Method for preparing nano-silver activated carbon with high specific surface area through semi-dry mechanical-chemical synergistic activation of corncobs

Abstract

The invention discloses a method for preparing high-specific-surface-area nano-silver activated carbon through semi-dry mechanical-chemical synergistic activation of corncobs, and relates to the technical field of activated carbon preparation. According to the method, agricultural waste corncobs are used as raw materials, and the nano-silver activated carbon with the high specific surface area is prepared through four key processes including pretreatment, ball-milling mixing and activation pretreatment, carbonization activation and aftertreatment and nano-silver loading. The method has the remarkable advantages that the preparation period is greatly shortened, the total period is shortened by 8 h compared with a traditional process, and efficiency is remarkably improved; the product performance is excellent, the specific surface area of the prepared nano-silver activated carbon is more than 1700m < 2 >. G <-1 >, and the micropore proportion is gt; the activated carbon prepared by the method has the advantages that the iodine adsorption value reaches 1353mg. G <-1 >, the yield is 48.63%, and the iodine adsorption value, the yield and the yield are respectively improved by 24.56 times, 3.83 times and 1.19 times compared with those of unmodified activated carbon. The corncob is converted into a high-performance nano-silver activated carbon carrier, and the method has wide application prospects in the fields of water treatment, medicine and the like.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of preparation of activated carbon, in particular to a method for preparing high specific surface area nanosilver activated carbon from corncob by a semi-dry mechanical-chemical synergistic activation method. BACKGROUND

[0002] Nanosilver is a metal silver element with a particle size of nanometer level. In recent years, due to its excellent properties in the aspects of optics, catalysis, conduction and antibiosis, nanosilver has been widely concerned, and in particular, it has good stability, heat resistance and broad-spectrum antibiosis in sterilization. However, nanosilver is difficult to separate from a solution, and nanosilver particles are prone to cluster aggregation, so it is necessary to load nanosilver on a carrier material. Therefore, loading nanosilver on a suitable carrier material becomes a core path to break through the above bottleneck, and the carrier material needs to meet five key requirements of high specific surface area, strong complexing capacity, stable binding force, high chemical stability and low cost. Activated carbon naturally meets the demand of nanosilver carrier due to its developed pore structure, rich surface functional groups, excellent adsorption performance, high chemical stability, good oxidation-reduction property and good electrical conductivity, and is widely used in the fields of medicine, water treatment and biology. Traditional activated carbon raw materials mainly depend on wood, coal and petroleum coke, and there are problems of high price and non-renewability. Corn cob, as an agricultural waste, has the advantages of huge output, wide source and low price, and is rich in lignocellulose. The activated carbon prepared by processing corn cob has a rich and unique porous structure and a large specific surface area, and becomes an excellent choice for replacing traditional raw materials and preparing high-performance activated carbon carriers.

[0003] Activated carbon is prepared based on the principle that carbon-containing materials are pyrolyzed and carbonized at a high temperature and finally exist in the form of microcrystalline carbon. The methods for preparing activated carbon mainly include physical activation, chemical activation and physical-chemical activation. The physical activation method is a method for activating raw materials at a high temperature by using active gases such as water vapor, flue gas, CO2 or N2 as a medium. The physical activation method has a relatively simple process, less liquid pollution, small environmental impact, mainly produces CO2 and H2O, and in most cases, the product does not need complex post-processing, so the physical activation method is a relatively clean and environmentally friendly activation technology. The chemical activation method is a method for high-temperature carbonization after impregnation of raw materials by using chemical activators such as H3PO4, ZnCl2, KOH and NaOH. The activated carbon prepared by the chemical activation method has high yield and developed pore structure, and has good adsorption performance. The physical-chemical activation method combines the physical activation and the chemical activation, realizes the complementary advantages of the two activation methods, and can obtain activated carbon with high adsorption performance.

[0004] Although the activated carbon prepared from corn cob has the advantages of raw materials, the existing three types of activation methods all have significant defects and deficiencies in actual application.

[0005] The physical activation method requires a large amount of activation gas, and needs to go through two steps of carbonization and activation. The required activation temperature is high, which is 800-1100°C. The physical activation method has defects of high energy consumption, high cost and low yield. Zhang T et al. (Zhang T, Walawender P W, Fan L, et al. Preparation of activated carbon from forest and agricultural residues through CO2 activation [J]. Chemical Engineering Journal, 2004, 105(1-2): 53-59.) used corn cob as raw material, carbonized at 500°C, and then activated at 800°C for 2h with CO2 as activation agent. The activated carbon obtained has a specific surface area of 975m 2 / g, but the yield is low, the carbonization yield is only 32%, and the activation loss rate is 45.2%. Chang C et al. (Chang C, Chang C, Tsai W. Effects of burn-off and activation temperature on preparation of activated carbon from corn cob a grow waste by CO2 and steam [J]. Journal of Colloid and Interface Science, 2000, 232(01): 45-49.) activated at 900°C with CO2 and steam respectively. The specific surface areas of the obtained activated carbons are 1705m 2 / g and 1315m 2 / g respectively, which have high adsorption capacity, but the loss rates are as high as 71wt% and 59wt%.

[0006] The chemical activation method has a lower activation temperature than the physical activation method, which is generally 400-900°C. The chemical activation method has defects of uneven penetration of activation agent, long impregnation time and process, low production efficiency, difficult recovery of activation agent, large water consumption, and complex subsequent wastewater treatment. The chemical activation agent has a large corrosion on equipment and causes serious environmental pollution. It is difficult to recycle pyrolysis energy, and the activated carbon prepared may have residual chemical drugs, which limits its application.

[0007] Physical-chemical activation method is an effective means to prepare high specific surface area activated carbon, which can significantly improve the pore structure and adsorption performance of the material. However, the existing technology has the key problems of high process complexity, long preparation time and high economic cost, which jointly restrict the conversion process to industrial scale production. The current physical-chemical activation technologies such as acid-gas combined activation method and microwave enhanced method, the former has great corrosion to the equipment, and produces a large amount of waste acid which causes damage to the environment, and the latter has high requirements for equipment, which is difficult to realize industrial production. Cheng Zhikuan et al. (Cheng Zhikuan, Yu Qing, Zhang Pan, et al. Microwave preparation of oil tea shell-based activated carbon and its adsorption of U(Ⅵ) [J]. Journal of Nanhua University (Natural Science Edition), 2019, 33(01): 16-21.) used zinc chloride as an activator to prepare oil tea shell-based activated carbon by microwave activation, and the obtained activated carbon had rich pore structure, but the preparation process was complex, the production cost was high, and it was difficult to realize industrialization.

[0008] The disclosure of the above background art content is only used to assist in understanding the inventive concept and technical solutions of the present application, and it does not necessarily belong to the prior art of the present patent application. In the absence of explicit evidence that the above content has been disclosed on the filing date of the present patent application, the above background art should not be used to evaluate the novelty and inventiveness of the present application.

SUMMARY

[0009] The present application aims to provide a method for preparing high specific surface area nanosilver activated carbon from corncob by semi-dry mechanical-chemical synergistic activation, to solve the technical problems of complex preparation process, expensive equipment, low efficiency and long production cycle of biomass activated carbon in the prior art.

[0010] To this end, the present application adopts the following technical solutions:

[0011] A method for preparing high specific surface area nanosilver activated carbon from corncob by semi-dry mechanical-chemical synergistic activation, comprising the following steps:

[0012] (1) Corncob pretreatment: cut the corncob into pieces, wash it with water, dry it, crush it with a crusher and sieve it, and then store it in a desiccator for future use;

[0013] (2) Ball milling mixing and activation pretreatment: weigh the treated corncob, mix it with the composite activator in proportion, and then put it into a ball mill jar for ball milling;

[0014] (3) Carbonization activation and post-treatment: put the milled mixture into a high-temperature tube furnace for pyrolysis; after activation, cool the furnace to room temperature; wash the prepared activated carbon with hydrochloric acid solution, then wash it thoroughly with pure water, dry it to constant weight, and obtain modified corncob activated carbon; grind and sieve it, and then store it in a desiccator for future use;

[0015] (4) Preparation of nano-silver activated carbon: weigh the modified corncob activated carbon and add it to an ethanol aqueous solution, then add a sodium borohydride solution, drop in a silver nitrate ethanol solution under stirring, continue the reaction, filter and wash with anhydrous ethanol, and dry to obtain nano-silver activated carbon.

