Ag@Fe3O4-coated U-shaped plastic optical fiber sensor for H2S detection

This work presents the fabrication of U-shaped plastic optical fiber (POF) sensors for hydrogen sulfide (H2S) detection, coated with Fe3O4 nanoparticles synthetized using the Pulsed Laser Ablation in Liquid (PLAL) technique. The Fe3O4 nanoparticles were synthetized in ultra-pure water and in silver nitrate solution, resulting in two colloidal samples with different morphological, optical, and structural properties. The Fe3O4 nanoparticles were coated onto one POF sensor, while the other sensor was coated with a nanostructure composed of Ag as the core and Fe3O4 as the shell (Ag@Fe3O4). The performance of both sensors was evaluated by exposing them to different concentrations of H2S and other gases such as CH4, H2, and CO2. All experiments were conducted at 25 °C. Results showed that the sensor coated with Ag@Fe3O4 was 12 times more sensitive to H2S compared to the sensor coated with Fe3O4, with a detection limit of 1 ppm and a rise time of 15 s. Moreover, the POF sensor coated with Ag@Fe3O4 presented high selectivity to H2S, making it a promising candidate for H2S detection in different applications. The sensor's performance was also evaluated with a relative humidity range of 20–90%, exhibiting a minimal 0.75% signal variation at 90% humidity.