Ultra-highly sensitive detection of ppb-level acetone gas using novel multicore-shell porous zinc oxide microspheres

Abstract In this study, novel multicore-shell ZnO microspheres were synthesized via a simple solvothermal method based on the coordination of salicylic acid under the protection of polyvinylpyrrolidone (PVP). In this process, as an organic acid, salicylic acid with a benzene ring structure rich in hydroxyl and carboxyl functional groups can not only play a structure-oriented role, but also can etch materials to form a hollow structure. Compared with traditional basic synthesis methods, the diversity of coordination forms makes the structure more abundant. The multicore-shell ZnO was annealed at 450, 600, and 750 °C respectively. Under the driving force of reducing the surface free energy, part of the multi-nucleus inside the microspheres aggregated to form large particles, and the other part adhered to the shell layer to grow. The crystallinity, morphology and surface composition of the ZnO microspheres were characterized by XRD, SEM, TEM, XPS, BET and FT-IR analyses. The multicore-shell ZnO-based sensor that exhibited excellent sensitivity to acetone (2 ppm, SRa/Rg = 8.6) at an optimal working temperature of 240 °C, with a low limit of detection of 100 ppb with a SRa/Rg = 2.9. The annealed ZnO-based sensors also performed well, among them, the product annealed at 750 °C (ZnO-750) is the best, with a response of 6.4 to 2 ppm acetone. The sensors exhibited satisfactory selectivity and can detect acetone in the presence of other interfering gases, including NO, CO, NH3, HCHO, CH3OH and C2H5OH. The outstanding sensitivity of the multicore-shell ZnO sensor to acetone can be attributed to its large specific surface area and pore volume, which favors gas adsorption, penetration and diffusion. For the annealed ZnO, we speculated that the specific exposed crystal plane (002) plays a decisive role in the good adsorption and reaction of acetone.