Metallic AgNPs Research Articles

Bio-surfactant mediated sustainable exfoliation of MoS2 and in-situ preparation of Ag@MoS2 nanocomposites for photocatalysis under sunlight in aqueous medium

Exfoliation of MoS2 has been performed in the aqueous solution of bio-based surfactant choline deoxycholate, ([Cho][Doc]), employing low-energy bath sonication. The ability of [Cho]+ to reduce the Ag+ under sunlight accompanied by the templating effect of [Doc]− has been exploited to decorate the exfoliated MoS2 in a single step. The dimensions as well as the extent of adherence of Ag NPs to MoS2 in Ag@MoS2 nanocomposites (NCs) have been controlled by adjusting the concentration of [Cho][Doc]. The prepared NCs have been characterized by UV–vis spectroscopy, atomic force microscopy (AFM), dynamic light scattering (DLS), zeta-potential measurements (ζ-potential), X-ray diffraction (XRD), Raman spectroscopy, X-ray photon spectroscopy (XPS), transmission (TEM) and high-resolution transmission electron microscopy (HR-TEM). The NCs have shown enhancement in photocatalytic activity compared to bare Ag NPs under sunlight in an aqueous medium. It has been observed that the Schottky junction between metallic Ag NPs and semiconductor MoS2 in NCs shows efficient charge separation by generating a continuum-charged region resulting in increased catalytic activity of NCs. The present work is expected to serve as a platform for preparing photocatalytic NCs sustainably employing various other 2D materials.

Trophic transfer of silver nanoparticles shifts metabolism in snails and reduces food safety

Food security and sustainable development of agriculture has been a key challenge for decades. To support this, nanotechnology in the agricultural sectors increases productivity and food security, while leaving complex environmental negative impacts including pollution of the human food chains by nanoparticles. Here we model the effects of silver nanoparticles (Ag-NPs) in a food chain consisting of soil-grown lettuce Lactuca sativa and snail Achatina fulica. Soil-grown lettuce were exposed to sulfurized Ag-NPs via root or metallic Ag-NPs via leaves before fed to snails. We discover an important biomagnification of silver in snails sourced from plant root uptake, with trophic transfer factors of 2.0–5.9 in soft tissues. NPs shifts from original size (55–68 nm) toward much smaller size (17–26 nm) in snails. Trophic transfer of Ag-NPs reprograms the global metabolic profile by down-regulating or up-regulating metabolites for up to 0.25- or 4.20- fold, respectively, relative to the control. These metabolites control osmoregulation, phospholipid, energy, and amino acid metabolism in snails, reflecting molecular pathways of biomagnification and pontential adverse biological effects on lower trophic levels. Consumption of these Ag-NP contaminated snails causes non-carcinogenic effects on human health. Global public health risks decrease by 72% under foliar Ag-NP application in agriculture or through a reduction in the consumption of snails sourced from root application. The latter strategy is at the expense of domestic economic losses in food security of $177.3 and $58.3 million annually for countries such as Nigeria and Cameroon. Foliar Ag-NP application in nano-agriculture has lower hazard quotient risks on public health than root application to ensure global food safety, as brought forward by the United Nations Sustainable Development Goals.

Green Synthesis of Silver Nanoparticles Using Allium cepa var. Aggregatum Natural Extract: Antibacterial and Cytotoxic Properties.

