Silver nanoparticles and silver ions stabilized in NaCl nanocrystals

This study presents a two-step synthesis of nanoparticles and the stabilization process of Ag ions in the matrix of NaCl nanocrystals. Ag⁺ ions are incorporated to NaCl with a new and attractive method that can be easily used for the different types of alkaline halides. The nanoparticles with predominant size found between 10 and 15 nm were stabilized on the surface and/or interior of NaCl nanocrystals using, in the first stages, the ionic-exchange property of zeolite A4. The optical properties of the materials were characterized through optical absorption, leading to well defined absorption bands located in the wave length values between 217–275 nm and 350–770 nm approximately, for Ag⁺ and AgNp, respectively. The antibacterial property of Ag ions and nanoparticles stabilized in NaCl was analyzed against gram-negative Escherichia Coli and Klebsiella bacteria. In order to quantify the antibacterial effect of Ag ions and nanoparticles the inhibition ratio was used as a parameter on the bacteria colonies grown in culture medium by conventional methods. Ag⁺ ions that were stabilized in NaCl nanocrystals show a mayor inhibition ratio in contact with Klebsiella bacteria, conversely Ag nanoparticles showed better results in contact with E. coli.     

Photo-induced growth of silver nanoparticles using UV sensitivity of cellulose fibers

A simple method has been demonstrated to grow silver nanoparticles on the surface of cellulose fibers. The preparation is based on photo-activation of surface by ultraviolet (UV) photons, followed by chemical reduction of silver nitrate. It is found that the concentration of silver nitrate in the solution is not a determining factor, while UV intensity affects the rate of initial growth and determines the final concentration of the loaded silver. We explain the phenomena based on a model including the number of reducing sites on the surface of cellulose fibers activated by UV photons, and a release mechanism that causes a slow rate of dissolution of silver back into the solution.     

Sonochemical deposition of magnetite on silver nanocrystals

Sonochemical irradiation of iron (II) acetate aqueous solution in presence of silver nanopowder resulted in deposition of magnetite nanoparticles on silver nanocrystals, and imparted them with magnetic properties. The Ag-Fe(3)O(4) nanocomposite is well attracted to a permanent magnet, and demonstrates superparamagnetic behavior typical of nanomaterials in a magnetic field. The characterization of the product by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR TEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS) reveal the presence of two phases of the silver and the magnetite, but no chemical interaction between them has been found. The strong anchoring of magnetite to the nanosilver surface was explained as a result of local melting of silver when the magnetite nucleus is thrown at the silver surface by high speed sonochemical microjets.     

Synthesis of silver nanoparticles and antimony oxide nanocrystals by pulsed laser ablation in liquid media

Pulsed laser ablation in liquid media (PLALM) is a prominent technique for the controlled fabrication of nanomaterials via rapid reactive quenching of ablated species at the interface between the plasma and liquid. Results on nanoparticles and nanocrystals formed by PLALM of silver (Ag) and antimony (Sb) solid targets in different liquid environments (Sodium Dodecyl Sulfate, distilled water) are presented. These experiments were done by irradiating solid targets of Ag and Sb with a nanosecond pulsed Nd:YAG laser output of wavelength 532 nm. Nanoparticles of silver and nanocrystals of antimony oxide (Sb₂O₃) obtained were characterized using UV-Vis spectrometry, Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), X-ray Energy Dispersion Analysis (EDAX) and X-ray diffractometry (XRD). The morphology of nanomaterials formed is studied as a function of surfactant environment. The silver nanoparticles obtained were spherical of size in the order of 10–35 nm in solution of SDS having different concentrations. In case of the Sb target, ablation was performed in two different molarities of SDS solution and distilled water. Nanocrystals of Sb₂O₃ in powder form having cubic and orthorhombic phases were formed in SDS solution and as fibers of nanocrystals of cubic Sb₂O₃ in distilled water.     

