Continuous MOF Membrane-Based Sensors via Functionalization of Interdigitated Electrodes

Three M-MOF-74 (M = Co, Mg, Ni) metal-organic framework (MOF) thin film membranes have been synthesized through a sensor functionalization method for the direct electrical detection of NO2. The two-step surface functionalization procedure on the glass/Pt interdigitated electrodes resulted in a terminal carboxylate group, with both steps confirmed through infrared spectroscopic analysis. This surface functionalization allowed the MOF materials to grow largely in a uniform manner over the surface of the electrode forming a thin film membrane over the Pt sensing electrodes. The growth of each membrane was confirmed through scanning electron microscopy (SEM) and X-ray diffraction analysis. The Ni and Mg MOFs grew as a continuous but non-defect free membrane with overlapping polycrystallites across the glass surface, whereas the Co-MOF-74 grew discontinuously. To demonstrate the use of these MOF membranes as an NO2 gas sensor, Ni-MOF-74 was chosen as it was consistently fabricated as the best thin and homogenous membrane, as confirmed by SEM. The membrane was exposed to 5 ppm NO2 and the impedance magnitude was observed to decrease 123× in 4 h, with a larger change in impedance and a faster response than the bulk material. Importantly, the use of these membranes as a sensor for NO2 does not require them to be defect-free, but solely continuous and overlapping growth.

Polyvinylidene Difluoride: A Universal Binder for Preparation of Solid Phase Microextraction Devices

<p>The communication describes the application of a fluorocarbon-based polymer as a high performance binder component for coatings suitable for a variety of solid phase microextraction (SPME) configurations. SPME devices are characterized by their ability to perform physicochemical extraction of chemical compounds from a given sample, rending said chemical compounds suitable for instrumental determinations; fundamentally speaking, physiochemical extraction is accomplished by thermodynamic equilibrium driven by diffusion and partitioning of chemical compounds. A polyvinylidene difluoride (PVDF) polymer was used to immobilize various sorbent particles on different supports to create different formats of SPME, namely fiber, thin-film membrane, and CBS devices. In this report, PVDF-based coatings are introduced as universal SPME coatings that are amenable to both gas chromatography (GC) and liquid chromatography (LC) while also improving the physical stability of the resulting device, in addition to eliminating the need for highly toxic reagents associated with the preparation of fully fluorinated based coatings previously reported in the literature. Additional incorporation of other polymers to increase coating porosity as well as the adhesion of PVDF on metal surfaces is also described.</p>

Polyvinylidene Difluoride: A Universal Binder for Preparation of Solid Phase Microextraction Devices

<p>The communication describes the application of a fluorocarbon-based polymer as a high performance binder component for coatings suitable for a variety of solid phase microextraction (SPME) configurations. SPME devices are characterized by their ability to perform physicochemical extraction of chemical compounds from a given sample, rending said chemical compounds suitable for instrumental determinations; fundamentally speaking, physiochemical extraction is accomplished by thermodynamic equilibrium driven by diffusion and partitioning of chemical compounds. A polyvinylidene difluoride (PVDF) polymer was used to immobilize various sorbent particles on different supports to create different formats of SPME, namely fiber, thin-film membrane, and CBS devices. In this report, PVDF-based coatings are introduced as universal SPME coatings that are amenable to both gas chromatography (GC) and liquid chromatography (LC) while also improving the physical stability of the resulting device, in addition to eliminating the need for highly toxic reagents associated with the preparation of fully fluorinated based coatings previously reported in the literature. Additional incorporation of other polymers to increase coating porosity as well as the adhesion of PVDF on metal surfaces is also described.</p>

Efficient high-pass filtering with practical, high-yield X-ray transmission mirror optics

Although the concept, first demonstration, and potential applications of X-ray transmission mirrors (XTMs) were initially described over 30 years ago, only a few implementations exist in the literature. This is attributed to the unsolved challenge of a thick frame supporting a thin, reflecting membrane which does not itself block the transmitted beam. Here, we introduce a novel approach to solve this problem by employing silicon microfabrication. A robust XTM frame has been fabricated by using a novel two-step etch process, which secures the thin-film membrane without blocking the transmitted beam. Specifically, we have fabricated delicate XTM optics with 90% yield, which consist of 280-nm-thick low-stress silicon nitride membrane windows that are 1.5 mm wide and 125 mm long on silicon substrates. The XTM optics have been demonstrated to be a more efficient high-pass X-ray filter; for example, when configured for 40% transmission of 11.3 keV photons, we measure the reduction of 8.4 keV photons by a factor of 56.