Environ. Sci. Technol. 2009, 43, 1553–1558
Degradation of Sulfur Mustard and Sarin over Hardened Cement Paste HAIRONG TANG, ZHENXING CHENG,* LIMING ZHOU, GUOMIN ZUO, AND LINGCE KONG The No.3 Department, Institute of Chemical Defense, P.O. Box 1048, Beijing 102205, China
Received June 22, 2008. Revised manuscript received December 29, 2008. Accepted December 29, 2008.
A study has been done to examine the degradation of sulfur mustard (HD) and sarin (GB) over hardened cement paste (HCP). The HCP behaved as a typical base like CaO and Ca(OH)2. The base sites over the HCP were not entirely poisoned by H2O and CO2 in air, and about 0.47 mmol/g base sites could still be evidenced by chemisorption of CO2. A large amount of water irreversibly adsorbed by HCP was experimentally demonstrated. Ten kinds of products through hydrolysis SN1 (C-Cl), elimination E1 or E2 (C-Cl, C-H), and addition-elimination (A-E) under the action of base sites and water from the degradation of HD over HCP were detected and identified by GC-FPD, GC-MS, and NMR approaches. Their distribution and kinds varied with time of degradation and water content. Both degradation activity and distribution of products from HD were strongly determined by the strength and density of base sites and the water content in HCP. The molecules of GB adsorbed over HCP in comparison with HD could be more quickly and completely degraded into hydrolyzed products such as isopropyl methylphosphonic acid and methylphosphonic acid by adsorbed water, in comparison with HD.
Introduction As the “king” of the chemical warfare agents (CWAs), the blister agent sulfur mustard (HD) is a persistent agent and difficult to decontaminate. Sarin (GB) is a highly toxic nerve agent and harmful to personnel even at extremely low concentrations in air. The degradation of HD and GB over environmental matrices (soil, hardened cement paste (HCP), asphalt, water, and etc.) may influence whether the contaminated area needs to be offered timely and sufficient remediation or more drastic decontamination procedures after an acceptable waiting period when attacked by HD or GB in battlefields, in destruction of CWAs, or following a terrorist attack. Degradation of CWAs over concrete has been studied previously. Groenewold et al. analyzed VX (O-ethyl S-(2(diisopropylamino)ethyl) methyl-phosphonothiolate) on the surface of concrete samples using an ion trap secondary ion mass spectrometer (IT-SIMS) in 2000 (1). In 2001, Wagner and his co-workers performed a study on the sorption and reaction of VX in an aged sample of concrete using 31P NMR (2), and in 2004, they examined the effect of droplet size on the degradation rate of VX in fresh concrete using the same method (3). In 1998, an extraction and GC method for analyzing the breakdown products of sulfur mustard on soil * Corresponding author phone: +86-10-69760164; fax: +86-1069760161; e-mail:
[email protected]. 10.1021/es801556r CCC: $40.75
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2009 American Chemical Society
and concrete was developed by Tomkins et al. (4). In 2001, Davis et al. reported the results of extracting sulfur mustard from concrete (5). We had studied the degradation of HD in HCP in 2006, and only 1,4-dithiane and sesquimustard were found at that time (6). Thereafter, Wagner et al. studied the persistence and reactivity of sulfur mustard on concrete quantitatively by both extraction and SSMAS (solid-state magic-angle spinning) techniques (7). Our previous study (8) revealed that HD could be degraded through hydrolysis SN1 (C-Cl), elimination E1 or E2 (C-Cl, C-H), and addition-elimination (A-E) under the action of acid-base sites and water (see the Supporting Information) over typical oxides. In its broadest sense, the word cement denotes any kind of adhesive. In building and civil engineering, it denotes a substance that can be used to bind together sand and broken stone, or other forms of aggregate, into a solid mass. This includes such materials as HCP, hardened cement mortars (HCM), and concrete. The main products of cement hydration are Ca(OH)2 and some colloidal products such as tobermorite gel and various Al3+-, Fe3+- and SO42--containing phases (9). CO2 (NH3) TPD (temperature programmed desorption) is a widely used method to characterize the base (acid) sites over the oxides, where CO2 (NH3) was used as probe molecule for base (acid) sites over solid surface (10, 11). So far no complete knowledge of how HD and GB degrade over concrete has been provided. The present work concerned characterization of acid-base properties for the HCP, investigation of the degradation of HD and GB over the HCP, analysis of their products, and the study of the effect of water content in HCP on degradation of HD and GB. The experimental data reported here would contribute to clarifying the mechanism for degradation of HD and GB over concrete and is beneficial to the establishment of remediation procedures for contaminated areas after a waiting period when attacked with HD or GB.
