Xueliang Qiao

Convenient synthesis of silver nanowires with adjustable diameters via a solvothermal method

Silver nanowires have been successfully synthesized via a simple solvothermal method by adding sodium sulfide (Na(2)S) into the solution. The Ag(2)S colloids produced in the initial stage help reduce the concentration of free Ag(+) ions in the initial formation of silver seeds and subsequently release Ag(+) ions to the solution. Otherwise, there is no oxidative etching owing to the absence of oxygen. In these cases, silver nanowires are grown preferentially. Furthermore, silver nanowires with adjustable diameters can be obtained by adjusting the concentration of Na(2)S. Electron microscopy, X-ray diffraction, and absorption spectra have been used to investigate the products, and a mechanism is proposed to interpret the controlled synthesis of silver nanowires. Finally, our results indicate that this approach provides a versatile route to prepare silver nanowires with controllable diameters.

Convenient, rapid synthesis of silver nanocubes and nanowires via a microwave-assisted polyol method

Silver nanostructures have been synthesized via a microwave-assisted polyol method by adding sodium sulfide (Na(2)S) into the solution. An interesting morphology evolution can be observed by adjusting the concentration of Na(2)S and the heating power. It is found that the ideal concentration of Na(2)S is 31.25-500 microM for the fast reduction of Ag(+) at 300 W under optimal conditions for producing monodispersed silver nanocubes. When the heating power is increased to 400 W, 62.5-250 microM is the ideal concentration of Na(2)S for the synthesis of silver nanocubes. On increasing the concentration of Na(2)S (>500 microM), a mixture of silver nanowires, nanocubes, bipyramids, and irregular/quasispherical particles is synthesized at 300 and 400 W. In particular, an increase in the concentration of Na(2)S to 750 microM at 400 W leads to the production of a quantity of silver nanowires. In addition, silver nanocubes with controllable sizes can be obtained by changing the concentration of Na(2)S and the heating power. Compared to traditional wet-chemical methods, this method has the advantage of a marked decrease in reaction time to 3.5 min. Finally, our work provides a simple strategy for fabricating silver nanostructures with controllable morphologies and sizes.

Preparation and Characterization of Nano-silver Loaded Montmorillonite with Strong Antibacterial Activity and Slow Release Property

Nano-silver loaded montmorillonite (Ag-MMT) was prepared by ion-exchange and then a UV-photoreduction two-step approach was applied. The silver content in Ag-MMT determined by Volhard method was about 6.4 wt%. The morphology and structure of as-synthesized Ag-MMT were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the Ag nanoparticles were spherical and their diameters were about 15–20 nm. Moreover, the structure of MMT did not change. The minimum inhibition concentration (MIC) of Ag-MMT was 100× −6 and the sterilizing efficiency (SE) of Ag-MMT was approximately 100% against Escherichia coli ATCC 11229 (E. coli). In addition, the slow release property of silver in Ag-MMT was also demonstrated.

Facile modification of nanoscale zero-valent iron with high stability for Cr(VI) remediation

In this study, a highly stable nanoscale zero-valent iron composite (HS-NZVI) was obtained via modifying nanoscale zero-valent iron (NZVI) with tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMOS), and used for Cr(VI) remediation in aqueous solution. The obtained HS-NZVI remained stable in water without being oxidized for over 12h. After four consecutive runs, the Cr(VI) removal efficiency of HS-NZVI maintained a value of more than 82%. Moreover, the Cr(VI) removal capacity per unit weight of NZVI in HS-NZVI reached 292.8mg/g within 60min at the initial Cr(VI) concentration of 120mg/L at pH5. The Cr(VI) removal efficiency of HS-NZVI increased with decreasing solution pH, and the experimental data for Cr(VI) removal by HS-NZVI were well-described by the pseudo-first-order reaction model. Additionally, scanning electron microscope (SEM) images, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) measurements of the product after reaction revealed that the mechanism of Cr(VI) remediation by HS-NZVI mainly involved adsorption, reduction and co-precipitation. Considering the advantages of easy preparation, excellent stability and reusability, and high Cr(VI) removal capacity as well as the magnetic recovery property, HS-NZVI is expected to have notably promising applications for the remediation of Cr(VI) contaminated sites.

Room-temperature synthesis of silica supported silver nanoparticles in basic ethanol solution and their antibacterial activity

A facile and environmentally friendly route was developed to synthesize silica supported silver nanoparticles (Ag NPs) through the reduction of silver ions in basic ethanol solution without adding any other reducing agents or surfactants at room temperature. The structure, morphology and composition of as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that the molar ratio of sodium hydroxide to silver nitrate was a decisive factor for the composition of the final products. If the molar ratio was larger than 1.1, the final product was pure silver particles; otherwise, part of the product was silver oxide. Moreover, it was also found that water had a negative influence on the formation of silver particles. For a simple experimental process, this is an efficient and facile method to synthesize silica supported Ag NPs in ethanol at room temperature. Additionally, since the as-prepared Ag NPs were not encapsulated with surface modifier, the Ag NPs with more active atoms exposed consequently exhibited excellent antibacterial activity against Escherichia coli.

