CN115634679B - Chitosan-based biochar with porous structure and high specific surface area, and preparation method and application thereof - Google Patents
Chitosan-based biochar with porous structure and high specific surface area, and preparation method and application thereof Download PDFInfo
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- 229920001661 Chitosan Polymers 0.000 title claims abstract description 172
- 238000002360 preparation method Methods 0.000 title claims abstract description 22
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- 238000000034 method Methods 0.000 claims abstract description 47
- 239000002957 persistent organic pollutant Substances 0.000 claims abstract description 45
- JRKICGRDRMAZLK-UHFFFAOYSA-L peroxydisulfate Chemical compound [O-]S(=O)(=O)OOS([O-])(=O)=O JRKICGRDRMAZLK-UHFFFAOYSA-L 0.000 claims abstract description 40
- 238000001354 calcination Methods 0.000 claims abstract description 34
- 239000011148 porous material Substances 0.000 claims abstract description 32
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- 238000006731 degradation reaction Methods 0.000 claims description 35
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- 239000000243 solution Substances 0.000 claims description 34
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- 238000001035 drying Methods 0.000 claims description 21
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- CHQMHPLRPQMAMX-UHFFFAOYSA-L sodium persulfate Substances [Na+].[Na+].[O-]S(=O)(=O)OOS([O-])(=O)=O CHQMHPLRPQMAMX-UHFFFAOYSA-L 0.000 claims description 9
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- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims description 4
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- RBTBFTRPCNLSDE-UHFFFAOYSA-N 3,7-bis(dimethylamino)phenothiazin-5-ium Chemical compound C1=CC(N(C)C)=CC2=[S+]C3=CC(N(C)C)=CC=C3N=C21 RBTBFTRPCNLSDE-UHFFFAOYSA-N 0.000 claims description 2
- XMEVHPAGJVLHIG-FMZCEJRJSA-N chembl454950 Chemical compound [Cl-].C1=CC=C2[C@](O)(C)[C@H]3C[C@H]4[C@H]([NH+](C)C)C(O)=C(C(N)=O)C(=O)[C@@]4(O)C(O)=C3C(=O)C2=C1O XMEVHPAGJVLHIG-FMZCEJRJSA-N 0.000 claims description 2
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- 239000002028 Biomass Substances 0.000 description 2
- XZMCDFZZKTWFGF-UHFFFAOYSA-N Cyanamide Chemical compound NC#N XZMCDFZZKTWFGF-UHFFFAOYSA-N 0.000 description 2
- 239000004100 Oxytetracycline Substances 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
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- IWVCMVBTMGNXQD-PXOLEDIWSA-N oxytetracycline Chemical compound C1=CC=C2[C@](O)(C)[C@H]3[C@H](O)[C@H]4[C@H](N(C)C)C(O)=C(C(N)=O)C(=O)[C@@]4(O)C(O)=C3C(=O)C2=C1O IWVCMVBTMGNXQD-PXOLEDIWSA-N 0.000 description 2
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- IWVCMVBTMGNXQD-UHFFFAOYSA-N terramycin dehydrate Natural products C1=CC=C2C(O)(C)C3C(O)C4C(N(C)C)C(O)=C(C(N)=O)C(=O)C4(O)C(O)=C3C(=O)C2=C1O IWVCMVBTMGNXQD-UHFFFAOYSA-N 0.000 description 2
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Abstract
The invention discloses a chitosan-based biochar with a porous structure and a high specific surface area, and a preparation method and application thereof, wherein the method comprises the following steps: firstly preparing chitosan hydrogel and chitosan aerogel, then heating the chitosan aerogel to 600-650 ℃ for calcination, washing, and then heating to 800-850 ℃ for calcination to obtain the chitosan-based biochar with a porous structure and a high specific surface area. The chitosan-based biochar prepared by the method comprises a large number of micropores, mesopores and macropores, has the advantages of high specific surface area, rich pore structure, good catalytic performance, strong anti-interference performance, environment friendliness and the like, can be used for activating persulfate to degrade organic pollutants in water, shows excellent removal effect and high removal efficiency, and has good application prospect. The preparation method has the advantages of simple process, low cost, no secondary pollution and the like, is suitable for large-scale preparation and is beneficial to industrial application.
Description
Technical Field
The invention belongs to the technical field of catalytic materials, and particularly relates to chitosan-based biochar with a porous structure and a high specific surface area, and a preparation method and application thereof.
