Preparation Of Molybdenum Oxide Based Nanomaterials And Research On Surface Enhanced Raman Spectroscopy

Surface-enhanced Raman Spectroscopy?SERS?means that the Raman spectrum signal intensity will be greatly enhanced when the sample molecules are adsorbed on the rough metal surface.SERS can overcome the deficiency of conventional Raman spectrum signal,such as weak signal and easy interference,and can realize trace detection of sample molecules.The commonly used noble metal SERS substrates exhibit excellent SERS activity due to strong localized surface plasmon resonance?LSPR?effects,but SERS applications are limited due to the disadvantages of high cost,poor biocompatibility,and poor stability.Some metal oxides have gradually been developed and applied to the study of SERS substrates,but poor SERS activity limits their application space.MoO₂ is a common cheap metal oxide,and is a potentially highly SERS active substrate material due to its special metal properties like good electrical conductivity and good chemical and thermal stability as well.The SERS performance of currently prepared MoO₂ substrate materials need to be further improved.In this paper,MoO₂nanomaterials with special morphologies were prepared and related tests were carried out.The research contens of this paper mainly includes the following three aspects:?1?The high purity and crystallinity MoO₂ hollow spheres were prepared by electrochemical anodization and hydrothermal combination process.The hollow spheres were proved to be self-assembled by conical nanoparticles according to SEM and TEM tests.Among them,the time of anodic oxidation and hydrothermal play an important role in the formation of MoO₂ hollow spherical structures,and the increase of hydrothermal temperature will decrease the size of MoO₂ conical nanoparticles.The products obtained after 2 hours anodizing and then 24 hours hydrothermal process have the desired hollow nanospherical structures.?2?SERS tests of the prepared MoO₂ hollow spheres were conducted using the Rhodamine 6 G?R6 G?as the detection molecule,the maximum enhancement factor?EF?is 3×10⁷,and the detection limit?LOD?is 10^-9M.Which are nearly the highest in all the oxides,almost close to that of noble metal Au and Ag.The stability and SERS enhancement mechanism of the MoO₂ hollow spheres are also discussed.The results show that this MoO₂ hollow spheres is an ideal SERS substrate material,which can maintain good SERS activity even after 500?high temperature.The LSPR effect caused by the high density free electron excitation of the MoO₂ hollow spheres themselves and the special hollow sphere structure formed by the closely arranged conical nanoparticles enhance the raman signal absorption are the main reasons for its high SERS activity.?3?A layer of Ag nanoparticles were deposited by ion sputtering on the surface of the prepared MoO₂ hollow spheres to synthesize the Ag/MoO₂ composite SERS substrates.The composite SERS substrate showed more excellent SERS activity activity compared with previous pure MoO₂ SERS substrates,which have a maximum EF of 10⁸for R6G and extremely low LOD of 10^–10 M.The high SERS activity originates from the physical enhancement initiated by the plasmon resonance between the Ag particles and the charge transfer-dominated chemical enhancement between the R6G and the Ag/MoO₂.