Unleashing Synergy: rGO Decorated on a Cobalt-Doped ZnFe₂O₄ Film to Detect Trace-Level NH₃ at Ambient Temperature with High Response and Cross-Selectivity

The development of reliable ammonia (NH3) sensors that function effectively at room temperature in mixed gas environments, especially at trace levels, remains a significant challenge due to issues like cross-selectivity. Detecting NH3 is crucial, as even low concentrations can negatively affect individuals with respiratory conditions or disabilities linked to environmental pollutants, and prolonged exposure can exacerbate conditions like asthma, chronic obstructive pulmonary disease (COPD), and other disabilities related to respiratory function. This study presents a sensor based on cobalt-doped ZnFe2O4 (Co-ZFO) loaded with reduced graphene oxide (rGO), fabricated using spray pyrolysis and spin-coating techniques, and this film was used to investigate the chemisorption, and transmission processes of NH3, enabling its trace detection even in complex mixed gas environments. The Co-ZFO/rGO film demonstrates superior NH3 sensing performance compared to standalone Co-ZFO and rGO films, showing a high response (S = 81 at 1 ppm), rapid response (65 s) and recovery (18 s) times, and excellent sensitivity (61.8 ppm–1) at room temperature. The sensor also exhibits strong selectivity (S ≈ 212 at 5 ppm of NH3) even in the presence of interfering gases such as ethanol, formaldehyde, and acetaldehyde. Furthermore, it offers a low theoretical limit of detection (0.004 ppb), high repeatability over 8 cycles, and outstanding long-term stability (RSD = 1.02%). These attributes highlight the Co-ZFO/rGO sensor’s potential for practical applications in trace-level NH3 detection under ambient conditions.