Application of Corn Stalk Activated Carbon in Catalytic Microbubble Ozone Polymerization for the Removal of Acetaminophen

Abstract

This invention relates to the field of wastewater treatment technology, specifically disclosing the application of corn stalk activated carbon in the catalytic microbubble ozone polymerization for the removal of acetaminophen. This invention uses agricultural waste corn stalks as raw material, preparing an activated carbon catalyst through joint activation with NaOH and ZnCl2. This catalyst is then added to wastewater containing acetaminophen, and ozone micro-nano bubbles are introduced. Under the synergistic effect of the catalyst and the microbubble ozone, acetaminophen undergoes a polymerization reaction on the catalyst surface, generating water-insoluble macromolecular polymers that deposit on the catalyst surface. The pollutant is then efficiently removed through simple solid-liquid separation. This invention, using corn stalks as raw material to prepare activated carbon material, has significant cost and industrial application advantages. It provides a highly efficient, recyclable, simple, economical, and environmentally friendly new approach for the deep treatment of acetaminophen-containing wastewater, with promising prospects for large-scale application.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to the application of corn stalk activated carbon in the catalytic microbubble ozone polymerization for the removal of acetaminophen. Background Technology

[0002] Acetaminophen (APAP) is one of the most widely used antipyretic and analgesic drugs globally. With the development of the pharmaceutical industry and the continuous growth in demand for medical medications, its production and use have expanded year by year. Because conventional municipal wastewater treatment processes have limited capacity to degrade drug-related micropollutants, incompletely removed APAP is discharged into the natural aquatic environment with the effluent, becoming a typical pharmaceutical and personal care product pollutant widely detected in surface water bodies. Long-term low-concentration residual APAP can have chronic toxicological effects on aquatic organisms and pose potential human health risks through drinking water circulation. Therefore, developing efficient purification technologies for APAP in water bodies is of significant practical importance.

[0003] Chemical oxidation methods, especially ozone oxidation technology, rely on the direct oxidation of ozone molecules in water and the indirect oxidation by hydroxyl radicals (‧OH) generated from their decomposition. This effectively destroys the molecular structure of APAP and exhibits strong mineralization capabilities, making it a research hotspot for APAP removal from water. Microbubble ozone technology further leverages its advantages, such as high gas-liquid mass transfer efficiency, long residence time in water, and spontaneous generation of ‧OH, achieving good treatment results even with relatively low ozone dosages. Introducing catalysts to promote ozone decomposition and increase free radical yield is a common method to enhance ozone oxidation performance. However, existing catalytic ozone oxidation systems require long treatment times or high oxidant dosages to achieve complete mineralization, increasing treatment costs and posing safety risks to wastewater.

[0004] Therefore, providing a new method that can achieve efficient removal of APAP within a short reaction time is of great significance for ensuring the ecological security of receiving water bodies. Summary of the Invention

[0005] To address the problems of long reaction times, high oxidant dosages, and the easy generation of highly toxic intermediate products in existing catalytic ozone oxidation degradation systems for acetaminophen, this invention provides an application of corn stalk activated carbon in the catalytic microbubble ozone polymerization removal of acetaminophen. This invention uses activated carbon prepared from agricultural waste corn stalks through joint activation with NaOH and ZnCl2 as a catalyst. In a microbubble ozone system, APAP is catalytically induced to polymerize on the catalyst surface. Subsequently, the polymer-loaded catalyst is separated from the water through solid-liquid separation, thus achieving efficient removal and recovery of acetaminophen.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the embodiments of the present invention is as follows: An application of corn stalk activated carbon in the catalytic microbubble ozone polymerization for the removal of acetaminophen, wherein the preparation method of the corn stalk activated carbon includes the following steps: Step a: Mix corn stalks, NaOH solution and ZnCl2 solution, then impregnate and activate them, and dry them to obtain activated corn stalks; Step b: Under an inert atmosphere, the activated corn stalks are carbonized at 550℃~650℃ for 1.5h~2.5h to obtain activated corn stalk carbon. The mass ratio of corn stalks, NaOH, and ZnCl2 is 1:(0.6~0.8):(0.2~0.4).

[0007] Unlike traditional deep mineralization methods, this approach utilizes a specific catalyst to induce the polymerization of APAP in an oxidizing environment, generating water-insoluble macromolecular polymers. These polymers are then removed from the water through solid-liquid separation and recycled. This provides a novel approach to the chemical transformation, solid-phase separation, and recycling of pollutants. This method alters the molecular morphology of pollutants through chemical polymerization, achieving highly efficient separation from the aqueous phase. It avoids the accumulation and release of toxic oxidation intermediates in water and can achieve high removal rates under relatively mild conditions.

[0008] This invention uses corn stalk activated carbon co-activated by NaOH and ZnCl2 as a catalyst to catalyze and induce the polymerization of APAP on the catalyst surface in a microbubble ozone system. This generates water-insoluble macromolecular polymers that deposit on the catalyst surface, and the pollutant can then be removed from the aqueous phase through simple solid-liquid separation. This method eliminates the need to wait for APAP to be gradually oxidized and decomposed into CO2 and H2O, thus achieving ideal removal efficiency in a shorter reaction time and significantly reducing ozone dosage and energy costs. This invention overcomes the limitations of traditional ozone oxidation systems, such as low free radical generation and limited pollutant mineralization. It significantly improves APAP removal efficiency under mild conditions of ambient temperature and pressure, reducing ozone dosage and water treatment operating costs, and is suitable for the deep purification of water bodies containing APAP, a novel pollutant.

[0009] As a specific embodiment of the present invention, the corn stalks are taken from rural farmland and urban farms. Before use, the corn stalks are cleaned, dried at 100℃~105℃ for 3h~4h, and ground into powder.

