Article pubs.acs.org/IECR
Engineering UiO-66-NH2 for Toxic Gas Removal Gregory W. Peterson,*,† Jared B. DeCoste,‡ Farzin Fatollahi-Fard,§ and David K. Britt§ †
Edgewood Chemical Biological Center, 5183 Blackhawk Road, Aberdeen Proving Ground, Maryland 21010-5424, United States Leidos, Inc., P.O. Box 68, Gunpowder, Maryland 21010-0068, United States § The Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States ‡
S Supporting Information *
ABSTRACT: The metal−organic framework UiO-66-NH2 was synthesized in a scaled batch of approximately 100 g. The material was then pressed into small pellets at pressures ranging from 5000 to 100000 psi to determine the effects on porosity and crystal structure. Nitrogen isotherm data and powder X-ray diffraction data indicate that the structure remains intact up to 25000 psi, with only a slight decrease in surface area. The structure exhibits significant degradation at pressures above 25000 psi. Subsequently, the powder was pressed at 5000 psi and then crushed and sieved into 20 × 40 mesh granules for evaluation against ammonia and cyanogen chloride in a breakthrough system simulating individual protection filters and respirator cartridges. The MOF showed capacity similar to that of a broad-spectrum carbon for both ammonia and cyanogen chloride; however, the breakthrough times, especially for cyanogen chloride, were dramatically reduced, likely as a result of mass-transfer limitations from the completely microporous MOF.
1. INTRODUCTION
hydrogen-bonding sites for NH3 sorption, as well as possible reactive sites for CNCl. Several studies have been conducted on how physical properties and performance are affected by pressurization and/or other methods of forming granules and particles.25−27 We previously investigated the effects of pressure on CuBTC and UiO-66 MOFs at pressures ranging from 1000 to 10000 psi, with results indicating that the UiO-66 material does not show degradation in surface area or performance.28 In this study, we investigated how pressure affects the physical properties and chemical removal performance of UiO-66NH2, with the objective of forming particles for simulated filter breakthrough testing against NH3 and CNCl. UiO-66-NH2 was chosen as a candidate material over UiO-66 because of its increased performance against ammonia (Figure S1, Supporting Information).
The ability to introduce active sites onto sorbents that are capable of reaction with both acidic and basic gases continues to be an area of interest. Specifically, many respirators used by emergency and/or military personnel require broad-spectrum chemical removal because of the wide variety of toxic chemicals used worldwide. The National Institute for Occupational Safety and Health (NIOSH) requires chemical, biological, radiological, and nuclear (CBRN) filters to provide protection against a wide variety of gases, including ammonia (NH3) and cyanogen chloride (CNCl).1 These two chemicals require different chemistries for removal. NH3 is typically removed through interaction with acidic sites or hydrogen-bonding sites,2,3 whereas CNCl requires hydrolysis and/or interaction with functional groups capable of reacting with the cyanide moiety.4,5 Several studies on activated, impregnated carbons have demonstrated the ability to create conflicting chemistries on a single sorbent.6,7 Yet, most of these efforts focus on postsynthetic impregnation techniques, creating a mobile active phase that shows poor aging characteristics as a result of deleterious interactions within the substrate. Over the past decade, metal−organic frameworks (MOFs) have been intensely studied for a variety of potential applications, including gas storage,8,9 catalysis,10,11 separations,12−14 and toxic gas removal.15−17 The ability to incorporate multiple functionalities18−20 into the backbone of MOFs is a major advantage over traditional activated, impregnated carbons. The UiO-66 series of MOFs are of particular interest because of their stability toward moisture and acids.21−23 UiO-66-NH2, which contains amine pendant groups on benzene dicarboxylate linkers, is capable of postsynthetic modification, allowing for further tailoring of functionality.24 However, even without modification, the amine groups provide © 2013 American Chemical Society
2. EXPERIMENTAL SECTION UiO-66-NH2 was synthesized by modifying established methods for large scale.29 Zirconium(IV) chloride (12 g) and water (3 mL) were added to 800 mL of N,N-dimethylformamide (DMF) and stirred until fully dissolved. 2-Aminoterephthalic acid (9.4 g) was added to 400 mL of DMF and stirred until fully dissolved. The solutions were mixed in a BüchiGlasUster Ecoclave 075 batch reactor with 1.6 L glass reactor vessel. The reactor was stirred at 500 RPM and held at 120 °C for 24 h. The pale yellow solid was isolated by filtration. Up to seven batches were mixed for subsequent steps. Samples were purified by Soxhlet extraction with methanol for 24 h. Excess solvent was removed by heating in air at 85 °C. Received: Revised: Accepted: Published: 701
October 8, 2013 December 12, 2013 December 18, 2013 December 18, 2013 dx.doi.org/10.1021/ie403366d | Ind. Eng. Chem. Res. 2014, 53, 701−707
Industrial & Engineering Chemistry Research
Article
at a rate necessary to achieve the desired challenge concentration. Water vapor was delivered to the system through a saturator cell within a water bath. The challenge was dosed to a packed bed until saturation (effluent = feed), after which the materials were purged with air to evaluate desorption. Effluent concentrations were monitored using Hewlett-Packard (HP) 5890 gas chromatographs equipped with a flame ionization detector (CNCl) and a photoionization detector (NH3). Microbreakthrough graphs are plotted on a mass-weighted basis to account for differences in density. Loadings were calculated in moles per kilogram by integrating the breakthrough curves to saturation. The standard system error is approximately 10%. Subsequent large-scale (multigram) NH3 and CNCl breakthrough testing was conducted using a push−pull-vented breakthrough system. Each gas was delivered directly from a cylinder through a mass flow controller and then mixed with a diluent air stream at a rate necessary to achieve the required challenge concentration. The diluent stream flow and humidity were controlled using a Miller-Nelson HCS-401 system. Test tubes were packed using a storm-filling method31 to a depth of 1.0 cm, simulating full-scale individual protection filters. The NH3 feed and effluent concentrations were monitored using a Miran 1A infrared detector and an Innova 1314 Photoacoustics Multigas monitor, respectively. The CNCl feed and effluent concentrations were measured using an HP5890 gas chromatograph equipped with a flame ionization detector. The breakthrough time was calculated when the effluent concentrations reached 17 and 8 mg/m3, corresponding to military toxic exposure limits for NH3 and CNCl, respectively.
Removal of solvent from the pores was achieved by evacuating the samples to
