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

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

Antimicrobial and anticoagulation activity of silver nanoparticles synthesized from the culture supernatant of Pseudomonas aeruginosa

Here, we describe biosynthesis of silver nanoparticles by reduction of aqueous Ag⁺ ions with the culture supernatant of Pseudomonas aeruginosa. The morphological, physiological, biochemical and molecular level identification of the strain GS1 resembles P. aeruginosa. The nanoparticles synthesized by P. aeruginosa were characterized by UV–vis spectroscopy, dynamic light scattering (DLS) and scanning electron microscopy (SEM). The size-distribution of nanoparticles was determined using a particle-size analyzer and the average particle-size was found to be 80 nm. The biological activities of the synthesized silver nanoparticles like antimicrobial activity were confirmed against Escherichia coli and Staphylococcus aureus and it have stable anti-coagulant effect.     

One-step electrodeposition synthesis of silver-nanoparticle-decorated graphene on indium-tin-oxide for enzymeless hydrogen peroxide detection

Silver-nanoparticles-decorated reduced graphene oxide (rGO) was electrodeposited on indium tin oxide (ITO) by a cyclic voltammetry method. The results of X-ray diffraction, Fourier-transform infrared transmission spectroscopy and Raman spectroscopy confirmed the simultaneous formation of cubic phase silver nanoparticles and reduction of GO through the electrodeposition process. Field emission scanning electron microscope images showed a uniform distribution of nanometer-sized silver nanoparticles with a narrow size distribution on the RGO sheets, which could only be achieved using silver ammonia complex instead of silver nitrate as precursor. The composite deposited on ITO exhibited notable electrocatalytic activity for the reduction of H₂O₂, leading to an enzymeless electrochemical sensor with a fast amperometric response time less than 2 s. The corresponding calibration curve of the current response showed a linear detection range of 0.1–100 mM (R² = 0.9992) while the limit of detection was estimated to be 5 μM.     

Preparation of stable cross-linked enzyme aggregates (CLEAs) of NADH-dependent nitrate reductase and its use for silver nanoparticle synthesis from silver nitrate

The NADH-dependent nitrate reductase from Fusarium oxysporum cell extract was directly immobilized as cross linked enzyme aggregates (CLEAs) and investigated for the synthesis of silver nanoparticles by a reduction of silver nitrate. The effects of precipitant type and cross-linking on activity recovery of enzyme in CLEAs were studied. After aggregation of enzyme with ammonium sulfate followed by cross-linking formed aggregates for 4 h with 8 mM glutaraldehyde, 93% activity recovery was achieved in CLEAs with enhanced thermal stability at 50 °C and 40 °C. Scanning electron microscopy analysis showed that immobilized NADH-dependent nitrate reductase was of spherical structure. CLEAs showed 90% catalytic yield even after 4 cycles of repeated use in silver nanoparticle synthesis at pH 7.2 and temperature 35 °C.     

Direct preparation of silver nanoparticles and thin films in CO2-expanded hexane

Small, uniform and suspended silver nanoparticles were directly prepared in CO₂-expanded hexane by reducing a synthesized metal precursor, silver isostearate, with hydrogen but without introducing additional capping agents. By increasing CO₂ pressure, the suspended silver nanoparticles could be further deposited on a solid substrate to form silver thin film via gas antisolvent and the subsequent supercritical drying processes. The silver thin films prepared by the aforementioned method possessed a uniform thickness of about 150 nm without surface cracking and low electrical resistivity (5.64 × 10⁻⁶ Ω cm) after applying an annealing process. Due to the deposition of nano-sized silver particles, the annealing temperature could be as low as 175 °C that is lower than the softening points of many transparent polymeric substrates used for fabrication of flexible conductive films.     

