Naja 2008 ZVI RDX EST
Published on: Mar 3, 2016
Transcripts - Naja 2008 ZVI RDX EST
(RDX) Using Zerovalent Iron
G H I N W A N A J A , ‡
A N N A M A R I A H A L A S Z , ‡
S O N I A T H I B O U T O T , †
G U Y A M P L E M A N , †
A N D J A L A L H A W A R I * , ‡
Defence Research Establishment, Valcartier (Quebec),
2459 Blvd Pie IX, Canada G0A 1R0, and Biotechnology
Research Institute, National Research Council of Canada,
Montreal, Quebec, Canada H4P 2R2
Received November 8, 2007. Revised manuscript received
March 18, 2008. Accepted March 27, 2008.
Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common
contaminant of soil and water at military facilities. The present
study describes degradation of RDX with zerovalent iron
nanoparticles (ZVINs) in water in the presence or absence of
a stabilizer additive such as carboxymethyl cellulose (CMC)
or poly(acrylic acid) (PAA). The rates of RDX degradation in
solution followed this order CMC-ZVINs > PAA-ZVINs > ZVINs
with k1 values of 0.816 ( 0.067, 0.082 ( 0.002, and 0.019 (
0.002 min-1, respectively. The disappearance of RDX was
accompanied by the formation of formaldehyde, nitrogen, nitrite,
ammonium, nitrous oxide, and hydrazine by the intermediary
formation of methylenedinitramine (MEDINA), MNX (hexahydro-
5-nitro-1,3,5-triazine), TNX (hexahydro-1,3,5-trinitroso-1,3,5-
triazine). When either of the reduced RDX products (MNX or
TNX) was treated with ZVINs we observed nitrite (from MNX
only), NO (from TNX only), N2O, NH4
+, NH2NH2 and HCHO. In the
case of TNX we observed a new key product that we
tentatively identiﬁed as 1,3-dinitroso-5-hydro-1,3,5-triazacyclo-
hexane. However, we were unable to detect the equivalent
denitrohydrogenated product of RDX and MNX degradation.
identiﬁed as N-nitroso-methylenenitramine (ONNHCH2NHNO2),
of RDX. Experimental evidence gathered thus far suggested that
ZVINs degraded RDX and MNX via initial denitration and
sequential reduction to the corresponding nitroso derivatives
prior to completed decomposition but degraded TNX exclusively
via initial cleavage of the NsNO bond(s).
The extensive use of explosives such as hexahydro-1,3,5-
trinitro-1,3,5-triazine (RDX) has led to widespread contami-
nation of soil and water (1, 2). RDX is known to be toxic to
various aquatic and terrestrial organisms (3), thus neces-
sitating its removal from polluted environments. Recently
our group has conducted several studies to elucidate the
conditions in an effort to help in the design of in situ
remediation strategies. For example we found that initial
denitration can lead to decomposition and the formation of
the two key intermediates 4-nitro-2,4-diazabutanal (NDAB)
and methylenedinitramine (MEDINA) whose formation
depends on the stoichiometry of the released nitrite ion. The
loss of 2 NO2
- from RDX normally leads to NDAB as has been
found during alkaline hydrolysis (4) and aerobic biodegrada-
tion with Rhodococcus sp. strain DN22 (5) and XplA (6).
Whereas the loss of 1 NO2
- leads to the predominant
formation of methylenedinitramine (MEDINA) as has been
observed during RDX treatment with diaphorase enzyme (7)
and XplA (6). RDX transformation to the corresponding
nitroso derivatives (8) has also been documented to occur
under various abiotic reducing and biotic anaerobic condi-
tions (9, 10). Although more recently Kemper et al. (11) did
not observe any of RDX nitroso products using hydrogen
sulﬁde and black carbon.
RDX removal using zerovalent iron has been extensively
reported (8, 12–14) where several products including MNX,
DNX, and TNX have been identiﬁed, but little is known on
how these nitroso products cleave. In the present study we
chose to examine highly reactive zerovalent iron nanopar-
ticles (ZVINs) capable of generating intermediates in suf-
ﬁcient concentrations to allow investigation of their decom-
position routes. Recently, zerovalent iron nanoparticles
(ZVINs) have been developed for several environmental
remediation technologies (15), especially for the treatment
of chlorinated organic compounds (16), metal ions (17),
pesticides (18), organic dyes (19) and inorganic anions (20).
