Superior bactericidal activity of SDS capped silver nanoparticles: Synthesis and characterization

Silver nanoparticles were synthesized through UV photo-reduction of silver nitrate aqueous solution, containing ethanol and sodium dodecyl sulfate (SDS) using an UV digester equipped with high pressure mercury lamp of 500 W. The synthesized nanoparticles were characterized by UV–vis spectroscopy (UV–vis), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima at 418 nm. TEM showed the spherical nanoparticles with size in 23–67 nm (average 45 ± 10 nm). The silver nanoparticles were stable for more than 8 months. The antibacterial activity of these SDS capped silver nanoparticles was tested using Pseudomonas aeruginosa as a model strain for gram-negative bacteria. SDS capped silver nanoparticles exhibit a much higher bactericidal activity compared to silver nanoparticles capped with other capping agents. Even at a low silver nanoparticle concentration of 5 μg/ml, complete inhibition of 10⁷ colony forming units (CFU) was achieved with SDS capped silver nanoparticles. This concentration is much lower than the values reported by other authors. This enhanced bactericidal activity is attributed to much efficient transport of silver nanoparticles by SDS to the outer membrane of cell wall compared to the other capping agents and have a better interaction of nanoparticles with the cell.     

Silver nanoparticles: Ultrasonic wave assisted synthesis, optical characterization and surface area studies

Silver nanoparticles have been successfully synthesized by the sonochemical route using sodium borohydride and sodium citrate as the reducing agents. The effect of the reducing agents on the particle size and morphology has been studied by carrying out the two reactions at the same ultrasound frequency (20 KHz). The strong reducing agent (NaBH₄) produced spherical silver nanoparticles of sizes 10 nm whereas sodium citrate led to much smaller silver nanoparticles of ~ 3 nm diameter. Powder X-ray diffraction studies reveal a high degree of crystallinity and monophasic silver particles. UV-Visible studies show the presence of a surface plasmon band at 405 nm. However the reflectance spectra give a broad band between 340 and 360 nm which is characteristic for the quasi-spherical silver nanoparticles. The specific surface area was found to be 2.6 and 13.1 m²/g and the pore radius was found to be 15.2 and 12.3 Å for silver nanoparticles obtained by the sodium borohydride and sodium citrate reduction respectively.     

Humic acid assisted synthesis of silver nanoparticles and its application to herbicide detection

Silver nanoparticles have been synthesized by reduction of silver nitrate in the presence of humic acids (HA) which acted as capping agents. The HA protected nanoparticles were found to be sensitive to increasing concentrations of sulfurazon-ethyl herbicide in solution which induced a variation in color of the nanoparticles solution from yellow to purple. The effect of the humic acid concentration used in the nanoparticles synthesis was studied by varying the [Ag⁺:HA] ratio content from [1:1] to [1:100]. UV–Vis spectroscopy was used to monitor the extinction spectra of silver nanoparticles after the synthesis and in the herbicide sensing experiments. An average silver nanoparticles size of 5 nm was confirmed by transmission electron microscope (TEM). When exposed to increasing concentration of sulfurazon-ethyl (0, 100, 200, 300, 400, 500 ppm), the solution of nanoparticles was found to changes from yellow color to orange red and purple with increasing herbicide concentration.     

Silver nanoparticles: Large scale solvothermal synthesis and optical properties

Silver nanoparticles have been successfully synthesized by a simple and modified solvothermal method at large scale using ethanol as the refluxing solvent and NaBH₄ as reducing agent. The nanopowder was investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), UV-visible and BET surface area studies. XRD studies reveal the monophasic nature of these highly crystalline silver nanoparticles. Transmission electron microscopic studies show the monodisperse and highly uniform nanoparticles of silver of the particle size of 5 nm, however, the size is found to be 7 nm using dynamic light scattering which is in good agreement with the TEM and X-ray line broadening studies. The surface area was found to be 34.5 m²/g. UV-visible studies show the absorption band at ∼425 nm due to surface plasmon resonance. The percentage yield of silver nanoparticles was found to be as high as 98.5%.     