[0016] Preferably, the composite activator in step (2) comprises the following raw materials: zinc chloride (ZnCl2), ammonium molybdate ((NH4)6Mo7O 24 ), titanium sulfate (TiOSO4), and choline chloride (C5H 14 ClNO), wherein the molar ratio of choline chloride (C5H 14 ClNO) to ammonium molybdate ((NH4)6Mo7O 24 ) is 2:1.

[0017] Preferably, the preparation process of the composite activator comprises the following steps:

[0018] a. Mix choline chloride and ammonium molybdate at a molar ratio of 2:1, and stir the mixture at 75-85°C for 30-60 min until a transparent and uniform eutectic liquid is formed;

[0019] b. Add zinc chloride to the eutectic liquid in step a, with an amount of 45%-55% of the mass of corncob; then add titanium sulfate, with an amount of 5%-10% of the mass of corncob;

[0020] c. Add deionized water to adjust the total liquid volume, so that the solid-liquid ratio of corncob / activator reaches 1:1-3 (g:mL);

[0021] d. Continue stirring at 55-65°C until all components are completely dissolved, forming a uniform composite activator solution.

[0022] Preferably, the specific operation of the corncob pretreatment in step (1) is as follows: cut the corncob into pieces, wash the surface dust with distilled water, and dry; crush it with a crusher and pass it through a 40-mesh sieve, then store it in a desiccator for future use.

[0023] Preferably, the specific operation of the ball-milling mixing and activation pretreatment in step (2) is as follows: weigh the treated corncob, mix the corncob with the composite activator at a solid-liquid ratio of 1:1-3 (g:mL), and place it in a ball mill tank for ball milling at a speed of 200-300 r·min -1 for 1-2 h.

[0024] Preferably, the specific operation of the ball-milling mixing and activation pretreatment in step (2) is as follows: weigh the treated corncob, mix the corncob with the composite activator at a solid-liquid ratio of 1:2 (g:mL), and place it in a ball mill tank for ball milling at a speed of 200 r·min-1 ball-milling time is 1.5 h.

[0025] Preferably, the specific operation of carbonization activation and post-treatment in step (3) is as follows: the mixture after ball-milling is placed into a high-temperature tube furnace under nitrogen protection, the heating rate is set to 10 ℃·min -1 , the carbonization temperature is set to 400-600 ℃, and the carbonization time is 2-4 h for anaerobic pyrolysis; after activation, the furnace is cooled to room temperature; the prepared activated carbon is washed with a hydrochloric acid solution with a concentration of 0.8-1.2 mol·L -1 , then washed with pure water until the pH is 6.5-7.5, dried to constant weight, and then modified corncob activated carbon is obtained; ground through a 100-mesh sieve and sealed in a desiccator for storage.

[0026] Preferably, the specific operation of carbonization activation and post-treatment in step (3) is as follows: the mixture after ball-milling is placed into a high-temperature tube furnace under nitrogen protection, the heating rate is set to 10 ℃·min -1 , the carbonization temperature is set to 600 ℃, and the carbonization time is 3 h for anaerobic pyrolysis; after activation, the furnace is cooled to room temperature; the prepared activated carbon is washed with a hydrochloric acid solution with a concentration of 1.0 mol·L -1 , then washed with pure water until the pH is 7, dried to constant weight, and then modified corncob activated carbon is obtained; ground through a 100-mesh sieve and sealed in a desiccator for storage.

[0027] Preferably, the specific operation of carbonization activation and post-treatment in step (3) is as follows: the mixture after ball-milling is placed into a high-temperature tube furnace under nitrogen protection, the heating rate is set to 10 ℃·min -1 , the carbonization temperature is set to 600 ℃, and the carbonization time is 3 h for anaerobic pyrolysis; after activation, the furnace is cooled to room temperature; the prepared activated carbon is washed with a hydrochloric acid solution with a concentration of 1.0 mol·L -1 , then washed with pure water until the pH is 7, dried to constant weight, and then modified corncob activated carbon is obtained; ground through a 100-mesh sieve and sealed in a desiccator for storage.

[0028] Preferably, the specific operation of carbonization activation and post-treatment in step (3) is as follows: the mixture after ball-milling is placed into a high-temperature tube furnace under nitrogen protection, the heating rate is set to 10 ℃·min -1 , the carbonization temperature is set to 600 ℃, and the carbonization time is 3 h for anaerobic pyrolysis; after activation, the furnace is cooled to room temperature; the prepared activated carbon is washed with a hydrochloric acid solution with a concentration of 1.0 mol·L -1The silver nitrate ethanol solution is added to the activated carbon, and the reaction is continued for 1 h. The activated carbon is extracted and washed with anhydrous ethanol for 3 times, and is dried at 50℃ for 12 h under vacuum to obtain the nano-silver activated carbon.

[0029] The beneficial effects of the present application compared with the prior art include:

[0030] (1) Shorten the preparation period: solve the problem of long time of traditional chemical activation and impregnation. To achieve the optimal iodine adsorption value, the ordinary activated carbon modified by the activator needs to be impregnated with the activator solution for 12 h for activation, while the ball milling + composite activator synergistically modified activated carbon does not need solution impregnation, and the mechanical activation and chemical activation are organically and synchronously carried out, which shortens the preparation period by 8 h, effectively shortening the preparation period.

[0031] (2) The yield, adsorption performance and micropore rate are greatly improved: The yield of nano-silver activated carbon is greatly increased, the bottleneck of low specific surface area and single pore structure of nano-silver activated carbon is broken, and nano-silver activated carbon with specific surface area > 1700 m 2 / g and micropore ratio > 70% is prepared. The yield of the ball milling + composite activator synergistically modified activated carbon is increased by 1.19 times, the iodine adsorption value is increased by 3.83 times, the specific surface area is increased by 24.56 times, and the total pore volume is increased by 17.14 times. The nitrogen adsorption isotherm of the ball milling + composite activator synergistically modified activated carbon shows a typical type I curve, indicating that it is mainly adsorbed by micropores and supplemented by mesopores; while the unmodified activated carbon tends to be type IV isotherm, and the adsorption characteristics are mainly mesoporous and the micropore development is limited.

[0032] (3) Reduce energy consumption and pollution: Avoid high-temperature activation (> 800℃) and chemical waste liquid discharge, realize process greenization. The activation temperature is reduced to 600℃, which effectively reduces the energy consumption; the semi-dry ball milling reduces the composite activator dosage by 60%, which effectively reduces the waste liquid discharge.

[0033] (4) Realize the high-value utilization of waste: The corn cob waste is converted into high-performance activated carbon, which provides a strong carrier for the subsequent loading of nano-silver. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the SEM characterization diagram of Example 1 and Example 2;

[0035] Figure 2 is the Fourier transform infrared spectrum diagram of Example 1 and Example 2;

[0036] Figure 3 is the XRD characterization diagram of Example 1 and Example 2;

[0037] Figure 4 is the influence diagram of Example 1, Comparative Example 1 and Example 2 on methylene blue adsorption value and iodine adsorption value, wherein Figure 4(a) is the adsorption effect graph of different activated carbons on iodine, Figure 4 (b) is the adsorption effect graph of different activated carbons on methylene blue;

[0038] Figure 5 is the graph of the results of kinetic model fitting of the adsorption kinetics experimental data of Example 1;

[0039] Figure 6 is the graph of the results of Langmuir model and Freundlich model fitting of the isothermal adsorption experimental data;

[0040] Figure 7 is the graph of the bacteriostatic rate results of the nanosilver activated carbon of Example 1 and the modified activated carbon of Example 2, wherein Figure 7 (a) is the graph of the bacteriostatic rate results of the blank control group, Figure 7 (b) is the graph of the bacteriostatic rate results of the modified activated carbon of Example 2, and

[0041] Figure 8 is the graph of the growth curves of Escherichia coli of the modified activated carbon of Example 2, the nanosilver activated carbon of Example 1 and the blank comparison sample;

