Preparation of monodisperse polystyrene/silver composite microspheres and their catalytic properties

This article presents a facile method for the preparation of polystyrene/silver (PS/Ag) composite microspheres. In this approach, monodisperse PS spheres were synthesized via dispersion polymerization and modified by sulfonation to obtain sulfonated PS spheres with sulfonic acid groups on the surfaces, and then adsorbed Sn²⁺ ions by electrostatic interaction and used as templates. PS/Ag composite microspheres were prepared successively by addition of [Ag(NH₃)₂]⁺ complex ions to the templates dispersion, adsorbing to the surfaces of templates, and then reduction of [Ag(NH₃)₂]⁺ complex ions to Ag nanoparticles by sodium potassium tartrate. The results showed that monodisperse PS spheres with sulfonic acid groups on the surfaces were coated by an incomplete and nonuniform coverage of Ag nanoparticles in the absence of Sn²⁺ ions. In the presence of Sn²⁺ ions, however, complete and uniform Ag nanoparticles coatings were obtained on the entire PS sphere. And the deposition density and size of Ag nanoparticles can be controlled by [Ag(NH₃)₂]⁺ concentration. The resulting PS/Ag composite microspheres were characterized by SEM, TEM, XRD, TGA, and UV-vis. Preliminary catalytical tests indicated these PS/Ag composite microspheres showed good catalytic properties.     

Gold nanoparticles/carbon nanotubes composite microspheres for catalytic reduction of 4-nitrophenol

The layer-by-layer assembly of polyethyleneimine and carbon nanotubes is carried out through the electrostatic interactions on colloidal polystyrene templates. The successful spherical growth of polyethyleneimine/carbon nanotube multilayers could be investigated by SEM. The subsequent in situ preparation and deposition of gold nanoparticles on the core–shell composites could yield novel microsphere complexes, which are characterized by SEM, TEM, EDX and XRD. The functional hierarchical microspheres with gold nanoparticles exhibit good catalytic activity in the reaction of reducing 4-nitrophenol to 4-aminophenol.     

Cellulose fibers modified with silver nanoparticles

Cellulose fibers modified with silver nanoparticles were prepared using N-methylmorpholine-N-oxide as a direct solvent and analyzed in this study. Silver nanoparticles were generated as a product of AgNO₃ reduction by means of three methods under varying light conditions (daylight and darkroom). Influence of generating conditions on the size, the type and the number weighting of created nanoparticles was examined. Dynamic Light Scattering technique (DLS) was used for determination of those parameters. DLS analysis showed that the best method, i.e. the one that allowed the generation of the greatest number of silver nanoparticles with the smallest diameter and the smallest agglomerates, was incubation of cellulose pulp with AgNO₃ in a darkroom for 24 h. Mechanical and hydrophilic properties of all obtained fibers were also determined. Results showed that the method of silver nanoparticles generation did not influence significantly mechanical and hydrophilic properties of the modified fibers, because in all cases only small decreases of the studied parameters were observed.     

Alga-mediated facile green synthesis of silver nanoparticles: Photophysical,catalytic and antibacterial activity

A facile, convenient and green method has been employed for the synthesis of silver nanoparticles (AgNPs) using dried biomass of a green alga, Chlorella ellipsoidea. The phytochemicals from the alga, as a mild and non-toxic source, are believed to serve as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of a surface plasmon resonance band at 436 nm and energy dispersive X-ray spectroscopy. The transmission electron microscopy images showed the nanoparticles to be nearly spherical in shape with different sizes. A dynamic light scattering study revealed the average particle size to be 220.8 ± 31.3 nm. Fourier transform infrared spectroscopy revealed the occurrence of alga-derived phytochemicals attached to the outer surface of biogenically accessed silver nanoparticles. The powder X-ray diffraction study revealed the face-centred cubic crystalline structure of the nanoparticles. The as-synthesized biomatrix-loaded AgNPs exhibited a high photocatalytic activity for the degradation of the hazardous pollutant dyes methylene blue and methyl orange. The catalytic efficiency was sustained even after three reduction cycles. A kinetic study indicated the degradation rates to be pseudo-first order with the degradation rate being 4.72 × 10⁻² min⁻¹ for methylene blue and 3.24 × 10⁻² min⁻¹ for methyl orange. The AgNPs also exhibited significant antibacterial activity against four selected pathogenic bacterial strains.     

