New approach for the removal of metal ions from water: Adsorption onto aquatic plants and microwave reaction for the fabrication of nanometals

Article abstract of DOI:10.1021/jp052844g

We adsorb heavy metal ions such as Ag⁺, Pb²⁺, and Ru³⁺ onto an aquatic plant and convert the adsorbed ions to the corresponding nanometallic particles by the polyol reaction carried out in a microwave oven. ? 2005 American Chemical Society.

Full text of DOI:10.1021/jp052844g

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5179
2005, 109, 15179-15181
Published on Web 07/21/2005
New Approach for the Removal of Metal Ions from Water: Adsorption onto Aquatic Plants
and Microwave Reaction for the Fabrication of Nanometals
†
‡
‡
‡
‡
§
B. Chefetz, L. Sominski, M. Pinchas, T. Ginsburg, S. Elmachliy, E. Tel-Or, and
A. Gedanken*,‡
Department of Soil and Water Sciences, The Hebrew UniVersity of Jerusalem, P.O. Box 12,
RehoVot 76100, Israel, Department of Chemistry and Kanbar Laboratory for Nanomaterials at the
Bar-Ilan UniVersity Center for AdVanced Materials and Nanotechnology, Bar-Ilan UniVersity,
Ramat-Gan 52900, Israel, and The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture,
The Hebrew UniVersity of Jerusalem, P.O. Box 12, RehoVot 76100, Israel
ReceiVed: May 30, 2005; In Final Form: July 8, 2005
+
2+
3+
We adsorb heavy metal ions such as Ag , Pb , and Ru onto an aquatic plant and convert the adsorbed
ions to the corresponding nanometallic particles by the polyol reaction carried out in a microwave oven.
Introduction
are present in industrial (e.g., Ag+ in photoprocessing) and
municipal effluents. They also present a variety of reduction
Heavy metals are toxic contaminants that must be removed
from wastewaters before being discharged to the environment.
A wide range of physical and chemical processes are available
for the removal of heavy metal ions during wastewater treatment.
These include ion exchange, electro-chemical precipitation,
filtration, and adsorption to commercial activated carbon. A
major drawback with precipitation is contamination of the
produced sludge, which limits its application in agricultural
fields. Ion exchange and adsorption to activated carbon are
efficient treatments, but they are not largely used due to the
high operational cost. Alternatively, aquatic plant materials have
shown a remarkably high sorption capacity for heavy metals
potentials, thus demonstrating the generality of the method.
Therefore, it is of great scientific and practical interest to reveal
the possible removal and recycling of these metal ions from
wastewater using low-cost treatments.
Experimental Section
Silver nitrate and ethylene glycol were purchased from Sigma-
Aldrich Co. and used without further purification. Azolla
8
filiculoides was grown in IRRI medium in the phytothron of
the Faculty of Agriculture, Hebrew University. X-ray diffraction
(XRD) analysis was performed with a Bruker AXS instrument
4-7
from wastewater. Therefore, plant materials that are available
in large quantities may have the potential to be used as
alternatively low- cost ($1 per 1 kg of aquatic plant) and
environmentally friendly sorbents.
(
model D8), using Cu KR radiation. Transmission electron
micrographs (TEM) were obtained by employing a JEOL-TEM
1
00SX microscope. The samples for TEM were prepared as
+
follows. Ag -adsorbed dry plants were pounded (dispersed) in
an agate mortar, and the powder was suspended in 2-propanol
1
1,13,14
The use of domestic multimode microwave (MW)
or
single-mode MW ovens9 for the fabrication of inorganic
nanomaterials is becoming a common technique. The main
advantage of this method when compared to other synthetic
techniques of nanoparticles is the short reaction time.
,12
(ethanol) by sonication in an ultrasonic bath for 20 min. Then
the suspension was layered on a copper grid (piece of 400 mesh
+
coated with carbon film) and dried in air. The quantity of Ag
ions adsorbed by the plant was calculated by differences between
In the current paper, we describe a combined procedure
composed of two known technologies, namely, adsorption of
metallic ions on aquatic plants and conversion of the adsorbed
heavy ions into metallic nanoparticles. The combined process
offers a promising approach for the removal of heavy metals
from wastewater and the recycling of adsorbed metals into
marketable products of metallic nanoparticles. In this study, the
+
the Ag concentration in the solution and the original amount.
+
The concentration of Ag ions in the solution was determined
+
using a well-known titration method. The Ag ions are titrated
with a 0.01 M solution of KSCN in the presence FeCl3 as an
16
indicator.
The starting materials for the reduction of Pb2+ and Ru3+
ions were Pb(NO3)2 and RuCl3, respectively. The concentration
+
2+
aquatic plant Azolla was used as the sorbent for Ag , Pb ,
2+
3+
was 0.02 M in ethylene glycol and ethanol for Pb and Ru ,
and Ru3 ions in an aqueous solution. These heavy metal ions
+
2+
respectively. The irradiation times were 3 min for Pb and 1
3
+
min for Ru .
*
Author to whom correspondence should be addressed. E-mail:
An ordinary household microwave oven (Spectra 900 W, 2.45
GHz), modified with a refluxing system, was used for the
microwave-assisted reduction. Dried Azolla biomass (0.7 g) was
placed in 60 mL of an aqueous solution (or ethylene glycol) of
0.02 M AgNO3. The reason for choosing this high concentration
gedanken@mail.biu.ac.il.
†
Department of Soil and Water Sciences, The Hebrew University of
Jerusalem.
‡
Bar-Ilan University.
§
The Robert H. Smith Institute of Plant Sciences and Genetics in
Agriculture, The Hebrew University of Jerusalem.
1
0.1021/jp052844g CCC: $30.25 © 2005 American Chemical Society

