Decontamination of Adsorbed Chemical Warfare Agents on Activated

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Decontamination of Adsorbed Chemical Warfare Agents on Activated Carbon Using Hydrogen Peroxide Solutions Ruth Osovsky,*,† Doron Kaplan,† Ido Nir,† Hadar Rotter,† Shmuel Elisha,† and Ishay Columbus*,‡ †

Department of Physical Chemistry and ‡Department of Organic Chemistry, Israel Institute for Biological Research, P. O. Box 19, Ness Ziona 74100, Israel S Supporting Information *

ABSTRACT: Mild treatment with hydrogen peroxide solutions (3−30%) efficiently decomposes adsorbed chemical warfare agents (CWAs) on microporous activated carbons used in protective garments and air filters. Better than 95% decomposition of adsorbed sulfur mustard (HD), sarin, and VX was achieved at ambient temperatures within 1−24 h, depending on the H2O2 concentration. HD was oxidized to the nontoxic HD-sulfoxide. The nerve agents were perhydrolyzed to the respective nontoxic methylphosphonic acids. The relative rapidity of the oxidation and perhydrolysis under these conditions is attributed to the microenvironment of the micropores. Apparently, the reactions are favored due to basic sites on the carbon surface. Our findings suggest a potential environmentally friendly route for decontamination of adsorbed CWAs, using H2O2 without the need of cosolvents or activators.

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INTRODUCTION A 2-fold challenge is encountered in the development of techniques for decontamination of equipment exposed to chemical warfare agents (CWAs): (1) the technique should be environmentally friendly, noncorrosive, and nonhazardous; (2) it should be universal and applicable for the major types of CWAs (nerve agents and mustard vesicants).1 A particular example of this complexity is the decontamination of chemical protective equipment, including gas-mask filters and activated carbon (AC)-based protective overgarments. Adsorbed CWAs on AC surfaces that are exposed to ambient temperature and humidity are stable for weeks to months. Consequently, contaminated protective equipment may pose a long-term environmental problem.2−4 Recently, our group has demonstrated the potential of hydrothermal treatment at elevated temperatures (>100 °C) to accelerate the degradation of adsorbed CWAs on AC.5,6 However, although such treatment is environmentally friendly, it can only be accomplished with complex and heavy apparatus. Alternatives which are based on decontamination at moderate temperatures, using water and mild water-soluble reagents, may become advantageous from the aspects of simplicity of equipment and portability. However, neat CWAs, especially the notoriously persistent vesicant sulfur mustard (HD) and the nerve agent VX (O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate), are difficult to decompose with water alone. The hydrolysis of HD via nucleophilic substitution (SN1) at ambient temperature gives the nontoxic thiodiglycol (TDG), and is fast (t1/2 ∼ 4 min) for solvated HD,7 but is © 2014 American Chemical Society

overall ineffective because of the poor solubility of HD in water. The hydrolysis of VX in neutral or basic solutions forms considerable amounts (depending on the pH) of the toxic S-(2(diisopropylaminoethyl) methylphosphonothioic acid (desethyl-VX).8 Past studies have shown that hydrogen peroxide (H2O2), alone or in the presence of auxiliary mild reagents, might be an appropriate decontaminant for CWA in the liquid or adsorbed phase.9−12 A mixture of aqueous H2O2 with an organic cosolvent rapidly dissolved HD and selectively oxidized it to the nonvesicant sulfoxide (HD-SO), with a half-life of 42 min. Further oxidation of HD-SO to the vesicant sulfone (HD-SO2) was reported to be slower by orders of magnitude (Scheme 1). Boosting the aqueous H2O2 with carbonate/bicarbonate to form monoperoxycarbonate (HCO4−) shortened the half-life to less than 5 min.9 Hydrogen peroxide is known to decompose the nerve agent sarin (isopropyl methylphosphonofluoridate) to the nontoxic product isopropyl methylphosphonic acid (IMPA) via generation of the nucleophile peroxyanion (OOH−, Scheme 1). In a neutral H2O2 solution, sarin exhibits an initial half-life of 67 h, apparently reacting with the background OOH−. When the pH drops, the rate of the reaction slows down, whereas the addition of a weak base (e.g., bicarbonate) accelerates the reaction and rapidly brings it to Received: Revised: Accepted: Published: 10912

