Ag Colloids Research Articles

Unraveling the physiochemical nature of colloidal motion waves among silver colloids.

Traveling waves are common in biological and synthetic systems, including the recent discovery that silver (Ag) colloids form traveling motion waves in H2O2 and under light. Here, we show that this colloidal motion wave is a heterogeneous excitable system. The Ag colloids generate traveling chemical waves via reaction-diffusion, and either self-propel through self-diffusiophoresis (“ballistic waves”) or are advected by diffusio-osmotic flows from gradients of neutral molecules (“swarming waves”). Key results include the experimental observation of traveling waves of OH− with pH-sensitive fluorescent dyes and a Rogers-McCulloch model that qualitatively and quantitatively reproduces the key features of colloidal waves. These results are a step forward in elucidating the Ag-H2O2-light oscillatory system at individual and collective levels. In addition, they pave the way for using colloidal waves either as a platform for studying nonlinear phenomena, or as a tool for colloidal transport and for information transmission in microrobot ensembles.

Synergistic Effect of Field Emission Properties on Growth of CNTs by One-Pot Preparation of Various Concentrations Composite Catalyst

Multi-walled carbon nanotubes (MWCNTs) were grown on Silicon (Si) substrate by using low-pressure chemical vapor deposition (LPCVD) technique where iron (Fe) and silver (Ag) colloidal solution act as a catalyst were prepared by chemical route. The as-prepared solutions in varied concentrations were deposited on a Si substrate using a spin coating process at 700[Formula: see text]rpm. The purpose of Fe in composite catalysts is to have high carbon solubility and diffusion rate, and Ag utilization can change catalyst activity temperature and enhance carbon yields. In this work, we demonstrate the growth of carbon nanotubes (CNTs) on different catalyst concentrations ([Formula: see text]Fe/[Formula: see text]Ag), ([Formula: see text]Fe/[Formula: see text]Ag), ([Formula: see text]Fe/[Formula: see text]Ag) and ([Formula: see text]Fe/[Formula: see text]Ag) catalytic films. Field Emission Scanning Electron Microscopy (FESEM) was used to image the morphologies of various catalyst concentrations MWCNTs. The natures of the synthesized CNTs were determined using Raman spectroscopy and it was revealed that as-prepared CNTs are MWCNTs due to the absence of radial breathing mode (RBM). Raman spectroscopy demonstrated the lower ID/IG ratio (Ratio of the intensity of D-Raman peak and G-Raman peak) of ([Formula: see text]Fe/[Formula: see text]Ag) MWCNTs. The ID/IG ratio for ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs was 0.76, while the ID/IG ratio for ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs was 0.89. The ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs were found to be more defective as compared to other. Electron Emission from ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs were much stronger than from other samples, as demonstrated by Field Emission measurement using diode configuration. The turn-on field for ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs was (0.92 V/[Formula: see text]m) which is slightly lower than that of ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs (1.83 V/[Formula: see text]m), indicating superior enhancement.

Synthesis of Biogenic Silver Nanocatalyst and their Antibacterial and Organic Pollutants Reduction Ability.

Plant-mediated nanoparticles are gaining popularity due to biologically active secondary metabolites that aid in green synthesis. This study describes a simple, environmentally friendly, dependable, and cost-effective production of silver nanoparticles utilizing Cucumis sativus and Aloe vera aqueous leaf extracts. The aqueous leaf extracts of Cucumis sativus and Aloe vera, which worked as a reducing and capping agent, were used to biosynthesize silver nanoparticles (AgNPs). The formation of surface plasmon resonance peaks at 403 and 405 nm corresponds to the formation of colloidal Ag nanoparticles. Similarly, the Bragg reflection peaks in X-ray diffraction patterns observed at 2θ values of 38.01°, 43.98°, 64.24°, and 77.12° representing the planes of [111], [200], [220], and [311] correspond to the face-centered cubic crystal structure of silver nanoparticles. Fourier transform infrared spectroscopy confirms that bioactive chemicals are responsible for the capping of biogenic silver nanoparticles. The size, structure, and morphology of AgNPs with diameters ranging from 8 to 15 nm were examined using transmission electron microscopy. Water contamination by azo dyes and nitrophenols is becoming a more significant threat every day. The catalytic breakdown of organic azo dye methyl orange (MO) and the conversion of para-nitrophenol (PNP) into para-aminophenol using sodium borohydride was evaluated using the prepared biogenic nanoparticles. Our nanoparticles showed excellent reduction ability against PNP and MO with rate constants of 1.51 × 10–3 and 6.03 × 10–4s–1, respectively. The antibacterial activity of the nanomaterials was also tested against four bacteria: Staphylococcus aureus, Klebsiella pneumoniae, Enterobacter, and Streptococcus pneumoniae. These biogenic AgNPs displayed effective catalytic and antibacterial characteristics by reducing MO and PNP and decreasing bacterial growth.

