Aggregation Of Ag Nanoparticles Research Articles

Formation of lipid corona on Ag nanoparticles and its impact on Ag+ ion dissolution and aggregation of Ag nanoparticles against external stimuli

The application of lipid coated nanoparticles has been expanding in nanoscience over the past few years. Lipid corona formation is one of the novel ways for the lipid conjugation around the nanoparticles. Although several properties of nanoparticles and lipids are well reported in literature in last few years, the dependency of lipid corona formation on metallic core and surface ligands is poorly understood. The aggregation, surface oxidation and metal ions dissolution of nanoparticles limit their usefulness in various applications. Besides all the reported methods to overcome all of these limitations, lipid corona could be an alternative, feasible, and more efficient method. In the current manuscript, we investigate the interaction of aromatic amino acids (tyrosine and tryptophan) functionalized silver nanoparticles (Ag-Tyr and Ag-Trp NPs) with different surface charged and phase states lipid vesicles and compare them with the reported amino acid functionalized gold nanoparticles (Au-AA NPs). The effectiveness of different zwitterionic and positively charged lipid coated Ag-Tyr and Ag-Trp NPs to prevent the aggregation and Ag+ ion dissolution of Ag NPs against different external stimuli (acidic pH, high NaCl concentration, and freeze-thaw cycles) are investigated. Our results reveal that surface ligands around the NPs play crucial role for lipid corona formation irrespective of the metallic core of NPs. Although all the lipid coated Ag NPs exhibit greater stability against external stimuli than native Ag NPs, zwitterionic lipid coated Ag NPs is better choice than positively charged lipid coated Ag NPs. This study on lipid corona and its stability will help the nanoresearcher to choose the suitable lipid for lipid corona formation.

Controllable growth of silver nanoparticles on titanium dioxide/nitrogen-doped carbon nanofiber/molybdenum disulfide: Toward enhanced photocatalytic-activating peroxymonosulfate performance and “memory catalysis”

The combination of photocatalysis and activating peroxymonosulfate (PMS) can generate more active species and degrade pollutants more efficiently. The introduction of “memory catalysis” in the photocatalytic-activating PMS system can further improve the catalytic degradation ability in the dark environment, because the stored electrons (e−1) during photocatalytic process can release in darkness to continue the degradation. In this paper, molybdenum disulfide (MoS2) nanosheets on titanium dioxide/nitrogen-doped carbon nanofibers (T/NC/MoS2 NFs) were prepared by electrospinning and hydrothermal treatment, and then silver (Ag) nanoparticles were deposited by photodeposition (PD) or dark deposition (DD) to form T/NC/MoS2@Ag NFs-PD and T/NC/MoS2@Ag NFs-DD, respectively. The influences of the two samples on the degradation of tetracycline (TC) and “memory catalysis” in photocatalytic-activating PMS systems were explored. The results show that T/NC/MoS2@Ag NFs-DD can remove TC more efficiently and reduce energy consumption. This is because the DD technology can effectively inhibit the growth and aggregation of Ag nanoparticles, thereby improving the e−1 storage capacity and the separation of photogenerated e−1 and holes (h+). Under outdoor solar irradiation, T/NC/MoS2@Ag NFs-DD showed excellent stability and high efficiency in catalytic degradation of a variety of organic pollutants. This study provides a new strategy to realize the efficient and energy-saving degradation of organic pollutants.

SYNTHESIS, CHARACTERIZATION OF CeO2@Ag HOLLOW SPHERES AND EVALUATION OF THEIR CATALYST ACTIVITY FOR THE REDUCTION OF 4-NP

A CeO2@Ag hollow spherical composite catalyst was synthesized with the template method. Firstly, a SiO2@CeO2 core-shell structure was synthesized using SiO2 spheres as the template, and then the SiO2 core was removed by etching to obtain hollow CeO2 spheres. The CeO2 hollow microspheres have a large specific surface area, which can effectively suppress the aggregation of Ag nanoparticles, leading to CeO2@Ag with a regular morphology and well dispersed Ag nanoparticles. There is a strong synergistic effect between CeO2 and Ag, which is beneficial to improving the catalytic performance. As a result, the CeO2@Ag hollow spherical composite catalyst can reduce 4-nitrophenol efficiently.

