Preparation Of Titanium Dioxide Nanotubes And Its Applicatopn In Treatment Of Dye Wasterwater

Dye wastewater without treatment discharge will pollute the environment because ofits high chroma, high toxicity and complex ingredients. It is not so good that use thegeneral methods such as chemical and biological treatment to degrade the dye wastewater.The TiO₂photocatalyst has attracted a great deal of attention in environmental wastewatertreatment, because it generates highly oxidative hydroxyl free radicals （·OH） resulting incomplete mineralization of many toxic and non-biodegradable organics. It also has thepotential to use of solar energy.However, the wide band-gaps （3.2eV） and high recombination rate of electron–holes inTiO₂photocatalysts give rise to a low quantum efficiency of photocatalytic reactions. One ofthe most important approaches was to dope TiO₂with transition metal elements, whichwould improve its photocatalytic activity. Compared with the titanium dioxide powder andthin film, TiO₂nanotube has great specific surface area and prominent absorption ability. It isa new way to improve the photocatalysis property of nanometer TiO₂via preparingnanometer TiO₂to nanotube, but there are seldom researches about photocatalysis propertyof metal ions doped TiO₂nanotubes. The adsorption of pollutants is the precondition ofphotocatalytic reaction. Furthermore, very few studies have been done with the focus onadsorption mechanism of organic pollutants on the surface of TiO₂nanotubes.In this paper, Fe-series doped TiO₂nanotubes were synthesized with a simplehydrothermal process using commercial titanium dioxide （Degussa P25） as precursors. Thesimples were characterized by scanning electron microscope techniques （SEM）,transmission electron microscopy （TEM）, X-ray diffraction （XRD）, theBrunauer–Emmett–Teller method （BET）, and the UV-Vis spectroscopy. SEM and TEMresults showed that regularly uniform nanotubes were fabricated by the hydrothermaltreatment, and they had homogeneous multi-walled tubular structures and open ends. TheXRD results indicated that titanium dioxide powders were completely transformed to TiO₂nanotubes and no anatase or rutile phase appeared in the obtained nanotubes. In terms ofthe morphology and the structure, there was no significantly difference between Fe-series doped TiO₂nanotubes and pure TiO₂nanotubes. The nitrogen adsorption–desorptionisotherm exhibited a Type IV adsorption isotherm, which is a typical characterization ofmesoporous materials. Absorbency was analyzed by the UV-Vis spectroscopy. Comparedwith P25, TiO₂nanotubes had better absorption ability. Fe-series doped TiO₂nanotubesgreatly extended the absorption edge to the visible light region, with the increase of addingamount of the ions.Adsorption of methylene blue over Ni²⁺-doped TiO₂nanotubes was studied. Factorsaffecting the adsorption process: Ni²⁺concentration, pH, contact time and temperaturewere investigated. Experiments results indicated that adsorption capacity of TiO₂nanotubes was better than that of nanopowder precursors. Adsorption capacity of preparedsamples increased with increasing of Ni²⁺concentration in titanate nanotubes, when Ni²⁺concentration achieved to5mol%（Ni-TNTS-5）, the sample had maximum adsorptioncapacity. With increasing of pH value, the adsorption capacity of samples increased as well.At pH value10, the adsorption capacity of Ni-TNTS-5reached a maximum value. It wasalso found that increasing temperature result in higher dye loadings per unit weight of thesorbent. The adsorption isotherms fitted well to Langlnuir and Freundich equation and thefront one is better suited. In addition, TiO₂nanotubes had better degradation property thanP25, and Ni²⁺-doped TiO₂nanotubes was better than pure TiO₂nanotubes. The stand orfall of adsorption performance is closely related to the photocatalytic activity. However, itdoesn’t mean that the catalyst will have better photocatalytic activity when it has betteradsorption performance.The photocatalytic activities of Fe-series doped TiO₂nanotubes were evaluated by thephotocatalytic degradation of methylene blue. Compared with pure TiO₂nanotubes, thephotocatalytic behavior of the Fe-series doped nanotubes was much more better under thesame condition, which was of the following order: Ni²⁺＞Fe³⁺＞Co²⁺＞pure. The usedsample could been recycled via simple gravity sedimentation method, and the recycled onealso had good degradation property.