[0010] In step a, the immersion activation temperature is 20℃~40℃, and the immersion activation time is 18h~22h.

[0011] In step a, the NaOH solution has a mass fraction of 30% to 40%, and the ZnCl2 solution has a mass fraction of 40% to 50%.

[0012] The combined activation of corn stalks using a 30%–40% NaOH solution and a 40%–50% ZnCl2 solution can form a rich hierarchical structure and oxygen-containing functional groups on the surface and inside the pores of the corn stalks, significantly increasing the specific surface area and the number of surface active sites of activated carbon, and providing sufficient interfacial space for the adsorption and polymerization reaction of APAP on the catalyst surface.

[0013] It should be noted that in step a, after adding NaOH solution and ZnCl2 solution, an appropriate amount of deionized water is added. The amount of deionized water added should be such that the solution completely submerges the corn stalk powder without significantly diluting the effective concentration of the activator. This ensures that the activator and corn stalk powder are in full contact, guaranteeing the uniformity and sufficiency of impregnation and activation, avoiding local under-activation or over-activation, thereby ensuring the uniformity of the pore structure of the obtained activated carbon catalyst and the batch stability of its catalytic performance.

[0014] In step b, the carbonization temperature is 600℃ and the carbonization time is 2 hours.

[0015] The catalyst prepared under the above process conditions has a large specific surface area, a porous structure, and abundant defects. Its overall framework is an amorphous carbon matrix formed by the carbonization of corn stalks. The interior is constructed with a hierarchical pore system consisting of micropores, mesopores, and a small number of macropores. Among them, the micropore size is dominant, providing sufficient adsorption sites for APAP. At the same time, the carbon surface contains abundant oxygen-containing functional groups, defect sites, and a small number of metal active sites, which can work together with ozone microbubbles to achieve efficient adsorption of APAP.

[0016] Based on this, the present invention also provides an advanced oxidation technology for removing APAP from wastewater, comprising the following steps: Add the corn stalk activated carbon described in any of the above-mentioned items to wastewater containing APAP, mix, and then introduce ozone microbubbles. Under the action of the corn stalk activated carbon and ozone microbubbles, APAP undergoes a polymerization reaction to remove acetaminophen.

[0017] Unlike traditional catalytic ozone oxidation methods that aim for complete mineralization, this invention utilizes corn stalk activated carbon in a microbubble ozone system to catalyze and induce the polymerization of APAP (amino acid polymerase), converting water-soluble small-molecule pollutants into water-insoluble large-molecule polymers that deposit on the catalyst surface. Subsequently, efficient pollutant removal is achieved through solid-liquid separation. This method differs from the gradual oxidation and decomposition of APAP into carbon dioxide and water, thus achieving ideal removal results in a shorter reaction time and significantly reducing ozone dosage and energy costs. Furthermore, the polymerization removal pathway focuses on the overall solid-phase formation of pollutants, effectively avoiding the accumulation and emission of highly toxic oxidation intermediates such as benzoquinone and short-chain carboxylic acids in water during traditional mineralization processes, significantly improving effluent safety. The entire treatment process is simple to operate; the catalyst can be separated from water using conventional methods such as precipitation or filtration, facilitating subsequent regeneration and recycling, resulting in significant environmental and economic benefits.

[0018] It should be noted that after the reaction, the corn stalk activated carbon catalyst carrying the polymerization product is separated from the water by solid-liquid separation methods such as precipitation or filtration. The separated catalyst is then washed with a mixed solution of acetic acid and ethanol to dissolve and remove the polymer deposited on the catalyst surface. It is then washed with deionized water until neutral and dried, thus achieving the regeneration of the corn stalk activated carbon and the resource reuse of the polymer. This regeneration method is simple to operate, has low solvent costs, and the regenerated activated carbon can be recycled multiple times for catalytic microbubble ozone polymerization to remove APAP, significantly reducing the long-term use cost of the catalyst. The recovered APAP can be used to make anti-corrosion primers, epoxy curing agents, phenolic resin modifiers, etc., further enhancing the comprehensive application value and promotion prospects of this method.

[0019] Furthermore, the amount of corn stalk activated carbon added is 0.45 g / L to 0.55 g / L.

[0020] Furthermore, the concentration of acetaminophen in the wastewater is 40 mg / L to 55 mg / L.

[0021] Furthermore, the pH of the wastewater containing acetaminophen is 6.5 to 7.5.

[0022] Furthermore, the polymerization reaction takes 25 to 35 minutes.

[0023] Furthermore, the ozone microbubbles have a particle size ≤50μm.

[0024] Furthermore, the flow rate of the ozone microbubbles is 0.25 L / min to 0.3 L / min.

[0025] In summary, this invention uses agricultural waste corn stalks as raw material, and prepares an activated carbon catalyst through joint activation with NaOH and ZnCl2. This activated carbon catalyst is then added to wastewater containing APAP, and ozone microbubbles are introduced. Under the synergistic effect of the catalyst and ozone microbubbles, APAP undergoes a polymerization reaction on the catalyst surface, generating water-insoluble macromolecular polymers that deposit on the catalyst surface. Simple solid-liquid separation then achieves efficient removal of the pollutants. Unlike existing catalytic ozone oxidation technologies that pursue deep mineralization, this invention uses the solid-phase polymerization of pollutants as its core mechanism, eliminating the need to wait for complete oxidation and decomposition of acetaminophen. Therefore, it can achieve ideal removal results in a shorter time, significantly reducing ozone dosage and energy costs. The treated catalyst, after regeneration by washing with acetic acid and ethanol, can be used to produce anti-corrosion primers, epoxy curing agents, phenolic resin modifiers, etc., further improving the comprehensive utilization value of resources and reducing overall treatment costs. This invention provides a new, efficient, low-toxicity, simple, economical, and environmentally friendly approach for the deep treatment of APAP-containing wastewater, with promising prospects for large-scale application. Attached Figure Description