The chemical content of plant excerpts can be efficiently employed to reduce the metal ions to nanoparticles in the one-pot green production method. Here, green production of silver nanoparticles (AC-AgNPs) is performed by means of Allium cepa var. Aggregatum (shallot) extract as a stabilizer and reducer. The shape, size, and morphology of resultant AC-AgNPs are examined by optical spectroscopy analysis such as UV for nucleation and coalescence processes of the AC-AgNPs. Through FTIR functional group is determined and through DLS size is defined, it was confirmed that metallic AgNPs were successfully synthesized through the green synthesis route, and these results agreed well with the results obtained in the XRD pattern along with TEM spectroscopy, where the TEM images confirm the formation of sphere-like nanostructures along with SAED analysis. The chemical characterization is performed with XPS; the obtained molecular species in the materials are determined from the energy profile. Antioxidant activity of AC-AgNPs versus DPPH substrate is carried out. Antibacterial activity is well established against Gram-negative and Gram-positive organisms. Cell viability is accomplished, followed by an MTT assay, and a cytotoxicity assay of AC-AgNPs on MCF—7 cell lines is also carried out. Highlights: (1). This study highlights the eco-friendly synthesis of silver nanoparticles from Allium cepa var. Aggregatum Natural Extract. (2). The synthesized AC-AgNPs were characterized by UV-VIS, FT-IR, XRD, TEM, and XPS. (3). The synthesized nanoparticles were well dispersed in nature and the size range of 35 ± 8 nm. (4). The anti-candidal activity of biosynthesized silver nanoparticles was evaluated against the following Gram-Negative organisms: Escherichia coli (E. coli), and the following Gram-positive organisms: Staphylococcus aureus strains. The biosynthesized AC-AgNPs showed enhanced antiseptic features anti both Gram-positive and negative organisms. (5). Besides, the in vitro cytotoxic outcomes of AC-AgNPs were assessed versus MCF-7 cancerous cells, and the reduction in the feasibility of cancer cells was established via MTT assay, which suggests potential biomedical applications.

Morphologically and hierarchically controlled Ag/Ag2MoO4 microspheres for photocatalytic hydrogen generation

This paper describes the synthesis of a novel spherical-shaped Ag/Ag2MoO4 nanocomposite using phosphomolybdic acid as the initial reaction precursor in a single-step photoreduction process, as well as its application for water-splitting hydrogen production. The formation of interconnected Ag/Ag2MoO4 spheres with an average diameter of 1–2 μm has been revealed by morphological details. The presence of metallic Ag on the surface of Ag2MoO4 with an average particle size of 0.5–1 nm was confirmed by the apparent resolution of transmission electron microscopic images and X-ray photoelectron spectroscopic details. The optical characterization suggested that metallic Ag NPs have an SPR effect. These Ag nanoparticles, when combined with phosphomolybdic acid, increased light absorptivity, resulting in a blueshift in the energy gap. The novel photochemical synthesis method resulted in the disorder–order structure and oxygen vacancies created during preparation for possible suppression of electron-hole recombinations. Under UV–Visible irradiation, the photocatalytic performance of the as-synthesized composite was tested for hydrogen production using ethanol as a sacrificial donor and Pt-as cocatalyst. Metallic Pt deposition on the surface of an Ag/Ag2MoO4 nanocomposite synergistically enhanced electron transport and accelerated proton reduction at an unprecedented rate. Despite the fact that the nanocomposite contains only 0.3% Pt0, the photocatalytic hydrogen production rate reached 0.4 mmol/h/g and remained stable at 0.63 mmol after four cycles of continuous catalytic process.. In 24 h of continuous reaction, total hydrogen evolution of 0.8 mmol was obtained by photocatalytic water splitting reaction with Pt0.3%/Ag/Ag2MoO4 nanocomposite without ethanol replenishment. The manuscript represents a novel synthesis approach for the development of spherical Ag/Ag2MoO4 nanocomposite imparting significant contribution towards practical application PMA based composite for various photocatalytic applications.

<i>Cocculus hirsutus</i> Leaf Assisted Green Synthesis of Ag-Au Bimetallic Nanoparticles and their Antioxidant Properties

Bimetallic nanoparticles (BMNPs) of silver and gold are synthesized by eco- friendly green chemical procedure using leaf extract of Cocculus hirsutus. Under the experimental condition most individual silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) are spherical whereas silver-gold bimetallic nanoparticles (Ag-Au BMNPs) found cloudy and lost their individual shape. Ag-Au BMNPs formed by the co-reduction of Au(III) and Ag(I) ions in aqueous leaves extract solution where the extract act as both reducing and capping agent. NPs were characterized with the help of UV-Vis absorption spectroscopy, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis. UV-Vis spectroscopy exhibit surface plasmon absorption maxima at 435 and 540 nm for AgNPs and AuNPs respectively whereas surface plasmon resonance (SPR) maxima for Au-Ag bimetallic appeared in between the peaks corresponding to pure silver and gold at the same reaction conditions. X-ray diffraction analysis confirmed that crystalline nanoparticles (NPs) are face centered cubic structure. The synthesized bimetallic nanocomposites show stronger scavenging ability, around 67% and 75% on hydroxyl radical and superoxide radicals at the concentration of 400 µg/ml respectively, compared to the mono metallic AgNPs and AuNPs, indicating stronger antioxidant properties of Ag-Au BMNPs.

