Environmental Engineering Reference
In-Depth Information
bulk particles was 185.5 and 9.5 m
2
/g, and the nominal particle sizes cal-
culated from BET measurements were 8.3 and 329.8 nm, respectively [42].
h e nanoparticles were able to simultaneously remove multiple metals (Zn,
Cd, Pb, Ni, Cu) in the aqueous phase. h e nanoparticles had more adsorp-
tion capacity than the bulk particles. Adsorption kinetics for heavy metals
followed a modii ed i rst-order model, and the nanoparticles had a faster
adsorption than the bulk ones. Langmuir isotherm was suitable to charac-
terize metal adsorption onto TiO
2
. By comparing the distribution coei -
cient (K
d
), TiO
2
nanoparticles performed better than commercial activated
carbon and other metal oxide nanoparticles. Liang
et al.
[44] concluded
that nano-TiO2 (diameter = 10-50 nm, BET surface area = 208 m
2
/g)
showed adsorptive capacity to Zn and Cd as 15.3 and 7.9 mg/g, respec-
tively, at pH = 9.0. h e presence of common cations and anions (100-5000
mg/L) had no signii cant inl uence on the targeted metal (Zn
2+
and Cd
2+
ions of 1.0 mg/mL) adsorption under the given conditions.
9.2.4
Nano Zinc Oxides (NZnOs)
Nano zinc oxide is widely used in the catalyst industry, and for gas sen-
sors, solar cells and so on [45, 46]. Besides some properties similar to
TiO
2
, ZnO nanoplates has many unique advantages, such as being sim-
ple, cheap, easy to prepare and convenient to tailor morphologically. As
an adsorbent, ZnO was mostly applied to eliminate H
2
S [47]. Lee
et al.
[48] prepared nanometer-size zinc oxide (ZnO) powder by solution-
combustion method (SCM). h e adsorption behavior of ZnO was com-
pared with two titanium dioxide powders, P25 and ZnO, prepared by a
homogeneous precipitation process at low temperature. h e zinc oxide
nanopowder showed higher removal rate of Cu
2+
ions from the solution.
h e plate-like nanostructured ZnO with high specii c surface area was
fabricated by various methods such as hydrothermal [49], solvothermal
[50], chemical vapor deposition [51], electrochemical deposition [52]
and microwave methods [45]. h e solvothermal-prepared ZnO nano-
plates [35] are composed of two terminal non-polar planes with several
microns in the planar dimensions and 10-15 nm in thickness. h e nano-
plates are porous with a pore diameter of 5-20 nm and a high specii c
surface area (147 m
2
/g). h ese nanoplates have an adsorption capac-
ity of >1600 mg/g for Cu(II) ions. h e adsorption isotherm is subject
to the Freundlich equation (K
F
= 324.22 (mg/g/mg)
−n
, n = 4.56), while
the commercial ZnO nanopowders follow a Langmuir isotherm model.
In addition, the metal sorbed nano-ZnO can be employed to fabricate
other environmental materials. Ma
et al.
[53] reported a novel strategy to
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