| With the improvement of people’s living standard, the demand for leather is increasing. Leather industry has obtained rapid development,which has become an important industry in the light industry in China,and China has become the largest producer of leather around the world.However, leather industry is also a high pollution industry. Pollutants in leather industry mainly included industrial waste water and industrial waste gas. Leather industry wastewater is a kind of industrial waste water with complex composition, deep color, many suspended substances, easy to corrupt, containing organic compounds, heavy metals and other harmful compounds. At the same time, the tanning process also produces a large amount of harmful industrial waste gas composed of a variety of’volatile organic compounds. So it is urgent to treat the pollutants in leather industry.Due to unique effects and excellent properties. TiO2 nanomaterials have received more and more attention in the field of photocatalytic degradation, environmental protection and so on. With the development of various method technologies, the size and morphology have become the key factor for the excellent performance and wide application of nanomaterials. Because the interaction between nanomaterials and the target material mainly occurs on the surface or at the interface, the high specific surface area of the nanosize is very favorable to play its photocatalytic performance. Meanwhile, the structure determines the performance. Nanostructures consisting by using nanoparticles as the basic unit in dimensions according to a certain arrangement possess special morphology structure, multiple dimensions and different surface properties. Therefore, nanostructured titanium dioxide materials have not only the special effect of nanoparticles but also new effects brought by the combination of the whole structure. Compared with the traditional disordered nanomaterials, nanostructured titanium dioxide nanomaterials exhibit high photocatalytic activity and more beneficial to the practical applications in degradation of pollutants.Thus, according to the characteristics of pollutants in leather industry,this paper selects organotin and hexavalent chromium in tannery waste water and N,N-dimethylformamide in the tannery waste gas as target substances, prepares three kinds of titanium dioxide nanomaterials with specific structures, analyze the photocatalytic mechanism to targets, study the influence factors during the photocatalytic reaction process, and explore the practical application of the nanomaterials in the treatment of tannery pollutants. The main contents are described as follows:1. Hierarchical TiO2 microspheres consisting nanostructures were prepared by employing a microwave-assisted solvothermal process of titanium glycerolate intermediate precursor in this work. The morphology of building units ranging from nanoribbons to nanowires can be control facilely by adjusting the reaction time. These building nano-units in the form of nanoribbons and nanowires endow the hierarchical TiO2 microspheres with a large specific surface area, an efficient light-scattering effect and electron transfer. Microwave technology provides the basis for rapid and controllable preparation of nanostructured titanium dioxide. The new nanoribbons and nanowires based hierarchical TiO2 microspheres are used as photoelectrocatalyst in the application of removal of TBT in tannery wastewater. In this photoelectrocatalytic process, HPLC-ICP-MS and a 117Sn-enriched TBT spike solution as an isotopic tracer the first time were taken and used to discuss and confirm the mechanism on photoelectrocatalytic degradation of TBT. And it was found that the photoelectrocatalytic activity of as-prepared hierarchical TiO2 microspheres by applying an external potential was much higher than the photocatalytic activity, because of the possibility of electrons separation, followed by reduction of electron recombination. The calculated kinetic constants of TBT degradation by photoelectrocatalysis and photocatalysis are 0.0488 min-1 and 0.0052 min-1, respectively. Kinetics of TBT removal by TiO2 photoelectrocatalysis and parameters such as dosage, voltage of potential,and the presence of inorganic Cr(Ⅵ) and organic formaldehyde were discussed in detail by describing the time-dependent concentration of TBT. Finally, photoelectrocatalytic reduction of TBT was applied to actual tannery wastewater samples collected from production lines to confirm the feasibility of this photoelectrocatalysis. ID-HPLC-ICP-MS and biological toxicity test were used to quantify and evaluate the ability of hierarchical TiO2 microspheres for treatment of wastewater,degradation of organic compounds TBT, and reducing the biological toxicity of water quality.2. Uniformly distributed TiO2 spheres with hollow structures assembled by nanoparticles were prepared based on a template-free solvothermal process in this work. This microstructure endows the TiO2 spheres with a large specific surface area. The synthesis of spherical TiO2 catalytic materials with hollow structure and high surface areas is based on a self-assembly process induced by a mixture of organic acetic acid and ethanol. The possible formation mechanism of TiO2 spheres is proposed and investigated by acid concentration-dependent and temperature-dependent experiments. An unusual and effective photoelectrocatalytic technique for Cr(VI) reduction was reported by applying electric field to photocatalysis of as-prepared Ti02 hollow spheres in this work with high specific surface area. The mechanism of photoelectrocatalytic reduction of Cr(Ⅵ) was described according to the simultaneous determination of Cr(VI), Cr(Ⅲ) and total Cr in the system by HPLC-ICP-MS, MP-AES and spectrophotometric study. As a result, it was found that the reaction rate constant of photoelectrocatalytic reduction (0.0362 min-1) of Cr(VI) exhibited an almost 3 fold improvement in activity as compared to that of photocatalysis (0.0126 min-1). In addition, the effect of parameters such as dosage, concentration,pH, voltage of potential, and the present of Pb and formaldehyde were also discussed. Moreover, this photoelectrocatalysis with TiO2 spheres exhibited excellent activity for reduction of Cr(VI) in actual tannery wastewater produced from three different tanning procedures.HPLC-ICP-MS and biological toxicity test were used to quantify and evaluate the ability of TiO2 hollow spheres for treatment of wastewater,reduction of inorganic metal ions Cr(VI), and reducing the biological toxicity of water quality.3. Free-standing crystallized doubly open-ended titanium dioxide nanotube (TiNT) array membranes were designed and prepared by improved approaches employing a lift-off process based on an anodization-annealing-anodization-etching sequence to detach and open the bottom of nanotube lays, followed by uniform Ag nanoparticles decorating using photodeposition method in this work. The decoration by noble metal material with excellent conductivity and large specific surface area, not only can extend absorption range of light, but also can significantly decrease recombination of photogenerated charge carries.Even more, the obvious convection effect of the doubly open-ended nanotube arrays structure is feasible to facilitate the penetration of reactant molecules through the entire interior space. Therefore, the defined geometry of nanotube, porous surface and highly order array channel make the doubly open-ended Ag/TiNT array membrane particularly suitable for flow-through photocatalysis. The doubly open-ended Ag/TiNT array membrane was used for the photocatalytic degradation of gaseous DMF at low concentration levels close to that found in tannery waste gas. The photocatalytic experiments were performed using headspace vials, and degradation process of target DMF was monitored and analyzed by the HS-GC-MS methodology. Based on the analysis of results from HS-GC-MS and IC, possible photocatalytic degradation mechanisms and pathways of DMF were proposed and it is found that demethylation is the main pathway of DMF degradation in photocatalytic reactions. The results of degradation process show that compared with conventional bottom-closed Ag/TiNT arrays and pure bottomless TiNT arrays, the doubly open-ended Ag/TiNT arrays exhibited higher photocatalytic property in degradation of pollutant DMF.Meanwhile, effects of nanotube arrays with different anodization time,reaction temperature and initial DMF concentration were investigated.Decontamination of actual tannery waste gas collected in leather factory was then examined to investigate the possibility to treat air contaminated with volatile organic compounds including DMF by photocatalysis on doubly open-ended Ag/TiNT array membrane. HS-GC-MS was used to quantify and evaluate the ability of doubly open-ended Ag/TiNT array membrane for treatment of waste gas, degradation of volatile organic compound DMF. |
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