Self-assembly And SERS Performance Of Nano-metal Mesh Film At Gas-liquid Interface

Compared with individual nanoparticles(NPs),the high-level assembly nano-structures with one-dimensional(ID),two-dimensional(2D)and three-dimensional(3D)structure features show a more abundant collective properties and synergistic effects,owing to their multi-scale,multiple components and multi-level special structures.More importantly,the fabrication of nanomaterial assembly with different functions provides the possibility of nano-electric devices.Noble metal NPs(such as Au,Ag)show excellent catalytic,optical and electronic performances,leading to a wide range of applications,including catalysis,biosensing,biomedicine and photonics.The Au(Ag)network structure formed by self-assemble exhibit high surface areas,and the interaction among the NPs,which would carry out charge transfer and energy transport more efficiently,thus showing improved catalytic,optical and electrical properties.The self-assembly nanoparticles method at gas-liquid interface is widely used in the characteristics of simple,universal and fast.Compared with unassembled single nanoparticle,Au and Au-Ag bimetallic NPs with different sizes are used as assembly units to produce 2D network-like NPs thin film at the gas-liquid interface.They have more advantages such as large surface area,coupling between inter-particles,interfacial properties and electronic structure characteristics between different components,which show significantly enhanced catalytic,electrical and SERS performance.Based upon the above research background,in this study,we report on a facile and new strategy for the assembly of Au NPs network-like thin film,which could self-assemble the Au NPs at the air-water interface without adding any additives under room temperature.The method does not require templates,surfactants,organic ligands and biomolecules to assist or induce the assembly of Au NPs.In addition,the Au,Au-Ag and Au-AuAg bimetallic network-like thin films with larger scale and higher stability can be obtained by further growth.Finally,the SERS performance of several NPs thin films was studied by using p-aminothiophenol(4-ATP)as probe molecule.This thesis mainly carries out the following two aspects of research work:(1)In this thesis,we propose a new strategy to synthesize Au NPs network-like thin film using sodium borohydride as the reducing agent,sodium citrate as the stabilizer,silver nitrate as the morphology control agent.The citrate-capped Au NPs are prepared at room temperature and assembled at constant temperature.The assembly behavior of Au NPs can be studied by changing the amount of sodium citrate,aging time,temperature and solvent(water or methanol)etc.It was demonstrated that the dipole interaction among the anisotropic inter-particles was the main driving force for the self-assembly of Au NPs network-like thin film at air-water interface.The amount of sodium citrate and silver nitrate play a key role in the regulation of the interaction of Au NPs.In addition,the aging temperature and the type of solvent have the certain impacts on the self-assembly of Au NPs network-like structure.Compared with unassembled Au NPs,the Au network thin films showed enhanced SERS performance for 4-ATP.(2)The Au-Ag and Au-AuAg bimetallic network-like thin film materials were obtained by the further growth method at the air-water interface,using the primary assembly structure of Au NPs as the basic building units.Au-Ag and Au-AuAg bimetallic nanostructure were prepared by reducing AgNO3 or a certain proportion of AgNO3 and HAuCl4 with ascorbic acid as reducing agent.The assembly behavior of Au-Ag bimetallic NPs can be regulated by changing the assembly condition.The results suggest that the further growth of Ag on the surface of primary Au nanostructure contributes to the formation of stable Au-Ag bimetallic nanostructured film.And the change of the relative volume ratio of AgNO3 and HAuCl4 could control the structure of Au-AuAg bimetallic thin film,which can remarkably improve the assembly efficiency.The Au-Ag and Au-AuAg bimetallic network-like thin film exhibit more excellent SERS performance than Au network thin film.The composite structure of Au and Ag as well as the relative content of Ag in bimetallic network thin film can have a great effect on SERS performance.