Effects of extracellular polymeric substances on silver nanoparticle bioaccumulation and toxicity to Triticum aestivum L.

The potential effects of extracellular polymeric substances (EPS) on the behavior and toxicity of silver nanoparticle (Ag-NPs) and silver sulfide nanoparticle (Ag2S-NPs) remains ambiguous. The interaction of EPS from Bacillus subtilis with Ag2S-NPs, metallic Ag-NPs, or ionic Ag, and the associated plant safety had been examined in this study. The biological impacts of Ag-NPs and Ag2S-NPs were Ag form-dependent and highly influenced by microbial EPS. Compared with metallic Ag-NPs, Ag2S-NPs exert inert biological impacts, as revealed by 3.44 times lower Ag bioaccumulation in wheat (Triticum aestivum L.) seedlings and nearly reduce plant biomass when wheat was subjected to 1.0 mg-Ag L−1 of Ag-NPs and Ag2S-NPs with the transfer factors of 151.56–930.87 vs. 12.52–131.81, respectively. These observations were coincident with the low dissolved Ag ([Ag]diss) in the Ag2S-NPs treatment than the Ag-NPs treatment (114.0 vs. 0.0791, μg L−1). Compared with the enhanced toxicity of Ag2S-NPs to wheat, Bacillus subtilis EPS significantly alleviate the phytotoxicity of Ag-NPs, as revealed by the relative root elongation (7.15–45.40% decrease vs. 2.39–11.75% increase), and malondialdehyde (1.47–83.22% increase vs. 8.57–25.25% decrease) and H2O2 (11.27–71.78% increase vs. 5.16–36.67% decrease) contents. These constrasting plant responses of B. subtilis EPS are mainly caused by their complexation property with toxic Ag+ and nutrient elements for wheat stressed by Ag-NPs and Ag2S-NPs, respectively. Our findings highlight the importance of rhizospheric EPS in affecting the biogeochemistry and ecotoxicity of metal nanoparticles including Ag-NPs and Ag2S-NPs in agricultural systems.

Structural, thermal and broadband NIR emission properties of Nd3+/Pr3+/Ag NPs co-doped tellurite glass

Nd3+/Pr3+ co-doped tellurite glasses containing metallic Ag NPs were synthesized by melt-quenching and heat-treating techniques. The amorphous structural nature, fundamental vibrational units and good thermal stability of the prepared tellurite glasses were confirmed by X-ray diffraction (XRD) pattern, Raman spectrum and differential scanning calorimeter (DSC) curve, respectively. The precipitated Ag NPs in a glass matrix with an average diameter ∼5 nm were revealed by transmission electron microscopy (TEM) image, and the radiative property of Nd3+ and Pr3+ ions was evaluated from the absorption spectrum by Judd-Ofelt theory. Under the excitation of 488 nm Xenon lamp, two broadband near-infrared emissions covering 800-1100 nm and 1250-1650 nm ranges were observed from the fluorescence spectrum. The former originated from the transitions of Pr3+:3P1,0→1G4, Pr3+:1D2→3F4,3, Nd3+:4F3/2→4I11/2 and Nd3+:4F3/2→4I9/2, while the latter was contributed by the Pr3+:1G4→3H5, Pr3+:1D2→1G4, Pr3+:3F3→3H4 and Nd3+:4F3/2→4I13/2 transitions. With the introduction of Ag NPs, the emission intensity of two broadband near-infrared emissions was further enhanced, in which the peak emission intensity of 1250-1650 nm band was increased by about 56% and the FWHM is up to 250 nm. The obtained results indicate that Nd3+/Pr3+/Ag NPs co-doped tellurite glass has great potential in realizing ultra-broadband near-infrared emission covering O-, E- and S-bands simultaneously.

