Experimental and theoretical studies of gold nanoparticle decorated zinc oxide nanoflakes with exposed {1 0 1¯ 0} facets for butylamine sensing

The exposed surface facets play an important role in determining the gas-sensing performance of nanostructured materials. This study reports the facile hydrothermal synthesis of zinc oxide nanoflakes with exposed {1 0 ¯10} facets, as confirmed by the high resolution transmission electron microscopy (HRTEM) and the corresponding selected area electron diffraction (SAED) analysis. The gas-sensing properties of the ZnO nanoflake sensor were investigated toward toxic n-butylamine, an important marker compound in food and medical industries. The pure ZnO nanoflake sensor exhibits a response of 23.9–50 ppm of nbutylamine at an optimum operating temperature of 300 ◦C. Density Functional Theory (DFT) simulations were used to study the adsorption behavior of n-butylamine on the ZnO(1 0¯1 0) surface. The results show that n-butylamine chemically adsorb on the ZnO(1 0¯1 0) surface through the formation of a bond between the nitrogen atom of the n-butylamine (C4H11N) and the surface Zn atom of ZnO. To further improve the gas-sensing properties, the as-prepared ZnO nanoflakes were subsequently loaded with three different quantities of Au (1.37, 2.82, and 5.41 wt% Au). The gas-sensing measurements indicate that the Au nanoparticle-decorated ZnO nanoflakes display superior sensing performance to non-modified ZnO nanoflakes by exhibiting 4–6 times higher response and an improved selectivity toward n-butylamine gas, along a decreased optimum operating temperature of 240 ◦C. Moreover, the response and recovery properties of the ZnO nanoflake sensor are improved by a factor of 1.5–2.5 depending on the Au loading. The enhanced sensing performance of the Au nanoparticle-decorated ZnO nanoflakes to n-butylamine gas can be attributed to the excellent catalytic activity of Au nanoparticles (NPs) which promotes a greater adsorption of oxygen molecules on the surface of ZnO and the presence of multiple electron depletion layers, specifically at the surface of ZnO and at the ZnO/Au interface, which greatly increases their conductivity upon exposure to the gas.