Background
Organic pollutants such as phenolic pollutants, antibiotics, dyes and the like are detected in a large amount in water environment, and the ecological environment and human health are threatened. Advanced oxidation technology based on catalyst activated persulfate shows great application prospect in water pollution control, wherein the property of the catalyst is a key factor influencing the technical effect. Biochar is a new type of carbon catalyst that has emerged in recent years and has the following advantages: (1) the cost is low, the preparation method is simple, and the recycling and carbonization reduction utilization of wastes can be realized; (2) the environment is friendly, the risk of secondary pollution is avoided, and the method can be popularized and applied in a large area; (3) the pore structure is rich and adjustable, and the specific surface area is large; (4) the surface oxygen-containing functional groups and carbon configurations are rich, and the functional modification is easy to realize. In the practical application process, the biological carbon activated persulfate shows good removal effect and practical application advantage when being used for treating organic pollutant water, namely, the biological carbon can obtain the effect comparable to that of graphene and a metal catalyst. However, in the practical application process, the preparation method and the regulation method of the biochar are not strong in pertinence due to the limitation of physical and chemical properties of the biomass, so that the catalytic activation effect of the biochar catalyst is limited, the removal effect and the removal efficiency of organic pollutants are not ideal, and the treatment time is too long. Therefore, how to select proper biomass materials and prepare the biochar catalyst with high catalytic performance by adopting a proper method is important to the practical application of a biochar-persulfate system. In addition, the advanced oxidation technology based on activated persulfate of the biochar catalyst is easy to be interfered by substances such as organic matters, common anions, halogen ions and the like in a water treatment system, so that the removal effect of organic pollutants is greatly reduced. In addition, in the practical research process of the inventor of the application, the defects of small specific surface area, single pore structure, poor catalytic performance and the like of the traditional chitosan-based biochar are also found, so that the chitosan-based biochar is difficult to effectively and rapidly remove organic pollutants in water. Therefore, the chitosan-based biochar catalyst has the advantages of high specific surface area, rich pore structure, good catalytic performance, strong anti-interference performance and environmental protection, and has very important significance for effectively activating persulfate and realizing high-efficiency degradation of organic pollutants.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the chitosan-based biochar with a porous structure and a high specific surface area, a rich pore structure, good catalytic performance, strong anti-interference performance, environmental friendliness and a preparation method and application thereof.
In order to solve the technical problems, the invention adopts the following technical scheme.
The preparation method of the chitosan-based biochar with the porous structure and the high specific surface area comprises the following steps:
s1, dissolving chitosan in an alkaline solution to obtain a chitosan solution, performing freeze-thawing cycle treatment on the chitosan solution, stirring, and drying to obtain chitosan hydrogel; the alkaline solution is a mixed solution containing potassium hydroxide and a nitrogen source;
s2, performing freeze drying treatment on the chitosan hydrogel obtained in the step S1 to obtain chitosan aerogel;
s3, heating the chitosan aerogel obtained in the S2 to 600-650 ℃ for calcining, washing and drying;
and S4, heating the product obtained after drying in the step S3 to 800-850 ℃ for calcining to obtain the chitosan-based biochar with a porous structure and a high specific surface area.
In the above method, it is further preferable that in the step S1, the alkaline solution is prepared by dissolving potassium hydroxide and a nitrogen source into a solvent, wherein the mass ratio of the chitosan to the potassium hydroxide to the nitrogen source to the solvent is 4-5:11-12:7-8:77-80, and the nitrogen source is at least one of urea, cyanamide and melamine; the solvent is water.
In the above method, it is further preferable that in the step S1, the freeze-thaw cycle is performed by sequentially performing a freeze treatment and a thaw treatment on the chitosan solution, and the freeze treatment and the thaw treatment are repeated, wherein the cycle number is not less than 3; the freezing treatment is carried out at the temperature of-20 ℃ to-40 ℃; the time of the single freezing treatment is 12-24 hours; the thawing treatment is carried out at the temperature of 4-6 ℃; the time of the single thawing treatment is 12-24 hours.
In the above method, it is further preferable that in S3, the calcination is performed under an inert atmosphere, the inert atmosphere is nitrogen, a temperature rising rate in the calcination process is 5 ℃/min to 10 ℃/min, and a calcination time is 2h to 2.5h.
In the above method, it is further preferable that in S4, the calcination is performed under an inert atmosphere, the inert atmosphere is nitrogen, a temperature rising rate in the calcination process is 5 ℃/min to 10 ℃/min, and a calcination time is 2h to 2.5h.
In the above method, it is further preferable that in S1, the stirring is performed at 0 ℃, the stirring time is 2 to 3 hours, the drying is performed under vacuum, the drying temperature is 15 to 35 ℃, and the drying time is 4 to 6 hours.
In the above method, it is further preferable that in S2, the freeze-drying is performed under vacuum.
In the above method, it is further preferable that in S3, the drying temperature is 80 to 120 ℃, and the drying time is 6 to 10 hours.
The present invention also provides a chitosan-based biochar having a porous structure and a high specific surface area, as a general inventive concept, prepared by the above-described preparation method.
The chitosan-based biochar having a porous structure and a high specific surface area as described above, further preferably, the chitosan-based biochar comprises three pore structures of micropores, mesopores and macropores, and the shellBET specific surface area of polysaccharide-based biochar 1600m 2 /g～2400m 2 Per gram, the pore volume of the chitosan-based biochar is 0.8cm 3 /g～1.2cm 3 /g。
The invention also provides an application of the chitosan-based biochar with a porous structure and a high specific surface area in treating organic pollutant wastewater.
The above application, further preferred, comprises the steps of: the chitosan-based biochar with a porous structure and a high specific surface area, persulfate and the water body containing the organic pollutants are mixed for degradation reaction, so that the degradation of the organic pollutants in the water body is completed.