Experimental Section Materials. The HCP specimen was prepared by mixing 42.5marked portland cement (60-67% CaO, 17-25% SiO2, 3-8% Al2O3, 0.5-6.0% Fe2O3) with water (3:1), the specimen was conserved by adding water for 3 months and then crushed into grains of a size about 10-20 mesh or into powders of less than 200 mesh. Both HD and GB have a purity >90% by GC-MS analyses. Characterization of HCP. The methods for TPD-MS in He and TPD of NH3 or CO2 in our experiments have been described previously (8). BET (Brunauer Emmett and Teller) surface area and pore volume were measured for the samples of HCP by N2 adsorption (-195 °C) with an Autosorb-1C (American Quantachrome Co.). Both physisorption and chemisorption of CO2 at a given temperature were also carried out with Autosorb1C after the samples of HCP had been pretreated in vacuum or helium at a given temperature (12). The experiments for sorption of H2O, HD, and GB vapors were carried out with static vacuum adsorption equipment, which was selfconstructed in our laboratory. The methods have been described in a previous paper (8). The pKa of HCP was determined by Hammett indicators titration as outlined by refs 13-18. The zero point of charge (ZPC) for HCP was determined as according to ref 19 and had been described in the previous paper (8). Adsorption of HD or GB Vapor over HCP. The experiments for sorption of HD or GB vapor were carried out on a static vacuum adsorption apparatus, where the vapor VOL. 43, NO. 5, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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pressure and the adsorption amount can be qualitatively measured. Upon degassing the system down to 5 × 10-5 Torr by diffusion pumps, HD or GB vapor was introduced into the adsorption tube and conserved for 2 h. Reaction of HD or GB over HCP. The degradation of HD or GB adsorbed from vapor over the surface of HCP was realized in air at 25 °C. In the vacuum sorption apparatus, about 3.0 g HCP was partially saturated with HD or GB vapor, and in turn, this sample was divided into several portions. Each portion was then stored in a closed 100 mL conical flask, where the amount of possibly desorbed HD or GB was negligible in comparison with that of adsorbed over HCP. HD and GB as well as its degraded products were extracted with anhydrous acetonitrile and ethanol, respectively. The extractions were carried out in a conical flask with 50 mL of solvent introduced and then extracted under ultrasonic conditions for 30 min. Three replicates were made for each sample in the extractions. The residue of GB in ethanol was quantitatively measured by a colorimetric method based on a Schoenemann reaction (20), while HD was measured by GC-FPD. The degradation of HD or GB droplets over HCP was evaluated in a similar way. The method was to properly mix 1.6 g of HCP (3.8 × 10-3 1.3 × 10-5 6.7 × 10-6
5.08 × 105 2.19 × 106 9.82 × 105 8.29 × 105 5.93 × 106 2.56 × 106 1.92 × 104 1.47 × 104 5.52 × 103 3.43 × 103 1.8 × 103 1.2 × 103 HZSM-5 > SiO2. Its kinetic parameters could be calculated to be k ) 1.3 × 10-4 s-1 and t1/2 ) 5.5 × 103 s for the degradation of 13 mg/g GB adsorbed over HCP in 20-30% RH air at 25 °C. The degradation rate constant was found to increase with augmentation of ambient temperatures from 2 to 40 °C. Moreover, the estimated activation energy, ∆Ea ) 33.0 kJ/ mol, was smaller than that of 43.9 kJ/mol for hydrolysis of
FIGURE 3. GC-FPD chromatograms for the residue of HD droplets over the HCP (top) without any pretreatment and (bottom) with pretreatment at 800 °C for (a) 0 days, (b) 0.5 days, (c) 3 days, and (d) 14 days at 25 °C. VOL. 43, NO. 5, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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GB dissolved in water. Again, the degradation of GB adsorbed over HCP could strongly be accelerated by air humidity, as shown in Table 3, and in 100% RH air the adsorbed GB could be completely degraded within 0.5 h. HCP has been shown by the above data to be able to quickly degrade GB adsorbed from vapor. Analysis of Products. The hydrolysis product of isopropyl methylphosphonic acid (IMPA, [M - H]- ) 137) and methylphosphonic acid (MPA, [M - H]- ) 95) could be identified using LC-MS for GB adsorbed on HCP. The 31P, 1 H, and 13C NMR spectra also demonstrated the production of the IMPA and MPA. Therefore, one could come to the conclusion that GB had certainly been hydrolyzed into IMPA or MPA. Moreover, GB droplets could be completely degraded over HCP, but it could not happen with HZSM-5 and SiO2. This would demonstrate that surface basicity was able to accelerate degradation of GB over oxide.