[0042] Figure 9 is the graph of the results data of the solid-liquid ratio single factor experiment;

[0043] Figure 10 is the graph of the results data of the ball milling speed single factor experiment;

[0044] Figure 11 is the graph of the results data of the ball milling speed single factor experiment;

[0045] Figure 12 is the graph of the results data of the carbonization temperature single factor experiment;

[0046] Figure 13 is the graph of the results data of the carbonization time single factor experiment;

[0047] Figure 14 is the graph of the results of iodine adsorption value and yield comparison experiment of Example 2 and Comparative Example 1 and Comparative Example 2;

[0048] Figure 15 is the Fourier transform infrared spectrum graph of Example 2 and Comparative Example 1;

[0049] Figure 16 is the nitrogen adsorption-desorption isotherm and pore size distribution curve graph of Comparative Example 1, wherein, Figure 16 (a) is the nitrogen adsorption-desorption isotherm graph of Comparative Example 1, Figure 16 (b) is the pore size distribution curve graph of Comparative Example 1;

[0050] Figure 17 is a nitrogen adsorption-desorption isotherm and pore size distribution plot of Example 2, wherein, Figure 17 (a) is a nitrogen adsorption-desorption isotherm plot of Example 2, Figure 17 (b) is a pore size distribution plot of Example 2. DETAILED DESCRIPTION

[0051] With reference to the following drawings, non-limiting and non-exclusive examples will be described. It is understood that the terms described in the present application are merely used to describe particular embodiments and are not used to limit the present application. In addition, for the numerical ranges in the present application, it is understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range within any stated value or stated range, and between any other stated value or stated range, is also included within the present application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range. With respect to "comprising," "including," "having," "containing," and like terms used herein, are open-ended terms, i.e., meaning including, but not limited to.

[0052] Example 1

[0053] A method for preparing high specific surface area nanosilver activated carbon from corncob by semi-dry mechanical-chemical synergistic activation, comprising the following steps:

[0054] (1) Corncob pretreatment: cut the corncob into pieces, wash the surface dust with distilled water, and dry; crush it with a crusher and pass it through a 40-mesh sieve, and store it in a desiccator for standby;

[0055] (2) Ball milling mixing and activation pretreatment: weigh the treated corncob, and uniformly stir the corncob and the composite activator at a solid-liquid ratio of 1:2 (g:mL), and place it in a ball mill tank for ball milling at a speed of 200 r·min -1 for 1.5 h;

[0056] (3) Carbonization activation and post-treatment: place the milled mixture into a high-temperature tube furnace, and perform anaerobic pyrolysis under nitrogen protection, with a set heating rate of 10℃·min -1 , a set carbonization temperature of 600℃, and a carbonization time of 3 h; after activation, cool the furnace to room temperature; wash the prepared activated carbon with a 1.0 mol·L -1 hydrochloric acid solution, and then wash it with pure water until the pH is 7, and dry it to a constant weight to obtain modified corncob activated carbon; grind it through a 100-mesh sieve, and store it in a desiccator for standby;

[0057] (4) Preparation of nano-silver activated carbon: The modified corncob activated carbon was weighed and added into 4:1 ethanol aqueous solution according to the solid-liquid ratio of 1:15 (g:mL), and then a sodium borohydride solution with a concentration of 0.1 mol·L-1 was added according to the solid-liquid ratio of 1:1 (g:mL). The silver nitrate ethanol solution with a concentration of 0.005 mol·L-1 was added dropwise into the mixture under stirring according to the ratio of 1:10. The reaction was continued for 1 h, and then the mixture was filtered and washed with anhydrous ethanol for 3 times. The nano-silver activated carbon was obtained by vacuum drying at 50℃ for 12 h. -1 -1 (4) Preparation of nano-silver activated carbon: The modified corncob activated carbon was weighed and added into 4:1 ethanol aqueous solution according to the solid-liquid ratio of 1:15 (g:mL), and then a sodium borohydride solution with a concentration of 0.1 mol·L-1 was added according to the solid-liquid ratio of 1:1 (g:mL). The silver nitrate ethanol solution with a concentration of 0.005 mol·L-1 was added dropwise into the mixture under stirring according to the ratio of 1:10. The reaction was continued for 1 h, and then the mixture was filtered and washed with anhydrous ethanol for 3 times. The nano-silver activated carbon was obtained by vacuum drying at 50℃ for 12 h.

[0058] The composite activator in step (2) comprises the following raw materials: zinc chloride (ZnCl2), ammonium molybdate ((NH4)6Mo7O 24 24), titanium sulfate (TiOSO4), and choline chloride (C5H 14 10ClNO), wherein the molar ratio of choline chloride (C5H 14 10ClNO) to ammonium molybdate ((NH4)6Mo7O 24 24) is 2:1.

[0059] The preparation process of the composite activator comprises the following steps:

[0060] a. Mix choline chloride and ammonium molybdate according to the molar ratio of 2:1, and stir the mixture at 80℃ for 45 min until a transparent and uniform eutectic liquid is formed;

[0061] b. Add zinc chloride to the eutectic liquid in step a, and the amount is 50% of the mass of corncob; then add titanium sulfate, and the amount is 8% of the mass of corncob;

[0062] c. Add deionized water to adjust the total liquid volume, so that the solid-liquid ratio of corncob / activator reaches 1:2 (g:mL);

[0063] d. Continue to stir at 60℃ until all components are completely dissolved to form a uniform composite activator solution.

[0064] Example 2

[0065] A method for preparing high specific surface area modified corncob activated carbon carrier by semi-dry mechanical-chemical synergistic activation of corncob, comprising the following steps:

[0066] (1) Corncob pretreatment: Cut the corncob into pieces, wash the surface dust with distilled water, and dry; crush it with a crusher and pass it through a 40-mesh sieve, and store it in a desiccator for standby;

[0067] (2) Ball milling mixing and activation pretreatment: Weigh the treated corncob, and stir the corncob and the composite activator uniformly according to the solid-liquid ratio of 1:2 (g:mL), and then put it into a ball mill tank for ball milling, and the ball milling speed is 200 r·min​-1 ball-milling time was 1.5 h;

[0068] (3) Carbonization activation and post-treatment: the mixture after ball-milling was put into a high-temperature tube furnace, and under nitrogen protection, the heating rate was set to 10℃·min -1 , the carbonization temperature was set to 600℃, and the carbonization time was 3 h for anaerobic pyrolysis; after activation, the furnace was cooled to room temperature; the prepared activated carbon was washed with a hydrochloric acid solution with a concentration of 1.0 mol·L -1 , then washed with pure water until the pH was 7, dried to constant weight, and then modified activated carbon was obtained; ground through a 100-mesh sieve and sealed in a desiccator for storage.

[0069] Comparative Example 1

[0070] Unmodified activated carbon was prepared under the same carbonization temperature and carbonization time as in Example 2.

[0071] Comparative Example 2

[0072] The method for preparing modified activated carbon was basically the same as in Example 2, except that in step (2), the corn cob and the composite activator were stirred uniformly at a solid-liquid ratio of 1:5 (g:mL) for 12 h, and activation was performed for 0.5 h without ball-milling.

[0073] The determination methods of the various indexes described below are as follows:

[0074] The determination method of the silver content of nano-silver activated carbon is as follows: a certain amount of prepared nano-silver activated carbon was placed in a porcelain evaporating dish after low-temperature drying in an oven for 2 h, and then placed in a muffle furnace at 900℃ for calcination; after complete ashing and cooling, the evaporating dish was taken out, added with an appropriate amount of concentrated nitric acid solution with a concentration of 250 ml·L -1 , heated and boiled for 5 min, cooled and filtered into a 250 ml conical flask, and the evaporating dish was washed with a concentrated nitric acid solution with a concentration of 30 ml·L -1 three times, and then added with 5 mL of ferric ammonium sulfate indicator with a concentration of 80 g·L -1 , and titrated with a sodium thiocyanate standard solution with a concentration of 0.1 mol·L -1 until the solution turned light brown red, and the color remained unchanged for 30 s as the end point. The formula used is as follows:

[0075]

[0076] In the formula: X—silver content in the carbon sample (%); C—concentration of the sodium thiocyanate standard solution (mol / L); V—amount of the sodium thiocyanate standard solution (mL); 0.1079—mass of 1.00 mL of the sodium thiocyanate standard solution in g equivalent to silver; m—mass of the carbon sample (g).

