Embedded SnO₂/Diatomaceous earth composites for fast humidity sensing and controlling properties

A tin oxide/diatomaceous earth (DE) composite was synthesized via the hydrothermal method without using a template or surfactant, and its humidity-sensing and controlling properties were investigated. The SnO₂/DE composites have a special embedded structure, in which SnO₂ nanoparticles are embedded in the DE porous frame. The optimal composites exhibit short response and recovery times (T = 3 and 8 s, respectively), and their response (S = 35.64) is 11.88 times higher than that of DE (S = 3). Furthermore, the optimal composite C-1:3 was tested to determine its humidity-controlling properties, which revealed that it possessed absorption (27 h, 12.04%) and desorption (5 h, 8.56%) characteristics. Regarding the selectivity, the C-1:3 sensor showed better sensing behavior to humidity than to NO₂, NH₃ and other gases. These beneficial properties of the composites are due to a honeycomb structure that endows the composite with a large specific surface area for adsorption of H₂O molecules and allows charge transfer between the embedded SnO₂ nanoparticles. The humidity-sensing mechanism is explained in detail by the Grotthuss proton transfer theory and density functional theory (DFT), which were used together with a Nyquist diagram to analyze the conditions of H₂O adsorption. This study demonstrates a novel strategy for designing a material that can rapidly sense and control humidity and provides insights into the application of the composite in sensing and controlling environmental humidity at room temperature.