Flow-through catalytic nanofiber membrane assembly of hierarchically porous structure with Ag nanoparticles immobilized for enhanced catalysis

A hierarchically porous flow-through catalytic nanofiber membrane immobilized with Ag nanoparticles (Ag/HP-FCNM) has been developed by combining electrospinning and sacrificial template. The characterization results of Ag/HP-FCNM imply that mesopores with an average size of 50 nm are successfully fabricated on Polyacrylonitrile (PAN) nanofibers, and 6 nm of Ag nanoparticles are immobilized in the mesopores, effectively preventing the aggregation of Ag nanoparticles and increasing the surface area. The HP-FCNM with Ag nanoparticles content of 35.02% has a permeance of 18680 L·m−2·h−1·bar−1 can enhance the contact between catalyst and reactant. During the process of p-Nitrophenol (p-NP) reduction by Ag/HP-FCNM under the flow-through mode, the apparent reaction rate constant (Kapp) of 272.45 min−1, treatment capability of 200.34 mmol·m−2·h−1 and specific treatment capability of 14.27 mmol·g−1·h−1 can be achieved. Furthermore, good applicability of the Ag/HP-FCNM is also demonstrated with excellent conversions (both above 99%) when treating o-Nitrophenol (o-NP) and Rhodamine B (RhB) at a concentration of 0.25 mM and a membrane flux of 192 L·m−2·h−1. Good stability can be still performed after 160 min of continuous use, which implies the prospect of the Ag/HP-FCNM.

Time-resolved in situ nanoparticle size evolution during magnetron sputtering onto liquids.

Despite extensive research since 1996, there are still open questions regarding the primary location of the nucleation process, the growth mechanism of the nanoparticles (NPs), and the influence of the liquid properties on the ultimate size of the NPs for the magnetron sputtering of metals onto liquids. Hence, for the first time to the authors' knowledge, the particle size evolution is in situ and in real-time examined during and after the sputtering of the silver atoms onto silicone oil, i.e., Sputtering onto Liquids (SoL) process. The particle size distribution (PSD) is measured via the Light Extinction Spectroscopy (LES) technique, and the deposition rate and stirring speed effects on the PSDs are analyzed. Based on De Brouckere mean diameters, the size evolution of silver nanoparticles (Ag NPs) over time is monitored. Ag NPs bigger than 20 nm are detected, and the PSDs are shown to be poly-disperse, which is also supported by the ex situ TEM measurements and in situ time-resolved absorption spectra. Moreover, it is shown that aggregation and growth of Ag NPs occur both at the plasma-liquid interface and inside the silicone oil during and after the magnetron sputtering. Despite the same amount of deposited silver, the growth kinetics of Ag NPs in silicone oil vary at different deposition rates. In particular, at higher deposition rates, larger NPs are formed. Stirring is seen to help disaggregate the particle lumps. Faster stirring does not substantially influence the final size but promotes the formation of smaller NPs (<20 nm). Also, low colloidal stability of Ag NPs in silicone oil is observed.

A novel inorganic redox buffer of r-GO/Ag@AgCl/TMMCl utilized as an effective ion-to-electron transducer for a solid contact calcium ion-selective electrode

The Ag@AgCl/1-tetradecyl-3-methylimidazolium chloride (TMMCl) reported as an inorganic redox buffer for solid contact ion-selective electrodes (SC-ISEs) suffers from minimized specific area for an aggregation of Ag nanoparticles and decreased electron transfer for a presence of AgCl coating. Herein, a novel optimized inorganic redox buffer of r-GO/Ag@AgCl/TMMCl with improved capacitance and electron transfer behaving well as an effective ion-to-electron transducer for a SC-Ca2+-ISE has been highlighted. With reduced graphene oxide (r-GO) introduced as a substrate, the produced Ag nanoparticles as well as the subsequently synthesized core-shell Ag@AgCl nanomaterials display high dispersity with diameters decreased to 10–40 nm. Cyclic voltammetry with better redox reversibility and higher areas for the r-GO/Ag@AgCl/TMMCl verifies its improved redox capacitance and acceleration in electron transfer. Taking advantage of the r-GO/Ag@AgCl/TMMCl, the fabricated SC-Ca2+-ISE exhibits a near Nernst slope about 28.5 mV/dacade between potentials to Ca2+ concentrations ranging from 10−6 to 10−3M. Additionally, a diminished Rbc and Rct as well as an increased capacitance are also exemplified by the EIS and chronopotentiometric techniques, which would ensure a fast and stable potentiometric response. Moreover, the fabricated SC-Ca2+-ISE displays a good selectivity and water layer resistance. Thanks to the increased redox capacitance of the r-GO/Ag@AgCl/TMMCl, the fabricated SC-Ca2+-ISE demonstrates stable potentiometric response and good E0 reproducibility.

