Preparation of 3-D ordered macroporous tungsten oxides and nano-crystalline particulate tungsten oxides using a colloidal crystal template method, and their structural characterization and application as photocatalysts under visible light irradiation

Three-dimensionally ordered macroporous (3DOM) tungsten(VI) oxide (WO(3)) was prepared using a colloidal crystal template method. Well-ordered 3DOM WO(3) was prepared with a high pore fraction using ammonium metatungstate ((NH(4))(6)H(2)W(12)O(40)), a Keggin-type dodecatungstate, as a tungsten precursor; WO(3) materials prepared by other commercially available W precursors, tungsten chloride (WCl(6)), tungsten(V) ethoxide (W(OEt)(5)), and phosphotungstic acid (H(3)PW(12)O(40)), have a low 3DOM pore fraction. These WO(3) materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET) analysis of nitrogen adsorption isotherm, and Raman spectroscopy. Non-porous WO(3) prepared from ammonium metatungstate without a poly(methyl metacrylate) (PMMA) template grew to crystal sizes of up to several micrometres with a low specific surface area (ca. 1-2 m(2) g(-1)). In the presence of a colloidal crystal template of PMMA spheres, WO(3) crystal grew in the nanometre-sized voids between the PMMA spheres, and the specific surface area thus increased up to ca. 30 times compared to non-porous WO(3). The surface area is tunable by changing the PMMA sphere diameter. Calcination of the 3DOM WO(3) produced WO(3) nano-crystalline particles by sintering-induced disassembly. After Pt-loading, these WO(3) materials showed higher photocatalytic activity compared to non-porous WO(3) for decomposition of acetic acid in air under visible light irradiation.