Tailoring Electrospun Carbon Nanofiber Properties for Improving Chemical Sorption

Activated carbon nanofiber (ACNF), as a novel electrospun polyacrylonitrile-based sorptive material, takes advantage of nanoscale fabrication to reduce mass transfer limitations while maintaining a membrane structure. Steam activated ACNF has been compared with commercial activated carbons and exhibits fast sorption rates and capacity for polycyclic aromatic hydrocarbons. However, to increase effectiveness for difficult to remove micropollutants, changes to the surface chemistry was required. For the initial modification to introduce carboxylic acids on the surface, a range of oxidants were compared including nitric acid, nitric acid and sulfuric acid, potassium permanganate, osmium tetroxide followed with potassium permanganate or oxone®, and ruthenium tetroxide. Among these reactions, permanganate or osmium tetroxide followed by permanganate pathways were favored because of the simple operation, potential for forming carboxylic acids, and limited degradation of the oxidized ACNF structure. Following carboxylation, various pathways to attach ethylenediamine (EDA) were tested to enhance surface interactions with charged pollutants. EDA was successfully attached using thionyl chloride or oxalyl chloride to form the reactive acyl chloride prior to a substitution reaction. The EDA functionalized materials had higher binding constants than the carboxylated control with Pb2+as indicated by less competition with an aqueous competing ligand. However, the direct chemical functionalization on ACNF reduced the pore structure and strength of the membrane form. Alternatively, functionalized CNT and CNF composites were prepared. Instead of direct modification of ACNF, CNT was pre- or post-functionalized and mixed into the CNF precursor solution with templating agent phthalic acid. With these components, mesopore dominant functionalized CNT and CNF composites were synthesized. Adsorption of pharmaceutical compounds was compared between ACNF and functionalized or non-functionalized CNF-CNT composites. Even with less surface area, CNF-CNT composites showed greater adsorption of most pharmaceutical compounds compared to ACNF, likely due to differences in pore size distributions. When the adsorption was normalized to surface area, both pre- and post-functionalized CNT composites demonstrated larger adsorption than non-functionalized materials. While various pathways have been identified that can aid in generating a nanofibrous carbon material to target micropollutants, alternative functional groups and/or alternative carbon backbones are needed to increase mesoporosity and effectiveness for a diversity of micropollutants.