γ-Ray synthesis of starch-stabilized silver nanoparticles with antibacterial activities

Silver nanoparticles (Ag NPs) are fabricated through γ-irradiation reduction of silver ions in aqueous starch solutions. The UV–vis analyses show smaller sizes of Ag NPs produced, with higher yields, as the irradiation doses and/or Ag⁺ concentrations are increased. Higher concentrations of starch enhance the yields of Ag NPs, with no significant effects on their size. The most economical Ag NPs are produced at 5 kGy γ-irradiation of a 2×10⁻³ M solution of AgNO₃ containing 0.5% starch. They show a relatively narrow size distribution, indicated by TEM and its corresponding size distribution histogram. The XRD pattern confirms the face-centered cubic (fcc) Ag NPs embedded in starch molecules. Interactions between these nanoparticle surfaces and starch oxygen atoms are indicated by FT–IR. Antibacterial activities of Ag NPs against Escherichia coli appear dependent on the γ-ray doses applied.     

Photocatalytic property of surface-modified TiO<Subscript>2</Subscript> nanobelts under visible light irradiation

A novel plasmonic photocatalyst, i.e., acid-etched TiO₂ nanobelts attached with Ag/AgI nanoparticles (NPs) was prepared by deposition–precipitation-photoreduction method. Such surface-modified nanobelts had larger area than the normal one. Ag NPs were formed from AgI by photo-reduction under Xenon lamp irradiation. X-ray diffraction, scanning electron microscopy analysis, UV–Vis diffuse reflectance spectra and fluorescence spectra were used to characterize the structure and optical properties of the sample. The obtained sample exhibited strong photodegradation of methyl orange (MO) under visible light irradiation, which were attributed to both the surface plasmon resonance of Ag NPs and the visible light actived AgI. The photodegradation was accomplished by the transfer of photoexcited electrons from the Ag NPs to the acid-etched TiO₂ nanobelts. After four cycles of photodegradation the photocatalyst was still stable. This novel photocatalyst had a high potential application in wastewater-treatment and biomedical engineering.     

Using a photochemical method and chitosan to prepare surface-enhanced Raman scattering–active silver nanoparticles

In this paper, we report a new strategy for the preparation of surface-enhanced Raman scattering (SERS)-active silver nanoparticles (Ag NPs), using a photochemical method and the presence of chitosan (Ch). First, Ag substrates were subjected to electrochemical oxidation/reduction cycles (ORCs) in deoxygenated aqueous solutions containing 0.1 M HNO₃ and 1 g L⁻¹ Ch (pH 6.9, adjusted by adding 1 M NaOH), resulting in Ag⁺–Ch complexes. These substrates were then irradiated with UV light at various wavelengths to yield the SERS-active Ag NPs. A stronger SERS effect was observed on the SERS-active Ag NPs prepared by using UV irradiation at 310 nm. The pH of the solution and the presence of Ch during the preparation process both affected the resulting SERS activities.     

Metallogel Template Fabrication of pH‐Responsive Copolymer Nanowires Loaded with Silver Nanoparticles and Their Photocatalytic Degradation of Methylene Blue

Poly(N,N′‐methylenebisacrylamide–4‐vinylpyridine) (P(MBA‐4VP)) nanowires loaded with silver nanoparticles (Ag NPs) have been fabricated by silver metallogel template copolymerization, and subsequently, silver ions are reduced instead of the template being removed. Ag NPs with a diameter of 5–15 nm were dispersed throughout the core of P(MBA‐4VP) nanowires. The size and distribution of the formed Ag NPs could be finely controlled by reduction time. The pH sensitivity of P(MBA‐4VP) nanowires offers the possibility of Ag NP release from the nanowires under acidic conditions. The photocatalytic performance of the P(MBA‐4VP) nanowires loaded with Ag NPs was evaluated for the degradation of methylene blue (MB) under UV light irradiation. Their rate of degradation is dependent on the content and size of the Ag NPs, as well as the pH values of the MB solution. Moreover, the P(MBA‐4VP) nanowires loaded with Ag NPs exhibited high photostability, and the photocatalytic efficiency reduced by only 1.81 % after being used three times.     