Stability and thermal conductivity of nanofluids of tin dioxide synthesized via microwave-induced combustion route

SnO₂ nanofluids were prepared by dispersing tin dioxide nanoparticles in deionized (DI) water as a base fluid. 4–5 nm tin dioxide crystals were synthesized via chloride solution combustion synthesis (CSCS) using SnCl₄ and sorbitol as a novel precursor and the fuel, respectively. Ammonium nitrate was also used as the combustion aid. The molar ratio of sorbitol plus ammonium nitrate to SnCl₄ was set at unity; whereas, the molar ratio of sorbitol-to-ammonium nitrate divided by that of stoichiometric value (Φ) was varied in the range of 0.5–1.4 in order to find the optimum values of specific surface area for the CSCS technique. Transition electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and Brunauer–Emmet–Teller (BET) techniques were employed for the characterization of the nanoparticles. Since SnO₂ nanoparticles form clusters within fluids, the fluids were ultrasonicated to improve the dispersion and stability of the nanoparticles. The colloidal stability of the SnO₂ nanofluids was quantitatively characterized by UV–vis spectrophotometric measurements. The results of the UV–vis experiments indicate higher dispersion together with enhanced stability for the nanofluid prepared by SnO₂ nanoparticles synthesized at Φ = 1.0. After 500 h sedimentation time, the relative concentration of the nanofluid with the highest stability is remained at around 77% of the initial concentration of the fluid.A transient hot-wire apparatus was used to measure the thermal conductivities of the nanofluids. In addition, the effects of pH and temperature on the thermal conductivity were also investigated. At 353 K, for the nanofluid prepared by SnO₂ nanoparticles synthesized at Φ = 1.0 at a weight fraction of 0.024%, thermal conductivity is enhanced up to about 8.7%, with an optimal pH = 8.     

Physical properties of V-doped TiO2 nanoparticles synthesized by sonochemical-assisted process

V-doped TiO₂ nanoparticles were synthesized by sonochemical process using titanium isopropoxide as a titanium source, vanadyl acetylacetonate as a dopant source. Sonication was conducted using sonic horn operated at 20 kHz for 20 min until the completely precipitated product was reached. The as-synthesized precipitates with various vanadium dopant (1–5 mol %) were calcined at 500–1000 °C for 4 h. The relevant physical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). The anatase phase TiO₂ nanoparticles can be synthesized by sonochemical process. Post calcinations process results in the anatase-to-rutile phase transformation and the enhancement in crystallinity with increasing temperature. The results also indicate good incorporation of V ions in TiO₂ lattices and significant effect of V dopant on alternation of interplanar spacing of TiO₂.     

Effects of hydrothermal process parameters on the physical,magnetic and thermal properties of Zn0.3Fe2.7O4 nanoparticles for magnetic hyperthermia applications

Effects of hydrothermal temperature and time on physical, magnetic and thermal properties of Zn-substituted magnetite nanoparticles (Zn_0.3Fe_2.7O₄) were assessed. The magnetic nanoparticles were synthesized via citric acid-assisted hydrothermal reduction route at temperatures of 150, 175 and 200 °C for duration of 10, 15 and 20 h. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and specific loss power (SLP) measurements. The results showed that temperature and time of the hydrothermal process both had significant effects on nanoparticles composition and properties. It was observed that at 150 °C, heat generation was insufficient to produce activation energy required for nucleation of Zn_0.3Fe_2.7O₄ spinel nanoparticles, even after a long time. At 175 °C, although temperature was low, but the suitable condition for nucleation of nanoparticles was made and spinel nanoparticles with the size of about 13 nm were formed after 15 h. Nonetheless, since crystallinity and SLP of the nanoparticles was low, they showed weak performance for magnetic hyperthermia. At 200 °C, the required activation energy was provided for nanoparticles nucleation; however, the spinel was oxidized to hematite, resulting in a decrease in thermal and magnetic properties. In overall, the nanoparticles synthesized at 200 °C for 15 h possessed the best characteristics of reasonable purity, saturation magnetization of about 35.9 emu/g and SLP of 18.7 W/g.     

Characterization of silica-coated silver nanoparticles prepared by a reverse micelle and hydrolysis–condensation process

Described herein is the synthesis of individually silica-coated silver nanoparticles using a reverse micelle method followed by hydrolysis and condensation of tetraethoxysilane (TEOS). The size of a silica-coated silver nanoparticle can be controlled by changing the reaction time and the concentration of TEOS. By maintaining the size of a silver nanoparticle as a core particle at around 7 nm, the size of a silica-coated silver nanoparticle increased from 13 to 28 nm as the reaction time increased from 1 to 9 h due to an increase in silica thickness. The size of silica-coated silver nanoparticles also increased from 15 to 22 nm as the TEOS concentration increased from 7.8 to 40 mM. The size of a silica-coated silver nanoparticle can be accurately predicted using the rate of the hydrolysis reaction for TEOS. Neither the dispersion nor the film of silica-coated silver nanoparticles exhibited any peak shifting during surface plasmon resonance (SPR) at around 410 nm, whereas, without silica coating, the SPR peak of Ag film shifted to 466 nm.     

