Degradation of Hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) Using

May 14, 2008 - 2459 Blvd Pie IX, Canada G0A 1R0, and Biotechnology. Research ... study describes degradation of RDX with zerovalent iron nanoparticles...
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Environ. Sci. Technol. 2008, 42, 4364–4370

Degradation of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) Using Zerovalent Iron Nanoparticles GHINWA NAJA,‡ ANNAMARIA HALASZ,‡ SONIA THIBOUTOT,† GUY AMPLEMAN,† 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 (hexahydro1-nitroso-,3,5-dinitro-1,3,5-triazine),DNX(hexahydro-1,3-dinitroso5-nitro-1,3,5-triazine), TNX (hexahydro-1,3,5-trinitroso-1,3,5triazine). 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-triazacyclohexane. However, we were unable to detect the equivalent denitrohydrogenated product of RDX and MNX degradation. Finally, during MNX degradation we detected a new intermediate identified as N-nitroso-methylenenitramine (ONNHCH2NHNO2), the equivalent of methylenedinitramine formed upon denitration 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).

Introduction The extensive use of explosives such as hexahydro-1,3,5trinitro-1,3,5-triazine (RDX) has led to widespread contamination of soil and water (1, 2). RDX is known to be toxic to various aquatic and terrestrial organisms (3), thus necessitating its removal from polluted environments. Recently our group has conducted several studies to elucidate the * Corresponding author phone: +1-514-496 6267; fax +1-514-496 6265; e-mail address: [email protected]. ‡ Biotechnology Research Institute. † Defence Research Establishment. 4364

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degradation pathways of RDX under various abiotic and biotic 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 biodegradation 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 conditions (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 nanoparticles (ZVINs) capable of generating intermediates in sufficient concentrations to allow investigation of their decomposition 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 environmental 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 reactivity 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 carboxymethyl cellulose. 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 distribution 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 nanoparticles, we thus investigated their reaction under the same conditions to gain further insight into the degradation pathway(s) of RDX.

Experimental Section 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 [15N]-RDX (98%) were obtained from Defence Research and Development Canada (Valcartier, QC). 10.1021/es7028153 CCC: $40.75

 2008 American Chemical Society

Published on Web 05/14/2008

Hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) (98%), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX) (56%), ring-labeled [15N]-MNX, ring-labeled [15N]-TNX, methylenedinitramine (MEDINA) and 4-nitro-2,4-diazabutanal (NDAB) 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(OsCH2sCOO-)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 carboxymethyl cellulose modified zerovalent iron nanoparticles (CMCZVINs) 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 Information. Physical Characterization. Transmission electron microscope (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 methanol and sonicated vigorously. Twenty µL of each sample 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 Services, 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 [15N]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 [15N]MNX and [15N]-TNX were used under the same conditions to help identify the degradation products. To determine the eventual fate of nitrogen-containing RDX degradation products such as NO2-, NH4+, N2O, MEDINA, and NH2NH2 we

allowed ZVINs (0.3 g L-1) to react with 20 mg L-1 of each chemical separately. 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, and hydrogen by a gas chromatograph (Hewlett-Packard 6890 GC, Mississauga, ON) connected to either a TCD or an ECD detector (23). Aliquots of the aqueous phase of the reaction mixtures were filtered through 0.22 µm filters (Millipore) prior to analyses of RDX, intermediates and final products. The nitroso derivatives MNX, DNX, and TNX and the ring cleavage products methylenedinitramine (MEDINA) and 4-nitro-2,4diazabutanal (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 ions were determined by spectroscopic methods as described 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 in shape and formed aggregates. The ZVINs featured a distinct 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 procedure forming iron nanoparticles with a median diameter of approximately 60.2 nm, whereas He et al. (22) reported CMC stabilized Fe-Pd nanoparticles with the average particle diameter of 4.3 nm. When using poly(acrylic acid) to prepare iron nanoparticles, Schrick et al. (21) observed iron aggregates measuring approximately 100 nm. The specific surface areas of ZVINs, CMC-ZVINs, and PAAZVINs were 42.6, 11.3, and 5.9 m2 g-1, respectively. These experimental surface areas were compared to the theoretical values calculated using eq 1 (28) (24.0, 51.3, and 4.4 m2 g-1 for ZVINs, CMC-ZVINs, and PAA-ZVINs, respectively). specific surface area )

