Synthesis of gold nanosheets and flower-like gold nanostructures

In this work, we report a simple and efficient method for the preparation of large gold nanosheets using H2O2 as the green reducing agent and starch as a stabilizer and shape-controlling agent. H2O2 provides a weak reducing capability that allows a kinetically controlled growth of nanosheets out of small flower-like nanostructures formed at the initial stage of particle growth. Small nanosheets with starch-bound {111} facet undergo oriented attachment and become large nanosheets with lateral size as large as 50 µm with the thickness of 20–50 nm. Without starch, gold quasi-microspheres with diameters of 5–10 µm are obtained as the dominant product as they grow out of the flower-like nanostructures by filling gold atoms in the gaps between nano-petals. This starch-enable selective formation of large nanosheets is rapidly and efficiently as a 100% conversion can be attained. Interestingly, micrometer-sized flower-like gold nanostructures with nanometer-thick petal assembly are obtained at the extremely high concentration of H2O2. The oriented attachment of the small gold nanosheets creates the basal sheets of the flower structures. Then, the growth of the starch-bound {111} facet nano-petals take place on the surface of the basal sheets causing the formation of flower-like gold nanostructures. We explore the applications of gold nanosheets as a pigment for decoration and a solid substrate for surface enhanced Raman spectroscopy. A single particle of the flower-like gold nanostructure can be employed as a substrate for surface enhanced Raman spectroscopy.