Optical and Structural Study of Biocompatible Silver-Chitosan Colloids

Nontoxic and biocompatible silver-chitosan colloids were prepared by direct chemical reduction. The Ag-chitosan colloids are drop cast on a glass slide and left to dry to obtain uniform, homogeneous films. The presence of chitosan prevented the growth of silver nanoparticles from agglomeration. The occurrence of localized surface plasmon resonance (LSPR) at ~ 400 nm in the optical absorption spectra indicated the formation of Ag nanoparticles which is the characteristic property of metal nanoparticles. The -prepared colloidal Ag nanoparticles are chemically stable and remain colloidal even after aging. The estimated average particle size is about 14nm and the face-centered cubic phase was observed in the XRD pattern. SEM images clearly showed the homogeneous distribution of silver nanoparticles.

Controlling the Shrinkage of 3D Hot Spot Droplets as a Microreactor for Quantitative SERS Detection of Anticancer Drugs in Serum Using a Handheld Raman Spectrometer.

Quantitative measurement is one of the ultimate targets for surface-enhanced Raman spectroscopy (SERS), but it suffers from difficulties in controlling the uniformity of hot spots and placing the target molecules in the hot spot space. Here, a convenient approach of three-phase equilibrium controlling the shrinkage of three-dimensional (3D) hot spot droplets has been demonstrated for the quantitative detection of the anticancer drug 5-fluorouracil (5-FU) in serum using a handheld Raman spectrometer. Droplet shrinkage, triggered by the shaking of aqueous nanoparticle (NP) colloids with immiscible oil chloroform (CHCl3) after the addition of negative ions and acetone, not only brings the nanoparticles in close proximity but can also act as a microreactor to enhance the spatial enrichment capability of the analyte in plasmonic sites and thereby realize simultaneously controlling 3D hot spots and placing target molecules in hot spots. Moreover, the shrinking process of Ag colloid droplets has been investigated using a high-speed camera, an in situ transmission electron microscope (in situ TEM), and a dark-field microscope (DFM), demonstrating the high stability and uniformity of nanoparticles in droplets. The shrunk Ag NP droplets exhibit excellent SERS sensitivity and reproducibility for the quantitative analysis of 5-FU over a large range of 50-1000 ppb. Hence, it is promising for quantitative analysis of complex systems and long-term monitoring of bioreactions.

Distance Learning: Homemade Colloidal Silver

To continue the experimental education of Chemical Engineering students during the SARS-Covid 19 pandemic, our school opted for assembling laboratory kits for each one of them and sending them by courier service to their homes. This arose much interest and was particularly successful in an Electrochemistry and Corrosion elective course, because up to 25 experiments were performed in each of the Fall 2020 and Spring 2021 semesters. By having their kits at home, students were also able to design experiments on their own. One such experiment –the preparation of a colloidal silver solution– only required readily available kit materials and some other home and kitchen items to produce an easily observable Ag colloidal solution. Lower classes (e.g., General Chemistry, High School Chemistry) should be able to reproduce this experiment as well. The entire procedure can be completed in 1 h.

Co-digestive ripening assisted phase-controlled synthesis of Ag-Sn intermetallic nanoparticles and their dye degradation activity.

