Design Of All-metal Plasmonic Nanostructures And Single-particle Studies Of The Catalytic Mechanism

Improving the utilization efficiency of solar energy has always been a research focus.Plasmonic metallic nanostructures are characterized by their strong interaction with resonant photons through an excitation of surface plasmon resonance(SPR).Optically excited plasmonic nanoparticles can activate chemical transformations directly on their surfaces,converting lowdensity solar energy into chemical energy.However,the quantum efficiency of photochemical processes is low because of the chemical inertness of the plasmonic metal and the low utilization of hot electrons.The lifetimes of hot charge carriers are extremely short,and they are prone to self-thermalization and eventually cooled by ultrafast electron-electron and electron-phonon scattering.In addition,the reaction mechanism of plasmon chemistry in metal catalysis is also controversial.To solve the above scientific problems is the key to realize the SPR effect in the application of solar energy conversion.However,it still has difficulties.The nanoparticles in heterogeneous catalysis synthesized by chemical methods are polydisperse in terms of size,shape,and grain structure,which hampers the generation of a deeper understanding for SPR mechanism.At the same time,traditional catalysis studies often target macroscopic systems containing a large number of nanoparticles,ignoring the disguise of individual properties that differ on average.High-resolution single-particle spectroscopy can reveal the mechanism of charge transfer and catalytic reaction at the single-particle scale,which is important to understand in situ the structure-activity relationship and design novel and efficient photocatalysts.This paper aims to enhance quantum efficiency of plasmon photocatalysis and explore the mechanism of plasmon-enhanced catalysis.Enhanced the light-harvesting ability and the separation of hot carrier by constructing a bimetallic plasmonic absorption center and optimizing the hybrid plasmonic nanostructurals;Expanded Cu-based plasmonic photocatalytic systems;revealed the mechanism of SPR-induced water activation and plasmon-enhanced nitrobenzene hydrogenation via single particle spectroscopy,and improved the photo-chemical conversion efficiency.(i)Construction of plasmonic nanomaterials:the utilization of hot electrons can be improved by adjusting the structure and composition.The internal recombination of hot carriers in SPR metal and the shielding effect of non-SPR metals(Pd,Pt,etc.)on SPR have been solved by the structural optimization design of hybrid SPR nanomaterials(the design of Pd-Ag@Au HNPs and laser-induced reshaping).The stability and SPR effect of SPR Cu have also been improved by SPR alloying strategy.(ii)The interface interaction between hybrid SPR metal and adsorption molecule was elucidated at single particle/single molecule level.By monitoring the surface product formation rate of single nanocatalites,the mechanism of SPR-induced non-competitive adsorption was revealed at the single particle level.The activation strategy of water molecules driven by SPR effect was proposed,and the activation mechanism of water molecules by hot carriers was clarified.The catalytic mechanism of nitrobenzene hydrogenation with formic acid as hydrogen donor was revealed.The exploration of the mechanism of plasmon chemistry can provide theoretically support for enhancing the photo-chemical conversion efficiency.The details are as follows:i)Given the inert chemical properties of SPR metal and the easy recombination of internal hot carriers,we designed and constructed two "antenna-reactor" plasmonic materials with excellent light absorption and catalytic activity:Pd-dotted Ag@Au hexagonal nanoplates(HNPs)were designed and synthesized by depositing mono-dispersed Pd nanodots on plasmonic Ag@Au core/shell HNPs,which act as the catalytically active site and light absorber simultaneously,and exhibit excellent catalytic performance(1062 h-1).Furthermore,a new method was proposed to optimize hybrid plasmonic nanomaterials considering the complex operation and poor reproducibility of the seed-mediate method.A novel bimetallic Pt-Au nanostructures(L-Pt-Au NRs)with modified optical and catalytic properties was designed and synthesized via a laser-induced reshaping process.ii)Further,given the limitation of high price of noble metal SPR materials,plasmonic Cubased nanomaterial was provided.To improve the stability and SPR effect of plasmonic Cu,we used a facile one-pot reaction strategy to synthesize uniform CuAg alloy nanoparticles,which exhibited excellent catalytic activity for the methanolysis of ammonia borane(AB).The contribution of hot electron-hole pairs,photo-induced thermal effects and the photo-induced local field enhancement to plasmon-enhanced methanolysis of AB has been discussed at singleparticle level.iii)The interfacial interactions between hybrid plasmonic nanomaterials/adsorbed molecules was investigated in situ at the single particle/molecule level by confocal microscopy spectroscopy.i)By monitoring the rate of product formation on the surface of a single nanocatalyst,it was confirmed at the single particle level that the hot electrons generated upon light irradiation can lead to the change of the catalytic mechanism,from a competitive mechanism to a noncompetitive Langmuir-Hinshelwood mechanism.And thus it can avoid the catalytic rate decay caused by the increase of reactant concentration.ii)The plasmon-enhanced water activation process is explored at both single-particle and ensemble levels.Based on single particle spectroscopy,the activation mechanism of hot carriers to water molecules is elucidated and direct evidence for charge transfer is provided.iii)The mechanism of SPR on the tandem reaction(nitrobenzene hydrogenation with formic acid as hydrogen donor)was investigated in situ at the single particle level.Plasmon-induced interaction between formic acid(FA),nitrobenzene and plasmonic nanostructures was explored in-situ by single-particle photoluminescence(PL)measurement.And it realized the highly selective hydrogenation of nitrobenzene to aniline under mild conditions by means of the SPR effect.Finally,it summarizes the main research contents and innovations of this paper.