3D flower-like Co3O4@ZnO nanostructures for trace-level acetone detection at low operating temperatures

Enhancing p-type metal oxide semiconductors (MOS) sensitivity at low temperatures is critical for detecting acetone, a toxic pollutant and diabetes biomarker. This study presents a 3D flower-like Co₃O₄@ZnO composite synthesized via additive-free hydrothermal method combined with inert gas calcination. The inert gas environment minimizes oxidation and oxygen interference, forming a robust nanoneedle-based hierarchical structure with high integrity, a large surface area (52.13 m²g⁻¹), and uniform mesopores (∼10 nm) to facilitate efficient gas diffusion and reactions. The ZnO-Co₃O₄ heterojunction enhances band-bending modulation and refines carrier dynamics by synergizing ZnO's exceptional carrier mobility with Co₃O₄’s robust redox catalytic activity, delivering markedly improved sensing performance. The optimized composite (CZ-3, Co₃O₄:ZnO = 0.5:0.5) demonstrated exceptional acetone sensing performance, achieving a 35.85% response to 100 ppm acetone at 150 °C, rapid response/recovery times of 40/28 s, a linear detection range of 1–150 ppm, and an ultra-low detection limit of 100 ppb. The sensor also exhibited a measurable response (0.35 %) to human exhaled breath, demonstrating its potential for non-invasive healthcare diagnostics. In contrast, the lower ZnO content in Co₃O₄ (CZ-1) sensor showed reduced performance, responding to 500 ppb acetone with a response of 29% to 100 ppm. These results emphasize the critical role of the heterojunction with an optimized balance of p- and n-MOS in enhancing sensing performance, highlighting a sustainable and scalable approach for advancing high-performance p-type MOS gas sensors. The proposed composite demonstrates significant potential for precise, low-temperature acetone detection in environmental monitoring and non-invasive healthcare diagnostics.