Synthesis and characterization of [Ce(BTC)]-MOF based capacitive and impedimetric dual-mode relative humidity sensor

Abstract

A dual-mode relative humidity (RH) sensor based on a cerium 1,3,5-benzenetricarboxylate metal–organic framework ([Ce(BTC)]-MOF) was synthesized and integrated into an Al/[Ce(BTC)]-MOF/Al surface-type device. The MOF was prepared via a mild solvothermal route and characterized by FTIR, X-ray diffraction and scanning electron microscopy, revealing a crystalline monoclinic phase with nanocrystallites (∼67 nm) and a highly porous, fibrous morphology favorable for water adsorption. The humidity sensor demonstrated both capacitive and impedimetric operation when tested between 40 and 87% RH at 1 kHz, 10 kHz and 100 kHz. At 1 kHz the capacitance increased by over three orders of magnitude, giving a sensitivity of 2924 pF/% RH, while the impedance decreased nearly a thousand-fold with a impedimetric sensitivity of −40 kΩ/% RH. The device exhibited a response time of ∼125 s and a recovery time of ∼12 s in capacitive mode, demonstrating reliable and repeatable performance. These results confirm that the [Ce(BTC)]-MOF thin film provides an efficient dual-mode sensing platform that combines high sensitivity with simple fabrication, making it a promising candidate for next-generation humidity-monitoring applications.