Fabrication, Characterization, and Gas Sensing Properties of Different Semiconductor Metal Oxide Nanostructures for LPG Detection: A Comparative Study

Abstract

The research explores how the structural, morphological, and electrical properties of nanostructured semiconductor metal oxides (SMOs), including Cu2O, ZnO, TiO2, and reduced graphene oxide (rGO), synthesized via electrochemical deposition and doctor blading techniques, influence their effectiveness in sensing liquid petroleum gas (LPG). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were used to assess the chemical composition and structure. Cu2O, ZnO, and TiO2 were found to exhibit significant polycrystalline structures, with increasing average crystallite sizes of approximately 42.8 nm, 70.1 nm, and 87.78 nm, respectively. The dominant (111) Cu2O phase displayed a homogeneous cuboid morphology. rGO exhibited a singleplane (002) microstructure with a crumpled paper texture and an average crystallite size of ~85.3 nm, indicating a successful hydrothermal reduction of graphene oxide (GO). UV-vis absorption spectra in the range of 200 – 800 nm revealed the presence of different energy bands in ZnO, TiO2, and rGO, alongside their major band energies of 3.2 eV, 3.3 eV, and 1.9 eV. Cu2O thin films, with the lowest band energy gap of 2.5 eV, exhibited high photocatalytic activity, potentially enhancing chemical reaction rates during gas sensing under light exposure. Additionally, alternating current (AC) impedance spectra of SMO indicated increased film conductivities with positive bias voltages. ZnO films showed the most significant gas response (~27%) for LPG sensing at 70 ℃, with response and recovery times of less than 20 seconds. A stable and considerably high LPG sensitivity of ~11% was discovered with Cu2O. This finding underscores the significance of its relatively small grain size in influencing its sensitivity to LPG.