Synthesis of poly(styrene-co-maleimide) and poly(octadecene-co-maleimide) nanoparticles and their utilization in paper coating

Aqueous polymer dispersions comprising of poly(styrene-co-maleimide) (SMI) or poly(octadecene-co-maleimide) (OMI) nanoparticles were synthesized by thermal imidization of the corresponding maleic anhydride copolymer precursors with ammonia using an organic solvent free process. Different reaction parameters such as temperature, time, agitation speed and stirrer geometry, and molar ratio of ammonia-to-anhydride were investigated in order to find optimal conditions. The obtained copolymer nanoparticles exhibited glass transition temperatures (T_g's) between 140 and 170 °C with particle sizes ranging from 50 to 230 nm. The compositional analysis was conducted by recording ¹H NMR and ATR-FTIR spectra. In addition, SMI dispersions were successfully spray dried and analyzed by SEM. Finally, the polymer dispersion's utility as auxiliary organic pigment in paper coating formulations was evaluated.     

Soda-lime glass-coating containing silver nanoparticles on Ti–6Al–4V alloy

The prevention and treatment of post-surgical infections is an ongoing concern. Post-surgical infections often cannot be treated with commercially available antibiotic-loaded bone cement as because higher doses of antibiotics are required. We describe here an approach to prevent implant infection through the use of glass coatings combined with silver nanoparticles deposited by sedimentation and heat-treated at 980 °C on titanium alloys. Silver is nontoxic to the human tissue and has been used as an anti-infective for centuries. The glass/silver coatings are composed of a soda-lime glassy matrix containing silver nanoparticles ranging from 2.6 to 20 wt.%. Optimum firing conditions have been determined for the fabrication of coatings that adhere well to the metal implant. These final coatings do not crack or delaminate. The biocidal activity of these coatings was also investigated. Coatings containing 20 wt.% of silver nanoparticles exhibited excellent biocidal activity (log η > 5) against Gram+, Gram? bacteria, and yeast after 24 h.     

Divalent silver oxide-diatomite hybrids: Synthesis,characterization and antibacterial activity

To produce better antibacterial and low water-soluble submicron powders of divalent silver oxide (AgO), divalent silver oxide-diatomite (AgO-d) hybrids were studied. AgO-d hybrids were prepared by chemical oxidation, using silver nitrate and diatomite as raw materials and potassium persulfate as oxidant. The results show that AgO-d hybrids with AgO weight percentage up to 20.8% are obtained by oxidation of Ag⁺ adsorbing on diatomite in alkaline solution (n(KOH)/n(AgNO₃)=7.5) for 1.5 h at 333.15 K. Products were characterized by laser particle sizer, SEM, XRD, XPS, FT-IR and atomic absorption spectrophotometer (AAS). AgO-d hybrids are composed of tetragonal cristobalite, amorphous silica, monoclinic divalent silver oxide and a few of cubic silver oxide. Element Ag can be released from AgO-d hybrids but the dissolution speed is slow, which is about 3.20×10^?2 mg (L h)^?1. Antibacterial effectiveness of AgO-d hybrids was tested against Staphylococcus aureus (S. aureus ATCC6538) and Escherichia coli (E. coli ATCC8099) by the shake-flask method. Results show that AgO-d hybrids possess excellent antibacterial properties. When the concentration of AgO-d hybrids is 10 mg L^?1 and the contact time with S. aureus and E. coli is 30 min, the bactericidal rates reach up to 99.974% and 99.944%, respectively.     

