Zinc oxide tetrapod sponges for environmental pollutant monitoring and degradation

Environmental monitoring systems enable the collection of information about the various environmental parameters, pollution levels, and the presence of environmental hazards affecting human and marine life. Highly sensitive, stable, and low-power-consuming sensors are vital for such operations. Nanomaterials with different surface morphologies can play a vital role in multiple applications, such as gas sensors, photocatalysts, erosion monitoring, or fine dust sensor. Zinc oxide (ZnO) tetrapod, in particular, shows 3D morphologies that exhibit exciting properties, making them applicable in several device engineering. This work provides a simple yet high-throughput single-step synthesis of ZnO tetrapod with different arm sizes using the flame transport method at various growth conditions. The physicochemical and structural properties have been deeply investigated to shed light on the formation of these 3D structures. The detailed mechanism of the ZnO tetrapod as a gas monitoring material and a photocatalyst has been presented in detail. The sponge-based ZnO gas sensor can selectively sense NO2 gas with a limit of detection (LOD) value of 8.56 ppb. In addition, ZnO tetrapods samples exhibit high photocatalytic activity toward methylene blue and methyl orange degradation under UV illumination. The reaction rate constants of 3.6 (2)·10-4 s-1 and 1.7 (1)·10-4 s-1 are determined for the photocatalytic decomposition of methylene blue and methyl orange, respectively. The results suggest that ZnO tetrapod-based sponges can be a promising material for building next-generation pollution monitoring and degradation systems.