[0026] Figure 1 SEM image of the straw activated carbon prepared in Example 1; Figure 2 TEM image of the straw activated carbon prepared in Example 1; Figure 3 EDS image of the straw activated carbon prepared in Example 1; Figure 4 This is the UV-Vis full spectrum scan of the activated carbon extract after the microbubble-coordinated ozone oxidation reaction in Example 4; Figure 5 The LC-MS parent APAP secondary mass spectrum of the activated carbon extract after microbubble synergistic ozone oxidation reaction in Example 4 is shown. Figure 6 The image shows the LC-MS dimer secondary mass spectrum of the activated carbon extract after the microbubble-coordinated ozone oxidation reaction in Example 4. Figure 7 The image shows the LC-MS trimer secondary mass spectrum of the activated carbon extract after the microbubble-coordinated ozone oxidation reaction in Example 4. Figure 8 This is a schematic diagram of the apparatus used in the experiment of catalytic microbubble ozone polymerization to remove APAP in Example 4 of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] To better illustrate the present invention, further examples are provided below.

[0029] Example 1 This embodiment provides a method for preparing straw activated carbon, including the following steps: Step a: Wash the corn stalks taken from rural farmland and urban farm with deionized water, dry them in an oven at 100°C for 3 hours, take them out and cool them to room temperature, then grind them into powder to obtain corn stalk powder. Step b: Weigh out NaOH solid and ZnCl2 solid according to the mass ratio of corn stalk powder, NaOH, and ZnCl2 of 1:0.7:0.3. Add appropriate amounts of deionized water to each and stir until completely dissolved to prepare a 35% NaOH solution and a 45% ZnCl2 solution. Add the NaOH solution and ZnCl2 solution to the corn stalk powder obtained in step a, and continue to add deionized water until the solution completely submerges the corn stalk powder. Stir to form a uniform paste. Seal the paste with sealing film to prevent the NaOH solution from absorbing moisture and carbon dioxide from the air. Activate the paste at room temperature for 20 hours. After removal, dry it in an oven at 100℃ for 3 hours to obtain activated corn stalk powder. Step c: Place the activated corn stalk powder obtained from step b into a tube furnace and carbonize it at 600°C for 2 hours under a nitrogen protective atmosphere. After cooling, remove the powder and wash it alternately with hydrochloric acid and deionized water until the washing solution is neutral. Place the washed solid in an oven at 100°C and dry it to constant weight. Grind the solid to obtain activated corn stalk carbon.

[0030] TEM and SEM images of the corn stalk activated carbon prepared in this embodiment are shown below. Figures 1-2 As shown in the SEM images, the activated carbon surface exhibits a rich hierarchical porous structure, containing numerous large pores with diameters of approximately 0.2–1.0 μm. These pores are interconnected and uniformly distributed, indicating that the combined activation by NaOH and ZnCl2 effectively etched the natural structure of the corn stalk, successfully constructing a well-developed porous system that provides ample mass transfer channels and active sites for subsequent reactions. TEM images further reveal the internal microstructure of the material, exhibiting typical amorphous carbon skeleton characteristics without obvious large particle agglomeration. Fine active component particles are uniformly distributed within the carbon matrix, providing a structural basis for the stable catalytic role of activated carbon in the microbubble ozone polymerization reaction.

[0031] The EDS diagram of the corn straw activated carbon prepared in this embodiment is shown in the figure below. Figure 3As shown in the figure, EDS analysis results indicate that the activated carbon is mainly composed of carbon (C) and oxygen (O), indicating that the material has carbon as its main framework and its surface contains abundant oxygen-containing functional groups, which can provide sufficient active sites for subsequent ozone catalytic reactions. At the same time, trace amounts of zinc (Zn) and sodium (Na) elements were detected in the energy spectrum, which originated from ZnCl2 and NaOH introduced during the activation process. This indicates that the two activators effectively played the role of pore-forming agents and introduced oxygen-containing functional groups during the preparation process, and the residual amount after subsequent washing is extremely low, which will not have an adverse effect on the overall catalytic performance of the activated carbon.

[0032] Example 2 In this embodiment, APAP is the target pollutant, and the adsorption performance of the corn straw activated carbon prepared in Example 1 by combining NaOH and ZnCl2 for activation is evaluated by the adsorption method alone.

[0033] Add 400 mL of APAP wastewater with a concentration of 20 mg / L to a 500 mL beaker. Weigh 0.2 g of the corn stalk activated carbon catalyst prepared in Example 1 (addition amount of 0.5 g / L) and add it to the beaker. Place a clean rotor in the beaker and put it on a magnetic stirrer. Adjust the speed to 500 r / min and react at room temperature for 30 min. Take 5 mL of water sample every 5 min, filter it through a 0.45 μm filter membrane, and measure the absorbance of APAP in the filtrate.

[0034] The removal rate of APAP is calculated using the following formula: Removal rate = (A0 - A) t ) / A0×100% In the formula, A0 is the absorbance of APAP in the initial solution, A t for t The absorbance of APAP in the solution at a given time.

[0035] The reaction kinetics were fitted using a pseudo-first-order kinetic model: ln(A0 / A t )= kt In the formula, A0 is the absorbance of APAP in the initial solution, A t Let be the absorbance of APAP in the solution at time t. k The reaction kinetic constant (min) -1 ), t The reaction time is in minutes.

