Preparation And Performances Of Several Transition Metal Oxides As SERS Substrates

Surface enhanced Raman scattering(SERS)attracted wide attention,and has widely applied in molecular detection,reaction kinetics,biosensors,explosives detection and art preservation.With the progress of the era and the life demand of people,SERS substrate is constantly improving.Primarily,there are two mechanisms responsible for the SERS effect.The first one is the electromagnetic enhancement mechanism,which belongs to the physical enhancement and occurs on the rough noble-metal surfaces(e.g.,silver or gold).In this case,the surface plasmon of a metallic substrate was excited by the incident light,which creates a strong local electric field.The surface plasmons interact with the molecule to enhance the Raman signal of the probe molecule.The second mechanism is the chemical enhancement mechanism for the chemisorption of probe molecules on the surface of transition metal or transition metal oxide.As the electromagnetic enhanced SERS substrates with excellent sensitivity,the noble-metal materials have been widely reported.However,they are expensive,low stability and poor biocompatibility,which largely limits the further development.As a typical chemically enhanced SERS substrate,transition metal oxide has attracted the eyes of people due to its advantages such as wide source material,the low cost of preparation,outstanding biocompatibility and stability and so on.However,the transition metal oxide cannot produce a large number of "hot spots" in the SERS detection,the sensitivity of the substrate is low and the utility value of the substrate is depressed.Therefore,we can improve the SERS performance of this type of substrate by adjusting the morphology of transition metal oxides,modifying carbon dots,making anoxic compounds or noble-metal dopants.The main contents and results of this thesis were listed as follows:1.The size of SiO2 nanospheres with a smooth surface was about 200-300 nm prepared via the well-known Stober process.Then the surface of SiO2 nanospheres is coated with a thin TiO2 precursor by chemical deposition and then calcined in a muffle furnace to form SiO2@TiO2(anatase)nanospheres.The shell was assembled by TiO2 nanoparticles,so that the surface of core-shell SiO2@TiO2 nanospheres became rough.The yolk-shell SiO2@TiO2(y-ST)nanospheres were prepared by using NH4F to etch the SiO2 core.Finally,the CDs were modified on the surface of y-ST nanospheres to form the yolk-shell SiO2@TiO2/CDs nanospheres.Following,yolk-shell SiO2@TiO2/CDs nanospheres as SERS substrates showed the relatively high enhancement effect,which made the detection limit of R6G can achieve to 6×10-8M.On the other hand,the fabricated yolk-shell SiO2@TiO2/CDs utilized as catalyst for the degradation of dinitrophenols(DNP)can greatly shorten reaction time to 120min,and DNP removal efficiency is 83%under simulated sunlight irradiation.The results indicate that the yolk-shell structure and modification of carbon dots(CDs)are the keys for enhancing SERS signals and photocatalytic performance.2.Cu-MOFs materials were synthesized by one-pot solvothermal reaction of Cu2+ and C9H6O6.Cu-MOFs were calcined in different gases at 300 ? to prepare SERS substrate with different composition.It was found that when the Cu-MOFs calcined at 300 ? at Ar-air the product was porous octahedral CuO without carbon.While the product was porous octahedron Cu2O after porous octahedral CuO calcined at 300 ?H2-Ar mix-gases,the morphology of Cu2O is still intact.In the detection process of dye molecules and organic substances,the detection signal of porous octahedron Cu2O was much higher than those of CuO material and contrast octahedron Cu2O.The prepared porous octahedral Cu2O also has a more sensitive detection effect for rich-thiol detection.The detection limit of 4-Mpy(4-Mercaptopyridine)is 5×10-10M on the porous octahedral Cu2O.The results show that porous octahedral Cu2O improved the SERS performance of the substrate.3.We have developed a new strategy by using Cu2O microspheres as both templates and reductants to prepare a novel SERS substrate.Ferrero Rocher chocolate-like Cu2O@Ag(FRC-Cu2O@Ag)microsphere substrates were prepared without adding any reductants and surfactants.A series of SERS performance tests showed that when the Cu2O template was partially exposed and the molar ratio of Ag:Cu is 1:1 in microspheres,the enhancement effect of SERS substrate is the best.It may be the results of the structure of Cu2O@Ag and the exposed Cu2O,which provide the chemical enhancement and the physical enhancement of Ag during the process of SERS enhancement.At the same time,4-MBA(4-Mercaptobenzoic acid)was acted as a probe molecule to detect the SERS properties of substrates.The signal of the 4-MBA with 1×10-11M was detected by the synergistic enhancement effect of the Cu2O sphere and Ag.In addition,the substrate material has excellent SERS properties which also can be applied to the detection of pesticide thiram residues in fruits and vegetables.