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Scheme 1

completion.9 Perhydrolysis of VX yields exclusively the nontoxic product ethyl methylphosphonic acid (EMPA) and not the toxic desethyl-VX (Scheme 1).9,13 Like for sarin, this reaction is incomplete in neutral to acidic solutions, even if H2O2 is in large excess, but the addition of a weak base can drive it to completion within a few minutes by providing the proper buffering capacity to maintain the OOH− level.9 The relative rapidity of decomposition of these CWAs by H2O2 has motivated recent research efforts that yielded formulations based on this oxidant, mostly mixed with other active ingredients.14,15 Sandia investigators reported a foam that employs an alkyl ammonium/bis-ammonium based surfactant that releases about 8% H2O2.14 Livermore researchers developed a gel that contains potassium peroxymonosulfate and fumed silica.15 Edgewood investigators developed the Decon Green formulation that incorporates H2O2 with K2CO3, K2MoO4, propylene carbonate, and a surfactant.16 The socalled modified VHP technique, which utilizes vaporized H2O2 and a low concentration of ammonia, was suggested for decontamination of CWAs in the gas phase.10 However, data on the effectiveness of the reported decontamination methods against adsorbed CWAs on ACs are still lacking. In this work, we show the feasibility of decontamination of CWA-loaded ACs in protective garments and filters at moderate temperatures (up to 50 °C), using aqueous solutions containing hydrogen peroxide as the sole constituent. The effects of the peroxide concentration and reaction temperature on the degradation rate were studied by solid-state MAS NMR spectroscopy. The later technique is well established for

monitoring decontamination processes in solid matrices,17,18 including ACs.3−6 We demonstrate that efficient destruction of adsorbed HD, sarin, and VX on AC with hydrogen peroxide can be achieved without additional cosolvents or activators.

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EXPERIMENTAL SECTION Activated Carbons. Highly microporous ACs (surface area > 1000 m2/g) were used throughout. Most experiments were performed on a 0.5 mm diameter, bead-form AC (0.63 cm3/g micropore volume) from a SARATOGA permeable protective garment (Blücher, Duesseldorf, Germany), labeled here S-AC. Some experiments were performed on a ∼0.4 mm diameter bead-form adsorbent, Ambersorb 572 (Rohm and Haas, Philadelphia, PA, USA; 0.41 cm3/g micropore volume), labeled A-AC, and PICACTIF-TA (PICA, Saint Maurice, France), a granular, ∼1.3 mm diameter nutshell-based AC (0.47 cm3/g micropore volume), labeled P-AC, and on two subfractions of P-AC, median diameters 0.15 and 1.1 mm, respectively, obtained by sieving. Prior to contamination with CWAs, the ACs were dried at 120 °C for 2−3 h. Chemicals. Caution. These experiments should only be performed by trained personnel using applicable safety procedures. H2O2 at 30 vol %, ammonia, sodium bicarbonate, sodium carbonate, and isopropanol were obtained from SigmaAldrich. Aqueous H2O2 solutions (3−20%) were freshly prepared before use. Nanopure water (Barnstead) was used throughout. HD* (13C-enriched HD), sarin, and VX were locally obtained. HD* was synthesized with 50% labeling of each ethylenic moiety to eliminate 13C−13C coupling effects 10913

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Table 1. Rates of Hydrolysis (Half-Life/Percent Decomposition) of Adsorbed HD, Sarin, and VX on S-AC in Watera 50 °C

room temperature agent

dry carbonb

humidified carbonb,c

immersed carbon

immersed carbon

HD sarin VX

no decomp. after 60 days no decomp. after 180 days t1/2 ∼ 14 days

t1/2 ∼ 45 days t1/2 ∼ 4 days t1/2 ∼ 14 days

t1/2 ∼ 4 daysd ∼55% decomp. after 2 days ∼10% decomp. after 2 days

t1/2 ∼ 16 hd ∼70% decomp. after 1 day ∼25% decomp. after 2 days

a

Detailed MAS NMR spectra are given in the Supporting Information, Figures S1−S5. bPrevious work.6 cPrehumidified AC (relative humidity (RH) = 75%, RT). dCorresponding MAS NMR spectra are given in Figure 1.