The Ag-Sn based system in the nano-size regime is one of the strongest candidates for lead-free solders. Besides, the investigation of several other applications of Ag-Sn nanostructures, especially in catalysis, remains scarce which makes it an interesting system to synthesize and explore its chemistry. In this report, nearly monodisperse ε-Ag3Sn intermetallic nanoparticles were prepared by a simple and convenient solution-based process of co-digestive ripening using Ag and Sn colloids obtained by the solvated metal atom dispersion (SMAD) method. Optimization of the temperature and stoichiometric ratio between the metal elements and the use of an appropriate capping agent are crucial factors to realise phase pure intermetallic nanoparticles. Ag3Sn nanoparticles with a size of 3.8 nm ± 0.6 nm were obtained within 12 h of reaction when tri-n-octylphosphine/tri-n-octylphosphine oxide was used as the capping agent at 205 °C. Interestingly, Ag3Sn@SnOx core-shell nanostructures were obtained by changing the capping agent to palmitic acid. These nanostructures were thoroughly characterized by powder X-ray diffraction, transmission electron microscopy (TEM and STEM-EDS), X-ray photoelectron spectroscopy and optical spectroscopy. Thereafter, Ag and Ag3Sn nanoparticles were utilized for photocatalytic degradation of methylene blue, methyl orange and a mixture of both the dyes.

Luminescence of colloidal quantum points Ag-=SUB=-2-=/SUB=-S/SiO-=SUB=-2-=/SUB=-, decorated by small nanoparticles Au

Ten-fold increase in quantum yield of defect luminescence was found in area 750 nm with simultaneuous growth of its attenuation from 4 to 200 ns, caused by decoration of quantum point (QP) Ag 2 S/SiO 2 (5.0±1.5 nm) surface with nanoparticles (NP) Au (2.0±0.5 nm). Based on analysis of luminescence kinetics at 77 and 300 K the conclusion was drawn on non-specific manifestation of plasmon-exiton interaction caused by polarization effects from NP Au at properties of small traps that participate in generation of defect luminescence kinetics of QP Ag 2 S/SiO 2 . Keywords: IR luminescence; luminescence attenuation kinetics; quantum points, plasmon nanoparticles, plasmon-exiton interaction.

Luminescence of colloidal quantum points Ag-=SUB=-2-=/SUB=-S/SiO-=SUB=-2-=/SUB=-, decorated by small nanoparticles Au

Ten-fold increase in quantum yield of defect luminescence was found in area 750 nm with simultaneuous growth of its attenuation from 4 to 200 ns, caused by decoration of quantum point (QP) Ag2S/SiO2 (5.0±1.5 nm) surface with nanoparticles (NP) Au (2.0±0.5 nm). Based on analysis of luminescence kinetics at 77 and 300 K the conclusion was drawn on non-specific manifestation of plasmon-exiton interaction caused by polarization effects from NP Au at properties of small traps that participate in generation of defect luminescence kinetics of QP Ag2S/SiO2. Keywords: IR luminescence; luminescence attenuation kinetics; quantum points, plasmon nanoparticles, plasmon-exiton interaction.

Green synthesis of well-dissolved high-stable silver nanoparticles using hydroxypropylmethyl cellulose as a protective agent

This paper presented the synthesis of Ag nanoparticles (Ag NPs) by the chemical reduction method which is simple and environmentally friendly. Silver nitrate, hydroxypropylmethyl cellulose (HPMC), and glucose were used as silver precursors, protective agents, and reducing agents, respectively. The effects of AgNO3 concentration, glucose concentration, HPMC content, reaction time, and reaction temperature on the formation of Ag NPs were investigated. The properties of Ag NPs were analyzed by transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy, and X-ray diffraction (XRD). The results indicated that when the HPMC content was 0.01%, AgNO3 concentration was 0.05 M and glucose reducing agent concentration was 0.4%, the best reaction occurred in 9 hours at 90oC. The Ag NPs prepared under HPMC protection possessed a face-centered cubic crystal structure (FCC), a spherical shape having average sizes in the range of 8 ‒ 12 nm. The Ag colloidal solution had a suitable zeta potential (-37.21 mV) to maintain the stability and to avoid the agglomeration of Ag NPs. In addition,the paper proposed a method to indirectly determine the Ag NPs content through the separation of Ag NPs from the colloidal solution by coagulation, using the electrolyte Al(NO3)3.9H2O.