[0077] The determination method of methylene blue adsorption amount is as follows:

[0078] A certain amount of methylene blue trihydrate is weighed to form a methylene blue solution with different concentrations. The absorbance of the methylene blue solution is measured at an absorption wavelength of 665 nm. A methylene blue standard curve is drawn, and the content of the methylene blue solution is calculated using the methylene blue standard curve. The adsorption amount and adsorption rate of the nanosilver activated carbon after adsorbing methylene blue are calculated using the following formula:

[0079] Adsorption amount:

[0080] Adsorption rate:

[0081] In the formula: q t —adsorption amount at time t (mg·g -1 ); η t —methylene blue removal rate at time t (%); C0—concentration of methylene blue solution before adsorption (mg·g -1 ); C e —concentration of methylene blue solution at time t (mg·g -1 ); V—solution volume (L); m—mass of nanosilver activated carbon (g).

[0082] The adsorption kinetics experiment is as follows: a certain amount of nanosilver activated carbon is weighed and placed in a conical flask, and 20 mL of methylene blue solution with a concentration of 100 mg·L-1 and the same pH is added. It is placed in a water bath constant temperature shaking incubator with a set temperature, and the adsorption experiment is carried out at different times at 30°C until the reaction reaches equilibrium. The experimental results are analyzed by kinetics fitting to explore the adsorption mechanism of nanosilver activated carbon.

[0083] Pseudo-first-order kinetic model: mathematical expression: ln(q e -q t ) = lnq e -k1t

[0084] Pseudo-second-order kinetic model: mathematical expression:

[0085] In the formula: q e —equilibrium adsorption amount (mg / g); k1, k2—adsorption rate constant; t—adsorption time (min).

[0086] The isothermal adsorption experiment is as follows: a certain amount of nano-silver activated carbon is weighed and placed in a conical flask, 20 mL of methylene blue solution with different initial concentrations but the same pH is added, and it is placed in a water bath constant temperature oscillator with a set temperature, and the adsorption experiment is carried out at 30°C, 40°C and 50°C until the reaction reaches equilibrium. The experimental results are fitted and analyzed by Langmuir isothermal adsorption model and Freundlich isothermal adsorption model to explore whether the adsorption process of nano-silver activated carbon is monolayer adsorption or multilayer adsorption, and whether there is interaction between the adsorbates.

[0087] The mathematical expression of Langmuir isothermal adsorption model is as follows:

[0088] The mathematical expression of Freundlich isothermal adsorption model is as follows:

[0089] In the formula: q e —equilibrium adsorption capacity (mg·g -1 ); q m —saturation adsorption capacity (mg·g -1 ); C e —concentration of methylene blue solution after adsorption equilibrium (mg·g -1 ); K L —Langmuir isothermal adsorption constant; K F —Freundlich isothermal adsorption constant; —Freundlich isothermal adsorption empirical constant.

[0090] The antibacterial performance test is as follows: the antibacterial performance of nano-silver activated carbon is explored, and the antibacterial rate and antibacterial kinetics of nano-silver activated carbon are tested with Escherichia coli as the antibacterial object. A certain amount of test sample is weighed and wrapped, and other experimental equipment required is placed in an autoclave, and sterilized at 103 Kpa and 125°C for 20 min. Then the antibacterial performance of Escherichia coli (ATCC25922) is tested according to the appendix A powder nano-inorganic material antibacterial performance test method in the national standard GB / T21510-2024 "Nano-inorganic material antibacterial performance test and detection method level evaluation".

[0091] Antibacterial kinetics research: a certain amount of modified activated carbon and nano-silver activated carbon is weighed in a sterilized conical flask, a certain amount of sterilized and 100-mesh-sieved silicon dioxide is added to the blank sample conical flask, 20 ml of Escherichia coli suspension is added respectively, and it is placed in a constant temperature shaking incubator at 37°C and sealed for shaking culture. The absorbance is measured at a wavelength of 600 nm. The formula used for calculating the antibacterial rate is as follows

[0092]

[0093] In the formula: R - bacteriostatic rate (%); A - average number of bacteria before the sample was shaken; B - average number of bacteria after the sample was shaken.

[0094] The formula used for calculating the yield of activated carbon is as follows:

[0095]

[0096] In the formula: Y - yield of activated carbon (%); w0 - mass of the crucible (g); w1 - total mass of activated carbon before carbonization plus crucible (g); w2 - total mass of activated carbon after carbonization plus crucible (g).

[0097] The determination of iodine adsorption value refers to the determination of iodine adsorption value in the experimental method for wooden activated carbon in the national standard GB / T 12496.8-2015. The iodine adsorption value is calculated according to the following formula:

[0098]

[0099] In the formula: I - iodine adsorption value of the sample (mg·g -1 ); C1 - concentration of iodine (1 / 2I2) standard solution (mol·L -1 ); C2 - concentration of sodium thiosulfate standard solution (mol·L -1 ); V2 - volume of sodium thiosulfate standard solution consumed (mL); m - mass of the sample (g); D - correction factor.

[0100] 1. Silver loading of the nano-silver activated carbon of Example 1 and characterization analysis of Example 1 and Example 2

[0101] 1.1 SEM analysis

[0102] The surface morphology and structure of the nano-silver activated carbon and modified activated carbon prepared in Example 1 and Example 2 were observed using SEM2000 to analyze the surface morphology and morphology of the samples. Figure 1 The SEM characterization results of the modified activated carbon of Example 2 and the nano-silver activated carbon of Example 1 are shown in the following figures. As can be seen from the SEM characterization picture of the modified activated carbon of Example 2, the surface of the modified activated carbon of Example 2 is smooth, and there is a grayish-white substance, which may be ash attached to the surface of the activated carbon after high-temperature carbonization, or it may be incomplete acid washing, with residual zinc chloride activator. As can be seen from the photo of the nano-silver activated carbon of Example 1, the silver particles do not agglomerate and are relatively uniformly loaded on the surface of the activated carbon, and the silver particles have reached the nanometer level. The silver loading of the nano-silver activated carbon of Example 1 is calculated by the formula, and the silver loading of the activated carbon is 0.32%.

[0103] 1.2 Fourier transform infrared spectroscopy analysis

[0104] The surface groups of Example 1 and Example 2 were qualitatively analyzed by Fourier transform infrared spectroscopy. An appropriate amount of potassium bromide was ground with the sample, and the sample was prepared by tabletting. The sample was scanned 16 times in the wavelength range of 400-4000 cm -1 -1. The Fourier transform infrared characterization of Example 1 and Example 2 is shown in Figure 2 Figure 2 It can be seen that the modified activated carbon of Example 2 and the nano-silver activated carbon of Example 1 both have an absorption peak caused by the stretching vibration of -OH group at a wave number of 3440 cm -1 -1. The modified activated carbon of Example 2 and the nano-silver activated carbon of Example 1 both have an absorption peak caused by the stretching vibration of C-H bond at a wave number of 2800 cm -1 -1. The modified activated carbon of Example 2 and the nano-silver activated carbon of Example 1 both have an absorption peak caused by the stretching vibration of C=O bond at a wave number of 1630 cm -1 -1. The modified activated carbon of Example 2 and the nano-silver activated carbon of Example 1 both have an absorption peak caused by the stretching vibration of C-N bond at a wave number of 1360 cm -1 -1. The spectra show that the modified activated carbon of Example 2 and the nano-silver activated carbon of Example 1 both contain abundant functional groups, which have an important influence on their adsorption performance. The functional groups such as hydroxyl groups can chemically react with some adsorbents, thereby enhancing their adsorption performance. The functional groups are not changed after loading silver.

