Interaction of Calix[4]arene thin films with chlorinated volatile organic compounds and calculation of diffusion coefficients

A group of molecules composed of lipophilic calix[4]arene derivatives containing phosphonic acid groups and modified at the lower rim were coated onto a substrate using the spin coating thin film fabrication method. To investigate their interactions in detail, chlorinated volatile organic compounds (Cl-VOCs) such as chloroform, dichloromethane, and carbon tetrachloride were selected. The properties of the thin films and their kinetic interactions with the selected chlorinated organic compounds were examined using the Surface Plasmon Resonance (SPR) technique. The interactions of the thin films with chlorinated organic vapors were evaluated in terms of the physical properties of the compounds, such as dipole moment, refractive index, vapor pressure, and molar mass. It was determined that dichloromethane and chloroform exhibited higher interaction levels with the thin films compared to carbon tetrachloride. Sensor parameters such as response/recovery times, repeatability, sensitivity, and detection and quantification limits (LOD and LOQ) were examined based on the kinetic interaction data. A sensitivity value of up to 1.29×10⁻³ response rate/ppm was calculated. LOD and LOQ values were found to be in the range of 2–3 ppm and 7–13 ppm, respectively. İn all measurements, response times were found to be in the range of 1–2 seconds, while recovery times ranged between 2–4 seconds. Additionally, the kinetic data were adapted to Fick's law of diffusion to calculate diffusion coefficients, adopting a two-region diffusion model. In this model, diffusion coefficients were found to be in the range of 0.21–12.09×10⁻¹⁵ cm²/s for the first region and 0.12–6.41×10⁻¹⁷ cm²/s for the second region.