Comparative investigation of interdigitated and parallel-plate capacitive gas sensors based on Cu-BTC nanoparticles for selective detection of polar and apolar VOCs indoors

Capacitive chemosensors are commonly found in two configurations: parallel-plate (PP) and interdigitated electrode (IDE) based on different sensing layers. Metal organic frameworks (MOFs) can play an important role as a dielectric layer of the capacitors because of their insulating properties. However, to date there are few reports on MOFs which were used as a key component of a capacitive sensors. In the limited reports on using MOFs in capacitive sensors, PP configuration was mostly considered. Within the class of MOFs, Cu-BTC (copper: 1, 3, 5-benzenetricarboxylate) is a well-studied structure. Although the structure of Cu-BTC has high porosity and large surface area which can improve the sensitivity of IDE capacitive sensors, there are no reports on using this kind of MOF for this purpose. This article is developed in the following order: first, the Cu-BTC nanoparticle is synthesised to make a Cu-BTC sensing layer. The dried Cu-BTC layer is characterized by infrared (IR) spectroscopy, X-ray diff; raction (XRD) analysis, scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. These characterization methods confirm the identity of the synthesized material, the nanoscale size of the particles, its VOCs stability and the rigidity of its structure. Secondly, for the first time, Cu-BTC nanoparticles are introduced as a sensing layer in IDE capacitive gas sensors. In order to reduce fabrication costs and time of the conducting elements in IDE configuration, a simple, fast and cost-effective method is introduced which does not need any equipment and pre-treatment for better adhesion. Third, to have a comparative investigation between the sensing performance of IDE and PP capacitive sensors, their performance in detection of some VOCs vapours is examined. Subsequently, the selectivity, recovery time, reproducibility, repeatability and reversibility, sensitivity and limit of detection (LOD) of the IDE and PP capacitive sensors are studied for detection of some VOCs such as acetone, toluene and dichloromethane with different dielectric constants. All experiments were carried out at different concentrations (250-1500 ppm) of VOCs in ambient conditions (atmospheric pressure, 25 degrees C and 10% relative humidity).