High Sensitivity and Low Detection Limit of Formaldehyde Sensor Based on In 2 O 3 @ZnO@ZIF-CoZn Core-Shell Nanofibers

High sensitivity and low detection limit of formaldehyde sensors are extremely essential for indoor air pollution monitoring. Herein, we propose a controllable strategy for the construction of metal-oxide semiconductor@metal organic framework (MOS@MOF) core-shell architectures as the sensing material. In2O3@ZnO core-shell nanofibers (IZO CSNFs) are prefabricated by combining electrospinning and atomic layer deposition (ALD) technique, where the ALD-ZnO layer can be regarded as a template to obtain cobalt-doped ZIF-8 (ZIF-CoZn) sheath. In comparison to initial IZO CSNFs, the response of the IZO@ZIF-CoZn sensor toward 50 ppm formaldehyde can be boosted from$6.6~^{\circ }$C to$39.4~^{\circ }$C at$260~^{\circ }$C, and the limit of detection can be as low as 2.1 ppb (@ 20% relative humidity). The enhanced performance of the IZO@ZIF-CoZn sensor should result from the highly efficient adsorption/decomposition of formaldehyde on the surface of ZIF-CoZn. In addition, the effects of core-shell structure, cobalt dopants, interference gases, and moisture on formaldehyde gas sensing are discussed. Our results provide insight into the enhancement mechanism of the MOS-based gas sensors by utilizing the functionalized MOF sheaths.