Fruit Biowaste Mediated Green Route Approach Silver Nanopartilces - As Antibacterial Material

Environmental free approach or green chemistry synthesis of metallic nanoparticles has become new growing branch of nanobiotehnology. In this present work a simple and environmental free biosynthesis silver nanoparticles (AgNPs) were prepared using Musambi Peels (MPs) aqueous extract as the reducing agent guided by the principles of green chemistry. The fruit waste aqueous extract was challenged with silver nitrate solution for the production of AgNPs in room temperature. The crystalline phase and morphology of AgNPs were determined from UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectra, X-raydiffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS).The UV-Vis spectrum indicated that the surface plasmon broad peak was observed nearby 450 nm throughout the reaction 30min-24h. XRD spectrum revealed that the average size of biowaste mediated AgNPs obtained approximately 46 nm by using the Debye-Scherrer equation. SEM image of AgNPs showed uniformly distributed on the surface of the cell with high agglomeration. EDS analysis revealed that the presence of silver was confirmed from the Ag peaks at 2.8-3.7 keV. In addition, the biowaste mediated AgNPsloaded disk were tested for antibacterial properties against Escherchia coli and Staphylococcus aureus and found that the obtained metallic AgNPs have been good antibacterial material for biological applications.

Soil chloride content influences the response of bacterial but not fungal diversity to silver nanoparticles entering soil via wastewater treatment processing

Silver nanoparticles (NPs) are among the most widely used nanomaterials and are entering soil ecosystems, mainly via biosolids in agriculture. When added directly to soils, metallic Ag-NPs have been shown to affect microbial communities, which underpin important ecosystem functions. During wastewater treatment processing, metallic Ag-NPs are rapidly converted to Ag2S, which is relatively insoluble and less toxic. Furthermore, recent evidence indicates that silver bioavailability is influenced by soil chloride content. Hence there is a need to understand how Ag2S, which forms from Ag-NPs during wastewater treatment, influences soil microbial diversity at varying salinity. In this study, after adding Ag-NPs to sludge (with most converted to Ag2S), we then applied the sludge to soil and examined how salinity influences the effects of 0 mg, 1 mg and 10 mg kg−1 Ag on bacterial and fungal diversity over time. Using high-throughput phylogenetic marker gene sequencing of 16S rRNA gene and ITS2 amplicons, we demonstrate that, despite being theoretically less toxic, wastewater treatment processed Ag-NPs can affect the composition of soil bacterial and fungal communities, and influence bacterial alpha diversity. In addition, we found that silver-associated changes in bacterial community composition were affected by soil chloride content, with more acute responses to silver being observed in more saline soils. This work highlights that the release of Ag-NPs and their conversion into Ag2S prior to addition to soils via realistic exposure pathways can alter microbial diversity and that these effects may be influenced by soil chloride content.

Optimization of Enterobacter cloacae mediated synthesis of extracellular silver nanoparticles by response surface methodology and their characterization

Synthesis of silver nanoparticles (AgNPs) with desired physicochemical properties using a cost-effective, energy, and time efficient way is vital. In this study, we have optimized the synthesis of AgNPs through protein containing cell-free supernatant of Enterobacter cloacae (SMP1). 23 full factorial central composite design (CCD) of the response surface methodology (RSM) was used for the process optimization. Individual and mutual interaction effects of the experimental variables including temperature, pH, inoculum size, and metal concentration were investigated on the synthesis of AgNPs. Results showed the involvement of 15 kDa protein in the synthesis of AgNPs. The optimized values of pH, temperature, cell-free culture supernatant (CFCS), and metal concentration were 10, 37 °C, 10% (v/v) and 2 mM, respectively. Characterization of AgNPs using UV-Vis spectroscopy reveals surface plasmon resonance peak at 450 nm. AFM and TEM micrographs revealed oval and spherical shaped AgNPs with the size of spherical (15–44 nm) and oval (20–46 nm wide and 240–325 nm long) and zeta potential of −41.3 mV under different experimental conditions. The EDS, X-ray elemental mapping, and FTIR reviled the presence of metallic AgNPs and signatures for nitrogen, carbon, oxygen, sulfur, and functional groups of different biomolecules.

Discerning the Sources of Silver Nanoparticle in a Terrestrial Food Chain by Stable Isotope Tracer Technique.