Metallic ion-based graphene oxide functionalized silk fibroin-based dressing promotes wound healing via improved bactericidal outcomes and faster re-epithelization

An ideal wound dressing material should enhance the wound healing process and must avoid bacterial contamination. In this study, the synergistic effect of graphene oxide (GO), silver (Ag) and magnesium (Mg) based silk electrospun nanofibrous film on wound healing was evaluated. It reports the influence of essential elements Mg and Ag during the skin regeneration process. Silver and magnesium nanoparticles were doped in graphene oxide. The goal of the present study was to fabricate an electrospun nanofibrous patch with nanoscale fillers to improve the wound recuperation manner and decrease the recuperation time to forestall microorganism infections and improve cellular behavior. Doping was done to insert Ag+ and Mg2+ ions in the crystal lattice of GO to overcome the disadvantage of aggregation of Ag and Mg nanoparticles. In this study, Mg2+ and Ag+ ions doped GO functionalized silk fibroin/PVA dressing material was prepared using the electrospinning technique. It was found that, Mg-GO@NSF/PVA and Ag/Mg-GO@NSF/PVA film possess good cytocompatibility, low hemolytic effect and effective antibacterial and anti-biofilm activities. Furthermore, their improved hydrophilicity and mid-range water vapor transmission rate allow them to be a suitable wound dressing material. Tensile strength of the composite silk film were enhanced relatively to silk/PVA film. The effect of prepared film on wound repair were investigated in excision rat model. It indicates, the wound covered with Ag/Mg-GO@NSF/PVA film showed the highest wound contraction rate and re-epithelization, allowing faster repair of wound sites. In conclusion, the development of metallic ions doped GO based silk fibroin/PVA is a promising approach towards development of antibiotic free wound dressing material. It prevents anti-biofilm formation and also provides adequate therapeutic effects for accelerating wound healing.

Probing the Interaction of Heavy and Transition Metal Ions with Silver Nanoparticles Decorated on Graphene Quantum Dots by Spectroscopic and Microscopic Methods.

We report a comprehensive study of the interaction of transition and heavy metal ions with graphene quantum dots-capped silver nanoparticles (AgGQDs) using different spectroscopic and microscopic techniques. High-resolution transmission electron microscopy studies show that the interaction of metal ions with AgGQDs leads to the formation of metal oxides, the formation of zerovalent metals, and the aggregation of Ag nanoparticles (AgNPs). The metal ions may interact with AgGQDs through selective coordination with -OH and -COOH functionalities, adsorption on the graphene moiety, and directly to AgNPs. For instance, the interaction of Cd2+ with AgGQDs altered the spherical shape of AgNPs into a chain-like structure. On the contrary, the formation of PbO is observed after the addition of Pb2+ to AgGQDs. Interestingly, the interaction of AgGQDs with Hg2+ results in the complete dissolution of Ag0 from the surface of GQDs and subsequent deposition of Hg0 on the graphene moiety of GQDs. Unlike transition metal ions, Cd2+, Pb2+, and Hg2+ can adsorb strongly on the graphene surface at the bridge, hollow, and top sites, respectively. This special interaction of heavy metal ions with the graphene surface would decide the mechanistic pathway in which the reaction proceeds. The transition metal ions Cu2+, Zn2+, Co3+, Mn2+, Ni2+, and Fe3+ induced the aggregation of AgNPs.

Effects of rice root exudates on aggregation, dissolution and bioaccumulation of differently-charged Ag nanoparticles.

