CN114887589A - Oxygen self-doping/high-specific-surface-area biomass porous carbon and application thereof - Google Patents

Abstract

The invention discloses oxygen self-doping/high-specific-surface-area biomass porous carbon and application thereof, wherein the oxygen content of the biomass porous carbon is 20% -23%, and the specific surface area is 3000-4000 m ² The walnut green husk activating agent is prepared by using walnut green husks as raw materials, performing superfine grinding and mechanical ball milling pretreatment, carbonizing in a nitrogen atmosphere, mixing with an activating agent for activating, and performing acid washing, water washing, filtering and vacuum drying. The biomass porous carbon prepared by the method has high specific surface area and oxygen content, the removal rate can reach 99% and the adsorption capacity can reach 465mg/g in the application of adsorbing cephalosporin antibiotics in water. The preparation method of the biomass porous carbon is simple, environment-friendly and low in cost, and is helpful for realizing walnutThe by-products are recycled, and meanwhile, the green, low-cost and efficient adsorbent material is provided for removing the antibiotics in the water body, and the method has a good popularization and application prospect.

Description

An oxygen self-doping/high specific surface area biomass porous carbon and its application

technical field

The invention belongs to the technical field of materials, and in particular relates to an oxygen self-doping/high specific surface area biomass porous carbon and its application.

Background technique

Cephalosporin antibiotics are derivatives of 7-aminocephalosporanic acid and belong to semi-synthetic β-lactam antibiotics. They have the characteristics of strong antibacterial effect, broad antibacterial spectrum, low sensitization and low toxicity. It is the most widely used class of antibiotics, accounting for more than 60% of global antibiotic production. However, the widespread use of cephalosporin antibiotics makes their residues in the environment increasingly serious. The long-term residual antibiotics in the water body will lead to the imbalance of the environmental microbial flora and induce the strong resistance of microorganisms, and also have a great impact on the ecological environment and human health. Therefore, there is an urgent need to develop efficient and low-cost treatment technologies for cephalosporin antibiotics in water bodies.

At present, the methods of removing antibiotics from water mainly include adsorption method, biological method, advanced oxidation method, etc. Among them, adsorption method has the advantages of high removal efficiency, wide application range, low cost, and environmental friendliness, and is widely used in the removal of water antibiotics. The development of low-cost and high-efficiency adsorbents is the key to the application of adsorption methods. Biomass porous carbon is a kind of carbon material with developed pore structure and stable physical and chemical properties, which is a kind of carbon material with developed pore structure and stable physical and chemical properties obtained after calcination of lignocellulosic biomass wastes with wide sources, low cost and easy regeneration as the main raw material. , dye decolorization adsorption, drug removal adsorption and other fields have attracted more and more attention. However, the pore volume and specific surface area of biomass carbon materials obtained by direct calcination of biomass are limited, and it is difficult to meet the requirements of efficient removal of antibiotics in water. Most biomass carbon materials need to be modified with metals to have good adsorption performance.

In summary, the removal of antibiotics from water using biomass porous carbon as adsorbent has the advantages of low adsorption cost and environmental friendliness. Limited efficiency and adsorption capacity limit their large-scale use.

SUMMARY OF THE INVENTION

In order to solve the shortcomings and deficiencies of the prior art, based on the structure and composition of biomass itself, the present invention proposes an oxygen self-doping/high specific surface area biomass porous carbon that can effectively remove antibiotics in water, thereby curbing cephalosporins. The spread of antibiotics in the environment and the improvement of resource utilization of walnut by-products.