In the application, it is further preferable that the adding amount of the chitosan-based biochar is 0.05 g-0.125 g of the chitosan-based biochar added into each liter of the organic pollutant-containing water body, the adding amount of the persulfate is 0.15 mmol-0.75 mmol of the persulfate added into each liter of the organic pollutant-containing water body, the persulfate is sodium persulfate, the initial concentration of the organic pollutant in the organic pollutant-containing water body is 50 mg/L-100 mg/L, the initial pH value of the organic pollutant-containing water body is 3-11, the organic pollutant in the organic pollutant-containing water body comprises at least one of a phenolic compound, a dye and an antibiotic, the phenolic compound is at least one of 2, 4-dichlorophenol and phenol, the dye is at least one of methyl orange and methylene blue, the antibiotic is at least one of oxytetracycline and tetracycline hydrochloride, the degradation reaction is carried out under the oscillation condition, the rotation speed of the oscillation is 120 r/min-200 r/min, and the degradation reaction time is between 35 and 5 min-60 min.
Compared with the prior art, the invention has the advantages that:
(1) Aiming at the defects of small specific surface area, small number of active sites, low catalytic activity, poor removal effect on organic pollution, slow mass transfer, low removal efficiency and the like of the existing biochar catalyst, the invention provides a preparation method of chitosan-based biochar with a porous structure and high specific surface area, which takes chitosan asThe preparation method comprises the steps of dissolving chitosan into a mixed solution (alkaline solution) containing potassium hydroxide and a nitrogen source, continuously shrinking and swelling the chitosan through freezing-thawing cycle treatment, enabling the potassium hydroxide and the nitrogen source to be coated inside the chitosan, forming a chitosan gel solution in the stirring process, removing a small amount of bubbles and carrying out chemical crosslinking reaction in the drying process to form chitosan hydrogel coated with the potassium hydroxide and the nitrogen source, then carrying out freeze drying treatment on the chitosan hydrogel, directly gasifying and removing solvent (such as water) molecules in the chitosan hydrogel in the freeze drying process to form loose porous chitosan aerogel, forming porous carbon aerogel, particularly forming porous structures in the subsequent calcination process, and finally carrying out calcination on the loose porous chitosan aerogel at 600-650 ℃ and 800-850 ℃ for two times in sequence, wherein the porous chitosan aerogel is calcined at 600-650 ℃ firstly, the chitosan is converted into carbon materials on the premise of retaining the original structures, and the porous structures are not only enabled to be further promoted to be formed into a pore agent and the solvent, but also enabling the porous structures to be better in the porous structures to be formed, and the porous carbon to be more porous and the porous carbon can be more porous and more porous than the porous carbon can be more completely removed through the porous carbon, and the porous carbon is more porous and has the porous carbon-containing the active carbon, the porous carbon is more porous and has the active carbon, the porous carbon is more completely washed and has the porous surface active sites more than the porous carbon is formed by the porous carbon and is more removed the active carbon and more than the porous carbon is more completely washed and more completely washed the active carbon porous carbon is prepared 2 CO 3 、K 2 O, KOH) can lead the original porous structure of the biochar not to be damaged in the subsequent calcination process at 800-850 ℃, and can further improve the graphitization degree of the biochar, so that the biochar has more excellent catalytic activity. Compared with the chitosan-based biochar prepared by the conventional method, the chitosan-based biochar prepared by the method comprises a large number of micropores, mesopores and macropores, wherein the mesopores (2-50 nm) occupy the largest proportion, have rich pore structures, not only can remarkably improve the specific surface area and the number of active sites of the chitosan-based biochar, but also can accelerate the transfer of substances in a catalytic degradation system, and meanwhile, the chitosan-based biochar has the advantages of high activity, low cost, and the likeThe graphitization degree of the glycosyl biochar is higher, so that the rapid degradation of organic pollutants can be realized, the efficient activation of persulfate can also be realized, the glycosyl biochar has the advantages of high specific surface area, rich pore structure, good catalytic performance, strong anti-interference performance, environment friendliness and the like, can be used for activating persulfate to degrade organic pollutants in water, shows excellent removal effect and efficient removal efficiency, and has good application prospect. In addition, the preparation method has the advantages of simple process, low cost, no secondary pollution and the like, is suitable for large-scale preparation, and is beneficial to industrial application.
(2) According to the preparation method disclosed by the invention, the chitosan can be quickly dissolved by framework and more holes can be formed by optimizing the mass ratio of the chitosan to the potassium hydroxide to the nitrogen source to the solvent (such as water) to be 4-5:11-12:7-8:77-80, so that the hole structure of the chitosan-based biochar can be optimized, the higher specific surface area can be obtained, and the organic pollutants in the water body can be quickly degraded by the chitosan-based biochar. In addition, the potassium hydroxide adopted in the invention is used as a solvent and a pore-forming agent, and cannot be replaced by other conventional pore-forming agents (such as zinc chloride and phosphoric acid), and substances with high nitrogen content such as urea, cyanamide, melamine and the like can be used as nitrogen sources, but the urea is an optimal nitrogen source because the urea is soluble in water, is low in price and is nontoxic in consideration of factors such as cost, environmental friendliness and the like.
