Phosphate constituent effects on the structure and photocatalytic properties of mesoporous tungsten oxides

Mesoporous WO3 replicas were synthesized by a hard template method using ammonium metatungstate (AMT) or phosphotungstic acid (PTA) as a tungsten source. The mesoporous WO3 replica synthesized from AMT (WO3-AMT) and PTA (WO3-PTA) consisted of a crystalline monoclinic phase and mixed crystalline tetragonal and monoclinic phases, respectively. The absorption of WO3-PTA in the visible region was stronger than that of WO3-AMT. These characteristics reflected the oxidation states, which were affected by the existence or non-existence of minor phosphate constituents in the mesoporous WO3 replica. WO3-PTA contained a phosphate constituent from the tungsten source. However, WO3-AMT and WO3-PTA have similar mesostructures and band-gap energies. WO3-AMT and WO3-PTA with Cu2+ ions showed 28.4 and 5.5 times higher photocatalytic activities than that of bare commercial TiO2 (P-25) in decomposition of acetic acid under visible-light irradiation. The phosphate in WO3-PTA functioned as a recombination center.

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► Ammonium metatungstate or phosphotungstic acid was used as a tungsten source.
► Mesoporous WO3 prepared from phosphotungstic acid contained phosphate constituents.
► Phosphate constituent influenced the oxidation state of the mesoporous WO3.
► Photocatalytic activity of the mesoporous WO3 was suppressed by the phosphate constituent.
► Photocatalytic activity of WO3 under visible light irradiation increased by the mesostructure and Cu2+ ions promoter.