[0036] The test results showed that after 5 minutes of reaction, the removal rate of APAP was 50.12%, and the reaction kinetic constant was 0.1391 min. -1 After 30 minutes of reaction, the removal rate of APAP reached 76.09%, and the reaction kinetic constant was 0.0477 min.-1 .

[0037] The above results demonstrate that the NaOH and ZnCl2 co-activated corn stalk activated carbon prepared in Example 1 has a good adsorption and removal capacity for APAP in water due to its well-developed hierarchical porous structure and abundant oxygen-containing functional groups on the surface.

[0038] Example 3 This embodiment investigated the effects of different preparation conditions on the pore structure of corn straw activated carbon jointly activated by NaOH and ZnCl2. The specific surface area, total pore volume and average pore size of the activated carbon obtained under different calcination temperatures, calcination times and activator ratios were characterized by the BET specific surface area test method. The test results are shown in Table 1.

[0039] Table 1. BET test results of corn stalk activated carbon As shown in Table 1, when the mass ratio of NaOH to ZnCl2 is 0.7:0.3, the calcination temperature is 600℃, and the calcination time is 2h, the specific surface area of ​​the prepared activated carbon reaches 466.105m². 2 / g, total pore volume is 0.475cm³ 3 / g, with an average pore size of 2.04nm, all three indicators are significantly better than other comparative conditions.

[0040] After increasing the calcination temperature from 600℃ to 700℃, the specific surface area of ​​the activated carbon increased from 466.105 m². 2 / g dropped sharply to 147.077m 2 / g, and the total pore volume also increased from 0.475cm³. 3 / g decreased to 0.145cm 3 / g indicates that the excessively high calcination temperature caused excessive shrinkage of the carbon skeleton and collapse of the pores, resulting in the sintering and closure of some microporous structures, which severely weakened the porosity of the activated carbon.

[0041] When the mass ratio of NaOH to ZnCl2 was adjusted from 0.7:0.3 to 0.5:0.5 (i.e., reducing the amount of NaOH and increasing the amount of ZnCl2), the specific surface area of ​​the resulting activated carbon decreased to 293.498 m². 2 / g, total pore volume decreased to 0.251cm³. 3 The / g indicates that NaOH plays a dominant role in etching and pore formation and building a high specific surface area carbon framework in the joint activation system. Insufficient NaOH will lead to insufficient activation.

[0042] Extending the calcination time from 2 hours to 3 hours increased the specific surface area of ​​the activated carbon from 466.105 m². 2 / g decreased to 316.771m 2 / g, total pore volume is 0.475cm³ 3 / g decreased to 0.399cm 3 / g indicates that excessive carbonization time can also cause excessive ablation of the pore structure, which is not conducive to maintaining a high specific surface area.

[0043] Example 4 This embodiment investigates the catalytic polymerization removal effect of the corn straw activated carbon jointly activated by NaOH and ZnCl2 prepared in Example 1 on APAP in an ozone microbubble synergistic oxidation system, and explores the reaction mechanism.

[0044] (1) Experiment on removal of APAP by catalytic microbubble ozone polymerization Prepare 5L of APAP solution with a concentration of 50.0 mg / L and inject it into an acrylic glass reactor (the reactor is cylindrical, 22 cm in diameter, 46 cm high, with a working volume of 5L). Figure 8 In the APAP solution, 2.5g of the corn stalk activated carbon catalyst prepared in Example 1 (addition amount of 0.5g / L) was added, the pH of the solution was adjusted to 7, and the catalyst was stirred evenly with a glass rod to fully disperse the catalyst in the APAP solution. The ozone microbubble generator was turned on to generate ozone microbubbles with a particle size ≤50.0μm and introduced into the reactor. The gas flow rate was maintained at 0.3L / min, and the ozone dosage was kept stable at 10mg / min. The experimental cycle was 30min, and samples were taken at the sampling port every 5min. The absorbance of APAP was measured after the water sample was filtered through a 0.45μm filter membrane, and the removal rate and reaction kinetic constant were calculated.

[0045] The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was 56.20%, and the reaction kinetic constant was 0.1651 min. -1 After 30 minutes of reaction, the removal rate of acetaminophen reached 91.80%, and the reaction kinetic constant was 0.0834 min. -1 Compared with the removal rate of only 76.09% achieved by adsorption alone for 30 minutes in Example 2, the introduction of microbubble ozone significantly improved the removal rate, indicating that the corn stalk activated carbon prepared in this example has good catalytic activity in the ozone microbubble system and can greatly enhance the removal effect of APAP.

[0046] (2) Investigation of reaction mechanism To investigate whether organic matter deposits on the surface of activated carbon during the reaction, the activated carbon catalyst after the reaction was recovered through solid-liquid separation, extracted with methanol and acetic acid, and the extract was subjected to UV-Vis full-spectrum scanning. The results are as follows: Figure 4As shown in the figure, the extract exhibits obvious absorption characteristics in the range of 200-450 nm, with a significant broadened absorption peak appearing near 245 nm. Compared to the characteristic peak of the APAP monomer at 243 nm, this peak shows a slight red shift and is broader and blunter, corresponding to the π-π* transition unique to aromatic rings, which is a typical characteristic absorption of aromatic oligomers. Tailing absorption is still present in the 270-300 nm range, indicating the presence of a product with a higher degree of conjugation in the system.

[0047] Further qualitative analysis of the methanol and acetic acid extracts using liquid chromatography-mass spectrometry (LC-MS) revealed the presence of multiple APAP polymerization products within the system. Besides the APAP parent compound (m / z 151), the main polymerization products were APAP dehydration coupling dimer (m / z 284) and dimer (m / z 302), with trace amounts of higher-order polymers such as trimer (m / z 453) also detected. This confirms that the removal of APAP in this reaction system is accompanied by significant molecular polymerization behavior.

