Facile fabrication of Ag@C@C8 nanoparticles as a SERS substrate and their environmental applications

After preparing carbon-coated silver (Ag@C) nanoparticles by a one-step hydrothermal synthesis method, the surface of the nanoparticles was modified with chlorodimethyloctylsilane (C8) to generate C8 functionalized Ag@C@C8 nanoparticles. The Ag@C@C8 nanoparticles were then employed as a substrate for surface enhancement Raman scattering (SERS). The high sensitivity, good uniformity, and long stability Raman signals for both probe dyes (rhodamine 6G and crystal violet) and a real sample (malachite green) in water demonstrated good performance of the as-synthesised Ag@C@C8 nanoparticles. SEM images and TEM images indicate the successful preparation of Ag@C nanoparticles. The results of energy disperse spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements all demonstrate that C8 is successfully functionalized on the surface of Ag@C nanoparticles. The combination of an agglomeration effect and the core-shell structure improves the sensitivity and stability of the substrate. The Raman performance of both Ag@C and Ag@C@C8 nanoparticles was evaluated using representative probe molecules such as rhodamine 6G, crystal violet and malachite green. The sensitivity and enhancement factor of Ag@C@C8 were evaluated using folic acid, a non-dye molecule. Additionally, malachite green in several actual water samples was also measured to evaluate the Ag@C@C8 nanoparticles. Then, using crystal violet as a probe molecule, the long-term stability of the Ag@C@C8 nanoparticles was investigated. The results indicate that for four weeks, the intensity deviations of different characteristic peaks were less than 17.5%, and there was no further downward trend. Our strategy partially overcomes the problem of easy oxidation of Ag nanoparticles by coating them with a thin carbon layer, and subsequent functionalization with C8 can increase the SERS sensitivity for certain pollutants due to a condensation effect.