Molecule-Assistant Construction Of Au Or Pt Nanocomposites And Their Catalytic Performances

Functional composites possess not only the properties related to their components but also new functions based on synergistic effect of components.The dissertation involves in synthesis of functional composites by combination of metal such as Au and Pt nanoparticles with metal-organic frameworks(MOFs)or semiconductors.Their localized surface plasmon resonance(LSPR)enhanced photocatalytic performance and chemoselective hydrogenation for ?,?-unsaturated aldehydes are further explored.The dissertation mainly includes three parts shown as follows.(1)Encapsulation of Au nanoparticles into UiO-66(NH2)is successfully achieved based on a molecule-assisted heterogeneous nucleation-growth strategy,resulting in the formation of single-core Au@UiO-66(NH2)structures.The molecules of HAc/Ar or CO2 introduced can facilitate nucleation and growth of UiO-66(NH2),favorably preventing Au nanoparticles from etching in the synthetic process.The phtocatalytic alcohol oxidation was chosen as the model reaction to explore the plasmonic sensitization mechanism for upgrading MOFs'photocatalytic performance.The results of the photocatalytic alcohol oxidation under irradiation of visible light reveal Au@Ui0-66(NH2)shows higher photocatalytic performance in compared with pure UiO-66(NH2).The conversion of benzyl alcohol to benzaldehyde over Au@UiO-66(NH2)is?6 times higher than UiO-66(NH2).(2)A serial of metal nanoparticles/TiO2 composites(Au/TiO2,Ag/TiO2,Cu/TiO2 and Pt/TiO2)are prepared by a double-solvothermal route with the aid of glycine.The experimental results of the phtocatalytic H2 evolution show that the Pt/TiO2 composite gives the highest photocatalytic efficiency of hydrogen evolution among all composites.Under the irradiation of UV-visible light,plasmonic Au/TiO2 and Ag/TiO2 exhibit higher photocatalytic activity for water splitting compared with UV-visible-light illumination.Upon UV-visible-light illumination,occurrence of light absorption in composites is originated from optical transition of TiO2(UV region)and LSPR effect of plasmonic metal(visible region).The charaterizations of transient absorption and photocurrent reveal occurrence of reverse charge transfer between them,the reverse charge transfer can alleviate photocatalytic performance of these composites to enhance.(3)NH2-MIL-125(Ti)nanocrystals are used as a self-sacrificial template to prepare porous hollow cages of titanium oxides(PCT)that are served as supports to anchor Pt-based nanoparticles via an amino acid-assistant solvothermal route.The formation of stable porous cages is attributed to titanium oxide sheets as morphological scaffolds to maintain the hollow structures.The selective hydrogenation of ?,?-unsaturated aldehydes was chosen as the model reaction,the experimental results of catalytic hydrogenation of four kinds of ?,?-unsaturated aldehydes over various composites of PCT anchored Pt-based nanoparticles reveal that Pt-Co nanoparticles loaded PCT(Pt-Co/PCT)composites give high conversion and high selectivity.Under 0.1 MPa H2 and 80? for 3 h,the Pt-Co/PCT composites exhibit 98.5%conversion of cinnamaldehyde with-91%selectivity for cinnamyl alcohol.In the selective hydrogenation process,catalytic performance of Pt-Co alloys can be adjusted by changing the atomic ratio of Pt and Co.