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Investigation The Effect Of Surface Plasmon Resonance On Charge Transfer Process Using Surface-enhanced Raman Scattering

Posted on:2022-08-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:L GuoFull Text:PDF
GTID:1481306332962329Subject:Analytical Chemistry
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Surface Enhanced Raman Scattering(SERS)technology was found on coarse silver electrode in 1974,it has attracted more and more attention of scientific researchers due to its excellent advantages,and has been widely used in various scientific research fields.There are two main enhancement mechanism for SERS that have be widely accepted by researchers,the Electromagnetic enhancement Mechanism(EM)and Chemical enhancement Mechanism(CM),the former need surface plasmon of metal nano particle resonance with incident light,produce Localized Surface Plasmon Resonance(LSPR),and for CM mechanism,charge transfer between SERS substrate and adsorbed molecule is necessary.When the LSPR of nanomaterials changes or there is no LSPR generation,the coupling between nanoparticles and incident light will have a great influence on the charge transfer process between two nanoparticles.Based on the above,we put forward the idea of using SERS spectrum to explore the charge transfer process between nanomaterials.Based on this idea,we constructed a series of metal-molecules-semiconductor core shell nanostructures,semiconductor-metal nanoparticles-molecules and semiconductor-molecules-semiconductor sandwich structures.The regulation of metal nanoparticles LSPR,semiconductor regulation of metal nanoparticles LSPR and materials without LSPR were tested,by observing and analyzing the changes of molecular Raman spectra,the influence of LSPR and other factors on the charge transfer process between materials was explored.This study is of great significance for improving photocatalytic efficiency and charge transfer process in photoelectric devices.In this paper,a series of nano-sandwich structured material systems were constructed to regulate the LSPR of nano-materials,and the charge transfer process was studied in depth using SERS technology.This paper is mainly composed of the following parts:1.By controlling the thickness of Cu2 O shell to adjust the LSPR of AuNRs,and the investigation of charge transfer process between the core and shell of AuNR-MBA@Cu2O structure.AuNRs with longitudinal LSPR and radial LSPR located in visible and ultraviolet regions were synthesized by seed growth method in two steps.And then,a layer of MBA molecules was assembled around the AuNRs by means of Au-S bond at the sulfhydryl end of the probe molecules,by controlling the amount added of AuNR-MBA,the thickness of Cu2 O shell was controlled,four groups of AuNRMBA@Cu2O assembles with different shell thicknesses were prepared.The as synthesized AuNR-MBA@Cu2O assembles were characterized by TEM,UV-Vis and XRD.The results show that we have successfully prepared four groups of AuNR-MBA@Cu2O assembles with different shell thicknesses.Combined with Raman spectrum at different laser line,the calculation of the ratio of specific peaks in Raman spectrum,and the energy levels of AuNRs,molecules,Cu2 O semiconductor determined by UPS,the charge transfer process of AuNRMBA@Cu2O assembles with different shell thicknesses were discussed.This is the first time to explore the charge transfer process between metal nanoparticles and semiconductor by using the system of probe molecules set between metal semiconductor core-shell structures,which provides a new idea for improving the photocatalytic efficiency and photocatalytic devices.2.Regulating the LSPR of AuNRs by adjusting the aspect ratio of AuNRs to investigate the charge transfer process between cores and shells of AuNRMBA@Cu2O.Based on the experiments in the previous chapter,AuNRs with different aspect ratios were designed and synthesized in this chapter,and a layer of MBA molecule was adsorbed on the AuNRs,and a layer of Cu2 O semiconductor material with the same thickness in different samples were grown around the MBA molecule,thus forming the core-shell structure of AuNR-MBA@Cu2O.By changing the length to diameter ratio of AuNRs,the SPR resonance absorption peak of AuNRMBA@Cu2O core-shell structure can be adjusted.Under different excitation laser line,through the relative intensity change of characteristic spectrum line in SERS spectrum of MBA molecules,combined with Lombardi's charge transfer theory,the CT process of passing molecules was deduced.At the same time,the influence of different matching between different SPR absorption peak positions and excitation light on the charge transfer degree is verified,the effect of the specific surface area of AuNRs with different aspect ratios on the charge transfer process was also found.In this chapter,different specific surface areas of AuNRs lead to a slight change in the position of the energy level of the Cu2 O shell to which they are bounded,thus affecting the electron transfer process in these three different substances.The work in this chapter shows that the larger the specific surface area of AuNRs,the more obvious the tendency of giving electrons,this also provides a new idea for the designation of optoelectronic devices involving metal nanostructures.3.Based on the research contents of the first two chapters,AuNRs and TiO2 NTs composite nanomaterials were designed to verify the influence of coupling of metal nanoparticles and semiconductor materials on the photocatalytic process.In the previous two chapters,we know that when metal nanoparticles are combined with semiconductors,a charge transfer process occurs between metal nanoparticles and the semiconductors.Based on the charge transfer characteristics between metal nanoparticles and semiconductors,we designed two kinds of AuNRs with different aspect ratios,and combined AuNRs with TiO2 NTs to form composites materials.UV-Vis-NIR spectroscopy was used to verify the influence of material composite on the absorption spectra of the two materials,the results show that when AuNRs are combined with TiO2 NTs,the absorbance in the visible near infrared band is greatly improved compared with that of pure TiO2 NTs.In the reaction of photocatalytic degradation of PATP molecules under 633 nm laser source,the difference of reaction rate of materials with different absorption spectra was tested,it is verified that when the absorption spectrum is closer to the wavelength of excitation light,the photocatalytic efficiency of the material is higher.This experiment provides a reference for the design of photocatalytic materials in the future.4.Based on the analyzation of SERS spectroscopy of molecules,the charge transfer process between semiconductor and semiconductor nanoparticles was analyzed,verifying the effect of charge transfer process between semiconductors by changing the assemble direction of molecules between two semiconductor nanoparticles.In this chapter,we have designed a semiconductor-molecular-semiconductor sandwich structure to verify the charge transfer process between different semiconductor materials.By measuring the energy band positions of the two kinds of semiconductor nanoparticles by UPS,combining with the excitation wavelength parameters,it was determined that the electrons transfer from Cd S nanoparticles to TiO2 nanoparticles.According to the Raman spectral data of the two kinds of assembly under the excitation light at 633 nm and 785 nm,the intensity of the characteristic spectrum peak is analyzed to obtain the information of charge transfer degree.The effect of different MBA assembly directions on charge transfer was verified-electrons flow more easily through the sulfhydryl end to the carboxyl end,and more difficult to flow from the carboxyl end to the sulfhydryl end.This provides a reference for the design and fabrication of quantum dot sensitized solar energy devices in the future.
Keywords/Search Tags:SERS, charge transfer, metal nanoparticles, semiconductor, sandwich structures, photocatalytic
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