Performance comparison of hematite (α-Fe2O3)-polymer composite and core-shell nanofibers as point-of-use filtration platforms for metal sequestration.

Point-of-use water treatment technologies can help mitigate risks from drinking water contamination, particularly for metals (and metalloids) that originate in distribution systems (e.g., chromium, lead, copper) or are naturally occurring in private groundwater wells (e.g., arsenic). Here, composite nanofibers of polyacrylonitrile (PAN) with embedded hematite (α-Fe2O3) nanoparticles were synthesized via a single-pot electrospinning synthesis. A core-shell nanofiber composite was also prepared through the subsequent hydrothermal growth of α-Fe2O3 nanostructures on embedded hematite composites. Properties of embedded hematite composites were controlled using electrospinning synthesis variables (e.g., size and loading of embedded α-Fe2O3 nanoparticles), whereas core-shell composites were also tailored via hydrothermal treatment conditions (e.g., soluble iron concentration and duration). Although uptake of Cu(II), Pb(II), Cr(VI), and As(V) was largely independent of the core-shell variables explored, metal uptake on embedded nanofibers increased with α-Fe2O3 loading. Both materials exhibited maximum surface-area-normalized sorption capacities that were comparable to α-Fe2O3 nanoparticle dispersions and exceeded that of a commercial iron oxide based sorbent. Further, both types of composite exhibited strong performance across a range of environmentally relevant pH values (6.0-8.0). Notably, core-shell structures, with a majority of surface accessible α-Fe2O3, performed far better than embedded composites in kinetically limited flow through systems than was anticipated from their relative performance in equilibrium batch systems. Core-shell nanofiber filters also retained much of the durability and flexibility exhibited by embedded nanofibers. Additional tests with authentic groundwater samples demonstrated the ability of the core-shell nanofiber filters to remove simultaneously both As and suspended solids, illustrating their promise as a nano-enabled technology for point-of-use water treatment.