Morphology-controlled WO3-x homojunction: hydrothermal synthesis, adsorption properties, and visible-light-driven photocatalytic and chromic properties

In this paper, a facile one-step hydrothermal method for the synthesis of crystalline-amorphous WO3-x core-shell nanopowders (nanoparticles, nanorods, and nanowires) is reported. The core-shell structure, the size and the morphology of the core, and the shell ratio can be controlled by pH, the content of oxalic acid and the content of ammonium tungstate. A possible formation and growth mechanism is proposed. It was found that oxalic acid determines the crystalline-amorphous core-shell structure and NH4+/OH- plays a key role in retarding the crystal growth along the [001] axis. The synthesis method may introduce a new way to monitor and tune the stoichiometric and substoichiometric composition of semiconductor oxide nanostructure. The homojunction exhibits an enhanced adsorption ability, obvious visible photocatalytic efficiency, and good photochromic and chemochromic properties.