The biological toxicity and eco-environmental risk of metal nanoparticles (MNPs) is closely related to their stability. The stability of MNPs not only depends on their own properties but also on the effects of biological and environmental factors. To better understand the interaction between biological factors and MNPs in aquatic environments, the effects of total rice root exudates (T-RRE) on the aggregation, dissolution and bioaccumulation of Ag nanoparticles (AgNPs) with different surface charges were investigated in detail. Results indicated that T-RRE can induce the aggregation and sedimentation, and hinder the dissolution of polyethyleneimine-coated AgNPs (AgNPs@PEI) with positive surface charges as well as reducing the bioaccumulation of Ag in rice roots. T-RRE had no obvious effect on the dispersion stability of AgNPs@Cit (negatively charged citrate-coated AgNPs) and AgNPs@PVP (near electrically neutral polyvinylpyrrolidone-coated AgNPs), although T-RRE could induce the dissolution of AgNPs@Cit and AgNPs@PVP. In the molecular fractions of T-RRE, high-molecular-weight root exudates (H-RRE) play a key role in inducing the aggregation of AgNPs@PEI and hindering the bioaccumulation of Ag in rice roots. Compared with H-RRE, low-molecular-weight root exudates (L-RRE) can promote the dissolution of AgNPs@Cit and AgNPs@PVP, but it can obviously promote silver accumulation in rice roots. The difference in charge intensity between L-RRE and T-RRE plays a key role in inducing the aggregation and dissolution of AgNPs with different charges. These findings provide a foundation for investigation of the interactions between rice root exudates and nanoparticles with different surface charges in complex environmental systems.

A direct method for detecting proteins in body fluids by Surface-Enhanced Raman Spectroscopy under native conditions

Surface enhanced Raman spectroscopy (SERS) is widely used in biomolecular detection. However, maintaining the native structure of proteins while obtaining sensitive and reproducible SERS signals of unlabeled proteins remains a challenge. In this study, dichloromethane (DCM) and CaCl2 were used to optimize the aggregation of Ag nanoparticles (AgNPs), and several proteins were analyzed comprehensively. Calcium ions removed citrate ions outside AgNPs, inducing hot spots and achieving high-sensitivity SERS signals of proteins. Furthermore, 20 random samples of 0.5 μg/mL hemoglobin were analyzed by this method. The obtained spectra showed good repeatability and a high quality. Using the peak intensity of DCM as internal parameter, the differences in peak intensities at the same position were analyzed to distinguish different proteins and evaluate changes in protein structure. Subsequently, the protein content in protein mixtures and serum was quantified and a good linear relationship between peak intensity and protein concentration was obtained. This method shows great promise in the fields of food testing and clinical diagnosis.

In Situ Functionalization of Silver Nanoparticles by Gallic Acid as a Colorimetric Sensor for Simple Sensitive Determination of Melamine in Milk.

A simple and green colorimetric sensing assay strategy for highly efficient determination of melamine has been fabricated, which is based on the redox reaction of gallic acid with Ag+. Monodispersed Ag nanoparticles (AgNPs) were obtained using gallic acid as a reducing and stabilizing agent. However, the aggregate behavior of AgNPs was observed, while the melamine was present in the reaction medium. As a result, the color of the solution changed from vivid yellow to brown, and the density of the color was quantitatively correlated with the melamine concentration. The aggregation of AgNPs could be attributable to the formation of hydrogen bonds between melamine and gallic acid. The designed sensor exhibited a good detection limit of 0.099 μM (0.012 ppm), which was much lower than the safety limit in China (1.0 ppm) and EU (2.0 ppm). Additionally, the sensing assay displayed good selectivity toward melamine over other coexisting substances. Consequently, the proposed colorimetric sensor was successfully used for the determination of melamine detection in raw milk samples.

