“Bi–O” vacancy-pairs induced photochromic behavior in Bi2WO6 ultrathin nanosheets

Developing cheap and efficient materials for enhancing the photochromic performance upon visible or solar light irradiation is a hot-topic in the field of solar energy conversion . However, few inorganic photochromic materials can provide satisfying applications due to their low coloring and bleaching efficiency as well as slight color change. Here, we synthesized the bismuth tungstate (Bi 2 WO 6 ) ultrathin nanosheets with the thickness of 1.29 nm via co-precipitation-hydrothermal method using cetyltrimethylammonium bromide (CTAB) surfactant . The prepared ultrathin nanosheets show the similar crystalline structure but a narrowed band gap of 2.73 eV, as compared with the 2.86 eV of pristine Bi 2 WO 6 . Additionally, the numerous [WO 6–x Br 2x ] species and abundant “Bi–O″ vacancy pairs on the surface can serve as active sites that suppress the recombination of photogenerated electron-hole pairs and capture the photogenerated electrons to form the color trapping centers. As a result, Bi 2 WO 6 ultrathin nanosheets exhibit excellent photochromic behavior upon solar light irradiation (coloring time of 5 s) and under dark atmospheric treatment (bleaching time of 35 min) compared with WO 3 -based photochromic materials (coloring time of 20–60 min and bleaching time of 3 h days).