Syntheses And Photocatalytic Properties Of Titanium-Oxo Clusters

Titanium-oxo clusters（TOCs）have shown promising photocatalytic performance in the applications such as photocatalytic H₂ production,CO₂ reduction,degradation of environmental pollutants,catalytic oxidative desulfurization,and so forth.Moreover,the precise crystal structure information of titanium-oxo clusters can provide structural models to study the structure-property relationship of catalytic materials at the cluster level.At present,the improvement of visible-light absorption and structural stability in aqueous reaction conditions are key issues for the research on titanium-oxo clusters.In this thesis,the designed synthses of titanium-oxo clusters were carried out via the strategies of ligand-functionalization and metal doping.The crystal structures of as-synthsized titanium-oxo clusters were characterized by single-crystal X-ray diffraction analysis.The physicochemical properties,spectrascopic and photoelectrochemical properties of the clusters were investigated.The photocatalytic properties of titanium-oxo clusters including photocatalytic oxidative desulfurization and photocatalytic dye degradation were studied.The influence of cluster structure on catalytic performance was analyzed and discussed.The main results in this thesis are summarized as follows:1.The 8-hydroxyquinoline functionalized titanium-oxo clusters of the formulation[Ti₉（μ₃-O）₇（μ₂-O）₃（μ₂-OⁱPr）（OⁱPr）₅（O₂C^tBu）₉（OQ）]·HOⁱPr（Ti₉OQ）and[Ti₁₂（μ₃-O）₈（μ₂-O）₆（μ₂-OⁱPr）₂（OⁱPr）₄（O₂C^tBu）₁₂（OQ）₂]·4H₂O(Ti₁₂OQ₂)（HOQ=8-hydroxyquinoline）were synthesized.The presence of 8-hydroxyquinoline ligands significantly extends the visible-light absorption range and effectively reduces the band gap（～2.4 e V）.The titanium-oxo clusters show favorable activity for the visible-light-driven photocatalytic oxidative desulfurization.The results demonstrate that the core structure clusters have significant influence on the photocatalytic activity of titanium-oxo clusters.2.The main group metal Ca-doped titanium-oxo cluster[Ca₂Ti₈（μ₃-O）₈（Ac O）₂（OⁱPr）₂（BA）₁₆]·4H₂O（BA=benzoate）was synthesized.Due to the unique{Ti₈Ca₂O₈}core structure and the coordination with sixteen bridging benzoate ligands,this cluster exhibits high structural stability in aqueous solutions with p H ranging from 2 to 12.Photocatalytic experiments for the degradation of methyl orange（MO）demonstrate the high photocatalytic activity and good recycling stability of the cluster.3.The rare earth metal Er-and Yb-doped titanium-oxo clusters[Er₂Ti₈（μ₃-O）₈（μ₂-O）₂（μ₂-OH）₂（BA）₁₆](Ti₈Er₂BA₁₆)and[Yb₂Ti₈（μ₃-O）₈（μ₂-O）₂（μ₂-OH）₂（BA）₁₆](Ti₈Yb₂BA₁₆)were synthesized.Due to the unique cage-like Ti₈Ln₂ core structure fully coordinated by sixteen benzoate ligands,the clusters exhibit high stability in both acidic and alkaline aqueous solutions.The clusters show good catalytic performance for photocatalytic degradation of methylene blue（MB）and photocatalytic desulfurization of dibenzothiophene（DBT）.The results show that Er³⁺is more favorable to improve the electron-hole separation efficiency,and thus improves the photocatalytic activity of Ti₈Er₂BA₁₆.4.ThetransitionmetalNi-dopedtitanium-oxoclusters[Ni₂Ti₄（μ₃-O）₂（μ₂-O）₂（BA）₁₂（CH₃CN）（H₂O）]?CH₃CN(Ti₄Ni₂BA₁₂)and[Ni₂Ti₄（μ₃-O）₂（μ₂-O）₂（O₂C^tBu）₆（MA）₄（OQ）₂]（Ti₄Ni₂OQ）were synthesized.Crystal structure analysis shows that Ti₄Ni₂BA₁₂ and Ti₄Ni₂OQ₂ have similar Ti₄Ni₂ core structure.The clusters show catalytic activity for the visible-light-driven photocatalytic oxidative desulfurization of DBT.The 8-hydroxyquinoline ligand acts as photosensitizer that effectively improves the visible-light photocatalytic performance of Ti₄Ni₂OQ₂.