Fabrication of pit-structured ZnO nanorods and their enhanced photocatalytic performance

ZnO nanorods have been successfully prepared at low temperature (60 °C) in the presence of ammonia via a simple aqueous solution-based chemical approach. After calcination at 300 °C, many unique pitted structures are found on the surface of ZnO nanorods, although the shape and size of ZnO nanorods have almost no changes. Furthermore, the pit-structured ZnO nanorods exhibit higher photocatalytic activity for methylene blue photodegradation with a rate constant (k) of 0.01402 min−1, which is about 3 times more than that of uncalcined sample. The formation of the pitted structures is presumably attributed to the decomposition of a trace amount of ZnO(NH3)n complex implanted into ZnO crystals. In addition, a photocatalytic mechanism is proposed to explain the enhanced photocatalytic activity of the pit-structured ZnO nanorods.

Green Synthesis of Highly Pure Nano-Silver Sols—Electrolysis

Abstract The highly pure nano-silver sols were prepared by an electrolysis method using two highly pure silver flakes as electrodes and deionized water as electrolytic solution, and PVP served as stabilizer. The effects of PVP content, electrolytic time and current density on the colloidal silver nanoparticles were researched. The results indicate that as-synthesized particles were spherical about 1∼3 nm in size, and monodispersed and its concentration reached to 130 μg/g under the condition of 5.0 wt% PVP with current density about 1∼2 mA/cm 2 for 150 min. Moreover, the nano-silver sol had such an excellent stability that it had not any change though it was placed in dark at room temperature for 6 months.

Reducing the cytotoxicity while improving the anti-cancer activity of silver nanoparticles through α-tocopherol succinate modification

By releasing Ag+ ions and generating reactive oxygen species (ROS), silver nanoparticles (Ag NPs) not only have good anti-tumor activity but also display cytotoxicity towards normal cells which limits their further application in the medical field. Up to now, there was still no appropriate method to reduce the cytotoxicity while improving the anti-cancer activity of Ag NPs. This paper focuses on counteracting the toxic side effect of the ROS from Ag NPs while simultaneously improving their anti-cancer effect. We used α-TOS to modify Ag NPs and investigated their bioactivity in vitro for the first time. The modified Ag NPs with a high α-TOS concentration not only show much higher anti-tumor activity than Ag NPs alone but also promote the survival of normal cell lines slightly, while the modified Ag NPs with a low α-TOS concentration display a lower cytotoxicity against normal cell lines without affecting their anti-cancer activity when compared to Ag NPs alone. Therefore, this work presents a higher potential for cancer treatment than using Ag NPs alone.

Facile preparation of Ag/Ni(OH)2 composites with enhanced catalytic activity for reduction of 4-nitrophenol

In this work, a facile and environmentally friendly process was developed for synthesis of Ag/Ni(OH)2 composites by only mixing an ethanol solution of AgNO3 with Ni(OH)2 at room temperature. The morphology and structure of the as-prepared Ag/Ni(OH)2 composites were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and X-ray photoelectron spectroscopy (XPS). It was found that the composites consist of ultrathin nickel hydroxide and silver nanoparticles (Ag NPs), the Ag NPs with an average diameter of around 4.7 nm evenly dispersed on the surface of Ni(OH)2 nanosheets. The catalytic properties of the obtained Ag/Ni(OH)2 composites were evaluated by the reduction of 4-nitrophenol (4-NP) using NaBH4 as a reducing agent. The results revealed that the obtained Ag/Ni(OH)2 composites exhibited an outstanding catalytic activity. In addition, the formation mechanism of Ag NPs was probed by ultraviolet-visible spectroscopy (UV-Vis). It was found that Ni(OH)2 as a substrate played an important role in the formation of silver particles, which not only acted as a superior adsorbent of silver ion but also a source of OH− that was able to accelerate the reaction. Electrochemical impedance spectroscopy (EIS) and fluorescence (FL) spectra were employed to indirectly elucidate the mechanism for reduction of 4-NP. The Ag/Ni(OH)2 composites are very promising catalytic candidates for the reduction of 4-nitrophenol because of their easy and simple preparation route and high catalytic activity.

Facile fabrication of silver nanoplates via a solvothermal method

This paper describes a simple solvothermal route to synthesize silver nanoplates by reduction of silver nitrate (AgNO3) with N,N-dimethylformamide. In this approach, ferric chloride (FeCl3) servers as the controlling agent, enabling the control over the concentration of free Ag+ ions in the solution. As the concentration of FeCl3 added to the reaction was increased, the morphologies of silver nanostructures evolved from triangular silver nanoplates to hexagonal silver nanoplates. The structures of these nanoplates were characterized by X-ray diffraction, electron microscopy and electron diffraction. A possible mechanism is proposed to interpret the shape-controlled synthesis of silver nanostructures. Finally, our results suggest that this method provides a convenient way to prepare silver nanostructures with different morphologies.