Fabrication,characterization, and thermal property evaluation of silver nanofluids

Silver nanoparticles were successfully prepared in two different solvents using a microwave heating technique, with various irradiation times. The silver nanoparticles were dispersed in polar liquids (distilled water and ethylene glycol) without any other reducing agent, in the presence of the stabilizer polyvinylpyrrolidone (PVP). The optical properties, thermal properties, and morphology of the synthesized silver particles were characterized using ultraviolet-visible spectroscopy, photopyroelectric technique, and transmission electron microscopy. It was found that for the both solvents, the effect of microwave irradiation was mainly on the particles distribution, rather than the size, which enabled to make stable and homogeneous silver nanofluids. The individual spherical nanostructure of self-assembled nanoparticles has been formed during microwave irradiation. Ethylene glycol solution, due to its special properties, such as high dielectric loss, high molecular weight, and high boiling point, can serve as a good solvent for microwave heating and is found to be a more suitable medium than the distilled water. A photopyroelectric technique was carried out to measure thermal diffusivity of the samples. The precision and accuracy of this technique was established by comparing the measured thermal diffusivity of the distilled water and ethylene glycol with values reported in the literature. The thermal diffusivity ratio of the silver nanofluids increased up to 1.15 and 1.25 for distilled water and ethylene glycol, respectively.     

A hybrid microreactor/microwave high-pressure flow system of a novel concept design and its application to the synthesis of silver nanoparticles

This article reports on a microreactor/microwave high-pressure flow hybrid apparatus of a novel concept design, which includes both the microreactor and a spiral reactor, and its efficient use in the synthesis of silver nanoparticles of relatively uniform sizes (4.3 ± 0.7 nm) under microwave irradiation. By contrast, under otherwise identical experimental conditions but with conventional heating, the nanoparticle size was non-uniform (8.3 ± 2.7 nm) and the spiral reactor walls were covered with a silver mirror deposit. Formation of the nanoparticles was monitored by UV–visible spectroscopy (plasmonic absorption band; LSPR), TEM and by small-angle X-ray scattering (SAXS). Both the spiral microreactor and the spiral quartz reactor of the hybrid system played an important role in the synthesis, with the microreactor providing the environment wherein mixing of the aqueous solution of [Ag(NH₃)₂]⁺ and the solution of glucose (the reducing agent) and poly(N-vinyl-2-pyrrolidone) (PVP; stabilizer/dispersing agent) occurred. The microwaves provided the thermal energy to effect a uniform growth of the silver nanoparticles at temperatures above 120 °C. Mixing the two solutions by conventional methods (no microreactor) failed to yield such nanoparticles even under microwave irradiation and no formation of a silver mirror occurred in the inner walls of the spiral reactor.     

A convenient approach to synthesize stable silver nanoparticles and silver/polystyrene nanocomposite particles

In this study, silver nanoparticles were prepared by the reduction of silver nitrate in SDS+ isopentanol/styrene/H₂O reverse microemulsion system using sodium citrate as reducing agent. The Ag/PS nanocomposite particles were prepared by in situ emulsion polymerization of the styrene system containing silver nanoparticles that did not separate from the reaction solution. The polymerization dynamic characteristic was studied, at the same time, silver nanparticles and the encapsulation of composite particles were characterized by Fourier‐transform‐infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X‐ray diffraction (XRD) measurement, UV–vis diffuse reflectance spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The results of TEM and UV–vis absorption spectra showed that well‐dispersed silver nanoparticles have a narrow size distribution. XRD showed that Ag and Ag/PS nanocomposite particles were less than 10 and 20 nm in size, which is similar to those observed by TEM. The results of XPS spectra revealed that the microemulsion system can stabilize the silver nanoparticles from aggregation and provided supporting evidence for the polystyrene encapsulated silver nanoparticle structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

银纳米粒子的绿色合成及其光谱特性

以糊精为还原剂和稳定剂,采用微波高压液相绿色合成法制备了黄色银纳米粒子。用吸收光谱和共振散射光谱研究银纳米粒子的光谱特性。结果表明,在优化的最佳条件下,用该法制备的纳米银最大吸收峰在418 nm处,最强共振散射峰在486 nm处,银纳米粒子颗粒呈球形,粒度均匀,平均粒径为20 nm,单分散性较好。该法操作简单反应快速。     

