Easy synthesis of nitrogen-doped graphene–silver nanoparticle hybrids by thermal treatment of graphite oxide with glycine and silver nitrate

Nitrogen-doped graphene–silver nanoparticle hybrids were prepared by thermal treatment of graphite oxide (GO) with glycine and silver nitrate at 500 °C. Glycine was used to reduce the nitrate ions, resulting in the decomposition of a glycine–nitrate mixture near 200 °C. The products of decomposition act as sources for nitrogen doping. The thermal treatment of a mixture of GO, glycine and silver nitrate results in the formation of silver nanoparticles at 100 °C, promotes the reduction of GO near 200 °C, and generates pyrrolic and pyridinic type nitrogen doping in graphene at 300 and 500 °C, respectively. The atomic percentage of nitrogen in as-prepared sample is about 13.5%. This approach opens up a new possibility for the synthesis of nitrogen-doped graphene decorated with various metallic nanoparticles, which could find important applications in the fields of energy storage and conversion devices.     

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.     

Ag Nanoparticles for Biomedical Applications—Synthesis and Characterization—A Review

Silver nanoparticles have been intensively studied over a long period of time because they exhibit antibacterial properties in infection treatments, wound healing, or drug delivery systems. The advantages that silver nanoparticles offer regarding the functionalization confer prolonged stability and make them suitable for biomedical applications. Apart from functionalization, silver nanoparticles exhibit various shapes and sizes depending on the conditions used through their fabrications and depending on their final purpose. This paper presents a review of silver nanoparticles with respect to synthesis procedures, including the polluting green synthesis. Currently, the most commonly used characterization techniques required for nanoparticles investigation in antibacterial treatments are described briefly, since silver nanoparticles possess differences in their structure or morphology.     

Development of a yellow ceramic pigment based on silver nanoparticles

In this study a yellow pigment was obtained for third-fire ceramic decorations, based on silver nanoparticles synthesised by the method of chemical reduction in aqueous phase, using silver nitrate and polyvinylpyrrolidone as raw materials. Monitoring of the nanoparticle synthesis reaction by UV–vis spectroscopy allowed optimum operating conditions to be defined in preparing these particles for use as chromophores. Under these conditions, a stable suspension of Ag nanoparticles, which were well dispersed and had an average diameter of 20–30 nm, was obtained. Polyvinyl alcohol and tetraethyl orthosilicate were then added to the nanoparticle suspension to obtain the pigment precursor. The pigment precursor was directly applied on to fired glazed ceramic tile. Subsequent thermal treatment at moderate temperature (700 °C) yielded a layer less than one micron thick, which generated an intense yellow colour.     

Oligoetherols and polyurethane foams obtained from melamine diborate

The method of synthesis of oligoetherols with 1,3,5-triazine ring and boron was established. The obtained oligoetherol is suitablse to obtaining polyurethane foams (PUFs) of enhanced thermal resistance and diminished flammability. The obtained PUFs can stand long term thermal exposure at 175 °C. The PUFs annealed at 150 and 175 °C showed improved compressive strength in comparison with not exposed to heating.     

Biosilicate® scaffolds produced by 3D-printing and direct foaming using preceramic polymers

Monolithic and powdered Biosilicate^®, produced by conventional glass-ceramic technology, have been widely recognized as excellent materials for bone tissue engineering applications. In the current research, we focus on an alternative processing route for this material, consisting of the thermal treatment of silicone polymers containing micro-sized oxide fillers, which offers a unique integration between materials synthesis and shaping. In particular, the new method allows obtaining highly porous Biosilicate^® glass-ceramics, in the form of 3D printed scaffolds and foams. 3D scaffolds were successfully fabricated by direct writing using an ink based on a silicone polymer and active inorganic fillers, followed by firing in air at 1000°C. The products showed regular geometries, large open porosity (~60 vol%) and still high compressive strength (~7 MPa). Open-cellular foams with porosity up to ∼80 vol% were also prepared from liquid silicones mixed with several fillers, including hydrated sodium phosphate. This specific filler acted both as a foaming agent, because of the gas release by dehydration occurring at low temperature, and as a provider of liquid phase upon firing in air, again at 1000°C.     

