The photochromic material, tungsten trioxide nanostructure has been successfully prepared by the simple precipitationmethod using nitric acid with the assistance of an oxalic acid. The effect of oxalic acid as the chelating agent on themorphologies, crystal structure, the optical properties and photochromic properties were investigated. The synthesizednanostructure characterized by X-ray diffractometer consisted of orthorhombic and hexagonal phase. The results fromscanning electron microscopy and transmission electron microscopy presented the flower-like shaped nanostructure formed bythe growth of many nanosheets. UV-vis spectrophotometer displayed the absorbance peak at lower than 550 nm. The band gapenergies of the products were decreased and the powder changed color from yellow to dark green after UV irradiation. Theproducts prepared with oxalic acid exhibited the highest photochromic effect due to the mixed phase of orthorhombic (81%)and hexagonal (19%) crystalline which having more defect concentration in its structure and the narrow band gap energy.

Keywords: Tungsten trioxide, Precipitation, Photochromic, Oxalic acid, UV light