化学还原法制备纳米银粒子及其表征

采用化学还原法, 通过一系列条件实验,借助紫外-可见分光光度计(UV-vis)得到最佳实验条件,在最佳实验条件下制得紫黑色溶胶,在40℃下真空干燥3h,获纳米银粉.制备的纳米银粉用X射线衍射仪(XRD)和透射电镜(TEM)分析表明,其粒径大小分布范围窄,形状为单一球形,平均粒径为18nm.     

pH effect on the aggregation of silver nanoparticles synthesized by chemical reduction

Silver colloidal nanoparticles were prepared according to the chemical reduction method in which the ascorbic acid was used as a reducing agent and sodium citrate as a stabilizing agent. The absorption spectra of all prepared samples obtained using the UV-Vis spectrophotometer showed a surface plasmon peak at a wavelength of about 420 nm. The size of the silver nanoparticles was controlled by changing the pH values of the reaction system. At high pH, smaller size silver nanoparticles were obtained compared to low pH values. This difference can be attributed to the difference in the reduction rate of the precursor. In addition to the inverse proportionality between the size and the pH value it is clear that increasing the pH value enables us to obtain spherical nanoparticles while at low pH, rods and triangular particle shapes were formed. Poor balance between nucleation and growth processes could be the cause of this result.     

Synthesis of silver nanoparticles by chemical and biological methods and their antimicrobial properties

Biogenic synthesis of nanoparticles offers an attractive alternate to chemical synthesis methods. Various hazard free, eco-friendly methods of synthesis of silver nanoparticles are in operation. In chemical reduction methods, the reducing agent is a chemical solution, whereas in biological ones, the collection of enzymes, especially nitrate reductase, plays this role. The highest antibacterial activity of silver nanoparticles synthesised by chemical and biological methods was found in Staphylococcus aureus and Escherichia coli. The paper aims to discuss some fundamental issues about non-biological methods and benefits about biological methods for silver nanoparticles synthesis and their antibacterial studies.     

Preparation of copper nanoparticles on carbon nanotubes by electroless plating method

Densely distributed copper nanoparticles have been deposited on the surface of carbon nanotubes with a size of ∼10 nm by the electroless plating method. It has been found that the pretreatment of the carbon nanotubes is very important to obtain the copper nanoparticles on the carbon nanotubes; in our experiments, one-step pretreatment of mixed HNO₃ and H₂SO₄ was found effective. In order to attain nanosized copper particles, the electroless plating parameters should be closely controlled; e.g., the pH value of the plating solution, the temperature, and the concentration and titrating speed of HCOH were critical.     

Preparation of coated iron powders by chemical plating

Small iron particles can be produced by reduction of γ-Fe2O3and α-FeOOH with hydrogen; they show outstanding magnetic properties and can be used for recording media. The main difficulty concerns the tendency of these particles to oxidize. We have studied a preparation process in two steps: a) reduction of iron oxides or oxy-hydroxides; b) chemical plating in the same furnace. The magnetic properties of the iron powders chiefly depend on the reduction step. The water content in the gas leaving the furnace has been shown to be the main parameter determining the obtainment of powders with high magnetic properties. The iron powders, which were pyrophoric, have been quenched in chemical plating bath of suitable formulation and coated with cobalt or copper. Typical magnetic properties are: saturation magnetization σsat= 130-165 emu/g, intrinsic coercivityjHc= 350-450 Oe; best magnetic properties: σsat=155 emu/g,jHc=700 Oe. The coated powders have been submitted to heat treatment in air saturated with water, showing a good resistance to oxidation.     

Evaluation of the wound healing efficacy of chemical and phytogenic silver nanoparticles

Wound healing requires a series of cellular events and a cascade of co‐ordinated and systemic biochemical events. Silver nanoparticles possess many beneficial properties for wound management including antibacterial, anti‐inflammatory and pro‐healing properties. In this study, the authors investigated the wound healing properties of Cinnamomum verum extract mediated nanosilver (CENS) particles in comparison with 1% povidone iodine, citrate mediate NS and CE treatments. The topical application of CENS showed good antibacterial activity and accelerated wound healing with complete epithelialisation and normal re‐growth of hair in all three models of study: namely, excision, incision and dead space models in rats compared with all other treatments. CENS was also found to promote collagen synthesis, stabilise wound besides countering oxidative stress and stimulating cellular proliferation CENS could be a novel therapeutic agent for wound management.Inspec keywords: silver, nanoparticles, nanomedicine, wounds, antibacterial activity, biomedical materials, biochemistry, cellular biophysics, proteinsOther keywords: wound healing efficacy, chemical nanoparticles, phytogenic silver nanoparticles, cellular events, systemic biochemical events, wound management, antibacterial properties, anti‐inflammatory properties, pro‐healing properties, Cinnamomum verum extract mediated nanosilver particles, CENS, complete epithelialisation, normal hair regrowth, excision model, incision model, dead space model, rats, collagen synthesis, oxidative stress, cellular proliferation, therapeutic agent, Ag     