water-immersed S-AC at RT or 50 °C was checked. The obtained degradation rates, as half-life or extent of decomposition, are given in Table 1. For reference, previous data on the stability of adsorbed CWAs on the dry and prehumidified AC are included. The results demonstrate the high stability of adsorbed CWAs on AC. Even on the water-immersed carbon the degradation rates are relatively slow, of the order of days. For example, the half-lifetime of adsorbed HD (Figure 1) on the AC is about 16

from the MAS NMR spectra. Authentic HD-SO was synthesized according to the literature.19 CWA Loading. For loading from the liquid phase, the contaminant (1.6 μL of HD*, 2 μL of sarin or VX) were added via syringe onto samples of ∼40 mg AC (5 wt % CWA loading). Loading from the vapor phase (5 wt %) was performed as described in our previous work.4 These loading levels are much lower than the adsorption capacity of the ACs. Carbon pH Determination. The basicity of the ACs surface was evaluated from pH measurements according to the mass titration technique.20 Weighted amounts of carbon (in 0.5 g increments) were sequentially added to a given volume (20 cm3) of aqueous 0.1 N NaCl, until the pH of the solution reached a plateau. The pH values of P-AC, A-AC, and S-AC were 9.8, 10.2, and 11.8, respectively. Decontamination Experiments. A sample of the contaminated carbon was suspended in 4 mL of the premixed decontamination solution in a closed vial. The suspension was stirred, for varying time durations, at either room temperature (RT, 25 ± 2 °C) or 50 °C. The reaction was stopped by filtration of the suspension through a Buchner funnel and rinsing the AC residue with water, using suction. In reference experiments, the AC was immersed in pure water instead of the reagent. For MAS NMR analysis, the AC was packed into a 4 mm diameter ZrO2 MAS NMR rotor and the rotor was capped with a KEL-F cap. MAS NMR Measurements. MAS NMR spectroscopy was used to estimate the amount of residual CWA on the AC and identify the degradation products. 31P and 13C MAS NMR spectra were obtained at frequencies of 202 and 125 MHz, respectively, on a 11.7 T (500 MHz) Avance spectrometer (Bruker, Bremen, Germany), equipped with a 4 mm standard CP-MAS probe, using direct excitation (no cross-polarization). The typical spinning rate was 5 kHz. 31P and 13C chemical shifts were referenced to external trimethyl phosphate and CDCl3, respectively, as 0 ppm. The pulse delay was 2 s, which is considered sufficient for relaxation in organophosphorous esters on solid matrices. Typically, 200−1000 transients were accumulated per spectrum. For verification of the products identity, some samples were extracted with CDCl3 (40 mg AC/ mL), and the filtered extract was analyzed by means of solution NMR. Degradation Rate Estimation. To facilitate comparison of degradation rates, half-life (t1/2) values were estimated by assuming a pseudo-first-order reaction. This approach provides a basis for comparison among rates occurring at different treatment conditions. To estimate the extent of degradation, a Lorenzian function was fitted to the NMR spectral peaks of the initial CWAs and reaction products, using deconvolution.

Figure 1. Selected 13C MAS NMR spectra of adsorbed HD on S-AC immersed in water after contamination at (a) 25 and (b) 50 °C. The assignment of the adsorbed products was done according to our previous work.5

h even at 50 °C. In general, the rate of degradation of sarin is faster than that of HD and VX. The slowest degradation rate of the adsorbed CWAs in water was found to be ∼10% decomposition after 2 days (VX at RT). In all cases, water promoted the hydrolysis of the CWAs to the nontoxic products: TDG from HD and IMPA and EMPA from sarin and VX, respectively. TDG is partially oxidized to TDGsulfoxide (TDG-SO, Figure 1b).5 Note that the observed reaction products as well as the CWAs themselves are all in the adsorbed state, as shown by the chemical shifts and line widths in the MAS NMR spectra. Typically, adsorption on a microporous AC shifts the MAS NMR resonances by about 5−10 ppm upfield and broadens the lines up to a δν1/2 of 300− 1000 Hz.3−5 Interestingly, the hydrolysis of adsorbed HD was much faster (∼10 fold) on the water-immersed AC than on the humidified AC. This result may arise from the low solubility of HD in water. Apparently, the bulk of water serves to better solubilize the adsorbed agent in the micropores, as explained later in this work. A much weaker difference in the hydrolysis