In order to achieve the above purpose, the oxygen content of the oxygen self-doping/high specific surface area biomass porous carbon of the present invention is 20% to 23%, the specific surface area is 3000 to 4000 m ² /g, the average pore size is 2.71 to 3.05 nm, and the total pore size is 2.71 to 3.05 nm. The volume is 1.59 to 2.26 cm ³ /g. It is prepared by the following method: after cleaning, drying and pretreatment of walnut green skin, carbonization is carried out in a tube furnace at 300-600 DEG C for 60-150 min under nitrogen atmosphere, and then cooled to room temperature; Activation treatment at 750～900℃ for 60～150min, after cooling to room temperature, pickling, water washing, filtration, and vacuum drying to obtain oxygen self-doping/high specific surface area biomass porous carbon; wherein, the biochar is mixed with an activator The mass ratio is 1:2 to 1:3, and the activator is any one of potassium hydrogen phthalate, potassium hydroxide and potassium carbonate.

In the above preparation method, the pretreatment method is as follows: the walnut green skin after washing and drying is pulverized by an ultra-high micro pulverizer, passed through an 80-100 mesh sieve, and then subjected to wet or dry mechanical ball milling for 4 to 6 hours. After drying.

In the above preparation method, preferably, the heating rate of the carbonization is 3-5°C/min, and the cooling rate is 5-10°C/min.

In the above preparation method, preferably the obtained biochar is mixed with an activator and activated at 800° C. for 90 minutes.

In the above preparation method, it is further preferred that the heating rate of the activation treatment is 3-5°C/min, and the cooling rate is 5-10°C/min.

In the above preparation method, preferably, the mixing mass ratio of the biochar to the activator is 1:2.5.

In the above preparation method, the pickling is washed with 1 mol/L hydrochloric acid or 1 mol/L nitric acid.

In the above preparation method, the temperature of the vacuum drying is 90-105° C., and the time is 8-12 h.

The oxygen self-doping/high specific surface area biomass porous carbon of the present invention can be used as an adsorbent for the removal of antibiotics in water, and the antibiotics are cefotaxime, cephalexin, cefazolin, ceftazidime, cefaclor, cefquinoxime, etc any one or more.

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

1. The present invention firstly adopts the mode of ultra-fine pulverization combined with mechanical ball milling to pretreat the walnut green peel, which greatly destroys the tight structure between cellulose, hemicellulose and lignin, and secondly adopts low-temperature carbonization treatment to destroy cellulose, Hemicellulose structure, decomposes and escapes volatile components, provides biochar with certain pore channels and high carbon content, and finally undergoes activation treatment to prepare three-dimensional pore channels, mainly mesopores, abundant active sites, Oxygen self-doping/high specific surface area biomass porous carbon with ultra-high specific surface area. Compared with the metal-loaded biomass carbon material, the biomass porous carbon of the present invention has a removal rate of up to 99% for antibiotics in water without metal loading, has good adsorption performance, and has a simple preparation process and low cost. It is inexpensive and has the potential for large-scale industrial application.

2. In the application of the oxygen self-doping/high specific surface area biomass porous carbon prepared by the present invention in the adsorption and removal of cephalosporin antibiotics in water, the removal rate of cefotaxime can reach 99%, and the adsorption capacity can reach 465 mg/g, which is far higher. data reported in the literature. In addition, in the removal of other cephalosporin antibiotics such as cephalexin, cefazolin, ceftazidime, cefaclor, cefquinoxime, etc., it also shows certain application potential and has certain universality. A green, low-cost and efficient adsorbent material is provided for the removal of antibiotics in water, and has a good prospect of popularization and application.

3. The present invention uses walnut by-products as biomass raw materials, and has the advantages of wide sources, low price, green environmental protection, etc., while realizing the resource utilization of biomass waste, it can also effectively reduce environmental pollution, and has a certain economy. and environmental significance.

Description of drawings

1 is the scanning electron microscope images of the biochar obtained after carbon carbonization in Example 1 (a, b) and the oxygen self-doped/high specific surface area biomass porous carbon obtained after activation (c, d).

2 is the transmission electron microscope images of the biochar obtained after carbon carbonization in Example 1 (a, b) and the oxygen self-doped/high specific surface area biomass porous carbon obtained after activation (c, d).

3 is the XPS full spectrum (a), C1s spectrum (b), N1s spectrum (c), and O1s spectrum (d) of the oxygen self-doped/high specific surface area biomass porous carbon prepared in Example 1.