(3) The invention also provides application of the chitosan-based biochar with the porous structure and the high specific surface area in treating organic pollutants, and degradation reaction is carried out by mixing the chitosan-based biochar with the porous structure and the high specific surface area, persulfate and the water body containing the organic pollutants, so that the degradation of the organic pollutants in the water body can be realized, and the chitosan-based biochar has the advantages of simple process, convenient operation, low treatment cost, high treatment efficiency, good removal effect and the like, and has important significance in effectively removing the organic pollutants in the water body and effectively treating the polluted water body. In the invention, when chitosan-based biochar activated persulfate with a porous structure and a high specific surface area is used for degrading organic pollutants, the high-efficiency degradation of the organic pollutants is realized through a non-free radical path, sulfate radicals and hydroxyl radicals are not generated in the degradation process, and the existence of singlet oxygen is not detected, so that the catalytic system constructed by the invention has good anti-interference performance, is hardly influenced by pH value change in the catalytic degradation reaction process, has little influence of common anions and natural organic matters in a water body on the degradation effect, and has the advantage of wide application range. Taking 2, 4-dichlorophenol and methyl orange as examples, when the chitosan-based biochar activated persulfate with porous structure and high specific surface area is adopted to degrade organic pollutants, the removal rate can reach more than 90% in the reaction for 5min, and the removal effect on the 2, 4-dichlorophenol in the water body is good in the pH value range of 3-11, and the practical application prospect is good.
Drawings
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
FIG. 1 is an SEM and TEM image of chitosan-based biochar having a porous structure and a high specific surface area, prepared in example 1 of the present invention.
FIG. 2 is a graph showing adsorption and desorption of chitosan-based biochar (BC-800) having a porous structure and a high specific surface area prepared in example 1 of the present invention and chitosan-based biochar (BC-700) prepared in comparative example 1.
FIG. 3 is a graph showing pore size distribution of the chitosan-based biochar (BC-800) having a porous structure and a high specific surface area prepared in example 1 of the present invention and the chitosan-based biochar (BC-700) prepared in comparative example 1.
FIG. 4 is a Raman spectrum of the chitosan-based biochar (BC-800) having a porous structure and a high specific surface area prepared in example 1 of the present invention and the chitosan-based biochar (BC-700) prepared in comparative example 1.
FIG. 5 is a graph showing the effect of removing 2, 4-dichlorophenol when activated with persulfate by chitosan-based biochar (BC-800) having a porous structure and a high specific surface area in example 2 of the present invention.
FIG. 6 is a graph showing the effect of chitosan-based biochar (BC-700) on removal of 2, 4-dichlorophenol when persulfate is activated in example 2 of the present invention.
FIG. 7 is a graph showing the effect of removing 2, 4-dichlorophenol when the chitosan-based biochar having a porous structure and a high specific surface area of example 3 of the present invention activates persulfate under different pH conditions.
FIG. 8 is a graph showing the effect of removing 2, 4-dichlorophenol when the chitosan-based biochar having a porous structure and a high specific surface area of example 4 of the present invention activates persulfate under different ionic conditions.
FIG. 9 is a graph showing the effect of removing methyl orange and terramycin when the chitosan-based biochar having a porous structure and a high specific surface area in examples 5 and 6 of the present invention activates persulfate.
Detailed Description
The invention is further described below in connection with the drawings and the specific preferred embodiments, but the scope of protection of the invention is not limited thereby. The materials and instruments used in the examples below are all commercially available. The initial pH of the organic contaminant water used in the present invention is 7 unless specifically stated.
Example 1:
the preparation method of the chitosan-based biochar with the porous structure and the high specific surface area comprises the following steps:
(1) Dispersing chitosan in a mixed solvent of potassium hydroxide, urea and water, wherein the mass ratio of the chitosan to the potassium hydroxide to the urea to the water is 4:11.04:7.68:77.28, fully stirring to dissolve the chitosan to obtain a chitosan solution, and then sequentially carrying out freezing treatment and thawing treatment on the chitosan solution, wherein the method specifically comprises the following steps of: freezing at-24 ℃ for 18h, thawing at 4 ℃ for 18h, performing total circulation treatment for 4 times to obtain a light yellow viscous solution, magnetically stirring the light yellow viscous solution for 2h under the water bath condition of 0 ℃ to obtain a chitosan gel solution, drying the chitosan gel solution in a vacuum drying oven at 30 ℃ for 6h, removing a small amount of bubbles and performing chemical crosslinking reaction to obtain the chitosan hydrogel. In this step, the chitosan solution is not effectively dissolved without being subjected to freezing treatment and thawing treatment.
(2) And freeze-drying the chitosan hydrogel, namely freezing the chitosan hydrogel in an ultralow temperature refrigerator, transferring the chitosan hydrogel to a vacuum freeze dryer, and drying the chitosan hydrogel at-30 to-45 ℃ to obtain loose chitosan aerogel.
(3) The chitosan aerogel is put into a tubular calciner for pyrolysis (calcination), and the concrete steps are as follows: at N 2 Heating from room temperature to 600 ℃ at a heating rate of 5 ℃/min under the atmosphere, preserving heat for 2 hours, taking out the product, washing with water to be neutral, and drying at 80 ℃ for 6 hours to obtain the Biochar-600.
