Construction Of Titanium-oxygen Clusters By Multi-component "Cooperative Coordination" Strategy And Its Application In Photo/Electrocatalysis

Titanium dioxide nanomaterials have become hot photocatalysts due to their low toxicity,easy preparation,cheap and stable properties,which have great potential applications in green energy and environmental treatment.As the structural model compounds of titanium oxide nanomaterials,crystalline titanium oxygen clusters are widely concerned by scientists because of their easy structure tailoring and tunable properties.However,due to the easy hydrolysis of the generally used titanium precursors,the synthesis of titanium oxygen cluster is not an easy task,how to achieve the precise regulation of the conformational relationship between the structure and properties of titanium oxygen clusters is a key problem to be solved in this field.In this thesis,we precisely constructed a series of titanium oxygen cluster with multiple modifiable sites by"co-coordination"of various ligands,and used them as secondary building blocks to realize the precise bottom-up assembly of titanium oxygen cluster,and investigated the effects of differences in the assembly method and micro-component differences on the photocatalytic performance of the compounds.We also investigated the effects of the differences in assembly methods and micro-components in the structure on the photocatalytic performance of the compounds.The following work was carried out:（1）Using ferrocene dicarboxylic acid（Fdc H₂）and butanedione oxime（Dmg H₂）as co-assembled ligands,we were successfully constructed a highly nucleated titanium oxygen cluster{Ti₂₂Fc₄}which modified with ferrocene groups The overall structure of the cluster can be regarded as a"trans"Dmg^2-ligand connecting two{Dmg₃@Fdc₂@Ti₁₁}substructures,which are two{Dmg@Fdc@Ti₅}substructures coupled by a{Ti@Dmg}unit.This structural evolution conjecture can be further supported by mass spectrometry experiments.The mass spectrometric study of the cluster crystal samples and the reaction mother liquor reveals that the two substructures are stable in solution.We conducted a detailed screening of the reaction conditions and successfully isolated single crystals of{Ti₁₁Fc₂}cluster and{Ti₅Fc}cluster from the reaction solution alone.We also found the two cluster structures are almost identical to the two substructures in{Ti₂₂Fc₄}cluster.Accordingly,we successfully realized the stepwise assembly from{Ti₅Fc}to{Ti₁₁Fc₂}and finally to{Ti₂₂Fc₄},thus providing an example for the precise assembly of highly nucleated titanium oxygen clusters.Meanwhile,we designed a visible light-induced photocatalytic amine oxidation system to test the photocatalytic activity of these ferrocene-modified titania oxygen clusters.Among them,{Ti₅Fc}showed the best photocatalytic activity with 99%conversion of benzylamine after12 h reaction.（2）In this section,the self-assembly behavior of ferrocene-functionalized chiral titanium oxygen clusters at the nanoscale is investigated for the first time.Using ferrocene carboxylic acid and ketoxime ligands co-assembled with Ti（IV）ions,we successfully constructed a series of{Ti₅Fc}clusters with planar chirality by introduced planar chirality of ferrocene into the layered{Ti₅}structure The obtained chiral{Ti₅Fc}clusters can be used as building blocks and continue to be assembled in various ways to form larger ordered structures.The assembly modes include:a pair of{Ti₅Fc}enantiomers or two homochiral{Ti₅Fc}units bridged by organic ligands to form a sandwich{Ti₁₀Fc}structure.Depending on the assembly mode,the planar chirality of{Ti₅Fc}can either be transferred to a larger cluster or disappear to form an endocyclic structure.The different assembly modes of chiral units can also effectively regulate the photoelectric activity of the resulting clusters.The{Ti₁₀Fc-6/7}obtained by different assembly modes can be used as a photocatalyst for the selective photocatalytic oxidation of thioether to sulfoxide or sulfone.This work not only represents an important breakthrough in the study of chiral nanocluster self-assembly,but also provides an important reference for understanding chiral transfer on the nanoscale（3）In this section,an example of columnar{Ti₈L₂}clusters with active coordination sites was synthesized by using pyrazine dicarboxylate ligands,which can be used as building blocks to construct titanium cluster-based one-dimensional linear coordination polymers by synergistic assembly with heterometallic ions Mn²⁺,Cu²⁺,Zn²⁺,Cd²⁺,Ce³⁺,Eu³⁺,Lu³⁺,or[Cu₂I₂]cluster units.The single crystal structure analysis shows that the structure of the one-dimensional chains and the three-dimensional spatial stacking pattern are highly tunable with the variation of the radius and coordination number of metal ions.A total of three different chain structures and three different chain stacking patterns were explored by varying the charge and radius of the bridging metal ions.The catalytic alcohol oxidation experiments show that this series of titanium cluster-based polymers are excellence photocatalysts for the selective oxidation of alcohols to ketones,where both the bridging metal centers and the photosensitive titanium clusters can be active catalytic sites and catalyze the oxidation of substrates through different reaction pathways.We have investigated the catalytic mechanism in detail using mass spectrometry,electron paramagnetic resonance spectroscopy,cavity,superoxide radical quenching experiments and proposed a possible catalytic mechanism for this reaction system.This study highlights the potential of titanium cluster-based materials with active metal catalytic sites for applications in photocatalytic organic oxidation.（4）In this chapter,four examples of bimetallic clusters{Ti₆Cu₂},{Ti₈Cu₂},{Ti₁₀Cu₂}and{Ti₆Co₁₂}were obtained using butanedione oxime and acetic acid or pyrazinedicarboxylic acid as co-assembled ligands with the introduction of different heterometallic ions.Structural analysis revealed that{Ti₆Cu₂}and{Ti₈Cu₂}are bowl-shaped and consisted of two{Ti₃}or{Ti₄}units bridged by two Cu²⁺ions.{Ti₁₀Co₂}has a trapezoidal ring structure with two Co ions bridged by two tetrahedral{Ti₄}units bridged by pyrazinedicarboxylic acid ligands.{Ti₆Co₁₂}has a hexagonal geometric macrocyclic structure similar to[18-MC-6].By loading{Ti₁₀Co₂}directly onto carbon cloth,we have systematically investigated for the first time the electrolytic hydrolysis performance of heterometallic titanium oxygen clusters as bifunctional electrocatalysts.The prepared{Ti₁₀Co₂}/CC electrode has excellent OER and HER performance,reaching OER and HER overpotential of 400 m V and 100 m V,respectively,at 10 m A/cm² current density.The monolithic water splitting device using{Ti₁₀Co₂}/CC electrode as cathode and anode can provide 10 m A/cm²current density with only 1.67V.