Production of novel microporous porphyrin materials with superior sensing capabilities

Abstract

New robust microporous cobalt 5,10,15,20-meso-tetraphenyl porphyrin (CoTPP) thin films for sensing applications have been produced by a novel plasma-based deposition technique named Glow Discharge Induced Sublimation (GDS). CoTPP films have been also produced by conventional vacuum evaporation (VE) and spin coating (SPIN) methods for comparison. The chemical properties of the films were assessed by FT-IR and ESI-MS analyses demonstrating the integrity and the purity of the GDS films. The physical properties of the samples were thoroughly analysed: thickness measurements coupled with surface density analyses showed the impressive free volume of the GDS samples (30 times higher than that of VE ones), SEM images show the extremely rough morphology of GDS samples, and physisorption measurements indicate both the extremely high specific surface area (184 m² g⁻¹) and the microporosity of the GDS porphyrin films. The sensing capabilities of the samples were investigated by exposing them to low concentrations of NO₂ and by monitoring their optical absorption changes. These measurements clearly demonstrate that the GDS process leads to superior sensing materials as a result of the distinctive attainable molecular architectures. GDS-grown CoTPP sensors exhibit very high intense and sensitive responses as well as faster responses and much lower detection limits (<1 ppm) than conventionally deposited ones. Finally, the repeatability and reproducibility of sorption–desorption processes demonstrate the robustness of these assemblies. The GDS method can be extended to several other organic receptors, opening the way for the production of new improved sensing materials.