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RESULTS AND DISCUSSION Decontamination by Hydrolysis in Water and Weakly Basic Solutions. Initially, the stability of adsorbed CWAs on 10914

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HD (>87%) decomposed within a day. A near-complete decontamination of HD (>97%) was accomplished within 2 days. During this period, there was no evidence of further oxidation of HD-SO to HD-SO2. This was also verified by solvent extraction of the reacted AC sample and solution 13C NMR analysis of the extract. A spectrum of the CDCl3 extract from a sample subjected to a mild treatment (3% H2O2 for 16 h) is shown in Figure 3a. It displays the characteristic signals of residual HD and HD-SO with no evidence of HD-SO2. By contrast, following a more aggressive treatment (30% H2O2, 16 h) the toxic HD-SO2 was observed, although as a minor product (Figure 3b). The identities of the HD-SO and HD-SO2 were verified by comparing spectra of CDCl3 extracts of the AC to the spectra of the authentic chemicals. Thus, treatment of adsorbed HD on AC with 3−30% H2O2 solutions yields mainly HD-SO via oxidation. Mild heating of the AC with 3% H2O2 solution to 50 °C accelerated the decomposition of adsorbed HD. At 50 °C (Figure 2b), from 5 h treatment on, there is no change in the spectra. The half-life at 50 °C was shorter by a factor of 4 than the half-life at RT (Table 2). This effect appears to be related to the activation energy of the reaction rather than to any specific effect, for example solvation of the adsorbed HD. Higher concentrations of H2O2 yielded the same HD oxidation products as the 3% solution. The degradation rate became higher as the H2O2 concentration increased from 3% to 20% (Figure 4 and Table 2). A near-complete decomposition (>95%) was achieved within 8−9 h with 10% H2O2 and within ∼4 h with 20% H2O2 solution. The degradation curve due to the 30% H2O2 treatment was almost the same as that due to the 20% treatment (Figure 4), indicating that the decomposition rate has reached a maximum. The preceding results were obtained from liquid-contaminated carbons. Another conceivable contamination scenario is adsorption of the CWA from the vapor phase. The appropriate 13 C MAS NMR spectra are displayed in Figure 5a. A comparison of the peak positions and line widths in these spectra to those of the spectra in Figure 2a indicates that practically all of the adsorbed HD resides within the micropores irrespective of the phase (vapor/liquid) from which it was loaded. The degradation profiles are displayed in Figure 5b. It can be seen that the rate of degradation when the CWA had been adsorbed from the vapor phase is roughly twice as fast as when adsorption had occurred from the liquid phase. This reaction rate difference is perhaps related to a difference in the uniformity of surface coverage by the CWA between loadings from the two phases. Loading from the liquid phase probably spreads the CWA over the carbon granules less evenly than loading from vapor. Thus, in the former case, some of the granules may be saturated, with less available reaction sites for the CWA than in the latter. Nerve Agents Decomposition. The 31P MAS NMR spectra of adsorbed sarin and VX on S-AC after exposure to 3% H2O2 solution are shown in Figures 6a and 7a, respectively. Both agents decompose to yield nontoxic acids. In Figure 7a, the higher signal-to-noise (S/N) ratio of EMPA vs that of VX is perhaps due to the better water solubility of the former, and consequently a weaker attraction to the solid phase. No evidence for the formation of the toxic desethyl-VX was observed. The obtained reaction products of sarin and VX are identical to the corresponding hydrolysis products. However, the decomposition rates obtained with H2O2 were much faster (by about 2 orders of magnitude) than those obtained with