Biomimetic fabrication of mulberry-like nano-hydroxyapatite with high specific surface area templated by dual-hydrophilic block copolymer

Novel porous and mulberry-like hydroxyapatite (HAp) nanoparticles with three-dimensionally hierarchical microstructures were developed by using the dual-hydrophilic block copolymer poly(methacrylate acid)-b-poly[N-(2-methacryloylxyethyl) pyrrolidone] (PMAA-b-PNMP) as the template. It was found that the morphology and Ca/P ratio of synthesized HAp was highly related to the concentration of block copolymer and solution pH, respectively. The morphological evolution of HAp nanoparticles in different conditions was investigated systematically by scanning electron microscopy (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The possible mechanism of PMAA-b-PNMP assisted mulberry-like HAp formation was also proposed based on the time-dependent TEM results. Attributing to the high specific surface area (SSA) of 119 m² g⁻¹, these mulberry-like HAp nanoparticles exhibited excellent adsorption ability for Congo Red (CR). The maximum adsorption capacity was 467 mg g⁻¹ according to the Langmuir monolayer adsorption model.     

Hydrothermal synthesis of metal nanoparticles using glycerol as a reducing agent

Metal and metal oxide nanoparticles were synthesized using supercritical water (SCW) as a reaction medium and glycerol as a reducing agent at 400 °C and 300 bar. X-ray diffraction (XRD) patterns confirmed that silver, copper and nickel nitrates were reduced to zero-valent metal nanoparticles. On the other hand, cobalt, iron and manganese nitrates were partially reduced into low-valent metal oxides. Scanning electron microscopy (SEM) images showed that the reduced metals and metal oxides were smaller than the metal oxides formed without glycerol. The difference in reduction behavior of elements is explained using their reduction potentials. Glycerol proved to be an effective reducing agent for hydrothermal applications.     

SBA-15-supported ionic liquid compounds containing silver salts: Novel mesoporous π-complexing sorbents for separating polyunsaturated fatty acid methyl esters

Novel π-complexing sorbents were prepared by covalently immobilizing ionic liquids (ILs) onto mesoporous SBA-15 using a one-pot sol–gel process followed by coating these SBA-15-supported IL compounds with silver salts. The mesoporous π-complexing sorbents were characterized by small angle X-ray scattering (SAXS), FTIR, TEM, SEM, nitrogen adsorption desorption isotherm, NMR, and nitrogen elemental analysis. Two advantages were obtained using these novel mesoporous π-complexing sorbents versus the traditional π-complexing sorbents formed by directly anchoring silver salts onto silica gel. (1) Higher extraction capacities were found. The extraction capacity for the polyunsaturated fatty acid methyl ester (PUFAME), methyl all-cis-5,8,11,14,17-eicosapentaenoate (20:5 or EPA), was 195 mg/g sorbent using the mesoporous AgBF₄/SBA-15 · IL · PF₆ sorbent. The capacity decreased to 121 mg/g sorbent with microporous complexing sorbent AgBF₄/SiO₂ · IL · PF₆. (2) Better reusability was also achieved. The supported IL phase immobilized and retained silver salt on SBA-15 due to the interaction between the ionic liquid’s imidazolium cations and silver ions. Eight successive sorption runs with the AgBF₄/SBA-15 · IL · PF₆ sorbent showed a satisfactory reusability. The traditional π-complexing sorbent has a silver salt directly anchored on silica without the supported ionic liquid phase. Higher silver leaching into organic solution occurred from the AgBF₄/SBA-15 sorbent determined by ICP-AES. The combined percentage (wt%) of the omega-3 PUFAMEs: 20:5 and methyl all-cis-4,7,10,13,16,19-docosahexaenoate (22:6 or DHA) stripped from the AgBF₄/SBA-15 · IL · PF₆ by 1-hexene was significantly enriched from 18% in the original cod liver oil to 90.5%.     

Sol–gel synthesis,characterization, and neurotoxicity effect of zinc oxide nanoparticles using gum tragacanth

The use of plant extract in the synthesis of nanomaterials can be a cost effective and eco-friendly approach. In this work we report the “green” and biosynthesis of zinc oxide nanoparticles (ZnO-NPs) using gum tragacanth. Spherical ZnO-NPs were synthesized at different calcination temperatures. Transmission electron microscopy (TEM) imaging showed the formation most of nanoparticles in the size range of below 50 nm. The powder X-ray diffraction (PXRD) analysis revealed wurtzite hexagonal ZnO with preferential orientation in (101) reflection plane. In vitro cytotoxicity studies on neuro2A cells showed a dose dependent toxicity with non-toxic effect of concentration below 2 µg/mL. The synthesized ZnO-NPs using gum tragacanth were found to be comparable to those obtained from conventional reduction methods using hazardous polymers or surfactants and this method can be an excellent alternative for the synthesis of ZnO-NPs using biomaterials.     

