In the temperature range of 300-500 degrees C, solid nanocrystalline oxides react nearly stoichiometrically with numerous halocarbons, sulfur, and organophosphorus compounds. In some cases, the reaction efficiencies can be improved by the presence of a small amount of transition-metal oxide as catalyst; for example, Fe2O3 on CaO and mobile intermediate species such as FeCl3 or Fe(SO3)x are important in the catalytic process. Herein, a series of environmentally problematic compounds are discussed, including CCl4, COS, CS2, C2Cl4, CHCl3, CH2Cl2, CH3Cl, and (CH3O)2P(O)CH3. Nanocrystals of CaO coated with a thin layer of Fe2O3 (or other transition metals) =[Fe2O3]CaO, or intimately mixed =Fe2O3/CaO were compared with pure CaO. It was found that (a) the presence of a small amount of surface [Fe2O3] or other transition-metal oxide can have a marked effect on the destructive adsorption activity, (b) for some reagents, such as CCl4, C2Cl4, SO2 and others, the nanocrystalline CaO can react in stoichiometric amounts, especially if a transition-metal oxide catalyst is present, (c) although the reaction with dimethylmethylphosphonate is surface-limited, the nanocrystalline calcium oxide performed well and in high capacity, (d) nanocrystalline calcium oxide exhibits near stoichiometric activitywith several interesting sulfur-containing compounds, such as COS and CS2, (e) unfortunately, most fluorocarbons were not destructively adsorbed at 500 degrees C under the conditions employed; however, some of these can be effectively mineralized over the calcium oxide at higher temperatures. These compounds include C2F6, C3F6, C2ClF3, and CHF3, and (f) upon reaction, surface areas decreased considerably, from about 100 to about 10 m2/g. The results of these experiments further demonstrate that, with the proper choice of catalytic material, some solid-gas reactions can be engineered to be rapid and essentially stoichiometric.

Nanocrystals of magnesium oxide react with organophosphorus compounds at room temperature by dissociative chemisorption, which we term "destructive adsorption". This process involves cleavage of P-O and P-F bonds (but not P-C bonds) and immobilization of the resultant molecular fragments. These ultrafine powders have unusual crystalline shapes and possess high surface concentrations of reactive edge/corner and defect sites, and thereby display higher surface reactivity, normalized for surface area, than typical polycrystalline material. This high surface reactivity coupled with high surface area allows their use for effective decontamination of chemical warfare agents and related toxic substances. Herein data is presented for paraoxon, diisopropylfluorophosphate (DFP), and (CH3CH2O)2P(O)CH2-SC6H5 (DEPTMP). Solid-state NMR and IR spectroscopy indicate that all OR and F groups dissociate; this leaves bound -PO4, -F, and -OR groups for paraoxon, DFP, and DEPTMP, respectively. For paraoxon, it was shown that one monolayer reacts. For DEPTMP, the OR groups dissociate, but not the P-CH2SC6H5 group. The nanocrystalline MgO reacts much faster and in higher capacity than typical activated carbon samples, which physisorb but do not destructively adsorb these phosphorous compounds.

Mg oxide nanoparticles are very reactive materials used to mitigate atmospheric pollution and to sequester polluting molecules. Using Fe K-edge XAFS, we have studied the structure of iron oxide-coated MgO nanoparticles before and after reaction with CCl4. Before reaction, the local structure around Fe is totally different from that in iron oxide coatings on SrO and CaO nanoparticles, although these coated materials were prepared in the same way. In SrO and CaO, the iron oxide coating has been shown to be well separated from the bulk of the nanoparticle, whereas in MgO, Fe was found to mix with MgO. After reaction with CCl4, Fe-Cl bonds can be detected when the coated nanoparticle is saturated. Such Fe-Cl EXAFS signals have not been observed in previously studied nanoparticles.

A new family of porous inorganic solids based on nanocrystalline metal oxides is discussed. These materials, made up of 4-7 nm MgO, CaO, Al2O3, ZnO, and others, exhibit unparalleled destructive adsorption properties for acid gases, polar organics, and even chemical/biological warfare agents. These unique sorption properties are due to nanocrystal shape, polar surfaces, and high surface areas. Free-flowing powders or consolidated pellets are effective, and pore structure can be controlled by consolidation pressures. Chemical properties can be adjusted by choice of metal oxide as well as by incorporating other oxides as monolayer films.