[0105] 1.3 XRD Test

[0106] The samples of Example 1 and Example 2 were subjected to XRD test to analyze the crystal structure of the samples. The XRD characterization of the modified activated carbon of Example 2 and the nano-silver activated carbon of Example 1 is shown in Figure 3 The X-ray diffraction patterns of the modified activated carbon of Example 2 and the nano-silver activated carbon of Example 1 are basically consistent, as can be seen from the pictures, indicating that the loading of silver does not change the structure of the activated carbon. The activated carbon loaded with silver has diffraction peaks at 2θ angles of 27.658°, 32.234°, 46.176°, 54.754° and 57.384°, corresponding to the crystal faces of Ag (111), (200), (220), (311) and (222), respectively. Thus, it can be determined that the nano-silver activated carbon surface has a crystal structure of silver.

[0107] 2. Analysis of Adsorption Performance of Nano-silver Activated Carbon

[0108] 2.1 Comparison of Different Activated Carbons

[0109] The methylene blue adsorption value and the iodine adsorption value of the nano-silver activated carbon prepared in Example 1, the unmodified activated carbon prepared in Comparative Example 1 and the modified activated carbon prepared in Example 2 were determined, Figure 4 is a graph showing the influence of Example 1, Comparative Example 1 and Example 2 on the methylene blue adsorption value and the iodine adsorption value. In the graph, Figure 4 ​(a) is a graph showing the effect of different activated carbons on the adsorption of iodine. Figure 4 (b) is a graph showing the effect of different activated carbons on the adsorption of methylene blue; the adsorption of methylene blue by activated carbon can reflect the number of small-sized mesopores in the activated carbon. Figure 4 (b) It can be seen that the unmodified activated carbon has the lowest methylene blue adsorption value. After modification, the adsorption of methylene blue increased by about 2.5 times. After loading silver, the adsorption of methylene blue decreased slightly, but still maintained a high adsorption capacity. The iodine adsorption value of activated carbon can reflect the number of micropores in the activated carbon. Figure 4 (a) It can be seen that the adsorption capacity of unmodified activated carbon for iodine is relatively weak. After modification, the adsorption capacity of activated carbon for iodine is increased by about 2.7 times. After loading silver, the adsorption capacity of activated carbon for iodine is reduced. The surface of modified activated carbon is covered by nano-silver particles. The number of micropores and mesopores is reduced, but it still maintains a large specific surface area and well-developed pore structure. This is conducive to the adsorption of bacteria by silver-loaded activated carbon, and provides a good working space for nano-silver particles to exert their antibacterial properties.

[0110] 2.2 Fitting of the Adsorption Kinetic Model of Nano-Silver Activated Carbon

[0111] The adsorption kinetics experimental data of Example 1 were fitted with a kinetic model, and the results are shown in [the table below]. Figure 5 Table 1 shows the corresponding kinetic parameters calculated after fitting. The correlation coefficient of the pseudo-first-order kinetic model is 0.3153, and the correlation coefficient of the pseudo-second-order kinetic model is 0.9999. By comparison, the adsorption kinetics of methylene blue by nano-silver activated carbon is more inclined to the pseudo-second-order kinetic model, and its adsorption process is chemisorption.

[0112] Table 1 Adsorption kinetic parameters of Example 1

[0113]

[0114] 2.3 Fitting the isothermal adsorption model of nano-silver activated carbon

[0115] Figure 6 The results are obtained by fitting the isothermal adsorption experimental data to the Langmuir and Freundlich models. Table 2 shows the corresponding isothermal adsorption parameters calculated after fitting. The goodness of fit of the Langmuir model at 30℃, 40℃, and 50℃ is 0.9816, 0.8068, and 0.8838, respectively. The goodness of fit of the Freundlich model at 30℃, 40℃, and 50℃ is 0.9816, 0.9985, and 0.9949, respectively. By comparison, the adsorption of methylene blue by nano-silver activated carbon is more consistent with the Freundlich isothermal adsorption model and is more inclined to multilayer adsorption.

[0116] Table 2 Fitting parameters of the isothermal adsorption model in Example 1

[0117]

[0118] 3. Antibacterial performance analysis in Example 1

[0119] Figure 7 This is a graph showing the antibacterial rate results of nano-silver activated carbon from Example 1 and modified activated carbon from Example 2. Figure 7 (a) is a graph showing the antibacterial rate results of the blank control group. Figure 7 (b) shows the antibacterial rate results of modified activated carbon in Example 2, and (c) shows the antibacterial rate results of nano-silver activated carbon in Example 1; through observation Figure 7 (a) and Figure 7 (b) shows that modified activated carbon does not possess antibacterial properties, while nano-silver activated carbon... Figure 7 (c) No colonies were generated, indicating that E. coli had been completely killed and the inhibition rate reached 100%. Figure 8 The figures show the growth curves of E. coli in the modified activated carbon of Example 2, the nano-silver activated carbon of Example 1, and the blank control sample. The 12-hour growth curves of E. coli in the modified activated carbon and the control sample show similar trends with no significant decrease, further indicating that the modified activated carbon itself does not have antibacterial properties. However, the 12-hour growth curve of E. coli in the silver-loaded activated carbon remains at 0, indicating that the nano-silver activated carbon completely inhibits the growth of E. coli. Loading silver can effectively improve the antibacterial performance of the modified activated carbon.

[0120] 4. Single-factor experiments for each process parameter

[0121] 4.1 Effect of solid-liquid ratio

[0122] Six 10.00g portions of pretreated corn cob raw material were weighed and mixed with corn cob using the same composite activator solution as in Example 2, at solid-liquid ratios of 1:1, 1:2, 1:3, 1:4, 1:5, and 1:6, respectively. The remaining operations were the same as in Example 2. The iodine adsorption value and yield of the six groups of activated carbon were measured, and the effects of different solid-liquid ratios on iodine adsorption value and yield were investigated using these as evaluation indicators.

[0123] The results of the single-factor experiment on solid-liquid ratio are as follows: Figure 9 As shown in the figure, with the increase of the solid-liquid ratio, the measured activated carbon yield data of the five groups generally showed an upward trend, and remained within a certain range around the mean. This indicates that the solid-liquid ratio has a certain influence on the yield, but there are no sharp or regular large fluctuations, suggesting that the solid-liquid ratio has no significant effect on the activated carbon yield. The iodine adsorption value showed a trend of first increasing sharply and then gradually decreasing. When the solid-liquid ratio was 1:1 to 1:2, it decreased from 984.3 mg·g -1 Increased to 1081 mg / g -1, the iodine adsorption value is low due to the low solid-liquid ratio, insufficient activation agent, insufficient activation of raw materials, poor pore development, and so on; when the solid-liquid ratio is 1:2, the activation agent is moderate, the pore structure is optimized, and the iodine adsorption value is increased; when the solid-liquid ratio is increased, the excessive composite activation agent can block the micropores, and at this time, the pore-forming capacity of the composite activation agent is lower than the blocking capacity, resulting in a decrease in the iodine adsorption value. Considering the iodine adsorption value and the yield data, 1:2 is selected as the optimal solid-liquid ratio for subsequent experiments.

[0124] 4.2 Influence of ball milling speed

[0125] Based on the above optimal solid-liquid ratio results, 5 portions of 10.00 g of pretreated corn cob raw materials were weighed, and the composite activation agent solution consistent with Example 2 was added, and then ball milling was carried out at 200 r·min -1 , 300 r·min -1 , 400 r·min -1 , 500 r·min -1 , and 600 r·min -1 for 2 h, and other conditions were consistent with the above conditions. Five groups of activated carbons were determined, and the iodine adsorption value and the yield of the activated carbon were used as evaluation indexes to investigate the influence of different ball milling speeds on the iodine adsorption value and the yield.

[0126] The ball milling speed single-factor experiment results are shown in Table 4.2. Figure 10 As can be seen from the table, when the ball milling speed increases from 200 r·min -1 to 600 r·min -1 , the iodine adsorption value of the nano-silver activated carbon decreases from 1117 mg·g -1 to 1060 mg·g -1 ; and the yield decreases from 60.66% to 54.51%, both showing a downward trend. It is possible that the high speed causes the ball milling medium to collide with the ball tank at high mechanical force, resulting in excessive refinement of the corn cob, destruction of the pore structure, agglomeration, and uneven activation. The excessively small particles cause pore blockage during the activation process, thereby reducing the adsorption capacity for iodine. Moreover, the excessively small particles are easily lost during the high-temperature activation process, thereby reducing the yield of the activated carbon. Considering the iodine adsorption value and the yield data, 200 r·min -1 is selected as the optimal ball milling speed for subsequent experiments.