rate between the humidified and water-immersed AC was observed for the nerve agents (Table 1). It is known that G-type nerve agents, such as sarin, decompose in the presence of a dilute base alone, for example, ammonia-based basic household cleaners.21 Hydrolytic decontamination of adsorbed CWAs by immersion and stirring of the AC in mild basic solutions, namely, 10 vol % NaHCO3 (pH ∼ 8.5), 10 vol % Na2CO3 (pH ∼ 10.1), and 1 vol % ammonia (pH = 11.25), was attempted. The MAS NMR spectra (not shown) proved that adsorbed sarin is only partially hydrolyzed after a 2 h treatment with NaHCO3, although it is completely hydrolyzed within 2 h by either ammonia or Na2CO3. Furthermore, adsorbed VX and HD were stable to basic hydrolysis in either of the above solutions. Thus, mildly basic hydrolysis is ineffective as a general purpose decontamination method for the adsorbed CWAs on the AC. Decontamination with Hydrogen Peroxide. In view of the relatively slow degradation of adsorbed CWAs in water, we examined the possibility to decontaminate the AC with hydrogen peroxide. The precontaminated S-AC was immersed in H2O2 solutions (3−30 vol %) at RT or 50 °C, and MAS NMR spectra were acquired as a function of time, up to 2 days. HD Decomposition. 13C MAS NMR spectra of adsorbed HD on S-AC and the products of its reaction with 3% H2O2 are shown in Figure 2. The HD resonances vanish with time,

Figure 2. 13C MAS NMR spectra of HD on S-AC undergoing oxidation in 3 vol % H2O2 at (a) RT and (b) 50 °C. An example of the deconvolution matching is presented (as the green traces for the individual peaks and the red trace for their calculated superposition) in the spectrum at 8 h.

concurrent with the appearance of resonances due to selective oxidation to HD-sulfoxide (HD-SO). The chemical shifts of HD-SO in organic solvents, for example CDCl3, are 36 and 55 ppm (Figure S7 in the Supporting Information). Again, the upfield chemical shifts (9−10 ppm) and the broad lines of the signals in Figure 2 correspond to adsorbed HD-SO in the micropores. To extract the relative intensities of the overlapping signals of HD and HD-SO, deconvolution matching was performed (an example is shown in the 8 h RT spectrum, Figure 2a). Interestingly, the hydrolysis product TDG is absent, probably because the hydrolysis of the adsorbed HD is slower than the oxidation. At room temperature, most of the adsorbed 10915

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Figure 3. 13C NMR spectra of CDCl3 extract of adsorbed HD after (a) 3% H2O2 treatment for 16 h and (b) 30% H2O2 treatment for 16 h. The minor byproduct is probably (ClCH2CH2SOCH2CH2)2O.

Table 2. Degradation Rates of Adsorbed HD, Sarin, and VX on S-AC under 0−20 vol % H2O2 Treatment at RT and 50 °Ca 50 °C

room temperature

a

agent

water

3% H2O2

10% H2O2

20% H2O2

water

3% H2O2

HD sarin VX

t1/2 ∼ 4 days ∼55% decomp. after 2 days ∼10% decomp. after 2 days

t1/2 ∼ 8 h t1/2 ∼ 1.7 h t1/2 ∼ 4.7 h

t1/2 ∼ 2.1 h t1/2 ∼ 0.7 h t1/2 ∼ 1.3 h

t1/2 ∼ 0.9 h t1/2 ∼ 0.3 h t1/2 ∼ 1.1 h

t1/2 ∼ 16 h ∼70% decomp. after 1 day ∼25% decomp. after 2 days

t1/2 ∼ 1.8 h t1/2 ∼ 0.5 h t1/2 ∼ 1.5 h

Detailed MAS NMR spectra and degradation curves are given in the Supporting Information, Figures S8−S13.

Figure 4. Decay of adsorbed HD on S-AC against time, in aqueous 0− 30 vol % H2O2 solutions at RT.

Figure 5. Oxidation of adsorbed HD vapor on S-AC in 3 vol % H2O2 at RT: (a) 13C MAS NMR spectra; (b) adsorbed vapor vs. adsorbed liquid degradation rates.

H2O (see Table 1). With 3% H2O2, near-complete decomposition was achieved within about 5 h for sarin, and within 24 h for VX. We conclude that the dominant degradation reaction of adsorbed sarin and VX in H2O2 is perhydrolysis rather than hydrolysis (see Scheme 1). Higher concentrations of H2O2 (10−30%) accelerated the degradation of sarin and VX (Figure 6b and Figure 7b, respectively). At concentrations of 10% (for sarin) and 20% (for VX) the degradation rate nearly reached its maximal level. About 95% of adsorbed VX decomposed within less than 5 h. CWA Decomposition on Other Activated Carbons. To examine the efficiency of perhydrolytic decontamination for other CWA-contaminated ACs, we applied the process on two other carbons, the beaded A-AC and the granular P-AC. These adsorbents are primarily designed for vapor filtration and water remediation, respectively. The ACs were contaminated with

