Design Of Plasmonic Metallic Nanostructures And Their Photoelectric Properties

In recent years,due to the unique and tunable localized surface plasmon resonance(LSPR),plasmonic metals can effectively improve the light absorption and conversion efficiency,which is conductive to their wide applications in many frontier fields such as catalysis,sensing,imaging,therapeutics,metamaterials,photolithography and so on.In particular,surfaceenhanced Raman scattering(SERS)spectroscopy(mainly enhanced by highly localized electromagnetic fields excited by LSPR)and photocatalytic reactions(induced by high-energy hot carriers during LSPR relaxation)have drawn enormous attention of researchers.In the research field of SERS with ultra-trace "fingerprint" information of molecules,highly active SERS substrates were prepared by regulating the microscopic configuration(such as morphology,size,composition,etc.)in recent years.Recently,the researchers pointed out that electronic transmission between components could promote the synergistic effect between them,which is expected to provide new opportunities for further optimization of SERS performance.In view of this,we constructed the plasmonic Au-Ag interface configuration and the composite of the plasmonic Au@Ag bimetals and the effective carrier CNTs.Making full use of the electron transfer at the interface to promote the synergistic coupling of all components,the enhanced SERS performances were further studied.Moreover,the hot electrons from plasmonic nanometals upon LSPR excitation have higher energy than the electrons excited by traditional semiconductors,implying the energetic hot carriers generated by visible-near-infrared(NIR)light excitation of plasmonic metals can effectively participate in photochemical reactions,which can promote the development of photocatalysis.However,the hot carriers produced by photoexcited plasmonic metals are easily recombined,which restricts their developments.Therefore,how to improve the separation efficiency of hot electrons and hot holes has become an urgent problem to be solved.In this paper,we introduced C60 as the electron acceptor and an effective applied electric field as an external driving to improve the separation efficiency of hot carriers on the surface of the plasmonic nanometal under photoexcitation.Meanwhile,we constructed the connected nanostructures as efficient transport channels for photoexcited electrons to further promote separation of hot carriers.Based on this,we explored a series of plasmon enhanced catalytic performances,which is possible to expand the application of direct plasmonic catalysts in practical applications.(1)Constructing the plasmonic Au@Ag core-shell nanorods and effectively regulating the interface configuration,the excellent SERS performance was further explored.Adjusting the Ag shell thickness,it is found that the SERS signal of the CV molecules corresponding to bimetallic Au@Ag core-shell nanorods was significantly enhanced when the Ag shell thickness was 7.3 nm,which was～25 times that of the bare Au nanorods.The experimental results showed that the SERS activity could be improved by accurately regulating the interface configuration of Au@Ag core-shell nanorods by changing the thickness of Ag shell.The improvement of SERS performance is mainly attributed to the efficient charge transfer at the interface between Ag shell and Au core,which could significantly promote the cooperative coupling of bimetals.And the corresponding plasmonic resonance mode in the visible to NIR region can be improved,enhancing the intensity of the local electric field around the nanocomposite under light excitation,which can further optimize the SERS performance.As the optimal SERS substrate,it was actually applied to the ultra-trace detection of levofloxacin and enrofloxacin antibiotics molecules(10-9 M),providing a basis for the ultra-sensitive SERS monitoring and evaluation of antibiotics in food safety and environmental pollutions.