Immobilization of silver nanoparticles on silica microspheres

The silver nanoparticles (Ag NPs) have been immobilized onto silica microspheres through the adsorption and subsequent reduction of Ag⁺ ions on the surfaces of the silica microspheres. The neat silica microspheres that acted as the core materials were prepared through sol–gel processing; their surfaces were then functionalized using 3-mercaptopropyltrimethoxysilane (MPTMS). The major aims of this study were to immobilize differently sized Ag particles onto the silica microspheres and to understand the mechanism of formation of the Ag nano-coatings through the self-assembly/adsorption behavior of Ag NPs/Ag⁺ ions on the silica spheres. The obtained Ag NP/silica microsphere conglomerates were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). Their electromagnetic wave shielding effectiveness were also tested and studied. The average particle size of the obtained Ag NPs on the silica microsphere was found that could be controllable (from 2.9 to 51.5 nm) by adjusting the ratio of MPTMS/TEOS and the amount of AgNO₃.     

Photoluminescence from colloidal silver nanoparticles

Highly luminescent singles of Ag sol with gradual changes were detected when adjusting the granularity and concentration of particles. It can be deduced that these Ag sols, composed of a large amount of silver nanoparticles and clusters, may have their surface energy bands alterable, which might be caused by the interactions between particles. A model that describes the shift of energy band is proposed, and it can be understood as the hybridization of elementary plasmons when interactions occur between particles. Besides, both hybridization and absorption-rescattering mechanisms were proposed to explain the changeable phenomena of photoluminescence with different concentrations.     

Evidence-based guidelines for the ultrasonic dispersion of cellulose nanocrystals

Nanoparticles possess unique, size-driven properties. However, they can be challenging to use as they easily agglomerate - their high surface area-to-volume ratio induces strong interparticle forces, generating agglomerates that are difficult to break. This issue prevails in organic particles as well, such as cellulose nanocrystals (CNCs); when in their dried form, strong hydrogen bonding enhances agglomeration. Ultrasonication is widely applied to prepare CNC suspensions, but the methodology employed is non-standardized and typically under-reported, and process efficiency is unknown. This limits the ability to adapt dispersion protocols at industrial scales. Herein, numerical simulations are used in conjunction with validation experiments to define and optimize key parameters for ultrasonic dispersion of CNCs, allowing an operating window to be inferred.     

Adhesion of silver nanoparticles on the montmorillonite surface

Adhesion of silver nanoparticles on the montmorillonite substrate was investigated using molecular modeling (force field calculations) and experiment (infrared spectroscopy, high-resolution transmission electron microscopy). Modeling revealed the preferred orientation of silver nanoparticles on the silicate substrate and showed the strong dependence of total energy and stability of nanocomposite structure on two factors: (1) the mutual crystallographic orientation of nanoparticle and substrate structure and (2) the size and thickness of the nanoparticle. The size of silver single crystalline domains calculated by modeling was in good agreement with the experimental observations. Molecular modeling in confrontation with high-resolution transmission electron microscopy analysis showed the prediction possibility as to the nanoparticles structure and stability of nanocomposite.     

Nanoplates controlled synthesis and catalytic activities of silver nanocrystals

The silver nanostructures, from nanoparticles (NPs) to nanorod and nanoplate, can be synthesized quantitatively with DMF (N,N^′$N,N^{\prime }$-dimethyl formamide) and PVA (Polyvinyl alcohol). Due to the anisotropic shape feature, the absorption spectra of the nanoplates prove to be quite different from that of spherical NPs. It may be due to the specific interaction between OH groups and Ag+ ions, which affect selective growth of various planes of silver nanocrystals. In addition, the catalytic activity of the obtained different shaped silver nanocrystals for hydrogen production has also been investigated. The silver nanoplates exhibit higher catalytic activities than silver NPs.     

Formation of silver nanoparticles on polypropylene microfibrous carriers

Methods of physical and numerical experiments are used to investigate formation of quantum dissipative silver nanostructures on polypropylene microfibrous condensed-state carriers under two-stage activation by UV- and microwave radiation. For these two nanoprocessing stages, two different mechanisms of quantum activated silver nanoparticle relaxation are suggested, including dissipation of their energy into the polymeric matrix through the exciton femtosecond and phonon picosecond channels. A comparison of the results of mathematical modeling and physical experiments testifies to the adequacy of these models to the physical processes of self-assembly and self-organization of polymeric biomimetic fibrous material modified by silver nanoparticles.     