Cellulose/silver nanoparticles composite microspheres: eco-friendly synthesis and catalytic application

Cellulose/silver nanoparticles (Ag NPs) composites were prepared and their catalytic performance was evaluated. Porous cellulose microspheres, fabricated from NaOH/thiourea aqueous solution by a sol–gel transition processing, were served as supports for Ag NPs synthesis by an eco-friendly hydrothermal method. The regenerated cellulose microspheres were designed as reducing reagent for hydrothermal reduction and also micro-reactors for controlling growth of Ag NPs. The structure and properties of obtained composite microspheres were characterized by Optical microscopy, UV–visible spectroscopy, WXRD, SEM, TEM and TG. The results indicated that Ag NPs were integrated successfully and dispersed uniformly in the cellulose matrix. Their size (8.3–18.6?nm), size distribution (3.4–7.7?nm), and content (1.1–4.9?wt%) were tunable by tailoring of the initial concentration of AgNO₃. Moreover, the shape, integrity and thermal stability were firmly preserved for the obtained composite microspheres. The catalytic performance of the as-prepared cellulose/Ag composite microspheres was examined through a model reaction of 4-nitrophenol reduction in the presence of NaBH₄. The composites microspheres exhibited good catalytic activity, which is much high than that of hydrogel/Ag NPs composites and comparable with polymer core–shell particles loading Ag NPs.     

Multifunctional PES fabrics modified with colloidal Ag and TiO2 nanoparticles

This study is aimed to highlight the possibility of engineering the multifunctional textile nanocomposite material based on the polyester (PES) fabric modified with colloidal Ag and TiO₂ nanoparticles (NPs). The effects of concentration of NPs as well as the order of Ag and TiO₂ NPs loading on antimicrobial, UV protective, and photocatalytic properties of PES fabrics were examined. The antimicrobial activity of differently modified PES fabrics was tested against Gram‐negative bacterium Escherichia coli, Gram‐positive bacterium Staphylococcus aureus, and fungus Candida albicans. The concentration of Ag colloid and the order of Ag and TiO₂ NPs loading considerably affected the antimicrobial efficiency of PES fabrics. The fabrics provided maximum UV protection upon surface modification with Ag and TiO₂ NPs. Ag NPs enhanced Ag NPs enhanced the photodegradation activity of TiO₂ NPs and total photodegradation of methylene blue was achieved after 24 hr of UV illumination. Copyright © 2010 John Wiley & Sons, Ltd.     

In situ synthesis of Ag nanoparticles in aminocalix[4]arene multilayers

The layer-by-layer (LbL) assembled thin films containing tetraamino-thiacalix[4]arenes (1) and tetraamino-calix[4]arenes (2) were used as nanoreactor to synthesize in situ Ag nanoparticles (Ag NPs). UV–vis spectra and AFM images demonstrate that Ag NPs are included in the (1/Ag NPs)_n and (2/Ag NPs)_n multilayer films. The silver ions are absorbed through cation–π interaction and calix[4]arene-metal ion coordination interaction and are reduced into Ag NPs by calix[4]arenes. TEM images indicated that Ag NPs within aminocalix[4]arene multilayers were highly dispersed and uniform. Moreover, the mean size of Ag NPs is smaller than 10 nm.     

Preparation of photocrosslinked sol‐gel composites based on urethane‐acrylic matrix,silsesquioxane sequences,TiO2, and Ag/Au Nanoparticles for use in photocatalytic applications

An acid urethane oligodimethacrylate based on poly(ethylene glycol) was synthesized and used in the preparation of hybrid composites containing silsesquioxane sequences and titania domains formed through sol‐gel reactions along with silver/gold nanoparticles (Ag/Au NPs) in situ photogenerated during the UV‐curing process. The photopolymerization kinetics studied by Fourier transform infrared spectroscopy and photoDSC showed that the photoreactivity of the investigated formulations depends on the amount of titanium butoxide (5–20 wt %) added in the system subjected to UV irradiation. The introduction of 1 wt % AgNO₃/AuBr₃ in formulations slightly improved the degree of conversion but diminished the polymerization rates. The formation of hybrid materials comprising predominantly amorphous TiO₂/SiO₂ NPs, with or without Ag/Au NPs, was confirmed through specific analyses. The evaluation of photocatalytic activity demonstrated that the synthesized hybrid films are suitable for the complete removal of organic pollutants (phenolic compounds) from water under UV irradiation (200–350 min) at low intensity (found in the solar radiation). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1189–1204     

A Blinking Mesoporous TiO2−x Composed of Nanosized Anatase with Unusually Long‐Lived Trapped Charge Carriers

A mesoporous TiO_2?x material comprised of small, crystalline, vacancy‐rich anatase nanoparticles (NPs) shows unique optical, thermal, and electronic properties. It is synthesized using polymer‐derived mesoporous carbon (PDMC) as a template. The PDMC pores serve as physical barriers during the condensation and pyrolysis of a titania precursor, preventing the titania NPs from growing beyond 10 nm in size. Unlike most titania nanomaterials, during pyrolysis the NPs undergo no transition from the anatase to rutile phase and they become catalytically active reduced TiO_2?x. When exposed to a slow electron beam, the NPs exhibit a charge/discharge behavior, lighting up and fading away for an average period of 15 s for an extended period of time. The NPs also show a 50 nm red‐shift in their UV/Vis absorption and long‐lived charge carriers (electrons and holes) at room temperature in the dark, even long after UV irradiation. The NPs as photocatalysts show a good activity for CO₂ reduction.     