Preparation of colloidal Ag nanoparticles

Nanostructures are significant materials because of their size and shape dependent properties. Among these, metal nanostructures have received a lot of attention in recent years because to their ability to tailor digital, optical, optoelectronic and catalytic capabilities by modifying their size, shape, composition, and crystallinity. Silver (Ag) have recently attracted a lot of research attention because to their critical roles in catalysis, organic labelling, optics, and data storage. Herein, we report the preparation of colloidal Ag nanoparticles by chemical precipitation method using chitosan molecules. The optical and structural measurements were studied for as prepared colloidal Ag nanoparticles, are stable, such as optical absorption, photoluminescence (PL), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) indicates that as prepared colloidal Ag nanoparticles are spherical in shape, fluorescent, highly stable. The estimated particle size is 17 nm, the observed phase of the Ag nanoparticles is fcc. The present method of synthesis of colloidal Ag nanoparticles is simple and cost effective.

Luminescent properties of colloidal Ag-=SUB=-2-=/SUB=-S quantum dots for photocatalytic applications

The structural and optical properties of colloidal Ag2S quantum dots in various environments are investigated. With the help of transmission electron microscopy, X-ray diffraction and energy-dispersive X-ray analysis the formation of colloidal Ag2S quantum dots with an average size of 2-3 nm with a monoclinic crystal lattice, and Ag2S/SiO2 core-shell systems based on them, has been established. The change in the luminescence quantum yield of quantum dots with the change of the surface environment state is shown. The decoration of TiO2 nanoparticles of 10-15 nm in size with Ag2S quantum dots was performed and the influence of the structure of the interfaces of quantum dots and their environment (2-mercaptopropionic acid, water, ethylene glycol, SiO2 dielectric shell with a thickness of 0.6 nm and 2.0 nm) on the formation of TiO2-Ag2S heterosystems was analyzed. For Ag2S quantum dots passivated with 2-mercaptopropionic acid, signs of charge phototransfer after adsorption on TiO2 nanoparticles surface have been established. Signs of reactive oxygen species appearance due to charge phototransfer in heterosystem are enstablished, based on methylene blue photobleaching under excitation of heterosystem outside of TiO2 fundamental absorption region, Keywords: Quantum dots, photocatalysis, luminescence, titanium dioxide, silver sulfide.

Luminescent properties of colloidal Ag-=SUB=-2-=/SUB=-S quantum dots for photocatalytic applications

The structural and optical properties of colloidal Ag2S quantum dots in various environments are investigated. With the help of transmission electron microscopy, X-ray diffraction and energy-dispersive X-ray analysis the formation of colloidal Ag2S quantum dots with an average size of 2-3 nm with a monoclinic crystal lattice, and Ag2S/SiO2 core-shell systems based on them, has been established. The change in the luminescence quantum yield of quantum dots with the change of the surface environment state is shown. The decoration of TiO2 nanoparticles of 10-15 nm in size with Ag2S quantum dots was performed and the influence of the structure of the interfaces of quantum dots and their environment (2-mercaptopropionic acid, water, ethylene glycol, SiO2 dielectric shell with a thickness of 0.6 nm and 2.0 nm) on the formation of TiO2-Ag2S heterosystems was analyzed. For Ag2S quantum dots passivated with 2-mercaptopropionic acid, signs of charge phototransfer after adsorption on TiO2 nanoparticles surface have been established. Signs of reactive oxygen species appearance due to charge phototransfer in heterosystem are enstablished, based on methylene blue photobleaching under excitation of heterosystem outside of TiO2 fundamental absorption region, Keywords: Quantum dots, photocatalysis, luminescence, titanium dioxide, silver sulfide.

Sensing the Anti-Epileptic Drug Perampanel with Paper-Based Spinning SERS Substrates.

