Controlled synthesis of Au-loaded Fe3O4@C composite microspheres with superior SERS detection and catalytic degradation abilities for organic dyes.

Bifunctional Au-loaded Fe3O4@C composite microspheres were controllably synthesized by coating of Au nanoparticles (NPs) on the surface of the poly(diallyldimethylammonium chloride) (PDDA) functionalized Fe3O4@C microspheres. The amount of Au loading can be effectively tuned by altering the feeding amounts of solution Au NPs or further growth. The obtained Au-loaded Fe3O4@C composite microspheres exhibit both superior surface-enhanced Raman scattering (SERS) sensitivity and catalytic degradation activity for organic dyes. The SERS signal intensity of methylene blue (MB) distinctly enhances with the increase of Au loading, which endows increased Raman 'hot spots' and provides a significant enhancement of the Raman signal through electromagnetic (EM) field enhancements. Furthermore, the catalytic experiments of the Fe3O4@C@Au composite microspheres with the highest Au loading demonstrate that the model organic dye of MB molecules could be degraded within 10 min and the catalytic activity could be recovered without sharp activity loss in six runs, which indicates their superior catalytic degradation activity. The reason could be mainly ascribed to the synergistic effects of small size of Au NPs, the good adsorption behavior of carbon layers and the excellent dispersivity of the composite microspheres induced by the sandwiched carbon layers. The results indicate that the bifunctional Au-loaded Fe3O4@C composite microspheres could be served as promising materials in wastewater treatment.