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Acknowledgments This work is financially supported by the National Key FundamentalResearchProgramofChina(Grantno.2006CB300401). Prof. Ming Zhang is thanked for valuable discussion.
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Supporting Information Available
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Schemes S1 and S2, Figures S1-S5, and Tables S1 and S2. This information is available free of charge via the Internet at http://pubs.acs.org.
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Literature Cited (1) Groenewold, G. S.; Appelhans, A. D.; Gresham, G. L.; Olson, J. E.; Jeffery, M.; Weibel, M. Characterization of VX on concrete using ion trap secondary ionization mass spectrometry. J. Am. Soc. Mass. Spectrom. 2000, 11, 69–77. (2) Wagner, G. W.; O’Connor, R. J.; Procell, L. R. Preliminary study on the fate of VX in concrete. Langmuir 2001, 17, 4336–4341. (3) Wagner, G. W.; O’Connor, R. J.; Edwards, J. L.; Brevett, C. A. S. Effect of drop size on the degradation of VX in concrete. Langmuir 2004, 20, 7146–7150. (4) Tomkins, B. A.; Sega, G. A.; Macnaughton, S. J. The Quantitation of sulfur mustard by-products, sulfur-containing herbicides, and organophosphonates in soil and concrete. Anal. Lett. 1998, 31, 1603–1622. (5) Davis, W. R.; Jensen, J. G.; McGuire, R. R.; Skoumal, M.; Fagan, M.W. An investigation into chemical warfare agent evaporation
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(17) (18) (19) (20) (21) (22)
from four substrates. AFRL-HE-WP-TR-2001-00882, UNCLASSIFIED Report (AD-B280-381); Airforce Research Laboratory: Wright-Patterson AFB, Dayton, OH, 2001; Appendix E. Tang, H. R.; Cheng, Z. X.; Xu, M; Huang, S. X.; Zhou, L. M. A preliminary study on sorption, diffusion and degradation of mustard (HD) in cement. J. Hazard. Mater. 2006, 128, 227–232. Brevett, C. A.; Sumpter, K. B.; Wagner, G. W.; Rice, J. S. Degradation of the blister agent sulfur mustard, bis(2-chloroethyl) sulfide, on concrete. J. Hazard. Mater. 2007, 140, 353– 360. Tang, H. R.; Cheng, Z. X.; Zhu, H. Y.; Zuo, G. M.; Zhang, M. Effect of acid and base sites on the degradation of sulfur mustard over several typical oxides. Appl. Catal. B: Environ. 2008, 79, 323–333. Taylor, H. F. W. The Chemistry of Cements; Academic Press: New York, 1964; Vol. 1, Chapter 1. Zhang, G.; Hattori, H.; Tanabe, K. Addition of acetone, catalyzed by solid base catalysts: magnesium oxide, calcium oxide, srontium oxide, barium oxide, lanthanum(III) oxide and zirconium oxide. Appl. Catal. 1988, 36, 189–197. Tanabe, K. Solid Acids and Bases, Tokyo, Kodansha; Academic Press: New York, 1970; pp 145-153. Buff, E. J. Autosorb-1 QA manual (05300-109), Rev. B. Quantachrome, FL, 2001; Chemisorption Part. Tanabe, K.; Yamaguchi, T. A novel method for measuring base strength distribution on basic solid catalysts under operating conditions. J. Res. Inst. Catal., Hokkaido Univ. 1964, 11, 179. Take, J.; Kikuchi, N.; Yoneda, Y. Base-strength distribution studies of solid-base surfaces. J. Catal. 1971, 21, 164–170. Tsuchiya, S.; Takase, S.; Imamura, H. Super basicity of rubidium oxide and caesium oxide, and their reaction profiles of isomerization of butanes. Chem. Lett. 1984, 661–664. Walling, C. The acid strength of surfaces. J. Am. Chem. Soc. 1950, 72, 1164–1168. Hammett, L. P. Reaction rates and indicator acidities. Chem. Rev. 1935, 16, 67–79. Hammett, L. P. Physical Organic Chemistry; MaGraw-Hill: New York, 1940; Chapter 9. Stumm, W.; Morgan, J. Aquatic Chemistry, an Introduction Emphasizing Chemical Equilibria in Natural Waters, 2nd ed.; John Wiley & Sons, Inc.: New York, 1981; pp 462. Franke, S. Lehrbuch der Milita¨rchemie, Band 2, Militarverlag der DDR: Berlin, 1977; pp 316-318. Reid, E. Organic Chemistry of Bivalent Sulfur; Chemical Publishing Co.: New York, 1960; Vol. II, Chapter 5. McGuire, R. R.; Haas, J. S.; Eagle, R. J. The decay of chemical weapons agents under environmental conditions. Master UCRLID-114107, 1993.
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