Zinc oxide nanonets with hierarchical crystalline nodes: High-performance ethanol sensors enhanced by grain boundaries

Abstract

Researchers commonly enhance the sensitivity of gas sensing nanomaterials by increasing the effective active area. It would be more straightforward to instead optimize the grain boundaries. In this work, Zn4CO3(OH)6·H2O was synthesized as a precursor to ZnO via a facile hydrothermal process and annealing, respectively. ZnO nanonets of hierarchical crystalline nodes with abundant grain boundaries was prepared. The nanonets exhibited an ultra-sensitive response value of 398, and a fast response time (4 s of exposure to 100 ppm ethanol), compared with traditional nanosheets. The sensing enhancement as per the grain boundary was modeled and experiments confirmed the model. Microstructural and microscopic analyses indicated that the sensitivity of the nanonets mainly is attributable to the abundant grain boundaries with lots of hierarchical crystalline nodes. The high-sensitive response and fast response time toward ethanol by the ZnO nanonets is considered to derive from the enhancement effect of grain boundaries in hierarchical crystalline nodes, which creates the additional depletion layers from abundant oxygen vacancies led to a substantial change in the surface potential, referring to the difference between in-air versus in-ethanol. The proposed high-performance sensor is inexpensive to fabricate, straightforward to synthesize, and advantageous for practical use.