Hollow mesoporous silica spheres supported Ag and Ag–Au catalyzed reduction of 4-nitrobenzo-15-crown

Hollow mesoporous silica (HMS) spheres of size within the range 120–220 nm have been prepared using propanol–water solvent as template and cetyltrimethylammonium bromide (CTAB) as stabilizer. HMS supported silver and silver–gold catalysts were prepared by impregnating metal nanoparticles on HMS and were characterized by ultraviolet–visible spectroscopy (UV–vis), dynamic light scattering (DLS), optical microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductive coupled plasma optical emission spectroscopy (ICP-OES) and N₂ adsorption–desorption. The reduction of 4-nitrobenzo-15-crown (4-NB-15-C) was compared using HMS supported silver and silver–gold nanocatalysts varying experimental parameters. Bimetallic Ag–Au/HMS nanocatalysts was found to be more active than monometallic Ag/HMS nanocatalyst.     

Polymer-assisted freeze-drying synthesis of Ag-doped ZnO nanoparticles with enhanced photocatalytic activity

Ag-doped ZnO nanoparticles with high and stable photocatalytic activity were prepared by polymer-assisted freeze-drying method with simple process and without organic solvents used. The structural morphology and optical properties of Ag-doped ZnO nanoparticles were characterized by X-ray Diffraction (XRD), Inductive Coupled Plasma Optical Emission Spectrometry (ICP-OES), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and high resolution TEM (HRTEM) with energy dispersive X-ray spectroscopy, Ultraviolet-visible Diffuse Reflectance Spectroscopy (UV–vis DRS), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transmission Infrared Spectroscopy (FTIR). Moreover, the thermoanalytical measurements (TGA–DTG) analysis is carried out for proper calcination temperature. XRD results show that Ag nanoparticles were successfully doped into ZnO lattice, and UV–vis DRS results indicate that the doped Ag nanoparticles result in ZnO exhibiting enhanced light trapping capability in the 400?nm and 600?nm range. The photocatalytic activity of Ag-doped ZnO was examined by analyzing the degradation of methyl orange (MO) and methylene blue (MB) dyes under UV light and solar light irradiation, and the results show that all Ag-doped ZnO nanoparticles exhibit better photocatalytic activity than those of pure ZnO nanoparticles at the same degradation conditions; especially the synthesized Ag-ZnO nanoparticles are easy to be recycled and have high photocatalytic stability. Based on the experimental results, the photocatalytic electron transfer path and the photocatalytic mechanism of Ag-ZnO nanoparticles under UV and solar irradiation conditions are explained and clarified.     

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.     

In situ fabrication of polyaniline‐silver nanocomposites using soft template of sodium alginate

Polyaniline (PANI)‐Ag nanocomposites were synthesized by in situ chemical polymerization approach using ammonium persulfate and silver nitrate as oxidant. Characterizations of nanocomposites were done by ultraviolet–visible ( UV–vis), Fourier transform infrared (FTIR), X‐ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). UV–vis, XRD and FTIR analysis established the formation of PANI/Ag nanocomposites and face‐centered‐cubic phase of silver. PANInanofibers were of average diameter ～ 30 nm and several micrometers in length. Morphological analysis showed that the spherical‐shaped silver nanoparticles decorate the surface of PANI nanofibers. Silver nanoparticles of average diameter ～ 5–10 nm were observed on the TEM images for the PANI‐Ag nanocomposites. Such type of PANI‐Ag nanocomposites can be used as bistable switches as well as memory devices. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The synthesis of Ag/AgCl/BiFeO3 photocatalyst with enhanced visible photocatalytic activity

A novel AgCl/Ag/BiFeO₃ photocatalyst was synthesized via an ultrasonic-assisted precipitation-photoreduction method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence emission spectra (PL) analysis were implemented to characterize the composition, morphology, structure, and optical property of the as-synthesized photocatalyst. For the decomposition of methyl orange (MO) and other organic dyes, AgCl/Ag/BiFeO₃ photocatalyst manifested much superior visible-light catalytic activity than pure BiFeO₃ and AgCl/Ag. Based on the trapping experiments and band structure analysis, a probable Z-scheme light catalytic mechanism was proposed.     