The applications of SERS in therapeutic drug monitoring, or other fields of analytical chemistry, require the availability of sensitive sensors and experimental approaches that can be implemented in affordable ways. In this contribution, we show the production of cost-effective SERS sensors obtained by depositing Lee-Meisel Ag colloids on filter paper either by natural sedimentation or centrifugation. We have characterized the morphological and plasmonic features of the sensors by optical microscopy, SEM, and UV-Vis spectroscopy. Such sensors can be used to quantify by SERS the anti-epileptic drug Perampanel (in the concentration range 1 × 10−4–5 × 10−6 M) by spinning them during the micro-Raman measurements on the top of a custom device obtained from spare part hard disk drives. This approach minimizes laser-induced heating effects and allows averaging over the spatial non-uniformity of the sensor.

Administration of Silver Nasal Spray Leads to Nanoparticle Accumulation in Rat Brain Tissues.

The use of commercial products containing engineered nanomaterials in realistic scenarios may lead to the accumulation of exogenous particles in brain tissues. In this study, we simulated the use of silver (Ag) nasal spray in humans using Sprague-Dawley rats at 0.04 mg/kg/day. Silver-containing particles were explicitly identified in the rat brain after the administration of nasal sprays containing colloidal Ag or silver ions (Ag+) for 2 weeks using multiple methods. The accumulation of Ag-containing particles showed a delayed effect in different brain regions of the rats, with the mass concentration of particles increasing continuously for 1-2 weeks after the termination of administration. The size of the observed Ag-containing particles extracted from the brain tissues ranged from 18.3 to 120.4 nm. Further characterization by high-resolution transmission electron microscopy with energy-dispersive spectroscopy showed that the nanoparticles comprised both Ag and sulfur (S), with Ag/S atomic ratios of 1.1-7.1, suggesting that Ag-containing particles went through a series of transformations prior to or during their accumulation in the brain. Collectively, these findings provide evidence for the accumulation and transformation of Ag-containing particles in the rat brain, indicating a realistic risk to brain health resulting from the application of Ag-containing commercial products.

Modifications induced in the optical properties of starch by embedded Ag nanoparticles

Bio-degradable polymers such as starch, chitosan, cellulose etc which are extracted from renewable resources are attracting increasing interest in the recent years due to their environmentally friendly nature, low cost and high availability. In the present work, synthesis of colloidal silver nanoparticles and subsequently Ag-starch nanocomposite films were carried out via a green process. For synthesis of Ag nanoparticles water, soluble starch and fructose have been used as solvent, reducing agent and stabilizing agent respectively. The effect of varying concentration of colloidal Ag nanoparticles on the optical and structural properties of starch was investigated. The structural analysis of the nanocomposites was carried out using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). Size of the Ag nanoparticles from TEM micrograph comes out to be 10.75 ± 0.8 nm in the starch matrix. UV-visible absorption was further utilized to ascertain various optical constants like optical energy gap, Urbach’s energy, optical conductivity etc. The optical energy gap of starch decreases from 4.08 eV to 2.21 eV for Ag-starch nanocomposite film containing 0.50 wt% of Ag nanoparticles and the Urbach’s energy increases from 0.77 eV to 1.37 eV. Copyright © 2017 VBRI Press.

Laser-assisted synthesis of Ag–Cu alloy nanoparticles with tunable surface plasmon resonance frequency in presence of external electric field

The present study aimed to synthesize the colloidal Ag–Cu alloy nanoparticles (NPs) in the presence of an external electric field. Synthesis of Ag–Cu alloy NPs is important because of their unique properties for antibacterial and antimicrobial activities. Colloidal Ag and Cu NPs were produced individually with nanosecond pulsed laser ablation in distilled water and were mixed in equal volume. The mixed colloid was postirradiated in the presence of an external DC electric field. The obtained colloidal NPs were characterized using various diagnostic methods. The results of this study demonstrated the long-term stability and oxidation resistance of colloidal Ag–Cu alloy NPs compared to the Ag and Cu NPs. Also, the results of this study showed that the external electric field reduces the average size of alloy NPs, and tune the surface plasmon resonance frequency.