15180 J. Phys. Chem. B, Vol. 109, No. 32, 2005
Letters
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1
days. The calculated adsorption capacity of the plants was
90 mg Ag /g biomass.
+
A new concept that is currently under study has shortened
the adsorption time from 7 days to 5 min.
+
The microwave irradiation of the adsorbed Ag biomass was
aimed at reducing the silver ions into the corresponding metallic
1
0
silver. Coupling microwave dielectric heating and the polyol
reaction has recently led to the fabrication of a long list of
9
-12
13
metallic nanoparticles
as well as binary and ternary
1
4
chalcogenide nanoparticles. The polyol process, described by
Figure 1. Adsorption kinetic of silver ions by Azolla biomass in EG
and water solutions.
1
5
Fievet, is completed in a much shorter time when conducted
under microwave power than under reflux conditions. The
identification of the product of the polyol reaction was done
by XRD analysis (Figure 2). The particle size calculated by the
Debye-Scherrer formula was 30 nm, and the major diffraction
peaks are assigned to pure metallic cubic silver. The intensities
and positions of the peaks are in a good agreement with literature
values of cubic silver (PDF: 4-783). The presence of impurities
such as silver oxide peaks was not detected. However, a very
small diffraction peak at 2θ ) 29.6° is measured and assigned
to the mineral residues left after the burning of the aquatic plant.
of Ag+ ions is that in this paper we intend to present a new
idea and are not concerned with treating real metallic wastes.
However, it is worth mentioning that according to Internet
1
7
sources “depending on the stage from which the wastes
originate and the type of film processed, the silver concentration
can range between 5 mg/L and 12,000 mg/L”. This means that
the concentrations used in the current experiments are not far
from reality.
The mixture was allowed to equilibrate at room temperature
+
for a few days to reach maximal Ag ion adsorption. Then, the
A TEM image of the Azolla biomass containing silver
nanoparticles after the microwave-assisted reduction (from
aqueous solution) is presented in Figure 3. Nanoparticles (20-
+
Ag -adsorbed plant biomass was dispersed in an ethylene glycol
9
solution and placed in the microwave reflux system for 3 min
for the reduction of adsorbed silver ions. Before the reaction,
argon was purged for 30 min through the solution, and then
the microwave oven was switched on under a continued flow
of argon. The power level of the oven was 50%. The resulting
product was centrifuged, washed with double-distilled water,
ethanol, and dried in a vacuum. The portion of the plant with
silver nanoparticles was heated under argon at 500 °C for 5 h
for residue analysis.
3
0 nm in size) are clearly observed on the surface of the plant
materials. The shapes of these particles are almost spherical,
and the identification of the nanoparticles as silver was aided
by XRD measurements. The TEM images obtained for the
reduced metallic silver from water or ethylene glycol (EG)-
adsorbed ions are almost identical. TEM images (Supporting
Information) of the material obtained after the burning of the
aquatic plants in argon show 20-30 nm silver particles similar
to their sizes in the Azolla. However, part of the silver is
aggregated in 300-500 nm particles as expected from annealing
nanoparticles at 500 °C.
Results and Discussions
The adsorption kinetics of silver ions onto Azolla biomass
are presented in Figure 1. The adsorption kinetics of the ions
by the biomass were similar in either ethylene glycol or water.
A similar process of adsorption and reduction was conducted
3
+
2+
with ions of Ru and Pb and yielded similar results. Ions
were adsorbed by the plant biomass and were further reduced
by microwave-assisted radiation. Experiments using another
+
In both solvents, 90% of the Ag ions (as determined by the
-
16
SCN titration ) were adsorbed by the Azolla biomass within
Figure 2. XRD of the product after annealing of the product of the microwave reduction in argon at 500 °C.

