In the synthesis of WO3, 1.056 g of APT and 0.935 g of NaCl were dissolved in 30 mL of deionized water under mechanical stirring for 20 min. The mixture was adjusted to pH 2 using 3 M HCl and stirred for another 3 h. About 50 mL of the resulting solution was transferred into a Teflon-lined autoclave and incubated for 24 h at 180 °C. The sediment was filtered and washed with deionized water several times. The precipitate was then dried in an oven at 60 °C for 24 h.