Syntheses of Mn3O4 and LiMn2O4 nanoparticles by a simple sonochemical method

Mn₃O₄ and LiMn₂O₄ nanoparticles were prepared by a simple sonochemical method which is environmentally benign. First, Mn₃O₄ nanoparticles were prepared by reacting MnCl₂ and NaOH in water at room temperature through a sonochemical method, operated at 20 kHz and 220 W for 20 min. Second, LiOH was coated onto the resulting Mn₃O₄ under the same sonochemical conditions as above. The thickness of coated LiOH on Mn₃O₄ obtained from the reaction ratio of 3:1 between LiOH and Mn₃O₄ was about 4.5–5.5 nm range. Then, by heating those LiOH-coated Mn₃O₄ particles at the relatively low temperature of 300–500 °C for 1 h, they were transformed into phase-pure LiMn₂O₄ nanoparticles of about 50 to 70 nm size in diameter.     

Solid phase preparation of submicron-sized SrTiO3 crystallites from SrO2 nanoparticles and TiO2 powders

Submicron-sized SrTiO₃ crystallites were prepared by a low temperature solid state method. The proposed preparation method involved two simple steps: firstly, SrO₂ nanoparticles of 35–90 nm were precipitated from the reaction of Sr(NO₃)₂ and H₂O₂ in an alkalescent aqueous solution (pH = 8) under the ambient condition; secondly, perovskite phase SrTiO₃ with a minor amount of SrCO₃ impurity were produced by heating the mixture of excessive SrO₂ nanoparticles and commercial TiO₂ powders in air at 700 °C for 10 h, which could be easily washed with 1 mol/l HNO₃ aqueous solution and distilled water to yield pure SrTiO₃ crystallites with the size of about 125–320 nm. The phase, purity and size of the as-obtained product were characterized by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM).     

The preparation of silver sulfide nanoparticles in lamellar liquid crystal and application to lubrication

The silver sulfide (Ag₂S) nanoparticles were prepared by the reaction of AgNO₃ and Na₂S in the lamellar liquid crystal (LLC) formed by Triton X-100, n-C₁₀H₂₁OH and H₂O. The size of the particles is about 2-3 nm. The existence of Ag₂S nanoparticles can improve the lubrication of the lamellar liquid crystal.     

Hydroxy propyl cellulose capped silver nanoparticles produced by simple dialysis process

Silver (Ag) nanoparticles (∼6 nm) were synthesized using a novel dialysis process. Silver nitrate was used as a starting precursor, ethylene glycol as solvent and hydroxy propyl cellulose (HPC) introduced as a capping agent. Different batches of reaction mixtures were prepared with different concentrations of silver nitrate (AgNO₃). After the reduction and aging, these solutions were subjected to ultra-violet visible spectroscopy (UVS). Optimized solution, containing 250 mg AgNO₃ revealed strong plasmon resonance peak at ∼410 nm in the spectrum indicating good colloidal state of Ag nanoparticles in the diluted solution. The optimized solution was subjected to dialysis process to remove any unreacted solvent. UVS of the optimized solution after dialysis showed the plasmon resonance peak shifting to ∼440 nm indicating the reduction of Ag ions into zero-valent Ag. This solution was dried at 80 °C and the resultant HPC capped Ag (HPC/Ag) nanoparticles were studied using transmission electron microscopy (TEM) for their particle size and morphology. The particle size distribution (PSD) analysis of these nanoparticles showed skewed distribution plot with particle size ranging from 3 to 18 nm. The nanoparticles were characterized for phase composition using X-ray diffractrometry (XRD) and Fourier transform infrared spectroscopy (FT-IR).     

Synthesis of Silver Nanoparticles by a Laser–Liquid–Solid Interaction Technique

Silver nanoparticles of high chemical homogeneity have been synthesized by a novel laser–liquid–solid interaction technique from a solution composed of silver nitrate, distilled water, ethylene glycol, and diethylene glycol. Rotating nickel, niobium, stainless steel, and ceramic Al₂O₃ substrates were irradiated using a continuous-wave CO₂ laser and Q-switched Nd–YAG laser ( = 1064 and 532 nm). The silver nanoparticles were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe x-ray microanalysis (EPMA). The shape of silver particles was dependent on the chemical composition and laser parameters. The synthesis mechanism of silver nanoparticles has been proposed to occur primarily at the laser–liquid–substrate interface by a nucleation and growth mechanism.     

