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

Abstract

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.