High-performance NO₂ gas sensors based on vanadium metal organic frameworks (V-MOFs) on flexible graphene electrodes

This research aimed to prepare vanadium metal organic frameworks (V-MOFs) with the organic ligands of terephthalic acid (PTA) and pyromellitic acid (PMA) by a one-step hydrothermal process. Organic ligands were pyrolyzed and the vanadium ion was oxidized after calcination to prepare V-MOF(PTA) and V-MOF(PMA) as NO₂ gas detection materials. The interdigital electrodes were performed by CO₂ laser induced polyimide films with porous graphene for flexible gas sensors. Characteristics of the synthesized material were examined and analyzed, including surface morphology, chemical composition, crystal property, and specific surface area. Furthermore, the sensor characteristics of the response, response/recovery time (t_s/t_c), repeatability, selectivity, and stability were tested by an ultraprecision electrometer. After gas detection, the V-MOF₁₂₀(PTA)-based gas sensor demonstrated a highest response of average 800.8 % at 100 ppm NO₂, fast t_s/t_c of average 230/39.8 s, a minimum sensing limit of 1 ppm, and excellent stability and repeatability. Additionally, the proposed sensor had good gas selectivity for NO₂ compared to ethanol, methanol, acetone, and ammonia under a concentration of 100 ppm at room temperature.