Environmental Engineering Reference
In-Depth Information
and PANI nanofibers (PANI-NFs) [14] were successfully grafted on a graphite oxide (GO) sheet using a rapid mixing reaction
method; both composite materials reached high capacitances of 555 and 480 F/g, respectively.
Moreover, multifunctional nanocomposites have also found great potential in biomedical applications, which can be attrib-
uted to the complex structure and functionalities inherent in this type of synergistic materials. Compared to the widely accepted
traditional metallic and ceramic biomaterials, multifunctional nanocomposites are able to offer high biocompatibility, light
weight, anticorrosion, relatively easy fabrication and processing, and low cost. In addition, it has been realized that the mis-
match in the mechanical elastic modulus and tensile strength between the metal and ceramic biomaterials and the targeting hard
tissues is due to the negative effects in tissue remodeling. Composites, however, can offer greater potential to structurally match
the biological environment, by adjusting the reinforcing material types and morphology, volume fraction, and interaction and
distribution in the matrix [15]. Furthermore, a broad range of functionalities and properties are able to be tailored into the
composite entity to suit various intended biological functions.
In this chapter, we mainly review and report the environmental applications of polymer-based and carbon-based multifunc-
tional nanocomposites, using our own research as well as published results by other groups. The targeting remediation is centered
on nanocomposite solid wastes, wastewater, heavy metals, arsenic, and organic dyes. In the following, we will also introduce the
major techniques used for developing these multifunctional nanocomposites in our lab, as well as the major corresponding
characterization and property analysis methods. Finally, we will give our opinion on the perspectives of multifunctional
nanocomposites, especially their potential for environmental remediation and sustainability. As a result, this chapter does not
extensively cover every aspect of multifunctional nanocomposites, but rather selectively reports what we have achieved to date.
4.2 Multifunctional nanocoMposites developMent:
froM fabrication to processing
In order to produce synergistic entity nanocomposites with multiple functionalities, the method of dispersion of the nanofiller in
the matrix and subsequent processing are crucial for their targeted properties and applications. Since nanofillers have diverse
chemical compositions and physical forms, it has been one of the most challenging and targeted topic of discussion in the nano-
composites regime. The traditional direct mixing method is not able to attain uniform dispersion and retain the strong connection
between the filler and the matrix, thus failing to achieve the desired properties. Scientists and researchers have explored alternative
means to integrate multiple components through either ex situ or in situ techniques. The key step very often lies at the surface
functionalization stage of one or more components simultaneously to the blending process. In the following, we will elaborate
what we have achieved in polymer-based nanocomposites as well as carbon-based nanocomposites.
4.2.1
fabrication and processing of Multifunctional polymer-based nanocomposites
Over the years, we have developed several effective methods to fabricate and process polymer-based multifunctional nanocom-
posites, namely, surface-initiated polymerization (SIP) and monomer-stabilized polymerization (MSP), which have been proven
to enhance the interaction between the polymer matrix and the nanofillers, improve the dispersion of the nanofillers in the
polymer matrix, and greatly contribute to the respective mechanical, magnetic, and conducting properties [16, 17]. In the SIP
method, briefly speaking, it typically starts with mixing the monomers and the nanofillers and then interconnection is initiated
when the preadsorbed catalyst or initiator starts polymerization of the monomers from the nanofiller surface. For example,
highly flexible polyurethane nanocomposites with high loading of iron nanoparticles (NPs) were successfully prepared using
the SIP method, and the resulting nanocomposites displayed favorable mechanical strength and magnetic properties. The SIP
scheme is demonstrated in Figure 4.1.
The SIP method has also been widely applied to other PNC systems, including conducting polymers PANI-, polypyrrole
(PPy)-, and thermoplastic polymers polypropylene (PP)-and polyethylene (Pe)-based. Nanofillers are generally nanostructured
ceramic and ceramic oxides, as well as the various carbon nanostructures. For example, magnetic polyaniline PNCs [18] were
successfully prepared using the SIP method and showed negative permittivity in both the neat PANI and the PANI-magnetite
nanocomposites. More interestingly, large-room-temperature magnetoresistance (MR) was observed in both the neat PANI and
the PANI-magnetite nanocomposites, with the latter being much larger (MR ~95%) than the former (MR ~53%). Furthermore,
temperature-dependent resistivity study indicated a variable range hopping (vRH) mechanism for the electron conduction in all
the materials in the aforementioned PANI PNCs.
In the PANI-barium titanate system synthesized from the SIP method, an interesting correlation was observed between the
particle size, loading level, and mixing methods of the ferroelectric barium titanate in the PANI matrix, and the corresponding