Facile synthesis of silver core - silica shell composite nanoparticles

Combining metal nanoparticles and dielectrics (e.g. silica) to produce composite materials with high dielectric constant is motivated by application in energy storage. Control over dielectric properties and their uniformity throughout the composite material is best accomplished if the composite is comprised of metal core - dielectric shell structured nanoparticles with tunable dimensions. We have synthesized silver nanoparticles in the range of 40-100nm average size using low concentration of saccharide simultaneously as the reducing agent and electrostatic stabilizer. Coating these silver particles with silica from tetraalkoxysilanes has different outcomes depending on the alcoholic solvent and the silver particle concentration. A common issue in solution-based synthesis of core-shell particles is heterogeneous nucleation whereupon two populations are formed: the desired core-shell particles and undesired coreless particles of the shell material. We report the formation of Ag@SiO(2) core-shell particles without coreless silica particles as the byproduct in 2-propanol. In ethanol, it depends on the silver surface area available whether homogeneous nucleation of silica on silver is achieved. In methanol and 1-butanol, core-shell particles did not form. This demonstrates the significance of controlling the tetraalkoxysilane hydrolysis rate when growing silica shells on silver nanoparticles.     

Green planting silver nanoparticles on Populus fibers and the catalytic application

Research on Chemical Intermediates - Preparation and application of ecofriendly materials is becoming an urgent topic. In this work, a green approach for producing silver nanoparticles (AgNPs)...     

One-step synthesis of Pt nanoparticles/reduced graphene oxide composite with enhanced electrochemical catalytic activity

A one-step electrochemical approach for synthesis of Pt nanoparticles/reduced graphene oxide(Pt/RGO) was demonstrated.Graphene oxide(GO) and chloroplatinic acid were reduced to RGO and Pt nanoparticles(Pt NPs) simultaneously,and Pt/RGO composite was deposited on the fluorine doped SnO 2 glass during the electrochemical reduction.The Pt/RGO composite was characterized by field emission-scanning electron microscopy,Raman spectroscopy and X-ray photoelectron spectroscopy,which confirmed the reduction of GO and chloroplatinic acid and the formation of Pt/RGO composite.In comparison with Pt NPs and RGO electrodes obtained by the same method,results of cyclic voltammetry and electrochemical impedance spectroscopy measurements showed that the composite electrode had higher catalytic activity and charge transfer rate.In addition,the composite electrode had proved to have better performance in DSSCs than the Pt NPs electrode,which showed the potential application in energy conversion.     

Novel Bi/BiOBr/AgBr composite microspheres: Ion exchange synthesis and photocatalytic performance

Novel Bi/BiOBr/AgBr composite microspheres were prepared by a rational in situ ion exchange reaction between Bi/BiOBr microspheres and AgNO₃. The characteristic of the as-obtained ternary microspheres was tested by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and photoluminescence (PL). Under visible light irradiation, Bi/BiOBr/AgBr microspheres exhibited an excellent photocatalytic efficiency for rhodamine B (RhB) degradation, which was about 1.4 and 4.9 times as high as that of Bi/BiOBr and BiOBr/AgBr, demonstrating that the highest separation efficiency of charge carriers in the heterostructured Bi/BiOBr/AgBr. The photocatalytic activity of Bi/BiOBr/AgBr microspheres just exhibited a slight decrease after three consecutive cycles. The photocatalytic mechanism investigation confirmed that the superoxide radicals (O₂^•−) were the dominant reactive oxygen species for RhB degradation in Bi/BiOBr/AgBr suspension.     

One-step synthesis of amino-dextran-protected gold and silver nanoparticles and its application in biosensors

A sensitive method for the detection of the lectin protein concanavalin A (Con A) was developed using amino-dextran (AD)-protected gold (AD-Au) and silver nanoparticles (AD-Ag) as sensitive optical probes. The AD-Au and AD-Ag nanoparticles were synthesized by directly applying amino-dextran as a reductive and protective reagent. The size of the nanoparticles could be altered by changing the molar ratio of AD to the metal salt. The amino-dextran bound to Con A by forming a 4:1 Au-Con A complex at neutral pH, and the nanoparticles were induced to aggregate by Con A. The absorption intensity of the nanoparticles decreased linearly with as the Con A concentration was increased from 3.85×10^–8 to 6.15×10^–7 M. The Au-Con A complex was dissociated by the disaccharide isomaltose, which has a higher affinities for Con A than Au; this competitive strategy could also be used to detect similar types of saccharides.     

