Environmental Engineering Reference
In-Depth Information
20.4 Nanofibers for Water Treatment Processes
Nanoiber has been broadly applied to refer to a iber with a diameter of <1 micron.
Polymeric nanoibers are rapidly inding their place in nanomaterials technology.
Nanoibers are an exciting new class of material used for several value-added applications
such as medical, iltration, barrier, wipes, personal care, composite, garments, insulation,
and energy storage. The focus in this work is the application of nanoibers in adsorption of
heavy metals from wastewater.
Electrospinning is the most popular method applied to prepare nonwoven nanoibers
made of organic polymers, ceramics, and polymer/ceramic composites. It has been exten-
sively explored as a simple and versatile method for drawing ibers from polymer solu-
tions (or melts). The electrospinning process involves a polymeric luid being extruded
from the oriice of a needle or pipette to form a small droplet in the presence of an electric
ield. When the electric ield is suficiently strong, charges build up on the surface of the
droplet and overcome the surface tension. A charged jet of luid is ejected from the tip of
the Taylor cone. The jet is then accelerated toward a grounded collector (Figure 20.6). The
discharged polymer solution jet undergoes a rapid whipping process through which the
solvent is evaporated; the liquid jet is stretched to many times its original length to produce
continuous, ultrathin ibers of the polymer. In the continuous feed mode (through the use of
a syringe pump), a mat of ultrathin ibers can be obtained within a relatively short period.
Biopolymers like cellulose and chitin and their derivatives are polymers that are abun-
dant, renewable, biocompatible, and biodegradable. These factors make them ideal choices
as sustainable feedstock for materials and products for use in the ields of iltration,
adsorption, and preconcentration of heavy metal pollutants. However, a major challenge
faces the application of these biopolymers because of their insolubility in most common
solvents. 66 Biosorption processes utilizing inexpensive biomass to sequester toxic heavy
metals is particularly useful for the removal of these contaminants from industrial eflu-
ents. 67 Chitin and chitosan have been used for the adsorption or the binding of heavy met-
als and dyes. Chitosan is a polycation polymer effective in coagulation and locculation
dewatering of activated sludge and hence used in wastewater treatment.
Grounded collector
Polymer solution
Stainless needle
Fiber experiencing
chaotic whipping
HVDC source
1 µm*
FIGURE 20.6
Schematic diagram of an electrospinning unit and SEM micrograph of electrospun mat (scale bar of 1 μm
indicated).
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