葡聚糖存在下微波高压合成银纳米粒子及其光谱特性

以葡聚糖为还原剂和稳定剂,采用微波高压液相绿色合成法制备了黄色银纳米粒子。用吸收光谱和共振散射光谱研究其制备条件的影响。在413nm处产生最大吸收峰,在486nm处产生一个最强共振散射峰。实验表明：该法制备的银纳米粒子粒径均匀,平均粒径为16nm,其稳定性和分散性好,合成方法简便、快捷。     

PLLA–silver nanoparticles bionanocomposite membranes: Preparation,antibacterial activity,and in vitro hydrolytic degradation assessment

Silver nanoparticles (AgNp) were synthesized in aqueous phase and transferred to chloroform using a fatty amine as phase transfer agent. Poly(l -lactic acid) (PLLA) membranes were prepared using the “functionalized” chloroform. The amount of AgNp in the chloroform was determined by atomic absorption spectroscopy. Thermogravimetric analysis, differential scanning calorimetry, and field emission scanning electron microscopy were used to characterize the membranes. A decrease of the thermal stability of the membranes was observed upon the addition of AgNp; meanwhile, the polymer crystallinity degree increased, making the membranes more fragile and brittle. The in vitro degradation assessments of the membranes in artificial saliva suggested that the time necessary to degrade the PLLA reduced by raising the concentration of the nanostructures. Additionally, the antibacterial assays demonstrated that the addition of only 13 ppm of AgNp were enough to inhibit the formation of biofilm over the bionanocomposite membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47998.     

Radiation synthesis and characterization of poly(vinyl alcohol)/poly(N-vinyl-2-pyrrolidone) based hydrogels containing silver nanoparticles

A series of PVA/PVP based hydrogels at different compositions were prepared by gamma irradiation. The gel fraction degree of swelling were investigated. Highly stable and uniformly distributed silver nanoparticles have been obtained onto hydrogel networks. The morphology and structure of (PVA/PVP) hydrogel and dispersion of the silver nanoparticles in the polymeric matrix were examined by scanning electron microscopy (SEM) and infrared spectroscopy (FT-IR), respectively. The formation of silver nanoparticles has been confirmed by ultraviolet visible (UV–vis) spectroscopy. A strong characteristic absorption peak was found to be around 420 nm for the silver nanoparticles in the hydrogel nanocomposite. The X-ray diffraction pattern confirmed the formation of silver nanoparticles with average particle size of 12 nm. The diameter distribution of silver nanoparticles was determined by dynamic light scattering DLS. Transmission electron microscope (TEM) showed almost spherical and uniform distribution of silver nanoparticles through the hydrogel network and the mean size of silver nanoparticles ranging is 23 nm. The good swelling properties and antibacterial of PVA/PVP-Ag hydrogel suggest that it can be a good candidate as wound dressing.     

Coating silver nanoparticles on poly(methyl methacrylate) chips and spheres via ultrasound irradiation

Ultrasound irradiation is used for anchoring silver nanoparticles with an average size of ～ 51 nm onto the surface of poly(methyl methacrylate) PMMA chips (2 mm diameter), and silver nanoparticles with an average size of ～ 20 nm onto the surface of the PMMA spheres (1–10 μm). The sonochemical reduction was carried out under argon atmosphere at room temperature. The silver nanoparticles were obtained by the irradiation of a mixture containing the PMMA, silver nitrate, ethylene glycol, ethanol, water, and 24% (wt) aqueous ammonia for 2 h, yielding a PMMA‐nanosilver composite. By controlling the atmosphere and reaction conditions, we could achieve the deposition of silver nanoparticles onto the surface of poly(methyl methacrylate). The silver‐deposited PMMA chips (loaded with 0.01–1.0 weight percent silver) were successfully homogenized in melt by extrusion and then injection molded into small, disc‐shaped samples. These samples were analyzed with respect to their directional spectral optical properties in UV, VIS, and IR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Ag@SiO_2核壳纳米粒子的制备与表征