Application of products of reaction between melamine and glycidol as substrates for oligoetherols and polyurethane foams containing 1,3,5‐triazine rings

Hydroxyalkyl derivatives of melamine were obtained by addition of melamine to glycidol. These derivatives were then used to obtain multifunctional oligoetherols by reaction with oxiranes and alkylene carbonates. The structure and properties of the oligoetherols were studied in detail. The oligoetherols were then used to obtain polyurethane foams of enhanced thermal stability. The foams showed marked thermal resistance at 200 °C. The beneficial feature of the obtained foams was their increased compression strength after thermal exposure. © 2013 Society of Chemical Industry     

An Alternative Method for the Incorporation of Silver in Ag-VOx/TiO2 Catalysts for the Total Oxidation of Benzene

An alternative way of synthesis, the “onion” method, was used to deposit silver nanoparticles on a VO_x/TiO₂ catalyst. This synthesis method consists in the impregnation of organic vesicles containing the metallic silver nanoparticles. In situ calcination is needed to remove the organic vesicles and to offer an access of the reactants to the silver nanoparticles. This removal is easier in presence of vanadium. The addition of silver induces a higher proportion of V⁵⁺. The Ag-VO_x/TiO₂ catalysts prepared with this method exhibit better performances in the total oxidation of benzene after moderate in situ calcination at 350 °C than at 450 °C. A synergy between silver and vanadium is evidenced after both kinds of calcination with a silver loading of 0.125 and 0.25 wt%. The extent of this synergy is higher after a moderate calcination. This effect is likely due to the fact that small nanoparticles prepared via the “onions” sinter less after in situ calcination at 350 °C than at 450 °C. A clear link between the extent of the synergy and the size of the silver nanoparticles is evidenced. A decrease of the nanoparticle size induces a higher extent for the synergy.     

Effect of the microwave-assisted hydrothermal synthesis conditions on the photocatalytic properties of BiNbO4 and silver nanocomposites

Developing new photocatalysts based on metal oxide semiconductors for dye degradation under sunlight irradiation is an expanding area of research. These studies mainly focus on efficiency enhancement by controlling the morphology and crystalline structures, lowering the bandgap energy, and adding co-catalysts. Here we describe the microwave-assisted hydrothermal synthesis of bismuth niobate nanostructures (BiNbO₄) and its decoration with silver nanoparticles through an in situ microwave-assisted reflux synthesis. The resultant catalyst was characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance, zeta power and electrochemistry. Furthermore, the photocatalytic activity was evaluated by quantifying hydroxyl and superoxide radicals generated by holes and electrons photogenerated on the catalyst surface, respectively, and through the degradation of Rhodamine B. The studies revealed that the crystalline structure strongly depends on the irradiation conditions, forming a mixture of triclinic and orthorhombic BiNbO₄. Also, the decoration method results in the formation of metallic Ag, AgO and Ag₂O. As a result, the catalyst formed by BiNbO₄ synthesized at 150 °C and 550 W irradiation power, decorated with silver nanoparticles, showed the highest photocatalytic activity (32.6%).     

Tailored Fe3C-derived carbons with embedded Fe nanoparticles for ammonia adsorption

Carbide-derived carbons are synthesized by chlorination of Fe₃C at temperatures ranging from 200 to 1000 °C. The complex extraction method of Fe from Fe₃C at moderate temperatures (600 °C) allows for the tailored inclusion of FeCl₂, FeCl₃, or Fe nanoparticles in the resulting CDC by controlling the synthesis conditions and post-treatment methods. In this study, we extend the synthesis to other temperatures in order to understand the role of chlorination temperature on the physical and textural properties of the resulting CDC. We also examine the activity of Fe₃C-CDCs with embedded FeCl₃ nanoparticles for ammonia adsorption. Materials synthesized at 600 °C show exceptional results in ammonia breakthrough experiments, and achieved dynamic loadings of 1.88 mmol g⁻¹ at 0% relative humidity and 3.44 mmol g⁻¹ at 75% relative humidity calculated at initial breakthrough when [NH₃] > 0 ppm. NH₃ temperature programmed desorption (NH₃-TPD) and Fourier Transform Infrared Spectroscopy (FTIR) experiments suggest that the uptake is primarily due to ammonia complexation with FeCl₃ nanoparticles under dry conditions, and additional interactions with trapped chlorine in the presence of water.     