The increasing use of silver-containing nanoparticles (NPs) in commercial products has led to NP accumulation in the environment and potentially in food webs. Identifying the uptake pathways of different chemical species of NPs, such as Ag2S-NP and metallic AgNPs, into plants is important to understanding their entry into food chains. In this study, soybean Glycine max L. was hydroponically exposed to Ag2S-NPs via their roots (10-50 mg L-1) and stable-isotope-enriched 109AgNPs via their leaves [7.9 μg (g fresh weight)-1]. Less than 29% of Ag in treated leaves (in direct contact with 109AgNP) was accumulated from root uptake of Ag2S-NPs, whereas almost all of the Ag in soybean roots and untreated leaves sourced from Ag2S-NPs. Therefore, Ag2S-NPs are phytoavailable and translocate upward. During trophic transfer the Ag isotope signature was preserved, indicating that accumulated Ag in snails most likely originated from Ag2S-NPs. On average, 78% of the Ag in the untreated leaves was assimilated by snails, reinforcing the considerable trophic availability of Ag2S-NPs via root uptake. By highlighting the importance of root uptake of Ag2S-NPs in plant uptake and trophic transfer to herbivores, our study advances current understanding of the biogeochemical fate of Ag-containing NPs in the terrestrial environment.

In vivo comparisons of silver nanoparticle and silver ion transport after intranasal delivery in mice

Silver nanoparticles (AgNPs) are widely available as consumer goods, and over-the-counter or nutraceutical products used for alleged therapeutic and antibacterial properties. Among these products, AgNP topical therapy is proposed for treating patients with upper airway bacterial rhinosinusitis. While silver ion release from AgNPs in biological systems is well known, limited investigations actually characterize this silver ion release and their subsequent biological effects distinct from delivered particulate metallic silver. This is in part due to the analytical complexity and difficulty involved in distinguishing silver ion release from metallic AgNPs in biological media. Therefore, this study compared intranasal administration of AgNPs versus soluble silver ion (AgNO3) control to examine their transport and biological differences in tissues. First, we compared bactericidal activities of AgNPs and AgNO3 in those bacteria commonly associated with clinical rhinosinusitis in vitro. Next, we evaluated silver residence time in the sinus cavity after intranasal delivery of AgNPs and AgNO3 to mice, and characterized tissue distribution of silver in the sinonasal mucosal epithelium. We found that AgNPs show reduced bactericidal activity compared to AgNO3 (i.e., MBC of 15ppm compared to 5ppm), and significantly lower residence times in the sinus cavity (AgNP concentrations of 3.76ppm after 3h compared to 9ppm for AgNO3). AgNPs were not readily taken up into or through respiratory epithelium, with very low silver levels found in blood and no detectable silver measured in the olfactory bulb and brain. Results indicate that limited tissue distribution of silver detected from AgNPs is due to AgNP dissolution to silver ion. AgNPs therefore demonstrate adequate safety through limited penetration and absorption, but limited potential therapeutic efficacy as antimicrobials in nasal applications, as concentrations of silver in the sinus cavity drop below the minimum bactericidal concentration within 3h.

Green synthesis of Ag nanoparticles in montmorillonite

The Ag-MMT nanocomposite, was formed from AgNO3/MMT suspension. AgNO3 and Urtica dioica leaf extract were used as a silver precursor and reducing agent, respectively. The nanocomposite was characterized by x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and UV–vis spectroscopy. The XRD showed the intercalation of Ag nanoparticles (Ag NPs) into the clay interlayer space. The UV–vis indicated a strong surface plasmon resonance (SPR) absorption band in the UV region, resulting from metallic Ag NPs. The intensity of the SPR band increased with time in the AgNO3/MMT suspension. But the result was opposite in case of Ag+ solution. The stability of Ag NPs in MMT was more than the stability without support. These results showed that Ag NPs can be used as effective growth inhibitors in different biological systems.