Green synthesis of silver nanoparticles using Piper longum catkin extract irradiated by sunlight: antibacterial and catalytic activity

Research on Chemical Intermediates - In this study, rapid and cost-effective biosynthesis of silver nanoparticles (AgNPs) was synthesized by using Piper longum (P. longum) catkin extract. The...     

Hyaluronan-assisted synthesis of silver nanoparticles and nanowires

Research on Chemical Intermediates - Silver nanowires (NWs) were successfully synthesized in high yield in cationic surfactant solutions of cetyltrimethylammonium bromide (CTAB) with hyaluronan...     

Probing silver nanoparticles during catalytic H2 evolution

Employing silver nanoparticles from a recently developed synthesis [Evanoff, D. D.; Chumanov, G. J. Phys. Chem. B 2004, 108, 13948] and a well-studied probe molecule, p-aminothiophenol, we follow changes at the surface of the particles during the conditioning and eventually the catalytic production of hydrogen from water using strongly reducing radicals. Injection of electrons into the particles causes pronounced variations in the intensity of the surface enhanced Raman scattering (SERS) spectrum of the probe molecule. These spectral changes are caused by changes in the Fermi-level energy that are in turn caused by changes in the silver ion concentrations or in the pH, or by changes in electron density in the particle. This correlation highlights the effect of the chemical potential on the SERS enhancement at the end of the particles synthesis. The intensity of the SERS spectra increases in the presence of the silver ions when excitation at 514 nm is utilized. When the Ag(+) ions in the colloidal suspension are completely reduced by the radicals and the particles operate in the catalytic mode, the SERS spectrum is too weak to record, but it can reversibly be recovered upon the addition of Ag(+). The effect of pH on the SERS intensity is similar in nature to that of the silver ions but is complicated by the pKa of the aminothiol and the point of zero charge (pzc) of the particles. It is hypothesized that as the particles cross the pzc (around neutral pH) the electrostatic interaction between the protonated amine headgroup of the probe and the positively charged surface increases the density of probe molecules in the perpendicular orientation at the expense of a competing species. This conversion results in enhanced SERS signals and is observable during the preconditioning stage of the particles. Indeed, adsorption isotherms of the probe indicate the presence of two species. In analogous previous observations these two species have been attributed to perpendicular and flat adsorption orientations of the deprotonated probe molecule relative to the particle surface. However, preliminary density functional calculations on relevant prototypes raise the possibility that the two species may be the probe molecule and a cationic form produced by charge transfer in the ground state from the chemisorbed probe to the metal. These two forms of the probe have differing electronic structures and vibrational frequencies, with perhaps differing orientations relative to the surface. Whichever is the correct interpretation, a neutral molecule in a flat orientation or a radical cation, this species is easier to replace than the other in competitive adsorption by ethanethiol.     

Bioinspired synthesis of multifunctional silver nanoparticles for enhanced antimicrobial and catalytic applications with tailored SPR properties

In the developing nanotechnology world, numerous attempts have been made to prepare the nobel metallic nanoparticles (NPs), which can improve their applicability in diverse fields. In the present work, the biosynthesis of silver (Ag) NPs has been successfully achieved through the medicinal plant extract (PE) of G. resinifera and effectively used for the catalytic and antibacterial applications. The size dependant tuneable surface plasmon resonance (SPR) properties attained through altering precursor concentrations. The X-ray and selected area diffraction pattern for Ag NPs revealed the high crystalline nature of pure Ag NPs with dominant (111) phase. The high-resolution TEM images show the non-spherical shape of NPs shifting from spherical, hexagonal to triangular, with wide particle size distribution ranging from 13 to 44 nm. Accordingly, the dual-band SPR spectrum is situated in the UV–Vis spectra validating the non-spherical shape of Ag NPs. The functional group present on the Ag NPs surface was analysed by FT-IR confirms the capping and reducing ability of methanolic PE G. resinifera. Further, the mechanism of antimicrobial activity studied using electron microscope showed the morphological changes with destructed cell walls of E. coli NCIM 2931 and S. aureus NCIM 5021 cells, when they treated with Ag NPs. The Ag NPs were more effective against S. aureus and E. coli with MIC 128 μg/ml as compared to P. aeruginosa NCIM 5029 with MIC 256 μg/ml. Apart from this, the reduction of toxic organic pollutant 4-NP to 4-AP within 20 min reveals the excellent catalytic activity of Ag NPs with rate constant k = 15.69 s^?1.     