[0048] Qualitative analysis of APAP and its coupling polymerization products in the reaction system was performed using secondary mass spectrometry (MS / MS). For example... Figure 5 As shown, with the APAP monomer (m / z 152.07) as the base peak (relative abundance 100%), a series of APAP characteristic fragment ions were generated after collisional dissociation: m / z 110.05 is the characteristic fragment of deacetylation, and m / z 85.94 and 65.03 are small molecule fragments of deeply cleaved benzene ring skeleton. The fragment ions matched the fragmentation pattern of acetaminophen standard, confirming that this substance is the APAP parent substrate.

[0049] like Figure 6 As shown, with the dehydrated coupled dimer (m / z 283.17) as the base peak, collision-induced fragmentation produces characteristic fragments at m / z 301.97, 257.98, and 240.94. Among them, m / z 301.97 corresponds to the intact undehydrated dimer skeleton fragment, while m / z 257.98 and 240.94 are APAP-derived fragments generated after the dimer skeleton breaks. This confirms that the substance is generated by the coupling of two APAP molecules via phenol-oxygen radicals and the unimolecular dehydration condensation.

[0050] like Figure 7 As shown, with the trimer (m / z 453.84) as the base peak, collisional dissociation causes the breakage of coupling C-C bonds, producing characteristic fragments of hydroxylated modified dimers at m / z 341.24 and characteristic fragments of APAP aromatic rings at m / z 114.09. This proves that the trimer is generated by the continuous free radical coupling polymerization of three APAP molecules, and the polymerization process is accompanied by hydroxyl radical oxidation modification.

[0051] The above mechanism investigation results fully reveal the polymerization path of APAP in the ozone microbubble-corn straw activated carbon system of the present invention: APAP undergoes a stepwise free radical coupling reaction on the catalyst surface under the induction of hydroxyl radicals, and successively generates water-insoluble macromolecular polymer products such as dimers and trimers. At the same time, the polymer skeleton undergoes hydroxylation and oxidation derivatization. Finally, the polymer is removed from the water along with the catalyst through solid-liquid separation, thus achieving efficient polymerization and removal of APAP.

[0052] Comparative Example 1 This comparative example provides a method for preparing straw activated carbon, which differs from Example 1 only in that it does not use the combined activation of NaOH and ZnCl2. Specifically, it includes the following steps: Step a: Wash the corn stalks taken from rural farmland and urban farm with deionized water, dry them in an oven at 100°C for 3 hours, take them out and cool them to room temperature, then grind them into powder to obtain corn stalk powder. Step b: Place the corn stalk powder obtained in step a into a tube furnace and perform high-temperature carbonization treatment at 600℃ for 2 hours under a nitrogen protective atmosphere. After cooling, remove the powder, wash it with deionized water until neutral, and place the washed solid in an oven at 100℃ to dry to constant weight. Grind the solid to obtain corn stalk activated carbon material that has not been activated by NaOH and ZnCl2.

[0053] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was only 0.64%, and the reaction kinetic constant was 0.0013 min. -1 After 30 minutes of reaction, the removal rate of APAP was only 1.91%, and the reaction kinetic constant was 0.0006 min. -1 .

[0054] Comparative Example 2 This comparative example provides a method for preparing straw activated carbon, which differs from Example 1 only in that the calcination temperature is changed to 500℃. The specific steps include: Step a: Wash the corn stalks taken from rural farmland and urban farm with deionized water, dry them in an oven at 100°C for 3 hours, take them out and cool them to room temperature, then grind them into powder to obtain corn stalk powder. Step b: Weigh out NaOH solid and ZnCl2 solid according to the mass ratio of corn stalk powder, NaOH, and ZnCl2 of 1:0.7:0.3. Add appropriate amounts of deionized water to each and stir until completely dissolved to prepare a 35% NaOH solution and a 45% ZnCl2 solution. Add the NaOH solution and ZnCl2 solution to the corn stalk powder obtained in step a, and continue to add deionized water until the solution completely submerges the corn stalk powder. Stir to form a uniform paste. Seal the paste with sealing film to prevent the NaOH solution from absorbing moisture and carbon dioxide from the air. Activate the paste at room temperature for 20 hours. After removal, dry it in an oven at 100℃ for 3 hours to obtain activated corn stalk powder. Step c: Place the activated corn stalk powder obtained from step b into a tube furnace and carbonize it at 500°C for 2 hours under a nitrogen protective atmosphere. After cooling, remove the powder and wash it alternately with hydrochloric acid and deionized water until the washing solution is neutral. Place the washed solid in an oven at 100°C and dry it to constant weight. Grind the solid to obtain corn stalk activated carbon.

[0055] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of APAP was only 6.28%, and the reaction kinetic constant was 0.013 min. -1 After 30 minutes of reaction, the removal rate of APAP was only 9.03%, and the reaction kinetic constant was 0.0032 min. -1 .

[0056] Comparative Example 3 This comparative example provides a method for preparing straw activated carbon, which differs from Example 1 only in that the calcination temperature is changed to 700℃. The specific steps include: Step a: Wash the corn stalks taken from rural farmland and urban farm with deionized water, dry them in an oven at 100°C for 3 hours, take them out and cool them to room temperature, then grind them into powder to obtain corn stalk powder. Step b: Weigh out NaOH solid and ZnCl2 solid according to the mass ratio of corn stalk powder, NaOH, and ZnCl2 of 1:0.7:0.3. Add appropriate amounts of deionized water to each and stir until completely dissolved to prepare a 35% NaOH solution and a 45% ZnCl2 solution. Add the NaOH solution and ZnCl2 solution to the corn stalk powder obtained in step a, and continue to add deionized water until the solution completely submerges the corn stalk powder. Stir to form a uniform paste. Seal the paste with sealing film to prevent the NaOH solution from absorbing moisture and carbon dioxide from the air. Activate the paste at room temperature for 20 hours. After removal, dry it in an oven at 100℃ for 3 hours to obtain activated corn stalk powder. Step c: Place the activated corn stalk powder obtained from step b into a tube furnace and carbonize it at 700°C for 2 hours under a nitrogen protective atmosphere. After cooling, remove the powder and wash it alternately with hydrochloric acid and deionized water until the washing solution is neutral. Place the washed solid in an oven at 100°C and dry it to constant weight. Grind the solid to obtain activated corn stalk carbon.

