Environmental Engineering Reference
In-Depth Information
6.2
cHalleNges of eNviroNMeNtal NaNotecHNology
With industrialization, many issues of water, air, and soil pollution have arisen gradually. An alarming situation is that, by the
end of 2025, more than 50% of the countries in the world will face freshwater shortage [39]. Water pollution will increase the
worldwide pressure on freshwater resources.
Water contaminants are generally divided into both organic and inorganic substances. Most of the contaminants are con-
tributed by industrial plants like mining, textile, leather, and paper production. Until now, a wide range of conventional
treatment techniques including chemical coagulation [40], activated sludge [41], biosorption [42], and plant accumulation
[43] have been extensively used to remediate these water pollutants. For example, Annadurai et al. [44] used chitosan as an
adsorbent material for reactive dye removal and demonstrated that a high absorption capacity of 91.47-130.0 mg/g toward
the removal of remazol black 13 dye could be achieved. Chen et al. [45] reported that the carboxymethylated bacterial
cellulose could efficiently remove copper and lead ions from aqueous solution. In another work, Fillipi et al. [46] introduced
a ligand-modified ultrafiltration system to selectively remove copper ions.
With superior advantages such as large surface area, reactive surface features, and quantum size-related properties, var-
ious NPs have been used for environmental remediation applications [47]. For instance, innovative granular activated carbon
composites doped with iron/palladium (Fe/Pd) bimetallic NPs can be used to physically absorb and chemically dechlorinate
polychlorinated biphenyls. Zirconia- and silica-supported zero-valent iron NPs' (ZVI NPs) ability to separate and reduce
pertechnetate ions from complex waste mixtures has been demonstrated [48]. However, one critical problem is that used
colloidal NPs such as noble metals (e.g., Au, Ag, and Pd) may lead to further environmental contamination in aqueous media
or soil. Therefore, the development of various supporting materials that can incorporate or immobilize reactive metal NPs
and can be easily separated from the environment is crucial in not only improving the longevity of the particles, but also in
avoiding secondary contamination of the environment.
6.3
electrospiNNiNg tecHNology
Since a series of patents on electrospinning process were issued to Formhals [49] in 1934, electrospinning technology has been
identified as one of the powerful techniques to produce fibers with diameters ranging from tens of nanometers to a few microm-
eters. Figure 6.1 shows a schematic of a basic setup of electrospinning technology, which consists of three major modules: a
high-voltage power generator, a syringe pump, and a collector. The needle connected to a syringe is used as a spinneret. With the
assistance of the pump, the polymer solution hosted in the syringe can be fed through the spinneret continuously and gently. The
mutual electrostatic repulsion between polymer chains causes a force directly counterbalancing the surface tension under the
applied voltage. Then, the hemispherical-shaped liquid can be distorted to form a conical shape known as the Taylor cone [50].
Syringe
Needle
Syringe pump
High DC generator
figure 6.1
Schematic illustration of a basic setup of the electrospinning technology.
