Environmental Engineering Reference
In-Depth Information
Proteins are another group of commonly found organic contaminants in water, par-
ticularly in wastewater. Speciic or nonspeciic protein adsorption can be achieved by
suitable surface chemical functionalization of the ibers. Carboxylated electrospun
carbon nanoibers were found to have better adsorption eficiency and higher per-
meability levels than the normal resin bed.
50
Bovine serum albumin (BSA) and lyso-
zyme were used as the models and it was shown that surface functionalization leads
to more speciic binding. Sun et al. presented that poly(vinylideneluoride-hexaluo-
ropropylene) (PVDF-HFP) nanoiber membranes show improved hydrophilicity and
protein fouling resistance via surface graft copolymerization of hydrophilic mono-
mers.
51
In another scenario, electrospun polycaprolactone nanoibers embedded with
LiCl induced a substantial increase in the protein adsorption.
52
LiCl is a kosmotrope
that promotes protein salvation in aqueous solutions. Protein (BSA and protamine as
models) loading on the ibers was nine times higher than that observed in the absence
of the salt. Moreover, the adsorption was found to be irreversible and no protein loss
was observed after repeated washings. These kinds of innovations open up ample
opportunities to explore an interesting state of use of electrospun nanoibers in bioma-
terials-based puriiers.
23.3.3 Removal of Particulate Contaminants
The separation of micron and submicron particulate contaminants has gained importance
in water puriication and efluent treatment. They clog or foul the ilters, thus reducing
the eficiency and output. Membrane-based ultra- and microilters can be used as a preil-
ter to remove these larger particles, so that the performance and lifetime of the main ilter
unit can be improved. Preilters currently available include sand beds and woven and
nonwoven ibrous meshes.
53
Electrospun nanoibers also ind applications as preiltration
membranes. Electrospun preilters have large surface area, hence high dirt loading capac-
ity. In one of the investigations, a preilter was developed using an electrospun nylon
6 ibrous membrane and polystyrene (PS) microparticles were used as a model (Figure
23.10).
54
Owing to its excellent chemical and thermal resistance and high wettability, it
showed 90% separation for 0.5-μm particles of PS. In an alternative approach, electrospun
nanoibrous membranes of PVDF were surface modiied via graft copolymerization using
methacrylic acid.
55
It was found that only the top layer has been modiied and the nanoiber morphology
remained intact. Furthermore, the surface modiication reduced the average membrane
pore size and showed better water lux (150%-200%), higher than the commercial mem-
brane. This proved that the nanoiber architecture is better and could result in energy-
conserving membranes.
Contamination of water from engineered nanomaterials will be an emerging problem
in the future due to the extensive use of nanomaterials in commercial products and their
improper disposal. Engineered nanoparticles fall into the category of particulate con-
taminants in a 1-100 nm size range. Surface-modiied electrospun PVA nanoibers were
employed for the removal of nanomaterials by Mahanta and Valiyaveettil.
56
The surface
hydroxyl groups of PVA nanoibers were modiied using thiols and amines to improve
the extraction eficiency of model nanoparticles (gold and silver). The extraction studies
revealed that the amine- and thiol-modiied PVA nanoibers showed ~90% extraction efi-
ciency for Ag and Au NPs.
