Free-standing MOF-derived hybrid porous carbon nanofiber mats
According to the present disclosure, a method of fabricating a metal-carbon fibrous structure is provided. The method comprises the steps of: (a) forming a fibrous support structure comprising composite nanocrystals and polymeric fibers, wherein each of the composite nanocrystals comprises metal ions connected by organic ligands; (b) growing the composite nanocrystals on the fibrous support structure; and (c) subjecting the fibrous support structure of step (b) to carbonization to form the metal-carbon fibrous structure, wherein the metal-carbon fibrous structure comprises metal nanoparticles derived from the composite nanocrystals comprising metal organic framework (MOF), particularly zeolitic imidazolate framework (ZIF). A metal-carbon fibrous structure comprising carbon based fibers arranged to form a porous network and the carbon based fibers are doped with metal nanoparticles, wherein the carbon based fibers have surfaces which comprise graphitic carbon, is also disclosed herein.
1. A method of fabricating a metal-carbon fibrous structure comprising the steps of:
(a) forming a fibrous support structure comprising composite nanocrystals and polymeric fibers by electrospinning a suspension, wherein the suspension comprises the composite nanocrystals and a polymer solution, wherein each of the composite nanocrystals comprises metal ions connected by organic ligands;
(b) growing the composite nanocrystals on the fibrous support structure; and
(c) subjecting the fibrous support structure of step (b) to carbonization to form the metal-carbon fibrous structure, wherein the metal-carbon fibrous structure comprises metal nanoparticles derived from the composite nanocrystals,
wherein the polymer solution comprises a polymer dissolved therein, and
wherein the composite nanocrystals and the polymer have a weight ratio of 2:8 to 6:4.
2. The method according to claim 1 , wherein the forming in step (a) comprises dispersing the composite nanocrystals in the polymer solution to form the suspension.
3. The method according to claim 2 , wherein the composite nanocrystals are formed by separately dissolving a metal nitrate or a metal chloride and the organic ligands in a solvent to form two solutions, mixing the two solutions to form a precipitate of the composite nanocrystals, and collecting and drying the precipitate to thereby form the composite nanocrystals.
4. The method according to claim 3 , wherein the organic ligands comprise imidazole based ligands.
5. The method according to claim 3 , wherein the precipitate is collected and dried in vacuum for 12 hours to 24 hours at 40° C. to 100° C.
6. The method according to claim 3 , wherein the composite nanocrystals comprise zeolitic imidazolate framework (ZIF) crystals.
7. The method according to claim 2 , wherein the polymer solution is formed by dissolving the polymer in an organic solvent at 50° C. to 80° C. for 0.5 hours to 2 hours.
8. The method according to claim 7 , wherein the polymer is selected from the group consisting of polyacrylonitrile, phenolic resins, polypyrrole, polystyrene, polymethylacrylonitrile, polyaromatic hydrocarbons, and biomass-derived polymers.
9. The method according to claim 2 , wherein the polymeric fibers comprise polyacrylonitrile, phenolic resins, polypyrrole, polystyrene, polymethylacrylonitrile, polyaromatic hydrocarbons, and biomass-derived polymers.
10. The method according to claim 1 , wherein the electrospinning is carried out with an air humidity of not more than 40%.
11. The method according to claim 1 , wherein the electrospinning is carried out at a voltage of 7.5 kV to 13 kV with a feeding rate of 0.5 ml/hour to 3 ml/hour.
12. The method according to claim 1 , wherein the growing in step (b) is carried out by contacting the fibrous support structure with an organic solution comprising a metal precursor and an organic linker to form a mixture, and incubating the mixture to grow the composite nanocrystals.
13. The method according to claim 12 , wherein the organic linker comprises an imidazole based linker.
14. The method according to claim 12 , wherein the incubating occurs at 40° C. to 80° C. for 1 hour to 3 hours.
15. The method according to claim 1 , wherein the carbonization is carried out in an inert environment and at a temperature of 600° C. to 1000° C. for 2 hours to 3 hours.
16. The method according claim 1 , wherein the metal-carbon fibrous structure comprises carbon and cobalt, carbon and iron, or carbon and zinc.
17. The method according to claim 1 , further comprising a step of calcinating the metal-carbon fibrous structure to yield a metal oxide-carbon fibrous structure.
18. The method according to claim 17 , wherein the calcinating is carried out in air at 200° C. to 350° C. for 0.5 hours to 3 hours.
19. The method according to claim 17 , wherein the metal oxide-carbon fibrous structure comprises Co 3 O 4 and carbon, ZnO and carbon, Fe 2 O 3 and/or Fe 3 O 4 and carbon.