Environmental Engineering Reference
In-Depth Information
polymerization [43]. In other words, AC is used as a substrate to
in situ
deposit Fe into its
micropores and mesopores. Fe-doped AC beads may then be milled to produce micro-
sized and nanosized particles that show increased reactivity. It has been shown that the
Fe-doped ACs prepared this way are more effective at removing dissolved arsenic from
water than those synthesized via the traditional route of preparing Fe-impregnated AC.
Alternatively, the polymeric beads may be milled to produce the nanoparticles and then
carbonized and activated to produce carbon-based nanoadsorbents.
36.5 Surface Morphology of a Hierarchical Web of ACF/
CNF and Micro-/Nanocarbon Particles
In this section, we present and discuss representative SEM images of these materials at
different stages of the preparation. As observed in the image of the as-received (untreated)
ACF substrate, shown in Figure 36.3a, the surface of the carbon ibers is smooth, with the
diameter in the range of 10-20 μm. The SEM image in Figure 36.3b shows the homogeneous
dispersion of nickel nitrate on the surface of the ACF substrate following the impregna-
tion and before the calcination step. Figure 36.3c presents an SEM image of the ACF sur-
face after the reduction step. Fine nanoparticles are uniformly dispersed on the surface
of the iber. No signs of any damage, including deformation and loss of integrity of the
iber, were observed in the samples. CNFs were grown uniformly and densely on the ACF
substrate, as shown in Figures 36.3d and e corresponding to 400,000× and 100,000× mag-
niications, respectively. The diameters of most of the CNFs are approximately 30-40 nm,
with a length of up to several microns. Bright, spherical nanoparticles can be observed at
the tip of the CNFs, with the size approximately the same as the diameter of the CNF (see
Figure 36.3d). However, in some cases, the diameters of the CNFs may not be the same
as that of the Ni particles because the Ni metal particles may undergo agglomeration,
sintering, and fragmentation during the growth of the CNFs. As seen in the SEM images,
the nanoibers are not straight but have a crooked morphology with a three-dimensional
network structure. The SEM image shown in Figure 36.3f shows the morphology of a CNF
after sonication, which essentially removed most of the Ni catalysts from the CNF. The
density distribution and average diameter of the CNFs remained almost unchanged after
sonication. In Section 36.4, it was mentioned that in the preparations of the Al-based CNFs
required for deluoridation applications, the parent catalyst, Ni, was removed after grow-
ing the CNF and the web was reprocessed by impregnating it with Al.
Figure 36.4a shows the SEM images of Al-CNF samples prepared after sonication of
Ni-CNF samples and reprocessing, viz. impregnation, calcinations, and reduction. As
observed, there is a distinct change in the morphology of CNFs after loading with Al.
The ibers were observed to be interwoven because of the agglomeration. The energy-
dispersive x-ray (EDX) spectra shown in Figure 36.4b revealed the presence of 5%-7% (w/w)
of Al with 0.4%-1.2% (w/w) of Ni.
Figure 36.5 shows SEM images of Fe-CNF adsorbents. These adsorbents were synthe-
sized in a one-step method for the removal of As from wastewater, in which Fe had dual
roles: (i) to grow the CNFs and (ii) to remove As. Figure 36.5a shows the uniform and well-
dispersed growth of the CNFs on the ACF substrate. The shining iron particles on the tip
of the nanoiber are evidence of the tip growth of the CNF. The diameter of the nanoiber