Synthesis and application of silver nanoparticles loaded on modified montorillonite

Na+montmorillonite (MMT) was modified with L-cystine, polyvinylpyrrolidone or mercaptoacetic acid and then silver (Ag) was loaded on the modified MMTs via ion-exchange reaction under microwave irradiation for 4 min, and finally the Ag ions were turned to Ag nanoparticles (Ag NPs) under the irradiation of an ultraviolet lamp. The Ag-loaded L-cystine-modified MMT (Ag@AA-MMT) with an Ag content of 10.93 wt% was the highest of all, suggesting the distinct advantage of microwave-assisted ion-exchange reaction on a modified MMT. X-ray photoelectron spectroscopy confirmed the successful loading of silver and the strong interaction between sulphur and Ag. Scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy and X-ray diffraction patterns proved the existence and formation mechanism of metallic Ag NPs. The Ag-loaded modified MMT has shown a slow release property and good thermal stability owing to the shielding effect of the MMT layers. The Ag@AA-MMT, showing a very excellent antibacterial property and catalytic activity, exhibited a wide range of potential applications.

Silver sulfide nanoparticles (Ag2S-NPs) are taken up by plants and are phytotoxic

Silver nanoparticles (NPs) are used in more consumer products than any other nanomaterial and their release into the environment is unavoidable. Of primary concern is the wastewater stream in which most silver NPs are transformed to silver sulfide NPs (Ag2S-NPs) before being applied to agricultural soils within biosolids. While Ag2S-NPs are assumed to be biologically inert, nothing is known of their effects on terrestrial plants. The phytotoxicity of Ag and its accumulation was examined in short-term (24 h) and longer-term (2-week) solution culture experiments with cowpea (Vigna unguiculata L. Walp.) and wheat (Triticum aestivum L.) exposed to Ag2S-NPs (0–20 mg Ag L−1), metallic Ag-NPs (0–1.6 mg Ag L−1), or ionic Ag (AgNO3; 0–0.086 mg Ag L−1). Although not inducing any effects during 24-h exposure, Ag2S-NPs reduced growth by up to 52% over a 2-week period. This toxicity did not result from their dissolution and release of toxic Ag+ in the rooting medium, with soluble Ag concentrations remaining below 0.001 mg Ag L−1. Rather, Ag accumulated as Ag2S in the root and shoot tissues when plants were exposed to Ag2S-NPs, consistent with their direct uptake. Importantly, this differed from the form of Ag present in tissues of plants exposed to AgNO3. For the first time, our findings have shown that Ag2S-NPs exert toxic effects through their direct accumulation in terrestrial plant tissues. These findings need to be considered to ensure high yield of food crops, and to avoid increasing Ag in the food chain.

Phytofabrication of biomolecule-coated metallic silver nanoparticles using leaf extracts of in vitro-raised bamboo species and its anticancer activity against human PC3 cell lines

The present study describes the biosynthesis of metallic silver nanoparticles (AgNPs) from silver ions using in vitro-grown leaf samples of Bambusa arundinacea (Ba) and Bambusa nutans (Bn) and their anticancer activity against human prostatic cancer cell lines (PC3). The metallic AgNPs were synthesized at room temperature by treating the leaf extracts of Bambusa arundinacea and Bambusa nutans with 2 mM silver nitrate using the boiled method. The characterization of synthesized BaAgNPs and BnAgNPs was performed using UV-Vis spectrum (absorption peak at 365 nm), FTIR, TEM (spherical shape), SEM (size of 30-90 nm), and EDX analysis. Cell viability assays were carried out to determine the cytotoxicity effect of AgNPs on the PC3 cancer cell line and the Vero normal cell line. The IC_50 values for BaAgNP- and BnAgNP-treated PC3 cancer cells were found to be 73.57 µg/mL and 84.88 µg/mL while the values for treated Vero cells were found to be 93.58 µg/mL and 96.41 µg/mL, respectively. The percentages of the apoptotic bodies by AO/EtBr staining were found to be 76% and 62% for BaAgNPs and BnAgNPs, respectively. The results strongly suggest that synthesized BaAgNPs show potential anticancer activity against human PC3 cell lines compared to BnAgNPs.

Trioctylphosphine and oleylamine induced thermoelectric power of Ag nanoparticles

In the present study Ag nanoparticles (NPs) of average particle size of 31-51 nm were prepared by the thermal decomposition method in the presence of appropriate concentration of Trioctylphosphine (TOP) and Oleylamine (OA). The X-ray diffraction measurements indicate the occurrence of face-centered cubic metallic Ag-NPs. The compacted pellets of these nanoparticles were investigated using thermoelectric power in the temperature range from 5 to 300 K. The observed thermoelectric power for all the samples are typical of a good metal and are found to be strongly dependent on grain size and the type of cappant used. The magnitude of thermo electric power increases as the particle size decreases. These results clearly indicate dominant role of disorder at grain boundaries and quantum confinement, which influence scattering of phonons and electrons in a significant way.