Direct foaming of macroporous ceramics containing colloidal alumina

Liquid foams containing Al₂O₃ nanoparticles were obtained after direct foaming of a colloidal alumina suspension with ammonium stearate. These systems were stable for at least 24 h and were comprised by small cells (<35 μm). Up to 10 wt% of these foams were added to an ultrastable Al₂O₃-stabilised one and resulted in macroporous samples with high total porosity (>70%). Their green mechanical strength was proportional to the amount of colloidal alumina added, but lower than a composition with calcium aluminate cement. When compared with compositions prepared with colloidal alumina suspension, the colloidal foams resulted in samples with a higher number of small pores (<30 μm) and lower linear shrinkage after firing at 1600 °C for 5 h (~9%). Thus, colloidal alumina foams can be used for processing macroporous refractory ceramics with smaller pores, lower dimensional changes after firing and higher porosity.     

A hybrid microreactor/microwave high-pressure flow system of a novel concept design and its application to the synthesis of silver nanoparticles

This article reports on a microreactor/microwave high-pressure flow hybrid apparatus of a novel concept design, which includes both the microreactor and a spiral reactor, and its efficient use in the synthesis of silver nanoparticles of relatively uniform sizes (4.3 ± 0.7 nm) under microwave irradiation. By contrast, under otherwise identical experimental conditions but with conventional heating, the nanoparticle size was non-uniform (8.3 ± 2.7 nm) and the spiral reactor walls were covered with a silver mirror deposit. Formation of the nanoparticles was monitored by UV–visible spectroscopy (plasmonic absorption band; LSPR), TEM and by small-angle X-ray scattering (SAXS). Both the spiral microreactor and the spiral quartz reactor of the hybrid system played an important role in the synthesis, with the microreactor providing the environment wherein mixing of the aqueous solution of [Ag(NH₃)₂]⁺ and the solution of glucose (the reducing agent) and poly(N-vinyl-2-pyrrolidone) (PVP; stabilizer/dispersing agent) occurred. The microwaves provided the thermal energy to effect a uniform growth of the silver nanoparticles at temperatures above 120 °C. Mixing the two solutions by conventional methods (no microreactor) failed to yield such nanoparticles even under microwave irradiation and no formation of a silver mirror occurred in the inner walls of the spiral reactor.     

Preparation and characterization of foam glass from waste container glasses and water glass for application in thermal insulations

Glass foams are modern developed building materials which are now favorably competing with conventional materials for applications in thermal insulation. In this study, glass foams are synthesized solely from waste container glasses of mixed colors using sodium silicate (water glass) as foaming agent. Several glass foams of 150 × 150 × 30 mm were prepared from waste glasses of 75 μm, 150 μm and 250 μm size with addition of 15 wt % sodium silicate respectively and pressed uniaxially under a pressure of 10 MPa. The prepared glass foams were then sintered at temperatures of 800 °C and 850 °C respectively. Tests such as bulk density, estimated porosity, flexural strength, compressive strength and microstructure evaluation were used to assess the performance of the developed glass foams. The results showed that with increasing temperature and grain sizes, the percent porosity of the developed foams increased while the bulk density decreased. The microstructure evaluation showed that the finer the grain sizes used, the more homogenized are the pores formed and the higher the temperature, the larger the pores but are mostly closed. Both compressive and flexural strength were found to decrease with grain sizes and higher temperatures. The thermal conductivities of all the developed foam glasses satisfy the standard requirement to be used as an insulating material as their thermal conductivities did not exceed 0.25 W/m.K.     