Enhancement of the photocatalytic performance of Ag-modified TiO2 photocatalyst under visible light

A highly visible-light photocatalytic active Ag-modified TiO₂ (Ag–TiO₂) was prepared by a simple sol–gel process using TiOSO₄ as the starting material, AgNO₃ as a silver doping source, and hydrazine as a reducing agent. The prepared Ag–TiO₂ samples were characterized by several techniques such as X-ray powder diffraction (XRD), BET surface area measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), energy dispersive X-ray spectrometry (EDX), X-ray absorption spectroscopy (XAS) and UV–vis diffuse reflectance spectroscopy (DRS). The Ag–TiO₂ photocatalyst, a mixture of amorphous and anatase phases, has a high surface area. The silver contents in the Ag–TiO₂ samples were determined by ICP measurements. The diffused reflectance UV–vis spectra indicated that the Ag–TiO₂ samples exhibited higher red shifts compared with the undoped TiO₂ sample. Indigo carmine degradation under visible irradiation indicated that the Ag–TiO₂ catalyst gave higher photocatalytic efficiency than those of commercial P25-TiO₂ and undoped-TiO₂ samples. The Ag–TiO₂ catalyst can be reused many times without any additional treatment.     

Growth mechanism and photocatalytic activity of chrysanthemum-like anatase TiO2 nanostructures

Chrysanthemum-like hierarchical anatase TiO₂ nanostructures self-assembled by nanorods have been successfully fabricated by a simple solvothermal route without using template materials or structure-directing additives. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectrometer system (Raman), UV–vis absorption spectroscopy (UV–vis) and N₂ adsorption–desorption measurement. The results indicate that synthesized chrysanthemum-like hierarchical anatase TiO₂ nanostructures have a spherical shape with an average diameter of 1.5 μm and they are composed of nanorods with a width of about 30 nm and a length of about 300 nm. The pore distribution of the sample exhibits two kinds of pores. Such mesoporous structure of the sample might be extremely useful in photocatalysis because they possess efficient transport pathways to the interior and supplies higher specific area for more pollutant molecules to be absorbed. In addition, the synthesized TiO₂ nanostructures show enhanced photocatalytic activity compared with commercial P25 for the degradation of RhB under UV light irradiation, which can be attributed to their special hierarchical structure and high light-harvesting capacity.     

Au–Pt nanoparticles in amine functionalized MCM-41: Catalytic evaluation in hydrogenation reactions

Nano-sized Au–Pt nanoparticles (Au–Pt-bi-MNPs) have been synthesized by the simultaneous reduction of HAuCl₄ and HPtCl₆ by NaBH₄ inside the channels of amine functionalized Si-MCM-41 (NH₂–Si-MCM-41) at ambient conditions. These materials were characterized using chemical analysis, UV–vis, XPS, XRD, FT-IR, Surface area and TEM analysis. The size of these alloyed nanoparticles (bi-MNPs) were found in the range of 2–4 nm. These nanoparticles were evaluated to study their catalytic activities towards hydrogenation of aromatic nitro compounds. The catalytic activity of the Au–Pt bi-MNPs was found to be superior to monometallic Au nanoparticles.     

Effect of different promoters on Ni/CeZrO2 catalyst for autothermal reforming and partial oxidation of methane

Ni/CeZrO₂ catalysts promoted by Ag, Fe, Pt and Pd were investigated for methane autothermal reforming and partial oxidation of methane. The catalysts properties were determined by BET surface area, X-ray diffraction (XRD), H₂ temperature-programmed reduction (TPR), temperature-programmed desorption of CO₂ (CO₂-TPD) and UV–vis diffuse reflectance spectroscopy (DRS). Nickel dispersions were evaluated using a model reaction, the dehydrogenation of cyclohexane. BET surface area results showed that the catalysts prepared by successive impregnation presented lower surface area which favored the smaller nickel dispersion. XRD analysis showed the formation of a ceria–zirconia solid solution. TPR experiments revealed that the addition of Pt and Pd as promoters increased the reducibility of nickel. CO₂-TPD results indicated that the AgNiCZ catalysts presented the best redox properties among all catalysts. The autothermal reforming of methane showed that, among different promoters, the sample modified with silver, AgNiCZ, presented higher methane conversion and better stability during the reaction. These results are related to the good reducibility and to the higher redox capacity observed in TPR and CO₂-TPD analysis. Samples prepared by successive impregnation technique resulted in a smaller catalytic activity. For partial oxidation of methane, just as happened in autothermal reforming, AgNiCZ also presented the best performance during the 24 h of reaction and the addition of silver by successive impregnation resulted in a lower methane conversion, probably, due to the smaller metal dispersion.     

