Simultaneous doping and heterojunction of silver on Na2Ta2O6 nanoparticles for visible light driven photocatalysis: the relationship between tunable optical absorption, defect chemistry and photocatalytic activity

In this work, we report the synthesis of Na2Ta2O6/Ag heterojunctions with the aim of tailoring their structural, electronic and photocatalytic properties. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, UV-vis optical diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The effects of silver doping and heterojunctions on the electronic structure and photodegradation of a rhodamine B dye solution were investigated experimentally and theoretically. It was found that silver played critical roles in modulating the electronic structure, defect chemistry and visible light photocatalytic activity. Partial incorporation of Ag ions into the Na2Ta2O6 host lattice led to a monotonous lattice expansion and introduced an interband for band gap narrowing. Meanwhile, some of the Ag ions were reduced, and crystallized into Ag nanoparticles on Na2Ta2O6 surfaces that can promote the visible light absorption efficiency of Na2Ta2O6/Ag heterojunctions. Moreover, the doping and heterojunction of silver can also result in the modulation of defective oxygen species that have a great impact on photocatalytic performance. As a consequence of the well-controlled electronic structure, surface defect chemistry, Ag particle size, BET surface area, and Ag+ doping effects, the photocatalytic performance of the Na2Ta2O6/Ag heterojunctions was optimized at an as-measured Ag/Ta molar ratio of 1.17.