Preparation of Ag SPR-promoted TiO2-{001}/HTiOF3 photocatalyst with oxygen vacancies for highly efficient degradation of tetracycline hydrochloride

In order to solve the problem of tetracycline hydrochloride (TCH) wastewater pollution, a photocatalyst for the efficient utilization of sunlight was proposed. In this work, a new method for the synthesis of three-dimensional flower-like Ag/TiO2-{001}/HTiOF3 photocatalyst was applied, where surface oxygen vacancies can induce Ag nanoparticles (NPs) to disperse on the surface of the photocatalyst, which avoids the aggregation of Ag NPs into large particles. The appropriate mesoporous structure of the photocatalyst makes TCH have a stronger affinity on its surface, which is more conducive to the subsequent photodegradation. Furthermore, the surface plasmon resonance (SPR) of Ag NPs extends the response region of photocatalyst to visible light, and the heterojunction formed with TiO2/HTiOF3 further stimulates the electrons in the oxygen vacancy region and inhibits the recombination of carriers. 10-Ag/TiO2/HTiOF3 showed the best degradation activity (96%) for TCH when the ratio of Ag and TiO2-{001}/HTiOF3 was 10%. In addition, the Ag/TiO2-{001}/HTiOF3 photocatalyst has excellent photocatalytic activity, structural stability and sedimentation performance. The prepared catalyst has practical application prospect.

Structure and Properties of Polyoxymethylene/Silver/Maleic Anhydride-Grafted Polyolefin Elastomer Ternary Nanocomposites.

In the present study, silver (Ag) nanoparticles and maleic anhydride-grafted polyolefin elastomer (MAH-g-POE) were used as enhancement additives to improve the performance of the polyoxymethylene (POM) homopolymer. Specifically, the POM/Ag/MAH-g-POE ternary nanocomposites with varying Ag nanoparticles and MAH-g-POE contents were prepared by a melt mixing method. The effects of the additives on the microstructure, thermal stability, crystallization behavior, mechanical properties, and dynamic mechanical thermal properties of the ternary nanocomposites were studied. It was found that the MAH-g-POE played a role in the bridging of the Ag nanoparticles and POM matrix and improved the interfacial adhesion between the Ag nanoparticles and POM matrix, owing to the good compatibility between Ag/MAH-g-POE and the POM matrix. Moreover, it was found that the combined addition of Ag nanoparticles and MAH-g-POE significantly enhanced the thermal stability, crystallization properties, and mechanical properties of the POM/Ag/MAH-g-POE ternary nanocomposites. When the Ag/MAH-g-POE content was 1 wt.%, the tensile strength reached the maximum value of 54.78 MPa. In addition, when the Ag/MAH-g-POE content increased to 15wt.%, the elongation at break reached the maximum value of 64.02%. However, when the Ag/MAH-g-POE content further increased to 20 wt.%, the elongation at break decreased again, which could be attributed to the aggregation of excessive Ag nanoparticles forming local defects in the POM/Ag/MAH-g-POE ternary nanocomposites. Furthermore, when the Ag/MAH-g-POE content was 20 wt.%, the maximum decomposition temperature of POM/Ag/MAH-g-POE ternary nanocomposites was 398.22 °C, which was 71.39 °C higher than that of pure POM. However, compared with POM, the storage modulus of POM/Ag/MAH-g-POE ternary nanocomposites decreased with the Ag/MAH-g-POE content, because the MAH-g-POE elastomer could reduce the rigidity of POM.

Rapid and sensitive SERS detection of food contaminants by using nano-Ag aggregates with controllable hydrophobicity

There is an increasing demand for rapid and sensitive detection of hydrophobic contaminants in foods. A rapid and sensitive surface enhanced Raman scattering (SERS) detection method was developed for this purpose, based on the surface modification of nano-Ag aggregates, which had rich hot spots and controllable hydrophobicity. Cationic surfactants with different carbon chain lengths were employed to modify the aggregation of Ag nanoparticles. The adsorption of cationic surfactants on nano-Ag aggregates increased the hydrophobicity of the surface of the nano-Ag aggregates as the SERS substrate. By changing the carbon chain length of the surfactant, the hydrophobicity of the SERS substrate was able to be tuned to match with the hydrophobicity of the contaminants to be detected. Different hydrophobic contaminants such as Auramine O, Sudan I and Sudan III could be quantitatively detected, with a detection limit as low as 6.1 × 10−8, 7.5 × 10−9, 2.1 × 10−9 mol L−1, respectively. Compared with the traditional inorganic salt aggregation method which was unable to meet the requirements of direct quantitative detection in the sample matrices, the developed method was confirmed to have the advantages of low detection limit, good reproducibility (relative standard deviation (RSD) is less 7.6%), short operation time (about 1 min), and no need of any complicate pretreatment for sample preparation.