[0127] 4.3 Influence of ball milling time

[0128] Based on the above optimal ball milling speed results, 5 portions of 10.00 g of pretreated corn cob raw materials were weighed, and the composite activation agent solution consistent with Example 2 was added, and then ball milling was carried out for 1 h, 1.5 h, 2 h, 2.5 h, and 3 h, respectively, and other conditions were consistent with the above conditions. Five groups of activated carbons were determined, and the iodine adsorption value and the yield of the activated carbon were used as evaluation indexes to investigate the influence of different ball milling times on the iodine adsorption value and the yield.

[0129] The results of the single-factor experiment of ball milling time are shown in Figure 11 Figure. It can be seen from the figure that the iodine adsorption value increases first and then decreases with the increase of ball milling time, and reaches a peak of 1137 mg·g -1 at 1.5 h. The yield reaches a maximum of 60.46% at 2 h, and then gradually decreases. This is because the corn cob is continuously refined under mechanical force, so that the zinc chloride can enter the inside of the corn cob fiber more fully, and the fiber is fully swelled, but if the time is too long, the pore structure will be damaged. With the increase of ball milling time, the corn cob is excessively refined and agglomerated, blocking the pores and damaging the adsorption structure, which may cause partial structure collapse or blockage, resulting in a decrease in iodine adsorption value and yield. Considering the iodine adsorption value and yield data, 1.5 h is selected as the optimal ball milling time for subsequent experiments.

[0130] 4.4 Effect of carbonization temperature

[0131] Based on the results of the above optimal ball milling time, 5 portions of 10.00 g of pretreated corn cob raw materials were weighed, and the composite activator solution consistent with Example 2 was added, and the carbonization temperature was set at 200℃, 300℃, 400℃, 500℃, 600℃, respectively. Other conditions are consistent with the above conditions. Five groups of activated carbons were determined, and the iodine adsorption value and yield of activated carbon were used as evaluation indexes to investigate the effect of different carbonization temperatures on the iodine adsorption value and yield.

[0132] The results of the single-factor experiment of carbonization temperature are shown in Figure 12 Figure. It can be seen from the figure that the iodine adsorption value increases with the increase of temperature, and the iodine adsorption value increases with the increase of temperature. The carbonization reaction of corn cob gradually occurs at 200-400℃, the internal structure begins to change and gradually forms microporous and mesoporous structure, and the specific surface area slowly increases, and the adsorption capacity of iodine slowly increases. At 400-600℃, the temperature is further increased, the carbonization degree is deepened, the structure is further optimized, the pore structure is more abundant, and the specific surface area continuously increases, so that the iodine adsorption value significantly increases, and reaches a maximum of 1289 mg·g -1 at 600℃.

[0133] The yield decreases with the increase of temperature, because the organic components in the corn cob undergo thermal decomposition reaction with the increase of carbonization temperature, and volatile organic compounds, water vapor and other substances continuously escape. The higher the temperature, the more intense the pyrolysis reaction, and more substances are volatilized in the form of gas, resulting in a decrease in the remaining solid product, so that the yield decreases.

[0134] The research shows that the vapor pressure of zinc chloride is closely related to the activation temperature. When the temperature is too high, zinc chloride will evaporate rapidly, which is toxic and can damage the nasal mucosa and respiratory tract, causing environmental pollution. When the temperature exceeds 600°C, a large amount of toxic hydrogen chloride gas will be emitted, which not only increases the consumption, but also increases the pollution to the environment, causing safety hazards and environmental pollution problems. In the experiment, in view of the above adverse conditions of zinc chloride in the composite activator at high temperature, no research on higher temperature was carried out. Considering the iodine adsorption value, yield, safety, energy saving and environmental protection, the carbonization temperature was selected as 600°C for the follow-up experiment.

[0135] 4.5 Effect of carbonization time

[0136] Based on the above results of the optimal carbonization temperature, 5 portions of 10.00 g of pretreated corn cob raw materials were weighed, and the carbonization time was set as 0.5 h, 1 h, 2 h, 3 h and 4 h after adding the composite activator solution consistent with Example 2. Other conditions were consistent with the above conditions. Five groups of activated carbon were determined, and the iodine adsorption value and yield of activated carbon were used as evaluation indexes to investigate the effect of different carbonization time on the iodine adsorption value and yield.

[0137] The results of single factor experiment of carbonization time are shown in Table 2. Figure 13 As can be seen from the figure, with the increase of carbonization time, the iodine adsorption value first increases and then decreases, and reaches the highest value of 1353 mg·g -1 When the carbonization time is more than 3 h, the pore structure of activated carbon is destroyed, the pore collapses, the specific surface area and pore volume decrease, and the iodine adsorption capacity gradually decreases.

[0138] The yield decreases continuously with the increase of carbonization time. The longer the carbonization time, the more tar is generated from lignocellulose in the raw material, which reduces the yield of carbon, and the volatile components in activated carbon are continuously lost, which gradually reduces the yield. Considering the iodine adsorption value and yield data, 3 h is selected as the optimal carbonization time for the follow-up experiment.

[0139] 5. Comparison of modified activated carbon of Example 2 with unmodified activated carbon of Comparative Example 1 and modified activated carbon of Comparative Example 2

[0140] 5.1 Measurement of optimal iodine adsorption value and yield and process comparison of Example 2 and Comparative Examples 1 and 2

[0141] Table 3 Comparison of process parameters of Example 2 and Comparative Example 2

[0142]

[0143] The iodine adsorption values ​​and yields of Example 2 were compared with those of Comparative Examples 1 and 2. The experimental results are shown in the figure below. Figure 14 Table 3 shows a comparison of the process parameters between Example 2 and Comparative Example 2.

[0144] Depend on Figure 14 A comparison of (a) Comparative Example 1 and (b) Example 2 shows that the iodine adsorption value of Comparative Example 1 is 280 mg·g. -1 The iodine adsorption value in Example 2 was 1353 mg·g. -1 The iodine adsorption value of Example 2 was approximately 4.83 times that of Comparative Example 1; the yield of Comparative Example 1 was 22.21%, while the yield of Example 2 was 48.63%, meaning the yield of Example 2 was 2.19 times that of Comparative Example 1. Therefore, under optimal process parameters, the adsorption performance and yield of the modified activated carbon after ball milling and composite activator modification are significantly higher than those of the unmodified corn cob activated carbon. This indicates that the mechanical-chemical synergistic method for preparing modified activated carbon can effectively improve its adsorption performance.

[0145] As can be seen from the comparison between Example 2 (b) and Comparative Example 2 (c) in the figure, the yield of Example 2 is not significantly different from that of Comparative Example 2; the carbon-iodine adsorption value of Comparative Example 2 is 1260 mg·g. -1 The iodine adsorption value of Example 2 was 93 mg·g higher than that of Comparative Example 2. -1 This study confirmed that the mechanochemical synergistic preparation of modified activated carbon can effectively improve its adsorption performance.

[0146] As shown in Table 3, to achieve the optimal iodine adsorption value, activated carbon modified with ordinary activators needs to be soaked in the activator solution for 12 hours for activation. However, activated carbon modified with ball milling and composite activators does not require soaking in the solution. Mechanical activation and chemical activation are carried out organically and simultaneously. In terms of preparation time, the total preparation time of Example 2 is shortened by 8 hours compared with Comparative Example 2, a reduction of 64%, which significantly shortens the preparation cycle.

