US 2019/0002309 Al  50  Jan. 3, 2019  [0483]  Further, the flexible CNF-CNT composite could be  modified for application in microbial fuel cells (MFCs),  which are a promising technology for recovery (and subse› quent conversion to electricity) of the potential energy in  wastewater. Although power generation efficiencies cur› rently limit widespread applicability of MF Cs, the develop› ment of improved anode materials could help to overcome  the barrier to application. Conventional anodes, such as  [0477]  Given that performance of the CNF-CNT compos› ite reflected performance of the embedded CNTs, the inclu› sion of CNTs with specific surface functionalities ( e.g.,  amine, carboxyl) in the electrospinning precursor solution  could yield composites that retain the behavior of those  functionalized  CNTs.  Through preliminary work not  included herein, we evaluated the inclusion of CNTs with  surface oxygen functional groups (introduced via aqueous  phase ozonation of the non-functionalized CNTs utilized).  We observed that inclusion of the ozonated CNTs yielded  [0482]  Beyond modification of the CNF-CNT composite  to improve targeted micropollutant removal, the composite  is an advanced nanocarbon platform broadly relevant to  energy and electrochemical applications. For example, sev› eral groups have demonstrated the utility of electrospun  carbon nanofiber networks as supercapacitors, which are a  promising energy storage alternative to batteries. Further,  the inclusion of CNTs in the flexible nano-carbon network  can improve the conductivity and specific capacitance of the  material. The mechanical stability of the material developed  in this study may enable practical application of such  CNF-CNT composites for energy storage, which is a vital  component of the transition to renewable (but intermittent)  energy sources, such as wind and solar.  [0481]  Deployment of CNF-CNT Composites in Energy  Applications  [0476]  The CNF-CNT composite developed in this study  contained non-functionalized CNTs, and exhibited perfor› mance trends that echoed removal performance of those  CNTs ( e.g., the composite was most effective for removal of  more hydrophobic species). The CNF-CNTcomposite could  be improved by modifying the composite surface to target  removal of more polar micropollutants. Methods for CNT  surface functionalization are well-established, and the  potential for various CNT surface functionalities (e.g., nitro› gen- or oxygen-containing groups) in improving removal of  specific pollutants has been extensively evaluated. However,  the aggressive chemical conditions (i.e., elevated tempera› tures, highly acidic solutions) necessary for CNT function› alization could not be applied for functionalization of CNF› CNT composites, as material structural integrity would be  sacrificed.  [0475]  Development of Functionalized CNF-CNT Com› posites  [0480]  Of course, beyond effects on material characteris› tics, both the inclusion of functionalized CNTs in CNF-CNT  composites and potential changes to pyrolysis temperatures  must be correlated with removal performance toward spe› cific micropollutant targets, with benchmarks to the perfor› mance of non-functionalized CNT and CNF-CNT compos› ites. For example, the use of CNTs with amine (-NH2),  carboxyl (-COOH), or hydroxyl (-OH) surface functional  groups may improve removal of contaminants that were  poorly or moderately retained (e.g., cotinine, metoprolol,  acetaminophen) through specific interactions, such as hydro› gen bonding.  [0479]  Further, based on the enhanced macroporosity  observed for CNF-CNT composites developed using the  aforementioned ozonated CNTs, lower carbonization (py› rolysis) temperatures may be useful to achieve a balance  between sufficient macroporosity to allow solution-phase  accessibility of embedded CNTs and maintaining nanofiber  integrity to produce a mechanically stable CNF-CNT com› posite. This effect may also extend to CNTs with nitrogen› containing surface functionalities.  [0474]  Further, we demonstrated application of the opti› mized composite in a flow-through system for lead removal  from both idealized (e.g., MES-buffered, no interfering  co-solutes) and complex ( e.g., real tap water) matrices.  Notably, acid regeneration of the composite (with 0.1 N  HNO$_{3}$ )  yielded -40% recovery of retained Pb, with >99% of  recovery occurring within the first 100 mL of regeneration  solution. Comparable treatment performance was observed  during application after regeneration. The rapid recovery of  retained Pb is notable, as it facilitates both composite  recovery and disposal/treatment of regeneration solutions.  Further, based on performance demonstrations that utilized  a minimal amount of material (-170 mg) at a high flux (-950  LMH) in real tap water from the University of Iowa, -10 g  of the nano fiber composite would be required for treatment  of a single users’ annual supply of drinking water ( assuming  consumption of 2 L/day, contaminated with -300 ug/L Pb).  In combination, these results highlight the unique potential  of these composites in enabling deployment of nanomate› rials for sustainable, effective drinking water treatment at a  range of scales.  particle loadings, aggregation within the polymer matrix  may limit further improvements in composite performance.  Additionally, we discovered that upon inclusion of SDS,  embedded nanoparticles in composites containing >0.5 wt%  nanoparticle loadings exhibited comparable reactivity to  unsupported (freely dispersed) nanoparticles across multiple  targets ( e.g., copper and lead). This was a notable result, and  demonstrated that a removable surfactant could assist in the  fabrication of composites that both immobilize nanopar› ticles and allow better utilization of their reactive surfaces  and associated uptake capacities. The optimized composite  (PAN 7 wt%, iron oxide nanoparticles 2 wt%, SDS 1 wt%)  was selected as a balance between utilization of embedded  nanoparticle capacity, and bulk composite capacity for cop› per and lead removal.  [0478]  The inclusion of CNTs with different types of  oxygen- and nitrogen-containing functional groups and the  retention of those functional groups during CNF fabrication  would ideally be investigated via energy dispersive x-ray  spectroscopy (EDX) and X-ray photoelectron spectroscopy  (XPS) analyses of CNTs before and after thermal processing  steps identical to those used for CNF fabrication. CNTs that  are able to retain their surface functionalities during thermal  processing should be incorporated in CNF-CNT composites,  with the use of EDX to probe material functionalization  (XPS would be less useful for CNF-CNT composites, as  CNTs are primarily embedded within nanofibers, thus lim› iting the contribution of their functional groups to the  surface composition of the CNF-CNT composite).  CNFs that were significantly weaker, due to a significantly  higher degree of macroporosity. While we hypothesize that  loss of surface oxygen groups from the CNT surfaces during  carbonization contributed to macroporosity generation, this  point is worthy of systematic investigation. 