Carbon nanofiber composites doped with different ZIF-8 nanoparticles for carbon dioxide capture
Topic(s) : Material science
Co-authors :
Yu-Chun CHIANG (TAIWAN)Abstract :
In order to develop appropriate adsorbents for CO2 capture, zeolitic imidazolate framework-8 (ZIF-8) nanoparticles were prepared and the ZIF-8 doped polyacrylonitrile (PAN) nanofibers were fabricated using the electrospinning technique, followed by the processes including stabilization, carbonization, and activation. The ZIF-8 samples with different ratios of the precursors and mixing processes for the ZIF-8 synthesis were considered, and different doping ratios were adopted. The properties of the products were investigated and their adsorption capacities of CO2 were discussed.
A rapid colloidal chemistry route was used to prepare ZIF-8 nanoparticles in methanol at room temperature. The mol ratios of zinc nitrate hexahydrate to 2-MeIM were set at 1:4, 1:8, and 1:16. After stirring rigorously and continuously for 30 min, the mixture was placed at room temperature to stand for 24 h. Finally, the white precipitate was collected and washed with methanol thoroughly several times by centrifugation to remove the excess 2-MeIM. Nanofiber composites were prepared using an electrospinning process. A ratio of 10, 30 or 50 wt. % of ZIF-8 to PAN was added into the PAN solution in DMAc and continuously stirred for 24 h at 60 °C in order to obtain a homogeneous polymer solution. The electrospinning was carried out under an applied electrical voltage of 15 kV onto a metal drum collector rotated at 300 rpm and covered with aluminum foil, and a tip-to-collector distance of 15 cm was used. The mixture solution was pumped at a flow rate of 1.0 ml/h, pushed by a syringe pump. Then, the electrospun fibers were subjected to the stabilization in air at 280 °C for 2 h, the carbonization in nitrogen at 800 °C for 1 h, and the activation with CO2 at 850 °C for 1 h.
Results show that the ZIF-8 with rhombus dodecahedron structure mixed with cube structure were observed, where the particle sizes ranged from 40 to 200 nm. The nodes occurred in the doped carbon nanofibers which were microporous materials. ZIF-8 doped samples exhibited a more curled morphology. The specific surface areas, pore volumes, and CO2 adsorption performance were improved for ZIF-8 doped fibers, compared with those of pure PAN fibers. The optimal adsorption capacities of CO2 at 25 oC、1 atm were 3.45 mmol/g on ZIF-8 (4MZ)/PAN, no matter for different ZIF-8 samples or different ratios of ZIF-8. This could be attributed to the specific surface area, pore volume, bulk nitrogen content and the Zn content. Freundlich equation could be used to fit the adsorption data of CO2 isotherms. The adsorption mechanisms of CO2 on the doped PAN nanofibers were believed to the comprehensive interactions of hierarchical porous structures, surface functional groups, and the zinc active sites.
A rapid colloidal chemistry route was used to prepare ZIF-8 nanoparticles in methanol at room temperature. The mol ratios of zinc nitrate hexahydrate to 2-MeIM were set at 1:4, 1:8, and 1:16. After stirring rigorously and continuously for 30 min, the mixture was placed at room temperature to stand for 24 h. Finally, the white precipitate was collected and washed with methanol thoroughly several times by centrifugation to remove the excess 2-MeIM. Nanofiber composites were prepared using an electrospinning process. A ratio of 10, 30 or 50 wt. % of ZIF-8 to PAN was added into the PAN solution in DMAc and continuously stirred for 24 h at 60 °C in order to obtain a homogeneous polymer solution. The electrospinning was carried out under an applied electrical voltage of 15 kV onto a metal drum collector rotated at 300 rpm and covered with aluminum foil, and a tip-to-collector distance of 15 cm was used. The mixture solution was pumped at a flow rate of 1.0 ml/h, pushed by a syringe pump. Then, the electrospun fibers were subjected to the stabilization in air at 280 °C for 2 h, the carbonization in nitrogen at 800 °C for 1 h, and the activation with CO2 at 850 °C for 1 h.
Results show that the ZIF-8 with rhombus dodecahedron structure mixed with cube structure were observed, where the particle sizes ranged from 40 to 200 nm. The nodes occurred in the doped carbon nanofibers which were microporous materials. ZIF-8 doped samples exhibited a more curled morphology. The specific surface areas, pore volumes, and CO2 adsorption performance were improved for ZIF-8 doped fibers, compared with those of pure PAN fibers. The optimal adsorption capacities of CO2 at 25 oC、1 atm were 3.45 mmol/g on ZIF-8 (4MZ)/PAN, no matter for different ZIF-8 samples or different ratios of ZIF-8. This could be attributed to the specific surface area, pore volume, bulk nitrogen content and the Zn content. Freundlich equation could be used to fit the adsorption data of CO2 isotherms. The adsorption mechanisms of CO2 on the doped PAN nanofibers were believed to the comprehensive interactions of hierarchical porous structures, surface functional groups, and the zinc active sites.