The Photocatalytic And Photoelectric Performance Of The Modified Preparation Of Nano TiO₂

Facing the worldwide energy shortage and environmental pollution problems,people need to develop a new energy to replace the traditional fossil fuels.In series of new energy,solar energy has unique advantages and great potential.For example,the solar cell can convert solar energy into electrical energy effectively,and the photocatalysis can translate the solar energy into chemical energy and also achieve the degradation of organic pollutants.As a common semiconductor material,TiO₂ has many advantages,including stable physical and chemical properties,friendly to the environment and low cost etc,which are widely applied in the solar cell,photocatalysis,water-splitting,lithium-ion batteries,gas sensors,and other fields.However,the TiO₂ has two inevitable problems,which are the recombination of photogenerated electron-hole pairs and the narrow response range to light.Hence,the modification research of TiO₂ has been always the frontier and hot topic.In this thesis,the work was developed based on TiO₂ nanocrystalline,including the immobilization,semiconductor compound and doping treatment.The magnetic Fe₃O₄loaded TiO₂?Fe-TiO₂?powders,heterostructured SrTiO₃-TiO₂ nanotube arrays?ST-TNTAs?and nitrogen doped TiO₂ nanorod arrays?N-TNAs?were received and applied in the degradation of organic dye pollutants and dye sensitized solar cells?DSSCs?.The main work is listed as follows:?1?Firstly,the porous TiO₂ nanoparticles were synthesized with titanium tetraisopropoxide as titanium source through the hydrolysis-hydrothermal method,and then mixed with ferric oxalate by a certain mass ratio.Finally,the magnetic Fe₃O₄immobilized porous TiO₂ nanoparticles were successfully obtained by calcination process.According to X-ray diffraction?XRD?,TiO₂ and Fe₃O₄ were composed of anatase phase and magnetite phase,respectively.The morphology test revealed the size of TiO₂nanoparticles was around 15 nm,while the size of Fe₃O₄ was too small to be observed.Mesoporous structure was found in the sample by N₂ adsorption-desorption isotherm measurements,and the Brunauer-Emmertt-Teller?BET?surface areas were decreased with the amount of immobilized iron.In the photocatalytic experiments,the Fe-TiO₂sample with a mass ratio of 1:200 exhibited an excellent photocatalytic activity for the degredation of the organic dyes X3B both in air and in the presence of H₂O₂,indicating a synergetic effect between photocatalysis and Fenton reaction.A little loss of iron in recycled samples was tested by inductive coupled plasma emission spectra?ICP?.The high stability and recovery of the photocatalyst was proved by the cycle experiment.As the existence of magnetic Fe₃O₄ in TiO₂,the photocatalyst could be easily collected by the magnet,which not only saved resources but also protect the environment.Therefore,the great potential of the Fe-TiO₂ photocatalyst should be considered in the practical application of the degradation of organic pollution.?2?In this research,heterostructured SrTiO₃-TiO₂ nanotube arrays on fluoride doped SnO₂ conductive glass?FTO?substrate were synthesized through a three-step in-situ hydrothermal reaction.According to morphology and crystal characterizations,the TiO₂nanotubes in ST-TNTAs vertically grew on the FTO substrate in single crystallized rutile phase,while the SrTiO₃ nanoparticles in cubic perovskite phase dispersed evenly on the surface of TiO₂,the grain size of which was about 30 nm.The sandwich shaped all-solid-state DSSCs were assembled with TiO₂ nanorods,nanotubes and ST-TNTAs as the photoanode,respectively,and the photoelectric performance was tested under simulated sunlight irradiation.In addition,the effects of the concentration of Sr?OH?₂,reaction time and temperature on the photoelectric properties were also studied.After the deposition of SrTiO₃ onto the surface of TiO_2,the Fermi level position of the composited semiconductor raised,which resulted in the increase of open circuit voltage(V_OC).Meanwhile,both short-circuit current density(J_SC)and photoelectrical conversion efficiency???increased first and then decreased with the amount of Sr element.In comparison to TiO₂ nanorod arrays and nanotube arrays,ST-TNTAs demonstrated both the highest photoelectrical conversion efficiency?5.42%?under the irradiation of the solar simulator and external quantum efficiency?EQE?at visible region,and also the lowest electron transfer resistance.Thus it can be proved that SrTiO₃ acted as a good medium for electron transfer between TiO₂ and photosensitizers.As a result,both the increased surface area of the nanotube relative to the nanorod and the matched bandgap structure in the composited structure of TiO₂ and SrTiO₃ improve the performance of the DSSCs.?3?In this study,highly ordered nitrogen doped TiO₂ nanorod arrays?N-TNAs?were prepared through a facile hydrothermal process with ammonium chloride as nitrogen source and butyl titanate as titanium source,and then were calcined at different temperatures.According to characterizations of XRD and field emission scanning electron microscopy?FESEM?,the rutile phase TiO₂ nanorods vertically grew on the FTO substrate.After nirtrogen doping,no other impurity phase was detected and the crystalline structure kept unchanged.With the increase of dopant amount,the diameter and length of TiO₂ nanorods first increased then decreased.In addition,doping amount and element valence of nitrogen in N-TNAs were further calculated by X-ray photoelectron spectroscopy?XPS?.Through the hydrothermal reaction,most of nitrogen was deposited on the surface of TiO₂ nanorods,and a small amount of nitrogen could enter into bulk TiO₂ and form Ti-N-O structure.When the N-TNAs were assembled into the DSSCs,with the increase of doped amount,photoelectrical conversion efficiency of the DSSCs first increased and then decreased with the photoelectric conversion efficiency of 3.16%,which was much higher than that of un-doped samples?1.62%?.After sintering treatment,photoelectrical conversion efficiency can be further increased to about 5.32%,which may be due to the conversion of surface adsorbed nitrogen to skeletal nitrogen during calcination process.The EIS showed the lowest electron transfer resistance of the calcined N-TNAs as DSSCs photoanode.Therefore,it is proved that N-TNAs should be considered as a potential photoanode for high-performance DSSCs.