Page 474 - Polymer-based Nanocomposites for Energy and Environmental Applications

Nanocomposite membrane for environmental remediation 427

2+
to 107 mL g 1 (Kd) for Sr . Different spectroscopic techniques including XRD,
FTIR, XPS, and Raman were employed to confirm the structural collapse of the
exchange materials. The adsorption mechanism of Na-TNB membrane was clarified
using the radioactive cations permanently trapped inside via producing a stable solid.
Moreover, the engineered multilayer membrane was found very capable in selectively
and quickly adsorbing oils up to 23 times the adsorbent weight via coating a thin layer
of hydrophobic molecules.
Consequently, there is a growing need for developing membrane materials capable
to accomplish complex functions such as removing radioactive pollutants and oil
spills from water. In membrane technology, to obtain the scalable fabrication of
membranes with good mechanical and thermal stability, superior resistance to radia-
tion and excellent recyclability are major challenges [161].
In many research areas including catalysis [162], optics [163], electronics [164],
and environment [165], micro- and nanosized materials have played magic roles
owing to their unique physical and chemical properties, and consequently, they also
present the potential to design novel inorganic ion exchangers that possibly overcome
the limitations mentioned above.
According to [160], layered titanates (Na 2 Ti 3 O 7 nH 2 O) have been prepared with
exchangeable sodium cations using concentrated NaOH solution via simple hydro-
thermal treatment of Ti precursor. Different morphologies of nanofibers and
nanosheets are achieved by proper control of the synthesis conditions. The metastable
layered structure of the titanates collapses as a result of irreversible ion exchange
2+
+
3+
2+
during the ion-exchange process. Target cations (e.g., Ag ,Cu ,Pb , and Eu )
are of great significance for the removal and subsequent safe disposal of hazardous
metal cations because of completely concentrated from water and then tightly
immobilized in the interlayer structure. Nanosheet ion-exchange behavior is conside-
red more efficient than that of the nanofibers and other inorganic ion exchangers
because of the larger surface area, less stable layered structure, and superior amount
of interlayer water of the nanosheets.
Titanate ion-exchange behavior is also very selective. The selectivity is greatly
influenced by valence, hardness, and radius of cations. Inner layer trapped cations
are released as a result of acid-induced phase transformation of the titanate nanosheets
to rutile. To synthesize the titanate nanostructures, the rutile can be used further as a
fresh Ti precursor, resulting in a full cycle of material usage. The nanosheets can find
some suitable applications in the decontamination and safe disposal of radioactive and
heavy metal cations and assemblage of valuable cations from water.
Similarly, to synthesize the titanates nearly to 100% conversion efficiency, various
Ti precursors such as rutile, anatase, and amorphous TiO 2 can be used [41].

15.11 Integrated CNT polymer composite membrane
with polyvinyl alcohol layer

In many industrial fields such as oil fields, petrochemical, metallurgical, pharmaceu-
tical, and others, high capacities of wastewater in the form of oil-water emulsion are
generated [166].