Abstract
ZnO is a suitable photocatalytic material from non-toxic, biocompatibility, low-cost, and strong photo-induced electron-hole pairs. However, ZnO has the limitation of absorbing visible light and fast recombination rate of electron-hole pairs. In this work, ZnO nanowires were modified with Ag nanoparticles. Owing to the improvement of the Ag/ZnO absorption ability, the photocatalytic performance could be enhanced. Moreover, the superior photocatalytic performance of the Ag/ZnO can be ascribed to the heterostructure which lowers the recombination rate of photo-excited electron-hole pairs. Compared to the traditional Si substrate, we took paper as substrates and grow ZnO nanowires by low-cost solution method to lower the price and applied in the industry. The scanning electron microscopy indicates the morphologies and structures of nanowires and nanoparticles, the ZnO nanowires modified with the best concentration of Ag nanoparticles showed the best photocatalytic performance under the condition of 2-min photoreduction with 5×10^(-2) M silver nitrate. The Ag nanoparticles formed nanoclusters or thin film on the top of ZnO nanowires, which lowers the photocatalytic performance, under the condition of 2.5-min photoreduction with 5×10^(-2) M silver nitrate or after 6-min photoreduction with 1×10^(-3) M silver nitrate. The energy dispersive spectrometer presents that there are no impurities inside the material. The photoluminescence spectra show that the decreasing of Ag/ZnO, especially the Ag/ZnO photoreduced with 5×10^(-2) M silver nitrate, compares to the as-grown ZnO, revealing that the recombination of electron-hole pairs is more likely reduced by high concentration and uniform distribution of Ag nanoparticles. The photocatalytic performance of the ZnO or Ag/ZnO nanowires on paper substrate with 1.5 cm by 1.5 cm surface area was evaluated by degrading a 10 µM rhodamine B solution under the illumination of ultraviolet light. The best first-order kinetic constant of the Ag/ZnO nanowires is 0.218 min^(-1). It is 1.93 times as high as as-grow ZnO nanowires (0.0113 min^(-1)). It showed a high-efficiency photocatalytic material by a simple photoreduction method successfully. The ZnO nanowires on paper substrate also showed a good response of the gas sensor, which has been utilized to sense 1 ppm NO gas under UV light and background ambient gas and showing response up to 89%. However, the ZnO nanowires modified with Ag nanoparticles were not able to be a good gas sensor device. Because the paper sucked up silver nitrate under the photoreduction, the Ag formed a continuous thin film on the paper. This Ag thin film lowers the resistance of the gas sensor material dramatically and diverts the electric current from the proper response region.