Study On Control Synthesis And Catalytic Performance Of Well-defined Gold Nanoclusters

Precisely controlled synthesis of gold nanoclusters at the atomic level has long been a major goal in nanoscience,due to their unique physical and chemical properties that differ from conventional gold nanopartilces.These atomically precise gold nanoclusters have been widely applied in nanoelectronics,novel catalysts,and biosensors,to name a few.Herein,we report the controlled synthesis of two different sized atomically precise gold nanoclusters Au144 and Au11.And then we investigate their catalytic properties.Finally,we demonstrate the surface modification of Au38S2?SAdm?20 nanoclusters using CDs.The main work of this thesis is listed as follows:?1?We present one-pot synthesis of Au144?SCH₂Ph?60 nanoclusters with moderate efficiency?ca.20%yield based on HAuCl4?.The Au144?SCH₂Ph?60 nanoclusters are obtained from the polydispersed Aun?SG?m nanoclusters in the presence of excess H-SCH₂Ph ligands via a combination of“ligand-exchange”and“size-foucing" processes.The as-prepared Au144?SCH₂Ph?60 nanoclusters are well determined by UV-vis and ESI-MS,and in conjunction with MALDI-MS and TGA.The purity of the Au144?SCH₂Ph?60 nanoclusters are further characterized by HPLC?SEC?.The PXRD analysis implies that the Au144?SCH₂Ph?60 nanoclusters do not adopt the face-centered cubic?fcc?structure.Further,the TiO2-supported Au144?SCH₂Ph?60 exhibits excellent catalytic activity?e.g.,92%conversion of methylphenylsulfide with 99%selectivity for sulfoxide?in the selective sulfoxidation.Size-dependence of the gold nanocluster is observed in the catalytic reactions and follows in order:Au144?SCH₂Ph?60>Au99?SPh?42>Au38?SCH₂CH₂Ph?24>Au25?SCH₂CH₂Ph?18.The larger sized gold nanoclusters give rise to better activity.?2?In this study,the atomically precise gold nanoclusters-Au11?PPh2Py?7Br3 are synthesized via facile "one-pot" procedure.Interestingly,in the chemoselective hydrogenation of nitrobenzaldehydes,the as-obtained cluster with ligand PPh2Py shows good catalytic efficiency in the absence of the base.The gold cluster and reaction pathway are well-determined by UV-vis,ESI and DFT calculations.It is found that one ligand?PPh2Py?removal is the first step to expose the core of the gold clusters to reactants,providing an active site for the catalytic reaction.This work demonstrates promise of functional ligand PPh2Py in the catalytic hydrogenation,thereby providing a more environmentally friendly reaction media.?3?We test the surface functionality of Au38S2?SAdm?20 nanoclusters?HS-Adm=adamantanethiolate?in the presence of ?-,?-,and y-cyclodextrins?CDs?.The supramolecular chemistry and host-guest interactions of CDs and the protecting ligands of nanoclusters are investigated using UV-vis,NMR spectroscopies,MALDI-MS and molecular dynamics simulations.In contrast to ?-CDs and y-CDs,the results show that two ?-CDs molecules can efficiently chemisorbe onto the surface of Au38S2?SAdm?20 nanoclusters to yield Au38S2?SAdm?20-??-CD?2 conjugates.The conjugates can largely improve the stability of the nanoclusters in the presence of oxidants,such as tert-butyl hydroperoxide?TBHP?.Further,the electrochemical properties of Au38S2?SAdm?20 and Au38S2?SAdm?20-??-CD?2 conjugates are well explored and compared.It is found that the ?-CDs molecular act as an umbrella to cover the fragile metal cores of the gold nanoclusters,thereby blocking direct interaction with agents?e.g.,oxidants?and quenching the charge transfer process between reactants and nanoclusters.