However, the integration of ZVI nanoparticles in environ-
mental processes has been held back by the key technical
barrier represented by the tendency of iron nanoparticles to
agglomerate and, thereby, rapidly lose their chemical reac-
tivity and mobility. Extensive studies have been devoted to
the stabilization of the ZVINs. While Schrick et al. (21) used
hydrophilic carbon as delivery vehicles to support ZVI
nanoparticles, He et al. (22) reported a new strategy for
stabilizing palladized iron nanoparticles with sodium car-
To our knowledge, no reports are available for the
degradation of RDX with ZVI nanoparticles whose unique
properties present a novel technological potential. The
current work examines the reaction between RDX and ZVINs
focusing on the identiﬁcation of the RDX transformation
pathway pinpointing the products, intermediates of the
reaction as well as their yields. For this purpose, ZVI
nanoparticles were used to degrade RDX in water in the
presence and absence of the two stabilizers, carboxymethyl
cellulose (CMC) and poly(acrylic acid) (PAA). Addition of the
polymeric stabilizers into the system is intended to keep the
nanoparticles well dispersed, to facilitate their even distribu-
tion and smooth penetration through soil when applied in
accelerated in situ RDX degradation at contaminated sites.
Finally, due to the formation of MNX and TNX as potential
RDX intermediates during RDX reduction with ZVI nano-
particles, we thus investigated their reaction under the same
conditions to gain further insight into the degradation
pathway(s) of RDX.
Chemicals. Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)
(>99%), hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) (99%)
and ring-labeled [15
N]-RDX (98%) were obtained from
* Corresponding author phone: +1-514-496 6267; fax +1-514-496
6265; e-mail address: email@example.com.
Biotechnology Research Institute.
Defence Research Establishment.
Environ. Sci. Technol. 2008, 42, 4364–4370
4364 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 12, 2008 10.1021/es7028153 CCC: $40.75 2008 American Chemical Society
Published on Web 05/14/2008
hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX) (56%),
N]-MNX, ring-labeled [15
were provided by Dr. R. J. Spanggord from SRI International
(Menlo Park, CA). Hydrazine sulfate (99%) was obtained from
Aldrich, Canada. Sodium borohydride (g98.5%) and poly-
(acrylic acid) (M.W. 1800) were purchased from Aldrich, and
sodium carboxymethyl cellulose, polymer of cellulose-
)n, CMC, (M.W. 90 000) and nitrous oxide
standard (1000 ppm) were procured from Sigma-Aldrich.
Ferrous sulfate (99%) and sodium hydroxide (99%) were
obtained from Anachemia and EMD, respectively. Nitrite
and ammonium standards (1000 ppm) were purchased from
Alltech. All other chemicals were reagent grade, and all
solutions were prepared using Milli-Q-UV Plus Ultrapure
water system (>18 MΩ, Millipore, MA).
Zerovalent Iron Nanoparticles Preparation. Zerovalent
iron nanoparticles (ZVINs), poly(acrylic acid) modiﬁed
zerovalent iron nanoparticles (PAA-ZVINs), and carboxym-
ethyl cellulose modiﬁed zerovalent iron nanoparticles (CMC-
ZVINs) were prepared according to the methods published
by Liu et al. (15), Schrick et al. (21) and He et al. (22),
respectively, with modiﬁcations detailed in the Supporting
Physical Characterization. Transmission electron mi-
croscope (TEM) micrographs were recorded using a Philips
CM20 200 kV electron microscope equipped with an Oxford
Instruments energy dispersive X-ray spectrometer (Link exl
II) and an UltraScan 1000 CCD camera. To obtain the TEM
images, the nanoparticle suspensions were diluted with
was then dropped on a holey carbon ﬁlm 300 mesh copper
grid and allowed to air-dry.
The N2sBET speciﬁc surface area of the nanoparticles
was measured using a TriStar 3000 gas adsorption analyzer
and the multipoint method (Micromeritics Analytical Ser-
vices, GA) with a resolution of 0.05 mmHg.
