Surfactant-free dispersion of silver nanoparticles into MWCNT-aqueous nanofluids prepared by one-step technique and their thermal characteristics

This paper reports a significant enhancement in the thermal conductivity of silver-nanoparticle-based aqueous nanofluids with the addition of negligible amounts of multi-walled carbon nanotubes (MWCNTs). The present work was conducted using purified MWCNTs/water nanofluids prepared by a wet grinding method. Silver nanoparticles were dispersed into the MWCNT/water nanofluids via a one-step method using pulse power evaporation, which was observed to improve the dispersibility and thermal conductivity of the nanofluids. A particle sizing system (PSS) and transmission electron microscopy (TEM) were used to confirm the size of silver nanoparticles in base fluids. The PSS measurement results reveal that the size of the silver nanoparticles was approximately 100 nm, which is in good agreement with the results obtained from TEM and SEM. The maximum absorbance (2.506 abs at a wavelength of 264 nm) and highest thermal conductivity enhancement (14.5% at 40 °C) were achieved by a fluid containing ‘0.05 wt% MWCNTs–3 wt% Ag’ composite.     

水杨酸壳聚糖/卵磷脂纳米粒的制备

采用溶剂注入法制备水杨酸壳聚糖/卵磷脂纳米粒。考察了粒子结构、形貌特征及表面电位等性能,并探讨了制备工艺对药物包封率的影响。确定最佳制备工艺为:卵磷脂质量浓度20 g/L、卵磷脂与壳聚糖及水杨酸与载体的质量比分别为3∶1和1∶6、水相pH=4。所制备的水杨酸壳聚糖/卵磷脂固体纳米粒子为球形粒子、表面电位+18.7 mV、包封率及载药量可分别达到55%和8.07%。     

γ-Ray assisted synthesis of silver nanoparticles in chitosan solution and the antibacterial properties

In the present study, chitosan had been utilized as a “green” stabilizing agent for the synthesis of spherical silver nanoparticles in the range of 5–30 nm depending on the percentage of chitosan used (0.1, 0.5, 1.0 and 2.0 wt%) under γ-irradiation. X-ray diffractometer identified the nanoparticles as pure silver having face-centered cubic phase. Ultraviolet–visible spectra exhibited the influence of γ-irradiation total absorbed dose and chitosan concentration on the yield of silver nanoparticles. The antibacterial properties of the silver nanoparticles were tested against Methicillin-resistant Staphylococcus aureus (MRSA) (gram-positive) and Aeromonas hydrophila (gram-negative) bacteria. This work provides a simple and “green” method for the synthesis of highly stable silver nanoparticles in aqueous solution with good antibacterial property.     

Synthesis of silver nanoparticles and antibacterial property of silk fabrics treated by silver nanoparticles

A silver nanoparticle solution was prepared in one step by mixing AgNO₃ and a multi-amino compound (RSD-NH₂) solution under ambient condition. RSD-NH₂ was in-house synthesized by methacrylate and polyethylene polyamine in methanol, which has abundant amino and imino groups. However, the characterization of silver nanoparticles indicated that these nanoparticles are easy to agglomerate in solution. Therefore, an in situ synthesis method of silver nanoparticles on the silk fabrics was developed. The examined results confirmed that the in situ synthesized silver nanoparticles were evenly distributed on the surface of fibers. The inhibition zone test and the antibacterial rate demonstrated that the finished fabrics have an excellent antibacterial property against Staphylococcus aureus and Escherichia coli. Moreover, the nanosilver-treated silk fabrics were laundered 0, 5, 10, 20, and 50 times and still retained the exceptional antibacterial property. When the treated fabrics were washed 50 times, the antibacterial rate is more than 97.43% for S. aureus and 99.86% for E. coli. The excellent laundering durability may be attributed to the tight binding between silver nanoparticles and silk fibers through the in situ synthesis. This method provides an economic method to enhance the antibacterial capability of silk fabrics with good resistance to washings.     

Functionalized silver doped hydroxyapatite scaffolds for controlled simultaneous silver ion and drug delivery

Bacterial infections are a major problem in bone tissue regeneration, thus it is essential to incorporate antibacterial properties within the bone scaffolds. Silver compounds are frequently used as antibacterial agents to prevent bacterial infections and numerous studies have shown that silver ions can be incorporated within the biocompatible and osteoconductive biomaterial hydroxyapatite (HAp) structure, but, so far, no study has thoroughly evaluated silver ion release rates in long term. Therefore, we have established a novel carrier system for local drug delivery based on functionalized silver doped hydroxyapatite with determined long term silver ion release rates. Silver ions from prepared scaffolds were released with a rate of 0.001±0.0005 wt%/h taking into account the incorporated silver amount. Moreover, lidocaine hydrochloride was incorporated in the prepared scaffolds, to provide local anesthetic effect. These scaffolds were functionalized with sodium alginate and chitosan and in vitro drug release rate in simulated body fluid was evaluated. The results suggested that the developed novel composite scaffolds possess the antibacterial activity up to one year as well as controlled anesthetic drug delivery up to two weeks.     

