Control of Micro- and Mesopores in Carbon Nanofibers and Hollow Carbon Nanofibers Derived from Cellulose Diacetate via Vapor Phase Infiltration of Diethyl Zinc

Abstract

Common thermoplastic polymers, such as poly(vinyl alcohol) and cellulose derivatives are abundant and inexpensive precursors for preparing carbon nanofibers. These polymers are soluble in common solvents and can be readily processed to prepare nanofibers with high external surface area. However, thermoplastic polymers undergo a melting transition upon heating, resulting in loss of initial morphology and low carbon yield. In this study, vapor infiltration of diethyl zinc (DEZ) is applied to modify electrospun cellulose diacetate (CDA) nanofibers before carbonization, resulting in excellent retention of the original fiber structure while maintaining a high surface area and pore size distribution. Our goal is to investigate the effect of inorganic modification on the morphology and structural properties of the carbon product from the CDA nanofibers. We found that the CDA nanofiber structure was preserved after incorporation of ∼10 wt % Zn by vapor infiltration of DEZ. In addition, we found the pore volume distribution of the CDA-based carbon nanofibers can be controlled by the amount of DEZ incorporated. Mesoporosity dominated with the incorporation of small amounts of DEZ up to ∼7 wt % Zn, above which the formation of micropores was favored. However, the carbon yield was lowered from ∼8 to <4 wt % as the DEZ cycle increased, possibly due to the catalytic oxidation effect of Zn on carbon. Our study on CDA-based carbon nanofibers shows that vapor infiltration of DEZ is an effective chemical treatment that makes common thermoplastics viable as precursors for synthesis of structural carbon nanomaterials, with tunable pore volume distribution. Finally, using a modified process with zinc oxide atomic layer deposition allowed for controlled subsurface chemical modification and hollow carbon nanofibers were produced with a higher surface area (∼1700 m2/g) and pore volume, a promising material for energy storage applications.