Zeolitic imidazolate framework-8 (ZIF-8)-coated In2O3 nanofibers as an efficient sensing material for ppb-level NO2 detection

The development of NO 2 gas sensors is of great importance for air quality monitoring and human health. In this work, In 2 O 3 and zeolitic imidazolate framework-8 (ZIF-8) heterostructures were synthesized and designed as efficient sensing materials for NO 2 detection. The ZIF-8 nanocrystals were uniformly deposited on In 2 O 3 nanofibers (NFs) by using a self-template strategy, where In 2 O 3 /ZnO NFs act as the source of Zn 2+ for the formation of ZIF-8 and as the template. By tuning the amount of Zn 2+ in the composite NFs, different morphologies from In 2 O 3 NFs with minimal ZIF-8 loading to an In 2 O 3 /ZIF-8 core-shell complex were obtained. The optimized In 2 O 3 /ZIF-8 NFs show a remarkably high response to 1 ppm NO 2 (R g /R a  = 16.4) and enhanced humidity resistance due to the hydrophobicity of ZIF-8 in comparison with those of the pristine In 2 O 3 NF sensor (R g /R a  = 4.9) at 140 °C. The gas sensing mechanism of In 2 O 3 /ZIF-8, which is based on electron transduction, surface chemistry, and the functional interface between the loaded ZIF-8 and In 2 O 3 matrix, was proposed. Additionally, the large number of pores, which were formed by the in situ conversion of ZnO grains in the matrix, ensures that all parts of the In 2 O 3 NFs are accessible to gases. This facile strategy paves the way for the design of metal oxide/MOF complex architectures with tunable metal centers for various applications, including gas sensing.