Photochemical decoration of silver nanoparticles on graphene oxide nanosheets and their optical characterization

Nanohybrid materials based on silver nanoparticles (Ag-NPs) and graphene oxide (GO) are attracting considerable research interest because of their potential many applications including surface-enhanced Raman scattering, catalysis, sensors, biomedicine and antimicrobials. In this study, we established a simple and effective method of preparing a finely dispersed Ag-GO aqueous solution using modified Hummer and photochemical technique. The Ag-NPs formation on GO nanosheets was analyzed by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. The average size of Ag-NPs on the GO nanosheets was approximately 6–7nm with nearly uniform size distribution. The Ag-GO nanohybrid also exhibits an adsorption band at 435nm because of the presence of Ag-NPs on the GO nanosheets. Photoluminescence emission of the Ag-GO nanohybrid was found at 400 and 530nm, which can be attributed to the interaction between the luminescence of exploited GO nanosheets and localized surface plasmon resonance from metallic Ag-NPs. The observed excellent optical properties of the as-prepared Ag-GO nanohybrid showed a significant potential for optoelectronics applications.

One-step/one-pot decoration of oxide microparticles with silver nanoparticles

HypothesisHeterogeneous nucleation of silver oxide (Ag2O) onto oxide microparticles (OMPs) followed by spontaneous thermal decomposition produce nanostructures made of OMPs decorated with silver nanoparticles (OMP|AgNPs). ExperimentsColloidal chemistry methods have been used to produce the decoration of OMPs with silver nanoparticles (AgNPs), by carrying out the Ag2O precipitation/thermal decomposition. The process is driven in water enriched acetone medium containing NaOH, NH3, AgNO3 and SiO2MPs as substrate. Optical and morphological properties of OMP|AgNPs were characterized by using STEM, EDS, HRTEM and Raman spectroscopy. FindingsA new synthetic method to decorate OMPs (TiO2, SiO2) with metallic AgNPs in a single step/single pot reaction is proven effective to produce OMP|AgNPs either in aqueous or water enriched media.

Ag/lamellar hosts composites: a route to morphology-controllable synthesis of Ag nanoparticles

An easy and novel routine are reported for the preparation of metallic silver nanoparticles (AgNPs) with controlled morphology, using Na+–magadiite swelled with hexadecyltrimethylammonium bromide (CTA+–magadiite) and a layered aluminophosphate with kanemite-type structure modified with n-dodecylammonium and n-butylammonium (but,dod-AlPO-kan) as hosts. For the preparation of the metallic AgNPs (Ag0) in the interlamellar space, the CTA+–magadiite and but,dod-AlPO-kan hosts were dispersed in N,N-dimethylformamide (DMF) solution with different AgNO3 concentrations. DMF acts as reducing agent of Ag+ ions leading to nanoparticles with disk-like morphology of magadiite silicate; these were characterized by TEM and UV–Vis spectroscopy. On the other hand, the AgNPs are intercalated in but,dod-AlPO-kan showing spherical-like morphology. The UV–Vis spectra of the nanocomposites based on Ag0 and magadiite silicate show bands at 565 nm that can be attributed to Ag0 nanodisks. The Ag-but,dod-AlPO-kan-based nanocomposites present a band at 422 nm attributed to the surface plasmon resonance of Ag0 nanospheres. The results of transmission electron microscopy agree very well with XRD and UV–Vis analysis, indicating the formation of AgNPs with different morphologies using the two kinds of lamellar materials. The magadiite host has an important role in the synthesis of Ag nanodisks, because it controls the growth of nanoparticles inside the interlayer region with disk-like morphology due the high interlayer interactions of the silicate, leading to the growth of nanoparticles in only two directions (xy plane). On the other hand, when but,dod-AlPO-kan is used a sphere-like morphology is preferred due the best accommodation of AgNPs between the layers of aluminophosphate host.