6 Fd

(1)

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 nanoparticles 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 surface area. Kinetics of RDX Degradation with ZVINs. Since the physicochemical properties of RDX indicate that it has an important potential for leaching, remediation treatments that 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

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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)). 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 g-1) 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). 4366

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The kinetics of RDX (82 µmol L-1) degradation was then followed in anoxic batch experiments using 0.3 g L-1 of the three types of ZVINs (nonstabilized ZVINs, and stabilized CMC-ZVINs and PAA-ZVINs). The comparison of the reactivity 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 RDX. 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 2. Time course of RDX (0.82 µmol L-1) degradation 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. a pseudofirst order constant k1 was obtained. The reaction constants (Supporting Information Table S-1) were determined (min-1) as well as the corresponding BET surface areanormalized rate constants (h-1 m-2 L). The results indicated that the CMC-ZVINs application produced the highest kinetic constant (0.816 min-1), almost 40 times higher than the ZVINs (0.019 min-1). 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 and 0.976 min-1 when ZVI powder was used to remediate RDXcontaminated 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 nanoparticles caused by the negatively charged carboxylic groups that inhibit aggregation and thus reduce the adhesion coefficient between the nanoparticles (21). The reactivity difference could also be partly attributed to the boron content 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 gasphase 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 accompanied 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 detected intermediates transformed further to eventually give N2O, NH4+, and N2 as the main N-containing products and

FIGURE 3. Time course of RDX degradation (82 µmol L-1) using 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. 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 molecules of N2O and 1.25 molecules of NO2-, NH2NH2, NH4+, 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 nanoparticles led to the same intermediate and final products. 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 [15N]-RDX and GC/MS analysis. We detected N2 with a molecular mass ion at both 28 Da (14N14N) and 29 Da (15N14N), confirming the formation of the gas (29 Da) from the original NsNO2 group in RDX and from further reduction of nitrite following initial denitration. 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 denitriVOL. 42, NO. 12, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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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 [15N]-TNX. 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 (Supporting 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 15N-labeled RDX (or [15N]-TNX) was used the product showed a m/z [M+H]+ of 242 Da, representing an increase of one Da due to the introduction of one 15N atom (the aza nitrogen) (Supporting Information Figure S-1). Furthermore we detected traces of nitric oxide (NO) during 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 4368

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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]- at 144 Da, representing an empirical formula of C3H7N5O2 (Figure 4b). When ring labeled [15N-TNX] was used, the [M - H]- was detected at 147 Da, representing an increase of 3 Da corresponding to the three 15N aza labeled N in the original nitramine (Figure 4c). We tentatively identified the initial TNX degradation intermediate as 1,3-dinitroso-5hydro-1,3,5-triazacyclohexane (Figures 4b and c). The expected 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]- at m/z 119 Da matching an empirical formula of CH4N4O3. When the ring-labeled [15N]-MNX was used the [M - H]- was detected at m/z 121 Da representing an increase of 2 Da,

FIGURE 5. Proposed pathway for degradation of RDX in the presence of ZVINs: (a) Denitration route; (b) Nitro reduction to nitroso followed by denitrosation of TNX formed. indicating the involvement of the two aza nitrogens in the formation of CH4N4O3. We tentatively identified the intermediate as N-nitroso-methylenenitramine (ONNHCH2NHNO2) (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 denitrohydrogenated intermediate I which would decompose in water to produce MEDINA (Figure 5, path a). The second route involved the stepwise reduction of the NsNO2 functional 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 denitrosation (cleavage of NsNO bond) followed by ring cleavage (Figure 5, path b). Environmental Significance. The use of CMC as stabilizers for ZVINs, which kept the metal well dispersed in water, degraded RDX forty times faster than the nonstabilized ZVINs. 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 present reaction system degraded RDX to obnoxious products such as formaldehyde (biodegradable), nitrous oxide, ammonia, 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 experimental findings can constitute the basis for the development of in situ remediation technologies for contaminated sites. Understanding the dynamics and pathways of RDX degradation would help optimizing the in situ remediation of water

contaminated with explosives including groundwater and marine sediment.

Acknowledgments 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 analyses. Financial support was provided by DRDC, Valcartier, Canada, and Office of Naval Research (ONR) U.S. Navy (Award N000140610251).

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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