Multiple-Yolk–Shell\nNiO Microspheres for Selective\nDetection of <i>m</i>‑Xylene

<i>m</i>-Xylene is a volatile organic compound\nthat is\nextensively used in various industrial processes. It is toxic, posing\nsignificant risks to human health and the environment. Therefore,\ndeveloping gas sensors with high sensitivity and selectivity for <i>m</i>-xylene detection is critical. In this work, we demonstrated\nthe synthesis of NiO-yolk double-shell (NiO-YDS) and NiO-yolk triple-shell\n(NiO-YTS) derived from NiO/Ni-BTC and NiO/Ni-PTA composites, respectively,\nusing the microwave-assisted solvothermal method from Ni-BTC-derived\nNiO spheres. The NiO/Ni-BTC composite has trimesic acid (H<sub>3</sub>BTC) as an organic linker, while NiO/Ni-PTA has <i>p</i>-terephthalic acid (PTA). We investigated the sensing properties\nof these materials for 2-butanone, 2-nonanone, 3-methyl-1-butanol,\nacetone, benzene, ethanol, methanol, and <i>m</i>-xylene.\nThese composites exhibited excellent sensitivity and selectivity for\ndetecting <i>m</i>-xylene under dry conditions. Specifically,\nthe NiO-YTS sensor showed a sensitivity of 217.5% to <i>m</i>-xylene, while the NiO-YDS sensor demonstrated a sensitivity of 179.8%\nat 350 °C in dry air. We emphasize the NiO-YTS composite due\nto its superior sensitivity and selectivity in detecting <i>m</i>-xylene compared with the NiO-YDS composite. The NiO-YTS sensor exhibited\nstable and reproducible sensing performance for 100 ppm of <i>m</i>-xylene under optimum working conditions, with a theoretical\ndetection limit of 5.43 ppb and relatively fast response time (89\ns) and recovery time (191 s). This work describes an easy method for\nsynthesizing NiO-YDS and NiO-YTS derived from NiO/Ni-BTC and NiO/Ni-PTA\ncomposites. It demonstrates that these composites represent a new\nclass of materials that can potentially enhance the sensitivity and\nselectivity of <i>m</i>-xylene gas sensors.