Environmental Engineering Reference
In-Depth Information
O
H
N
COO
H
3
N
N
H
COO
n
figure 7.1
Natural phytochelatin.
Eu
3+
/Tb
3+
Au
Au
Au
N
CH
3
SH
2
C
N
BT
figure 7.2
Design strategy for luminescent nanomaterials. reproduced with permission from ref. [9]. © American Chemical Society.
ligand shell) were synthesized (Fig. 7.2) [9] by capping monothiol derivatives of 2,2′-dipyridyl onto the surface of Au NPs
(Au-BT). The high local concentration of the chelating ligands (~5 M) around the Au NP makes these particles excellent ion
sponges, and their complexation (1:3 complexation between eu
III
/Tb
III
ions and bipyridines) with eu
III
/Tb
III
ions yields
phosphorescent nanomaterials. The red-emitting Au-BT:eu
III
complex exhibited a long lifetime of 0.36 ms with six line-like
emission peaks, whereas the green-emitting Au-BT:Tb
III
complex exhibited a lifetime of 0.7 ms with four line-like emission
peaks. These phosphorescent nanomaterials, designed by linking BT:eu
III
complexes to Au NPs, were further used as sensors for
metal cations. Using tea polyphenols (TPs) as a reductant, Ag NPs supported on halloysite (1:1 aluminosilicate clay mineral with
the empirical formula Al
2
Si
2
O
5
(Oh)
4
) nanotubes (hNTs) were greenly synthesized [10] for photocatalytic decomposition of
methylene blue (MB). hNTs were initially functionalized by
N
-β-aminoethyl-γ-aminopropyl trimethoxysilane (AeAPTMS) to
introduce amino groups to form N-hNTs to fasten the Ag NPs; then the Ag NPs were synthesized and “anchored” on the surface
of the hNTs. The chelating interaction between the Ag NPs and N atoms together with the TP molecules was revealed. The
photocatalytic activity measurements of the prepared AgNPs@N-hNTs catalyst, evaluated by the decomposition of MB,
exhibited excellent catalytic activity and high adsorption capability to MB.
Nano zero-valent iron (nZVI) technology is becoming an increasingly popular choice for environmental remediation and
remediation of contaminated sites as iron is inexpensive, nontoxic, and environmentally compatible [11]. Nanoparticles are
attractive for remediation of various contaminants because of their unique physicochemical properties, especially its high
surface area over iron filings. At the same time, it is difficult to obtain pure nZVI without impurities of 15 other possible
compounds (oxides and hydroxides). It could be reached using chelating agents. Thus, synthesis of air-stable nZVI is undertaken
in the presence of ethylene diamine tetraacetic acid (eDTA), diethylenetriamine pentacetic acid (DTPA), nitriloacetic acid
(NTAc),
trans
-1,2-diaminocyclohexane-
N
,
N
,
N
′,
N
′-tetraacetic acid (CDTA), hydroxyethylenediaminetetraacetic acid (heDTA),
triethylene tetraamine (TrTA), and
N
-cetyl-
N
,
N
,
N
-trimethyl ammonium bromide (CTAB) chelating agents [12]. The chelating
effect was found to be the best for eDTA, NTAc, and heDTA, but the least for CDTA and CTAB. hydroxyl groups, lone pair
electrons on the nitrogen atom, and steric effects of the cyclohexane ring and bulky surroundings played an important role in
providing air stability toward synthesized nZVI. Chitosan-Fe
0
NPs (chitosan-Fe
0
), prepared using nontoxic and biodegradable
chitosan (see section N-Containing Ligands) as a stabilizer [13, 14], were used for Cr(VI) removal from water. The overall
disappearance of Cr(VI) may include both physical adsorption of Cr(VI) onto the chitosan-Fe
0
surface and the subsequent
reduction of Cr(VI) to Cr(III). It was revealed that after the reaction, relative to Cr(VI) and Fe(0), Cr(III) and Fe(III) were the