Preparation of nanostructured porous carbon composite fibers from ferrum alginate fibers

Nano‐microstructured porous carbon composite fibers (Fe₂O₃@C/FeO@C/Fe@C) were synthesized by the thermal decomposition of ferrum alginate fibers. The ferrum alginate fiber precursors were prepared by wet spinning, and calcined at 300–1000°C in high purity nitrogen. The resulting composite fibers consist of carbon coated Fe₂O₃/FeO/Fe nanoparticles and porous carbon fibers. All the prepared nanostructures were investigated using thermal gravimetry, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscope (TEM), and nitrogen adsorption–desorption isotherm. The results show that there are five stages in the decomposition process of the ferrum alginate fibers. Transitions between the five stages are affected by the decomposition temperature. XRD results show that maghemite (Fe₂O₃), wüstite (FeO), martensite (Fe) nanoparticles were formed at 300–500°C, 600–700°C, 800–1000°C, respectively. Scanning electron microscopy and TEM results indicate that the composite fibers consist of nanoparticles and porous carbon. The diameter of the nanosized particles increased from 100 to 500 nm with increasing reaction temperature. The nitrogen adsorption–desorption results also show that the composite fibers have a micro‐ and mesoporous structure. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and catalytic behavior of hollow Ag/carbon nanofibers

A novel carbon nanofiber containing silver nanoparticles (NPs) with hollow structure was fabricated via co-electrospinning and in situ reduction. The hollow structure avoided the waste of silver NPs embedded in the nanofibers while ensuring high specific surface area. The formation of silver NPs was confirmed by Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The catalytic behavior of the nanofibers obtained to the reduction of methylene blue with NaBH₄ was tracked by UV–visible spectroscopy. The results showed that carbon nanofibers containing silver NPs with hollow structure possessed significant catalytic properties.     

Electron Beam Synthesis and Characterization of Poly Vinyl Alcohol/Poly Acrylic Acid Embedded Ni and Ag Nanoparticles

Electron beam irradiation was applied to prepare poly (vinyl alcohol) and poly (acrylic acid) P (PVA/AAc) containing nickel and silver nanoparticles. The prepared P (PVA/AAc)–Ni and P (PVA/AAc)–Ag nanoparticles were characterized by Fourier-transform infrared, UV–Visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscope (TEM). The electrical conductivity and thermal gravimetrical analysis (TGA) have been investigated. Bacterial sensitivity toward nickel and silver nanoparticles was studied. The XRD and TEM confirmed that by increasing the Ni or Ag contents from 10 to 150?mmol in the copolymers, the metal particle size increases from 27.6 to 45.6?nm for Ni and from 14.8 to 37.4?nm for Ag. Meanwhile, the mean size particle increases from 33.02 to 45.05?nm for Ni and from 15.5 to 44.03?nm for Ag. The electrical conductivity of the polymer containing Ag is higher than that of Ni and it increased by increasing the metal content. The TGA studies confirmed that, the thermal stability increase by the introduction of metal into polymeric complex. Bacterial sensitivity to metal nanoparticles was found to vary depending on the microbial species. Disc diffusion studies with P. aeruginosa, E. coli and K. pneumoniae revealed greater effectiveness of the silver nanoparticles compared to the nickel nanoparticles, S. aureus depicted the highest sensitivity to nanoparticles compared to the other strains and was more adversely affected by the nickel nanoparticles.     