Rheology and colloidal structure of silver nanoparticles dispersed in diethylene glycol

Rheological behavior of agglomerated silver nanoparticles (~ 40 nm) suspended in diethylene glycol over a wide range of volumetric solids concentrations (? = 0.11–4.38%) was studied. The nanoparticle suspensions generally exhibited a yield pseudoplastic behavior. Bingham plastic, Herschel–Bulkley and Casson models were used to evaluate the shear stress-shear rate dependency. Analyzing the effect of silver concentrations on the yield stress and viscosity of the suspensions followed an exponential form, revealing an increase in the degree of interparticle interactions with increasing solid concentrations. Fractal dimension (D_f) was estimated from the suspension yield stress and ? dependence, and was determined as D_f = 1.51–1.62 for the flocculated nanoparticle suspensions. This suggested that the suspension structure was probably dominated by the diffusion-limited cluster–cluster aggregation (DLCA) due mostly to the strong attractions involved in the interparticle potentials. Maximum solids concentration of the suspensions was determined to be ?_m = 11%.     

Facile corrosion synthesis and sintering of disperse pure tetragonal zirconia nanoparticles

Disperse pure tetragonal zirconia (t-ZrO₂) nanoparticles smaller than 10 nm are essential for preparation of structural and functional zirconia materials, but syntheses of t-ZrO₂ nanoparticles using inorganic zirconium salts usually result in severe agglomeration. In this paper, we report a hydrothermal corrosion approach for improving the dispersity of t-ZrO₂ nanoparticles synthesized by precipitation using zirconium oxychloride without any surfactants. Disperse pure t-ZrO₂ nanoparticles with average sizes of 4.5 and 6 nm and size distributions of 2–11 and 3–12 nm were obtained by calcining precipitates at 400 °C for 2 h and 500 °C for 0.5 h followed by HCl corrosion at 120 °C for 75 h, respectively. Disperse t-ZrO₂ nanoparticles with an average size of 6 nm and a size distribution of 3–12 nm were pressed into green compacts at 500 MPa and sintered by two-step sintering (heating to 1150 °C without hold and decreasing to 1000 °C with a 10 h hold). The sintered bodies are dense pure monoclinic ZrO₂ nanocrystalline ceramic with a relative density of 99.9% and an average grain size of 110 nm.     

Kinetics of magnetite nanoparticles formation in a one step low temperature hydrothermal process

In the present study, a one step hydrothermal process was employed to synthesize magnetite nanoparticles using oleic acid as surfactant agent at 140 °C. Effects of reaction time and alkalinity were studied on particles size and morphology. By changing these parameters, some monodisperse spherical nanoparticles with mean particle size between 2.71 and 13.88 nm were synthesized and characterized via TEM, XRD, VSM, TGA and FT-IR techniques. Assuming the Avrami behavior of particles formation, a kinetics equation was proposed for the transformation rate at 140 °C. Using some simplifying assumptions, nucleation and growth rates were calculated for the hydrothermal formation of magnetite nanoparticles at 140 °C.     

Polysilazane-derived antibacterial silver–ceramic nanocomposites

Functional ceramic composites consisting of a dispersion of silver nanoparticles in a silicon (carbon)nitride matrix (nc-Ag/Si(C)N) were prepared via the polymer–ceramic route. Mixtures of 3 wt% as-synthesized Ag nanoparticles with a commercial polysilazane were pyrolysed under flowing nitrogen and/or ammonia. Bulk samples as well as coatings were investigated. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal analysis (TGA, DTA), absorption spectroscopy (UV–vis) and infra red (IR) spectroscopy were used to characterize the products. The results indicate that the silver nanoparticles do not influence the cross-linking and pyroylsis process of the polysilazane precursor. At temperatures in the range of 800–1000 °C (H)Si(C)N matrices are obtained, which contain silver particles with an average size of 5–7 nm. Antibacterial tests on the pyrolysed material revealed strong activity against Escherichia coli and Staphylococcus aureus, suggesting the composites to be promising candidates for applications in fields such as the biomedical or food industries.