Catalytic and SERS Application of Gold Nanoparticles with Different Size

Author:Chong Han Bao

Supervisor:li guang


Degree Year:2019





Gold nanoclusters(NCs)and nanoparticles(NPs)which are characteristic for high surface-volume ratio and quantum size effect have been blooming along with the advances of nanomaterial science.Due to their extraordinary catalytic properties,they have been widely used in catalysis,which become a new research area rapidly.Since their size varies,and they are usually protected by ligands and carried by supports,besides,alloyed NPs are usually prepared to give rise to better catalysts,the size,ligand,support and alloy contribute to their catalytic capability.Thanks to inertness,biocompatibility of gold,surface plasma resonance and enormous surface-enhanced Raman scattering,bigger gold NPs(>10 nm)are investigated for SERS property comprehensively.The paper features synergistic effect of alloys,ligand effect of gold NCs in selective reduction,water-soluble gold NPs for their catalytic application along with recyclable Au nanorods(NRs)blended with graphene for their SERS investigation.Chapter 1.Alloy gold nanoclusters(NCs)have attracted tremendous attention by the nanomaterial chemists on account of their extraordinary properties.Herein,we report a photo-induced oxidation catalysis by four kinds of gold NCs.Due to the synergistic effect the alloyed NCs Au25-xAgx-were found to be the best among the tested catalysts,exhibiting complete conversion and exclusive selectivity.The phenomenon expands the scope of photocatalysts,rendering us more opportunities to explore more efficient catalysts.Chapter 2.It was well-established that the thiolate ligands laid significant influence on the catalytic properties of protected Au nanoclusters(NCs for short),especially the selectivity.In this work,catalytic nitro reduction is investigated over NCs catalyst.The electron-withdrawing effec tof thiolates renders the surface positively charged,which results in less aniline derivatives.The conversion is found to augment a lot after complete removal of capping thiolates,owing to the accessibility of active sites on Au NCs.Furthermore,a range of functionalized substrates(supporting Au NCs)are investigated for the universality of this catalytic reaction,and the composite catalysts show good tolerance to functional groups.Moreover,the exterior ligands were gradually peeled off by thermal treatment through controlling the temperature under vacuum,and the as-prepared catalysts were characterized by TEM,FTIR measurements.Using these catalysts,the relationship between the extent of ligand removal and the catalytic activity/selectivity was investigated.Chapter 3.A new protocol for generating carboxylic acid by oxidizing aldehyde is developed,using biomass starch protected gold nanoparticles(NPs)as catalyst.The heterogeneous catalysis system is composed of soluble catalysts and insoluble substrate.The gold catalyst is prepared,preserved and practiced for catalytic oxidation all in water.After reaction conditions optimized,H2O2 is found the best oxidizing agent with complete conversion.The Au NPs show overwhelming selectivity that aldehyde is oxidized into carboxylic acid while alcoholic hydroxyl group stay intact.Organic components are extracted by organic solvent and gold NPs in water are separated by skimming,correspondingly.Chapter 4.SERS is one of the analytical techniques with single-molecule sensitivity,thereby offering wide applications in materials researches,analytical science and industry.However,whatever the metal nanoparticles or the nanocomposites,these traditional SERS substrates are mainly one-time use,which increases the costs of SERS as well as the difficulty of subsequent validation experiments.Therefore,the development of reusable SERS substrates has attracted much interest.Herein,we developed a stable and reusable SERS-active platform by simply depositing graphene oxide on SiO2/Si substrate and then Au NRs coated onto the surface.Compared with Au nanorods,graphene oxide/Au NRs shows better Raman enhancements and better reusability,which could be ascribed to the improved specific binding of an analyte to a substrate,good dispersion of Au NRs in the graphene oxide and improved thermal stability.