Graphene-based Materials For Surface Enhanced Infrared Absorption Spectroscopy And Electrocatalysis

Monolayer graphene,the thinnest two-dimensional atomic crystal material,is of perfect structure,possessing unique physical and chemical properties.The large delocalized ? bond in graphene is composed of a huge cloud of electrons.When other electrons from the outside impacts on graphene at certain site,it will arouse ripples on the surface of graphene,suggesting that graphene can excite surface plasmon resonance like precious nanostructured metals.However,distinct from surface plasmon excited by the traditional micro or nano-structured metal antenna,the plasmons excited from graphene antenna have the extremely shorter plasmon wavelength than the incident wavelength and unprecedented strong field confinement,making it a promising alternative of the metal antennas.More attractively,graphene can be more easily to be physically and chemically doped.Thus,it is convenient to tune plasmon position of graphene antenna by various gating methods without further changing of antenna shape and easily realize the regulation of the plasma resonance frequency in infrared and terahertz(THz)ranges,which has substantially potential prospect for biosensors.In addition,graphene has the advantages of good conductivity,large specific surface area,easy preparation,and adjustable structure and surface chemical properties,making it suitable to be used as electrochemical substrate material for energy storage and conversion systems.Currently,in order to meet the different needs of research and application,the most essential technological challenge is focusing on designing methods which enables to precisely and controllablely synthesize high quality graphene nanosheets in large scale or functionalize it with desired physical and chemical properties for any targeted purposes.As these issues to be addressed,the following researches have been carried out.(1)Graphene plasmon enhanced IR biosensing for in-situ detection of aqueous-phase molecules with an attenuated total reflection modeA new strategy is proposed for in situ monitoring of biomolecular interactions in water phase,which is based on the chemical doped-graphene nano antenna as the infrared enhancement substrate using an attenuated total reflection mode in infrared spectroscopy.This IR sensor includes a boron-doped graphene nanodisk array fabricated on top of a ZnSe prism surface that supports attenuated total reflection surface-enhanced infrared absorption spectroscopy(ATR-SEIRA).Our ATR-SEIRA platform is efficient and straightforward for in situ,real-time and label-free monitoring the interaction of biomolecules without interference from the environments,allowing us to extract instant spectroscopic information in a complex biological event.The regulation of graphene plasmon frequency has been achieved by controling the geometry using the nanospheres lithography and adjusting electronic structure by boron doping level.Utilizing the near-field enhancement of graphene plasmon,the affinity interaction of L-selectin with its aptamer has been investigated as a model system to evaluate the specific protein recognition process.The binding kinetics and affinity of protein-aptamer recognition process are obtained and the sensitivity detection limit of 0.5 nM target protein is achieved.The present work presents a novel application of graphene plasmonics in aqueous solution and offers a promising sensing platform for investigating interfacial bio-recognition reactions and structure-function of biomolecules.(2)Pyridinic nitrogen-doped single-layer graphene catalyzes two-electron transfer process of oxygen reduction reactionA post-treatment approach is presented to prepare nitrogen doped single-layer graphene with the solo pyidinic N-C configuration.Only one type of pyridinic N is doped in the graphene lattice,which can be used as an ideal platform to investigate its catalytic activity toward oxygen reduction reaction(ORR),estimate its role duing the ORR process and clarify the electrocatalytic reaction sites of nitrogen doped graphene,which will be beneficial for the reasonable and efficient design of nitrogen doped graphene based catalysts.Nitrogen doped graphene is synthesized via ultraviolet/ozone(UV/O3)irradiation followed by NH3 annealing.X-ray photoelectron spectroscopy analysis reveals that the nitogen doping level can be actively modulated by altering the oxidation and annealing conditions.Electrochemical results demonstrate that ORR on the pyridinic N doped graphene sheet occurs via a two-electron transfer process,indicating that the pure pyridinic N doped graphene catalyzes the electrochemical reduction of oxygen via a 2e to form hydrogen peroxide,but not via the 4e process to water.The present work provides unambiguous influence of doped N configuration on the ORR,and on the other hand,provides a strategy for designing efficient electrocatalysts for produce hydrogen peroxide which is an important industrial reagents.(3)Low-loading cobalt coupled with nitrogen-doped porous graphene as excellent electrocatalyst for oxygen reduction reactionWe have developed a facile and green method to synthesize the composite of nitrogen-doped porous graphene with low-loading cobalt(Co-N-rGO)acting as a highly active non-precious metal catalyst for the oxygen reduction reaction(ORR),resulting from its well-constructed porosity,high specific surface area and a synergistic effect between the doped nitrogen-atoms and cobalt species.First,nitrogen doped graphene hydrogels(N-rGO)with high specific surface area are synthesized via the reduction of a graphene oxide(GO)colloidal solution in the presence of urea under hydrothermal condition.Subsequently,Co2+ ions are absorbed onto the N-rGO sheets by noncovalent coordination/electrostatic interactions due to the contained oxygen and nitrogen species in graphene structure.Finally,a second solvothermal process is used in ethanol solution to prepare the Co-N-rGO samples.In alkaline media,kinetic parameter analysis shows a high selectivity to an apparent four-electron transfer process on the Co-N-rGO catalyst for ORR with an average electron transfer number of 3.97.Compared to commercial Pt/C,the Co-N-rGO catalyst displays better durability and methanol tolerance ability toward ORR.