Study On The Mechanism And Application Of Plasmon-enhanced Interband Hot Holes

Recently,plasmonic metal nanoparticles（NPs）are widely used in various fields such as photocatalysis,photoelectrochemistry,and nano-biosensing.The optical properties of NPs arise from the collective oscillation of their conduction electrons,known as localized surface plasmon resonance（LSPR）,which occurs due to the interaction between incident light and the free electrons in these metal NPs.Upon excitation,the energy of the metal is primarily dissipated through three mechanisms:photothermal effect,near-field enhancement,and generation of thermal carriers.The utilization and control of highly energetic carriers（hot electrons and hot holes）are the most common mechanism exploited in plasmon-mediated catalysis,although photothermal effect and near-field enhancement have been reported for photocatalytic reactions.Hot electrons have found wide applications in plasmon-mediated chemical reactions,while the simultaneously generated hot holes,which possess lower reactivity and shorter lifetimes,are usually ignored.Therefore,exploring the rational and efficient utilization of hot holes holds significant importance in nanoplasmonic chemistry.Plasmonic metal NPs can generate hot carriers through two processes:intraband transitions and interband transitions,which exhibit differences in different energy states,populations,and dynamics,leading to distinct catalytic performances.In particular,the LSPR characteristic absorption band of Au NPs is close to the excitation wavelength of intraband thermal carriers.In this case,the extraction and utilization of hot electrons are more favorable than that of hot holes,thus driving the reduction process in photocatalysis.Moreover,although interband transition efficiently creates“deeper”hot holes below the Fermi level（E_f）,which can be used as a strong oxidase in photocatalytic reactions,their efficiency is limited due to weaker corresponding light absorption.To address these challenges,we utilize the unique advantage of the fact that the interband transition wavelength of Au is in the visible light range and has excellent spectral overlap with Ag LSPR.The works in this dissertation aim to enhance the generation of interband hot carriers by harnessing the LSPR properties of noble metals.Based on this concept,we further develop novel systems that utilize interband hot holes in areas such as photocatalysis,photoelectrochemical（PEC）sensing,nanozyme,and colorimetric detection.The main achievements are as follows:（1）Plasmons of Ag resonate with interband transitions in Au to boost the quantity and energy of hot holes.The interband absorbance of Au is weaker than that based on its plasmonic effect,resulting in a low oxidation capacity.Herein,Ag@Au NPs are synthesized via an anti-galvanic reaction by quickly reducing Au precursors on Ag NPs.We explore the plasmon resonance of Ag NPs,which overlaps with the interband transition of Au,to actualize an increased amount of higher energetic interband hot holes in Ag@Au core-shell NPs.Photoelectrochemical measurements for different Ag@Au structures confirm that the Ag-core-enhanced electromagnetic field mainly contributes to the enlarged number of hot holes.Moreover,the valence-band hybridization and electron transfer at the interface of Ag and Au play an improved role in the enhanced oxidation potential of hot holes.By exemplifying that Ag@Au NPs generate more and hotter holes than Au NPs do,this work proposes that hot carriers of both plasmonic resonance of Ag and interband of Au together boost the quantity and energy of hot holes.（2）Hot hole multiplication is achieved from silver plasmon-resonated gold interband transitions for enhanced photoelectrochemical sensing.Compared with the widespread exploitation of hot electrons in plasmonic NPs,hot holes generated from plasmonic metal interband transitions,are often overlooked in PEC sensing.Benefiting from the enhanced interband hot hole of Ag@Au,which react with electron donor（Ascobic acid,AA）can generated a larger photocurrent than that of Au NPs.Inspired by the rapid development of PEC enzymatic biosensor,herein,we combine the advantages of Ag@Au and enzyme sensing for enhanced hot holes generation,which provides great potential for PEC detection of glucose.Glucose oxidase（GOx）catalyzes glucose to generate H₂O₂,which can compete with hot hole and react with AA,resulting in a reduced photocurrent signal.With satisfactory accuracy and good practicability,the PEC sensing platform based on Ag@Au NPs possesses a detection limit of 77 n M for glucose,exhibiting significantly higher sensitivity compared to that using Au NPs.This work exemplifies the applications of interband hot-hole initiated by plasmons and may inspire more strategies to explore the utilization of hot holes in PEC.（3）The enzymatic activity of MoS₂ is modulated using plasmon-enhanced interband hot holes in Ag@Au for polyphenol detection.In addition to utilizing the inherent properties of Ag@Au for designing direct PEC sensor,we also explored the regulation of MoS₂ enzymatic activity using interband hot holes.Firstly,MoS₂ was covalently attached to the surface of Ag@Au,forming Ag@Au@MoS₂ plasmonic nanozymes（PNzymes）.Compared to monometallic-modified MoS₂ structures,the dual-metal core-shell modification significantly enhanced the peroxidase-like activity of MoS₂ under light irradiation.Through the investigation of the mechanism behind the enhanced catalytic performance,we found that the interband hot holes generated in this structure can sensitize and produce singlet oxygen（¹O₂）radicals,which play a crucial role in regulating the nanozyme activity.We applied this PNzyme for colorimetric detection of tannic acid,achieving lower detection limits and improved sensitivity compared to that obtained in dark conditions.Furthermore,by incorporating different polyphenolic compounds into the Ag@Au@MoS₂ PNzyme-catalyzed TMB oxidation system,hydroxyl groups could capture the holes and inhibit the formation of TMB oxidation products.This enabled the design of a multi-analyte colorimetric sensing array for polyphenolic antioxidants.Different phenolic compounds could be effectively distinguished by measuring the absorbance changes at different time points.The results showed that the detection system based on light-illuminated Ag@Au@MoS₂ PNzyme exhibited higher sensitivity compared to that obtained in dark conditions.This work presents a novel approach for modulating nanozyme activity based on plasmon-enhanced interband hot carriers and demonstrates its application in constructing highly sensitive sensing systems,offering insights for the development of additional nanozyme modulation mechanisms and their applications in biosensing.