This work proposes precursor pyrolysis, ultrasonic exfoliation and hydrothermal methods as well as high-temperature calcination strategies to fabricate heterostructured g-C3N4/ZnO composites with excellent ethanol vapour sensing properties. The structure, composition and morphology of the as-prepared g-C3N4/ZnO composites were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Then, the sensing properties of the g-C3N4/ZnO composites for ethanol (C2H5OH) were studied, and g-C3N4 doping with different mass ratios was used to control the gas-sensing properties of the composites. Compared with pure ZnO and g-C3N4, the performance of g-C3N4 with 1% doping content is the best, and the gas sensing activity of the 1% g-C3N4/ZnO composite is greatly improved at the optimal working temperature (280 °C). The response to 100 ppm ethanol reaches 81.4, which is 3.7 times that of the pure ZnO-based sensor under the same conditions. In addition, the sensor has good selectivity as well as fast response and recovery speeds (24 s and 63 s, respectively). Finally, a reasonable gas sensing enhancement mechanism is proposed, and it is believed that the constructed g-C3N4/ZnO micro flower-like heterostructure and the distinct positions of the valence and conduction bands of ZnO and g-C3N4 lead to the obtained sensor exhibiting a large specific surface area and increased conductivity, thereby improving the g-C3N4/ZnO-based sensor sensing performance.
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