Solid state sensor based on meso-tetra (p-nitrophenyl) porphyrin deposited glass plate for the determination of trace level HCl gas

A novel solid-state sensor based on meso-tetra (pnitrophenyl) porphyrin (MTNP) deposited glass plate for the detection of HCl gas was developed and described in this study. Initially, the MTNP molecule was synthesized by Lindsey method and characterized by UV-vis and FT-IR spectroscopic techniques. Addition of HCl into the MTNP-DMF solution leads to the protonation of MTNP which is evidenced from the colour change from dark brown to fluorescent green and it was followed by absorption and fluorescence spectral techniques. Protonation of MTNP leads to changes in Soret and Q bands of the porphyrin. Interestingly, deprotonation on MTNP occurs by the addition of trimethylamine into the same solution and the solution turns into its origin. Further, detection of HCl gas using MTNP deposited glass plate (solid state sensor) was demonstrated. The solid-state sensor was characterized by UV-vis, fluorescence and scanning electron microscopy (SEM). The SEM image shows discrete aggregates after the solid-state sensor was exposed to HCl gas. Detection of HCl gas monitored at 464 nm and the sensitivity of the solid-state sensor were achieved up to 30 ppm. The sensor fails to detect below 5 ppm of the HCl gas and is also slightly affected by humidity.