(2)The overgrowth of the Au@Ag core-shell nanoparticles(NPs)on the one-dimensional carrier of carbon nanotubes(CNTs)were realized,and the enhanced SERS performance was investigated by making full use of interfacial charge transfer channels.The results showed that the SERS intensity of CV molecules corresponding to CNTs/Au@Ag(Ag:8.6%)was about 12.3 times of that of CNTs/Au by optimizing the composition of Ag.It is indicated that compared with CNTs/Au nanostructure,the constructed CNTs/Au@Ag(Ag:8.6%)nanocomposite had better SERS activity.This study confirms that in addition to the physical enhancement of Au@Ag core-shell structure and the coupling effect among adjacent Au@Ag NPs,the charge transfer at the interface between plasmonic metals and CNTs can promote the electron-phonon coupling effect on CNTs and induce the chemical enhancement,which also contribute to the improvement of SERS performance.Accordingly,CNTs/Au@Ag(Ag:8.6%)was used as the optimal SERS substrate for the detection of food coloring of patent blue V molecules(nanomolar level,nM),creating advantages for subsequent sensitive SERS monitoring in the field of food safety.(3)The nanocomposite with high dense C60 layer wrapping around the icosahedral(Ih)Au outer surface was synthesized,and the enhanced photocatalysis of Ih Au@C60 core-shell nanostructures were explored.Experimental data showed that the photodegradation efficiency of Ih Au@C60 core-shell nanostructures to CV molecules was～1.9 times that of Au NPs.It is proved that the enhancement of photodegradation efficiency is due to the construction of Ih Au core and the introduction of the C60 tight shell as the electron acceptor.Compared with bare Au NPs,the constructed core-shell composite has a wider LSPR response across the visible-NIR region,effectively improving the utilization of sunlight.Meanwhile,upon light excitation,C60 acts as an electron acceptor to transfer hot electrons from the photoexcited Ih Au surface to the C60 shell through the interface,thus achieving efficient separation of hot electrons-hot holes on the Ih Au and improving the corresponding photocatalytic activity.In addition,we found that a large number of hydroxyl radicals(·OH)as strong oxidants were generated with the participation of hot holes and OH-under alkaline conditions,which greatly improved the photocatalytic activity.Our research results provide a novel method for designing direct plasmonic photocatalysts with high performance.(4)The hierarchical Au pine needles(H-Au PNs)were constructed and the LSPR response was improved by external electric field driven,and the catalytic conversion performance was explored.It was found that the conversion rate constant of 4-nitrothiophenol(4-NTP)to 4,4’dimercaptoazobenzene(DMAB)on the surface of H-Au PNs under photoexcitation was～14 times that of traditional Au NPs.Compared with Au NPs,the "lightning rod effect" of H-Au PNs tends to make the hot electrons spontaneously accumulate towards the tips.In addition,the transient photocurrent intensity of H-Au PNs assisted by external electric field(-0.8V)was～11.2 times that of the one without electric field,facilitating the photoelectrochemical(PEC)hydrogenation reaction of 4-NTP on the Au surface.The realization of hydrogenation reaction is attributed to the optimization of LSPR effect by external field regulation,which effectively improves the separation efficiency of hot electrons-hot holes and reduces the photoelectric chemical potential on H-Au PNs.This makes the hydrogenation reaction of 4-NTP molecules be realized with the assistance of water splitting rather than the introduction of additional hydrogen sources.Regulating the LSPR effect of the nanometal by external field provides a new opportunity for direct plasmon driven catalytic conversion.(5)By introducing the LSPR effect of plasmonic Au into Pt-based electrocatalysts,the enhancement of electrocatalytic performance driven by LSPR was explored.Alloyed Au5Pt9 nanoframes were loaded on two dimensional(2D)hexagonal boron nitride(h-BN)nanosheets.The obtained h-BN/Au5Pt9 nanoframes exhibited a remarkable higher PEC activity,which was～3.93 times that of the traditional h-BN/Pt nanocomposite.Furthermore,it can be used as a PEC biosensor to achieve accurate and sensitive glucose monitoring of human tear.It can be concluded that introducing Au with LSPR property can effectively improve the activity of Ptbased electrocatalysts.The enhanced catalytic activity is mainly due to the LSPR effect of framework-like Au/Pt with the high capacity of harvesting light in the broad wavelength range.Meanwhile,the connected framework-like structure,as an electron transport channel,can accelerate the separation of hot carriers under PEC driven,which significantly improves the catalytic performance.The introduction of nanometals with pronounced LSPR properties into traditional electrocatalysts provides new opportunities for the development of other PEC biosensors for biomedical applications.