Synthesis of copper nanoparticles catalyzed by pre-formed silver nanoparticles

Synthesis of well dispersed copper nanoparticles was achieved by reduction of copper nitrate in aqueous solution using hydrazine monohydrate as a reducer in the presence of preformed silver nanoparticles as catalysts. It has been demonstrated that addition of silver nanoparticles to the reaction mixture leads to formation of aqueous dispersion of copper nanoparticles and also results in a drastic reduction in reaction time compared to procedures reported in the literature. The absorption spectrum of the dispersions, HR-TEM and STEM images and XRD pattern indicate the formation of copper nanoparticles with particle size in the range of 5–50 nm.     

In situ bioinspired synthesis of silver chloride nanocrystals on silk fibroin fibers

Silver chloride (AgCl) nanocrystals were formed and grown on silk fibroin fibers (SFFs) by a room-temperature process. Practically, the degummed SFFs were immersed into silver nitrate solution and sodium chloride solution in turn. The amino acids on the SFF surface were negatively charged in alkaline impregnant, providing locations to immobilize silver ions and form silver chloride seeds. AgCl nanocrystals can further grow into cubic AgCl nanocrystals with an edge of about 100 nm. The morphologies of the AgCl nanocrystals were mostly influenced by the concentration of sodium chloride solution and the special configurations of the SFFs. The target AgCl/SFF nanocomposites constructed by AgCl nanocrystals and substrate SFFs could be used as photocatalysts in water splitting and antibacterial agents. This work provides an important example in the introduction of natural biofibers to the synthesis of functional hybrid nanocomposites by a green and mild technique.     

Corrosion processes of triangular silver nanoparticles compared to bulk silver

Excessive corrosion of silver nanoparticles is a significant impediment to their use in a variety of potential applications in the biosensing, plasmonic and antimicrobial fields. Here we examine the environmental degradation of triangular silver nanoparticles (AgNP) in laboratory air. In the early stages of corrosion, transmission electron microscopy shows that dissolution of the single-crystal, triangular, AgNP (side lengths 50–120 nm) is observed with the accompanying formation of smaller, polycrystalline Ag particles nearby. The new particles are then observed to corrode to Ag₂S and after 21 days nearly full corrosion has occurred, but some with minor Ag inclusions remaining. In contrast, a bulk Ag sheet, studied in cross section, showed an adherent corrosion layer of only around 20–50 nm in thickness after over a decade of being exposed to ambient air. The results have implications for antibacterial properties and ecotoxicology of AgNP during corrosion as the dissolution and reformation of Ag particles during corrosion will likely be accompanied by the release of Ag⁺ ions.     

Cytotoxicity and physico-chemical evaluation of acetylated and pegylated cellulose nanocrystals

The high hydrophilicity of cellulose nanocrystals (CNC) may result in poor dispersion in some matrices and solvents. So in this work, two different methodologies were used to reduce the hydrophilicity of CNC. In the first methodology, CNC were acetylated (CNC-Ac) in a mixture of acetic and hydrochloric acid, and in the second methodology, polyethylene glycol (PEG) was adsorbed onto CNC surface (CNC-PEG) under stirring in aqueous solution. CNC obtained by both methods were characterized by transmission electron microscopy (TEM), infrared spectroscopy (FTIR), X-ray diffraction (XRD), dynamic light scattering (DLS), zeta potential, and thermogravimetric analysis (TGA). Images of TEM showed that the intrinsic morphology of cellulose was preserved after both treatments. FTIR confirmed acetylation reaction by the presence of a new band at 1732 cm^?1 (acetate groups) and the consumption of OH groups. XRD showed a reduction in the crystallinity index for both applied methodologies. DLS showed reduced stability in water for CNC-Ac and CNC-PEG. Values of zeta potential changed after acetylation, from ??45 mV (CNC) to ??1 mV (CNC-Ac), and after adsorption of PEG, to ??26.7 mV (CNC-PEG). TGA showed a reduction in the thermal stability after both treatments and a change in the main degradation behavior for CNC-PEG. MTT assays showed that both proposed functionalizations induce cell proliferation, being even more evident for acetylation because, in addition to viability increase with time, it increased with the sample concentration.     

