Tuning of the crystal engineering and photoelectrochemical properties of crystalline tungsten oxide for optoelectronic device applications

Abstract

The photocatalysis, chromism, and sensing capabilities of nanostructured tungsten oxides, such as tungsten trioxide (WO₃), its suboxides (WO_x, 0 < x < 3) and hydrates (WO₃·nH₂O, n = 1/3 (0.33), 0.5, 0.75, 1, 2, etc.), tungsten bronzes M_xWO₃ (M = Li, Na, K, Rb, Cs and NH₄), and metal tungstates (such as Bi₂WO₆ and CuWO₄) have attracted much attention. To improve these properties, many strategies have been pursued, such as morphology control, doping, and heterostructuring. Crystal facet engineering has recently become a very important method of fine-tuning the physicochemical properties of semiconductors. The photocatalytic reactivity of a photocatalyst is significantly affected by its surface environment, including its surface electronic and atomic structures, which strongly depend on the crystal facets. It is believed that crystals with different exposed facets will have different properties, with the exposure of highly activated facets enhancing the photocatalytic and sensing properties. This article describes the syntheses of 2D WO₃ crystals with the {002} facet primarily exposed, octahedral WO₃ or WO₃·nH₂O with exposed {111} facets, and WO₃ films with dominant orientations, such as orientation along the {002} facet. WO₃ doping, WO₃-based heterostructuring and their applications are also presented in this paper.