Investigation of polyvinyl alcohol nanocomposite hydrogels containing chitosan nanoparticles as wound dressing

Polymeric hydrogels, water-swollen 3?D networks of the polymers, have found wide ranges of applications in the medical fields, such as wound care and wound dressing, in order to prevent infections. Prevention from microorganisms transfer in to the wounds is one of the ideal wound dressing duties of polyvinyl alcohol (PVA) hydrogels. In this study, at the start, under optimal conditions, nanoparticles of chitosan using ionotropic gelation method were synthesized and in the next step in order to achieve particles with a minimum size, they were evaluated by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). Then after to obtain a wound dressing with preferable properties, nanocomposite hydrogels using a combination of PVA and 5, 10 and 15?wt% chitosan nanoparticles were prepared through freezing-thawing cycles. The necessary features of PVA nanocomposite hydrogels for wound dressing were investigated. The dispersion state of nanoparticles and structure of samples were evaluated by SEM microscopy. The nanoparticle size and the nanoparticle size distribution of chitosan was determined using the dynamic light scattering test at the nanometer scale. The physical behavior of hydrogels such as swelling and gel fraction was studied and their mechanical properties were investigated by compressive test. Finally the antimicrobial test and biocompatibility as cell viability were carried out. The results proved that the PVA nanocomposite hydrogels fulfill the requirements of a good wound dressing with desirable characteristics such as favorable swelling and acceptable strength, excellent barrier against microbial penetration.     

Hydrothermal synthesis of well-stable silver nanoparticles and their application for enzymeless hydrogen peroxide detection

We reported on a facile hydrothermal synthesis of well-stable silver nanopartiles (AgNPs) from an aqueous solution of AgNO₃ and poly[(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11), a kind of cationic polyelectrolyte, at 100 °C without the extra introduction of other reducing agents and protective agents. Transmission electron microscopy (TEM) observation reveals that the AgNPs thus formed mainly consist of small nanoparticles about 5 nm in diameter. It is found that such dispersion can form stable AgNPs-embedded films on bare electrode surfaces and these nanoparticles exhibit remarkable catalytic performance for hydrogen peroxide (H₂O₂) detection. The sensor has a fast amperometric response time of less than 2 s. The linear range is estimated to be from 1 × 10⁻⁴ M to 0.18 M (r = 0.998) and the detection limit is estimated to be 3.39 × 10⁻⁵ M at a signal-to-noise ratio of 3, respectively.     

One-step synthesis of silver nanoparticles embedded with polyethylene glycol as thin films

Silver nanoparticles (Ag NPs) embedded and stabilized with polyethylene glycol (PEG) were synthesized as colloids by heating and exposure to sunlight (direct and indirect) irradiation as green method. The deposition of Ag NP-PEGs onto Si-wafers was also made using the electrospray ionization deposition technique. The generating of Ag NP-PEGs as colloids was examined by UV–visible spectroscopy (UV–Vis) and transmission electron microscopy (TEM). The chemical composition of the resulted nanocomposites was evaluated by Fourier transform infrared (FTIR) and that of thin-film surfaces by X-ray photoelectron spectroscopy. Structure–property relationships of Ag-PEG nanocomposites prepared by heating were discussed in dependence on the time of heating. The UV–visible results confirmed the successful synthesis of spherical Ag NPs with absorption peaks at a wavelength of λ = 413 nm for the heating method and at λ = 418 as well as 449 nm for direct and indirect exposure to the sunlight. Ag-PEG nanocomposite thin films showed excellent antimicrobial activity. These results revealed that the Ag-PEG nanocomposites thin films can be used as potential materials in biomedical applications.     

Preparation of colloidal silver nanoparticles by chemical reduction method

Colloidal silver nanoparticles were obtained by chemical reduction of silver nitrate in water with sodium borohydride (NaBH₄) in the presence of sodium dodecyl sulfate (SDS) as a stabilizer. The obtained nanoparticles were characterized by their UV-vis absorption spectra and transmission electron micrograph (TEM) images. The UV-vis absorption spectra showed that NaBH₄ served not only as a reducing agent but also as a stabilizer, which protects the aggregation of silver nanoparticles. The TEM images showed that the particles were dispersed better with increasing the NaBH₄ concentration.     

