Enhancement Of Etching And Oxidation Reaction Based On Nanoplasmonics And Interband Transition Effect

Plasmonic metallic(Au,Ag,Cu,etc.)nanoparti cles are characterized by their unique surface catalytic properties and adjustable light absorption ability.The localized surface plasmon resonance(LSPR)effect is the collective oscillation of free electrons in metal nanoparticles driven by the electrom agnetic field of incident light.The effect of LSPR excitation can be divided into three categories such as hot carriers,electromagnetic field enhancement,and photothermal effect.Silver nanoparticles(AgNPs)have stronger light absorption properties tha n gold nanoparticles(AuNPs).However,AuNPs are illuminated with visible light(λ<520 nm),interband transitions(from the d band to unoccupied states above the Fermi level)occur due to its relatively lower interband energy(~2.3 e V),resulting in the generation of hot holes with extremely high energies.Using these energetic hot holes,the oxidation reaction can be promoted.It is important to note that,photo-generated holes possess faster relaxation dynamics and lower mobility than electrons,making it more difficult to trap and make use of them to promote the overall photo-driven oxidation reaction efficiency.Therefore,it is immediately urgent to find a hole reservoir to extend the lifetimes of photo-generated holes and further reserve them.As changing the morphology of noble metal nanoparticles will influence the excitation wavelength,surface area,and active sites,it is necessary to accurately customize the morphology and structure of nanoparticles to optimize their optical properties and catalytic performance.The etching reaction of metal nanoparticles,regarded as a kinetically sluggish oxidation reaction,can accurately reshape the morphology of nanoparticles.As an attractive process for analytical and biomedical applications,controlled etching of noble metal nanoparticles by various chemicals has been reported,including halogen anions,metal cations,biomolecules,and oxidants.However,these methods will greatly change the surface environment of nanoparticles and affect their subsequent application.In this situation,it has broad prospects to construct an etching strategy without additional oxidants.Bimetallic core-shell nanoparticles can combine the chemical and optical properties of two metal materials at the same time.By controlling the size and morphology of the metal core and the thickness of the shell,the core-shell nanoparticles have both wavelength-tunable light absorption and scattering properties in the whole visible and near-infrared bands.In this thesis,on the basis of the LSPR properties of AgNPs and AuNPs,we propose that AgNPs can be controllably etched by energetic hot holes generated by AuNPs,and tannic acid(TA),the surfactant of AgNPs,acts as the hole reservoir.Furthermore,Ag@Au core-shell nanoparticles were synthesized to improve the catalytic activity of photoelectron-oxidation of aniline to polyaniline,while the electrochemical workstation and dark-film microscopy were combined to study the catalytic process.The main research contents are as follows:1.Synthesized AgNPs reduced with TA and AuNPs modified with citric acid were mixed and stirred intensively,then we introduced a visible light illumination to the above-mentioned plasmonic nanoparticles mixture of AgNPs and AuNPs.We found an obvious blueshift of the LSPR peak of AgNPs,which indicates the etching of AgNPs.Nonetheless,the LSPR characteristic peak position of AuNPs is kept unchanged.Subsequently,it was confirmed that the existence of AuNPs and light illumination was indispensable in the etching reaction of AgNPs,and the influence of excitation wavelength and power on the etching reaction was further explored.It was proved that the reaction was triggered by energetic hot holes generated by the interband transition of AuNPs.Finally,the influen ce of field enhancement and photothermal effect on the etching reaction was excluded.2.On the basis of energetic hot holes generated by the interband transition of AuNPs,we communicate a novel method employing TA as the hole reservoir to promote the etching reaction of AgNPs.The experimental results show that only using TA as a capping ligand could store photo-generated holes.The unique hole reservoir effect is attributed to TA molecules rich in hydroxyl can store the energetic hot holes generated by AuNPs,which are stored on the surface of AgNPs through phenol-quinone conversion,and finally released in large quantities and attacked AgNPs in coordination with the newly photogenerated hot holes of AuNPs to make them etched into Ag~+ions.Tannic acid,as a hole reservoir,stores hot holes and then releases a large amount of energy after storage.Meanwhile,the newly generated hot holes can inject into the catechol group to realize the phenol-quinone dynamic equilibrium.As a consequence,studies on mani pulating photo-generated hot holes for extending their lifetimes,further reserving hot holes,and conclusively releasing massive energy to trigger almost impossible kinetically sluggish oxidation reactions have a promising development prospect.3.Based on the LSPR effect of Ag and the interband transition of Au,Ag@Au bimetallic core-shell NPs were constructed by reducing the reduction potential of Au to prevent the galvanic exchange process.Furthermore,Ag@AuNPs were used as the high-efficiency photoelectronic catalyst.In this work,both the LSPR effect of Ag and the interband transition of gold in the Ag@Au core-shell nanoparticles are cooperatively used to enhance the optical absorption in the blue light band to generate more high-energy hot holes.The enhanced oxidation performance of Ag@Au is verified by the photoelectron-oxidation of aniline to polyaniline.When the reaction was carried out under 470 nm excitation,Ag@Au could generate a thicker polyaniline shell,corresponding to the color convers ion from blue to orange in the dark field microscopy images.In this work,the LSPR performance of Ag core in Ag@Au core-shell nanostructure was used to enhance the interband transition of Au shell to generate more energetic hot holes,and the enhanced oxi dative polymerization process of aniline on the Ag@Au nanoparticles was monitored by dark-field imaging.