Ethyl Acetate Detection Using Mixed-Phase In₂O₃ Nanorods

Detecting microbial volatile organic compounds (MVOCs) is critical for public health and food quality control applications but often requires complex analytical approaches. Ethyl acetate, an MVOC produced during the fermentation of bread and beer by Saccharomyces cerevisiae, holds significance in food quality control. Semiconductor metal oxides, particularly In₂O₃, are promising materials for MVOC sensing due to their cost-effectiveness, stability, and tunable sensing properties at the nanoscale. Enhanced sensing performance can be achieved by engineering heterostructures combining cubic and rhombohedral phases of In₂O₃ nanorods. In this work, In₂O₃ nanorods were synthesized via microwave-assisted hydrothermal method followed by calcination at 600, 500, and 400 °C to obtain single-phase cubic (In₂O₃-600) and mixed-phase cubic-rhombohedral (In₂O₃-500 and In₂O3-400) structures. The In₂O₃-500 heterostructure nanorods exhibited an enhanced response of 548 to ethyl acetate at 350 °C in dry air. It also showed a fast response time (1.8 s), a selectivity ratio of 2.1, and a theoretical detection limit of 525 ppb. Moreover, the material maintained a high response under 90% relative humidity (RH), demonstrating robustness under realistic operating conditions. These findings can be attributed to the synergistic effect of heterojunctions formed between the cubic and rhombohedral phases at the nanoscale, providing numerous active sites and defect-driven reactivity. The post-mortem characterization of the nanorod sensor was conducted using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) to assess the long-term stability of the material.