Green synthesis of silk sericin-capped silver nanoparticles and their potent anti-bacterial activity

In this study, a ‘green chemistry’ approach was introduced to synthesize silk sericin (SS)-capped silver nanoparticles (AgNPs) under an alkaline condition (pH 11) using SS as a reducing and stabilizing agent instead of toxic chemicals. The SS-capped AgNPs were successfully synthesized at various concentrations of SS and AgNO₃, but the yields were different. A higher yield of SS-capped AgNPs was obtained when the concentrations of SS and AgNO₃ were increased. The SS-capped AgNPs showed a round shape and uniform size with diameter at around 48 to 117 nm. The Fourier transform infrared (FT-IR) spectroscopy result proved that the carboxylate groups obtained from alkaline degradation of SS would be a reducing agent for the generation of AgNPs while COO⁻ and NH₂ ⁺ groups stabilized the AgNPs and prevented their precipitation or aggregation. Furthermore, the SS-capped AgNPs showed potent anti-bacterial activity against various gram-positive bacteria (minimal inhibitory concentration (MIC) 0.008 mM) and gram-negative bacteria (MIC ranging from 0.001 to 0.004 mM). Therefore, the SS-capped AgNPs would be a safe candidate for anti-bacterial applications.     

Use of silver nanoparticles as an electron transfer facilitator in electrochemical ligand-binding of haemoglobin

Silver nanoparticles have an activity for high intensity electron transfer. They can facilitate the electron transfer from the redox centre of a protein, as a high volume molecule, to the electrode surface. In this study, silver nanoparticles were deposited on the surface of a graphite carbon electrode in the 1 V potential region. Deposition of silver nanoparticles, with a diameter between 70 and 150 nm, was observed on the graphite electrode by transmission electron microscopy (TEM). The results demonstrated that the fine redox waves of haemoglobin could be achieved after modification of the graphite electrode by silver nanoparticles. The cathodic and anodic peaks of haemoglobin were at −135 and +375 mV vs. Ag/AgCl, respectively. The effect of guanosine 3′,5′-triphosphate (GTP), guanosine diphosphate (GDP) and guanosine monophosphate (GMP) on the structure of haemoglobin was investigated. It was observed that GTP shifts the cathodic and anodic peaks positively, indicating the transfer of the haem group to the surface of protein as a reflex of easier oxidation and reduction, while GDP and GMP do not show this behaviour. GTP binds with haemoglobin, while GDP and GMP do not.     

Immobilization of silver nanoparticles on polyethylene terephthalate

Two different procedures of grafting with silver nanoparticles (AgNP) of polyethylene terephthalate (PET), activated by plasma treatment, are studied. In the first procedure, the PET foil was grafted with biphenyl-4,4′-dithiol and subsequently with silver nanoparticles. In the second one, the PET foil was grafted with silver nanoparticles previously coated with the same dithiol. X-ray photoelectron spectroscopy and electrokinetic analysis were used for characterization of the polymer surface at different modification steps. Silver nanoparticles were characterized by ultraviolet-visible spectroscopy and by transmission electron microscopy (TEM). The first procedure was found to be more effective. It was proved that the dithiol was chemically bonded to the surface of the plasma-activated PET and that it mediates subsequent grafting of the silver nanoparticles. AgNP previously coated by dithiol bonded to the PET surface much less.     

One-pot synthesis of gelatin-based,slow-release polymer microparticles containing silver nanoparticles and their application in anti-fouling paint

Gelatinous polymer matrix microparticles containing silver nanoparticles (AgNPs) were prepared by a novel method to obtain quasi non-swelling anti-fouling paint additives with slow-release characteristics. A w/o type dispersion were elaborated with the aqueous phase of gelatin, urea, silver-nitrate and formaldehyde dispersed in linseed oil. Gelatin was cross-linked by formaldehyde, together with urea for limiting the swelling of the product. Silver-nitrate was reduced with the assistance of gelatin and formaldehyde into homogenously dispersed AgNPs. The microparticles and embedded AgNPs were visualized by scanning and transmission electronmicroscopy. Encapsulated AgNPs with ∼18 nm crystallite size were identified by X-ray powder diffraction. Characterization of gelatin–urea–formaldehyde polymer matrices was carried out by attenuated total reflectance FTIR spectroscopy. Silver dissolution from microparticles and paints with AgNP-containing microparticles was measured by inductively coupled plasma spectrometer and resulted in highly sustained release, compared to unmodified gelatin microparticles and paints containing uncapsulated silver salts. A 7-month-long fouling experiment run in natural sweetwater media showed that solvent-based acrylic paint with AgNPs-containing gelatinous microparticles as additives offered resistance against biofouling at low Ag-release ratio.     

