Two-Dimensional Hierarchical Ag-Doped TiO2 Nanocatalysts:Effect of the Metal Oxidation State on the PhotocatalyticProperties

摘要

This paper reports the synthesis of two-dimensional, hierarchical, porous, and (001)-faceted metal (Ag, Zn, and Al)-doped TiO2 nanostructures (TNSs) and the study of their photocatalytic activity. Two-dimensional metal-doped TNSs were synthesized using the hydrolysis of ammonium hexafluorotitanate in the presence of hexamethylenetetramine and metal precursors. Typical morphology of metal-doped TNSs is a hierarchical nanosheet that is composed of randomly stacked nanocubes (dimensions of up to 5 μm and 200 nm in edge length and thickness, respectively) and has dominant (001) facets exposed. Raman analysis and X-ray photoelectron spectroscopy results indicated that the Ag doping, compared to Zn and Al, much improves the crystallinity degree and at the same time dramatically lowers the valence state binding energy of the TNS and provides an additional dopant oxidation state into the system for an enhanced electron-transfer process and surface reaction. These are assumed to enhance the photocatalytic of the TNS. In a model of photocatalytic reaction, that is, rhodamine B degradation, the AgTNS demonstrates a high photocatalytic activity by convertingapproximately 91% of rhodamine B within only 120 min, equivalent toa rate constant of 0.018 m^–1 and ToN and ToF of94 and 1.57 min^–1, respectively, or 91.1 mmol mg^–1 W^–1 degradation when normalizedto used light source intensity, which is approximately 2 times higherthan the pristine TNS and several order higher when compared to Zn-and Al-doped TNSs. Improvement of the crystallinity degree, decreasein the defect density and the photogenerated electron and hole recombination,and increase of the oxygen vacancy in the AgTNS are found to be thekey factors for the enhancement of the photocatalytic properties.This work provides a straightforward strategy for the preparationof high-energy (001) faceted, two-dimensional, hierarchical, and porousAg-doped TNSs for potential use in photocatalysis and photoelectrochemicalapplication.