Study on the Preparation and Properties of TiO2-based Heterostructures

Author:Jia Chang Chao

Supervisor:yang ping

Database:Doctor

Degree Year:2018

Download:186

Pages:198

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In this thesis,based on the morphological synthesis of TiO2 materials,the preparation and properties of heterojunctions,which composed of TiO2 as the modification materials and the matrix materials,were studied.The thesis attends to synthesize different morphologies of TiO2 materials and study the effects of microstructure,phase composition and defects on their properties.TiO2 as the modification materials are used to form composites with Ag nanowires and rGO,as well as their properties are researched.TiO2 as the matrix material,we introduce SnO2 to vary the morphologies of heterojunctions,and study their applications in photocatalysis,lithium-ion batteries,and sensing.The specific research contents are as follows:1.The morphological synthesis of TiO2 materials and their properties study.(1)TiO2 hollow structure makes full use of incident lights to enhance its own photocatalytic properties.Monodispersed mesoporous anatase TiO2 hollow microspheres with controllable morphology and size are prepared via thioglycolic acid(TGA)chemically induced self-assembly.We study the preparation process on the morphologies,and discuss the formation mechanism of TiO2 hollow spheres.Among them,the self-assembly of Ti-oxo clusters formed by hydrolysis of tetrabutyl titanate(TBT)played a key role in the formation of spherical structure,then with the synergistic effects of thermodynamics(Ostwald ripening process)and kinetics(gas release),various morphologies are controlled to prepare.In the photocatalytic degradation of organic pollutants and photocatalytic hydrogen production,hollow spheres exhibit superior performance compared to solid sphere structures.(2)Anatase and rutile mixed-phase hollow TiO2 hierarchical boxes were prepared by a Topotactic synthetic method.The CaTiO3 microcubes were used as sacrificial templates to make the phases distribute uniformly in the hollow boxes.When the phase composition of the sample is similar with that of P25(80%anatase and 20%rutile),it exhibits an excellent photocatalytic properties.Anatase and rutile are closely contacted in the hierarchical boxes,which improve the separation efficiency of photo-generated carriers,and the hollow structure can make full use of incident light.As a result,the experimental results show that in the photocatalytic degradation of methylene blue organic pollutants,the degradation rate of the TiO2 hierarchical hollow structure is 2.7times higher than that of P25 nanoparticles.(3)TiO2-B samples self-doped by Ti3+were prepared using a mixed solvent of ethylene glycol and water.In the preparation process,ethylene glycol was oriented adsorbd on the surface of TiO2 to form a layered structure.The viscosity of the solvent and reductivity induce the material to form Ti3+.The number of lamellae and the thickness of the TiO2-B spheres can be easily adjusted.The layered structure of TiO2 has a large specific surface area and shows excellent photocatalytic performance due to the presence of Ti3+in the TiO2-B material.After H2O2 oxidation treatment with the sample,the number of surface defects in the TiO2-B sample decreases,which reduces the photocatalytic activity of the samples.It indicates that the defect plays an important role in the photocatalytic performance.2.Different morphologies of silver nanowire/titanium dioxide(Ag NW@TiO2)composite photocatalyst.AgNW@TiO2 necklace-like heterostructures were prepared for the first time.They were prepared by a two-step synthesis method.Firstly,uniform silver nanowires were prepared and then TiO2 was deposited on the surface.The use of thioglycolic acid(TGA)molecules as linkers solves the problem of lattice mismatch between the Ag NW core and TiO2.The addition amount of water and the dielectric constant of the solvent are important factors in the formation of necklace-like heterostructures.By changing the amount of tetrabutyl titanate(TBT),the diameter of the TiO2 beads can be changed.The photocatalytic activity of necklace-like Ag NW@TiO2was evaluated by degradation of methyl orange(MO)under ultraviolet(UV)light.The results show that the molar ratio