Study On The Preparation Of Novel Photocatalytic Nanomaterials And Their Application In Photodegradation Of Environmental Pollutants

Along with the development of global industrialization process, environment pollution becomes more and more serious. Environmental issues have already become the most important problem which influence human survival and development in21st century. In recent years, photocatalytic reaction has become an ideal environment pollution control and clean energy production technology with its greenhouse depth of reaction and directly using solar energy as the light source to drive the reaction unique performance. There are many different interaction between light and substances. Photocatalytic reactions is one way to use light on substance transformation, which involve the combined action of light and catalyst. Photocatalytic technology is the interdisciplinary emerging research field which involve catalytic chemistry, photoelectric chemistry, semi-conductor physics, materials science and environmental sciences. Photocatalytic oxidation has been considered as the most promising technology to solve environmental pollution problems and has become the research focus in the field of environment.Titanium oxide (TiO2) has been considered as one of the most promising photocatalysts because of its compelling advantages such as superior photoactivity, non-toxicity, chemical stability and capability of photooxidative destruction of most organic pollutants. TiO2has been extensively studied as a fascinating photocatalyst for the photodegradation of organic contaminants, solar energy, gas sensors and water splitting for hydrogen production. The research of TiO2application has caused great interest since the first discovery of water splitting on the surface of TiO2-based photochemical electrode by Fujishima and Honda. Unfortunately, as is known, the wide band gap of TiO2(3.2eV) allows it to absorb only UV light, limiting its possibility of employing visible light which occupies the major part of solar light. Furthermore, the high rate of recombination of photogenerated electron/hole pairs often results in a low quantum yield and poor efficiency of photocatalytic reactions because of the poor rate of electrons and holes that reach the interface between the photocatalysts and water where the degradation is inherent to take place. Many works have been devoted such as non-metal ion doping, metal ion doping, noble metal deposition, sensitization with dyes and combination with metal oxides and narrow band gap semiconductors.The main work of this paper is focus on the modification of TiO2, including combination with semiconductor, doping, noble metal deposition and combination with graphene. These methods can effectively extend the photoresponse of TiO2to the visible-light region and accelerate the electron transfer, thus improving the photocatalytic efficiency. The matials were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectrum (DRS) and so on. The photocatalytic efficiency was verified by photodegradation of methyl orange (MO) and methylene blue and the scheme was also discussed. There are mainly four parts in the paper:Chapter1:OverviewIn this part, we have mainly introduced the recent research process of photocatalyts and the application of photocatalytic technology involving organic contaminants, solar energy, gas sensors and water splitting for hydrogen production. We have state briefly the environmental pollution status and the application of TiO2in water pollution. Meanwhile, we also summarized the defects of TiO2and the main modified methods. Finally, we emphatically pointed out the purpose and significance of the dissertation, its innovation spot and content as well.Chapter2:Enhanced visible-light-induced photoelectrocatalytic degradation of dye by CdS sensitized TiO2nanotube arrays electrodeIn this work, CdS sensitized TiO2nanotube arrays (CdS/TiO2NTs) electrode was synthesized with the CdS deposition on the highly ordered titanium dioxide nanotube arrays (TiO2NTs) by sequential chemical bath deposition method (S-CBD). The as-prepared CdS/TiO2NTs was characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and UV-vis diffuse reflectance spectrum (DRS). The results indicated that the CdS nanoparticles were effectively deposited on the surface of TiO2NTs and the absorption spectrum of TiO2NTs was extended to visible region. The amperometric I-t curve on the CdS/TiO2NTs electrode was also presented. It was found that the photocurrent density was enhanced significantly from0.5mA/cm2to1.85mA/cm2upon illumination with applied potential of0.5V at the central wavelength of253.7nm. The photoelectrocatalytic (PEC) activity of the CdS/TiO2NTs electrode was investigated by degradation of methyl orange (MO) in adueous solution. Compared with TiO2NTs electrode, the degradation efficiencies of CdS/TiO2NTs electrode increased from78%to99.2%under UV light in2h, and from14%to99.2%under visible light in3h, which was caused by effective separation of the electrons and holes due to the effect of CdS, hence inhibiting the recombination of electron/hole pairs of TiO2NTs.Chapter3:Nitrogen doped TiO2Coupled with Graphene sheets nanocomposites as photocatalysts for Enhanced photocatalytic degradation of organic dyeWe synthesized nitrogen doped TiO2(TiON) and then obtain TiON-graphene composite (TiON-GR) via a one-step hydrothermal reaction. The photocatalytic (PC) properties of this composite material were investigated by degradation of methylene blue (MB) unded UV and visible light irradiation. The as-prepared TiON-GR photocatalyst was characterized by SEM, TEM, EDX, XRD, FTIR and UV-Vis DRS. In the photodegradation of methylene blue, a significant enhancement in the reaction rate was observed with TiON-GR, compared to the bare TiO2. Additionally, we have investigated the effect of different ratios of graphene on the photocatalytic activity of TiON-GR systematically.Chapter4:Au/TiO2-GR composites as a novel photocatalyst for Enhanced photocatalytic degradation of methylene blueIn this chapter, through the hydrolysis of isopropyl titanate, we get titanium dioxide and then get titanium dioxide crystals through annealing. With high purity graphite as raw materials, we have obtained the graphene oxide and then mixed with titanium dioxide to obtain the TiO2-GR by reduction of graphene oxide. Then the gold nanoparticles was deposited on TO2-GR by phtocatalytic reduction of HAuCl4to get Au/TiO2-GR nanocomposite materials. Material has a strong adsorption performance towards methylene blue and can accelerate the methylene blue get adsorption balance in material surface in the degradation of process, thus improving degradation efficiency. We also compared the degradation effect of methylene blue with TiO2, TiO2-GR and Au/TiO2-GR. We found that through the gold deposition and combination with graphene can greatly improve the performance of the photocatalytic degradation of titanium dioxide. The as prepared Au/TiO2-GR material has absorption toward visible light and can efficiently separate the electron-hole pairs, thus improving the photocatalytic ability of TiO2.