Environmental Engineering Reference
In-Depth Information
OH
OH
π
C
π
π
C
π
O
O
OH
OH
π
C
CH
3
C
π
O
π
π
CH
3
O
NaOCl
+
OH
OH
π
C
π
O
CH
2
CH
3
π
CH
2
CH
3
C
π
O
CH
3
CH
3
OH
C
π
O
OH
C
π
π
π
O
H
3
C
H
3
C
Raw CNTs
Oxidized CNTs
BTEX
π-π interaction
figure 5.1
Diagram of the mechanism of BTEX adsorption on NaOCl-oxidized CNTs. Adapted with permission from Ref. [19],
© Elsevier.
reduces the aggregation potential of MWCNTs and consequently results in maintaining the active surface area of the
materials, which is responsible for the material's effectiveness.
5.2.2
Nanocomposites for BteX removal
gold NP-poly(dimethylsiloxane) (Au-PDMS) nanocomposite was employed by gupta and Kulkarni [8] for the removal of
BTEX compounds from water. The Au-PDMS nanocomposite was prepared by incorporating the highly compressible porous
foam PDMS with Au NPs (10-15 nm). Au-PDMS exhibits high swelling ability (~600%) against BTEX. Swelling ability is a
property that has been utilized to remove oil spills from water. The use of Au NPs in nanocomposites results in a highly expanded
porous PDMS structure compared to normal PDMS. Furthermore, an increase in the percentage of Au in the nanocomposite
results in an increase in the degree of compressibility of the PDMS foam. The sorbent capacity of the Au-PDMS nanocomposite
for BTEX in aqueous solution was nearly six times higher than that of PDMS foam without the Au NPs. An advantage of using
the Au-PDMS nanocomposite for adsorbing BTEX from water compared with sorbents in the form of particulates is its capacity
to be molded into any shape during or after synthesis and to fit into water bodies for practical applications.
5.3
NaNomaterials for chloroBeNzeNe removal
large quantities of chlorobenzenes are widely employed for many industrial processes [21]. Because of their extensive use over
several decades, chlorobenzenes are common in natural and engineered environmental systems. Chlorobenzenes contaminate
groundwater, wastewater, and the marine environment. Because of their acute toxicity, chlorobenzenes are of grave health and
environmental concern. The u.S. Environmental Protection Agency has listed dichlorobenzene (DCB), 1,2,4-trichlorobenzene
(1,2,4-TCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), and hexachlorobenzene (HCB) as priority pollutants [22]. Adsorption
is the traditional method for the removal of chlorobenzenes. Besides adsorption, advanced oxidation processes (AOPs) are
successfully employed to destroy chlorobenzenes. Various types of NMs have recently been utilized in the removal of chloro-
benzenes from aqueous solutions through adsorption and AOPs.
5.3.1
metal oxides for chlorobenzene degradation
Selli et al. [23] compared the efficiency of three different advanced oxidation techniques, that is, photolysis, photocatalysis
using TiO
2
NPs, and sonolysis, for the degradation and mineralization of 1,4-DCB. The results showed that photocatalysis
on TiO
2
achieved faster removal of 1,4-DCB as compared to sonolysis and direct photolysis. The highest degradation and
mineralization rate of 1,4-DCB was attained under sonophotocatalytic conditions (i.e., the combined use of photocatalysis
and sonolysis).