Superhydrophobic to superhydrophilic wettability transition of functionalized SiO2 nanoparticles

The superhydrophobic and superhydrophilic surfaces and their transitions are of great interest for the production of self-cleaning, anti-biofouling, or corrosion-resistant materials. This work reports the wettability transition from superhydrophobic to superhydrophilic SiO₂ nanoparticles functionalized with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS) and induced by temperature. The functionalization of these nanoparticles was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy. The functionalization of SiO₂ nanoparticles with POTS resulted in superhydrophobic surfaces with water contact angles up to 157°. A sudden transition to superhydrophilic behavior with water contact angles (WCA) below 5° was observed when the sample was heat-treated at 500 °C, despite the presence of fluorine on the surface of these nanoparticles, as confirmed by XPS and transmission electron microscopy. XPS suggested that the transition was caused by the change in orientation of the fluoroalkyl molecules and its partial decomposition due to the loss of the –CF₃ group, resulting in shorter chains with a tail-end group with C–O bonds, which promoted the superhydrophilicity.     

Recycling of extracted titanium slag and gold tailings for preparation of self-glazed ceramic foams

Self-glazed ceramic foams were successfully synthesized via powder sintering method, using extracted titanium slag (ETS) and gold tailings (GT) as raw materials without adding any sintering aids and foaming agents. Influence of ETS addition and sintering temperature on crystal phase evolution, physical–mechanical properties, and micro-morphology of ceramic foams was systematically studied. Results indicated that products sintered at 1180 °C with 30 wt% ETS and 70 wt% GT showed the best performance, i.e., bulk density of 1.66 g cm^?3, flexural strength of 20.4 MPa, water absorption of 0.14%, open porosity of 0.23%, and glaze Vickers hardness of 6.5 GPa. Moreover, it was observed that there existed strong correlation between bulk density and bending strength. Self-glazed ceramic foams developed in this study are expected to be used as building envelope materials and provide new ideas for effective reuse of other similar solid wastes.     

A green chemical method for synthesis of ZnO nanoparticles from solid-state decomposition of Schiff-bases derived from amino acid alanine complexes

As a part of the desire to save the environment via green chemistry practices, we report a novel method to synthesize ZnO nanoparticles from nontoxic and biocompatible chemicals where no pollutant or combustible side product is produced. In this recipe, a binary Zn(II) Schiff-base complex is obtained from alanine where water is used as solvent and a biologically compatible amino acid instead of toxic amines is used as a nitrogen source. The Schiff-base complex is subsequently heat treated to synthesize ZnO particles via a solid-state decomposition process. The effect of post heat treatment temperature (400, 500, and 600 °C) on microstructure and defect content of ZnO nanoparticles is investigated. The formation of single phase ZnO particles is confirmed by XRD θ–2θ patterns and FTIR spectra. TEM and SEM micrographs indicate the formation of nanoparticles with a particle size of 50–110 nm for different heat treatment temperatures. Combing XRD, FTIR, and PL results, it is revealed that the samples heat treated at intermediate temperatures (500 °C) possess the lowest defect concentration and a favorable crystallinity. This study emphasizes on green chemistry and synthesis of nanomaterials through ecofriendly methods to save our planet and its reservoirs for future and next generations.     

Green hydrothermal synthesis of high aspect ratio wollastonite nanofibers: Effects of reaction medium,temperature and time

Wollastonite 1D nanostructures have attracted widespread concern for their wide applications in biomedical, constructions and many more, which however have been synthesized via high temperature solid state method or wet precipitation method which required organic template. Herein, a controllable green hydrothermal route is used to produce high aspect ratio wollastonite nanofibers. The effect of hydrothermal synthesis parameters on the aspect ratio of synthetic wollastonite nanofibers (SWN) were investigated and the hydrothermal formation mechanism was proposed. The formation of nanofiber starts from the nuclei formation in supersaturated solution then followed by the crystal growth. The synthesis reactions were conducted under different conditions with reaction medium containing different ethanol composition and temperature from 160 °C to 240 °C for 8 h to 32 h. The SWN produced was characterized using XRD, FTIR, TGA and FESEM analysis techniques. It is proven that all wollastonite produced were in nanofiber form with the average aspect ratio ranging from 10 to 20, except for those synthesized at 160 °C which mainly has irregular grain shape. The reaction medium consisting of 80% water and 20% ethanol, which was heated at 200 °C for 16 h, resulted in SWN with the highest aspect ratio of 20.15. The study demonstrated that the hydrothermal synthesis parameters can be manipulated to produce SWN with various aspect ratios to meet its demand in different applications.     

