An approach to detecting a reducing gas by radial modulation of electron-depleted shells in core–shell nanofibers

Abstract

Based on the radial modulation of electron-depleted shell layers in SnO₂–ZnO core–shell nanofibers (CSNs), a novel approach is proposed for the detection of very low concentrations of reducing gases. In this work, SnO₂–ZnO CSNs were synthesized by a two-step process: core SnO₂ nanofibers were first prepared by electrospinning, followed by the preparation of ZnO shell layers by atomic layer deposition. The radial modulation of electron depletion in the CSN shells was accomplished by controlling the shell thickness. The sensing capabilities of CSNs were investigated with respect to CO and NO₂ that represent typical reducing and oxidizing gases, respectively. In the case of CO at a critical shell thickness, the CSN-based sensors showed greatly improved sensing capabilities compared with those fabricated on the basis of either pure SnO₂ or pure ZnO nanofibers. In sharp contrast, CSN sensors revealed inferior sensing capabilities for NO₂. The results can be explained by a model based on the radial modulation of the electron-depleted CSN shells. The model suggests that CSNs comprising dissimilar materials having different energy-band structures represent an effective sensing platform for the detection of low concentrations of reducing gases when the shell thickness is equivalent to the Debye length.