Tunable Gas-Sensing Properties of Three-Dimensional, Hollow, and Porous In ₂ O ₃ -Based Chemiresistive Sensors for Isoprene Detection: Studies by Modulating the Size of Polystyrene Templates

In this work, the polystyrene (PS)-templated three-dimensional (3D) ordered, hollow, and porous In 2 O 3 structures-based chemiresistive sensors for isoprene detection in the range of 100 ppb–5 ppm are investigated. The morphology of the In 2 O 3 structure was controlled by different PS sphere sizes of 200, 500, 700, 1000 nm, and 1500 nm, respectively. The materials were investigated through various characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) characterization techniques. The In 2 O 3 -500 sensor exhibited a maximum response ( R a / R g ) of 4.32–5 ppm isoprene concentration at an operating temperature of 270 °C, an experimental detection limit of 100 ppb, a low theoretical detection limit of 6.50 ppb, and quick response/recovery times of 14/14 s, respectively. The sensor’s response was also examined under humidity exposure of 30% RH to 80% RH, repeatability over 3600 s, and long-term stability of 11 days under 5 ppm isoprene concentration at operating temperature of 270 °C. The notable sensing performance of In 2 O 3 to isoprene is attributed to the controlled morphology, porous structure, low gas transport resistance, and an effective electron transfer between In 2 O 3 material and isoprene through an active modulation of the depletion layer. This study delivers a template-based method to effectively control the morphology, structures, and response characteristics of metal oxides for gas sensing applications.