以NaBH4作还原剂,TEOS为前体,采用反相微乳液法制得粒径50～100nm的Ag@SiO2核壳纳米粒子,其中Ag核为面心立方结构,壳层为无定形SiO2。考察催化剂加入的先后和微乳液R值(R=n水/n表面活性剂)对Ag@SiO2核壳纳米粒子形成的影响。用TEM、UV-Vis、XRD对纳米粒子的形貌及性质进行表征。结果表明:催化剂若先于TEOS加入,易得到Ag@SiO2核壳纳米粒子,随着R值的增加,Ag核的粒径变大,纳米粒子逐渐由单核变成多核。催化剂若后于TEOS加入,则形成负载型Ag/SiO2复合物。Ag核被SiO2壳包覆后的等离子共振吸收峰发生了微弱红移。而当壳厚80nm时,由于SiO2的散射作用,吸收峰会发生蓝移。     

BIOTECHNOLOGY AND BIOENGINEERING Roles of biomolecules in the biosynthesis of silver nanoparticles: Case of gardenia jasminoides extract

Rapid development of biosynthesis of metal nanoparticles using plants has attracted extensive interests to further investigate this novel and eco-friendly method. In the biosynthesis process, the plant may act as reducing agent, capping agent or shape directing agent. However, identifying specific roles of various components in the plant is challenging. In this study, we use biosynthesis of silver nanoparticles with Gardenia jasminoides Ellis ex-tract to address this issue. The formation process of silver nanoparticles is investigated and the nanoparticles are characterized with the ultraviolet-visible spectroscopy, Fourier transform infrared spectra and scanning electron mi-croscopy. The results indicate that the Gardenia jasminoides Ellis extract can reduce silver ions to form silver nanoparticles, stabilize the nanoparticles, and affect the growth of silver nanocrystal to form silver nanowires. Only geniposide in the extract exhibits good shape-directing ability for silver nanowires. It is found that bovine albumin is a potential capping agent, whereas rutin, gallic acid and chlorogenic acid possess reducing and capping ability.     

表面活性剂对金属纳米材料的影响

金属纳米材料极易于形成尺寸可控的纳米晶,银纳米在一些明确定义的物理和化学属性方面的特殊应用强烈依赖于其尺寸、形状、表面形貌和化学组成.由于裸露的纳米颗粒表面积大,表面自由能高,颗粒极易发生团聚,稳定性差,因此需要采用不同的表面活性剂对纳米银的表面进行化学修饰,以提高其稳定性.     

One pot synthesis of nano Ag in calcium alginate beads and its catalytic application in p‐Nitrophenol reduction with kinetic parameter estimation and model fitting

In this work, one step process of synthesis of silver nanoparticles (Agnp) embedded in insitu formed calcium alginate (CA) beads is stated. CA, formed from the reaction between sodium alginate and calcium hydroxide, acts as reducing and stabilizing agent as well as support for nanoparticles. The reaction mechanism for the formation and stabilization of Agnp is proposed where the vicinal dihydroxy groups of alginate are assumed to act as the reducing agent for Ag⁺ to Ag°. Transmission electron microscopy (TEM), x‐ray diffraction (XRD), UV‐vis spectroscopy, field emission scanning electron microscopy (FESEM), and atomic absorption spectroscopy (AAS) were used to characterize the Agnp. The formation of spherical nanoparticles with average size range of 4‐5 nm was confirmed by TEM. Catalytic activity of this nano silver‐calcium alginate (Agnp‐CA) composite was evaluated in the reduction of p‐nitrophenol. Concentrations of sodium alginate, calcium hydroxide, and AgNO₃ are found to be the parameters that critically affect the synthesis of Agnp. The efficacy of the catalyst is expressed on the basis of suitable reaction parameters. Both pseudo‐homogeneous and heterogeneous kinetic models are proposed for the reaction to find the best model and the Eley‐Riedel model is found to fit well with the experimental data. The novelty of this work is that the tandem process of CA bead formation, Agnp formation, and Agnp entrapment in CA have been transformed into a single‐step process. Moreover, elaborations of each step of the ionic mechanisms of Agnp formation and p‐NP reduction with Agnp and the establishment of a heterogeneous kinetic model for the reaction are reported for the first time here.     

