In Situ Monitoring Of Plasmonic Catalytic Reaction And Its Condition Optimization

Nowadays,with the increasing of energy exhaustion and environment pollution,light-driven chemical transformations have attracted tremendous interest.It has advantages in environmental protection and energy conservation relative to the traditional high-temperature catalytic reactions,and is a new means ofattractive and sustainable development.In photocatalytic reaction process,the energy of photons is applied to drive various chemical reactions,including solar production of fuels,water splitting,degradation of organic molecules,etc.While these photocatalytic processes are potential very useful,their efficiency is far too low for practical large scale applications.Over the past several years,a new method for improving the efficiency of photocatalytic processes has emerged,involving the strong plasmon resonance of Ag and Au nanoparticles,these plasmonic nanostructures have gradually become a new paradigm for photocatalytic heterogeneous catalysts.A collective oscillation will occur when the free electrons on the plasmonic metal surface vibrate at the same frequency as the photons,called SPR?surface plasmon resonance?,these resonances lead to enhanced light absorption,and such“optical antenna”effects result in strongly enhanced electromagnetic fields near the nanoparticle surface.Hot carriers are generated during SPR decay process,it is reported that these hot electrons induce chemical transformation directly on the surface of plasmonic metal nanoparticles.Generation of energetic hot electrons is an intrinsic property of any plasmonic nanostructure under illumination.Simultaneously,a striking advantage of metal nanocrystals over semiconductors lies in their very large absorption cross sections.Therefore,metal nanostructures with strong plasmonic resonances are very attractive for photocatalytic applications in which excited electrons play an important role.However,the central questions of plasmonic hot electrons are the number of optically-excited energetic electrons in a nanocrystal and how to use it effectively.The main content of this paper is to synthesize core-shell nanoparticles with different heterogeneous structures around the core of classical plasmonic Au nanoparticles,and the characterization analysis was carried out by means of Transmission Electron Microscope?TEM?,Finite-Difference Time-Domain?FDTD?,X-ray Photoelectron Spectroscopy?XPS?.We discussed the hot electrons induced chemical reactions generated by plasmon relaxation as the main content,and Surface Enhanced Raman spectroscopy?SERS?is used to explore the influence of hot electrons on the reaction process in different heterostructures.In addition,various optimization conditions for plasmonic reactions are discussed.The main research contents are as follows:?1?Au seeds with different particle sizes?15nm,25nm,45nm?were synthesized by sodium citrate reduction method.Since the Au particle size has the longest plasmonic lifetime at 22 nm,three spherical Au-metal/semiconductor/insulator nanoparticles were synthesized by using Au with a size of about 25 nm:Au@Ag,Au@Ag₂S,Au@SiO₂.?2?The morphology of the three nanoparticles were characterized by TEM and SEM,and the optical properties were investigated by UV-Vis,then the FDTD was used to simulate the electromagnetic field distribution at 633 nm laser illumination when they were as the single layer films.And evaluating whether they can act as SERS substrates and their hot electrons excitation capabilities.?3?These nanoparticles were simultaneously used as photocatalysts and SERS enhancement substrates to participate in the photocatalytic reaction of p-nitrothiophenol?pNTP?,and the chemical reaction process canl be monitored in real time by SERS technology.The reaction of pNTP molecules is only driven by hot electrons,so we can evaluate the hot electrons utilization of three core-shell catalysts by the changes in Raman spectra.?4?We optimized the plasmonic catalytic reaction by changing the photocatalytic environment.In this work,we discuss it from three aspects?laser power,reducing agent,hot spot?,and the process of catalytic reaction was mainly monitored by SERS technology.In addition,the color of the pNTP solution would change after the reducing agent was added,so we also discussed the reduction process through the changes of Ultraviolet-Visible Spectroscopy?UV-Vis?.