(4) The Biochar Biochar-600 is put into a tube calciner for pyrolysis (calcination), specifically: at N 2 Under the atmosphere, heating from room temperature to 800 ℃ at a heating rate of 5 ℃/min, preserving heat for 2 hours, taking out and grinding to obtain the chitosan-based biochar with a porous structure and a high specific surface area, which is named BC-800.
The two-step calcination method adopted in the invention forms the biochar with a porous structure after primary calcination, and then the biochar is washed to remove K remained on the surface of the biochar 2 CO 3 、K 2 O, KOH, and then performing the second calcination, if the second calcination is directly performed without washing, the residual substances are attached near the pore structure, so that the porosity of the material is obviously reduced, and finally, the chitosan-based biochar with large specific surface area and rich pore structure cannot be obtained. In addition, if the chitosan aerogel is directly calcined by heating to 800 ℃, the carbon product cannot be obtained, but a white alkaline solid which is easily soluble in water is formed, because: the residual potassium hydroxide in the chitosan aerogel is pyrolyzed and activated at high temperature, namely KOH+C- & gt K mainly occurs 2 CO 3 +K 2 O+H 2 The reaction, that is, potassium hydroxide etches away some of the carbon to form a porous carbon material, and the higher the temperature, the faster the reaction proceeds. Therefore, the chitosan-based biochar with large specific surface area and rich pore structure can be obtained by adopting the two-step calcination method.
The chitosan having a porous structure and a high specific surface area prepared in example 1 of the present inventionThe base biochar has rich pore structure, comprises three structures of micropores, mesopores and macropores, wherein the medium Kong Zhanbi is highest, the average pore diameter is 3.43nm, and the BET specific surface area is 1748m 2 Per g, wherein the specific surface area of the micropores is 73.24m 2 Specific surface area of mesoporous is 1674.9m 2 Per g, pore volume of 0.976cm 3 /g, wherein the pore volume of the micropores is 0.0059cm 3 Per g, mesoporous volume of 0.97cm 3 And/g, the proportion of the mesoporous is the largest.
FIG. 1 is an SEM and TEM image of chitosan-based biochar having a porous structure and a high specific surface area, prepared in example 1 of the present invention. As can be seen from FIG. 1, the material has a large number of macropores formed, and the pore diameter thereof is concentrated between 1 and 3. Mu.m. In addition, the formation of graphitized carbon can be observed in the TEM image at high magnification.
Comparative example 1:
a method for preparing chitosan-based biochar, which is different from the preparation method in example 1 in that pyrolysis is performed only once, comprising the steps of:
the loose chitosan aerogel prepared in example 1 was put into a tube calciner for pyrolysis (calcination), specifically: at N 2 Under the atmosphere, heating from room temperature to 700 ℃ at a heating rate of 5 ℃/min, preserving heat for 2 hours, taking out the product, washing with water to be neutral, and drying at 80 ℃ for 6 hours to obtain the chitosan-based biochar, which is named as BC-700.
FIG. 2 is a graph showing adsorption and desorption of chitosan-based biochar (BC-800) having a porous structure and a high specific surface area prepared in example 1 of the present invention and chitosan-based biochar (BC-700) prepared in comparative example 1. FIG. 3 is a graph showing pore size distribution of the chitosan-based biochar (BC-800) having a porous structure and a high specific surface area prepared in example 1 of the present invention and the chitosan-based biochar (BC-700) prepared in comparative example 1. As can be seen from fig. 2 and 3, the pores of the chitosan-based biochar (BC-800) with porous structure and high specific surface area of the present invention are mainly distributed in the mesoporous range, and the pore structure mainly comprising mesopores is more favorable for rapid transfer of substances. It can be obtained by combining fig. 1, fig. 2 and fig. 3 that the chitosan-based biochar with porous structure and high specific surface area of the invention has a three-level pore structure of micropores, mesopores and macropores, and mainly has mesopores of 2-50 nm.
FIG. 4 is a Raman spectrum of the chitosan-based biochar (BC-800) having a porous structure and a high specific surface area prepared in example 1 of the present invention and the chitosan-based biochar (BC-700) prepared in comparative example 1. From raman analysis of fig. 4, it was found that ID/ig=0.967 of BC-800 in example 1 and ID/ig=0.982 of BC-700 in comparative example 1, it was found that the graphitization degree of the material was increased after two-step calcination compared to one-step calcination. The chitosan-based biochar with the porous structure and the high specific surface area is used for activating persulfate to degrade organic pollutants through a non-free radical path, namely, the chitosan-based biochar serves as a transmission medium to transfer electrons from the pollutants to the persulfate, so that the high graphitization degree is favorable for degradation reaction.
As can be seen from FIGS. 2, 3 and 4, the specific surface area of BC-800 in example 1 is 1748m 2 Per g, the specific surface area of BC-700 in comparative example 1 is only 275.23m 2 Per gram, the total pore volume is only 0.1802cm 3 And/g. Therefore, the two-step calcination method can further pyrolyze the carbon material, so that the graphitization degree of the material is improved, the pore number and pore capacity of the material are increased, the specific surface area and pore volume of the material are obviously increased, and the chitosan-based biochar with better catalytic activity is obtained.