Letters
J. Phys. Chem. B, Vol. 109, No. 32, 2005 15181
and a major part of the particles remain monodispersed. This
material is available free of charge via the Internet at http://
pubs.acs.org.
References and Notes
(
(
1) Ho, Y. S.; McKay, G. Water, Air, Soil Pollut. 2004, 158, 77-97.
2) Turkman, A. E.; Aslan, F.; Ege, I. Fresenius EnViron. Bull. 2004,
1
2
1
3, 574-580.
(3) Cheung, C. W.; Ko, D. C. K.; Porter, J. F.; McKay, G. Langmuir
003, 19, 4144-4153.
(
4) Kadirvelu, K.; Faur-Brasquet, C.; Le Cloirec, P. Langmuir 2000,
6, 8404-8409.
5) Oliveira, L. C. A.; Petkowicz, D. I.; Smaniotto, A.; Pergher, S. B.
C. Water Res. 2004, 38, 3699-3704.
6) Wase, D. A. J.; Forster, C. F. Biosorbents for Metal Ions; Taylor
and Francis: London, 1997.
7) Ajmal, A.; Rao, A. K. R.; Rais, A.; Jameel, A. J. Hazard. Mater.
(
(
(
B 2000, 79, 117-131.
(
8) Kuyucak, N.; Volesky, B. Biotechnol. Lett. 1989, 10, 137-142.
(9) Komarneni, S.; Li, D. S.; Newalkar, B.; Katsuki, H.; Bhalla, A. S.
Langmuir 2002, 18, 5959-5962.
Figure 3. TEM picture of the Azolla plant after the reduction of the
adsorbed silver ions.
(10) Pastoriza-Santos, I.; Liz-Marzan, L. M. Langmuir 2002, 18, 2888-
2
894.
(
11) Harpeness, R.; Gedanken, A. Langmuir 2004, 20, 3431-3434.
(12) Katsuki, H.; Komarneni, S. J. Mater. Res. 2003, 18, 747-750.
aquatic plant (Pistia) were also successful and yielded similar
results. Thus, we suggest that the described technology can be
used for removal of metal ions from water and transforming
them to nanoparticles.
(13) Zhu, J. J.; Palchik, O.; Chen, S. G.; Gedanken, A. J. Phys. Chem.
B 2000, 104, 7344-7347.
14) Grisaru, H.; Palchik, O.; Gedanken, A.; Palchik, V.; Slifkin, M.
(
A.; Weiss, A. M. Inorg. Chem. 2003, 42, 7148-7155.
(15) Fievet, F.; Lagier, J. P.; Figlarz, M. MRS Bull. 1989, 29.
(
16) Kolthoff, I. M.; Sandell, E. B. Textbook of QuantitatiVe Inorganic
Analysis, 3rd ed.; Macmillan: New York, 1958.
Supporting Information Available: TEM images of the
silver nanoparticles after burning in argon at 500 °C. These
images demonstrate that the material is only partially aggregated
(
17) Photographic Processing Waste Management; Office of Environ-
mental Health and Safety, Weill Cornell Medical College: New York; http://
www.med.cornell.edu/ehs/updates/silver.htm.