Environmental Engineering Reference
In-Depth Information
predominant species on the surface of chitosan-Fe 0 . Chitosan has also been found to inhibit Fe(III)-Cr(III) precipitation due to
its high efficiency in chelating Fe(III) ions. In addition, immobilization of bimetallic NPs (Fe/Ni and Fe/Pd NP systems
(<40 nm)) in polymer membrane (such as cellulose acetate, polyvinylidene fluoride (PVDF), polysulfone, chitosan) media led
to the creation of materials for remediation of organic contaminants [15]. The second dopant metal (such as Ni, Pd) plays a very
important role in terms of catalytic property (hydrodechlorination) and a significant reduction in the formation of intermediates.
In addition to the rapid degradation (by Fe/Ni) of TCe to ethane, a complete dechlorination of selected PCBs (trichloroethylene
(TCe) and selected polychlorinated biphenyls (PCBs)) using milligram quantities of immobilized Fe/Pd NPs in the membrane
domain was achieved.
7.3
N-CoNtaiNiNg ligaNds
Among simple N-containing ligands, we note ethylenediamine (en), whose complexes have been used as precursors of compounds
having catalytic activities. Thus, mesoporous Co-doped ZnS and ZnO nanoplates were fabricated [16] by calcination of a
Zn 0.95 Co 0.05 S(en) 0.5 complex (en = ethylenediamine), which was hydrothermally synthesized using ethylenediamine as a single
solvent and chelating agent. Photocatalytic performance of the prepared materials was studied for decomposition of the azo dye
(acid red 14). The Zn 0.95 Co 0.05 S calcined at 500°C exhibited the highest photocatalytic activity under ultraviolet (UV) irradiation
and also showed photocatalytic performance under visible light irradiation. Composite ruthenium-containing silica nanomaterials
([ruO 2 ]@SiO 2 ) from amine-stabilized ruthenium NPs as elemental bricks were found to possess a high specific surface area
making them attractive materials for catalysis [17]. Bifunctional h 2 N-(Ch 2 ) x -Si(Oet) 3 amines were used as stabilizing ligands
( x = 3, 11) for the synthesis of ruthenium NPs, from [ru(COD)(COT)] (COD = 1,3-cyclooctadiene, COT = 1,3,5-cyclooctatriene)
as the metal precursor. The functionalization [18] of Fe 3 O 4 NPs with carboxyl (succinic acid), amine (ethylenediamine), and thiol
(2,3-dimercaptosuccinic acid) led to the formation of nanoadsorbents showing superparamagnetic behavior at room temperature
with strong field-dependent magnetic responsivity. These products were found to be useful in enhancing the efficiency of these
NPs for the removal of toxic metals (Cr 3+ , Co 2+ , Ni 2+ , Cu 2+ , Cd 2+ , Pb 2+ , and As 3+ ) and bacterial pathogens ( Escherichia coli ) from
water. Depending on the surface functionality (COOh, Nh 2 , or Sh), magnetic nanoadsorbents capture metals either by forming
chelate complexes or by the ion exchange process or electrostatic interaction. It was observed that the capture efficiency of
bacteria strongly depends on the concentration of nanoadsorbents and their inoculation time.
Pyridine-containing derivatives are also common chelators for trace amounts of metals. Thus, silica-coated Fe 3 O 4 NPs were
modified with 2,6-diaminopyridine and used for selective magnetic solid-phase extraction of trace amounts of metal ions
(Cu(II) and Zn(II)) [19]. Their quantitative extraction from mixed-ion solutions was accomplished at an optimal ph value of 6
within less than 10 min. Magnetic NPs (MNPs) prepared from Fe 3 O 4 and functionalized with pyridine were applied as an
adsorbent for the solid-phase extraction of trace quantities of Pd(II) [20]. The pyridine group was immobilized on the surface
of the MNPs by covalent bonding of isonicotinamide. The modified MNPs can be readily separated from an aqueous solution
by applying an external magnetic field. The detection limit and preconcentration factor were found to be 0.15 µg/l and 196,
respectively. In addition, the technique for the solid-phase extraction of gold using various kinds of pyridine-functionalized
nanoporous silica prior to its determination in various samples using flame atomic absorption spectroscopy (FAAS) was
developed [21].
Multiwalled carbon nanotubes (MWCNTs) were dispersed and loaded with 1-butyl-3-methylimidazolium hexafluorophos-
phate ([BMIM]PF 6 ), supported on sawdust and used as a new adsorbent for preconcentration of trace amount of Bi [22]. Bi(III)
ions were retained by the adsorbent MWCNT-[BMIM]PF 6 in a column after the formation of anionic complex BiI 4 with iodide
BiI 4 complexes through electrostatic interactions with positively charged imidazolium ion. The method was applied for detecting
Bi(III) in river water, tap water, and drug samples. Chelating polymer sorbents (oligomer containing a bis(pyrazole-1-yl)methane
fragment, Fig.  7.3) can be used in analytical chemistry and the environmental protection sphere to recover, separate, and
concentrate heavy and rare metals from natural and industrial waters [23]. Modified magnetite NPs functionalized with triazene
groups (Fig. 7.4) were designed and prepared for extraction/preconcentration of sub-ppb levels of mercury ions in water and fish
samples prior to their determination with inductively coupled plasma optical emission spectrometry (ICP-OeS) [24]. In the
separation process, an aqueous solution of hg 2+ ions was mixed with 150 mg of Fe 3 O 4 magnetite NPs modified with
1-( p -acetylphenyl)-3-( o -ethoxyphenyl)triazene (AeT) and then an external magnetic field was applied for isolation of magnetite
NPs containing mercury ions. The sorption capacity of functionalized Fe 3 O 4 NPs under optimum conditions was found to be
10.26 mg of hg 2+ per gram at ph 7 with a preconcentration factor of 500 (2 ml of elution for a 1000 ml sample volume).
PANi (Fig.  7.5) is known as a classic material and supporting agent in nanotechnology. The ability of organometallic
titanium-PANi hybrid materials to function as gas sensors at room temperature was investigated [25]. To form these hybrid
materials, commercially available PANi powders were directly added into organometallic titanium sols, synthesized using
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