Simple and Environmentally Compatible One-pot Synthesis of Au Nanoparticles from Bulk: Separation of Au, Ag, and Cu in Water

Abstract

Simple and environmentally compatible one-pot synthesis of Au nanoparticles, starting from dissolving bulk Au into mixed aqueous solution of poly(N-vinyl-2-pyrrolidone), potassium iodide, and iodine and ending by isolating Au nanoparticles produced by reducing the dissolved Au ions with sodium citrate, was developed to provide a novel method to separate Au from mixtures of Au, Ag, and Cu.Au nanoparticles have received much attention from the viewpoint of novel properties such as catalyses 1 and optics 2 because they have quite different properties from bulk Au. On the other hand, bulk Au is known to be chemically stable and have excellent electroconductivity. Thus, the noble metal elements of not only Au but also Ag, Cu, Pd, and Pt have been used for various applications, for example, mobile phones, personal computers, and automobile catalysts. Simple and environmentally compatible methods for recovery of noble metals from used electronic equipment are expected to be developed.3 However, much energy and special reagents are required such as strong acid or base to collect or recover noble metal elements because of their chemical stability. Previously, Nakao reported a method to dissolve noble metal elements into a halogen-halide-organic solvent system. [4][5][6][7] This method does not use strong acid, for example aqua regia, but requires the use of an organic solvent like acetonitrile or methanol. In the present study, we would like to report a selective one-pot synthetic method of Au nanoparticles from bulk by dissolving it into an aqueous solution of poly(N-vinyl-2-pyrrolidone) (PVP), potassium iodide, and iodine. This method has several advantages with respect to environmental load because the solvent is only water, no aqua regia is used, and the separation is carried out by ultrafiltration. It is very useful that Au nanoparticles can be obtained directly from discarded electronic products.The schematic chart of synthesis of Au nanoparticles is shown in Scheme 1. PVP (K30, average molecular weight 40000, 630 mg, 5.6 mmol in monomer unit) was put into a 200-mL two-neck flask with deionized water (70 mL), and the mixtures were stirred at room temperature for 10 min. Potassium iodide (93 mg, 0.56 mmol) was added to the mixtures. After 10 min stirring, iodine (70 mg, 0.28 mmol) was added to the mixtures under stirring. After further 10 min stirring, a noble metal wire (Au, Ag, Cu, Pd, or Pt, ¼ 0:2 mm, 0.05 mmol) was added, and the mixtures were heated at 80 C in an oil bath with a reflux condenser and heated for 24 h. Then, trisodium citrate (200 mg, 0.78 mmol) dissolved in deionized water (20 mL) was added to the reaction mixtures, which were stirred for 10 min. Finally 0.1 mmol L À1 sodium hydroxide (10 mL, 1.0 mmol) was added to the mixtures, which were stirred for 20 min.The extent of dissolved metals in solution was determined by measuring weight of wire after the reaction. Within 24 h 100 wt % of Cu and 96.3 wt % of Au were dissolved, but Ag was not. In the case of Ag wire, a weight increase was observed wh...

Functionalized nanoparticle interactions with polymeric membranes

“…Separation of ionic and NP forms of silver has also been reported [29]. Other groups have similarly purified Au [30] and iron oxide [31, 32] during NP synthesis. Another need in the environmental research field is to collect and concentrate environmental NPs.…”