A Blinking Mesoporous TiO2−x Composed of Nanosized Anatase with Unusually Long-Lived Trapped Charge Carriers

A mesoporous TiO_2−x material comprised of small, crystalline, vacancy-rich anatase nanoparticles (NPs) shows unique optical, thermal, and electronic properties. It is synthesized using polymer-derived mesoporous carbon (PDMC) as a template. The PDMC pores serve as physical barriers during the condensation and pyrolysis of a titania precursor, preventing the titania NPs from growing beyond 10 nm in size. Unlike most titania nanomaterials, during pyrolysis the NPs undergo no transition from the anatase to rutile phase and they become catalytically active reduced TiO_2−x. When exposed to a slow electron beam, the NPs exhibit a charge/discharge behavior, lighting up and fading away for an average period of 15 s for an extended period of time. The NPs also show a 50 nm red-shift in their UV/Vis absorption and long-lived charge carriers (electrons and holes) at room temperature in the dark, even long after UV irradiation. The NPs as photocatalysts show a good activity for CO₂ reduction.     

Biosynthesis and characterization of silver nanoparticles using strawberry seed extract and evaluation of their antibacterial and antioxidant activities

Synthesis of nanomaterials is an emerging field due to their fascinating properties for applications in different field and green synthesis offers various advantages versus physical and chemical methods. Herein, green protocol has been adopted for the synthesis of silver nanoparticles (Ag NPs) using seeds extract of strawberry. The Ag NPs were characterized using advanced techniques comprising UV/Vis, XRD, FTIR, SEM, DLS and EDX. The λ_max for the Ag NPs was recorded at 405 nm. The functional groups present in the extract and involved in Ag ions reduction were determined using FTIR analysis. The SEM-EDX analysis confirmed the mono-dispersive nature of Ag NPs along with confirmation of elemental composition. The nanoparticles size distribution was recorded in 50-70 nm range. Bio-fabricated Ag NPs were appraised for antioxidant activity (DPPH with % inhibition 56.61 and ABTS with % inhibition 77.81) and antimicrobial activity, i.e., Escherichia coli, Salmonella typhimurium, Shigella sonnei, Halomonas halophile, Staphylococcus aureus and Bacillus subtilis. It is concluded that these synthesized NPs could probably be applied as potent antibacterial and antioxidant materials.     

Oak gum mediated green synthesis of silver nanoparticles under ultrasonic conditions: Characterization and evaluation of its antioxidant and anti-lung cancer effects

Herein, we represent the bio-synthesis of silver nanoparticles (Ag NPs) employing Oak gum as the green template, an efficient natural and non-toxic reductant and stabilizer based on its phytochemicals by using ultrasonic irradiation. The characterization of as-synthesized Ag NPs was performed through Fourier transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), elemental mapping, UV–Vis and X-ray diffraction (XRD). After the characterization, the synthesized Ag NPs/O. Gum was engaged in biological assays like study of anti-oxidant properties by DPPH mediated free radical scavenging test using MeOH and BHT as reference molecules. Thereafter, on having a significant IC₅₀ value in radical scavenging assay, we extended the bio-application of the desired nanocomposite in anticancer study of A549, Calu6 and H358 human lung cell lines in-vitro through MTT assay. They had very low cell viability and high anti-human lung cancer activities dose-dependently against the cell lines without any cytotoxicity on the normal cell line (MRC-5). The IC₅₀ of Ag NPs/O. Gum was found 161.25, 289.26 and 235.29 µg/mL against A549, Calu6 and H358 cell lines, respectively. Maybe significant anti-human lung cancer potentials of Ag NPs/O. Gum against common lung cancer cell lines are related to their antioxidant activities. So, these results suggest that synthesized Ag NPs/O. Gum as a chemotherapeutic nanomaterial have a suitable anticancer activity against lung cell lines.     

