Synthesis Of Metal Nanoclusters And Their Catalytic Applications

Ultra-tiny metal nanoclusters with precise atom arrangement have attracted abundant attention recently,due to their unique electronic structures and the subsequent unusual physical and chemical properties,which make them have promising application potentials in numerous fields,such as catalysis,chemical sensors,electronics,biological labeling and biomedicine.As for catalysis,atomically precise metal nanoclusters become a class of model catalysts owing to their high monodispersity,determined composition and atomically precise and tunable structures,which is beneficial for us to further understand the relationship between the structure and activity of the catalysts.In recent years,great progress has been achieved in size-controlled synthesis,separation and purification,characterization and application study.In this dissertation,several different metal nanoclusters including palladium,platinum and nickel nanoclusters were prepared through the facile wet chemical method using different thiol ligands.Meanwhile,a series of structural characterizations of the synthesized metal nanoclusters were carried out by various analytical tecniques and investigated the application of the metal nanoclusters in catalysis and electrochemical sensing.The main works are outlined as follows:1.The synthesis,characterizations and catalysis applications of the palladium-based nanoclusters(1)Based on DMF-mediation and ligand-exchange reaction,atomically precise Pd5(C12H25S)13 nanoclusters are successfully synthesized.By loading the as-prepared Pd5 nanoclusters on multiwalled carbon nanotubes and the following pyrolysis to remove the thiolate ligands,the surface-cleaned Pd5 clusters can serve as efficient electrocatalysts for the oxygen reduction reaction and the ethanol oxidation reaction.The Pd5 clusters showed higher mass and specific activities and better durability than the commercial Pd/C catalyst for the oxygen reduction reaction.As for the ethanol oxidation reaction the Pd5 clusters exhibited lower onset potential,peak potential and much smaller charge transfer resistance than the commercial Pd/C catalyst.(2)A simple one-step method is developed to synthesize sub nano meter-sized Pd clusters with the molecular formula of Pd6(C12H25S)11 in the room temperature by using oleylamine(OAm)as the solvent and 1-dodecanthiol(DT)as both protectingligand and the reducing agent.The ligand-free Pd NCs showed an ultrahigh catalytic activity for the reduction of 4-nitrophenol(4-NP)to 4-aminophenol(4-AP)and were superior to other reported Pd-based nanocatalysts.The present work not only provides a facile method for synthesizing ultrasmall metal clusters but also indicates that sub-nanometersized Pd clusters can be used as highly efficient catalyst for the degradation of environmental pollutants.2 The synthesis,characterizations and electrochemical applications of the platinum-based nanoclusters(1)Water-soluble Pt21(C4O4SH5)21 nanoclusters was synthesized in aqueous phase by using K2PtCl4 as the Pt(II)source and mercaptosuccinic acid as both ligand and reducing agent.By loading the Pt NCs on reduced graphene oxide nanosheets(rGO)and the following removal ligands upon annealing treatment,the obtained surface-clean Pt NCs/rGO with low platinum content exhibited higher hydrogen evolution reaction(HER)catalytic performance and more superior stability than commercial Pt/C.This work clearly indicates that Pt catalyst on cluster scale can obviously improve the catalytic performance.Therefore,this study provides an effective avenue to enhance the utilization of noble metals and to develop high-performance and cost-effective catalysts.(2)Using the reducibility of oleamine at high temperature,the platinum nanoclusters with the molecular formula of Pt5(C12H25S)13 was synthesized.The Pt NCs were then loaded on carbon black and calcinated at three different temperatures(300?,410? and 600?)according to the thermogravimetric curve of the nanoclusters.The related experiments indicated that the ligand can be removed at 300?.Because of the low loading of the clusters,the high temperature calcination cannot lead to the aggregation of Pt NCs.The ligand-free Pt NCs can be used as a non-enzymatic electrochemical sensing material for the detection of dopamine with high selectivity and wide linear range.3 The synthesis,characterizations and electrochemical sensing applications of the nickel-based nanoclustersA simple method was developed to synthesize atomically precise Ni clusters with the molecular formular of Ni6(C12H25S)12 and its single crystal was also obtained.In the structure of Ni6(C12H25S)i2 clusters,the six nickel atoms form a hexagonal ring with pairs of sulfur atoms uniformly situated above and below the plane of the nickel ring,resembling a double crown.It was found that the Ni6 clusters exhibited higher electrocatalytic activity than Ni nanoparticles towards ascorbic acid oxidation.This work not only provides a straightforward method for synthesizing atomically precise metal clusters but also indicates that ultrasmall Ni clusters can be used as highly efficient catalysts for the electrochemical detection of ascorbic acid.