Low-temperature synthesis of flower-like ZnO microstructures supported on TiO2 thin films as efficient antifungal coatings for bamboo protection under dark conditions

Abstract

Bamboo is readily infected with fungi because of its abundant sugar, starch and protein content, which greatly restricts its utilization. To develop a highly effective environmentally sound antifungal agent for bamboo, flower-like ZnO microstructures supported on TiO2 thin films have been synthesized on bamboo surfaces by a facile two-step low-temperature hydrothermal method. According to the results of various analytical techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared–attenuated total reflectance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, the bamboo substrate combined with anatase TiO2 by a hydrogen bonding or ligand exchange reaction between F― and –OH. The F― ions on the TiO2 surface combined with [Zn(NH3)4]2+ via electrostatic adsorption, contributing to the formation of a flower-like ZnO microstructure, and were then deposited on the TiO2 thin films. Moreover, the antifungal activities of the samples against a hybrid fungi group consisting of Trichoderma viride Pers. ex Fr (T. viride), Penicillium citrinum Thom (P. citrinum), and Aspergillus niger v. Tiegh (A. niger) were investigated during a three-month period under dark conditions. The results showed that pure TiO2 thin films coated on bamboo presented better antifungal activities, with a 21-day inhibition, than that of the pristine bamboo, with a 5-day inhibition. The flower-like ZnO microstructures supported on the TiO2 thin films bamboo exhibited effective antifungal capability, with a 90-day inhibition. The efficient antifungal behavior is due to the increased generation of reactive oxygen species (ROS) from the coatings by a possible synergistic effect between the ZnO and TiO2 nanoparticles in attacking fungi and causing their death.