[0057] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of APAP was only 17.18%, and the reaction kinetic constant was 0.0377 min. -1 After 30 min of reaction, the removal rate of acetaminophen was only 30.23%, and the reaction kinetic constant was 0.0120 min. -1 .

[0058] Comparative Example 4 This comparative example provides a method for preparing straw activated carbon, which differs from Example 1 in that the ratio of corn straw:NaOH:ZnCl2 is 1:0.5:0.5, and specifically includes the following steps: Step a: Wash the corn stalks taken from rural farmland and urban farm with deionized water, dry them in an oven at 100°C for 3 hours, take them out and cool them to room temperature, then grind them into powder to obtain corn stalk powder. Step b: Weigh out NaOH solid and ZnCl2 solid according to the mass ratio of corn stalk powder, NaOH, and ZnCl2 of 1:0.5:0.5. Add appropriate amounts of deionized water to each and stir until completely dissolved to prepare a 35% NaOH solution and a 45% ZnCl2 solution. Add the NaOH solution and ZnCl2 solution to the corn stalk powder obtained in step a, and continue to add deionized water until the solution completely submerges the corn stalk powder. Stir to form a uniform paste. Seal the paste with sealing film to prevent the NaOH solution from absorbing moisture and carbon dioxide from the air. Activate the paste at room temperature for 20 hours. After removal, dry it in an oven at 100℃ for 3 hours to obtain activated corn stalk powder. Step c: Place the activated corn stalk powder obtained from step b into a tube furnace and carbonize it at 600°C for 2 hours under a nitrogen protective atmosphere. After cooling, remove the powder and wash it alternately with hydrochloric acid and deionized water until the washing solution is neutral. Place the washed solid in an oven at 100°C and dry it to constant weight. Grind the solid to obtain activated corn stalk carbon.

[0059] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was only 24.92%, and the reaction kinetic constant was 0.0574 min. -1After 30 minutes of reaction, the removal rate of acetaminophen was only 31.11%, and the reaction kinetic constant was 0.0125 min. -1 .

[0060] Comparative Example 5 This comparative example provides a method for preparing straw activated carbon, which differs from Example 1 in that the ratio of corn straw:NaOH:ZnCl2 is 1:0.3:0.7, and specifically includes the following steps: Step a: Wash the corn stalks taken from rural farmland and urban farm with deionized water, dry them in an oven at 100°C for 3 hours, take them out and cool them to room temperature, then grind them into powder to obtain corn stalk powder. Step b: Weigh out NaOH solid and ZnCl2 solid according to the mass ratio of corn stalk powder, NaOH, and ZnCl2 of 1:0.3:0.7. Add appropriate amounts of deionized water to each and stir until completely dissolved to prepare a 35% NaOH solution and a 45% ZnCl2 solution. Add the NaOH solution and ZnCl2 solution to the corn stalk powder obtained in step a, and continue to add deionized water until the solution completely submerges the corn stalk powder. Stir to form a uniform paste. Seal the paste with sealing film to prevent the NaOH solution from absorbing moisture and carbon dioxide from the air. Activate the paste at room temperature for 20 hours. After removal, dry it in an oven at 100℃ for 3 hours to obtain activated corn stalk powder. Step c: Place the activated corn stalk powder obtained from step b into a tube furnace and carbonize it at 600°C for 2 hours under a nitrogen protective atmosphere. After cooling, remove the powder and wash it alternately with hydrochloric acid and deionized water until the washing solution is neutral. Place the washed solid in an oven at 100°C and dry it to constant weight. Grind the solid to obtain activated corn stalk carbon.

[0061] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was only 18.80%, and the reaction kinetic constant was 0.0417 min. -1 After 30 minutes of reaction, the removal rate of acetaminophen was only 36.03%, and the reaction kinetic constant was 0.0149 min. -1 .

[0062] Comparative Example 6 This comparative example provides a method for preparing straw activated carbon, which differs from Example 1 only in that the calcination time is changed to 1 hour. The specific steps include the following: Step a: Wash the corn stalks taken from rural farmland and urban farm with deionized water, dry them in an oven at 100°C for 3 hours, take them out and cool them to room temperature, then grind them into powder to obtain corn stalk powder. Step b: Weigh out NaOH solid and ZnCl2 solid according to the mass ratio of corn stalk powder, NaOH, and ZnCl2 of 1:0.7:0.3. Add appropriate amounts of deionized water to each and stir until completely dissolved to prepare a 35% NaOH solution and a 45% ZnCl2 solution. Add the NaOH solution and ZnCl2 solution to the corn stalk powder obtained in step a, and continue to add deionized water until the solution completely submerges the corn stalk powder. Stir to form a uniform paste. Seal the paste with sealing film to prevent the NaOH solution from absorbing moisture and carbon dioxide from the air. Activate the paste at room temperature for 20 hours. After removal, dry it in an oven at 100℃ for 3 hours to obtain activated corn stalk powder. Step c: Place the activated corn stalk powder obtained from step b into a tube furnace and carbonize it at 600°C for 1 hour under a nitrogen protective atmosphere. After cooling, remove the powder and wash it alternately with hydrochloric acid and deionized water until the washing solution is neutral. Place the washed solid in an oven at 100°C and dry it to constant weight. Grind the solid to obtain corn stalk activated carbon.

