Modern society has experienced various environmental problems due to the increase of population, urban industrialization and improvement of living standard. People of large cities live in indoor space more than 90 % every day. Thus indoor environment has a great influence on individual lives and the...
Modern society has experienced various environmental problems due to the increase of population, urban industrialization and improvement of living standard. People of large cities live in indoor space more than 90 % every day. Thus indoor environment has a great influence on individual lives and they want the quality of air. In order to save energy and increase efficiency, building is becoming more airtight, and there is a growing demand for indoor air quality.
The concentration of CO2 doesn’t directly affect the human body, but it causes unpleasantness, fatigue and headache if it exceeds 1000 ppm. Especially, the classrooms and library reading rooms, which are closed and isolated from outside, risen to more than 2000 ppm. Therefore, it is necessary to effectively maintain the concentration of CO2 in the indoor spaces.
Techniques for capturing CO2 include an absorption using alkali solutions and dry adsorption by porous adsorbents. In practical fields, MEA (monoethanolamine) is typical solution used mainly for absorption process, but it is not suitable for application to the indoor environment due to poor regeneration performance, corrosion of equipment and harmfulness to human body.
Adsorption methods have a less capturing capacity of CO2 than absorption methods, nevertheless it is more suitable for indoor environment because of constant performance with satisfactory regeneration and harmless to the human body. Examples of dry adsorption agents include activated carbon pellets, activated carbon fibers, activated carbon nanofibers, zeolites, and metal organic frameworks.
In this work, the activated carbon nanofiber adsorbents were prepared with some parameters of polymer precursor, an electric voltage, and stabilization technique, chemical activation or physical activation. In order to capture gaseous CO2 present in indoor level, CO2 should be selectively adsorbed rather than nitrogen, which presents 78% of the air. Therefore the Van der Waals force should be increased for this purpose. In order to increase the Van der Waals force, the specific surface area, micropore volume and nitrogen functional group are very important factors in order.
In this study, PAN (polyacrylonitrile) was used for electrospinning. The surface area and micropore volume of the prepared thin fiber bundle were increased by impregnation of KOH and ammonia gas was used to enhance the surface alkalinity which can provide the increase selective adsorption capacity of CO2 through formation of nitrogen functional groups. Compared with the control group (AnF-0), the specific surface area and pore volume of AnF-2 impregnated with 2 M KOH concentration increased from 168 to 569 m2/g and from 0.096 to 0.277 cm3/g. The K-AnF-0.05 prepared by adding 0.05 g of KOH to the precursor PAN solution increased the specific surface area and pore volume from 168 to 537 m2/g and from 0.096 to 0.215 cm3/g. In addition, N-AnF-0.05 prepared by amination with NH3 gas has a specific surface area and pore volume increased by 5% from 537 to 559 m2/g and 0.215 to 0.227 cm3/g compared with K-AnF-0.05. In the case of N-AnF-0.05 with surface amination treatment, 0.472 mmol / g in low level CO2 capture and selectivity increased to 37.8. This is because the ratio of pyridine, pyrrole and pyridone, which are favorable for selective adsorption of carbon dioxide, accounts for 91%, and the adsorption amount and selectivity are increased 36 times and 380 times, respectively, compared with AnF-0.
Modern society has experienced various environmental problems due to the increase of population, urban industrialization and improvement of living standard. People of large cities live in indoor space more than 90 % every day. Thus indoor environment has a great influence on individual lives and they want the quality of air. In order to save energy and increase efficiency, building is becoming more airtight, and there is a growing demand for indoor air quality.
The concentration of CO2 doesn’t directly affect the human body, but it causes unpleasantness, fatigue and headache if it exceeds 1000 ppm. Especially, the classrooms and library reading rooms, which are closed and isolated from outside, risen to more than 2000 ppm. Therefore, it is necessary to effectively maintain the concentration of CO2 in the indoor spaces.
Techniques for capturing CO2 include an absorption using alkali solutions and dry adsorption by porous adsorbents. In practical fields, MEA (monoethanolamine) is typical solution used mainly for absorption process, but it is not suitable for application to the indoor environment due to poor regeneration performance, corrosion of equipment and harmfulness to human body.
Adsorption methods have a less capturing capacity of CO2 than absorption methods, nevertheless it is more suitable for indoor environment because of constant performance with satisfactory regeneration and harmless to the human body. Examples of dry adsorption agents include activated carbon pellets, activated carbon fibers, activated carbon nanofibers, zeolites, and metal organic frameworks.
In this work, the activated carbon nanofiber adsorbents were prepared with some parameters of polymer precursor, an electric voltage, and stabilization technique, chemical activation or physical activation. In order to capture gaseous CO2 present in indoor level, CO2 should be selectively adsorbed rather than nitrogen, which presents 78% of the air. Therefore the Van der Waals force should be increased for this purpose. In order to increase the Van der Waals force, the specific surface area, micropore volume and nitrogen functional group are very important factors in order.
In this study, PAN (polyacrylonitrile) was used for electrospinning. The surface area and micropore volume of the prepared thin fiber bundle were increased by impregnation of KOH and ammonia gas was used to enhance the surface alkalinity which can provide the increase selective adsorption capacity of CO2 through formation of nitrogen functional groups. Compared with the control group (AnF-0), the specific surface area and pore volume of AnF-2 impregnated with 2 M KOH concentration increased from 168 to 569 m2/g and from 0.096 to 0.277 cm3/g. The K-AnF-0.05 prepared by adding 0.05 g of KOH to the precursor PAN solution increased the specific surface area and pore volume from 168 to 537 m2/g and from 0.096 to 0.215 cm3/g. In addition, N-AnF-0.05 prepared by amination with NH3 gas has a specific surface area and pore volume increased by 5% from 537 to 559 m2/g and 0.215 to 0.227 cm3/g compared with K-AnF-0.05. In the case of N-AnF-0.05 with surface amination treatment, 0.472 mmol / g in low level CO2 capture and selectivity increased to 37.8. This is because the ratio of pyridine, pyrrole and pyridone, which are favorable for selective adsorption of carbon dioxide, accounts for 91%, and the adsorption amount and selectivity are increased 36 times and 380 times, respectively, compared with AnF-0.
Keyword
#CO2 adsorption, Electrospinning, Activated carbon nanofiber
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