Nanostructured Gold Plasmonics And Molybdenum Disulfide For Synergistic Sensing And Catalysis

2D nanostructures are attracting an increasing amount of interests in the fields of biomedicine,electronic devices,clean energy,and chemical sensors,due to those layered plane structures,as well as unique physical and chemical properties.Nevertheless,recent practical applications of 2D materials are still restricted as their detrimental impacts.Significantly,pristine 2D materials cannot overcome limited issues in practical applications.Hence,the integration of 2D materials with either zero-dimensional or three-dimensional nanostructures,which take the 2D structures as cores,is promoting the bio-sensing,clean energy and catalysis,due to the enhanced synergistic impacts.This thesis highlights the preparation routes of 2D layered MoS₂nanosheets with a liquid-phase exfoliation approach.Meanwhile,MoS₂ nanosheets are combined with plasmonics of gold nanoparticles,forming heterostructures.The integrated heterostructures can address those detrimental impacts of pristine 2D nanostructures due to synergistic effects.Firstly,semiconducting MoS₂ nanosheets and plasmonic gold nanoparticles are considered as biological nano-probes,contributing to the development of gel-electrophoresis-based immunoassays for fast,simple,and visual monitoring of tumor biomarkers.Moreover,this thesis explores the in-situ growth of gold atomic clusters on defects of semiconducting MoS₂,which results in the formation of heterostructures with diverse morphologies.With the exploitation of optical properties of heterostructures,precise size identification of exfoliated MoS₂ is well established.Finally,the electrocatalytic HER performance of Au/MoS₂ heterostructures is studied.The electrochemical results indicate that the site-selective modification of gold ACs can largely affect the activity of MoS₂ defects HER catalysis.Moreover,with photonic irradiation in the processes of electrochemical measurements,excited hot electrons from gold plasmonics can remarkably enhance the electrocatalytic activities of donator-adjacent semiconductor defects.This study deeply enhances the reaction mechanism of plasmonic-enhanced electrocatalytic performance of semiconductors.The main contents of this dissertation are summarized as follows:1.Preparation of MoS₂ Nanosheets and Gold Nanoparticles with Precise Size RegulationBased on liquid-phase exfoliation of MoS₂ crystals,2D nanosheets with thicknesses of 1-10 nm are stably dispersed in surfactant aqueous solutions.However,in the processes of preparation,sonication induced direction-irregular cutting forces to bulk crystals results in the formation of size-inhomogeneous 2D nanostructures.In this part of thesis,based on differential-zone centrifugation strategies,a size screening route is developed for thickness-dependent separation of 2D nanosheets.Moreover,as control experiments,gold nanoparticles with various diameters are presented.With the bottom-up synthesis route,precursors of gold nanomaterials are incubated with diverse ratios of reducing agents of citrate ions,gold nanoparticles with sizes ranging from 13 to 37 nm are obtained.Finally,with the comparison of stability between those two nanomaterials,it is proved that with the modification of proteins,the irreversible aggregation behaviors are prevented,while the stabilities of nanostructures are enhanced.2.Nanostructured Gold and MoS₂ Nanosheets Served As Synergistic Probes for Visual ImmunoassaysHomogeneous MoS₂ nanosheets with desired uniformity,chemical inertness,and semiconducting characteristic,rivaling gold nanoparticles in optically sensing applications,contribute to development of alternative visual 2D nano-probes.Furthermore,MoS₂ nanosheets coupling with proteins exhibit high performance in stability and selectivity,and distinguishing running shifts of antibody-anchored conjugates in gel electrophoresis are observed,which are visually responsive to those specific antigen due to aggregation-induced steric effect.This assay enables the easy and fast monitoring of tumor biomarkers just according to the naked-eye identification of band location,presented by colorful nano-conjugates.The visual immunoassay with the synergistic effect of gel electrophoresis and 2D semiconductors definitely pushes a significant progress on“home-made”tests for disease early diagnosis.3.Plasmonic Au/MoS₂ heterostructures with synergistic impacts for precise size identification of exfoliated nanosheetsWith the integration of liquid-phase exfoliation and differential-zone centrifugation treatments,MoS₂ samples with diverse sizes are collected.A portion of MoS₂nanosheets aqueous dispersions is added into