Influence of ultraviolet irradiation and heat treatment on the morphology of silver nanoparticles in photothermorefractive glasses

This paper reports on the experimental results of the investigation into the influence of ultraviolet irradiation and heat treatment on the absorption spectra of photothermorefractive glasses containing silver nanoparticles. It is demonstrated using numerical simulation methods that the spectral shift and the modification of the absorption bands associated with the plasmon resonances of silver nanoparticles are determined primarily by the variations observed in the shape of silver nanoparticles and by the formation of “core-shell” nanostructures.     

Synthesis,characterization, and antibacterial property of eco-friendly Ag/cellulose nanocomposite film

This paper reports silver/cellulose nanocomposite film and its antibacterial activity. A wet and porous cellulose film was served as support for silver nanoparticles synthesis by a hydrothermal method. Stable silver nanoparticles were synthesized using the cellulose film acting as both reducing and stabilizing agent without using any toxic chemicals. The characterization of the synthesized nanocomposite proves that silver nanoparticles are not only deposited over the cellulose surface but also nucleated and grew inside the cellulose film. Silver nanoparticle size and distribution were tuned to improve the antibacterial activity, and the synthesized nanocomposite film shows significant antibacterial action.     

Nanohybrid polymer prepared by successive polymerization of methacrylate monomer containing silver nanoparticles in situ prepared under microwave irradiation

The well-dispersed silver nanoparticles were prepared in reactive methacrylate monomers under microwave irradiation without polymerization. In contrast to conventional heating, the synthesis of Ag nanoparticles proceeded uniformly throughout the reaction vessel only under microwave irradiation, reaching the completion of the reaction simultaneously in the whole reaction solution. Successive polymerization of the monomer containing the resulting nanoparticles has successfully produced a monohybrid of the silver nanoparticles dispersed in polymer matrix.     

Preparation and catalytic properties of platinum dioxide nanoparticles: A comparison between conventional heating and microwave-assisted method

Using platinum chloride, sodium hydroxide, sodium acetate, and polyvinylpyrrolidone as starting materials, platinum dioxide nanoparticles with small particle diameter and narrow distribution were prepared by microwave irradiation and conventional heating, respectively. UV–vis spectrophotometer was used to trace the hydrolytic decomposition of platinum chloride and the formation of platinum dioxide nanoparticles. X-ray powder diffraction and transmission electron microscopy were employed to characterize the crystalline structure and the morphologies of the obtained nanoparticles. Gas chromatography was performed to investigate their catalytic properties for hydrogenation of cyclohexene. The results revealed that (i) the obtained nanoparticles have the same crystalline structure; (ii) the nanoparticles obtained by microwave irradiation were smaller and more narrowly distributed than those obtained by conventional heating; (iii) the activation time of the catalyst markedly influences the catalytic activity; (iv) the particles obtained by microwave irradiation showed higher catalytic activity than those obtained by conventional heating for hydrogenation of cyclohexene.     

Molasses-Silver Nanoparticles: Synthesis,Optimization, Characterization,and Antibiofilm Activity

Biofilms are matrix-enclosed communities of bacteria that are highly resistant to antibiotics. Adding nanomaterials with antibacterial activity to the implant surfaces may be a great solution against biofilm formation. Due to its potent and widespread antibacterial effect, silver nanoparticles were considered the most potent agent with different biological activities. In the present investigation, silver nanoparticles (AgNPs) were newly synthesized as antibiofilm agents using sugarcane process byproduct (molasses) and named Mo-capped AgNPs. The synthesized nanoparticles showed promising antimicrobial activity against S. aureus ATCC 6538 and C. albicans DAY185. Statistically designed optimization through response surface methodology was evaluated for maximum activity and better physical characteristics, namely the nanoparticles’ size and polydispersity index (PDI), and it was revealed that molasses concentration was the main effective factor. Minimal biofilm eradication concentration (MBEC) of Mo-capped AgNPs against S. aureus ATCC 6538 and C. albicans DAY185 was 16 and 32 µg/mL, respectively. Scanning electron microscope study of Mo-capped AgNP-treated biofilm revealed that AgNPs penetrated the preformed biofilm and eradicated the microbial cells. The optimally synthesized Mo-capped AgNPs were spherically shaped, and the average size diameter ranged between 29 and 88 nm with high proportions of Ag⁺ element (78.0%) recorded. Fourier-transform infrared spectroscopy (FTIR) analysis indicated the importance of molasses ingredients in capping and stabilizing the produced silver nanoparticles.     

