Synthesis, Characterization, and Ethanol Gas Sensing Applications of Graded Structured ZnO/g-C3N4 Micrometer Spheres

A gas sensor is a detection device that can transform the information of gas concentration into an electrical signal. Its core is gas-sensitive material. Among the gas-sensitive materials, semiconductor materials have been paid more attention. In this work, starting from the metal oxide semiconductor material ZnO, to further improve its performance, graded structured ZnO/g-C3N4 microspheres were prepared by a combination method of hydrothermal reaction and high-temperature calcination, and the optimal g-C3N4 doped ratio was adjusted in ZnO/g-C3N4. The structure and morphology of the synthesized samples were characterized via X-Ray powder Diffraction (XRD), Scanning Electron Microscopy (SEM), and N2 adsorption-desorption. The gas-sensitive properties of the ZnO/g-C3N4 composite and pure ZnO to ethanol are compared and investigated. It was found that the response of the ZnO/g-C3N4 composite to 100 ppm ethanol at 260 °C was 26.36, which was 2.19 times higher than that of pure ZnO. This experiment's response and recovery time are 26 s and 31 s. The results show that ZnO/g-C3N4 composites have better gas-sensitive properties than pure ZnO and g-C3N4. Among them, the sample (the g-C3N4 doping content was 5 wt%,) has the best gas sensitivity. The gas-sensitive property of the ZnO/g-C3N4 graded structure microspheres to ethanol was attributed to the unique graded structure of the material and the n-n heterojunction. The heterogeneous structure of ZnO/g-C3N4 composite inhibits the recombination of electrons and holes and electrons are faster transferred to the material’s surface, resulting in improved gas sensitivity. Furthermore, the gas sensor exhibited excellent selectivity, good repeatability, and long-term stability to ethanol, indicating that ZnO/g-C3N4 nanocomposites will be a promising application prospect for ethanol sensors.