liquid sarin as described above and were treated with 3−20% H2O2 solutions. The results are depicted in Figure 8. The same reaction products as those with the S-AC were obtained (Figure S14 in the Supporting Information). Also, the same qualitative dependence of the sarin degradation rate on the H 2O2 concentration was observed in the three adsorbents. At the higher H2O2 concentrations (10−20%), the initial degradation rates (until 50% degradation) were fast (1−3 h) for A-AC and P-AC as well as for S-AC. Toward the end of the decomposition (90−95%), larger differences were observed, the order of the degradation rate being S-AC > A-AC > P-AC. The decrement of the rate in these ACs vs S-AC may be attributed to differences between their micropore volumes and/ or basicity. 10916

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the degradation rates depended on the granule size. These tests were run on subfractions of P-AC, median diameter of 0.15 and 1.1 mm, contaminated with sarin. The degradation profiles (Figure S15 in the Supporting Information) were found to be similar, irrespective of the granule size. This result excludes a significant diffusive restriction in the degradation reactions. Mechanism and Rates. The results of the degradation of adsorbed HD in the presence of hydrogen peroxide indicate that the dominant decomposition reaction is oxidation. The product is the nonvesicant HD-sulfoxide. In contrast to oxidation of the dispersed agent in the aqueous phase, which requires a cosolvent,9 the adsorbed HD on the activated carbon is efficiently decomposed without additional components or activators. The NMR spectral evidence (chemical shifts and line widths of the signals) supports the notion that the reaction occurs within the micropores. Apparently, this microenvironment facilitates the decomposition. On the basis of the same spectral evidence, the reaction product is adsorbed, probably at the vicinity of the decomposition site. Our results indicate that the oxidation rate increases with the H2O2 concentration up to a maximum level at a concentration of 20−30%. Probably, below this level, the concentration of H2O2 within the micropores is rate-determining. This assumption can be illustrated with a crude estimation of the capacity of the micropores to H2O2. For the S-AC, the micropore volume is about 25 μL/(40 mg of sample). After adsorption of the CWA (∼2 μL, 0.0124 mmol), 23 μL remains available for the H2O2 solution. For a 3% solution, 0.7 μL (0.023 mmol) of H2O2 can occupy the micropores. Probably, this small excess (∼2-fold) of H2O2 limits the rate of oxidation of adsorbed HD. For the 10− 20% H2O2 solutions, the excess of H2O2 over HD is higher and the oxidation rate increases accordingly. However, it may be envisaged that accumulation of the adsorbed reaction product in the micropores slows down the oxidation. Thus, it may be possible that, for the 30% H2O2 solution, inhibition by the reaction product balances the promotion of the oxidation such that the rate reaches a plateau. The results of the degradation of adsorbed organophosphorous nerve agents (sarin and VX) in the presence of hydrogen peroxide indicate that the dominant decomposition reaction is perhydrolysis. The products are the nontoxic methylphosphonic acids. A prerequisite for perhydrolysis is adequate concentration of the peroxy ion, OOH−, meaning that the reaction rate is favored at basic pH. Previously, Wagner and Yang added basic ingredients to facilitate the decontamination of nerve agents in solution via perhydrolysis.9 Yet, our results display rapid decomposition of the adsorbed nerve agents on AC in H2O2 without further additives, suggesting the existence of sufficiently basic sites within the micropores. Indeed, the initial pH levels of the examined ACs are basic (9.8−11.8). Similarly to HD degradation, the rate of degradation of adsorbed sarin and VX increased with the H2O2 concentration and reached a plateau at 20−30%. Possibly, analogous to the oxidation of adsorbed HD, accumulation of the various degradation products of the adsorbed nerve agents near the active sites inhibits perhydrolysis. Thus, for the nerve agents as well as for HD, the maximum degradation rate is obtained at H2O2 concentrations of 20−30%. Presumably, at these concentrations, the number of basic sites becomes rate-limiting. According to the literature, it is reasonable to expect that aqueous concentrated hydrogen peroxide will modify the surface composition of the ACs and increase its acidity, concomitantly with its reaction with the adsorbed species. In

Figure 6. (a) 31P MAS NMR spectra of sarin on S-AC undergoing perhydrolysis in 3 vol % H2O2 at RT. (b) Comparison of the degradation curves obtained with 0−30 vol % H2O2.

