Fabrication of Ag/Ag3PO4/TiO2 heterostructure photoelectrodes for efficient decomposition of 2-chlorophenol under visible light irradiation

TiO2 nanotube arrays were decorated with Ag/Ag3PO4 nanoparticles through a sequential chemical bath deposition and followed by partial reduction of Ag+ ions in the Ag3PO4 nanoparticles to Ag0 under UV irradiation. The structure and optical properties of the Ag/Ag3PO4/TiO2 nanotube electrode were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy and electrochemical techniques. The photoelectrocatalytic (PEC) activity of the composite electrode was evaluated by the decomposition of 2-chlorophenol under visible light irradiation (λ > 420 nm). Clusters of Ag/Ag3PO4 nanoparticles were successfully formed on the surface of the TiO2 nanotubes (NTs) causing no damage to the ordered structure of the nanotubes. The PL intensity of Ag/Ag3PO4/TiO2 NTs was much lower than that of TiO2 nanotubes. The p-type Ag3PO4 and Ag nanoparticles deposited on the TiO2 NTs could promote the transfer of photo-generated electrons, which inhibited the recombination of electrons and holes effectively, leading to a significant increase in the photocurrent density. Moreover, the Ag/Ag3PO4/TiO2 heterostructure photoelectrodes showed much higher PEC activity than the pure TiO2 NTs for the degradation of 2-CP aqueous solution under visible light irradiation. The enhanced PEC activity could be attributed to the visible-light photocatalytic activity of Ag3PO4 and the heterostructure between Ag3PO4 and TiO2. The electron spin resonance (ESR) spin-trap study further demonstrated that ˙OH could be generated on the Ag/Ag3PO4/TiO2 NTs under visible light irradiation.