Effect of solution pH on as-synthesized and calcined WO3 nanoparticles synthesized using sol-gel method

Tungsten oxide nanoparticles are particularly suitable for a wide range of applications like non-invasive cancer treatment, water treatment, gas sensing, and so on. In this paper, the effect of the solution pH on as-synthesized WO3 nanoparticles and calcined WO3 nanostructures at 500 °C is investigated to achieve appropriate WO3 nanoparticles with a simple and low-price sol-gel method. The results declare that solution pH significantly affects the morphology, crystallinity, chemical bonds, and optical properties of WO3 nanoparticles. Increasing solution pH from 1 to 2 with the step of 0.5 leads to crystal phase transition and increment of the hexagonal phase percentage. The size of nanoparticles increases with increasing the solution pH in as-synthesized. So, it turns out that solution pH affects the particles growth process. In addition, the results reveal that increasing the solution pH leads to a blue shift at the optical absorption edges. Also, the indirect energy bandgap of WO3 particles increases/decreases with increasing pH in the case of as-synthesized/calcined samples. The energy bandgaps of calcined samples were generally lower than as-synthesized ones. The sample prepared at pH = 1 shows the highest absorption (about ten times higher than other samples at λ = 300 nm) and low reflection in the whole range of the spectrum that makes it a worthy candidate for photocatalysis applications.