Surface-enhanced Raman Spectroscopy Detection Of Uranium Compounds Based On Silver Substrates

The corrosion of uranium(U)materials will change its structure and properties,which brings huge safety risk for humans.While the widespread use of uranium has also generated large amounts of radioactive nuclear wastes.Once it flows into the environment,it will pose great threat to human health.Therefore,it is necessary to promote the work of the early corrosion products detection and the nuclear emergency detection.The currently developed detection technologies are difficult to satisfy the fast,accurate and highly sensitive functions.Surface-enhanced Raman spectroscopy(SERS)technology has the advantages of high sensitivity,near-field enhancement,and fingerprints spectrum.The current research on SERS detection of uranyl compounds is mainly focused on the design of SERS substrates with strong electromagnetic enhancement effect to improve the analytical sensitivity for UO22+ in solution.While the research for the adsorption mechanism of UO22+ on the SERS substrates is slightly inadequate,especially the reason for the shift and broadening of the v1 symmetrical stretching vibration frequency of UO22+is not clear.In addition,it is difficult to detect the uranyl species absorbed on the solid media surfaces and also difficult to enhance the signal of uranium oxides.In order to solve some problems existed in uranium compounds analysis by SERS technology,three types of SERS substrates such as tape wrapped silver nanorods coated with inert alumina,silver nanorods flexible substrate,and silver nanoparticles sols were prepared and utilized to study the SERS of uranium compounds.The tape collected and in situ study strategies were proposed to discuss the reasons for the shift and broadening of UO22+ peak.The analytical capabilities for U22+ detection by these three types of substrates were also studied.And the feasibility study to quickly identify uranium oxides by SERS technology was discussed.The main research conclusions are as follows:1.The alumina coated silver nanorods(AgNRs@Al2O3)were fabricated by using physical vapor deposition and atomic layer deposition technologies.A tape-wrapped SERS(T-SERS)technique was established by using the transparent tape to quickly collect surface pollutant molecules through“paste&peel off”procedure and then pasting the tape again on the AgNRs@Al2O3 substrate for SERS measuements.The rapid detection of uranyl compounds from irregular solid surfaces were realized by T-SERS strategy.The charge transfer interaction between uranyl and substrates results in the shift of uranyl peak towards lower wavenumbers.The signal of 9 μg/cm2 U22+ adsorbed on the stainless steel discs surface by T-SERS substrate can be easily detected.Combined with roughened silver,gold and Ag2O substrates,the adsorption enhancement mechanism of UO22+ on silver was discussed.The results showed that UO22+ was absorbed on the surface of the silver-based SERS substrate by Ag-O-UO22+ interaction.The charge was transferred from silver to uranium atoms,weakening the bond strength of the O=U=O,which causes the symmetrically stretching vibration frequency of UO22+ moving toward lower wavenumbers.2.AgNRs SERS tape flexible substrate was prepared through a“paste&peel off”procedure by using the tape to transfer the active AgNRs structure from the rigid silicon surface to the flexible transparent tape surface.The in situ SERS analysis technology for uranyl compounds was established with a back-in measurement method after pasting the SERS tape on the surface that needed to be detected.The strategy for in-situ study of UO22+by the flexible AgNRs tape avoids the interference of UO22+ hydrolysis.The research results showed that the reason for the broadening of UO22+ peak is from the several interactions between UO22+ and silver with various oxidation states.The signal of 0.9 μg/cm2 UO22+ on the stainless steel discs surface as well as 100 nmol·L-1 in solution can be easily detected,exhibiting the strong analytical performance of AgNRs SERS tape.3.Citrate-stabilized AgNPs sol was prepared by chemical reduction method.UO22+ can be captured on the“hot spots”of AgNPs through the strong interaction from uranyl with citrate and silver.The quantitative detection of UO22+ with a detection limit as low as 60 nmol·L-1 was achieved with the residual citrate as the internal reference to standardize the peak strength of VO22+.The SERS study of uranium oxides with AgNPs was conducted for the first time.The signal of UO2-the oxidation corrosion product of U-0.79wt.%Ti alloy-was evidently enhanced.The peak position of UO2 is located at 758 cm-1 with an apparent enhancement factor of about 103.The corrosion oxidation products of uranium-titanium alloys can be identified by SERS technique,showing the application prospect of SERS for studying uranium corrosion process kinetics and corrosion mechanism.In this paper,T-SERS,in-situ SERS,and SERS quantitative analysis techniques were constructed through these three types of substrates,which can be used for rapid and sensitive analysis of uranium compounds at different scenarios in uranium corrosion and nuclear emergency response process.The related research results are expected to be utilized for rapid detection of uranyl species and also other molecules in the actual environment.We believe that these established general techniques will support the SERS development toward practical direction.