Cooperative catalytic activity of cyclodextrin and Ag nanoparticles immobilized on spherical polyelectrolyte brushes

Spherical polyelectrolyte brushes (SPB) loaded with silver nanoparticles (Ag‐NP) were synthesized, and they were characterized in aqueous solution using TEM, ICP‐AES and UV‐vis spectroscopy. While the size distribution of the Ag‐NP synthesized at a given temperature is quite uniform this distribution varies with change in synthesis temperature. The Ag‐NP have a strong catalytic effect on the reduction of 4‐nitrophenol to 4‐aminophenol by NaBH4. The addition of α‐cyclodextrin (α‐CD) further accelerates this 4‐nitrophenol reduction and modifies the associated activation parameters. This is attributed to α‐CD complexing 4‐nitrophenol in the vicinity of the Ag‐NP surface and thereby aiding the catalysis. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1977–1982, 2014     

Nanostructure silver-doped zinc oxide films coating on glass prepared by sol–gel and photochemical deposition process: Application for removal of mercaptan

Silver-doped zinc oxide (SDZO) films have been grown on glass substrate by a novel combination of sol–gel and photochemical deposition processes (SGPD). The effect of sintering on structural, electrical and optical properties was investigated. The films were characterized by UV–vis absorption spectroscopy (UV–vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The result of X-ray photoelectron spectroscopy (XPS) revealed that the binding energy of Ag 3d_5/2 for SDZO shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between silver and zinc oxide. The XRD spectra of the SDZO films indicate that silver was incorporated in the hexagonal crystal structure of zinc oxide. SEM micrographs show the uniform distribution of spherical grains of about 73 nm grain size for the pure zinc oxide thin films. The results indicated that silver doping photochemical deposition was a feasible method to tune the optical properties of zinc oxide nanostructures. SDZO films coated on glass were applied for the photodegradation of mercaptan in water. SDZO films were applied for degradation of mercaptobenzoxazole which reduced the mercaptan concentration to more than 98%.     

Synthesis and intercalation of silver nanoparticles in kaolinite/DMSO complexes

Ag nanoparticles were synthesized in the interlamellar space of a layered kaolinite. Disaggregation of the lamellae of the nonswelling kaolinite was achieved by the intercalation of dimethyl sulfoxide (DMSO). The kaolinite was suspended in aqueous AgNO₃ solution and the adsorbed Ag⁺ ions were reduced on the surface of kaolinite lamellae with NaBH₄ or UV light irradiation. The silver nanoparticles formed were characterized by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). We studied the effects of the two reduction methods on the size and the size distribution of Ag nanoparticles and how clay mineral structure is altered as a consequence of particle formation. It was established that the size of Ag nanoparticles depends on both silver content and the reduction method. Photoreduction of silver led to the formation of relatively large Ag nanoparticles (diameter 8–14 nm).     

Development of alginate-gum acacia-Ag0 nanocomposites via green process for inactivation of foodborne bacteria and impact on shelf life of black grapes (Vitis vinifera)

The main objective of this investigation is to develop sodium alginate-gum acacia-silver nanocomposite films (AGA-Ag⁰ NC) to inhibit the growth of foodborne and to extend the shelf life of food. The Ag nanoparticles were generated in sodium alginate-gum acacia (AGA) blend matrix through reduction by basil leaves (Tulasi). The formation of Ag⁰ was monitored by UV–vis spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), thermogravimetrical analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The absorption band at 420 nm in UV–vis spectrum and change in the band positions in FTIR spectrum of AGA-Ag⁰ NC compared to that of AGA corresponds to the formation of Ag nanoparticles. The XRD profile of AGA-Ag⁰ NC exhibits characteristic d-lines of Ag nanoparticles. The spherical shape of Ag nanoparticles uniformly formed throughout the films was recognized in SEM image with a size of ~ 4 ± 1 nm as observed by TEM. The water uptake and mechanical properties of the films were also studied. The AGA-Ag⁰NC films offered excellent antimicrobial activity against various foodborne bacteria and shelf life of food enhanced efficiency of the AGA-Ag⁰NC films is also tested on grape fruit (Vitus vinifera). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47331.     