Silver nanoparticles active as surface-enhanced Raman scattering substrates prepared by high energy irradiation

In surface-enhanced Raman scattering (SERS) technique the preparation of metal substrates containing minimum hindrance from impurities is an important issue. The synthesis of silver nanoparticles (Ag NPs) active as SERS substrates and having the above-mentioned advantage, were obtained by electron beam irradiation of Ag⁺ aqueous solutions. Ag⁺ ions were reduced by free radicals radiolytically generated in solution without the addition of chemical reductants or stabilizing agents.The metal colloids were characterised by UV-Vis spectroscopy and scanning electron microscopy, monitoring the nanoparticles’ growth process that depends on the irradiation dose and the initial AgNO₃ concentration. Nanoparticles of long-time stability and with different size and shape, included silver nanocubes, were synthesised by varying the irradiation dose. Different tests on the SERS activity of Ag NPs obtained by electron beam irradiation were performed by using benzenethiol as a probing molecule, achieving a good magnification of the adsorbate Raman bands.     

Preparation and characterization of multi‐walled carbon nanotubes decorated with silver nanoparticles through ultraviolet irradiation reduction

A facile, green and efficient approach was applied to synthesize multi‐walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (MWNT‐Ag) for further potential application. Oxidized MWNTs were decorated with silver nanoparticles (Ag NPs) via a method combining ultraviolet irradiation‐induced reduction and conventional silver mirror reaction without any reducing agent. The obtained product was characterized using various methods. X‐ray diffraction proved that the Ag NPs were synthesized successfully. Moreover, Ag NPs with a diameter of 80 nm, attached onto MWNTs, could be clearly observed in field emission scanning electron microscopy images, which also confirmed Ag NPs. Energy‐dispersive spectroscopy and transmission electron microscopy also indicated the presence of Ag NPs. Furthermore, thermogravimetric analysis was used to measure the content of Ag NPs in MWNT‐Ag, the result indicating that the weight content of Ag NPs was up to 31.88%. UV–visible absorption spectroscopy was adopted to evaluate the dispersion property of MWNT‐Ag. The result illustrated that MWNT‐Ag had a good dispersibility and stability in water. Characterization was also carried out through Fourier transform infrared spectroscopy, Raman spectroscopy and dynamic light scattering analysis.     

Spectrophotometric and physicochemical investigations of Congo,alizarin red dyes and BSA interactions with Au,Ag and Au/Ag mix nanoparticles,and their antimicrobial activities

Individual and mix metal nanoparticles of Ag and Au have been prepared by the reducing method where citrate was used as reducing/stabilizing agent. The prepared NPs were characterized with UV/Visible and transmission electron microscopic (TEM) tools. The characteristic peak in UV/Visible at 525, 444 and 531 nm for Au, Ag and Ag/Au mix NPs respectively, gave primary confirmation of prepared NPs. TEM analysis showed the size of nanoparticles as 44.04, 19.78 and 30.93 nm for Ag, Au and Ag/Au mix NPs respectively. Congo and alizarin red dye interactions studies have been performed with prepared NPs to see the removal of the pollutants from water. Congo dye has shown weaker interaction as compared to alizarin due to structural symmetry. Amongst all, the AgNPs have shown maximum 67% and 75% interactions with Congo red and alizarin respectively due to high negative charges on the surface. The Au, Ag and Au/Ag mix NPs have shown stronger interaction with bovine serum albumin (BSA) protein up to 51, 59, 55% respectively, estimated through UV/Vis and physicochemical analysis. The biological evaluations of the prepared NPs have shown their antibacterial activity against Gram + ve and –ve species showing up to 9 cm zone of inhibition. The BSA interaction and antibacterial activity of NPs reveal the importance of NPs in medicinal field.     

Studies on green synthesized silver nanoparticles using Abelmoschus esculentus (L.) pulp extract having anticancer (in vitro) and antimicrobial applications

Silver nanoparticles (Ag NPs) were successfully synthesized using AgNO₃ via an eco-friendly and simple green route using Abelmoschus esculentus (L.) pulp extract at room temperature. The phytochemicals present in A. esculentus (L.) pulp extract were used both as a reducing and a stabilizing agent for the synthesis of Ag NPs. The stabilization of Ag NPs with phytochemicals was justified using Fourier-transform infrared spectroscopy. The size of the as-synthesized Ag NPs was examined using dynamic light scattering and confirmed by transmission electron microscopy. The crystalline nature of Ag NPs had been identified using X-ray diffraction. The present study demonstrated the efficacy of Ag NPs against Jurkat cells in vitro. Our study also showed that the IC₅₀ dose of Ag NPs leads to the increase in intracellular reactive oxygen species and significantly diminished mitochondrial membrane potential, indicating the effective involvement of apoptosis in cell death. The synthesized Ag NPs also exhibited good antimicrobial activity against different gram class bacteria.     

