Photochemical synthesis of colloidal gold nanoparticles

Monodisperse gold nanoparticles protected by small organic molecules or by macromolecules with different sizes and shapes are widely used as a precursor material in various applications of gold nanotechnology. However, their preparation is still a formidable task. In this paper the use of photochemically assisted syntheses of monodisperse gold nanoparticles is summarized and some preparations by the authors’ group are introduced. These include spherical and rod-like particles, bimetallic composite nanoparticles, and syntheses using complex intramolecular photoreduction to generate the reducing agent.     

Femtosecond laser synthesis of bimetallic Pt-Au nanoparticles

Bimetallic Pt-Au nanoparticles were successfully synthesized by irradiating the metal precursor solution with high intensity femtosecond laser. The intense optical field created by femtosecond laser pulse induced the production of highly charged ions and molecules due to the optical decomposition of metal precursor molecules. Further collisions with molecules result in subsequent growth of the nuclei and codeposition of Pt and Au atoms on the nuclei to form the larger ones. The method is a simple, easy-to-control and environmentally benign process. The average size and morphology of bimetallic nanoparticles were examined by transmission electron microscope. The compositional distributions of Pt and Au of individual Pt-Au nanoparticles were examined by X-ray energy dispersive spectroscopy (EDS).     

Microfluidic-enabled ambient-temperature synthesis of ultrasmall bimetallic nanoparticles

The production of bimetallic nanoparticles with ultrasmall sizes is the constant pursuit in chemistry and materials science because of their promising applications in catalysis,electronics and sensing.Here we report ambient-temperature preparation of bimetallic NPs with tunable size and composition using microfluidic-controlled co-reduction of two metal precursors on silicon surface.Instead of free diffusion of metal ions in bulk system,microfluidic flow could well control the local ions concentration,thus leading to homogenous and controllable reduction rate among different nucleation sites.By controlling precursor concentration,flow rate and reaction time,we rationally design a series of bimetallic NPs including Ag-Cu,Ag-Pd,Cu-Pt,Cu-Pd and Pt-Pd NPs with ultrasmall sizes(~3.0 nm),tight size distributions(relative standard deviation(RSD)<21%),clean surface,and homogenous elemental compositions among particles(standard deviation(SD)of weight ratios<3.5%).This approach provides a facile,green and scalable method toward the synthesis of diverse bimetallic NPs with excellent activity.     

包覆型铜-银双金属粉的制备

为了提高铜粉的抗氧化性能,在超细铜粉表面包覆一层具有优良导电性和抗氧化的银,以乙酰丙酮(Acac)为Cu2+的螯合剂,采用置换反应法制备与原超细铜粉粒度相同的包覆型铜-银双金属粉.采用X射线衍射仪(XRD)、煅烧后增重等手段分析包覆型铜-银双金属粉的抗氧化性能,并用扫描电子显微镜(SEM)表征了其表面形貌.结果表明,乙...     

A universal nanoreactor strategy for scalable supported ultrafine bimetallic nanoparticles synthesis

Supported bimetallic catalysts have become an important class of catalysts in heterogeneous catalysis. Although well-defined bimetallic nanoparticles (BNPs) can be synthesized by seeded-growth in liquid phase, uniform deposition of these BNPs onto porous supports is very challenging. Here, we develop a universal nanoreactor strategy to directly fabricate the PdAu BNPs in the solid support of coral-like nitrogen-doped mesoporous polymer (NMP) with uniform dispersion in a large scale. This strategy is based on coordination chemistry to introduce the high-quality seeds of Pd nanoclusters and the Au ions into the NMP, and thus to be used as a nanoreactor for seeded growth of PdAu BNPs in solid state during thermal reduction. Many other supported Pd-based BNPs (diameters ranging from 2 to 3 nm) have also been successfully synthesized by adoption of this strategy, including PdRu, PdCo, PdNi, PdZn, PdAg and PdCu BNPs. As an example, the as-synthesized Pd₁Au_1/4 sample shows enhanced catalytic performance in formic acid (FA) dehydrogenation compared with the monometallic analogues, indicating the synergistic effect between Pd and Au. In addition, the Pd₁Au_1/4 product is molded into monolith without any binders due to its coral-like structure. The Pd₁Au_1/4 monolith shows considerable activity in FA dehydrogenation with a turnover frequency (TOF) value of 3684 h⁻¹ at 333 K, which is recycled five times without changes in activity. We believe that the nanoreactor strategy provides an effective route to synthesize various supported bimetallic catalysts that have potential for applications in green and sustainable catalytic processes.     

New synthesis approach for low temperature bimetallic nanoparticles: size and composition controlled Sn-Cu nanoparticles

A various size of Sn-Cu nanoparticles were synthesized by using a modified polyol process for low temperature electronic devices. Monodispersive Sn-Cu nanoparticles with diameters of 21 nm, 18 nm and 14 nm were synthesized. In addition, the eutectic composition shift was also observed in nano-sized particles as compared with bulk alloys. By controlling the size and eutectic composition, a significant melting temperature depression of 30.3 degrees C was achieved. These melting temperature depression approaches will reduce adverse thermal effects in electronic devices and provide the synthesis guidelines for bimetallic nanoparticles with a low melting temperature.     

