Preparation of MOF-derived ZnO/Co 3 O 4 nanocages and their sensing performance toward H 2 S.

We report a type of micro-electro-mechanical system (MEMS) H 2 S gas sensors with excellent sensing performance at the ppb level (lowest detection limit is 5 ppb). The sensors were fabricated with ZnO/Co 3 O 4 sensing materials derived from Zn/Co-MOFs by annealing at a suitable temperature of 500 °C. ZnO/Co 3 O 4 -500 exhibits the highest response when exposed to 10 ppb H 2 S gas at 120 °C, and the response/recovery times are 10 s/21 s. Moreover, it exhibits outstanding selectivity, long-term stability (retained 95% response after 45 days), and moisture resistance (only a minor fluctuation of 2% even at 90% RH). This can be ascribed to the fact that ZnO/Co 3 O 4 -500 has regular morphology, abundant oxygen vacancies (52.8%) and high specific surface area (96.5 m 2 g -1 ). This work provides not only a high performance H 2 S MEMS gas sensor but also a systematic study of the effect of the annealing temperature on the sensing performance of ZnO/Co 3 O 4 sensing materials derived from bimetal organic frameworks.