Removal of anionic azo dye from aqueous solution via an adsorption-photosensitized regeneration process on a TiO2 surface.

Textile dye effluents are typically characterized by strong color and recalcitrance, even at very low concentration. The process of enrichment of anionic azo dye on the surface of TiO(2) fibers followed by photosensitization degradation under ambient air conditions was extensively investigated. Adsorption isotherms and zeta potentials were used to describe the "dye/TiO(2) surface" interface, taking into account the effects of pH on the nature and population of the surface groups on the TiO(2) fibers. The extent of the photocatalytic degradation of dye on TiO(2) surface was determined by FTIR. N(2) adsorption isotherms and optical spectra were employed to investigate the effect of photosensitization. The adsorption of dyes on the TiO(2) surface occurs via electrostatic attraction through the formation of single- or multidentate-coordinated surface complexes. Almost complete photobleaching of the absorption band at 534 nm is achieved in ~4 h. Dye-sensitized TiO(2) fiber could absorb part of the visible light spectrum (λ < 600 nm). Interfacial electron transfer can potentially alter the degradation efficiency. The regenerated TiO(2) fiber could be reused for subsequent decolorization without a decline in adsorption efficiency compared with freshly prepared TiO(2) samples, which may be attributed to preservation of the hierarchical pore structure and restoration of the original surface properties. In summary, we propose an efficient "adsorption-photoregeneration-reuse" process applying TiO(2) fibers for the degradation of dyes in water.

Low-temperature hydrothermal synthesis of N-doped TiO2 from small-molecule amine systems and their photocatalytic activity.

Nitrogen-doped TiO2 nanopowders have been successfully synthesized by a one-step hydrothennal route under soft-chemistry conditions (150 degrees, 8 h) without high-temperature calcination using seven different types of nitrogen dopants: methylamine, ethylamine, diethylamine, ethylenediamine, triethylamine, triethanolamine and ammonia. X-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption isothenns and Fourier transform infrared spectroscopy were used to analyse the as-synthesized TiO2 powders. The results indicated that nitrogen was doped effectively and the structure and morphology of the titania samples were strongly influenced by the nitrogen sources. Among the investigated nitrogen sources, the diethylamine system was clearly superior to the other small-molecule amine or ammonia systems due to the broad-spectrum response (between 400 and 700 nm) of the interstitial nitrogen-doped TiO2 nanopowders. The diethylamine N-doped TiO2 had the largest pore volume (0.39 ml x g(-1)) and showed a well-aligned anatase phase. The visible-light photocatalytic degradation of liquid X-3B used as a probe reaction demonstrated that the removal rate over the diethylamine material reached 99.7% in 90 min.