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. 

[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. 

[0475] Development of Functionalized CNF-CNT Com› posites 

[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. 

[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 

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. 

[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). 

[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. 

[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. 

[0481] Deployment of CNF-CNT Composites in Energy Applications 

[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. 

[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 