Example 2:
the application of chitosan-based biochar with a porous structure and a high specific surface area in treating organic pollutants, in particular to the use of chitosan-based biochar with a porous structure and a high specific surface area to activate persulfate to degrade 2, 4-dichlorophenol in water, comprising the following steps:
taking 40mL of 50 mg/L2, 4-dichlorophenol solution, respectively adding 0.003g and 0.005g of chitosan-based biochar with porous structure and high specific surface area prepared in the example 1, adding 0.3mL of 0.1mol/L sodium persulfate solution, and carrying out degradation reaction for 90min under the oscillation condition of 30 ℃ and the rotating speed of 150r/min to finish the degradation of 2, 4-dichlorophenol in the water body.
Control group one: the chitosan-based biochar having a porous structure and a high specific surface area prepared in example 1 was added only, and sodium persulfate was not added, except that the same conditions as in example 2 were used.
Control group two: the chitosan-based biochar prepared in comparative example 1 was used instead of the chitosan-based biochar having a porous structure and a high specific surface area prepared in example 1, and the other conditions were the same as in example 2.
Control group three: the chitosan-based biochar prepared in comparative example 1 was added only to degrade 2, 4-dichlorophenol in a water body, and sodium persulfate was not added, except that the conditions were the same as in example 2.
In the oscillation treatment process, sampling and measuring the concentration of the 2, 4-dichlorophenol in the 5 th, 15 th, 30 th, 45 th, 60 th and 90 th min, and calculating the removal rate of the 2, 4-dichlorophenol.
FIG. 5 is a graph showing the effect of removing 2, 4-dichlorophenol when activated with persulfate by chitosan-based biochar (BC-800) having a porous structure and a high specific surface area in example 2 of the present invention. FIG. 6 is a graph showing the effect of chitosan-based biochar (BC-700) on removal of 2, 4-dichlorophenol when persulfate is activated in example 2 of the present invention. As can be seen from fig. 5 and 6, the chitosan-based biochar prepared by the two-step calcination method is superior to the biochar obtained by pyrolysis at 700 ℃ in both adsorption effect and catalytic effect because: the specific surface area and the pore volume of the chitosan-based biochar prepared by the two-step calcination method are obviously increased, and the graphitization degree of the biochar is improved through pyrolysis at a higher temperature, so that the transfer of electrons is facilitated.
Example 3:
the influence of chitosan-based biochar with a porous structure and a high specific surface area on the degradation effect of organic pollutants under different pH conditions is examined, specifically, 2, 4-dichlorophenol in water bodies with different pH values is degraded by using chitosan-based biochar with a porous structure and a high specific surface area to activate persulfate, and the method comprises the following steps:
5 parts of 40mL and 50 mg/L2, 4-dichlorophenol solution are taken, the pH values of the solution are respectively regulated to 3, 5, 7, 9 and 11, 0.005g of chitosan-based biochar with a porous structure and a high specific surface area prepared in the example 1 is respectively added, then 0.3mL and 0.1mol/L sodium persulfate solution is added, and degradation reaction is carried out for 45min under the oscillation condition of 30 ℃ and the rotating speed of 150r/min, so that the degradation of 2, 4-dichlorophenol in the water body is completed.
And in the oscillation treatment process, sampling and measuring the concentration of the 2, 4-dichlorophenol in the 5 th, 15 th, 30 th and 45 th min, and calculating the removal rate of the 2, 4-dichlorophenol.
FIG. 7 is a graph showing the effect of removing 2, 4-dichlorophenol when the chitosan-based biochar having a porous structure and a high specific surface area of example 3 of the present invention activates persulfate under different pH conditions. As can be seen from FIG. 7, after 5min of treatment, the chitosan-based biochar with a porous structure and a high specific surface area has the removal efficiency of more than 80% on 2, 4-dichlorophenol when persulfate is activated under acidic, neutral and alkaline conditions, and after 45min of treatment, the chitosan-based biochar with a porous structure and a high specific surface area has the removal efficiency of more than 90% on 2, 4-dichlorophenol when persulfate is activated under acidic, neutral and alkaline conditions, which shows that the chitosan-based biochar with a porous structure and a high specific surface area has an excellent pH adaptation range and has a good application prospect in the aspect of treating phenolic wastewater.
Example 4:
the influence of chitosan-based biochar with a porous structure and a high specific surface area on the degradation effect of organic pollutants under different ionic conditions is examined, specifically, 2, 4-dichlorophenol in water bodies containing different ions is degraded by using chitosan-based biochar with a porous structure and a high specific surface area to activate persulfate, and the method comprises the following steps:
4 parts of a 40mL, 50mg/L solution of 2, 4-dichlorophenol, 2 parts of which were added with NaCl to give a solution of Cl - The concentration is 10mM, 400mM respectively, and 2 parts of NaHCO is added 3 To make HCO in solution 3 - The concentration is 10mM and 400mM respectively, then 0.005g of chitosan-based biochar with porous structure and high specific surface area prepared in the example 1 is added respectively, then 0.3mL of 0.1mol/L sodium persulfate solution is added, and degradation reaction is carried out for 45min under the oscillation condition of 30 ℃ and the rotating speed of 150r/min, thus completing the degradation of 2, 4-dichlorophenol in the water body.
