Spray dried TiO2/WO3 heterostructure for photocatalytic applications with residual activity in the dark

Synthesizing titanium dioxide with energy storage ability represents a paradigm-shift for photocatalytic applications. We prepared titania tungstated photocatalysts (TiO2/WO3) by sol-gel and crash precipitation methods followed by spray drying to produce a micro-sized hybrid material. X-ray diffraction confirmed the tetrahedral and monoclinic crystalline structure of TiO2 and WO3 in the hybrid material calcined at 600 degrees C. Spray drying a suspension of titanium hydroxide alone creates spherical 20 mu m TiO2 particles, whereas a suspension of ammonium paratungstate dissolved in hydrochloric acid produces 7 mu m median size needle like WO3 particles. According to SEM-EDX images, spray drying both semiconductors together produces a homogeneously distributed mixture of the powders. The TW0.075 (titanium dioxide/tungsten oxide having 0.075 molar ratio of tungsten precursor) hybrid powder, with a surface area of 221 m(2)/g, 2.88 eV band gap energy, and 21.5% of anatase [001] facets (Raman analysis), decreased the electron-hole recombination with 1594 ns of carrier lifetime (PL-TRPL analysis). TW0.075 outperforms the rest of the samples in the UV degradation of the model pollutant methylene blue (MB), converting 90% MB in 100 min (30 min dark + 40 min light + 30 min dark), thus demonstrating energy storage ability in the absence of UV irradiation. Hydroxyl radicals (OH center dot) and superoxide anions (O-2 center dot(-)) are the species mainly involved in the pollutant degradation. We propose the transfer pathways mechanism of the photogenerated charge carriers in the hybrid samples.