ZnO nanorod-coated quartz crystals as self-cleaning thiol sensors for natural gas fuel cells

ZnO nanorods were directly grown on quartz crystals in zinc nitrate hexahydrate solution. When exposed to hexanethiol vapor, the hexanethiol molecules adsorbed onto the nanorod-coated surface. Subsequent exposure of the adsorbed hexanethiol molecules to UV irradiation led to the photodegradation of the molecules. The adsorption and photocatalytic degradation processes were monitored by measuring changes in the resonant frequency of the crystal using a quartz crystal microbalance (QCM). The frequency change due to the adsorption of hexanethiol molecules onto the ZnO nanorod-coated quartz crystal was 10 times that observed using a quartz crystal coated with a plain ZnO film, due to the higher surface area of the nanorods compared to the film. UV irradiation of the nanorod-coated quartz crystals on which hexanethiol was adsorbed caused the frequency to return to the value for the bare ZnO surface, indicating that the hexanethiol molecules adsorbed on the ZnO surfaces were completely removed. The complete removal of hexanethiols was confirmed by X-ray photoelectron spectroscopy analysis. The results highlight the potential of ZnO nanorod-grown QCMs as self-cleaning sensors capable of long-term operation under harsh conditions.