Room-temperature reactions of the chemical warfare agents VX, GD, and HD with nanosize CaO (AP-CaO), and HD with commercial CaO have been studied using solid-state MAS NMR. VX and GD hydrolyze to yield surface-bound complexes of nontoxic ethyl methylphosphonate and pinacolyl methylphosphonate, respectively. The kinetics are characterized by an initial fast reaction followed by a slower, diffusion-limited reaction. Similar behavior is observed for HD on either dried or hydrated AP-CaO and CaO, On partially hydrated AP-CaO (but not CaO), a rather fast steady-state elimination of HCl occurs after an induction period. This behavior is attributed to acid-catalyzed surface reconstruction (to regenerate fresh surface) and the formation of CaCl2 which is known to be more reactive than CaO. The product distribution for HD is about 80% divinyl sulfide and 20% thiodiglycol and/or sulfonium ions, which apparently reside as surface alkoxides. Such kinetic behavior was not evident for the common mustard simulant 2-chloroethyl ethyl sulfide (CEES) on partially hydrated AP-CaO, which exhibited only the typical fast/diffusion-limited reaction.

Sr and Ca oxide nanoparticles are very reactive materials used to mitigate atmospheric pollution and to sequester polluting molecules. We have studied the structure of SrO nanoparticles, using Sr K-edge and Fe K-edge XAFS, that were prepared with various reactivities, with or without a Fe2O3 coating, and before and after reaction with CCl4 or SO2. For CCl4, the polluting fraction of the reagent is totally absorbed in the bulk particle. For SO2, the results show a total reaction for the Aerogel Preparation (AP) compound. For the coated particles before reaction, the iron oxide has a very disordered structure, and it is mixed with small metallic iron clusters for Conventional Preparation (CP) compounds.

The Sr and Fe sites structural environment in uncoated SrO and Fe2O3-coated SrO nanoparticles used as destructive adsorbents in the CCl4 decomposition have been investigated for the first time by extended X-ray absorption fine structure (EXAFS). It was found that the local structure of the Sr ions depends on the synthetic procedure used to prepare the nanoparticles. The short-range order exhibited by the sol-gel prepared SrO particles (AP-SrO) and the conventionally prepared (CP-SrO) particles is not as high as that of the commercial strontium oxide. The Sr local structure observed for the non-Fe2O3-coated samples after CCl4 decomposition shows that the Sr environment is only made of Cl ions for the AP sample and made of both Cl and O ions for the CP sample, indicating that the AP-SrO sample was more reactive with CCl4. The enhancement of the reactivity toward the CCl4 decomposition by the iron oxide coating was evidenced from the EXAFS investigation of both the Sr and the Fe local structure after CCl4 decomposition on Fe2O3-coated CP-SrO and Fe2O3-coated AP-SrO. It was found that the SrO inner layers are involved in the reaction since only Cl ions were detected as Sr neighbors and that no Cl ions were detected in the iron environment of this sample, suggesting that the iron oxide coating the sample surface is continuously renewed during the reaction.

Core–shell nanoparticles of metal oxides ([Fe2O3]MgO, [Fe2O3]CaO, [V2O3]MgO, and the other first-row transition metal shell materials coated on nanoparticles of MgO or CaO) have been studied as destructive adsorbents for CCl4, CHCl=CCl2, C6H4Cl2, CH3P(O)(OCH3)2, and SO2. A catalytic effect due to the transition metal shell material has been observed, where solid state ion–ion exchange takes place, thus allowing penetration into the MgO or CaO particles and thereby regenerating the transition metal oxide for additional catalytic action. Due to this catalytic effect, the destructive adsorption reaction became nearly stoichiometric, and therefore much higher capacities for destruction/immobilization of the adsorbate under study were realized. For example, the reaction CCl4+[V2O5]MgO → CO2+[V2O5]MgCl2is greatly enhanced by the presence of the V2O5, and VCl5or VCl3appear to be intermediates in the process. The catalytic effects are proposed to be due to the intermediacy of transition metal chlorides, phosphates, or sulfites, which are mobile and seek out reactive sites on the MgO or CaO nanoparticles where ion–ion exchange can most readily take place, thereby regenerating the transition metal oxide catalyst.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTEnhancing Effect of Fe2O3 on the Ability of Nanocrystalline Calcium Oxide to Adsorb SO2Shawn Decker and Kenneth J. KlabundeView Author Information Department of Chemistry, Kansas State University Manhattan, Kansas 66506 Cite this: J. Am. Chem. Soc. 1996, 118, 49, 12465–12466Publication Date (Web):December 11, 1996Publication History Received11 July 1996Published online11 December 1996Published inissue 1 January 1996https://pubs.acs.org/doi/10.1021/ja962371ehttps://doi.org/10.1021/ja962371erapid-communicationACS PublicationsCopyright © 1996 American Chemical SocietyRequest reuse permissionsArticle Views780Altmetric-Citations59LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Calcium,Metal oxide nanoparticles,Nanoparticles,Oxides,Reactivity Get e-Alerts