Large scale photochemical synthesis of M@TiO<Subscript>2</Subscript> nanocomposites (M = Ag,Pd, Au,Pt) and their optical properties,CO oxidation performance,and antibacterial effect

Well-dispersed M@TiO₂ (M = Ag, Pd, Au, Pt) nanocomposite particles with a diameter of 200–400 nm can be synthesized on a large scale by a clean photochemical route which does not require any additives using spherical rutile nanoparticles as a support. The sizes of Pt, Au, and Pd nanoparticles formed on the surface of TiO₂ particles are about 1 nm, 5 nm, and 5 nm, respectively, and the diameter of Ag nanoparticles is in the range 2–20 nm. Moreover, the noble metal nanoparticles have good dispersity on the particles of the TiO₂ support, resulting in excellent catalytic activities. Complete conversion in catalytic CO oxidation is reached at temperatures as low as 333 and 363 K, respectively, for Pt@TiO₂ and Pd@TiO₂ catalysts. In addition, the antibacterial effects of the as-synthesized TiO₂ nanoparticles, silver nanoparticles, and Au@TiO₂ and Ag@TiO₂ nanocomposites have been tested against Gram-negative Escherichia coli (E. coli) bacteria. The results demonstrate that the presence of the TiO₂ matrix enhances the antibacterial effect of silver nanoparticles, and the growth of E. coli can be completely inhibited even if the concentration of Ag in Ag@TiO₂ nanocomposite is very low (10 μg/mL).      

Palladium infiltration in high surface area microporous silica nanoparticles

Metallic Pd clusters were embedded into a host matrix of microporous SiO₂ nanoparticles via a solution reduction of Pd(NO₃)₂ by hydrazine hydrate. The infiltration of 33 wt.% Pd leads to a 13% porosity loss of SiO₂ nanoparticles, which demonstrated an initial surface area of 748 m²/g. The presence of Pd in the pores was demonstrated by EDS spectroscopy and by X-ray diffraction. The metallic guest species presumably reside in the accessible micropores with an estimated size about 1.3 nm. Hydrogen uptake was measured for Pd-infiltrated SiO₂ nanoparticles. A possible mechanism for the formation of composite nanoparticles is proposed based on electrostatic interaction between Pd²⁺ and SiO₂ nanoparticles.     

Spectroscopic investigations of nanoporous SiO2 impregnated with Ag β-diketonates from supercritical solution of carbon dioxide

Porous materials based on SiO₂ containing nanoparticles of silver (NP Ag) are perspective objects for different medico-biological and optoelectronic applications. In the present work nanoporous glasses Vycor (pore size ∼4 nm) and synthetic opal matrices (OM, void size ∼40 nm) impregnated with β-diketonates of silver (Ag(hfac)COD) via solution of supercritical carbon dioxide were studied. Paramagnetic molecules Cu(hfac)₂ were used as spectroscopic probes permitting to obtain the information about the incorporation of similar organometallic molecules into these matrices. Spectra of absorption and electronic paramagnetic resonance (EPR) in the samples of porous SiO₂ containing Ag(hfac)COD were studied before and after heat treatment in air atmosphere. In both materials impregnated at temperature above 50 °C the absorption band at 420-430 nm (the plasmon resonance (PR) band)) typical for nanoparticles of metallic Ag is observed. This band increases in the intensity at heat treatment or at an increase in temperature of impregnation processing. Features of the formation of the PR band in each case depends on sizes and shape of voids in the samples as well as on conditions of heat treatment. The states of paramagnetic centers formed after Ag(hfac)COD introduction are analyzed.     

