Defect Engineering of Air-Treated WO3 and Its Enhanced Visible-Light-Driven Photocatalytic and Electrochemical Performance

In this paper, we reported that oxygen vacancies could be introduced in tungsten oxide hierarchical nanostructures through air treatment at certain temperatures. The production of oxygen vacancies may be due to two mechanisms, i.e., critical phase transition and nanoscale inhomogeneous deformation, depending on the annealing temperature or time and the size of the building block. The oxygen vacancies can be introduced at 300 and 350 degrees C when critical phase transformation from orthorhombic WO3 center dot 0.33H(2)O to hexagonal WO3 takes place or 350 and 400 degrees C when nanoscale inhomogeneous deformation occurs in the nanobelts. Moreover, the oxygen vacancy concentration is also influenced by the annealing time. For comparison, the oxygen vacancies are also introduced by hydrogen treatment. It is found that a certain amount of oxygen vacancies introduced by air treatment could trap and transfer electrons, thus decreasing the electron-hole recombination rate and improving the conductivity, while an abundance of oxygen vacancies introduced by hydrogen treatment could facilitate the electron-hole pair recombination and destroy the hexagonal tunnel structure, resulting in lower photocatalytic activity and electrochemical performance. Through air treatment, the constant rate of photocatalytic performance in degrading rhodamine B under visible light irradiation can reach 0.0300 min(-1), and the specific capacitance can improve to 166.7 F/g. It is suggested that both photocatalytic activity and electrochemical performance can be greatly improved by introducing a proper concentration of oxygen vacancies through air treatment.