ZnO Nanosheets Abundant in Oxygen Vacancies Derived from Metal‐Organic Frameworks for ppb‐Level Gas Sensing

TLDR

Reproducible ppb‑level gas sensing is essential for widespread sensor networks in industrial safety and air quality monitoring, yet sensor inhomogeneity remains a challenge. The authors propose chip‑level pyrolysis of ZIF‑L films to produce porous, hierarchical ZnO nanosheets, aiming to enhance surface homogeneity and gas‑sensing performance. They generate adjustable oxygen vacancies in the ZnO nanosheets by pyrolyzing ZIF‑L films, fine‑tune the electronic structure, and confirm vacancy presence with multiple characterization techniques. The vacancy‑rich ZnO nanosheets show markedly improved sensitivity and faster response to ppb‑level CO and VOCs such as 1,3‑butadiene, toluene, and tetrachloroethylene, attributed to unpaired electrons, bandgap narrowing, higher surface area, and hierarchical porosity, demonstrating the method’s potential for scalable, high‑performance ultratrace gas sensors.

Abstract

Surmounting the inhomogeniety issue of gas sensors and realizing their reproducible ppb-level gas sensing are highly desirable for widespread deployments of sensors to build networks in applications of industrial safety and indoor/outdoor air quality monitoring. Herein, a strategy is proposed to substantially improve the surface homogeneity of sensing materials and gas sensing performance via chip-level pyrolysis of as-grown ZIF-L (ZIF stands for zeolitic imidazolate framework) films to porous and hierarchical zinc oxide (ZnO) nanosheets. A novel approach to generate adjustable oxygen vacancies is demonstrated, through which the electronic structure of sensing materials can be fine-tuned. Their presence is thoroughly verified by various techniques. The sensing results demonstrate that the resultant oxygen vacancy-abundant ZnO nanosheets exhibit significantly enhanced sensitivity and shortened response time toward ppb-level carbon monoxide (CO) and volatile organic compounds encompassing 1,3-butadiene, toluene, and tetrachloroethylene, which can be ascribed to several reasons including unpaired electrons, consequent bandgap narrowing, increased specific surface area, and hierarchical micro-mesoporous structures. This facile approach sheds light on the rational design of sensing materials via defect engineering, and can facilitate the mass production, commercialization, and large-scale deployments of sensors with controllable morphology and superior sensing performance targeted for ultratrace gas detection.