Synthesis of silver chromate nanoparticles: Parameter optimization using Taguchi design

The Taguchi method of experimental design is very well suited to improving the production process of synthetic nanoparticles. The current application of the Taguchi method was successful in optimizing the experimental parameters affect on synthesis procedure of silver chromate nanoparticles. Ultrafine silver chromate particles were synthesied by precipitation method using addition of silver ion solution to the chromate reagent. The effect of reaction conditions such as: silver and chromate concentrations, flow rate of reagent addition and temperature on the particle size of synthesized silver chromate particles were investigated. The effect of these factors on the diameter of silver chromate particles were quantitavely evaluated by the analysis of variance (ANOVA). The results showed that silver chromate particles can be synthesized by controlling silver concentration, flow rate and temperature. Finally, the optimum conditions for synthesis of silver chromate particles by this simple and fast method were proposed. The results of ANOVA showed that 0.001 mol/l silver ion concentration, 40 ml/min flow rate for addition of silver reagent to the chromate solution and 0°C temperature are optimum conditions for producing silver chromate particles with 100 ± 33 nm width. On the other hand, the Ag₂CrO₄ nano-superstructures were synthesized by electrosynthesis method. The results showed that Ag₂CrO₄ nanoparticles synthesized by this method have 75 nm average diameter.     

Synthesis of silver nanoparticles from carboxylate precursors under hydrogen pressure

A direct, high yield synthesis for preparing narrow-size silver nanoparticles by decomposition of silver carboxylate precursor under H₂ pressure (3 bars) in solution is reported. The method corresponds to that for nanoparticles synthesised by thermal decomposition of carboxylic acid silver salts, but is faster, reproducible, versatile, and easier to control. Most of carboxylate groups are reprotonated upon the presence of dihydrogen and subsequent reduction of Ag⁺ produces spherical particles of dimensions 4–6 nm. The IR studies indicate that aliphatic carboxylates chemisorb on the nanoparticle surface with the two oxygen atoms coordinated mostly symmetrically and forming bridging bidentate Ag–O bonds. This implies strong interactions between the surfactant and Ag nanoparticle and enhances the stability of Ag colloid. There are some sites yet, probably at vertex or facet atoms of the nanoparticle, which form linkages of chelating bidentate or ionic character. Silver particles can be additionally capped in situ either by aliphatic primary amines or thiols forming mixed carboxylate/amine or carboxylate/thiol protecting monolayer. It is demonstrated that coordination of the second ligand adjusts physicochemical properties of nanoparticles. In the dual passivating system both amine and thiol were found to be tightly bounded to the silver nanoparticle surface.     

Synthesis of titanium dioxide nanoparticles by reactive DC magnetron sputtering

Nanometer-sized titanium dioxide (TiO₂) particles were prepared on carbon substrates by reactive direct-current magnetron sputtering. By performing measurements with high resolution electron microscopes, the mean nanoparticle diameter and the coverage fraction of the substrate by the nanoparticles (NPs) were measured at 19 nm and 30%, respectively. Moreover, electron diffraction analysis showed that the TiO₂ NPs' crystalline structure on the carbon substrate was a mixture of anatase and rutile. Finally, we provided information on the TiO₂ initial growth stage: crystalline NPs were formed after deposition of amorphous nanoparticles on the substrate and heating.     

Comparative antibacterial activity of silver nanoparticles synthesised by biological and chemical routes with pluronic F68 as a stabilising agent