Figure 4 is the XPS full spectrum (a), C1s spectrum (b), N1s spectrum (c) and O1s spectrum of the oxygen self-doping/high specific surface area biomass porous carbon prepared in Example 1 after adsorbing cefotaxime Figure (d).

5 is the nitrogen adsorption and desorption isotherm (a) and pore size distribution curve (b) of the oxygen self-doping/high specific surface area biomass porous carbon prepared in Example 1.

Figure 6 is the removal rate of cefotaxime by oxygen self-doping/high specific surface area biomass porous carbon prepared under different activation ratios in Example 2.

7 is the removal rate of cefotaxime by oxygen self-doping/high specific surface area biomass porous carbon prepared at different activation temperatures in Example 3.

8 is the removal rate of cefotaxime by oxygen self-doping/high specific surface area biomass porous carbon prepared under different activation times in Example 4.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

Example 1

The green walnut peel was washed and dried in an oven at 105°C, pulverized by an ultra-fine pulverizer, passed through an 80-mesh sieve, ball-milled by a wet machine for 5 hours, and then dried at 105°C to constant weight. Then, it was put into a porcelain boat, heated to 600 °C for 120 min at a heating rate of 5 °C/min in a tube furnace with _N2 , and cooled to room temperature at a cooling rate of 10 °C/min to obtain biochar. Biochar and potassium hydroxide were mixed and ground at a mass ratio of 1:2.5, and under high-purity nitrogen, the temperature was increased to 800°C at a heating rate of 5°C/min for 90 minutes, and then the temperature was lowered at a rate of 10°C/min. After cooling to room temperature, the obtained product was repeatedly filtered and washed to neutrality through 1 mol/L hydrochloric acid and distilled water, dried in a vacuum drying oven at 105°C, ground and sieved to obtain oxygen self-doped/high specific surface area biomass porous carbon. Figures 1 and 2 are the SEM and TEM images of the walnut green skin at different stages. It can be seen from the figures that the surface of the walnut green skin after carbonization is rough and uneven, and there is no obvious pore structure. After activation, the surface is etched, and a large number of similar Due to the porous structure of the honeycomb, and the distribution is relatively uniform, mainly micropores and mesopores, which successfully increase the specific surface area of porous carbon. The existence of micropores and mesopores provides active sites for adsorption, which is beneficial to the adsorption. Adsorption on Porous Carbon. From the X-ray photoelectron spectra in Figures 3 and 4, it can be seen that the C1s of the two materials are divided into three peaks, and both peaks appear at 284.6 eV, which correspond to the CC bond and C=C of the two materials. bond, the peak of biomass porous carbon at 284.6 eV corresponds to C=O bond, and the peak of adsorbed biomass porous carbon at 286.73 eV corresponds to C in the bound state of CO. Figures 3(c) and 4(c) are N1s peaks, which are divided into three peaks. All peaks appear at around 530.01 eV, corresponding to carbonyl groups. Biomass porous carbon has COC at 532.71 eV, and after adsorption Later, -COOH appeared at 533.99 eV, and cefotaxime contained -COOH, indicating that cefotaxime was adsorbed on the carbon body by biomass porous carbon. The nitrogen adsorption/desorption isotherms and pore size distribution curves in Fig. 5 show that the adsorption curve of the biomass porous carbon belongs to the type I adsorption curve. When the pressure is close to 1, adsorbate condensation occurs, resulting in a certain upward curve of the curve. The oxygen content of the biomass porous carbon is 22%, the specific surface area is 3233m ² /g, the pore size is within 10nm, the average pore size is 2.782nm, and the total pore volume is 1.875cm ³ /g. mainly, which is very favorable for adsorption.

