Stress-induced chemical detection using flexible metal-organic frameworks.

Abstract

In this work we demonstrate the concept of stress-induced chemical detection using metalorganic frameworks (MOFs) by integrating a thin film of the MOF HKUST-1 with a microcantilever surface. The results show that the energy of molecular adsorption, which causes slight distortions in the MOF crystal structure, can be efficiently converted to mechanical energy to create a highly responsive, reversible, and selective sensor. This sensor responds to water, methanol, and ethanol vapors, but yields no response to either N 2 or O 2. The magnitude of the signal, which is measured by a built-in piezoresistor, is correlated with the concentration and can be fitted to a Langmuir isotherm. Furthermore, we show that the hydration state of the MOF layer can be used to impart selectivity to CO 2. We also report the first use of surface-enhanced Raman spectroscopy to characterize the structure of a MOF film. We conclude that the synthetic versatility of these nanoporous materials holds great promise for creating recognition chemistries to enable selective detection of a wide range of analytes. A force field model is described that successfully predicts changes in MOF properties and the uptake of gases. This model is used to predict adsorption isotherms for a number of representative compounds, including explosives, nerve agents, volatile organic compounds, and polyaromatic hydrocarbons. The results show that, as a result of relatively large heats of adsorption (> 20 kcal mol-1) in most cases, we expect an onset of adsorption by MOF as low as 10-6 kPa, suggesting the potential to detect compounds such as RDX at levels as low as 10 ppb at atmospheric pressure.

Photoluminescent Porous Modular Lanthanide–Vanadium–Organic Frameworks

“…[1] The seemingly endless combination of various metal centres with multipodal organic ligands results in the formation of fascinating architectures, which may lead to applications of industrial interest. Examples of the applications of functional MOFs encompass sensors (for solvents, [2] pH or gases [3] ), gas storage, [4] batteries [5] and magnetic [6] and photoluminescent [7] materials. The design of MOF structures is currently based on typical bottom-up synthetic approaches that use the concept of rigid building blocks (secondary building units -SBUs).…”

Chemical structure, network topology, and porosity effects on the mechanical properties of Zeolitic Imidazolate Frameworks

“…This is especially important for averting excessive structural distortion and framework collapse that can permanently impair their sorption properties. Another example lies in the construction of sensing devices using MOF-type materials (12), whereby a sufficiently high elastic modulus (stiffness) is a prerequisite to induce high responsiveness, in addition to the need for minimizing elastic hysteresis.…”

Metal–organic framework growth at functional interfaces: thin films and composites for diverse applications

“…52 Using a 15 MOF thin film deposited onto an AFM cantilever however, small guest-dependent changes in lattice dimensions arising from molecular adsorption can be probed directly by measuring mechanical stress induced at the interface. 53 Allendorf et al have deposited 100 nm thick films of HKUST- 20 1 on modified piezoresistant microcantilever surfaces using both LbL and single step approaches. Guest-dependent changes in the HKUST-1 lattice were measured for both the hydrated and dehydrated MOF, the latter accessed in -situ by applying a DC voltage across the piezoresistor of the cantilever.…”

“…9) but does not elicit a response to gases such as N 2 , O 2 and CO 2 . 53 On the other hand the sensor does respond to CO 2 when the MOF is in its dehydrated state (Fig. 9, inset), likely arising from strong interactions between the 30 analyte (CO 2 ) and the open metal sites of the framework.…”

“…For LSPR very small changes in refractive index 10 (RI) are measured allowing changes in deposited film thickness, density fluctuations and molecular adsorption processes to be monitored, whereas coupling of surface plasmons with vibronic oscillations can enhance otherwise weak Raman signals by up to 14 orders of magnitude in SERS. Both methods have previously 15 been used, respectively, to monitor LbL growth of MOF thin films on SAMs 38 , and to study the structure of such films after loading with Ag nps 53 when insufficient material prohibits the use of diffraction methods. 30 LSPR spectroscopy is most widely used for the detection of biomolecular species, where large changes in RI observed upon surface adsorption are more easily discerned than those of small (e.g.…”