Hydrophobic interaction-mediated reversible adsorption–desorption of nanoparticles in the honeycomb-patterned thermoresponsive poly(N-isopropylamide) hydrogel surface

Hydrophobic interaction-mediated reversible adsorption–desorption of Ag nanoparticles in water solutions was studied in surface-tailored poly(N-isopropylacrylamide) (PNIPAAm) hydrogel film. Surface-tailoring of PNIPAAm hydrogel was performed by the preparation of the hydrogel as a honeycomb-patterned film using a honeycomb-patterned PS film as a template. The surface morphology and hydrophobic interaction of the patterned hydrogel surface were significantly altered by temperature change of the aqueous solution that came in contact with the gel. The surface of the hydrogel became hydrophobic for adsorption at a higher temperature than the lower critical solution temperature of 32 °C, but became hydrophilic with decreased adsorptivity at lower temperature condition. Adsorptivity was obtained through measuring the concentration of the silver nanoparticles using UV–vis spectroscopy in an aqueous solution. A reversible adsorption–desorption of nanoparticles dependent on the temperature in the hydrogel surface obtained in this study clearly suggested that the hydrophobic interaction was reversibly changed in the patterned temperature-responsive hydrogel surface, similar to various biological systems in nature.     

Radiation synthesis and characterization of polyvinyl alcohol/chitosan/silver nanocomposite membranes: antimicrobial and blood compatibility studies

Polyvinyl alcohol/chitosan/silver (PVA/CS/Ag) nanocomposite membranes were synthesized by γ-radiation with promising antimicrobial and biomedical applications. The nanocomposite membranes were prepared by mixing PVA and CS solutions with different copolymer compositions in the presence of silver nitrate (AgNO₃) and glutaraldehyde as cross-linker, followed by in situ reduction with γ-radiation at different doses. The nanocomposite membranes were characterized by ultraviolet spectroscopy (UV), Fourier transform infrared, X-ray diffraction (XRD) and transmission electron microscopy (TEM). UV studies showed a strong peak around λ _max at 430 nm due to surface plasmon resonance of silver nanoparticles formed during irradiation. As the irradiation dose increased from 25 to 75 kGy, the plasmon band is shifted from 430 to 418 nm with high intensity, indicating the formation of smaller particles. TEM investigation showed uniform distribution of silver nanoparticles (AgNPs) in the membranes with mean diameter of 32–19 nm. XRD results confirmed that the mean diameter of AgNPs estimated from the Debye–Scherrer formula was in the range of 27.5–12.8 nm which confirms the TEM results. The PVA/CS/Ag nanocomposite membranes exhibited good antibacterial activity and were found to cause significant reduction in microbial growth. The nanocomposite membranes showed non-thrombogenicity effect and slightly haemolytic potential, suggesting their promising use in biomedical applications.     

Plant mediated green biosynthesis of silver nanoparticles using Vitex negundo L. extract

In the present study silver nanoparticles (Ag-NPs) were synthesized from aqueous silver nitrate through a biosynthetic route using water extract of Vitex negundo L. extract which acted as a reductant and stabilizer agents, simultaneously. Formations of Ag/V. negundo were determined by UV–vis spectroscopy where surface plasmon absorption maxima can be observed at 423–432 nm. The XRD analysis shows that the Ag-NPs are of face centered cubic structure. TEM images show the well dispersed of Ag-NPs with average particle size less than 20 nm. The FT-IR spectrum indicates the presence of V. negundo in capping with silver nanoparticles.     

Preparation and characterization of smart hydrogel nanocomposites sensitive to oxidation–reduction

Honeycomb-patterned hydrogel films sensitive to environmental oxidation–reduction supporting nanoparticle by adsorption were fabricated through the photopolymerization of ruthenium(4-vinyl-4′-methyl-2,2′-bipyridine)bis(2,2′-bipyridine)bis(hexaflurophosphate) and N-isopropylacrylamide. Nanoparticle adsorption by the hydrogel film was controlled by the dynamic changes in the surface morphology of the film in relation to environmental oxidation–reduction, which induces change of the oxidized and reduced states of ruthenium ion included in the hydrogel. For the adsorption of nanoparticles in the patterned hydrogel film, silver nanoparticles were immobilized in the hydrogel surface. Adsorptivity was obtained through measuring the released concentration of the silver nanoparticles using UV–vis spectroscopy in an aqueous solution. Desorption of Ag nanoparticles from the hydrogel surface was found to be larger in the oxidizing solution than in the reducing solution.