And in the oscillation treatment process, sampling and measuring the concentration of the 2, 4-dichlorophenol in the 5 th, 15 th, 30 th and 45 th min, and calculating the removal rate of the 2, 4-dichlorophenol.
FIG. 8 is a graph showing the effect of removing 2, 4-dichlorophenol when the chitosan-based biochar having a porous structure and a high specific surface area of example 4 of the present invention activates persulfate under different ionic conditions. As can be seen from FIG. 8, when Cl is present - 、HCO 3 - Even if Cl - And HCO 3 - The concentration is up to 400mM, and the removal efficiency of the chitosan-based biochar with a porous structure and a high specific surface area to 2, 4-dichlorophenol is over 94% when the chitosan-based biochar with a porous structure and a high specific surface area activates persulfate, so that the chitosan-based biochar with a porous structure and a high specific surface area has good anti-interference capability while maintaining high degradation efficiency, and has good practical application prospect.
Example 5:
the application of chitosan-based biochar with a porous structure and a high specific surface area in treating organic pollutants, in particular to the use of chitosan-based biochar with a porous structure and a high specific surface area to activate persulfate to degrade methyl orange in water, comprising the following steps:
taking 2 parts of 50mg/L methyl orange solution, wherein the volumes of the methyl orange solution are 60mL and 80mL respectively, adding 0.005g of chitosan-based biochar with a porous structure and a high specific surface area prepared in the example 1 respectively, adding 0.3mL and 0.1mol/L sodium persulfate solution, and carrying out degradation reaction for 90min under the oscillation condition of 30 ℃ and the rotating speed of 150r/min to finish the degradation of the methyl orange in the water body.
In the oscillation treatment process, sampling and measuring the concentration of the methyl orange in 15min, 30min, 45min, 60min and 90min, and calculating the removal rate of the methyl orange.
Example 6:
the application of chitosan-based biochar with a porous structure and a high specific surface area in treating organic pollutants, in particular to the use of chitosan-based biochar with a porous structure and a high specific surface area to activate persulfate to degrade terramycin in water, comprising the following steps:
taking 2 parts of 50mg/L terramycin solution, wherein the volumes of the terramycin solution are 40mL and 60mL respectively, adding 0.005g of chitosan-based biochar with porous structure and high specific surface area prepared in the example 1 respectively, adding 0.3mL and 0.1mol/L sodium persulfate solution, and carrying out degradation reaction for 150min under the oscillation condition of 30 ℃ and the rotating speed of 150r/min to finish the degradation of terramycin in the water body.
During the oscillation treatment, the terramycin concentration is measured by sampling at the 5 th, 15 th, 30 th, 45 th, 90 th and 150 th min, and the terramycin removal rate is calculated.
FIG. 9 is a graph showing the effect of removing methyl orange and terramycin when the chitosan-based biochar having a porous structure and a high specific surface area in examples 5 and 6 of the present invention activates persulfate. As can be seen from fig. 9, the method of the present invention can rapidly remove methyl orange, and the removal rate thereof decreases with the increase of the contaminant content, because: the amount of biochar as an activator is limited, so that it provides limited activation sites, and as degradation reaction proceeds, a part of degradation products adhere to the surface of the biochar, and also catalytic activity of the biochar is reduced. When the chitosan-based biochar with a porous structure and a high specific surface area is used for removing 2, 4-dichlorophenol, the removal efficiency is reduced along with the increase of the concentration of pollutants. In addition, the reaction system has a certain removal effect on terramycin, which proves that the chitosan-based biochar with a porous structure and a high specific surface area has a wider application range. However, under the same conditions, the removal efficiency of terramycin is lower than that of 2, 4-dichlorophenol and methyl orange when the chitosan-based biochar with porous structure and high specific surface area activates persulfate, and the degradation time is obviously longer than that of the chitosan-based biochar, which may be caused by the following reasons: oxytetracycline has a lower electron donating ability than 2, 4-dichlorophenol and methyl orange, and is more difficult to transfer electrons to persulfates through biochar.
As can be seen from the results, compared with the chitosan-based biochar prepared by the conventional method, the chitosan-based biochar prepared by the preparation method disclosed by the invention comprises a large number of micropores, mesopores and macropores, wherein the mesopores (2-50 nm) occupy the largest proportion, have a rich pore structure, not only can obviously improve the specific surface area and the number of active sites of the chitosan-based biochar, but also can accelerate the transfer of substances in a catalytic degradation system, and meanwhile, the graphitization degree of the chitosan-based biochar is higher, so that the rapid degradation of organic pollutants can be realized, the efficient activation of persulfate can also be realized, and the chitosan-based biochar has the advantages of high specific surface area, rich pore structure, good catalytic performance, strong anti-interference performance, environment friendliness and the like, can be used for activating persulfate to degrade organic pollutants in water, has excellent removal effect and efficient removal efficiency, and has good application prospect. In addition, the preparation method has the advantages of simple process, low cost, no secondary pollution and the like, is suitable for large-scale preparation, and is beneficial to industrial application.
