Environmental Engineering Reference
In-Depth Information
washed by resuspending the material in absolute ethanol. This procedure was repeated
three times. After the inal centrifugation, the particles were dried in a freeze dryer for ~45
min and the prepared particles were stored at <4°C. The ferrous iron was reduced to the
zerovalent iron by addition of borohydride according to the following reaction:
2
+
−
0
−
+
2
Fe
+
BH
+ →+
3
HO
2
Fe
HBO
+ HHH
aq
4
+ 2
(3 7.1)
()
aq
4
()
aq
2
()
l
()
s
2
3
()
aq
()
2
()
g
37.2.1.2 Synthesis of Iron Oxide Nanoparticles
IONPs were synthesized by a modiied coprecipitation method [54]. In this method, fer-
romagnetic iron oxide nanoparticles were synthesized by using coprecipitation of ferrous
Fe(II) and ferric Fe(III) ions in an alkaline medium. First, 3.25 g (0.020 mol) FeCl
3
and 2.00 g
(0.010 mol) FeCl
2
·4H
2
O powder was dissolved in 60 ml aqueous acid, obtained by combin-
ing 50 ml deionized water with 10 ml of 1 mol/dm
3
HCl solution. The molar ratio of Fe(II)/
Fe(III) solution was 0.5. Then, the resulting solution of Fe(II)/Fe(III) was added dropwise
into 100 ml of 1 mol/dm
3
NaOH solution under vigorous stirring. After all the Fe(II)/Fe(III)
solution was added, the reaction mixture was stirred for a further 30 min to prevent any
coagulation of particles. Next, the obtained colloidal solution was centrifuged at 3000 rpm
(Beckman GP centrifuge) at ambient conditions for 15 min, and the precipitate was washed
several times with deionized water to remove any remaining Cl
−
and Na
+
ions in the pre-
cipitate. Finally, the precipitate was dried at 60°C in an oven. The obtained iron oxide
particles were ground thoroughly, and the obtained iron oxide powder was used for other
experiments [55]. Synthesized particles were characterized by the x-ray diffraction (XRD),
transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) techniques.
37.2.1.3 Synthesis of Gibbsite Nanoparticles
Gibbsite nanoparticles were synthesized by a previously described method [56]. An amor-
phous aluminum hydroxide suspension was produced by a titration of 1 mol/dm
3
AlCl
3
with
6 m o l/d m
3
NaOH until pH reached ~4.6. The suspension was stirred throughout the process.
Particular attention was paid to minimize CO
2
contamination of the solution by continuous
nitrogen purging (99.99%). At the end of the titration, the suspension was sealed and stirred
continuously at least for 6 h. It was transferred into dialysis membranes and was subjected
to dialysis against double-distilled water. After 2 days, the excess liquid phase was separated
from aluminum hydroxide gel and the dialysis was continued at 50°C for 60 days. The dialysis
was performed using prewashed and hydrated cellulose dialysis membranes (Sigma-Aldrich,
D-9402). The open end of each bag was sealed with dialysis clips (Sigma-Aldrich, Australia).
The dialysis water was refreshed daily and maintained at a constant temperature throughout
this process. Synthesis particles were characterized by using XRD, TEM, and BET techniques.
37.2.1.4 Synthesis of Ag Nanoparticles from Bacteria
The pure cultures of
Bacillus cereus
,
Bacillus subtilis
,
Bacillus koreensis
, and
Bacillus megate-
rium
strains were prepared and they were inoculated in MGYP nutrient media (glucose 1%,
malt extract 1%, yeast extract 0.3%, peptone 0.5%) [57]. After inoculation of the microbes in
media, silver AgNO
3
was added in the concentration of 100 mg/l in different sets of lasks.
The concentration of silver salt was gradually increased from 100 to 20,000 mg/l to check
the tolerance of microbes at higher concentration of metal salts. Temperature and rotations
were maintained at 37°C and 100 rpm, respectively.