Reaction of RDX with ZVINs. Deionized water (10 mL)
was mixed with 3 mg of ZVINs (methanol solution) in 15 mL
serum bottles and crimp-sealed with Teﬂon-coated septa.
The solution was either made anaerobic by purging the
headspace for 10 min with argon or kept under a blanket of
air for the aerobic experiments. Following 15 min of gentle
shaking (rotary shaker, 150 rpm) to equilibrate the pH value
(5.9-6.1), 0.82 µmol of RDX in methanol (0.2 mL) was added
to each bottle and the reaction was allowed to take place at
room temperature. In some experiments ring-labeled [15
RDX was used under the same conditions to help identify
RDX products. All experiments were made in triplicate.
Controls containing ZVINs in water with no RDX were also
performed to ensure the ZVINs stability in water. Controls
containing RDX in water with no ZVINs were not necessary
since RDX hydrolysis could be neglected within the range of
pH values examined (4). The reactions were stopped after 3,
6, 10, 20, 40, 60, 120, 240, and 480 min. For each time
measurement three bottles were sacriﬁced for analysis.
Parallel RDX anoxic batch experiments were performed using
CMC-ZVINs and PAA-ZVINs (0.3 g L-1
of nanometal) to
compare their reactivity with the nonstabilized ZVINs based
on the same initial iron nanoparticle concentration.
Other batch experiments were conducted using ZVINs
(0.3 g L-1
) and either MNX (80 µM) or TNX (80 µM) to
determine products formed and thus know their role in the
degradation of RDX. In some experiments ring-labeled [15
MNX and [15
N]-TNX were used under the same conditions
to help identify the degradation products. To determine the
eventual fate of nitrogen-containing RDX degradation prod-
ucts such as NO2
+, N2O, MEDINA, and NH2NH2 we
allowed ZVINs (0.3 g L-1) to react with 20 mg L-1 of each
Chemical Analysis. The gas phase in the headspace of
the chemical assays was sampled using a gastight syringe
(250 or 100 µL) and then analyzed for nitrogen, nitrous oxide,
GC, Mississauga, ON) connected to either a TCD or an ECD
detector (23). Aliquots of the aqueous phase of the reaction
to analyses of RDX, intermediates and ﬁnal products. The
products methylenedinitramine (MEDINA) and 4-nitro-2,4-
diazabutanal (NDAB) were analyzed as described by Hawari
et al. (24) and by Bushan et al. (25). Formaldehyde, formic
acid, ammonium, nitrate, nitrite were analyzed as described
by Monteil-Rivera et al. (26). Denitrosation of TNX was
followed by monitoring nitric oxide (NO) using Apollo 4000
free radical analyzer (WPI, U.S.) speciﬁc for NO analysis.
Whereas hydrazine formation was monitored by analyzing
aliquots of the reaction mixture after derivatization with
salicylaldehyde (98%, Aldrich) followed by LC/MS analysis
as described by Monteil-Rivera et al. (26). The concentration
of iron in CMC-ZVINs and PAA-ZVINs, ferric, and ferrous
by Schrick et al. (21).
Results and Discussion
ZVI Nanoparticle Characterizations. The TEM images
(Figure 1) indicated that the three types of nanoparticles
(ZVINs, CMC-ZVINs, and PAA-ZVINs) were mostly spherical
core and amorphous shell structure as clearly presented in
Figure 1b. The TEM images (Figure 1e) also showed that the
CMC-ZVINs had the smallest average particle diameter of 15
( 4 nm compared to the ZVINs with 32 ( 7 nm and to the
PAA-ZVINs with 173 ( 40 nm as an average particle diameter.
These measurements were in agreement with those found
in the literature. For instance, Sun et al. (27) used the same
of approximately 60.2 nm, whereas He et al. (22) reported
diameter of 4.3 nm. When using poly(acrylic acid) to prepare
measuring approximately 100 nm.
ZVINs were 42.6, 11.3, and 5.9 m2
, respectively. These
experimental surface areas were compared to the theoretical
values calculated using eq 1 (28) (24.0, 51.3, and 4.4 m2
for ZVINs, CMC-ZVINs, and PAA-ZVINs, respectively).
specific surface area )
where F and d are the particle density (7.8 × 106 g m-3) and
diameter (m), respectively.