The oxygen self-doping/high specific surface area biomass porous carbon prepared above is used as an adsorbent for the removal of cephalosporin antibiotics in water. Weigh 4 mg of adsorbent, put it in 100 mL of cefotaxime aqueous solution with a concentration of 20 mg/L, and add KCl to adjust the ionic strength to 0.04 mol/L, the initial pH of the solution is 5, the adsorption temperature is 42 ° C, and the adsorption is 90 min. The mixed solution was passed through a 0.22 μm filter membrane, and the absorbance of the filtrate was measured at 238 nm with distilled water as a reference to determine the concentration of cefotaxime in the aqueous solution. The removal rate of cefotaxime was calculated as 95.38% and the adsorption capacity was 464.99 mg/g. .

Example 2

In this example, biochar and potassium hydroxide were mixed and ground at mass ratios of 1:2, 1:2.5, and 1:3, respectively. Under high-purity nitrogen, the temperature was raised to 800 °C at a heating rate of 5 °C/min. Activated at ℃ for 120 min, and then lowered to room temperature at a cooling rate of 10 ℃/min. Other steps are the same as in Example 1. The specific surface areas of the obtained biomass porous carbon were 3125m ² /g, 3142m ² /g and 3187m ² /g, respectively, the average pore sizes were 2.741nm, 2.771nm and 2.828nm, and the total pore volumes were 1.732cm ³ /g, 1.794 cm ³ /g, 1.934 cm ³ /g.

The removal rate of cefotaxime by biomass porous carbon prepared under different activator ratios is shown in Figure 6. With the increase of the activator ratio, the specific surface area and adsorption performance of porous carbon continued to increase. When the activation ratio was 1:2.5, the adsorption amount and removal rate reached the maximum value, which were 191.08 mg/g and 97.97%, respectively. The average pore size of porous carbon reached 2.771 nm, and the adsorption capacity and removal rate decreased when the activation ratio was greater than 1:2.5.

Example 3

In this example, biochar and potassium hydroxide were mixed and ground at a mass ratio of 1:2.5, and the temperature was raised to 700°C, 750°C, 800°C, 850°C, 900°C, activated for 120min, and then lowered to room temperature at a cooling rate of 10°C/min. Other steps are the same as in Example 1. The specific surface areas of the obtained biomass porous carbon are 2919m ² /g, 3099m ² /g, 3142m ² /g, 3283m ² /g, 3155m ² /g, respectively, and the average pore size is 2.717nm, 2.728nm, 2.771nm, ^2.914 nm and 3.046 nm, and the total pore volumes were 1.599 cm ³ /g, 1.762 cm ³ /g, 1.794 cm ³ /g, 2.069 cm 3 /g, and 2.169 cm ³ /g, respectively.

The removal rate of cefotaxime by biomass porous carbon prepared at different activation temperatures is shown in Figure 7. The specific surface area and adsorption performance of porous carbon increased with the increase of activation temperature. When the activation temperature was 800 °C, the adsorption performance of porous carbon reached the maximum, the adsorption capacity was 195.96 mg/g, the removal rate was 97.98%, and the activation temperature was greater than 800 °C. The adsorption performance showed a downward trend after ℃. This is because the activation temperature plays a key role in the reaction. When the activation temperature is less than 800°C, part of the carbon body is etched, and the etching reaction rate of the activator is low. When the activation temperature is higher than 800°C, the etching reaction is excessive. This leads to the formation of macropores, which increases the average pore size and is not conducive to adsorption.

Example 4

In this example, biochar and potassium hydroxide were mixed and ground at a mass ratio of 1:2.5, and under high-purity nitrogen, the temperature was raised to 800°C at a heating rate of 5°C/min, and activated for 30, 60, and 10 minutes, respectively. 90, 120, 150 min, and then drop to room temperature at a cooling rate of 10°C/min. Other steps are the same as in Example 1. The specific surface areas of the obtained biomass porous carbon were 3132m ² /g, 3984m ² /g, 3233m ² /g, 3142m ² /g, 3402m ² /g, and the average pore sizes were 2.798nm, 2.717nm, 2.782nm, 2.771 nm, 2.832 nm, and the total pore volumes were 1.879 cm ³ /g, 2.256 cm ³ /g, 1.875 cm ^{3 /g, 1.794 cm 3 /g, and 2.016 cm 3 / g} , respectively.

