Fabrication of “tree-like” three-layer ZnO nanorods/SnO2 nanorods/silica micropillars micro-nano structure for gas sensor application

Herein, a three-dimensional tree-like hierarchical heterostructure consisting of ZnO nanorods, SnO 2 nanorods, and silica micropillars was successfully fabricated via dry etching, thermal oxidation, and hydrothermal growth for high-performance ethanol gas sensing. In this rational architecture, silica micropillars serve as mechanical trunks to construct a porous framework, while SnO 2 and ZnO nanorods act as branched sensing units, jointly forming a multilevel functional sensing layer. Structural and morphological characterizations confirm the high crystallinity, uniform element distribution, and large specific surface area. XPS analysis reveals that the ternary composite possesses abundant surface chemisorbed oxygen species, which provide substantial active sites for gas adsorption and redox reactions. Benefiting from the synergistic effects of the hierarchical porous structure and valid heterojunction interfacial modulation, the optimized ZnO/SnO 2 /silica sensor exhibits an outstanding ethanol-sensing response (R air /R gas ) of 6.11 toward 500 ppm ethanol at 300 °C, which is significantly higher than those of binary ZnO/silica (3.56) and SnO 2 /silica (4.5) sensors. The enhanced sensing performance is mainly attributed to the enlarged gas-contact surface area, increased chemisorbed oxygen content, and efficient electron regulation at the ZnO/SnO 2 interface. This work offers a facile and reliable strategy for the design and preparation of high-performance integrated metal oxide gas sensors based on micro-nano hierarchical composite structures.