Study On Doped And Intercalted Layered Tetratitanates For Efficient Photocatalysis

With the development of technology and economy, issues of energy crisis andenvironmental contamination have become increasingly prominent. In recent years,semiconductor photocatalysis has been widely applied to solar energy conversion andenvironmental purification, which provides an effective approach to solve theproblems. However, some important factors severely hinder the development of thesemiconductor photocatalysis and its application, such as low rate of solar energyutilization and low quantum yield. So preparation of new efficient photocatalysts is ofgreat significance.K2Ti4O9is a layered titanate with a high photocatalytic activity and can beemployed as basic building blocks for preparation of new-type photocatalysts. In thisdissertation, Firstly, K2Ti4O9has been used to prepare Cu-doped titanate by theconventional solid state reaction. It is also be used for the synthesis of transition metalions intercalated nanocomposites and different semiconductors pillarednanocomposites via an exfoliation-restacking route. The as-prepared samples wereinvestigated by means of XRD, SEM, UV-Vis DRS, XPS, N2adsorption-desorptionisotherms and other technology. The photocatalytic activities of these samples werealso evaluated.Firstly, Cu-doped titanate (K2+2xTi4-xCuxO9) was prepared by a solid statereaction. After the doping, the Cu-doped titanate still maintains the same layeredstructure. The Ti4+ions in lattice were partially replaced by the copper ions.Compared with that of pure titanate, the UV-Vis absorbance spectra of theseCu-doped samples showed a shift to longer wavelength with the increase of theamount of the Cu dopant. When the doping amount reached to0.3%, the Cu-dopedtitanate showed the best photocatalytic activity for the degradation of MB under UVirradiation, which was1.6times greater than that of K2Ti4O9.Secondly, K2Ti4O9prepared by the solid state reaction was firstly exfoliated intoTi4O92-nanosheets by the chemical way. Utilizing the restacking properties of exfoliated2D titanate nanosheets, Co-Ti4O9, Cu-Ti4O9and Ni-Ti4O9intercalatednanocomposites have been synthesized by assembling Ti4O92-nanosheets with Co2+,Cu2+and Ni2+, respectively. All of the intercalated nanocomposites exhibited poroustextures with high specific surface areas which were4~6times greater than that ofH2Ti4O9. The UV-Vis DRS and XPS results suggested that the onset wavelengths ofthe as-prepared nanocomposites red-shifted to the visible light region, as a result ofthe strong interaction between the host and the guest. The photocatalytic activity testsdemonstrated that the intercalated materials can efficiently degrade MB moleculesunder visible-light irradiation.Finally, CrOx-H2Ti4O9and CdS-H2Ti4O9pillared nanocomposites wassuccessfully fabricated via an exfoliation-restacking route under different conditions.The gallery heights of CrOx-H2Ti4O9and CdS-H2Ti4O9were about1.7and2.3nm,respectively. They also had expanded specific surface areas of52and98m2/g andaverage pore diameters of about36and2.7nm, respectively. The analysis resultsfrom UV-Vis DRS and XPS suggested that there existed an electronic coupling in theheterostructure fabricated by the host and the guest, which made the absorptionwavelengths of CrOx-H2Ti4O9and CdS-H2Ti4O9have red-shifts to566and548nm.Both CrOx-H2Ti4O9and CdS-H2Ti4O9showed high photocatalytic activities.CrOx-H2Ti4O9can efficiently degrade MB molecules under visible-light irradiation,and CdS-H2Ti4O9was an effective catalyst for photocatalytic hydrogen evolutionfrom water splitting under visible-light irradiation. CdS-H2Ti4O9-300pillarednanocomposite obtained by the heat treatment a H2evolution rate of358.6μmol.h-1.g-1, which is68.6,57.6and9.6times those of K2Ti4O9，H2Ti4O9and CdS,respectively. It is notable that the pillared material exhibited a good stability and anexcellent repeatability.