the HAuCl₄ solutions,and reactions rapidly occur in the high-temperature condition with the color changes of mixtures.The color changes of reaction mixtures are exactly recorded,which could reflect the reaction proceedings.Experimental results demonstrate that the shell-core heterostructures of gold/MoS₂ are formed with the reaction between HAuCl₄ and MoS₂ nanosheets.The morphologies and sizes of heterostructures could affect the plamonic characteristics,which could be monitored with discriminated optical absorption phenomenon.The peaks of plasmonic absorption are not influenced by the concentration of MoS₂,reaction temperature,but they change with the size diversity of exfoliated MoS₂.A size identification route is developed for MoS₂ plane scale.Meanwhile,localized surface Plasmon resonance characteristics of shell-core Au/MoS₂ heterostructures can further contribute to optical sensors,electronic devices,and biomedicine.4.Defects of MoS₂ Nanosheets Spontaneously Modulate the Site-Selective Growth of Gold NanocrystalsDefects in layered molybdenum disulfide（MoS₂）cause large variation of electric and optical properties,and thus understanding MoS₂ defect-involved reaction mechanism can excavate unearthed characteristics with significant applications.Herein,MoS₂ defect-oriented growths of Au NCs on LPE nanosheets are theoretically and experimentally performed with programmable heterostructures.Evidences prove that Mo-terminated active defects can spontaneously reduce[AuCl₄]^-anions,and oxidized Mo species are dissociated from solid nanosheets.Primarily,nanosheet edges guide the epitaxial branch of Au NCs,which is followed with emerging NCs growths at their planar defects.Subsequently,defect-attached NCs continue to grow,successively involving size-evolution processes of LaMer growth and planar packages of aggregative growth.As a consequence,heterogeneous Au atomic layers occupy MoS₂ basal planes,and shell-core Au/MoS₂ heterostructures are presented with localized surface plasmon resonance.Atomic Au and MoS₂ layer heterostructures of nanosheets,nanourchins,and nanoparticles,exhibit manipulated synergetic performances in plasmonics.Overall,MoS₂ defect-oriented Au NCs growths,tunable morphological and synergistic plasmonic characteristics impart high inspiration in exploiting layered MoS₂-based heterostructure optical properties,as well as biomedicine,clean energy,and sensing applications.5.Oriented Growth of Gold Nanoplasmonics on MoS₂ Nanosheets for Enhanced Electrocatalytic Hydrogen EvolutionOn a basis of MoS₂ defect-oriented growth of gold nanostructures,gold nanoparticles are fixed on diverse sites of nanosheets,forming the morphology-discriminated Au/MoS₂ hybrid nanocomposites,such as nanosheets,nanourchins,nanoparticles.Additionally,the electrochemical properties of nanohybirds are exploited.It is proved that the site-selective decoration of gold nanomaterials could remarkably improve the hydrogen reduction performance of MoS₂ in acidic medium.Meanwhile,Au/MoS₂ nanourchins,taking Au components as antennas and MoS₂ as the main body,exhibit the optimal catalytic activity due to the highest synergistic effect.The overpotential value of current density（10 mA/cm²）is estimated to be 214 mV and the Tafel slope is 58.2 mV/dec..With the measurements of electrochemical impedance for diverse nanostructures,it is demonstrated that the enhanced characteristics of MoS₂electrocatalytic HER are ascribed to the accelerated electrons transport in catalysts.6.Principle of Proximity:Plasmonic Hot Electrons Motivate Donator-Adjacent Semiconductor Defects with Enhanced Electrocatalytic Hydrogen EvolutionElectrocatalytic MoS₂ HER suffers from practical barriers.Herein,the construction of Au plasmonics and layered MoS₂ is manipulated with the aim of optimal synergistic catalysis.Under photonic irradiation,hot electrons excited from Au nanostructures are injected into MoS₂ semiconductors,which remarkably increases the carrier density of catalyst to match the energy level of HER.Obeying the principle of proximity,localized MoS₂ defect-adjacent Au plasmonics exhibit a more valid pathway,transferring hot electrons from donators to receptors of catalytic sites,in comparison to planarly attached Au nanostructures.Additionally,planar Au decoration improves the electron transport rate between catalysts and electrode substrates,and plasmonic synergistic catalysis stability is strengthened.The synergy of dual function of location-discriminated Au nanostructures with plasmonic excitation accounts for superior electrocatalytic performances,which imparts high inspiration in expanded heterostructures and integrated plasmonic techniques for both catalysis and devices.