Effective mesoporous nanocrystalline C-doped TiO(2) photocatalysts were synthesized through a direct solution-phase carbonization using titanium tetrachloride and diethanolamine as precursors. X-ray photoelectron spectroscopy (XPS) results revealed that oxygen sites in the TiO(2) lattice were substituted by carbon atoms and formed a C-Ti-O-C structure. The absorption region of the as-prepared TiO(2) was extended to the visible light region in view of the substitution for oxygen sites by carbon atoms. The photocatalytic activities of the as-prepared samples were tested in a flow system on the degradation of NO at typical indoor air levels under simulated solar-light irradiation. The samples showed a more effective removal efficiency than commercial photocatalyst (P25) on the degradation of the common indoor pollutant NO. The parameters significantly affecting the mesoporous structure and removal efficiency on indoor air were also investigated.

In this study, porous Bi2WO6 microsphere photocatalysts were obtained via the ultrasonic spray pyrolysis method using bismuth citrate and tungstic acid as precursors in basic aqueous solution. The characteristics of the resulting samples were investigated in detail by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption, X-ray photoelectron spectroscopy, and UV−vis diffuse reflectance spectroscopy. The resulting porous Bi2WO6 microsphere was of high crystallinity, which means fewer traps and stronger photocatalytic activity. The band-gap energy of Bi2WO6 microspheres estimated from the (αhν)2 versus photon energy (hν) plots was 2.92 eV. The formation of the porous structure in the as-prepared microspheres can be ascribed to the existence of citrate anions and in situ generated carbon residues that can serve as capping agents and templates, respectively, during the synthesis processes. It was found that the synthesis temperature was an important parameter controlling the morphology of the Bi2WO6 microspheres. As compared with the bulk Bi2WO6 sample, the resulting porous Bi2WO6 microspheres demonstrated superior photocatalytic activities on the removal of NO under either visible light or simulated solar light irradiation. The highest NO removal rates were 110 and 27 ppb/min for the porous Bi2WO6 sample under solar light and visible light (λ > 400 nm) irradiation, respectively. On the basis of the analysis of the characterization and experimental observations, a possible mechanism on the formation of porous Bi2WO6 microspheres was also proposed.

The morphology-controlled fabrication of nano-/microstructured functional materials has opened up new possibilities to enhance their physical and chemical properties and remains a great challenge. This work represents a one-pot template-free fabrication and growth mechanism of novel rose-like uniform (BiO) 2 CO 3 hierarchical hollow microspheres, which are self-assembled by single-crystal nanosheets. The observation of time-dependent evolution of crystal structure and morphology revealed that the growth mechanism of such a novel structure might involve a unique multistep pathway. First, an amorphous particle was formed during a nucleation and aggregation process. Then, the intermediate (BiO) 4 CO 3 (OH) 2 of embryonic stacked buds with attached particles were produced due to Ostwald ripening. The driving force for the formation of such embryonic structure is the intrinsic dipole field introduced by the nanosheets as a result of selective adsorption of the citrate ions on some polar surfaces of the nanoparticles. Subsequently, all the particles were consumed and (BiO) 4 CO 3 (OH) 2 crystals started to transform to (BiO) 2 CO 3 phase by means of repeated reaction-dissolutionrecrystallization process in a homocentric layer-by-layer growth style, where carbonate ions substituted OH À groups. Monodisperse buds were then generated and the size of the hollow in the center becomes smaller to reduce surface energy. Finally, all (BiO) 4 CO 3 (OH) 2 transformed to (BiO) 2 CO 3 phase and uniform monodisperse (BiO) 2 CO 3 roses were produced through layers splitting driven by the OH À group deintercalating from the interlayer spaces of (BiO) 4 CO 3 (OH) 2 . More interestingly, the novel (BiO) 2 CO 3 microspheres exhibited outstanding activities under both UV and visible light irradiation for indoor NO removal, far exceeding that of commercial P25, synthetic C-doped TiO 2 and (BiO) 2 CO 3 with particle morphology due to the special hierarchical morphology and band gap structure.