The observed difference between the calculated and
measured areas may be caused by the density difference
(27). In fact, the surfaces of those different types of nano-
particles differed whereby iron was largely present as iron
hydroxides with the ZVINs, and it was surrounded by
polymers in the two other cases coating the nanoparticles
with a thick ﬁlm and thus decreasing the value of the speciﬁc
Kinetics of RDX Degradation with ZVINs. Since the
physicochemical properties of RDX indicate that it has an
rapidly transform RDX and promote its degradation are of
great importance. In the present study, ZVINs (3 g L-1
completely degraded 82 µmol L-1
of RDX in ﬁve minutes
under both aerobic (98.3%) and anaerobic (100%) conditions.
However, when reducing the amount of ZVINs to 0.3 g L-1
VOL. 42, NO. 12, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 4365
less than 5% of RDX degraded under aerobic conditions, but
more than 75% of the nitramine degraded under anaerobic
conditions in one hour. Hundal et al. (29) reported the
complete transformation of RDX (144 µmol L-1
) with micro
ZVI (10 g L-1
) in 96 h, but Wanaratna et al. (13) reported that
50 µmol L-1
of RDX can be degraded using micro ZVI in less
than 10 min at pH 3.5 by applying an excess amount of ZVI
(32 g L-1
). In the present study, the rapid removal of RDX
with ZVINs was attributed to the high reactivity of the nano
metal (30–32) due to the small particle size (32 nm) offering
a large surface area (42.6 m2
) to facilitate the reaction.
The slow-down of RDX degradation in the presence of air
was attributed to the possible corrosion of the surface of Fe
due to its reaction withy oxygen (33).
The kinetics of RDX (82 µmol L-1
) degradation was then
followed in anoxic batch experiments using 0.3 g L-1
three types of ZVINs (nonstabilized ZVINs, and stabilized
CMC-ZVINs and PAA-ZVINs). The comparison of the reac-
tivity was based on the same amount of nano metal. Within
one hour, more than 75% of RDX was degraded using the
three types of nanoparticles (Figure 2), with CMC-ZVINs
showing the highest degradation percentage. The latter was
very reactive and 6 min were sufﬁcient to degrade 100% of
Assuming that RDX degradation followed a second order
reaction rate with respect to RDX and iron concentrations
(13), and by maintaining the change in the iron concentration
insigniﬁcant compared to the change in RDX concentration,
FIGURE 1. TEM micrographs of the (a) nonstabilized ZVINs and (b) its enlargement; (c) CMC-ZVINs; and (d) PAA-ZVINs.; (e)
probability density function of the particle size distribution of the iron nanoparticles (2 corresponds to the CMC-ZVINs (n ) 100), 0
to the ZVINs (n ) 100), and b to PAA-ZVINs (n ) 45)).
4366 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 12, 2008
a pseudoﬁrst order constant k1 was obtained. The reaction
constants (Supporting Information Table S-1) were deter-
) as well as the corresponding BET surface area-
normalized rate constants (h-1
L). The results indicated
). The obtained values fall within the range of
those found in the literature. The k1 constant values obtained
by Wanaratna et al. (13) varied between 0.095 min-1
when ZVI powder was used to remediate RDX-
contaminated water. Oh et al. (8) estimated the k1 constant
at 0.016 min-1
(value close to the one obtained in the present
study) when following the degradation of RDX using iron
having 25.8 m2
of surface area per liter of solution.
The high reactivity of the CMC-ZVINs has been observed
by He et al. (22) who reported that the stabilized nano reagent
can degrade trichloroethylene 17 times faster than the
nonstabilized ZVINs. This high reactivity of the CMC-ZVINs
could be explained by the higher dispersion of the nano-
particles caused by the negatively charged carboxylic groups
that inhibit aggregation and thus reduce the adhesion
coefﬁcient between the nanoparticles (21). The reactivity
of these particles since different ratios of iron to boron were
used during the syntheses. Indeed, it has been speculated in
several studies that boron may be responsible for the unique
reactivity of ZVINs (prepared using borohydride reducing
agent) when compared to nano iron synthesized by the gas-
phase reduction of iron oxides (34, 35). However, since in
the present case the reactivity was compared for the same
amount of nano metal, the effect of boron on the RDX
degradation could not be deﬁnitively determined.