Multicolor Layer-by-Layer films using weak polyelectrolyte assisted synthesis of silver nanoparticles

In the present study, we show that silver nanoparticles (AgNPs) with different shape, aggregation state and color (violet, green, orange) have been successfully incorporated into polyelectrolyte multilayer thin films using the layer-by-layer (LbL) assembly. In order to obtain colored thin films based on AgNPs is necessary to maintain the aggregation state of the nanoparticles, a non-trivial aspect in which this work is focused on. The use of Poly(acrylic acid, sodium salt) (PAA) as a protective agent of the AgNPs is the key element to preserve the aggregation state and makes possible the presence of similar aggregates (shape and size) within the LbLcolored films. This approach based on electrostatic interactions of the polymeric chains and the immobilization of AgNPs with different shape and size into the thin films opens up a new interesting perspective to fabricate multicolornanocomposites based on AgNPs.     

Improved photovoltaic performance of silicon nanowire/organic hybrid solar cells by incorporating silver nanoparticles

Silicon nanowire (SiNW) arrays show an excellent light-trapping characteristic and high mobility for carriers. Surface plasmon resonance of silver nanoparticles (AgNPs) can be used to increase light scattering and absorption in solar cells. We fabricated a new kind of SiNW/organic hybrid solar cell by introducing AgNPs. Reflection spectra confirm the improved light scattering of AgNP-decorated SiNW arrays. A double-junction tandem structure was designed to manufacture our hybrid cells. Both short-circuit current and external quantum efficiency measurements show an enhancement in optical absorption of organic layer, especially at lower wavelengths.     

Synthesis and characterization of bimodal silver nanoparticles by using semi-batch method

Synthesis of silver nanoparticles stabilized by myristic acids is reported. Bimodal shape of silver nanoparticles was formed by feed rate control using semi-batch method. The synthesized nanoparticles were re-dispersible in solution such as α-terpineol. The α-terpineol solution of these nanoparticles exhibited a surface plasmon resonance in the range around 430 nm. This broad absorption band depicted that the silver nanoparticles have an enhanced stability with increasing chain length of the fatty acid. The size of nanoparticles was influenced by the experimental conditions such as temperature, feed rate and reaction time. The nanoparticles were characterized by TEM, UV and XRD analyses.     

Properties of GaN-based light-emitting diodes on patterned sapphire substrate coated with silver nanoparticles prepared by mask-free chemical etching

This study reports on the use of a template that is made of silver nanoparticles (ANPs) that are dispersed on a patterned sapphire substrate (PSS) to improve the light output power of GaN-based light-emitting diodes (LEDs). The dipping of a sapphire substrate in hot H₂SO₄ solution generates white reaction products that are identified as a mixture of polycrystalline aluminum sulfates. These white reaction products can act as a natural etching mask in the preparation of an ANP-coated PSS (PSS-ANP) template. The optimal annealing temperature and time, surface morphology, and optical characteristics of the PSS-ANP template were investigated. The light output power of an LED that is bonded to the PSS-ANP template is approximately double than that of an LED that is not.     

Characterization of silver and silver/nickel composite particles prepared by spray pyrolysis

Pure silver and silver/nickel composite particles were prepared by spray pyrolysis of aqueous solutions of AgNO₃, and mixed salts of AgNO₃ and Ni(NO₃)₂·6H₂O, respectively. In the case of pure silver, reduction to metallic silver and subsequent sintering to highly spherical and dense particles took place immediately and almost simultaneously once favorable conditions for the former were imposed, irrespective of the nature of the carrier gas. For the composite particles, the high rates of reduction and sintering of the silver were still maintained, while crystallization of the silver, and the reduction and sintering of the nickel were considerably retarded, compared to the spray pyrolysis of each pure salt. Once the counterpart salt was added, the size of the composite particles increased compared to that of each pure metallic particles, but it was little affected by the furnace set temperature, the residence time and the molar ratio of the two precursor salts. Within single particles, an increase in either the temperature or the residence time caused segregation—silver in the shells and nickel in the cores—and improved the particles' surface smoothness and sphericity accordingly.     

Comparison of adsorptive features between silver ion and silver nanoparticles on nanoporous materials

The removal of Ag⁺ or AgNPs released from nano-products or effluent of WTP is important to reduce the potential risk of AgNPs. In this work, we prepared bimodal nanoporous silica (BNS) to compare the removal efficiency of Ag⁺ and AgNP with unimodal nanoporous silica (NS). To determine the adsorption capacity of Ag⁺ and AgNPs on NS and BNS, isotherm and kinetics studies was carried out at different concentrations. The results showed BNS with a bimodal nanoporous structure and a large external surface showed a higher uptake capacity and faster adsorption rate.