Dual-Active-Site Synergy in Metal–Organic Framework-Derived Er:CeO ₂ /ZnO Nanofibers Enabling Humidity-Independent Triethylamine Detection at Room Temperature

The development of gas sensors that combine high sensitivity and selectivity with stable operation at room temperature under high humidity remains a pivotal challenge for reliable breath analysis. This work presents a rational design and facile synthesis of three-dimensional hierarchical beaded Er 3+ -doped CeO 2 /ZnO (Er:CeO 2 –ZnO) heterojunction nanofibers (NFs) via a ZIF-8-templated electrospinning strategy. This integrated approach converges multiple material design principles. It employs a ZIF-8-derived porous ZnO scaffold for enhanced gas accessibility, in situ formed n-n heterojunctions for efficient charge separation, and Er 3+ -induced oxygen vacancies in CeO 2 for optimized surface chemistry. Comprehensive characterization confirms the successful integration of these components and the creation of abundant active sites. The optimized sensor exhibits exceptional room-temperature triethylamine (TEA) sensing performance, including a high response, a low detection limit (56 ppb), fast response/recovery kinetics (16 s/58 s to 10 ppm TEA), and excellent selectivity. Remarkably, the sensor demonstrates outstanding long-term stability (over 120 days) and humidity-independent performance across a wide relative humidity range (25–90% RH). Kinetic analysis of the sensing transients reveals biphasic behavior, providing direct evidence for a dual-active-site synergistic mechanism involving oxygen vacancy-rich regions for gas adsorption/activation and heterojunction interfaces for charge separation. Furthermore, a dynamic self-refreshing mechanism is proposed to elucidate the exceptional humidity tolerance. This work provides fundamental insights into the design of multifunctional sensing materials and presents a highly promising candidate for reliable gas detection in complex, humid environments such as exhaled breath analysis.