An inward replacement/etching route to controllable fabrication of zinc sulfide nanotube arrays for humidity sensing

Well-aligned arrays of polycrystalline ZnS nanotubes with close-tips have been successfully prepared by using ZnO nanorod arrays grown on zinc substrate as sacrificial precursors. The method is based on chemical conversion and inward etching of the ZnO sacrificial precursors. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images show that the highly ordered ZnS nanotube arrays are 300 nm in average diameter, 6–8 μm in length and about 60 nm in wall thickness. A room temperature photoluminescence-type gas sensing device based on the nanostructured arrays has been established to investigate their humidity sensing properties. ZnS nanotube array-based sensor presents higher response and quicker response/recovery than the intermediate ZnO/ZnS nanorod arrays and the precursor ZnO nanorod arrays, respectively. Moreover, the ZnS nanotube array-based sensor exhibits good linearity in response to relative humidity (RH) and reliable reproducibility in a wide range of RH at room temperature. Compared with powder-form nanomaterials, the as-prepared nanotube arrays as the humidity sensing materials can provide much more open surfaces between neighboring nanotubes and inner surfaces inside the nanotubes and allow for easy diffusion and efficient transportation of sensed gas. As a prototype sensor, the nanotube arrays can avoid tedious process of fabricating a sensor from powder and may hold great potential applications in humidity sensing.