The removal rate of cefotaxime by biomass porous carbon prepared under different activation time is shown in Figure 8. When the activation time is short, the specific surface area and adsorption performance of porous carbon increase with the increase of time, and the adsorption performance of porous carbon is the best at 90 min. The adsorption capacity and removal rate are 193.55 mg/g and 99.25%, respectively. The adsorption capacity and removal rate decreased with the increase of time. This is because the length of the activation time determines the degree of activation of the porous carbon. When the activation time is less than 90min, the activation of the porous carbon is incomplete and the adsorption performance is poor. The number of micropores also increases with the increase of time. At this time, the adsorption performance is also the best. When the activation time is longer than 90min, some micropores are corroded into macropores with the progress of the reaction, and the number of macropores also increases as the activation time becomes longer, so the adsorption performance appears. Downward trend.

In the above embodiment, the used activator potassium hydroxide can also be replaced with potassium hydrogen phthalate or potassium carbonate of equal quality, and its effect is equivalent to the potassium hydroxide activation effect.

Claims (10)

1. An oxygen self-doping/high specific surface area biomass porous carbon is characterized in that: the biomass porous carbon has an oxygen content of 20-23% and a specific surface area of 3000-4000 m ² The preparation method comprises the following steps: cleaning, drying and pretreating walnut green husks, carbonizing the walnut green husks in a tubular furnace at 300-600 ℃ for 60-150 min in a nitrogen atmosphere, cooling the obtained product to room temperature, mixing the obtained biochar with an activating agent, activating the obtained product at 750-900 ℃ for 60-150 min, cooling the obtained product to room temperature, and then performing acid washing, water washing, filtering and vacuum drying to obtain the oxygen self-doping/high specific surface area biomass porous carbon; the mixing mass ratio of the biochar to an activating agent is 1: 2-1: 3, and the activating agent is any one of potassium hydrogen phthalate, potassium hydroxide and potassium carbonate.

2. The oxygen autodoped/high specific surface area biomass porous carbon of claim 1, characterized in that: the pretreatment method comprises the following steps: and (3) crushing the walnut green husks subjected to water washing and drying by using an ultrahigh micro crusher, sieving by using a sieve of 80-100 meshes, and drying after mechanically ball-milling for 4-6 hours by using a wet method or a dry method.

3. The oxygen autodoped/high specific surface area biomass porous carbon of claim 1, characterized in that: the temperature rising rate of carbonization is 3-5 ℃/min, and the temperature reduction rate is 5-10 ℃/min.

4. The oxygen autodoped/high specific surface area biomass porous carbon of claim 1, characterized in that: mixing the obtained charcoal with activating agent, and activating at 800 deg.C for 90 min.

5. The oxygen autodoped/high specific surface area biomass porous carbon of claim 1 or 4, characterized in that: the temperature rise rate of the activation treatment is 3-5 ℃/min, and the temperature reduction rate is 5-10 ℃/min.

6. The oxygen autodoped/high specific surface area biomass porous carbon of claim 4, characterized in that: the mixing mass ratio of the biochar to the activating agent is 1: 2.5.

7. The oxygen autodoped/high specific surface area biomass porous carbon of claim 1, characterized in that: the acid washing is carried out by adopting 1mol/L hydrochloric acid or 1mol/L nitric acid.

8. The oxygen autodoped/high specific surface area biomass porous carbon of claim 1, characterized in that: the temperature of the vacuum drying is 90-105 ℃, and the time is 8-12 h.

9. Use of the oxygen self-doped/high specific surface area biomass porous carbon of claim 1 as an adsorbent for antibiotic removal in water.

10. The use of the oxygen self-doped/high specific surface area biomass porous carbon as an adsorbent in water antibiotic removal according to claim 9, wherein: the antibiotic is any one or more of cefotaxime, cephalexin, cefazolin, ceftazidime, cefaclor and cefquinome.

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