Highly concentrated Ag nanoparticles (above 20 g L−1) synthesized by the reaction AgNO3 with BPEI exhibited long-term stability over more than 40 days.

In this work, a simple, fast, and room temperature aqueousphase route was developed to synthesize highly aniotropic silver (Ag) nanoplates with controllable sizes from 1 to 17 mm. Our simple synthetic protocol involves the direct reduction of polyethyleneimine (PEI) stabilized silver chloride (AgCl) nanoparticles with hydrogen peroxide (H 2 O 2 ) in the presence of pyrrolidone in an aqueous-phase at room temperature for short reaction time of 10 min. In the growth mechanism study, we found that the AgCl nanoparticles (seeds) were formed by the precipitation reaction of AgNO 3 with NaCl in the presence of PEI at the early stage, and after the addition of H 2 O 2 , Ag + in AgCl was reduced to Ag 0 , making small Ag nanoparticles. Then large Ag nanoplates were formed by attachment and fusion of the small Ag nanoparticles. Cytotoxicity of Ag nanoplates was tested with by human adipose derived stem cells. Ag nanoplates showed no cytotoxicity upto 50 mM/ml while 5 mM/ml of Ag nanoparticles treatment showed high cytotoxicity. Also Ag nanoplates treated cells showed reduced pro-apoptotic gene expressions copampared to Ag nanoplates treatment. This modality may lead to further bio-application based on Ag nanoplates.

A simple and fast synthetic route to ultra-highly concentrated silver nanoparticles with long-term stability by reducing AgNO3 with ascorbic acid in the presence of polyethyleneimine (PEI) as a stabilizer in an aqueous phase is reported. The concentration of silver precursor was as high as 2000 mm (200 g of Ag nanoparticle per liter of water) and the reaction time was less than 10 min. The resulting silver nanoparticles show long-term stability after two months of storage at room temperature without any signs of particle aggregation or precipitation in an aqueous phase. The successful ligand exchange of PEI-stabilized silver nanoparticles to polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) without particle aggregation is also demonstrated. In addition, the catalytic activities of silver nanoparticles stabilized by various stabilizers prepared by the ligand exchange method was investigated. The PEI-stabilized silver nanoparticles exhibited a higher stability than those of PEG- and PVP-stabilized silver nanoparticles in the diffusion-controlled catalytic reduction of 4-nitrophenol to 4-aminophenol by NaBH4 .

This work describes a simple and aqueous-phase route for synthesis of Cu nanowires (Cu NWs) having a long length of 140−180 µm, a high aspect ratio of more than 350, and long-term stability. High-quality Cu NWs were synthesized by reduction of CuCl 2 with ascorbic acid in the presence of branched polyethyleneimine (BPEI) in an aqueous solution at 90 °C. The synthesized uniform Cu NWs showed long-term stability without the formation of Cu oxides on the surface of the NWs after being stored at room temperature for 40 days. Interestingly, we found that Cl − in the reacting solution played a key role in the formation of long Cu NWs. We also investigated the influence of various experimental conditions including the weight ratio of BPEI/CuCl 2 , the pH of the reacting solution, and the reaction temperature on the length, morphology, and stability of Cu NWs.branched polyethyleneimine (BPEI) in an aqueous-phase at 90 °C. The synthesized uniform Cu NWs showed long-term stability without formation of Cu oxides on the surface of the NWs after being stored at room temperature for 40 days. Interestingly, we found that Cl − in the reacting solution played a key role in the formation of long Cu NWs. We also investigated the influence of various experimental conditions including the weight ratio of BPEI/CuCl 2 , the pH of the reacting solution, and the reaction temperature on the length, morphology, and stability of Cu NWs. Experimental SectionMaterials. BPEI (MW = 750,000, 50 wt.% solution in water), cupric chloride (CuCl 2 , ≥99%), copper(II) nitrate (Cu(NO 3 ) 2 ), ascorbic acid (C 6 H 8 O 6, purity ≥99%), sodium hydroxide (NaOH, ≥98%),and nitric acid (HNO 3 , ~ 70 %) were purchased from Aldrich and were used without further purification. Synthesis of Cu NWs.In a typical synthesis, 0.135g of CuCl 2 and 0.04g of BPEI were dissolved in 2 mL of deionized water in air under magnetic stirring at room temperature. Meanwhile, 3mL of 0.167 M aqueous ascorbic acid was added to the reaction solution using a micropipette (final volume of the solution was 5 ml and the weight ratio of BPEI/CuCl 2 was 0.3). The pH of the resulting solution was 2.9. The resulting mixture was aged at 90°C for 3 h, and was then cooled down to room temperature. The product was collected by repeated centrifugation and washing with water three times to remove the excess reagents.Characterization. TEM and high-resolution TEM (HRTEM) images were captured using a JEM-2100F microscope operating at 200 kV. Scanning electron microscopy (SEM) images were obtained using a LEO SUPRA 55 microscope. Powder X-ray diffraction (XRD) patterns were obtained using a Rigaku D-MAX/A diffractometer at 35 kV and 35 mA. Fourier transform infrared spectroscopy (FTIR) analysis was performed using a Jasco FTIR-6100 equipped with an ATR assembly in transmission mode. X-ray photoelectron spectroscopy (XPS) data was obtained using a Thermo Scientific K-Alpha spectrometer. Results and Discussion 5We observed a growth behavior of the Cu NWs by taking samples at various reaction stages and a...

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