Environmental Engineering Reference
In-Depth Information
table 8.1
performance of various types of Cnts in the adsorption of heavy metal ions
maximum
adsorption
capacity,
q
m
(mg/g)
Adsorbed
materials
Adsorbents
Details
Reference
mWCNTs (HNO
3
)
Pb(II)
85
The high adsorption rate of Pb(II) is attributed to the oxygenous
functional groups formed on the surface of mWCNTs that
react with Pb(II) to form salt or complex deposited onto the
surface of mWCNTs.
[33]
SWCNTs (NaClO)
Zn(II)
43.66
The attachment of oxygen-containing functional groups increase
CNTs hydrophilicity and the ion exchange capacity for Ni(II)
adsorption.
[35]
mWCNTs (NaClO)
32.68
mWCNTs
Zn(II)
10.21
The adsorption of Zn(II) depends on the chemical interaction
between Zn(II) and surface functional groups on CNTs rather
than surface area and pore volume.
[37]
mWCNTs (HNO
3
/H
2
SO
4
)
18.14
mWCNTs (HNO
3
)
27.20
mWCNTs (KmnO
4
)
28.01
CNTs
Cd(II)
1.1
The oxidation ability of HNO
3
is the highest.
[42]
CNTs (H
2
O
2
)
2.6
The highest adsorption in KmnO
4
can be attributed to the
adsorbed residual mnO
2
particles on CNTs.
CNTs (KmnO
4
)
11.0
CNTs (HNO
3
)
5.1
mWCNTs
Cu(II)
8.25
modification with NaOCl and HNO
3
increases the area of active
adsorption sites of CNTs and the proportion of available
adsorption sites.
[43]
mWCNTs (HNO
3
)
13.87
The oxidizing ability of NaOCl exceed that of HNO
3
mWCNTs (NaClO)
47.39
mWCNTs (NaClO)
Ni(II)
38.46
The adsorption performance of both mWCNTs and SWCNTs
remain stable after 10 cycles of sorption/desorption process.
[53]
SWCNTs (NaClO)
47.85
mWCNT/Poly(2-aminothiphenol)
(P2AT)
Cd(II)
178.7
metal ions are adsorbed by sharing an electron pair of =N
and —S— in P2AT with Cd(II) and Pb(II).
[18]
Pb(II)
186.4
mWCNT/poly(acrylamide)
(PAAm)
Pb(II)
35.7
The amide functional groups in PAAm and PDmA act as
efficient anchors for Pb(II).
[48]
The sorption of mWCNT/PAAm is higher because of the higher
amide group content.
mWCNT/Poly(
N
,
N
-
dimethylacrylamide) (PDmA)
25.8
mWCNT/tri(2-aminoethyl)amine
(TAA)
Pb(II)
38
The high adsorption of Pb(II) can be attributed to the
coordination interaction between the nitrogen group in TAA
and metal ions
[49]
mWCNT/2-vinylpyridine (VP)
Pb(II)
37.0
The pyridyl group in VP has a strong affinity to interact with Pb(II)
[54]
Thermodynamic studies provide an overview of the macroscopic properties of heavy metal adsorption onto CNTs and are
conducted based on the thermodynamic parameters enthalpy change (Δ
H
°), Gibbs free energy change (Δ
G
°), and entropy
change (Δ
S
°). The adsorption of heavy metals onto CNTs generally involves a positive enthalpy change (Δ
H
°), indicating that
the adsorption process is endothermic, and a negative Gibbs free energy change (Δ
G
°), indicating that the sorption of the heavy
metal on CNTs occurs spontaneously. Δ
G
° becomes more negative with increased temperature because of the endothermic
characteristics. A more negative Δ
G
° indicates more efficient adsorption at a higher temperature. Δ
S
° of the adsorption usually
has a positive value, which means an increase in the degree of freedom at the solid-liquid interface, and increases the probabilities
of heavy metal adsorption onto CNTs [32, 38, 40, 43, 46, 48].
8.4
adsorption of baCterial pathoGens
The exceptional adsorption ability of CNTs is not limited to heavy metal ions. Srivastava et al. [66] revealed the potential of
CNTs to adsorb and remove bacterial pathogens from contaminated water without any surface modification. Numerous studies
[67-70] have also demonstrated that CNTs possess high binding affinity toward bacteria such as
Bacillus subtilis
,
Escherichia
coli
, and
Staphylococcus aureus
because of their high aspect ratio and large surface area. The interaction between CNTs and
bacteria basically relies on physical adsorption, wherein bacteria are spontaneously adsorbed in the mesopores and macropores