Products and Degradation Pathways. Figure 3 represents
RDX degradation with the simultaneous appearance of the
ring cleavage products (MEDINA, HCHO, NO2
- N2O, NH4
NH2NH2, and N2). The degradation of RDX was also ac-
companied by the formation of the nitroso derivatives (MNX,
DNX, and TNX) (Supporting Information Table S-2A). Most
of the detected products have been observed during the RDX
degradation with micro ZVI (8, 14). However, in the present
study several new products were detected giving new insights
into the initial steps involved in the degradation pathways
of RDX (discussed below).
At the end of the reaction, which lasted 4 h, most of RDX
, and N2 as the main N-containing products and
HCHO as the main C-containing product. In all 2.86 HCHO
molecules were produced per one RDX molecule cleaved,
accounting for more than 95.6% of the total carbon in RDX
after cleavage (Supporting Information Table S-2B). In the
case of nitrogen-containing degradation products, 1.44
and N2 were produced, accounting for more than 79% of the
total nitrogen of RDX after cleavage (Supporting Information
Table S-2B). The presence of the stabilizer did not seem to
drastically affect product distribution. As shown in Tables
S-2 and S-3 RDX degradation using the three types of iron
But the nitroso intermediates seemed to disappear faster in
the presence of CMC and PAA.
The identity of nitrogen as an RDX degradation product
was conﬁrmed using the ring-labeled [15
N]-RDX and GC/MS
analysis. We detected N2 with a molecular mass ion at both
28 Da (14
N) and 29 Da (15
N), conﬁrming the formation
of the gas (29 Da) from the original NsNO2 group in RDX
and from further reduction of nitrite following initial deni-
tration. When either NO2
- or N2O was allowed to come in
contact with ZVINs we detected N2 and NH4
+. Nitrous oxide
is a decomposing product of MEDINA in water (36) but it
could also arise from the reduction of NO2
- by ZVINs (data
not shown). Comparatively, NH4
+ was weakly degraded into
N2 and was probably adsorbed on the surface of the
nanoparticles. The iron-aided NO2
- reduction into N2 has
already been reported by Huang et al. (37). The present
experimental ﬁndings mimic the generally known denitri-
FIGURE 2. Time course of RDX (0.82 µmol L-1
expressed in percentage using the three types of iron
nanoparticles. (O corresponds to the CMC-ZVINs, 9 to the
ZVINs, and 4 to PAA-ZVINs). The concentration of iron
nanoparticles was 0.3 g L-1. The standard deviations were
within 5% of the corresponding values.
FIGURE 3. Time course of RDX degradation (82 µmol L-1
ZVINs (0.3 g L-1
) showing the formation of (a) formaldehyde,
nitrous oxide, and MEDINA; (b) ammonium, nitrogen, and nitrite.
The standard deviations were within 7% of the corresponding
values, except for nitrogen where the standard deviation was
within 15% of the value.
VOL. 42, NO. 12, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 4367
ﬁcation process in an anoxic environment or in the presence
of speciﬁc kind of anaerobic bacteria (38).
Hydrazine (NH2NH2) was also detected as has been the
case when HMX was treated with ZVI (26). As it is toxic, we
conducted experiments to determine its origin in the
degradation process and its eventual fate. We found that
NH2NH2 was a transient species which was transformed
further to give NH4
+. After nine days, almost 90% of the initial
amount of hydrazine disappeared (Figure S-1). When TNX
was treated with ZVINs under the same conditions used for
RDX, hydrazine was also detected, suggesting that NH2NH2
might have originated from the NsNO functional group of
TNX formed during RDX reductive transformation (Sup-
porting Information Table S-4). The hydrazine derivative was
detected at a retention time of 15 min with a m/z [M+H]+
of 241 Da, but when the 15
N-labeled RDX (or [15
used the product showed a m/z [M+H]+
of 242 Da,
representing an increase of one Da due to the introduction
of one 15
N atom (the aza nitrogen) (Supporting Information
treatment of RDX with ZVINs (Figure 4a). To conﬁrm the
origin of its formation we treated TNX with the nano metal
under the same conditions and found appreciable amounts
of NO being formed that did not persist indeﬁnitely (Figure
4a). The formation of NO from TNX was consistent with the
observation of the novel intermediate II with [M - H]-
144 Da, representing an empirical formula of C3H7N5O2
(Figure 4b). When ring labeled [15
N-TNX] was used, the [M
was detected at 147 Da, representing an increase of
3 Da corresponding to the three 15
N aza labeled N in the
original nitramine (Figure 4c). We tentatively identiﬁed the
initial TNX degradation intermediate as 1,3-dinitroso-5-
hydro-1,3,5-triazacyclohexane (Figures 4b and c). The ex-
pected denitrohydrogenated product of RDX (I) (Figure 5)
was not detected. Presumably the latter was less stable than
II under these reducing conditions. For example, Bonner et
al. (39) reported that intermediate I was unstable and
decomposed into MEDINA.
