Metal organic frameworks (MOFs) are hybrid crystalline materials, exhibiting high specific surface areas, controllable pore sizes and surface chemistry. These properties have made MOFs attractive for a wide range of applications including gas separation, gas storage, sensing, drug delivery and catalysis. This review focuses on recent progress in the application of MOF materials as catalysts for CO2 conversion through chemical fixation, photocatalysis and electrocatalysis. In particular, this review discusses the co-relationship between the physicochemical properties of MOF materials including their catalytic performance as well as their stability and recyclability under different reaction conditions, relevant to CO2 conversion. Current modification techniques for improving MOF performance are highlighted along with the recent understanding of their electronic properties. The limitations of MOF based catalysts are also discussed and potential routes for improvement are suggested.

Metal organic framework based catalysts for CO2 conversion

Surface acoustic wave (SAW) carbon dioxide and methane sensors were developed by integrating the nanoporous zeolitic imidazole framework-8 (ZIF-8) metal organic framework (MOF) with SAW delay lines for near room temperature applications. The SAW reflective delay lines with operating frequency 436 MHz were custom fabricated on Y-Z LiNbO_3, coated with 100 to 300 nm thick ZIF-8, and tested for various gases in N_2 environment at room temperature and one atmospheric pressure. The resulting sensors were selective to CO_2 and CH_4 against other gases such as CO, H_2, and air with a relatively large response to CO_2 as compared to CH_4 with full reversibility and repeatability. The MOF was also applied to bulk wave-based quartz crystal (AT-cut, resonance frequency 9 MHz) microbalance (QCM) devices and tested for various concentrations of CO_2 and CH_4. The sensors showed linear responses to the gas concentrations which was used to evaluate the sensor sensitivities. For 200 nm thick films, the SAW sensitivity to CO_2 and CH_4 were 0.394 deg/vol-\% (1.44 ppm/vol-\%) and 0.021 deg/vol-\% (0.08 ppm/vol-\%), respectively against the QCM sensitivities 2.18 Hz/vol-\% (0.24 ppm/vol-\%) and 0.09 Hz/vol-\% (0.01 ppm/vol-\%), respectively to the gases. The SAW sensor sensitivities were also evaluated for various thicknesses of the films and were found to increase with the thickness in the studied range. In addition, the MOF-coated SAW delay line had a good response in wireless mode, demonstrating its potential to operate remotely for detection of the gases at atmosphere and emission sites across the energy infrastructure.

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Zeolitic imidazole framework-coated acoustic sensors for room temperature detection of carbon dioxide and methane

The integration of nanoporous materials such as metal organic frameworks (MOFs) with sensitive transducers can result in robust sensing platforms for monitoring gases and chemical vapors for a range of applications. Here, we report on an integration of the zeolitic imidazolate framework - 8 (ZIF-8) MOF with surface acoustic wave (SAW) and thickness shear mode quartz crystal microbalance (QCM) devices to monitor carbon dioxide (CO2) and methane (CH4) under ambient conditions. The MOF was directly coated on the Y-Z LiNbO3 SAW delay lines (operating frequency, f0 = 436 MHz) and AT-cut quartz TSM resonators (resonant frequency, f0 = 9 MHz) and the devices were tested for various gases in N2 under ambient conditions. The devices were able to detect the changes in CO2 or CH4 concentrations with relatively higher sensitivity to CO2, which was due to its higher adsorption potential and heavier molecular weight. The sensors showed full reversibility and repeatability which were attributed to the physisorption of the gases into the MOF and high stability of the devices. Both types of sensors showed linear responses relative to changes in the binary gas compositions thereby allowing to construct calibration curves which correlated well with the expected mass changes in the sorbent layer based on mixed-gas gravimetric adsorption isotherms measured on bulk samples. For 200 nm thick films, the SAW sensitivities to CO2 and CH4 were 1.44 × 10-6/vol% and 8 × 10-8/vol%, respectively, against the QCM sensitivities 0.24 × 10-6/vol% and 1 × 10-8/vol%, respectively, which were evaluated as the fractional change in the signal. The SAW sensors were also evaluated for 100 nm-300 nm thick films, the sensitivities of which were found to increase with the thickness due to the increased number of pores for the adsorption of a larger amount of gases. In addition, the MOF-coated SAW delay lines had a good response in wireless mode, demonstrating their potential to operate remotely for the detection of the gases at emission sites across the energy infrastructure.

/pdf/zeolitic-imidazolate-framework-coated-acoustic-sensors-for-d6b7ly6wab.pdf

Mohd Shariff Az

Papers

Zeolite Imidazole Frameworks Membranes for CO2/CH4 Separation from Natural Gas: A Review