A sensitive turn-off-on fluorometric sensor based on S,N co-doped carbon dots for environmental analysis of Hg(II) ion.

A simple and sensitive fluorescence turn-off-on sensor was established by means of S,N co-doped carbon dots (S,N-CDs) and Ag nanoparticles (AgNPs) for the determination of Hg2+ . For this purpose, blue emissive S,N-CDs were hydrothermally synthesized and characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy. We observed that the fluorescence intensity of the as-prepared S,N-CDs was impressively quenched by AgNPs. The quenching mechanism was studied and attributed to nanosurface energy transfer and the inner filter effect between S,N-CDs and AgNPs. Furthermore, by adding Hg2+ , the fluorescence intensity of S,N-CDs/AgNPs was restored as a result of aggregation of AgNPs in the presence of Hg2+ . Based on these facts, S,N-CDs and AgNPs were exploited to design a sensitive turn-off-on sensor for analysis of Hg2+ . The recovered fluorescence signal was proportional to the concentration of Hg2+ in the range 1.5-2000 nM with a detection limit of 0.51 nM. The established sensor was used with satisfactory results for measurement of Hg2+ in environmental water samples.

Chemical reduction of Ag+ to Ag employing organic electron donors: evaluation of the effect of Ag+-mediated cytosine-cytosine base pairing on the aggregation of Ag nanoparticles.

Ag+-mediated base pairing is valuable for synthesising DNA-based silver nanoparticles (AgNPs) and nanoclusters (AgNCs). Recently, we reported the formation of a [Ag(cytidine)2]+ complex in dimethyl sulfoxide (DMSO), which facilitated the evaluation of the effect of cytosine-Ag+-cytosine (C-Ag+-C) base pairing on the degree of AgNP aggregation in solution. As an aprotic solvent, DMSO was expected to dissolve the [Ag(cytidine)2]+ complex, and powerful reducing agents, such as organic electron donors. In this study, the chemical reduction of a cytidine/Ag+ system using a powerful reducing agent tetrakis(dimethylamino)ethylene (TDAE) was investigated. 1H/13C/15N NMR spectroscopic evidence was obtained to identify the iminium dication (TDAE2+), which is an oxidised form of TDAE. The results were compared with those obtained using another organic electron donor, tetrathiafulvalene (TTF), which exhibits a relatively lower reduction activity than TDAE. AgNPs prepared via redox reaction between [Ag(cytidine)2]+ and organic electron donors (TDAE and TTF) were characterised using UV-Vis spectroscopy and nanoparticle tracking analysis. It was found that the formation of C-Ag+-C base pairing inhibited the aggregation of AgNPs in solution. In addition, in the presence of cytidine, the total concentration of the AgNP solution was affected by the reduction activity of the reducing agent.

Sb2O3 functionalized Plasmon, photoluminescence and Faraday rotation in glass

This paper reports the influence of antimony ions and Sb2O3 reduced Ag0 on the magnetic and Faraday rotation of diamagnetic glasses for the first time. High Verdet constant diamagnetic glasses with compositions of xSb2O3–(15–x)B2O3–35PbO–45Bi2O3–2Ag2O–3ZnO were fabricated and characterized. Ag nanoparticles were realized in glass using Sb2O3 as reducing agent through single-step melting quenching technique. The structure, spectral along with optical, magnetic and Faraday rotation properties were investigated through XRD, FT-IR, Raman, XPS, UV-VIS, luminescence and VSM measurements. Due to the big optical basicity of glass matrix and the reducing property of Sb2O3, Ag+ ions were reduced to Ag0 accompanied with the conversion from Sb3+ to Sb5+. Raman spectra revealed the presence of SbO3, BiO3, PbO4, and BO3, BO4 units in glasses, with the increase of Sb2O3, Ag-O and B-O vibration decreased and 10-15% Sb2O3 doped samples crystallized into ceramics. XPS analysis displays the co-existence and evolutions of antimony and silver species as a function of Sb2O3 content. SPR absorption peaks of Ag nanoparticles in glasses red-shifted from 525nm to 600nm, indicating the aggregation of Ag nanoparticles into bigger sized Ag3 clusters which present emission peaks around 560nm. The electron transitions between Sb3+ and Sb5+ show emission around 560nm while Sb5+ ions show emission at 800nm. All glasses exhibited diamagnetic properties due to the diamagnetic character of glass matrix and doping ions. Both the high polarizability of diamagnetic Sb3+&Sb5+ and Ag0 SPR effects contributed to an enhancement of Faraday rotation of glasses, the 3%Sb2O3 doped glass showed the highest Verdet constant of 0.2047min/G.cm at 594nm which therefore might be an attractive candidate for magneto optical device applications.

