<p>In this work, a plasma jetting technique was used to create iron oxide nanoparticles (NPs). The best exposure duration for gas-sensing applications was determined by analyzing the effects of plasma exposure times (8 min, 12 min, 16 min, 20 min, and 24 min) on the structural, optical, and morphological characteristics. Ferric oxide phases, Fe₃O₄ and Fe₂O₃, were formed at 33.2° and 35.7° angles, according to X-ray diffraction. As the duration of plasma exposure increased, crystallinity improved. The structure of the nanoparticles changed from clumped aggregates at low exposure intervals (8 min) to regular particles with increasing plasma exposure time, according to scanning electron microscopy. Iron and oxygen were found at 61.42% and 38.58%, respectively, according to energy-dispersive X-ray spectroscopy (EDS). With a shift toward higher wavelengths, photoluminescence spectroscopy showed maxima at 371, 478, 588, 726, and 867 nm. Redshift was the longest. Atomic force microscopy revealed that the optimal sample had a roughness of 50–60 nm. The material demonstrated an n-type sensitivity of 304% at 150°C with a reaction time of 10 s and a recovery time of 61 s upon exposure to hydrogen sulfide gas. The sensitivity value for the oxidizing gas was 268%, and it took 10 s to respond and 63 s to recover. These results highlight Fe₃O₄ nanoparticles prepared by plasma jet as promising, low-cost sensors for monitoring environmental gases.</p>