Co-effect of soft template and microwave irradiation on morphological control of gold nanobranches

Short-range order sodium dodecyl sulfate (SDS)-bound micelles and long-range order poly(vinylpyrrolidone) (PVP)–SDS supramolecular assemblies in PVP–SDS aqueous solution illustrate the potential template application in directing hierarchical assembly of inorganic nanostructure. In this paper, ginger-like Au nanobranches with equivalent circle diameter around 50 nm were prepared in PVP–SDS aqueous solution under microwave irradiation through a one-pot, facile, rapid, and morphology-controlled synthesis route. Based on the experimental results, the possible growth mechanism of the ginger-like gold nanobranches is inferred to be a template-mediated and microwave-assisted hierarchical assembly via the unique co-effect of PVP–SDS soft template and microwave irradiation. At first, the precursors AuCl ₄ ⁻ surrounding the SDS-bound micelles were rapidly reduced to Au⁰ by sodium citrate assisted by microwave irradiation and simultaneously assembled into abundant Au nanocrystals with diameters around 10 nm according to the bound micelle templates. And then several tiny Au nanocrystals linked by PVP chains within a limited space were instantly mediated by the long-range order PVP–SDS supramolecular assemblies to fabricate into polycrystal ginger-like Au nanobranches. X-ray diffraction (XRD) pattern indicates that the Au nanobranches are face-centered cubic phase, which is verified by high-resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) pattern.