Efficient synthesis of 3-methylindole using biomass-derived glycerol and aniline over ZnO and CeO2 modified Ag/SBA-15 catalysts

An efficient mesoporous catalyst of Ag/SBA-15 modified with ZnO and CeO2 was successfully constructed with the purpose of efficiently synthesizing 3-methylindole by biomass-derived glycerol and aniline, which up to 62% yield and 75% selectivity for 3-methylindole were achieved when Ag loading was 1.00 mmol/g−1, ZnO or CeO2 content was 1.00 or 0.05 mmol/g−1, respectively. And only 3% yield decreased when the catalyst was circulated five times. The characterizations researches on N2 physical adsorption, Fourier transform infrared (FT-IR), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX), temperature programmed reduction of hydrogen (H2-TPR), X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature programmed desorption (TPD) of NH3 and CO2, thermogravimetric and differential thermal analysis (TG-DTA) indicated that adding the promoter of ZnO to Ag/SBA-15 increased the dispersion of the silver particles significantly and controlled the aggregation of Ag nanoparticles during the reaction remarkably because doping ZnO greatly increased the polarity of the composite carrier SBA–15–ZnO and brought about the interaction between Ag and carrier enhanced. CeO2 could promote the reduction of Ag2O and suppress the formation of carbon deposition effectively. In addition, doping ZnO and CeO2 increased the number of the weak-acid centers of the SBA-15 supported Ag-based catalyst observably, thereby the catalyst of Ag/SBA-15-ZnO-–ZnO–CeO2 acquired a good selectivity. Moreover, the reaction pathway for 3-methylindole synthesis by biomass-derived glycerol and aniline was probed in depth and a reasonable route was proposed.

The medium effect on electrodissolution of adsorbed or suspended Ag nanoparticles

Electrochemical behaviour of six types of Ag nanoparticles (three stabilised by citrate and three others stabilised by polymers) was studied on carbon screen-printed electrode and glassy carbon rotating disc electrode. A stationary electrode was used as a support for adsorbed nanoparticles, whereas the rotating disc electrode was applied for experiments in nanoparticles suspension. Peak shaped cyclic voltammograms obtained for immobilised nanoparticles indicate their electro-dissolution and electrodeposition of silver in the backward scan. The given peak shape and its position on potential scale depend both on the type of nanoparticles and the supporting electrolyte. When aggregation of Ag nanoparticles was detected by UV–vis spectroscopy, splitting of an anodic peak corresponding to electrodissolution of silver in neutral phosphate buffer or NaOH solution is seen. Injection of a fraction of microgram of Ag nanoparticles was detected in chronoamperometric experiments on rotating disc electrode. However, in the presence of H2O2, the effect of nanograms of silver was seen on voltammetric curve indicating electrocatalytic amplification.

Controlled aggregation of Ag nanoparticles on oxide templates on nitinol by electrodeposition

Nitinol is an unusual material for hard-tissue replacements because of their unique superelasticity, biocompatibility, and low elastic modulus. Nitinol surface was modified by plasma electrolytic oxidation with an aim to produce oxide film on the surfaces for inhibiting Ni ion release. In addition, various Ag structures were constructed on the oxide templates on nitinol using electrodeposition in an AgC2H3O2-based solution for improving the antibacterial ability. Control of the electrolyte by collagen concentration caused a change in Ag shape and aggregation. Preferred growth along Ag (1 1 1) by orientated attachment of the Ag led to the formation of Ag dendrites in the AgC2H3O2 solution. Spherical Ag nanostructures, which were well dispersed on the templates, were obtained by electrodeposition in an AgC2H3O2-collagen solution on templates. Increasing the concentration of collagen caused aggregated Ag to form coarse spherical structures with a non-uniform distribution.