Surfactant-free preparation expanded graphite coupled with Ag nanoparticles as SERS high sensor via optimizing electromagnetic enhancement and adsorption behavior

The work reported on the preparation of expanded graphite (EG) coupled with Ag nanoparticles for quick water contaminant adsorption, followed by trace molecules sensing using SERS technique. The surfactant-free composites of Ag/EG were obtained by a simple and controllable “mix-and-heat” mechanochemical method. Most of the analytes were found to be adsorbed within 15 min without any additional physical or chemical activation and its adsorption behavior at room temperature fitted pseudo-second-order kinetic models. As SERS enhanced substrate, less than 10 ppb of crystal violet (CV) and methylene blue (MB) could be determined via Ag/EG. What's more, the Ag/EG substrate could adapt to strong acid and alkali environment and could be stored for as long as 120 days. Therefore, the composites Ag/EG could be used as a reliable SERS active substrate. Moreover, the substrate could be reused at least four times. In addition, ‘adsorption-filtration’ was conducted through a homemade filter and the filter membrane was employed as substrate support instead of silicon wafers. Such results reveal that Ag/EG as a solid SERS substrate has great potential value for practical applications. And the study provides a new strategy for the development of high-performance sensing of the target analyte in the future.