Maximizing the Oxygen Evolution Reaction by Optimizing Ionomer Structure in Anion Exchange Membrane Electrolysis

From fundamental studies of cationic membranes we were able to show that very high anionic conductivities could be achieved in thin robust membranes with controlled water contents. Over the last several years we have further developed these advanced anion exchange membranes (AEMSs) to improve both their chemical and mechanical stability. One of these polymers is being commercialized as the TuffBrane material and we are now deploying this membrane in devices for electrochemical energy conversion or water purification. While there has been a large amount of work to develop electrocatalysts for fuel cells, much of this was optimized using rotating disk electrodes in aqueous solvents. In solid state electrochemical energy conversion devices using polymer electrolytes, the electrolyte is a polymer with a local morphology and chemistry. This has led us to conclude that it is the polymer/catalyst interfaces that must be understood and improved to achieve the maximum performance in these devices. We have used a toolbox of random, di-block, and triblock polymers where the hydrophobic component or block is polycyclooctene, poly isoprene, or their hydrogenated analogues, polyethylene or polymethylbutylene. The hydrophilic component or block is derived from polychloromethylstyrene via quaternization with trimethylamine or methyl pyrrolidine to give the more stable MPRD cation. We have begun our studies using Ag as a model system although our plans are to extend these studies to Ni. Our first studies used commercial Ag colloids as catalyst particles; these studies showed that we could actually change the degree of crystallinity of the polyethylene block in triblock anion exchange polymers and so alter the polymers water uptake. We then extended this work to spin coated thin films on atomically flat silicon wafers or the same substrate with a Ag coating, and where able to show a number of these polymers had very strong vertical alignment using grazing Incident Small Angle X-Ray Scattering. This has led us to show that the cation can dramatically effect the activity of the electro catalyst via its interaction with the catalyst surface. Our work using Ni foam electrodes in separated anode experiments is showing that the same polymers can also dramatically affect the onset potential and Tafel slope for the oxygen evolution reaction in carbonate electrolyte with or without the addition of the Ag colloids. Extending these studies to single cell electrolysis we see interesting effects in both demonized water, carbonate and hydroxide electrolytes. The results of these studies will be discussed in this paper.The work was sponsored by the Army Research Office under grant, W911NF-17-1-0568

Deposition of colloidal metal nanoparticles on zinc oxide nanorods and their influence on visible photoluminescence

We examine the influence of colloidal Au and Ag nanoparticles (NP) on hydrothermally grown ZnO nanorods (NR). Individual 60 nm diameter NP and small NP assemblies without formation of large aggregates were deposited on poly-L-lysine covered NR films using the dip-coating method. The evaluation of morphological and optical properties of the obtained ZnO-metal hybrids was done using scanning electron microscopy, photoluminescence (PL) and diffuse reflection spectroscopy. The presence of Au NP selectively suppressed the PL components near 560 nm wavelength associated with ZnO surface defects, whereas equally sized Ag NP resulted in a much smaller change of PL signal, barely above the noise level. The presented results may be useful for tuning the optical properties of hybrid materials in development of sensor or photovoltaic devices.

Trapping analytes into dynamic hot spots using Tyramine-medicated crosslinking chemistry for designing versatile sensor

HypothesisDue to the intrinsic nature of the surface-enhanced Raman scattering (SERS), the detection of molecules with weak binding affinities toward metal substrates is critical for development of a universal SERS sensing platform. We hypothesized the physical trapping of small pesticide molecules for active hot spot generation using tyramine-mediated crosslinking chemistry and silver nanoparticles (Ag NPs) enhances SERS detection sensitivity. ExperimentsTyramine-mediated crosslinking chemistry for sensor application was validated by ultraviolet–visible absorption spectroscopy, scanning electron microscopy, dynamic light scattering, and Raman spectroscopy. SERS sensing platform using tyramine-mediated crosslinking reaction was systematically studied for detection of 1,4-dyethylnylbenzene as a model analyte. This sensor system was applied to detect two other pesticides, thiabendazole and 1,2,3,5-tetrachlorobenzene, which have different binding affinities toward metal surfaces. FindingsThe SERS signal of 1,4-dyethylnylbenzene obtained using this sensor system was 3.6 times stronger than that obtained using the Ag colloidal due to the nanogap of approximately 1.3 nm within the generated hot spots. This sensor system based on tyramine-mediated crosslinked Ag NPs was evaluated as a promising tool to achieve a solution based sensitive detection of various pesticide molecules that cannot be adsorbed on the surfaces of typical SERS substrates such as metal nanoparticles.