The authors report the comparative antibacterial activity of silver nanoparticles synthesised by biological (using Fusarium oxysporum) and chemical routes in the presence and absence of pluronic F68 as a stabilising agent. The production of silver nanoparticles was evidenced by UV–visible spectra, with absorbance at about 420 nm in the case of both biological and chemical synthesis. X‐ray diffraction pattern confirmed the presence of face‐centred cubic structure (FCC plane). The nanoparticles characterised by transmission and scanning electron microscopy showed spherical silver nanoparticles with size range of 5–40 and 10–70 nm in the case of biologically and chemically synthesised nanoparticles, respectively. Addition of pluronic F68 showed the stabilisation of silver nanoparticles. Antibacterial efficacy of silver nanoparticles demonstrated different inhibitory activity against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Overall, biologically synthesised silver nanoparticles showed higher activity as compared with chemically synthesised nanoparticles. Silver nanoparticles synthesised in the presence of pluronic F68 by the chemical route exhibited synergism in antibacterial activity as compared with those synthesised without pluronic F68. On the contrary, biogenic silver nanoparticles without pluronic F68 showed higher antibacterial potential.Inspec keywords: antibacterial activity, nanofabrication, silver, X‐ray diffraction, biomedical materials, nanomedicine, transmission electron microscopy, scanning electron microscopy, ultraviolet spectra, visible spectra, materials preparation, nanoparticlesOther keywords: pluronic F68, stabilising agent, comparative antibacterial activity, Fusarium oxysporum, UV‐visible spectra, biological synthesis, chemical synthesis, X‐ray diffraction pattern, face‐centred cubic structure, FCC plane, transmission electron microscopy, scanning electron microscopy, spherical silver nanoparticles, antibacterial efficacy, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, synergism, biogenic silver nanoparticles, wavelength 420 nm, size 10 nm to 70 nm, size 5 nm to 40 nm, Ag     

CeF3 nanoparticles: synthesis and characterization

CeF₃ nanoparticles 5-10 nm in size were prepared using the polyol method. CeCl₃ and HF were heated up in ethylene glycol. At a temperature of 180 °C crystalline CeF₃ nanoparticles were formed. The material was washed with ethanol, centrifugated and dried. The particles were characterized by EDX, XRD and TEM.     

Photochemical synthesis and characterization of Ag/TiO2 nanotube composites

TiO₂ nanotubes were fabricated by a hydrothermal method. Silver nanoparticles with diameters around 3–5 nm were loaded onto the surface of TiO₂ nanotubes via a deposition approach followed by a photochemical reduction process under ultraviolet irradiation. Transmission electron microscopy (TEM), N₂ adsorption measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis), and fluorescence spectroscopy (FL) were applied to characterize the as-prepared Ag/TiO₂ nanotube composites. The photocatalytic activity of the as-prepared materials was investigated by photodegrading of methyl orange. The results showed that silver particles were in zero oxidation state and highly dispersed on the surface of TiO₂ nanotubes when the concentration of Ag⁺ was low. The presence of metallic silver can help the electron-hole separation by attracting photoelectrons. The Ag/TiO₂ nanotube composites with a suitable amount of silver showed a further improvement on the photocatalytic activity for degradation of methyl orange in water.     

Reduction, aggregation and physicochemical properties of silver nanoparticles in propan-2-ol:cyclohexane mixtures induced by a high energy electron beam

Radiolytic reduction of silver and gold ions and subsequent formation of their aggregates have been studied in propan-2-ol:cyclohexane mixture using pulse radiolysis technique. The silver sol, produced on irradiation of Ag⁺ solution with a train of electron pulses, has been characterized using XRD and TEM. The size of the particles has been found to be in the range of 30-50 nm. The silver sol emit light with a maximum at 340 nm on irradiation with a high energy electron beam. The intensity of emission has been found to decrease with decrease in concentration of Ag particles. Formation of colloidal gold has also been observed on irradiation of NaAuCl₄ solution in propan-2-ol:cyclohexane by train of electron pulses. The particles so formed are oxidized on exposure to air. No light emission has been observed from Au sol.     

Preparation of linoleic acid-capped silver nanoparticles and their antimicrobial effect

Silver nanoparticles have been prepared through the chemical reduction of silver ions by ethanol using linoleic acid as a stabilising agent. This colloidal solution shows an absorption band in the visible range with an absorption peak at 421 nm. The peaks in the X-ray diffraction (XRD) pattern matches well with the standard values of the face-centred-cubic form of metallic silver. Transmission Electron Microscope (TEM) micrograph shows a nearly uniform distribution of the particles with an average size of 8 nm. This linoleic acid-capped silver nanoparticles show antimicrobial activity against Escherichia coli and Staphylococcus aureus.