Eco-friendly synthesis and antibacterial activity of silver nanoparticles reduced by nano-wood materials

Hydrothermal treatment of nano-structured wood, prepared by precision grinding, with cationic silver was found to give silver nanoparticles (Ag NPs) of 2–40-nm size range embedded in the wood tissue. The size and distribution of Ag NPs depended strongly on the starting silver ion concentration and reaction temperature. Higher temperature tended to give larger size and wider distribution. The obtained Ag NPs were characterized using various methods, including high-resolution transmission electron microscopy, UV–visible spectroscopy, and X-ray diffraction. The antibacterial effect of the product against Escherichia coli was evaluated by static and dynamic culture experiments, revealing that the Ag NPs-loaded nano-wood materials have great promise as antimicrobial agents against E. coli.     

Ultrasonic green synthesis of silver nanoparticles mediated by Pectin: Characterization and evaluation of the cytotoxicity,antioxidant, and colorectal carcinoma properties

Regarding applicative, facile, green chemical research, a bio-inspired approach is being reported for the synthesis of Ag nanoparticles by pectin as a natural reducing and stabilizing agent without using any toxic and harmful reagent. The biosynthesized Pectin/Ag NPs were characterized by advanced physicochemical techniques like ultraviolet–visible (UV–Vis), Fourier Transformed Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HR-TEM), Energy Dispersive X-ray spectroscopy (EDX), and X-ray Diffraction (XRD) study. It has been established that pectin-stabilized silver nanoparticles have a spherical shape with a mean diameter from 15 to 20 nm. After that, the biological performance of those biomolecules functionalized Ag NPs was investigated. In the MTT assay, human colorectal carcinoma (HCT-8 [HRT-18], Ramos.2G6.4C10, HT-29, and HCT 116) and normal cell lines (HUVEC) were used to study the cytotoxicity and anticancer potential of human colorectal over the AgNO₃ and Pectin/Ag NPs. The cell viability of Pectin/Ag NPs was very low against human colorectal carcinoma cell lines without any cytotoxicity on the normal (HUVEC) cell line. The best anti-human colorectal carcinoma properties of Pectin/Ag NPs against the above cell lines was in the case of the HCT 116 cell line. The antioxidant properties of the AgNO₃ and Pectin/Ag NPs were calculated against DPPH free radicals. The IC50 of Pectin/Ag NPs was 167 µg/mL. According to the above results, the Pectin/Ag NPs may be administrated to treat human colorectal carcinoma in humans.     

X-ray and UV photoelectron spectroscopy of Ag nanoclusters

The main purpose of the present work is to analyze a series of Ag nanoparticles (NPs) with different size or ligand functionalization by using X-ray photoelectron spectroscopy (XPS) and to identify the differences in the band-shape and energy peak position of photoemission spectra due to the particle dimension. A transmission electron microscopy characterization was performed, to verify the consistency of the results. Three types of samples were prepared starting from AgNO₃ water solution and adding different capping agents. In the first two cases, the formation of NPs was promoted by the reduction of silver ions Ag⁺¹ to metallic Ag⁰ through the addition of sodium borohydride, whereas in the last case, it was triggered by the exposure to UV light. Depending on the size of the NPs, a different physical behavior can be recognized. NPs with diameter of about 5 nm are characterized by the phenomenon of localized surface plasmon resonance (LSPR). The other type of samples having a diameter of about 1.5 nm presents discrete energy levels instead of electronic bands, and in this case, a typical fluorescence phenomenon can be observed. In the latter case, we can refer to such systems as nanoclusters. The XPS analyses were focused on the Ag 3D spectra looking for the possible shifts of the Ag doublet as a function of the particles size. The ultraviolet photoelectron spectroscopy with He II source was used for the investigation of possible changes in the valence band.     

Synthesis,Characterization, and Photocatalytic Properties of Ag/TiO2 Composite Nanofibers Prepared by Electrospinning

Ag nanoparticles (Ag NPs) embedded titanium dioxide (TiO₂) nanofibers were fabricated by colloidal sol process, electrospinning, and calcination technique. Calcination of the electrospun nanofibers were heat treated at 600°C for 180 minutes in air atmosphere. X-ray diffraction patterns exhibited that the anatase phase and silver coexisted in the resulted Ag NPs/TiO₂ nanofibers; transmission electron microscopy demonstrated Ag NPs well spread in the porous microstructure of composite fibers. The prepared nanofibers were utilized as photocatalyst for degradation of methyl orange. The degradation rate of methyl orange dye solution containing Ag/TiO₂ composite nanofibers is 99% only after irradiation for 3 hours. It is proposed that these new Ag NPs/TiO₂ composite nanofibers will have potential application in water pollution treatment.