Preparation And Catalysis Of Single/Double Gold Based Nanoparticles And The Study Of Dynamic Raman Spectroscopy

Due to the unique physical and chemical properties of gold-based nanoparticles have been applied in catalysis,SERS and drug loading and other fields.The properties of gold-based nanoparticles are closely related to their size,morphology and composition.The catalytic performance of nanoparticles can be obviously enhanced by the branched structure on the surface.In this paper,the catalytic properties of gold nanoparticles and Au-Pd bimetallic nanoparticles with different sizes and morphologies,as well as the detection and regulation of dynamic Raman spectra in plasmons formed by gold nanoparticles,were been studied,including the following four parts:?1?In order to investigate relationship between the structure and performance of gold nanoparticles,the catalytic properties of gold nanoparticles were evaluated in the reduction of 4-nitrophenol by Na BH₄.Using catalyst suspensions with identical amounts of gold,the following key results were obtained:first,the nanostars showed increased activity as compared to spherical gold nanoparticles;second,larger gold nanostars showed higher activity,likely because of the abundance of flat/spiky features on these particles,which show high metal utilization;third,treatment of the nanostar colloid with cucurbit[7]uril can be used to balance catalyst stability and activity;fourth,as expected from the decreasing in specific surface area,the specific activity of the spherical nanoparticles decreased with increasing particle size.?2?We prepared Au-Pd bimetallic nanostarss?Au-Pd NSs?with a uniform size,well-defined dendritic morphology,and homogeneous alloy structure in an aqueous solution by seed-mediated synthesis.The prepared bimetallic NSs were fully characterized using a combination of transmission electron microscopy,Ultraviolet-Visible?UV-vis?spectroscopy,inductively coupled plasma optical emission spectroscopy,and cyclic voltammetry measurements.The catalytic activities of the prepared Au-Pd nanoparticles for 4-nitrophenol reduction were also investigated,and the activities are in the order of Au-Pd NSs?AuM core?>Au-Pd NSs?Au₁Pd₁core?>Au-Pd NSs?Au core?,which could be related to the content and exposed different reactive surfaces of Pd in alloys.This result clearly demonstrates that the superior activities of Au-Pd alloy nanodendrites could be attributed to the synergy between Au and Pd in catalysts.Take Au-Ad NSs?Au core?as an example,we studied the formation mechanism of Au-Pd NSs.We show that Au-Pd nanostars?NSs?with tunable SPR absorption?from 536 nm to 583 nm?,nanoparticles size and palladium content?less than7 wt%?can be obtained by adjusting the ratio of ascorbic acid and chloroauric acid.These synthesized Au-Pd NSs could be utilized efficiently for the reduction of4-nitrophenol and nitrobenzene and the Suzuki coupling reaction.Enhanced catalytic activity could have resulted from easy accessibility of the active sites,star-like structure and Pd-rich surface.?3?We studied the dynamic changes of intermolecular interactions at the carboxyl/carboxyl interfaces between a pair of molecules trapped in a plasmonic nanocavity formed between a gold nanoparticle?GNP?and a gold nanoelectrode?GNE?.The development of intermolecular interactions,including the appearance of hydrogen bonds?h-bonds?,during and after single GNP collision events on the GNE,was monitored by time-resolved surface-enhanced Raman spectroscopy at a tens of milliseconds time resolution.Spectral fingerprints of the carboxyl group corresponding to non-specific intermolecular interactions and h-bonds are identified.Furthermore,we demonstrated that the strength of intermolecular interaction could be mechanically modulated by changing the applied bias at the GNE,which resulted in small and controllable changes in the nanogap distance.Unlike non-specific intermolecular interactions,the intermolecular h-bonds can only be formed stochastically and are more sensitive to the gap distance modulation.This report demonstrates a new approach to modulate and probe intermolecular interactions within nanogaps.?4?Using the metal-molecular junction-metal structure as a probe,we monitored the process of reduction of 4-nitrothiophenol by photocatalytic?hot electron?and chemical catalytic?Na BH₄?,through the dynamic Raman spectroscopy.Furthermore we probed the dynamic Raman single of the formation and destruction of Cu²⁺chelation in molecular junction.When a DC voltage was applied to GNE of 4-MBA/Cu²⁺/4-MBA junction,the Raman intensity increase under negative voltage and weaken under positive voltage.After applying an AC voltage?-0.5±0.2 V 1Hz?,the Raman intensity varies with AC voltage at the same frequency.Thus,We have achieved the purpose of electric field regulating Raman intensity.