Figure 7. (a) 31P MAS NMR spectra of VX on S-AC undergoing perhydrolysis in 3 vol % H2O2 at RT. (b) Comparison of the degradation curves obtained with 0−30 vol % H2O2.

Figure 8. Degradation curves obtained for adsorbed sarin on (a) A-AC and (b) P-AC treated with 0−20 vol % H2O2.

In view of size differences between the various ACs examined in this work, pilot experiments were performed to find whether 10917

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Biological Center: Aberdeen Proving Ground, MD, USA, September 2004. (11) Wagner, G. W.; Sorrick, D. C.; Procell, L. R.; Brickhouse, M. D.; McVey, I. F.; Schwartz, L. I. Decontamination of VX, GD and HD on a surface using modified vaporized hydrogen peroxide. Langmuir 2007, 23, 1178−1186. (12) Wagner, G. W.; Procell, L. R.; Sorrick, D. C.; Lawson, G. E.; Wells, C. M.; Reynolds, F. M.; Ringelberg, D. B.; Foley, K. L.; Lumetta, G. J.; Blanchard, D. L., Jr. All-weather hydrogen peroxidebased decontamination of CBRN contaminants. Ind. Eng. Chem. Res. 2010, 49, 3099−3105. (13) Daniel, K. A.; Kopff, L. A.; Patterson, E. V. Computational studies on the solvolysis of the chemical warfare agent VX. J. Phys. Org. Chem. 2008, 21, 321−328. (14) Sandia National Laboratories. Sandia decon formulation for mitigation and decontamination of CBW agents, 2013; http://www. sandia.gov/SandiaDecon/. (15) Raber, E.; McGuire, R. Oxidative decontamination of chemical and biological warfare agents using L-Gel. J. Hazard. Mater. 2002, 93, 339−352. (16) Wagner, G. W.; Procell, L. R.; Henderson, V. D.; Sorrick, D. C.; Yang, Y.-C. Decon green, the environmentally-friendly decontaminant, report document page; U.S. Army Edgewood Chemical Biological Center: Aberdeen Proving Ground, MD, USA, July 2003. (17) Mizrahi, D. M.; Columbus, I. 31P MAS NMR: A useful tool for the evaluation of VX natural weathering on various urban matrixes. Environ. Sci. Technol. 2005, 39, 8931−8935. (18) Mizrahi, D. M.; Goldvaser, M.; Columbus, I. Long term evaluation of the fate of sulfur mustard on dry and humid soils, asphalt, and concrete. Environ. Sci. Technol. 2011, 45, 3466−3472. (19) Popiel, S.; Witkiewicz, Z.; Szewczuka, A. The GC/AED studies on the reactions of sulfur mustard with oxidants. J. Hazard. Mater. 1995, 123B, 94−111. (20) Barton, S. S.; Evans, M. J. B.; Halliop, E.; MacDonald, J. A. F. Acidic and basic sites on the surface of porous carbon. Carbon 1997, 35 (9), 1361−1366. (21) Wagner, G. W. Decontamination of chemical warfare agents using household chemicals. Ind. Eng. Chem. Res. 2011, 50, 12285− 12287.

preliminary experiments, exposure of fresh S-AC to 10% H2O2 for 1−3 h changed its pH to 9−10. Still, it seems that the remaining basic sites in the micropores in the ACs studied in this work maintain a sufficient level of OOH− to drive the decontamination of HD, sarin, and VX to completion within the accuracy of the MAS NMR analysis. Consequently, CWAcontaminated activated carbons can be rapidly and efficiently decontaminated with aqueous H2O2 solutions without any additional cosolvents or activators.

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ASSOCIATED CONTENT

S Supporting Information *

Figures S1−S15, NMR spectra and degradation curves. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*(I.C.) Phone: +97289381453; fax: +97289381548; e-mail: [email protected]. *(R.O.) E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was internally funded by the Israeli Prime Minister’s office. REFERENCES

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dx.doi.org/10.1021/es502981y | Environ. Sci. Technol. 2014, 48, 10912−10918