[0063] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was only 24.72%, and the reaction kinetic constant was 0.0568 min. -1 After 30 minutes of reaction, the removal rate of APAP was only 41.76%, and the reaction kinetic constant was 0.0180 min. -1 .

[0064] Comparative Example 7 This comparative example provides a method for preparing straw activated carbon, which differs from Example 1 only in that the calcination time is changed to 3 hours. The specific steps include the following: Step a: Wash the corn stalks taken from rural farmland and urban farm with deionized water, dry them in an oven at 100°C for 3 hours, take them out and cool them to room temperature, then grind them into powder to obtain corn stalk powder. Step b: Weigh out NaOH solid and ZnCl2 solid according to the mass ratio of corn stalk powder, NaOH, and ZnCl2 of 1:0.7:0.3. Add appropriate amounts of deionized water to each and stir until completely dissolved to prepare a 35% NaOH solution and a 45% ZnCl2 solution. Add the NaOH solution and ZnCl2 solution to the corn stalk powder obtained in step a, and continue to add deionized water until the solution completely submerges the corn stalk powder. Stir to form a uniform paste. Seal the paste with sealing film to prevent the NaOH solution from absorbing moisture and carbon dioxide from the air. Activate the paste at room temperature for 20 hours. After removal, dry it in an oven at 100℃ for 3 hours to obtain activated corn stalk powder. Step c: Place the activated corn stalk powder obtained from step b into a tube furnace and carbonize it at 600°C for 3 hours under a nitrogen protective atmosphere. After cooling, remove the powder and wash it alternately with hydrochloric acid and deionized water until the washing solution is neutral. Place the washed solid in an oven at 100°C and dry it to constant weight. Grind the solid to obtain activated corn stalk carbon.

[0065] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was only 36.93%, and the reaction kinetic constant was 0.0922 min. -1 After 30 minutes of reaction, the removal rate of acetaminophen was only 57.44%, and the reaction kinetic constant was 0.0285 min. -1 .

[0066] Comparative Example 8 This comparative example investigated the differences in adsorption performance of the corn stalk activated carbon jointly activated by NaOH and ZnCl2 prepared in Example 1 for different target pollutants. The preparation process was exactly the same as steps a to c in Example 1, except that the target pollutant was replaced by bisphenol A instead of APAP.

[0067] Adsorption performance was tested under the same experimental conditions as in Example 2. 400 mL of 20 mg / L bisphenol A solution was added to a 500 mL beaker, along with 0.2 g of the corn stalk activated carbon catalyst prepared in Example 1. The experiment was conducted under the same stirring conditions and reaction time.

[0068] The test results showed that after 5 minutes of reaction, the removal rate of bisphenol A was 32%, and the reaction kinetic constant was 0.077 min. -1 After 30 minutes of reaction, the removal rate of bisphenol A was 62%, and the reaction kinetic constant was 0.0325 min. -1 .

[0069] Compared to the 76.09% removal rate of APAP under the same conditions for 30 minutes in Example 2, the removal rate of bisphenol A in this comparative example is significantly lower. This difference indicates that the NaOH and ZnCl2 combined activated corn stalk carbon prepared in Example 1 exhibits different adsorption affinities and removal effects on different types of phenolic pollutants. Its removal performance for APAP is superior to that for bisphenol A, which may be related to the differences between the two pollutants in terms of molecular size, functional group composition, and hydrophobicity. This also further confirms the good compatibility between the catalyst of this invention and APAP.

[0070] Comparative Example 9 This comparative example further investigated the differences in adsorption performance of the corn stalk activated carbon jointly activated by NaOH and ZnCl2 prepared in Example 1 for different target pollutants. The preparation process was exactly the same as steps a to c in Example 1, except that the target pollutant was replaced by phenol instead of APAP.

[0071] Adsorption performance was tested under the same experimental conditions as in Example 2. 400 mL of phenol solution with a concentration of 20 mg / L was added to a 500 mL beaker, and 0.2 g of the corn stalk activated carbon catalyst prepared in Example 1 was added. The experiment was conducted under the same stirring conditions and reaction time.

[0072] The test results showed that after 5 minutes of reaction, the removal rate of phenol was 42.31%, and the reaction kinetic constant was 0.1089 min. -1 After 30 minutes of reaction, the phenol removal rate was 65.38%, and the reaction kinetic constant was 0.0346 min. -1 .

[0073] Comparative Example 10 This comparative example provides a method for preparing corn stalk activated carbon using only NaOH as an activator. The only difference from Example 1 is that the activator in step b is changed from the combined use of NaOH and ZnCl2 to the use of only NaOH. The amount of NaOH used is the same as that in Example 1, and the other conditions remain unchanged.

[0074] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was 41.51%, and the reaction kinetic constant was 0.1073 min. -1 After 30 min of reaction, the removal rate of acetaminophen was 71.95%, and the reaction kinetic constant was 0.0424 min. -1 .

[0075] Comparative Example 11 This comparative example provides a method for preparing corn stalk activated carbon using only NaOH as an activator. The only difference from Example 1 is that the activator in step b is changed from the combined use of NaOH and ZnCl2 to the use of ZnCl2 alone. The amount of ZnCl2 used is the same as that in Example 1, and the other conditions remain unchanged.

[0076] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was 33.85%, and the reaction kinetic constant was 0.0413 min. -1After 30 min of reaction, the removal rate of acetaminophen was 48.75%, and the reaction kinetic constant was 0.0223 min. -1 .

