Environmental Engineering Reference
In-Depth Information
Table 3.1
Summary of particle size dependence adsorption studies.
Material
Particle sizes Adsorbate
Size dependence
Explanation
suggested
Hysteresis?
Other comments
TiO
2
, anatase
(Zhang
et al.
,
1999)
6 nm, 16 nm
Organic
acids
Molar surface free
energy higher for
smaller particles
N/A
K
ads
(6 nm)
K
ads
(16 nm)
(up to 70-fold
increase)
>
TiO
2
, anatase*
(Gao
et al.
,
2004)
Cd
2+
8-145 nm
K
ads
much larger for bulk
than for NP's
Intraparticle electrostatic
repulsion in
aggregated NPs; Ti
site disorder in
small NPs
No,
completely
reversible
Degree of aggregation not
quantitatively assessed
TiO
2
, anatase*
(Giammar
et al.
, 2007)
20-33 nm vs
520 nm
Pb
2+
Surface geometry and
bonding
N/A
Aggregation state and
morphology of particles
not characterized
K
ads
and
max
much
larger for bulk than
NP's
Γ
7 nm, 25 nm,
88 nm
Cu
2+
SA normalized
sorption onto
7 nm
Distorted bonding
geometry at intersec-
tions of crystal faces
N/A
88 nm sample had variable
morphology and more
aggregation
α
-Fe
2
O
3
,
hematite
(Madden
et al.
, 2006)
>
25 nm = 88 nm
5 nm, 25 nm,
75 nm
Hg
2+
SA-normalized
sorption onto
5 nm
Surface geometry of
atoms less favourable
for bonding; charge
distribution
N/A
α
-FeOOH
(Waychunas
et al.
, 2005)
<
25 nm = 75 nm
Fe
3
O
4
(Yean
et al.
,
2005)
11.72 nm,
20 nm,
300 nm
As (V) and
As (III)
Γ
max
for 11.72 nm
particles greater
More surface sites due
to less aggregation
Yes, greater
for 20 nm
than 300 nm
20 nm, 300 nm variable
morphology, aggregated.
NOM decreased As
adsorption.
* One or more samples contained rutile-phase TiO
2
.
Note
: SA = surface area, NP = nanoparticle, N/A = hysteresis data not available, NOM = natural organic matter.
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