[0147] 5.2 Fourier Transform Infrared Spectroscopy Analysis of Example 2 and Comparative Example 1

[0148] Qualitative analysis of the surface groups of the products of Example 2 and Comparative Example 1 was performed using Fourier transform infrared spectroscopy. An appropriate amount of potassium bromide was ground into a fine powder. An appropriate amount of the dried sample was then uniformly mixed with the potassium bromide powder and compressed into a tablet. The analysis was conducted at wavelengths of 400-4000 cm⁻¹. -1 The measurement was performed by scanning 16 times within the range. The infrared spectra results are as follows: Figure 15 As shown. Comparing the two spectra, it can be seen that at 3397 cm⁻¹... -1 The absorption peak in Comparative Example 1 represents the stretching vibration of the hydroxyl (OH) functional group, while the peak in Example 2 shifted to 3444 cm⁻¹. -1, the absorption peak intensity of Example 2 is enhanced, indicating that the number of hydroxyl functional groups is increased after modification. 2830 cm -1 The C-H stretching vibration absorption peak appears. 2360 cm -1 The absorption peak at 1631 cm -1 The absorption peak at 1592 cm -1 , 1600 cm -1 The aromatic ring C=C stretching vibration absorption peak appears, and the absorption peak intensity of Example 2 is enhanced, indicating that the aromatic structure is increased after modification. 1363 cm -1 The absorption peak at 775 cm -1 , 669 cm -1 and 418 cm -1 Low wave number region absorption peak, the characteristic difference before and after modification is small, and there is no obvious change in the corresponding functional groups.

[0149] The yield, iodine adsorption value, specific surface area, total pore volume and average pore diameter of the product of Example 2 and Comparative Example 1 were measured, and the data are shown in Table 4.

[0150] Table 4 Comparison of data of Example 2 and Comparative Example 1

[0151]

[0152] 5.3 Specific surface area and pore size analysis of activated carbon of Example 2 and Comparative Example 1

[0153] The specific surface area of activated carbon was analyzed by the (BET) specific surface area test method. By introducing N2 into the sample at low temperature to be adsorbed on the surface, the adsorption amount was calculated according to the pressure or weight change before and after adsorption at adsorption equilibrium, and then the specific surface area and pore structure of the sample were obtained according to the N2 adsorption amount and adsorption isotherm shape. Figure 16 is the nitrogen adsorption-desorption isotherm and pore size distribution curve diagram of Comparative Example 1, wherein, Figure 16 (a) is the nitrogen adsorption-desorption isotherm diagram of Comparative Example 1, Figure 16 (b) is the pore size distribution curve diagram of Comparative Example 1; Figure 17 is the nitrogen adsorption-desorption isotherm and pore size distribution curve diagram of Example 2, wherein, Figure 17 (a) is the nitrogen adsorption-desorption isotherm diagram of Example 2, Figure 17 (b) is the pore size distribution curve diagram of Example 2.

[0154] The results of specific surface area and pore size analysis of activated carbon are as follows Figure 16 , 17As shown in the figure, Example 2 differs significantly from Comparative Example 1. The specific surface area of ​​Example 2 is as high as 1740.98 m². 2 ·g -1 The comparative example 1 was only 68.10m. 2 ·g -1 Example 2 is approximately 25.6 times that of Comparative Example 1. As shown in Table 4, the total pore volume of Example 2 is 0.8461 cm³. 3 ·g -1 This is significantly higher than the 0.04663 cm in Comparative Example 1. 3 ·g -1 Example 2, through optimization, formed a richer pore structure, with micropores and mesopores dominating the pore size distribution, while Comparative Example 1 was dominated by mesopores and the development of micropores was limited.

[0155] The difference in specific surface area is reflected in the adsorption performance. The nitrogen adsorption isotherm of the modified activated carbon exhibits a typical Type I curve, indicating that it mainly uses microporous adsorption, with an adsorption volume of 605 cc·g at a relative pressure of 0.9. -1 Comparative Example 1 shows a temperature close to Type IV, with obvious mesoporous adsorption characteristics; the adsorption volume under the same pressure is only 34.7 cc·g. -1 The adsorption pore volume and desorption pore volume of Example 2 were significantly higher than those of Comparative Example 1, indicating that its pore structure was more effective and had better connectivity.

[0156] 6. Conclusion

[0157] This study, through systematic experiments and characterization analysis, determined the optimal technical scheme for preparing high specific surface area nano-silver activated carbon carriers from corn cobs using a semi-dry mechanical-chemical synergistic activation method. Its core conclusions and advantages are based on the activation mechanism of lignocellulose, the mechanochemical effect, and the principle of multi-component synergistic action, which can be elaborated from four aspects: process optimization, performance improvement, greenness, and resource utilization.

[0158] From the perspective of process optimization, the experiment used the single-factor variable method to screen out the optimal combination of key process parameters: corn cobs, after pretreatment and crushing through a 40-mesh sieve, were mixed with a composite activator at a solid-liquid ratio of 1:2, and then heated at 200 r·min. -1 Ball milling was performed at a certain speed for 1.5 hours, followed by milling at 10℃·min under a nitrogen protective atmosphere. -1 The heating rate was increased to 600℃ for carbonization for 3 hours, followed by treatment with 1.0 mol·L⁻¹ -1 Modified corn cob activated carbon was obtained by washing with hydrochloric acid and rinsing with pure water until neutral, and then drying. In the nano-silver loading stage, the modified activated carbon was added to a 4:1 ethanol aqueous solution at a solid-liquid ratio of 1:15, and 0.1 mol·L⁻¹ was added proportionally. -1 Sodium borohydride solution with 0.005 mol·L⁻¹ -1The silver nitrate ethanol solution is filtered, washed with anhydrous ethanol for three times, and vacuum dried at 50°C for 12h to obtain the nano-silver activated carbon. The process breaks through the core bottleneck of traditional chemical activation: the traditional chemical activation needs 12h of immersion to make the activated carbon reach the optimal iodine adsorption value, while the technology uses the mechanical force effect (friction, shear, impact) generated by ball milling to destroy the dense crystalline structure of corn cob lignocellulose, promotes the rapid penetration of the composite activator into the intermolecular gap of the raw material, eliminates the solution immersion step, shortens the activation period from 12.5h of the traditional process to 4.5h, with a reduction of 64%, and significantly improves the production efficiency.

[0159] In terms of product performance improvement, experimental data and characterization results confirm that the activated carbon and nano-silver activated carbon prepared by the technology have achieved breakthroughs in structure and function. The specific surface area of the modified corn cob activated carbon is 1740.98m 2 ·g -1 , which is 25.6 times that of the unmodified activated carbon (68.10m 2 ·g -1 ), the total pore volume (cm 3 ·g -1 ) is 17.14 times that of the unmodified sample (0.04663cm 3 ·g -1 ), and the micropore ratio is more than 70%, the nitrogen adsorption-desorption isotherm shows a typical type I curve, indicating that it has a multi-level pore structure with micropore adsorption as the main and mesopore as the auxiliary, while the unmodified activated carbon isotherm tends to type IV, mainly mesoporous with limited micropore development. In terms of adsorption performance, the iodine adsorption value of the modified activated carbon is 1353mg·g -1 , which is 3.83 times that of the unmodified activated carbon (280mg·g -1 ), and 93mg·g -1 higher than that of the traditional zinc chloride modified activated carbon (1260mg·g -1After loading of nano-silver, the adsorption of methylene blue by activated carbon decreased slightly, but still maintained a high adsorption capacity, and the adsorption kinetics fitted the pseudo-second-order model (fitting correlation coefficient 0.9999), and the isothermal adsorption was more suitable for Freundlich model, indicating that the adsorption process was mainly chemical adsorption and tended to be multilayer adsorption. The antibacterial performance test showed that the nano-silver activated carbon had a 100% inhibition rate on Escherichia coli, and could completely inhibit the growth of Escherichia coli within 12 hours, while the modified activated carbon had no antibacterial property, confirming the successful loading and function of nano-silver. These performance improvements are due to the mechanical-chemical synergistic mechanism: the eutectic liquid formed by choline chloride and ammonium molybdate improves the dispersibility of the activator, titanium sulfate assists in regulating the pore structure, and ball milling pretreatment introduces a large number of lattice defects and active sites, further reducing the activation energy barrier of the composite activator (especially zinc chloride), promoting the swelling, dehydration and pore-forming effect of zinc chloride, and finally building a developed and excellent connectivity pore network to provide sufficient sites for adsorption and nano-silver loading.