Carbon microspheres with supported silver nanoparticles prepared from pollen grains

In this paper, we present a new method to fabricate carbon microspheres with supported silver nanoparticles on the surfaces. In this method, pollen grains were first treated with AgNO(3) aqueous solution, then preoxidized in air at 300 degrees C and carbonized in nitrogen at 600 degrees C, resulting in the silver/carbon nanocomposites. The silver/carbon nanocomposites were characterized by means of SEM, TEM, TG, and XRD. The size and distribution of the silver nanoparticles on the carbon microsphere surface could be controlled by tuning the AgNO(3) treatment conditions.     

Preparation, microstructure characterization and catalytic performance of Cu/ZnO and ZnO/Cu composite nanoparticles for liquid phase methanol synthesis

Stearate@Cu/ZnO nanocomposite particles with molar ratios of ZnO?∶?Cu = 2 and 5 are synthesized by reduction of the metal-organic Cu precursor [Cu{(OCH(CH(3))CH(2)N(CH(3))(2))}(2)] in the presence of stearate@ZnO nanoparticles. In the case of ZnO?∶?Cu = 5, high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) combined with electron-energy-loss-spectroscopy (EELS) as well as attenuated total reflection Fourier transform infrared (ATR-IR) spectroscopy are used to localize the small amount of Cu deposited on the surface of 3-5 nm sized stearate@ZnO particles. For ZnO?∶?Cu = 2, the microstructure of the nanocomposites after catalytic activity testing is characterized by HAADF-STEM techniques. This reveals the construction of large Cu nanoparticles (20-50 nm) decorated by small ZnO nanoparticles (3-5 nm). The catalytic activity of both composites for the synthesis of methanol from syn gas is evaluated.     

Preparation,characterization, and antibacterial activity of composite material: Cotton fabric/hydrogel/silver nanoparticles

A new composite cotton fabric with hydrogel containing silver nanoparticles (AgNPs) has been synthesized by two steps, and simultaneous in situ synthesis of AgNPs under visible light irradiation has been performed. The influence of silver nitrate concentration upon the hydrogel and AgNP properties was studied by colorimetric analysis, scanning electron microscopy, and transmission electron microscopy. The antibacterial activities of the composite materials have been investigated against Acinetobacter johnsonii and Escherichia coli in agar medium and meat-peptone broth. The results showed high inhibition activity toward both test cultures which were better expressed against A. johnsonii.     

Green synthesis and characterization of polymer-stabilized silver nanoparticles

Silver nanoparticles (Ag-NPs) were synthesized using a facile green chemistry synthetic route. The reaction occurred at ambient temperature with four reducing agents introduced to obtain nanoscale Ag-NPs. The variables of the green synthetic route, such as acidity, concentration of starting materials, and molar ratio of reactants were optimized. Dispersing agents were employed to prevent Ag-NPs from aggregating. Advanced instrumentation techniques, such as X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–vis), and phase analysis light scattering technique (ZetaPALS) were applied to characterize the morphology, particle size distribution, elemental composition, and electrokinetic behavior of the Ag-NPs. UV–vis spectra detected the characteristic plasmon at approximately 395–410 nm; and XRD results were indicative of face-centered cubic phase structure of Ag. These particles were found to be monodispersed and highly crystalline, displaying near-spherical appearance, with average particle size of 10.2 nm using citrate or 13.7 nm using ascorbic acid as reductants from particle size analysis by ZetaPALS, respectively. The rapid electrokinetic behavior of the Ag was evaluated using zetapotential (from −40 to −42 mV), which was highly dependant on nanoparticle acidity and particle size. The current research opens a new avenue for the green fabrication of nanomaterials (including variables optimization and aggregation prevention), and functionalization in the field of nanocatalysis, disinfection, and electronics.