Facile synthesis,antibacterial mechanisms and cytocompatibility of Ag–MnFe2O4 magnetic nanoparticles

Magnetic MnFe₂O₄ nanoparticles containing 0, 1 and 3 at.% silver, respectively were synthesized by one-pot sol-gel method for antibacterial applications in biomedical fields. Material characterizations indicate that MnFe₂O₄ begins crystallization at 134 °C and oxidation at 450 °C, the grain size and agglomeration degree increase with the silver content and silver exists as metallic state for the particles. The saturation magnetization decreases with the sintering temperature and slightly increases with the silver content, with the maximum of 50.0 emu/g obtained. Antibacterial tests by plate counting and PI-Hoechst 33342 staining suggest that the antibacterial activity of Ag–MnFe₂O₄ nanoparticles is silver content-dependent. Silver ions concentration measurement, β-galactosidase activity assay and transmission electron microscopic observation show that the antibacterial activity is dominated by the actions of the released silver ions, rather than the membrane cell impairment or reactive oxygen species-induced oxidative stress mechanism. MC3T3-E1 cell test demonstrates the best cytocompatibility of the nanoparticles with 3 at.% silver, which is likely related to the reduced cell endocytosis of the aggregated particles. The combination of magnetism, antibacterial activity and biocompatibility would make Ag–MnFe₂O₄ nanoparticles a potential multi-functional material in various biomedical applications.     

Seed Layer-Assisted Chemical Bath Deposition of Cu2O Nanoparticles on ITO-Coated Glass Substrates with Tunable Morphology,Crystallinity, and Optical Properties

A seed layer-assisted chemical bath deposition method performed at low temperature has been developed to grow uniform and high-quality crystal cuprous oxide (Cu₂O) nanoparticles on transparent conductive/glass substrates. The annealing process by continuous beam (CW) of CO₂ laser was used prior to growing the Cu₂O nanoparticles. In this study, the controlled synthesis of Cu₂O films was investigated by controlling the growth temperatures at 55 °C, 60 °C, 65 °C, and 70 °C, respectively. The modified seeding substrate reflect enhanced structural properties with laser annealing temperature of 450 ℃. In addition, Cu₂O nanoparticles with flower-like stricter show a greater density containing a smaller particle with 75 nm average dimension and flower particle size was about 85 nm. Results suggest an effective synthesis route for developing high-quality Cu₂O nanoparticles for optical and electronic applications.

     

Creating new materials with melamine resins

Acid catalyzed condensation of hexa-methoxy methyl melamine (HMMM) in aqueous phase leads to new functional particles and up to now unknown lamellar mesoscopic gels. The investigation with transmission electron microscopy (TEM) shows that the polymer formation starts with nonspherical nanoparticles. Dynamic light scattering experiments reveal a particle size of about 60–100 nm. Atomic force microscopy (AFM) measurements disclose nonuniform flat particles with an aspect ratio of about 0.3. These nanoparticle dispersions form thermoreversible gels. Molecular modeling investigations indicate energy minimized layer-by-layer condensation of the melamine resin molecules. The next step in growth is the nucleation of the nanoparticles via the narrow sides. This forms nonperfect lamellar layers. This time, we get a thermoreversible gel which is fluid at 80 °C and gets fixed at 20 °C. Out of these platelet structures as precursors, a mesoporous, nonthermoreversible gel with essentially lamellar sides and pore sizes about 10 μm is formed. Scanning electron microscopy (SEM) studies show very uniform wall and plate sizes with a directed three-dimensional structure.