Photocatalytic decompositions of gaseous HCHO over Ag/TiO2 nanotube arrays

TiO2 nanotube arrays prepared by electrochemical anodization method attract considerable interest as a practical air purifier, as the nanotube arrays may form a TiO2 film with a porous surface and straight gas diffusion channel. Here, the TiO2 and Ag/TiO2 nanotube arrays with different Ag amount are used to degrade gaseous HCHO pollutants. The photocatalytic results confirm that the HCHO-degrading efficiency of the TiO2 nanotube arrays may vary with the amount of Ag nanoparticles, and the Ag amount within a certain range significantly improves the degradation rate of HCHO molecules. The main final product after HCHO degradation is detected to be CO2. Ag nanoparticles effectively act as electron trappers prohibiting the recombination of photo-excited electrons and holes, hence increasing the photocatalytic efficiency. However, excessive Ag nanoparticles form new recombination center of photo-excited electrons and holes to decrease the photocatalytic efficiency.