Environmental Engineering Reference
In-Depth Information
O
CO
CH
3
O
CC
CH
2
CH
2
CH
OH
CH
2
O
C
O
CH
2
CH
CH
2
O
CH
2
CH
3
n
CH
3
CH
3
OH
H
2
+
RO
OR
FeNP
FeNP
figure 4.2
Scheme of the vinyl ester stabilization of iron NPs; OR represents the hydroxyl group in the vinyl ester. Adapted with permission
from Ref. [17]. © elsevier.
Fe(NO
3
)
3
·
9H
2
O
Fe
2
O
3
NPs
PVA matrix
PVA matrix
NaCl
Fe(NO
3
)
3
·
9H
2
O
Dissolve in DI wate
r
Evaporation
Annealing
NaCl 190°C, air
NaCl
PVA
Annealing
750°C, N
2
Fe(core)/C(shell) NPs
HCl (pH=1)
Fe/C core shell NPs
figure 4.3
Schematic of the formation of Fe@C NPs. Adapted with permission from Ref. [23]. © RSC.
4.2.2
fabrication and processing of Multifunctional carbon-based nanocomposites
In general, carbon-based nanocomposites may be prepared via two pathways. One is by directly using carbon-based chemical
structures (carbon nanotubes, carbon NFs, carbon nanoplatelets, graphene, and/or graphite) as the composite matrix and doping
other fillers into it. The limited doping level and the chemical mechanical compatibility between the carbon matrix and the nano-
fillers have witnessed a great change in this research field. The other is by starting with PNCs, and, through carbonization and/or
graphitization, forming carbon-based nanocomposites. As PNCs have been developed over a much longer period, various tech-
niques and/or potential to make well-compatible and synergistic composites are available. The carbon-based nanocomposites in
our research were generally derived using the second pathway, and it typically resulted in complex carbon structures; the nanofill-
ers incorporated initially often facilitate this carbonization process, resulting in various preferred carbon nanostructures.
Carbon-stabilized iron NPs have been prepared using poly(vinyl alcohol) (PvA) as the carbon source, and carbonization was
achieved by annealing at a high temperature of 750°C. briefly speaking, iron nitrate, sodium chloride, and PvA were dissolved
in deionized water at an iron nitrate to sodium chloride ratio of 1 : 20. The solution was then heated to 70°C to remove deionized
water. The solid sample was further heat-treated through two necessary steps. First, it was heated at 190°C in a tube furnace for
about 2 h under air atmosphere to produce Fe(NO
3
)
3
, and then it was decomposed to form Fe
2
O
3
NPs. In the second step, PvA
was carbonized and Fe
2
O
3
was reduced by the carbon decomposed from PvA to Fe NPs at 750°C in a nitrogen atmosphere, and
the resulting carbon served as a protection shell against oxidation of the iron in air. Salt, NaCl, was initially added to serve as a
spacer to prevent iron NP aggregation during the formation process. When the core-shell C@Fe NPs were formed, NaCl was
removed by washing with deionized water multiple times. Hydrochloric acid at a pH of 1.0 was used to remove uncoated Fe
NPs as well as to introduce carboxylic acid on the NP surfaces. Finally, the sample was dried in a vacuum oven at 40°C for 24
h to remove any residual water and acid. Finally, the sample was dried in a vacuum oven at 40°C for 24 h to remove any residual
water and acid. A schematic of the carbonization of PvA and the formation of core-shell C@Fe is shown in Figure 4.3 [23].