Synergistic antimicrobial effects of polyaniline combined with silver nanoparticles

Silver/polyaniline nanocomposites (Ag NPs/PANI) containing PANI nanofiber and Ag nanoparticles were synthesized by one-step approach without using any extra reducing agent or surfactant and applied to new antimicrobial agents. Morphologies and crystallinity of the nanocomposites were characterized with SEM and XRD. The results showed that the average diameter of the PANI nanofibers is around 50–150 nm, and the average particle size of Ag NPs is around 100 nm. The crystallinity of PANI gets better with increasing silver nitride concentration. UV–vis absorption spectroscopy analysis indicated that the Ag NPs have some effect on the microstructure of PANI. The antimicrobial properties of Ag NPs/PANI against Gram-negative Escherichia coli, Gram-positive Staphylococcus aureus and fungous Yeast were evaluated using viable cell counts. The test results demonstrated that Ag NPs/PANI have enhanced antimicrobial efficacy compared to that of pure Ag NPs or pure PANI under the same test condition. The mechanism of the synergistic antimicrobial effect of Ag NPs with PANI was also proposed. In addition, thermal gravity analysis indicated that pure PANI and Ag NPs/PANI exhibit better thermal stability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and antibacterial effects of PVA‐PVP hydrogels containing silver nanoparticles

The poly(vinyl alcohol)/poly(N‐vinyl pyrrolidone) (PVA–PVP) hydrogels containing silver nanoparticles were prepared by repeated freezing–thawing treatment. The silver content in the solid composition was in the range of 0.1–1.0 wt %, the silver particle size was from 20 to 100 nm, and the weight ratio of PVA to PVP was 70 : 30. The influence of silver nanoparticles on the properties of PVA–PVP matrix was investigated by differential scanning calorimeter, infrared spectroscopy and UV–vis spectroscopy, using PVA–PVP films containing silver particles as a model. The morphology of freeze‐dried PVA–PVP hydrogel matrix and dispersion of the silver nanoparticles in the matrix was examined by scanning electron microscopy. It was found that a three‐dimensional structure was formed during the process of freezing–thawing treatment and no serious aggregation of the silver nanoparticles occurred. Water absorption properties, release of silver ions from the hydrogels and the antibacterial effects of the hydrogels against Escherichia coli and Staphylococcus aureus were examined too. It was proved that the nanosilver‐containing hydrogels had an excellent antibacterial ability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 125–133, 2007     

Fabrication and Characterization of Gelatin Stabilized Silver Nanoparticles under UV-Light

Silver nanoparticles (Ag-NPs) were successfully synthesized using the UV irradiation of aqueous solutions containing AgNO(3) and gelatin as a silver source and stabilizer, respectively. The UV irradiation times influence the particles' diameter of the Ag-NPs, as evidenced from surface plasmon resonance (SPR) bands and transmission electron microscopy (TEM) images. When the UV irradiation time was increased, the mean size of particles continuously decreased as a result of photoinduced Ag-NPs fragmentation. Based on X-ray diffraction (XRD), the UV-irradiated Ag-NPs were a face-centered cubic (fcc) single crystal without any impurity. This study reveals that the UV irradiation-mediated method is a green chemistry and promising route for the synthesis of stable Ag-NPs for several applications (e.g., medical and surgical devices). The important advantages of this method are that it is cheap, easy, and free of toxic materials.