Tuning photoluminescence of ZnS nanoparticles by silver

We report the results of investigation of the interaction of silver with presynthesized ZnS nanoparticles (NPs) that was stabilized by cetyl trimethyl ammonium bromide (CTAB). The photoluminescence properties of ZnS NPs were followed in the presence of Ag⁺ ions, Ag NPs and by the synthesis of Ag@ZnS core-shell nanoparticles. We observed that CTAB stabilized ZnS NPs emitted broadly in the region from 350–450 nm, when excited by 309 nm light. In the presence of Ag⁺ ions the emission peak intensity up to 400 nm was reduced, while two new and stronger peaks at 430 nm and 550 nm appeared. Similar results were obtained when Ag NPs solution was added to ZnS solution. However, when Ag@ZnS NPs were synthesized, the emission in the 350–450 nm region was much weaker in comparison to that at 540 nm, which itself appeared at a wavelength shorter than that of Ag⁺ ion added ZnS NPs. The observations have been explained by the presence of interstitial sulfur and Zn²⁺, especially near the surface of the nanocrystals and their interaction with various forms of silver. In addition, our observations suggest that Ag⁺ ions diffuse into the lattice of the preformed ZnS NPs just like the formation of Ag⁺ doped ZnS NPs and thus changes the emission characteristics. We also have pursued similar experiments with addition of Mn²⁺ ions to ZnS and observed similar results of emission characteristics of Mn²⁺ doped ZnS NPs. We expect that results would stimulate further research interests in the development of fluoremetric metal ion sensors based on interaction with quantum dots.     

Deposition of silver nanoparticles on dendrimer functionalized multiwalled carbon nanotubes: synthesis, characterization and antimicrobial activity

The nanohybrids composed of silver nanoparticles and aromatic polyamide functionalized multiwalled carbon nanotubes (MWCNTs) is successfully synthesized and tested for their antibacterial activity against different pathogens. Prior to deposition of silver nanoparticles, acid treated MWCNTs (MWCNTs-COOH) were successively reacted with p-phenylenediamine and methylmethacrylate to form series of NH2-terminated aromatic polyamide dendrimers on the surface of MWCNTs through Michael addition and amidation. Existence of high abundance of amine groups on the surface of functionalized MWCNTs (f-MWCNTs) provided sites for formation of silver nanoparticles by the reduction of aqueous solution of AgNO3. The silver nanoparticles formed in the resulted f-MWCNTs-Ag nanohybrids were determined to be face centered cubic (fcc) symmetry. The structure and nature of f-MWCNTs and f-MWCNTs-Ag nanohybrids were characterized by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction analysis (XRD), Raman spectroscopy and thermogravimetric analysis (TGA). The dispersion state of f-MWCNTs and immobilization of silver nanoparticles on the surface of f-MWCNTs were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Elemental composition of f-MWCNTs-Ag nanohybrids was determined by energy dispersive X-ray spectroscopy (EDS). The antimicrobial activity of f-MWCNTs-Ag nanohybrids were estimated against E. coli, P. aeruginosa and S. aureu and compared with MWCNTs-COOH and f-MWCNTs. The results indicate that functionalization of MWCNTs with aromatic polyamide dendrimers and successive deposition of Ag nanoparticles could play an important role in the enhancement of antimicrobial activity.     

Deposition of Ti-N compounds by thermionically assisted triode reactive ion plating

Details are given of the influence of the ion current density on the properties of Ti-N compounds deposited at low temperatures (<600°C) by a thermionically assisted triode reactive ion-plating technique. As the chamber pressure increases, greater specimen currents are necessary, both to prevent the deposition of powdery TiN and also to ensure reaction for the formation of Ti₂N and TiN at lower partial pressures of nitrogen. The ionization efficiency, being related to both pressure and current density, is suggested as a suitable parameter for defining optimum conditions. An ionization efficiency of about 0.3% is identified as the minimum required for the deposition of cohesive TiN, whilst values above this improve the densification and the hardness.     

