ratio of sodium lignin sulfonate to potassium formate is 1:2, and the resulting porous carbon is denoted as LBCs-2; when silica is used as an auxiliary pore-forming agent, the mass ratio of sodium lignin sulfonate to silica is 1:1, and the resulting porous carbon is denoted as LBCs-3; when SiO2 and HCO2K are used as auxiliary pore-forming agents, the mass ratio of sodium lignin sulfonate, HCO2K, and SiO2 is 1:2:1, and the resulting porous carbon is denoted as LBCs-4. (6) Norfloxacin was dissolved in deionized water as a stock solution, and then diluted to a background solution containing 0.02 M NaCl, pH = 7.0±1; all adsorption experiments were carried out in stoppered glass conical flasks; (7) Place the sodium lignosulfonate-based porous carbon prepared in step (5) and 200 mL of norfloxacin solution into a 250 mL stoppered glass conical flask and shake at 180 rpm at 25 °C to adsorb and remove norfloxacin from the aqueous solution; wherein the amount of LBCs-3 and LBCs-4 is 20 mg each; the amount of LBCs-2 is 10 mg; mix LBCs-2 with a norfloxacin solution with a concentration of 50 mg / L, mix LBCs-3 with a norfloxacin solution with a concentration of 45 mg / L, and mix LBCs-4 with a norfloxacin solution with a concentration of 40 mg / L.

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