Thermoplastic starch nanocomposites reinforced with cellulose nanocrystals: effect of plasticizer on properties

The objective of this study was to characterize cellulose nanocrystals /TPS-based nanocomposites. Nanocrystalline cellulose was isolated from cotton linters using sonochemical method and characterized through WXRD, TEM, and FTIR. These nanocrystals were then dispersed in glycerol and sorbitol plasticized starch using a Fluko high shear homogenizer in varying proportions and films were cast. The films were characterized using WXRD, SEM, and mechanical properties. TEM images of nanocrystals revealed a diameter of 20–30 nm and length 200–300 nm. XRD results for nanocomposite films for both the plasticizers showed 2θ peaks at 14.8°, 16.7,° and 22.5°. Elastic modulus increased with addition of cellulose nanocrystals and tan δ shifted toward higher temperature for both the plasticizers. Mechanical properties improved more than 200% for both glycerol and sorbitol plasticized nanocomposites.     

稀土镧对薄膜中银纳米粒子的细化作用

通过更换基底材料,证实了稀土镧对AgBaO薄膜中银纳米粒子的细化作用.用LewisCampbell的薄膜理论分析表明,稀土镧对银纳米粒子的细化作用机理是,基底吸附稀土镧增强了基底对银原子的等效吸附能和基底表面徙动激活能,使镧和银结合形成的复合小银粒子在基底表面的徙动扩散运动受到削弱,进而减少了相互团聚所致.基底表面徙动激活能增量在0.04—0.07eV之间,相应的基底对银原子的等效吸附能增量在0.08—0.42eV之间 关键词： 细化 稀土 纳米粒子 粒度     

Nanocomposites of magnetic cobalt nanoparticles and cellulose

Polymeric matrices with stabilized metallic nanoparticles constitute an important class of nanostructured materials, because polymer technology allows fabrication of components with various electronic, magnetic and mechanical properties. The porous cellulose matrix has been shown to be a useful support material for platinum, palladium, silver, copper and nickel nanoparticles. In the present study, nanosized cobalt particles with enhanced magnetic properties were made by chemical reduction within a microcrystalline cellulose (MCC) matrix. Two different chemical reducers, NaBH₄ and NaH₂PO₂, were used, and the so-formed nanoparticles were characterized with X-ray absorption spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These experimental techniques were used to gain insight into the effect of different synthesis routes on structural properties of the nanoparticles. Magnetic properties of the nanoparticles were studied using a vibrating sample magnetometer. Particles made via the NaBH₄ reduction were amorphous Co-B or Co oxide composites with diminished ferromagnetic behaviour and particles made via the NaH₂PO₂ reduction were well-ordered ferromagnetic hcp cobalt nanocrystals.     

Investigation of size distribution of silver nanoparticles

In this work, we present a physical methodology of preparing silver nanoparticles suspended in the deionized water. For this purpose, we apply the DC spark method and present the size distribution (by Zetasizer) and optical properties (by UV/VIS) of the nanoparticles in two different voltages. The obtained results using the DC spark method show that the fabrication of silver nanoparticles in deionized water without any surfactants and stabilizers is relatively cheap and pollution free. Using the method, we could prepare the silver nanoparticles smaller than 5 nm.     

Optical extinction spectroscopy of single silver nanoparticles

The extinction spectrum of single silver nanoparticles with size ranging from 20 to 80 nm is investigated with the spatial modulation spectroscopy technique using either a tunable laser or a white lamp as the broadband source. Results are in good agreement with the prediction of the Mie theory, permitting to extract the nanoparticle size from the measured absolute value of the optical extinction cross-section. In contrast, the deduced refractive index of the nanoparticle environment and the reduction of the electron mean free path show a large dependence on the precise value of the bulk silver dielectric function.