Ag包覆SnO_2制备工艺及其性能研究

采用包覆工艺制备了AgSnO_2电接触材料,通过分散剂种类、球磨时间、活化剂种类等工艺参数的优化,制备了性能合格的AgSnO_2电接触材料。实验结果表明,聚乙二醇对SnO_2颗粒具有较好的分散作用,但不能完全消除SnO_2颗粒团聚;液态球磨能获得组织均匀的AgSnO_2材料,但材料的电阻率过高;活化剂Bi_2O_3和CuO的加入能有效地提高材料的致密度和降低电阻率;在加入0.25%Bi_2O_3+0.25%CuO并液态球磨4h后的试样致密度为98.2%,电阻率为2.25μΩ·cm。     

化学镀法制备Ag/Al复合粉末

通过化学镀的方法在铝粉表面包覆银,研究了铝粉化学镀银的原理,探讨了氨水、银氨离子、稳定剂、温度和pH对化学镀银的影响。结果表明氨水可以增加镀液稳定性,改善镀层形貌;银氨离子浓度对镀层银含量以及粉末电阻率影响明显;少量稳定剂可以增强镀液稳定性,过量导致镀层疏松多孔;温度和pH的提高可以增加银的析出量,但也会导致镀液的分解。     

碳纳米管的化学镀银

碳纳米管因其优异的力学、物理性能，是一种理想的复合材料增强体。通过化学镀可在碳纳米管表面镀上一层连续的银镀层，以增强碳纳米管与金属基体的界面结合力．本文研究了在碳纳来管上化学沉积银的工艺及其影响因素．SEM、TEM观察表明：氧化、活化及镀是影响镀层质量的最重要因素．尽可能多的活化点以及尽可能慢的镀速将大大改善镀层质量。     

Preparation of pH-responsive silver nanoparticles by RAFT polymerization

Silver nanoparticles were prepared by chemical reduction of AgNO₃ in the presence of the PDMAEMA-b-PPA, which was synthesized by the reversible addition-fragmentation transfer technique. The formation of the silver nanoparticles was determined by the transmission electron microscopy (TEM) images and UV–Vis absorption spectra. The average size of the silver nanoparticles was shown to 11.4 nm. Particularly, the pH-responsive property of the silver nanoparticle was further observed. It was characterized by the zate potential, the UV–Vis spectra, and TEM images. The results show that the pH-responsive property is attributed to the aggregate of the silver nanoparticles as a function of pH. The characteristic is expected to apply in the nanoscale optical biosensor and biomaterials.     

Formation of aligned silver nanoparticles by ion implantation

Synthesis of metal nanoparticles by ion implantation has a number of advantages. Nevertheless, certain remaining difficulties must be overcome in order to optimize the characteristics of ion-implanted nanocomposites. The principle among these are the lack of control over the size distribution and position of the precipitates within the implanted layer. Two-dimensionally ordered arrangements of Ag nanoparticles are formed in Ag-implanted silica glass by post-implanted Cu ions. The spherical Ag nanoparticles are formed to align at the same deep depth in the silica. Cross-sectional transmission electron microscopy revealed that the Ag nanoparticles are a size of 35-48 nm in diameter. The evolution of nanoparticles is characterized by transmission electron microscopy.     

Deposition of platinum nanoparticles on carbon nanotubes by supercritical fluid method

Carbon nanotube-supported platinum nanoparticles with a 5-15 nm diameter size range can be synthesized by hydrogen reduction of platinum(ll) acetylacetonate in methanol modified supercritical carbon dioxide. X-ray photoelectron spectroscopy and X-ray diffraction spectra indicate that the carbon nanotubes contain zero-valent platinum metal and high-resolution transmission electron microscopy images show that the visible lattice fringes of platinum nanoparticles are crystallites. Carbon nanotubes synthesized with 25% by weight of platinum nanoparticles exhibit a higher activity for hydrogenation of benzene compared with a commercial carbon black platinum catalyst. The carbon nanotube-supported platinum nanocatalyst can be reused at least six times for the hydrogenation reaction without losing activity. The carbon nanotube-supported platinum nanoparticles are also highly active for electrochemical oxidation of methanol and for reduction of oxygen suggesting their potential use as a new electrocatalyst for proton exchange membrane fuel cell applications.