Likewise when MNX was treated with the nano metal we
observed nitrite, indicating initial denitration, and traces of
NO possibly from the denitrosation of its reduced TNX
product (Figure 4a). Denitration of MNX was supported by
the detection of another new intermediate with [M - H]-
the ring-labeled [15
N]-MNX was used the [M - H]-
detected at m/z 121 Da representing an increase of 2 Da,
FIGURE 4. (a) Nitric oxide (NO) production during TNX, MNX, and RDX (80 µmol L-1
) degradation with ZVINs (0.3 g L-1
); (b) ES(-)
ion mass spectrum of denitrosed hydrogenated compound (II) from TNX; (c) ES(-) ion mass spectrum of denitrosed hydrogenated
compound (II) from [15
4368 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 12, 2008
indicating the involvement of the two aza nitrogens in the
formation of CH4N4O3. We tentatively identiﬁed the inter-
mediate as N-nitroso-methylenenitramine (ONNHCH2-
NHNO2) (III). Compound III is the equivalent of MEDINA
formed following denitration of RDX (Figure 5). We did not
observe MEDINA when MNX was treated with ZVINs,
suggesting that NO originated from its reduced product TNX.
Supporting Information Table S-4 summarizes the product
distribution observed from MNX and TNX treatment with
ZVINs (Figure 5).
Experimental evidence gathered thus far on products
distribution, stoichiometry, and time courses indicate that
RDX degraded via two initial routes. The ﬁrst route involved
initial denitration of RDX giving the suspected unstable
in water to produce MEDINA (Figure 5, path a). The second
route involved the stepwise reduction of the NsNO2 func-
tional groups to give MNX, DNX, and TNX. Likewise MNX
would undergo either denitration prior to ring cleavage or
reduction to eventually give TNX which underwent denit-
rosation (cleavage of NsNO bond) followed by ring cleavage
(Figure 5, path b).
Environmental Signiﬁcance. The use of CMC as stabiliz-
ers for ZVINs, which kept the metal well dispersed in water,
The use of surfactants in many industrial remediation
technologies often enhances the remediation process by
increasing mobility and solubility in water of insoluble or
sparingly soluble contaminants that, in turn, improves their
mass removal and the overall process performance. Also the
such as formaldehyde (biodegradable), nitrous oxide, am-
monia, and nitrogen. Although the three nitroso products
MNX, DNX, and TNX were also detected as RDX products
none of these hazardous chemicals persisted indeﬁnitely
rather they all degraded further to produce HCHO and
hydrazine, the latter degraded to ammonia. These experi-
mental ﬁndings can constitute the basis for the development
of in situ remediation technologies for contaminated sites.
Understanding the dynamics and pathways of RDX degra-
dation would help optimizing the in situ remediation of water
contaminated with explosives including groundwater and
We thank Mr. Dashan Wang from the ICPET for the
transmission electron microscope images. We also thank Dr.
Fanny Monteil-Rivera for helpful discussions and Louise
Paquet and Stephane Deschamps for conducting the analy-
ses. Financial support was provided by DRDC, Valcartier,
Supporting Information Available
Experimental section (ZVI nanoparticles preparation and
modiﬁcation), Figure S-1 and Tables S-1, S-2, S-3 and S-4 as
mentioned in the text. This material is available free of charge
via the Internet at http://pubs.acs.org.
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