Precise Synthesis Of Noble Metal Multilayer Hollow Structure

The noble metal nanoalloy structures not only possess basic properties such as small size effect,quantum size effect and surface effect,but also can easily tune the electronic structures and synergistic effects between different components,which endows themselves highly adjustable and diverse properties and applications compared with single metal materials.In particular,multilayer noble metal hollow nanostructures have been attracted considerable attention in energy storage and conversion,biosensors,and catalysis due to their desirable properties of low density,high specific surface area,rich catalytic active sites,and high loading capacity.However,it is still challenging to realize the precise synthesis noble metal multilayer hollow materials with controllable structure.In this thesis,the precise synthesis of multilayer hollow nanostructures with different morphologies could be achieved through galvanic replacement reactions based on different metal activity and standard redox potentials of precious metals such as gold,silver,platinum,and palladium.Furthermore,the applications in plasmon-enhanced Raman spectroscopy,nanozyme catalysis,p-nitrophenol catalytic hydrogenation,and chiral functionalization was explored.The main research contents are listed as follows:1.Precise synthesis of multilayer hollow superstructures with ultra-high density optical hot spotsGold nanospheres（Au NPs）with uniform morphology were firstly synthesized by seed growth method.Au@Ag core-shell nanocubes with different thicknesses were then prepared using Au NPs as nucleus.Following that,through the galvanic replacement reaction of HAu Cl₄ and Ag taken as sacrificial templates,porous hollow nanostructures（multi-Au@Au Ag NPs）with different layers and hot spots enhancement factors could be obtained.Transmission electron microscope（TEM）,scanning electron microscope（SEM）and energy dispersive spectrometer（EDS）were further used and the results verified the successful synthesis of the multilayer hollow structure.For five-layer porous hollow nanostructures（penta-Au@Au Ag NPs）with electromagnetic enhancement intensity up to 221,the finite difference time domain（FDTD）theoretical simulation showed enhanced electronic fields at high-density hot spots in their nanogaps and nanocavity.Moreover,penta-Au@Au Ag NPs could achieve highly sensitive surface enhanced Raman spectroscopy（SERS）detection of molecules such as methylene blue,crystal violet,2-aminobiphenyl,uracil,uric acid,and thiediazole copper.2.Precise synthesis of multilayer hollow nanostructures with adjustable elementsAu@Pt,Au@Pd hollow nanostructures using Au NPs as the core were firstly synthesized based on the galvanic replacement reactions between sacrificial templates Ag,Pt and Pd.Multiplex noble metal multilayer hollow structures were then fabricated by adjusting deposition times of Ag and the way of spatial permutation of metals.The results of TEM,SEM and EDS verified the successful synthesis of the multielement and multilayer hollow nanostructure.The catalytic activity of multilayer Pd and Pt hollow nanostructures was further investigated based on the specificity of elemental properties.The results showed that multilayer Pd hollow nanostructures exhibited intrinsic peroxidase-like activity,catalyzing the classical peroxidase substrate3,3’,5,5’-tetramethylbenzidine（TMB）by hydrogen peroxide（H₂O₂）.Besides,Pt hollow nanostructures showed excellent catalytic hydrogenation activity for p-nitrophenol（4-NP）.3.Precise synthesis of multilayer hollow nanostructures with stepwise chiral amplificationAu@Ag NRs with controllable size were firstly prepared using anisotropic double-surface gold nanorods（Au NRs）obtained by seed growth method.Using L-cysteine as the chiral molecules,hollow nanorods（L-Au@Au Ag NRs）with built-in gaps and plasma circular dichroism（PCD）response were synthesized by the galvanic replacement reaction.PCD signal could be amplified by optimizing the size of the nanogap and the concentration of chiral molecules.The results showed that L-Au@Au Ag NRs exhibited the highest PCD response when the concentration of Ag NO₃and L-cysteine reached 0.67 m M and 10 m M,respectively.Benefited from the two-layer hollow structure,a 2.37-fold amplification of PCD signal could be achieved.