Preparation Of Hollow Transition Metal(Fe,Co,Ni)Hydroxides And Oxides For SERS Applications

In the past few decades,researches of surface enhanced Raman spectroscopy?SERS?substrate have been essentially dominated by noble metal materials such as Au and Ag.However,inevitable shortages,such as high price,poor reproducibility and low structural homogeneity,have tremendously limited the practical application of precious metal substrates.In recent years,in order to achieve the transition and transformation from precious metal substrates to non-precious metal substrates,much efforts have been devoted to the fabrication of non-noble metal SERS substrates.Non-noble metal substrate materials have problems with low sensitivity,and the nature of the enhancement mechanism is not fully understood.In this paper,a kind of hollow transition metal?Fe,Co,Ni?hydroxides and oxides substrates with hollow morphology was prepared,which achieved higher sensitivity in SERS detection.Furthermore,a charge transfer-based mechanism of M?OH?_x has been revealed.Cube and octahedral Cu₂O are used as templates for the preparation of transition metal hydroxide microcages which are matched with the size and morphology of the precursor by a“cooperative etching”strategy.The results showed that the prepared M?OH?_x?M=Fe,Co,Ni?micro-cage exhibits significant SERS performance for different dye molecules with a detection limit of 10^-6-10^-7 mol/L,the trend of enhancement factor is Ni?OH?₂>Co?OH?₂>Fe?OH?₃.The nature mechanism of SERS chemical enhancement effect is discussed through the systematic comparison of SERS properties of different transition metal hydroxides and oxides substrates,The results show that SERS activity is mainly derived from the strong coupling between nitrogen and metal centers.The formation of Fe-N,Co-N and Ni-N bonds changes the chemical environment around the probe molecules,causing rearrangement of electron clouds and promoting efficient charge transfer process.M?OH?_x?M=Fe,Co,Ni?hollow octahedral microcages are calcined at a suitable temperature and time to obtain transition metal oxides with different crystallinity.The experimental results showed that the prepared amorphous metal oxide has good morphology uniformity and structural stability,and achieves sensitive detection of the SERS signal for probe molecule,the detection limit is 10^-6-10^-7 mol/L.Hollow micro cage morphology provides ideal conditions for light capture,effectively increasing the adsorption surface area ofdye molecules.The amorphous structure of oxides exhibits a long-range disorder of internal atoms,reducing the binding of surface electrons and achieving high efficiency charge transfer process,which leads to an increase in the intensity of the detected molecules.This work may open up new horizons for expanding the variety of high-performance SERS substrates and provides some new cognition into the research of SERS chemical enhancement mechanisms.