The above description is only of the preferred embodiment of the present invention, and is not intended to limit the present invention in any way. While the invention has been described in terms of preferred embodiments, it is not intended to be limiting. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention or equivalent embodiments using the method and technical solution disclosed above without departing from the spirit and technical solution of the present invention. Therefore, any simple modification, equivalent substitution, equivalent variation and modification of the above embodiments according to the technical substance of the present invention, which do not depart from the technical solution of the present invention, still fall within the scope of the technical solution of the present invention.
Claims (10)
1. The preparation method of the chitosan-based biochar with the porous structure and the high specific surface area is characterized by comprising the following steps of:
s1, dissolving chitosan in an alkaline solution to obtain a chitosan solution, performing freeze-thawing cycle treatment on the chitosan solution, stirring, and drying to obtain chitosan hydrogel; the alkaline solution is a mixed solution containing potassium hydroxide and a nitrogen source, and is prepared by dissolving the potassium hydroxide and the nitrogen source into a solvent, wherein the mass ratio of the chitosan to the potassium hydroxide to the nitrogen source to the solvent is 4-5:11-12:7-8:77-80;
s2, performing freeze drying treatment on the chitosan hydrogel obtained in the step S1 to obtain chitosan aerogel;
s3, heating the chitosan aerogel obtained in the S2 to 600-650 ℃ for calcining, washing and drying;
s4, heating the product obtained after drying in the S3 to 800-850 ℃ for calcining to obtain the chitosan-based biochar with a porous structure and a high specific surface area; the chitosan-based biochar comprises three pore structures of micropores, mesopores and macropores.
2. The method for preparing chitosan-based biochar having a porous structure and a high specific surface area according to claim 1, wherein in S1, the nitrogen source is at least one of urea, melamine and melamine; the solvent is water.
3. The method for preparing chitosan-based biochar having a porous structure and a high specific surface area according to claim 2, wherein in S1, the freeze-thaw cycle is performed by sequentially performing the freeze treatment and the thaw treatment on the chitosan solution, and the above freeze treatment and the thaw treatment are repeated for a cycle number of not less than 3 times; the freezing treatment is carried out at the temperature of-20 ℃ to-40 ℃; the time of the single freezing treatment is 12-24 hours; the thawing treatment is carried out at the temperature of 4-6 ℃; the time of the single thawing treatment is 12-24 hours.
4. The method for preparing chitosan-based biochar having a porous structure and a high specific surface area according to any one of claims 1 to 3, wherein in S3, the calcination is performed under an inert atmosphere, the inert atmosphere is nitrogen, a temperature rising rate in the calcination process is 5 ℃/min to 10 ℃/min, and a time of the calcination is 2h to 2.5h;
and S4, calcining is performed under an inert atmosphere, wherein the inert atmosphere is nitrogen, the heating rate in the calcining process is 5 ℃/min-10 ℃/min, and the calcining time is 2 h-2.5 h.
5. The method for producing chitosan-based biochar having a porous structure and a high specific surface area according to any one of claims 1 to 3, wherein in S1, the stirring is performed at 0 ℃, the stirring time is 2 to 3 hours, the drying is performed under vacuum, the drying temperature is 15 to 35 ℃, and the drying time is 4 to 6 hours;
s2, performing freeze drying under vacuum conditions;
and S3, the drying temperature is 80-120 ℃, and the drying time is 6-10 h.
6. A chitosan-based biochar having a porous structure and a high specific surface area, characterized in that the chitosan-based biochar is produced by the production method according to any one of claims 1 to 5.
7. The chitosan-based biochar having a porous structure and a high specific surface area according to claim 6, wherein the BET specific surface area of the chitosan-based biochar is 1600m 2 /g～2400m 2 Per gram, the pore volume of the chitosan-based biochar is 0.8cm 3 /g～1.2cm 3 /g。
8. Use of a chitosan-based biochar having a porous structure and a high specific surface area according to claim 6 or 7 for the treatment of wastewater containing organic pollutants.
9. The use according to claim 8, characterized by the steps of: the chitosan-based biochar with a porous structure and a high specific surface area, persulfate and the water body containing the organic pollutants are mixed for degradation reaction, so that the degradation of the organic pollutants in the water body is completed.
10. The use according to claim 9, wherein the chitosan-based biochar is added in an amount of 0.05g to 0.125g per liter of the organic pollutant-containing water body, the persulfate is added in an amount of 0.15mmol to 0.75mmol per liter of the organic pollutant-containing water body, the persulfate is sodium persulfate, the initial concentration of the organic pollutant in the organic pollutant-containing water body is 50mg/L to 100mg/L, the initial pH value of the organic pollutant-containing water body is 3 to 11, the organic pollutant in the organic pollutant-containing water body comprises at least one of a phenolic compound, a dye and an antibiotic, the phenolic compound is at least one of 2, 4-dichlorophenol and phenol, the dye is at least one of methyl orange and methylene blue, the antibiotic is at least one of terramycin and tetracycline hydrochloride, the degradation reaction is carried out under an oscillation condition, the rotation speed of the oscillation is 120r/min to 200 ℃ and the degradation reaction time is between 5min to 35 min.
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