Synthesis of potassium tungsten oxide nano/microwires by heat treatment of tungsten foils

Abstract

A simple method for synthesis of K2W6O19 nano/microwires with potassium hydroxide as catalyst on a tungsten foil via a unique two-step heating process has been reported. At first step, the temperature was raised to 390°C at a ramping rate of 30°Cmin−1 and kept at this point for half an hour. In the second step, the temperature was then raised to 400, 600 or 800°C at the same rate and maintained for 2h. The synthesized samples were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD). Scanning electron microscopy images show that the best temperature for growth of nanowires with 50 to 90nm widths and several ten micrometers length over the entire sample surface is 600°C. The XRD data shows that most of nanowires comprised (002) orientation with K2W6O19 structure. According to XPS results, the increasing annealing temperature increases W6+ state on the surface. The photocatalytic degradation of methylene blue over the sample annealed at 600°C exhibited the grown nanowires that have the best photocatalytic activity. In addition, a vapor–liquid–solid mechanism was proposed for describing the growth process of nanowires.