[0160] From the perspectives of greenness and economy, the present technology effectively solves the problems of high energy consumption and high pollution of traditional activation processes. Traditional physical activation requires high temperature of 800-1100℃, while the present technology controls the carbonization temperature at 600℃, significantly reducing energy consumption; at the same time, the semi-dry ball milling process reduces the amount of composite activator (with zinc chloride as the core) by 60% (solid-liquid ratio 1:2) compared to traditional chemical activation (solid-liquid ratio 1:5), reducing the amount of waste liquid discharged in the subsequent washing process, reducing wastewater treatment costs, and avoiding the generation of toxic gases (such as hydrogen chloride) due to excessive evaporation of zinc chloride at high temperatures, improving process safety and environmental friendliness. In addition, the raw material used in the process is corn cob, an agricultural waste, which is widely available, low in price and rich in lignocellulose. Through the present technology, it is converted into a high-value nano-silver activated carbon carrier, realizing the high-value utilization of waste, conforming to the concept of circular economy, and having both environmental and economic benefits.

[0161] In summary, the present technology combines mechanical force effect and chemical activation through semi-dry mechanical-chemical synergistic activation technology, breaking through the technical limitations of traditional activated carbon preparation in terms of process optimization, performance improvement, green economy and resource utilization, and preparing high specific surface area nano-silver activated carbon with excellent adsorption performance and antibacterial function, providing a feasible technical path for the preparation of agricultural waste resourceization, high-performance adsorbent and antibacterial materials, and having significant academic value and industrial application potential.

[0162] While there have been described herein the exemplary embodiments of the present application, various modifications can be made to the embodiments described and illustrated herein, without departing from the spirit of the application. Additionally, many modifications can be made to adapt a particular situation to the teachings of the present application without departing from the central concept of the present application. Accordingly, the present application is not limited to the embodiments described herein but can be practiced with the scope of the claims attached hereto. The disclosure of elements of the application in the specification and drawings is not an admission that any of the elements are known or that they are part of prior art. All publications and patent documents cited herein are incorporated by reference for the purposes of making and describing the claimed application as known to and available to those in the art to which the claimed application pertains.

[0163] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All publications mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. In case of conflict, the content of the present specification will control.

[0164] The embodiments described above are only preferred embodiments of the present application, and are not intended to limit the scope of the present application. Any modifications made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process, characterized in that, Includes the following steps: (1) Corn cob pretreatment: Cut the corn cob into pieces, wash with water, dry, crush with a crusher, sieve, and store in a desiccator for later use. (2) Ball milling and activation pretreatment: Weigh the treated corn cobs, mix the corn cobs and composite activator in proportion, and place them in a ball mill jar for ball milling. (3) Carbonization activation and post-treatment: The ball-milled mixture is placed in a high-temperature tube furnace for pyrolysis; after activation, the furnace is cooled to room temperature; the obtained activated carbon is washed with hydrochloric acid solution, then thoroughly washed with pure water, and dried to constant weight to obtain modified corn cob activated carbon. Grind and sieve, then store in a desiccator in a sealed container for later use. (4) Preparation of nano-silver activated carbon: Weigh the modified corn cob activated carbon and add it to the ethanol aqueous solution, then add sodium borohydride solution, and add silver nitrate ethanol solution dropwise while stirring. Continue the reaction, filter and wash with anhydrous ethanol, and dry to obtain nano-silver activated carbon.

2. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 1, characterized in that, The composite activator in step (2) includes the following raw materials: zinc chloride, ammonium molybdate, titanium sulfate and choline chloride, wherein the molar ratio of choline chloride to ammonium molybdate is 2:

1.

3. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 2, characterized in that, The preparation process of the composite activator includes the following steps: a. Mix choline chloride and ammonium molybdate at a molar ratio of 2:1, and stir the mixture at 75-85℃ for 30-60 minutes until a transparent and homogeneous eutectic liquid is formed; b. Add zinc chloride to the eutectic liquid described in step a, in an amount of 45%-55% of the corn cob mass; then add titanium sulfate, in an amount of 5%-10% of the corn cob mass; c. Add deionized water to adjust the total liquid volume so that the solid-liquid ratio of corn cob / activator reaches 1:1-3 (g:mL); d. Stir continuously at 55-65℃ until all components are completely dissolved to form a homogeneous composite activator solution.

4. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 1, characterized in that, The specific operation of the corn cob pretreatment in step (1) is as follows: cut the corn cob into pieces, wash off the surface dust with distilled water, and dry it; crush it with a pulverizer and pass it through a 40-mesh sieve, and store it in a desiccator for later use.

5. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 1, characterized in that, The specific operation of ball milling and activation pretreatment in step (2) is as follows: Weigh the treated corn cob, mix the corn cob and composite activator at a solid-liquid ratio of 1:1-3 (g:mL) evenly, place them in a ball mill jar for ball milling, and the ball milling speed is 200-300 r·min. -1 The ball milling time is 1-2 hours.

6. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 1, characterized in that, The specific operation of ball milling, mixing and activation pretreatment in step (2) is as follows: Weigh the treated corn cob, mix the corn cob and composite activator at a solid-liquid ratio of 1:2 (g:mL), place them in a ball mill jar and ball mill at a speed of 200 r·min. -1 The ball milling time is 1.5 hours.

7. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 1, characterized in that, The specific operations for step (3) carbonization activation and post-treatment are as follows: The ball-milled mixture is placed in a high-temperature tube furnace, and under nitrogen protection, the heating rate is set to 10℃·min. -1 The carbonization temperature was set at 400-600℃, and the carbonization time was 2-4 hours for anaerobic pyrolysis. After activation, the furnace was cooled to room temperature. The obtained activated carbon was then treated with a solution of 0.8-1.2 mol·L⁻¹. -1 The modified corn cob activated carbon was washed with hydrochloric acid solution and then thoroughly washed with pure water until the pH reached 6.5-7.

5. It was then dried to constant weight to obtain modified corn cob activated carbon. It was then ground through a 100-mesh sieve and stored in a desiccator in a sealed container for later use.

8. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 1, characterized in that, The specific operations for step (3) carbonization activation and post-treatment are as follows: The ball-milled mixture is placed in a high-temperature tube furnace, and under nitrogen protection, the heating rate is set to 10℃·min. -1 The carbonization temperature was set at 600℃ and the carbonization time was 3 hours for anaerobic pyrolysis. After activation, the furnace was cooled to room temperature. The resulting activated carbon was then treated with a 1.0 mol·L⁻¹ solution. -1 The modified corn cob activated carbon was washed with hydrochloric acid solution, then thoroughly washed with pure water until the pH reached 7, and dried to constant weight. It was then ground through a 100-mesh sieve and stored in a desiccator in a sealed container for later use.

9. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 1, characterized in that, Step (4) The specific operation for preparing nano-silver activated carbon is as follows: Weigh the modified corn cob activated carbon and add it to an ethanol aqueous solution of 3-5:1 at a solid-liquid ratio of 1:10-20 (g:mL). Then add 0.08-0.12 mol·L⁻¹ at a solid-liquid ratio of 1:0.8-1.2 (g:mL). -1 A sodium borohydride solution with a concentration of 0.003-0.008 mol·L⁻¹ was added dropwise with stirring at a ratio of 1:8-12. -1 The silver nitrate ethanol solution was reacted for 0.5-1.5 hours, filtered, washed 3-5 times with anhydrous ethanol, and vacuum dried at 45-55℃ for 11-13 hours to obtain nano-silver activated carbon.

10. The method for preparing high specific surface area nano-silver activated carbon from corn cobs using a semi-dry mechanical-chemical synergistic activation process according to claim 1, characterized in that, Step (4) The specific operation for preparing nano-silver activated carbon is as follows: Weigh the modified corn cob activated carbon and add it to a 4:1 ethanol aqueous solution at a solid-liquid ratio of 1:15 (g:mL). Then add 0.1 mol·L⁻¹ activated carbon at a solid-liquid ratio of 1:1 (g:mL). -1 A sodium borohydride solution was added dropwise at a ratio of 1:10 with stirring to a concentration of 0.005 mol·L⁻¹. -1 The silver nitrate ethanol solution was reacted for another 1 hour, filtered, washed three times with anhydrous ethanol, and dried under vacuum at 50°C for 12 hours to obtain nano-silver activated carbon.

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