The Preparation Of Novel Nano-structured Photocatalysts For The Degradation Of Dye Wastewater

Titanium dioxide ?TiO₂? has attracted enormous attentions from scientists and engineers over the past decades, owing to its superior photo catalytic activity, low cost, abundant resource, nontoxic nature and high photo corrosion resistance. The current widely used photocatalysts titanium dioxide has a narrow range of visible light absorption and low photoelectric conversion, thus it is significant to design new material and nano-structure with high photocatalytic activity.In this study, we mainly carry out the controllable synthesis of TiO₂ nanostructures; Bi2?OH?2SO4 and Bi6S2O15 new oxy-acid salt photocatalysts and BiOCl bismuth defect photocatalysts. And it is systematically studied the mechanism of enhanced photoactivity and the improved energy efficiency. The main contents of this thesis are as follows:1. For the first time, anatase TiO₂ twin crystals have been synthesized by a simple hydrothermal method. The effect of reaction time, temperature, the concentration of HF and the amount of water on the morphology and properties of the samples were investigated. The samples are characterized using X-ray diffraction?XRD?, scanning electron microscopy ?SEM?, high-resolution transmission electron microscopy ?HRTEM?, selected area electron diffraction ?SAED?, UV-vis diffused reflectance spectra ?UV-DRS?, and nitrogen sorption isotherms. It is found that a prolonged reaction time significantly contributes to the structure evolution and that twin crystals form via the Oriented Attachment ?OA? and Ostwald Ripening?OR?-controlled secondary growth mechanism. Remarkably, the photoactivity of TiO₂ twin crystals is 2.57 and 8.74 times higher than single crystalline anatase TiO₂ nanosheets and rutile TiO₂, respectively. This has been mainly ascribed to the unique twin crystals structure.2. Herein, we have mainly investigated energy bands and photochemical properties of Bi6S2O15 and Bi2O?OH?2SO4,which have the very similar layered structure. It is found that the hydroxyl shifted the conduction band and valence band of Bi2O?OH?2SO4, compared with those of Bi6S2O15. Moreover, the main oxidative species over Bi6S2O15 and Bi2O?OH?2SO4 are holes ?h+? and hydroxyl radicals ?·OH?for the degradation of rhodamine B ?RhB? dye, respectively. This obvious difference has been mainly attributed to the presence of hydroxyl, which has changed energy band structure and band gap. In addition, we have also investigated the morphology-dependent properties of Bi2O?OH?2SO4. Under ultraviolet light irradiation ???420 nm?, Bi2O?OH?2SO4 microspheres show an activity 1.3 times and 2.2 times higher than long flakes and straw sheaves for the degradation of rhodamine B ?RhB?, respectively.3. Herein, the BiOCl nanosheets without and with surface bismuth vacancy?BOC, V-BOC? are prepared by a simple hydrothermal method. It is found that the new surface defect states caused by bismuth vacancy have greatly up-shifted the valence band and efficiently enhanced the separation and transfer rates of photogenerated electron and hole. It is amazing that the photocatalytic activity of V-BOC is 13.6 times higher than that of BOC for the degradation methyl orange ?MO?. We can develop an efficient photocatalyst by the introduction of defects.