of TiO2 to Ag and the diameter of TiO2 beads have a synergistic effect on photocatalytic activity.The highest photocatalytic activity was found when the molar ratio of Ti to Ag in the TiO2 heterostructure was 2.8.In order to improve the photocatalytic activity of AgNW@TiO2 material,three kinds of Ag NW@TiO2heterostructures with core shell,necklace-like,and particle deposited were prepared.The existence of TGA and the solvents polarity to regulate the coating state of TiO2 on the Ag NW surface.The molar ratio of TiO2 to Ag is critical to the photocatalytic activity.The close contact between Ag NW@TiO2 samples with core-shell structure shows superior performance compared to the other two samples.3.Fabrication rGO and TiO2 heterostructures to enhance their photocatalysis.Full spectrum Z-scheme rGO/TiO2-Bronze(TiO2-B)/W18O49 photocatalyst is fabricated by a two-step solvothermal method.The ternary heterostructure has ability to absorb sunlight ranging from UV to near infrared(NIR)regions,which makes full use of solar energy for efficient photocatalytic degrading organic pollutants.TiO2-B nanosheets tightly attached on the rGO firstly,and then W18O49 nanowires grew on rGO/TiO2-B.The light absorption intensity increased with the addition of rGO in the composite,as well as the localized surface plasmon resonance effect arising from the nonstoichiometric ratio of W18O49,which are in favour of the absorption range of the rGO/TiO2-B/W18O49composite material broadening to NIR range.Z-scheme photocatalytic mechanism of rGO/TiO2-B/W18O49 is verified by electron spin resonance test.The conduction band of TiO2-B and the valence band of W18O49 are used in the photocatalytic degradation of rhodamine B,facilitating the efficient separation of photogenerated carriers.As a result,the rGO/TiO2-B/W18O49 heterostructure exhibits an excellent photocatalytic performance under full spectrum irradiation.4.The morphology and phase composition of TiO2 are regulated by SnO2 as well as studied in photocatalysis,Li-ion batteries,and gas sensing areas.The CaTiO3 precursor was prepared by a Topotactic synthetic method and converted into TiO2 by ion exchange.The waxberry-like anatase/rutile mixed-phased TiO2 hollow structure was successfully prepared,and an appropriate amount of SnCl4 was added in the initial stage of the reaction,the TiO2@SnO2 hierarchical structure can also be successfully prepared.The structural characteristics of the samples are that rutile TiO2 nanorods nearly radial alignment growth on the external surface of the hollow sphere composed of anatase TiO2and SnO2 nanoparticles.The addition of SnO2 not only adjusts the morphology of the product,but also changes the ratio of anatase and rutile phases in the composite.(1)In the study of photocatalytic properties,methylene blue was degraded using low-power UV light to evaluate its photocatalytic performance.The hollow structure enhances light-harvesting ability,and the appropriate proportion of phase composition improves the charge separation.SnO2 nanomaterials were added into the TiO2 matrix material,making that the waxberry-like TiO2@SnO2-5%sample exhibits an excellent photocatalytic performance and good cycle stability.(2)The synthesized TiO2 and TiO2@SnO2 hierarchical structures were used as anode materials for lithium ion batteries.Compared with TiO2 samples,the TiO2@SnO2-5%shows the improved lithium storage capacity,cycling performance and rate properties.After adding a small amount of SnO2,the impedance of the TiO2 electrode significantly decreased.The hollow hierarchical structure with different compositions provide much more active sites,and well connect interface among anatase,rutile,and SnO2,facilitating the electron and ion transport quickly and efficiently.(3)TiO2 hierarchical structure uniformly decorated with SnO2 nanoparticles gives an excellent performance in the detection of triethylamine(TEA)gas.As a novel sensing material,TiO2@SnO2 shows a higher response in low concentration of TEA and a rapid responding speed in comparison with individual TiO2 components.At the case of 5 ppm TEA gas under the operation temperature of 240℃,the response value of TiO2@SnO2sample is up to 21.6,which is three times higher than that of TiO2 sample.The responding speed of TiO2@SnO2 sensors elevates 28%in comparison with TiO2.