Formation of large H2O2-reduced gold nanosheets via starch-induced two-dimensional oriented attachment

We report here a simple yet efficient approach for fabricating large gold nanosheets using H2O2 as the reducing agent with starch as the stabilizer and shape-controlling agent. The weak reducing capability of H2O2 enables a kinetically controlled growth of nanosheets out of flower-like nanostructures formed at the early stage. Small nanosheets with starch-bound {111} facet undergo oriented attachment and become large nanosheets having lateral size as large as 50 mu m with 20-50 nm thickness. Without starch, gold quasi-microspheres with diameters of 5-10 mu m become the dominant product as they also 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 rapid and efficient as a 100% conversion could be attained even at a high concentration of gold ions (25.4 mM). A large-scale production of 2.5 g glittering gold nanosheets with a 5-L batch 10 h synthesis was demonstrated. The synthetic protocol was not only achieving atomic economy using an environmental friendly reducing reagent and renewable stabilizer, the mass-scale production prototype was accomplished at room temperature without a need for extensive waste treatment. The slightly acidic starch solution obtained after the reaction was recycled for the next synthesis or neutralized before discharging.