| Two-dimensional materials exhibit more excellent physical and chemical properties than bulk materials to due to its unique structure.Compared with bulk materials,two-dimensional materials with nanometer thickness have a highly exposed surface,which greatly improves the utilization of atoms.More importantly,the physical and chemical properties of two-dimensional materials can be adjusted through surface regulation.Transition metal carbide or nitride(MXene)as a new type of two-dimensional material has attracted the attention of the research community because of its excellent optical and electrical properties.Titanium carbide(Ti3C3)as a typical representative in the MXene family have high chemical reactivity with the exposed Ti atoms on its surface that are easily combined with electron-rich groups,which provides a theoretical basis and conditions for the surface regulation of Ti3C2.This thesis focuses on the surface regulation of two-dimensional Ti3C2 nanosheets From a new perspective of synthesis,the effect of surface structure on Ti3C2 chemical stability and surface enhanced Raman scattering(SERS)performance is systematically studied.The main research contents are as follows(1)Surface regulation of Ti3C2 nanosheetsThe regular and ultrasmall Ti3C2 sheets covered with OH/F or aluminum oxyanions were obtained by adjusting the etching environment,etching depth and shear force to adjust the size and surface structure of Ti3C2 sheets.It found that the surface structure is affected by the etching environment,and the etching depth and shear force determine the size of the nanosheets,XPS and STEM proving that the aluminum oxyanions is successfully modified on the Ti3C2 surface.This study provides a simple method for designing the surface structure of two-dimensional materials,and solves the problem of regulating the surface of two-dimensional MXene,laying a foundation for the application of MXene in the fields of optics and electricity(2)Study on the chemical stability of Ti3C2The chemical stability of Ti3C2 nanosheets in H2O2 medium and air environment was analyzed by optical photos and XRD characterization,and the evolution of phase,morphology and optical behavior during oxidation was mainly explored.The results show that the ultrasmall size Ti3C2 nanosheets passivated by aluminum oxyanions on the surface have higher structural stability,because the re-crystallization of ultrasmall size Ti3C2 to TiO2 requires extensive activation of atomic diffusion,which makes the phase transition more difficult.At the same time,the electronic and optical characteristics of Ti3C2 during the oxidation process were tracked by ultraviolet(UV)and fluorescence(PL)characterization.The results show that the ultraviolet absorption peak will gradually change or disappear with the deepening of oxidation degrees,and Fluorescence will occur when the partial conversion of regular Ti3C2 to TiO2.It may help researchers functionalize MXene sheets with more chemically inert groups to enhance their stability.(3)SERS activity of surface-modified Ti3C2It proposed a strategy of surface modification Ti3C2 to improve its SERS performance,achieved a rare high sensitivity enhancement,its detection limit is close to pM level,and the enhancement factor is as high as 1.1×107.The enhancement principle of the SERS active substrate is clarified,the surface modification of aluminum oxyanions can effectively adjust the interaction between the substrate and the analytical molecule making the analytical molecule assume a flat configuration on the surface of the substrate,which facilitates charge transfer between the substrate and the analyte.This is a manifestation of the chemical enhancement mechanism.It was found that the Ti3C2 substrate modified with aluminum oxyanion exhibits good uniformity,reproducibility and stability in SERS applications due to its low roughness and uniform surface and charge.This study confirmed that surface modification is a feasible solution to improve the SERS effect,and solved the problems of low detection limit,poor uniformity,poor reproducibility and poor stability of traditional SERS substrates.(4)Surface-modified Ti3C2 for inherent fingerprint retention and universality of SERS detection moleculesThe effect of surface structure on the molecular orientation of the analysis was studied,and it found that the analysis molecule on Ti3C2 substrate modified with aluminum oxyanions adopts a flat-lying that is similar to the configuration on a blank substrate,and a side-lying can be observed on the Ti3C2 substrate modified with OH/F.It clarified the strength of the interaction between the substrate and the analytical molecule.Because the F group of the Ti3C2 modified with OH/F and the S atom of the methylene blue molecule repel each other,the interaction strength of the Ti3C2 modified with OH/F and the analytical molecule is much smaller than that of the Ti3C2 modified with aluminum oxyanions.It is found it is an important factor to maintain the analysis of the inherent fingerprint characteristics of the molecule by using a configuration similar to that on the blank substrate.In addition,it was found that the Ti3C2 substrate modified with aluminum oxyanions also shows good SERS performance for different organic dyes and trace harmful compounds,and has a strong fluorescence suppression effect on R6G molecules.This work solves the problem of detection distortion due to enhanced substrate interference with the inherent structure and conformation of molecules,and introduces a new perspective for the application of two-dimensional nanomaterials in SERS. |
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