Preparation And Photocatalytic Properties Of Modified TiO₂ Nanomaterials With Low Dimensions By Hydrothermal Method

Energy source and Environmental problems have become the important situations during modern society development.As a result,material science,which is represented by new energy materials and environmental-friendly materials,plays an irreplaceable role in science research.Low-dimension nanomaterial is an important area in material science because of its unique structure,large surface area and surface activity.As a famous semiconductor,TiO2,with low cost and harmless to environment,could be useful in both solar energy and waste decomposition areas.The main disadvantages of TiO2 are the low ef:ficiency of sunlight absorption caused by the wide band gap,and the high ratio of recombination of electron-hole pairs in the bulk materials.So in this thesis,hydrothermal method is used to change the structure of TiO2 into nanosheets and nanotubes,which widen the surface area of TiO2 and make it easier to combine with other materials.Then the cerium and two-dimension MoS2 are used to modify TiO2,in order to expand the light-absorption area.The specific work is listed below:Hydrothermal method has been used to prepare different ratio cerium doped TiO2 nanotubes.HRTEM,XRD,XPS and UV-Vis have been used to characterize the structure and properties of the samples.The TEM pictures,XRD and XPS all show that the cerium ions exist in the doping samples.It can be observed from HRTEM images that the CeO2 crystals appears around the TiO2 crystals.The result of XRD shows that as doping ratio growing up,the peaks become wider and lower,which indicate that the size of crystal is decrease,as well as the crystallinity.The peak of CeO2 shows in the result,too.XPS result shows that the chemical status of Ti ions could be divided into Ti4+ and Ti3+,while the unique structure of Ti-O-Ce could be formed.The ratio of Ce/Ti in the sample is close to the original doping ratio.It is shown in the UV-Vis result that the absorbing edges of all the samples are showing red shift,reaching the area of visible light.Among all the samples,the cut-off wavelength of 25%Ce-doped sample is larger,which indicates a lowest band-gap of 2.48eV.The experiment proves that cerium doping could modulate the band gap of TiO2 and enhance its light absorption.The results of photocatalysis indicate that the sample of 0.5%Ce-doping get the highest efficiency,which the degradation ratio is close to 90%after 3h reaction towards RhB solution.Hydrothermal method has been used to produce the metallic phase of MoS2,and structure and properties have been characterized.The SEM images indicate the surface of metallic MoS2 is different from the original semiconductor phase,while on the other hand,it shows the same main peaks on XRD result between metallic and semiconductor phase MoS2.H2O peak was observed in the metallic samples,which related to the calculation result of metallic MoS2 crystal structure.TEM result shows that the interplanar distance of metallic MoS2 is different from semiconductor phase.The calculation from XPS result shows the excess of S2',which could contribute to the negative potential on metallic MoS2 surface.The difference on Raman result could be a easy method to distinguish metallic with semiconductor phase of MoS2.In order to characterize the physical absorption ability of MoS2,four different kinds of dye solution are used,which could be divided into cation dyes and anion dyes.It is observed that metallic phase MoS2 has great absorption ability towards cation dyes,which is opposite towards anion dyes.The semiconductor MoS2 shows the same trend,but due to its hydrophobicity,the amount of absorption is not high.The surface structure,excessive S2-ions and the OH-on metallic surface,which as the calculation of my colleague,is the main reason to keep metallic MoS2 hydrophilic,could be the reasons to explain the result of preferential ion absorption.To get more evidence,the metallic MoS2 was stored in solution with different pH for 48h.It is observed that metallic MoS2 changed into semiconductor when kept in acid solution,while on the other hand,dissociated into smaller pieces when in the base solution,which could prove that it has concerned with the OH-on the surface of metallic MoS2.Hydrothermal method was used to prepare metallic MoS2-TiO2 nanotubes and semiconductor MoS2-TiO2 nanotubes.SEM,TEM,XRD,XPS,Raman,UV-Vis have been used to characterize.The results of SEM,TEM,XRD,Raman and XPS all prove the two material's combination.TEM result also shows the difference between metallic MoS2 and semiconductor ones in interplanar space.XPS result also shows the changing of binding energy between Mo and S in the metallic-TiO2 sample,which indicates that the combination effect the structure of metallic MoS2,but the change is not shown in the result of semiconductor MoS2-TiO2 samples.The UV-Vis result shows that the composite sample improves the absorption in visible light area.Rhodamine B has been used as target to characterize the photocatalytic ability of different ratio and different phase MoS2-TiO2 samples.The result indicate that,adding semiconductor MoS2 would improve the physical absorption to the target dye solution,which the reason could be that TiO2 improves the hydrophily of semi-MoS2,while metallic MoS2 improves the photocatalysis of TiO2 nanotubes,because of the high conductivity leading to the separation rate of electron-hole pairs.