[0077] Comparative Example 10, using only NaOH as an activator, showed a 71.95% removal rate of acetaminophen after 30 minutes of reaction under the same experimental conditions as Example 2. Comparative Example 11, using only ZnCl2 as an activator, achieved a removal rate of only 48.75% under the same conditions after 30 minutes. Both figures are lower than the 76.09% removal rate of the activated carbon prepared by combined activation in Example 1.

[0078] The above results indicate that only when NaOH and ZnCl2 are used together can they synergistically enhance each other and construct an activated carbon catalyst with high specific surface area, well-developed hierarchical porous structure and abundant surface active sites, thereby achieving efficient adsorption and enrichment of acetaminophen and subsequent catalytic conversion, fully demonstrating the necessity of joint activation by NaOH and ZnCl2.

[0079] Comparative Example 12 This comparative example provides a method for preparing activated carbon from corn stalks using Ca(OH)2 and ZnCl2 in combination. The only difference between this method and Example 1 is that the activator NaOH in step b is replaced with Ca(OH)2. The amount of Ca(OH)2 used is the same as that of NaOH used in Example 1 in terms of alkali metal molar equivalents, and all other conditions remain unchanged.

[0080] The activated carbon prepared in this comparative example was subjected to adsorption performance testing under the same experimental conditions as in Example 2. The test results showed that after 5 minutes of reaction, the removal rate of acetaminophen was 40.71%, and the reaction kinetic constant was 0.1046 min. -1 After 30 min of reaction, the removal rate of acetaminophen was 58.74%, and the reaction kinetic constant was 0.0295 min. -1 .

[0081] This comparative example shows that not all alkaline activators can produce the same synergistic activation effect with ZnCl2 as NaOH. Due to its suitable alkalinity and good solubility, NaOH is irreplaceable in the process of co-activating corn stalks with ZnCl2 to prepare high-performance activated carbon catalysts.

[0082] Comparative Example 13 This comparative study investigated the removal effect of NaOH and ZnCl2 combined with activated corn stalk carbon prepared in Example 1 on APAP when ozone microbubbles were replaced with microbubble oxygen.

[0083] Microbubble catalysis experiments were conducted under the same conditions as in Example 4, except that the ozone microbubble generator was replaced with an oxygen microbubble generator. Oxygen microbubbles were introduced into the solution containing APAP and the catalyst at the same flow rate, while other conditions remained consistent with Example 4. Test results showed that after 5 minutes of reaction, the APAP removal rate was 53.73%; after 30 minutes of reaction, the APAP removal rate was 53.42%, and extending the reaction time did not significantly improve the removal rate.

[0084] Compared to the 91.80% removal rate of the ozone microbubble system in Example 4 after 30 minutes, the removal rate of APAP in this comparative example, after replacing ozone microbubbles with oxygen microbubbles, decreased significantly and reached equilibrium after 5 minutes of reaction, without increasing further with reaction time. This indicates that the polymerization capacity of oxygen microbubbles alone is limited. Combined with the results of detecting a large amount of polymerization products in the activated carbon extract in Example 4, this comparative example further confirms that ozone microbubbles are the key active component in the system for generating hydroxyl radicals and initiating free radical coupling polymerization of APAP on the catalyst surface. The synergistic catalytic effect between ozone microbubbles and corn stalk activated carbon is the core mechanism for achieving efficient APAP polymerization and removal; both are indispensable.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of corn stalk activated carbon in the catalytic microbubble ozone polymerization for the removal of acetaminophen, characterized in that, The preparation method of the corn stalk activated carbon includes the following steps: Step a: Mix corn stalks, NaOH solution and ZnCl2 solution, then impregnate and activate them, and dry them to obtain activated corn stalks; Step b: Under an inert atmosphere, the activated corn stalks are carbonized at 550℃~650℃ for 1.5h~2.5h to obtain activated corn stalk carbon. The mass ratio of corn stalks, NaOH, and ZnCl2 is 1:(0.6~0.8):(0.2~0.4).

2. The application as described in claim 1, characterized in that, In step a, the immersion activation temperature is 20℃~40℃, and the immersion activation time is 18h~22h.

3. The application as described in claim 1, characterized in that, In step a, the NaOH solution has a mass fraction of 30% to 40%, and the ZnCl2 solution has a mass fraction of 40% to 50%.

4. A method for removing acetaminophen from wastewater, characterized in that, Includes the following steps: The corn stalk activated carbon described in any one of claims 1 to 3 is added to wastewater containing acetaminophen, mixed, and ozone microbubbles are introduced. Under the action of the corn stalk activated carbon and ozone microbubbles, acetaminophen undergoes a polymerization reaction to remove acetaminophen.

5. The method for removing acetaminophen from wastewater as described in claim 4, characterized in that, The amount of corn stalk activated carbon added is 0.45 g / L to 0.55 g / L.

6. The method for removing acetaminophen from wastewater as described in claim 4, characterized in that, The concentration of acetaminophen in the wastewater is 40 mg / L to 55 mg / L.

7. The method for removing acetaminophen from wastewater as described in claim 4, characterized in that, The pH of the wastewater containing acetaminophen is 6.5~7.

5.

8. The method for removing acetaminophen from wastewater as described in claim 4, characterized in that, The polymerization reaction takes 25 to 35 minutes.

9. The method for removing acetaminophen from wastewater as described in claim 4, characterized in that, The ozone microbubbles have a particle size ≤50μm.

10. The method for removing acetaminophen from wastewater as described in claim 4, characterized in that, The flow rate of the ozone microbubbles is 0.25 L / min to 0.30 L / min.

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