Photochemical synthesis of gold nanoparticles via controlled nucleation using a bioactive molecule

Synthesis of gold nanoparticles had been achieved using dopamine hydrochloride (dhc), an important bioactive molecule in a photochemical way. Solutions containing sodium dodecyl sulfate (SDS), HAuCl₄ and dhc were photoirradiated to form gold nanoparticles. Gold nanoparticles in different size range was obtained by varying the concentration of dhc. The growth of different-sized gold with time was monitored. The particles were characterized by absorption spectra and TEM analysis. The procedure involved a new technique for gold nanoparticle preparation and was simple, reproducible and required single step.     

Templated synthesis of Ag-Au bimetallic nanoparticles by amphiphilic PVC-g-PSSA graft copolymer film

Amphiphilic comb-like copolymer consisting of a poly(vinyl chloride) (PVC) backbone and poly(styrene sulfonic acid) (PSSA) side chains, i.e. PVC-g-PSSA at 68:32 wt.% was synthesized via atom transfer radical polymerization (ATRP). This self-assembled graft copolymer film was used to template the growth of Ag-Au bimetallic nanoparticles in the solid state by introducing NaBH₄ as a reducing agent. The in situ formation of Ag-Au bimetallic nanoparticles in the graft copolymer film was confirmed by UV-visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). High resolution TEM picture showed the formation of spherical Ag-Au core-shell nanoparticles. To the best of our knowledge, this is the first report on the solid-state synthesis of Ag-Au bimetallic core-shell nanoparticles using amphiphilic comb-like copolymer film.     

Large scale synthesis of FeS coated Fe nanoparticles as reusable magnetic photocatalysts

The FeS coated Fe nanoparticles were prepared by using high temperature reactions between the commercial Fe nanoparticles and the S powders in a sealed quartz tube. The simple method developed in this work is effective for large scale synthesis of FeS/Fe nanoparticles with tunable shell/core structures, which can be obtained by controlling the atomic ratio of Fe to S. The structural, magnetic and photocatalytic properties of the nanoparticles were investigated systematically. The good photocatalytic performance originating from the FeS shell in degradation of methylene blue under visible light and the high saturation magnetization originating from the ferromagnetic Fe core make the FeS/Fe nanoparticles a good photocatalyst that can be collected and recycled easily with a magnet. An exchange bias up to 11 mT induced in Fe by FeS was observed in the Fe/FeS nanoparticles with ferro/antiferromagnetic interfaces. The enhanced coercivi-ty up to 32 mT was ascribed to the size effect of Fe core.     

A library of carbon-supported ultrasmall bimetallic nanoparticles

Small-sized bimetallic nanoparticles that possess numerous accessible metal sites and optimal geometric/electronic structures show great promise for advanced synergetic catalysis but remain synthetic challenge so far. Here, an universial synthetic method is developed for building a library of bimetallic nanoparticles on mesoporous sulfur-doped carbon supports, consisting of 24 combinations of 3 noble metals (that is, Pt, Rh, Ir) and 7 other metals, with average particle sizes ranging from 0.7 to 1.4 nm. The synthetic strategy is based on the strong metal-support interaction arising from the metal-sulfur bonding, which suppresses the metal aggregation during the H₂-reduction at 700 °C and ensure the formation of small-sized and alloyed bimetallic nanoparticles. The enhanced catalytic properties of the ultrasmall bimetallic nanoparticles are demonstrated in the dehydrogenation of propane at high temperature and oxidative dehydrogenations of N-heterocycles.

     

Gas-liquid detonation synthesis of graphite coated copper nanoparticles and tribological performance as lubricant additives

Graphite coated copper (Cu@G) nanoparticles were successfully prepared by a gas-liquid detonation method, using copper acetate, ethanol, hydrogen and oxygen as the detonation precursors. The composition, morphology and microstructure of detonation products were analyzed by X-ray diffraction (XRD) and transmission electron microscopy-energy dispersive X-ray spectrometry (TEM-EDX). And a four-ball wear test was carried out to clarify the tribological properties of the mixed lubricating oils, which mainly consisted of the SN150 base oils containing five different concentrations of Cu@G nanoparticles. The results indicated that Cu@G nanoparticles are made up of face-centered cubic (FCC) copper nanocrystal and graphitic shells. The size distribution of core-shell structural products is mainly in range of 10–40 nm and the graphitic shells is about 4–8 nm. From the four-ball tests, the friction coefficient and wear scar diameter (WSD) decrease firstly and then increase with the increase of the contents of Cu@G nanoparticles. When the content of Cu@G nanoparticles is 0.6%, there is a minimum friction coefficient and WSD.     

Iron nanoparticles from blood coated with collagen as a matrix for synthesis of nanohydroxyapatite

A simple wet precipitation technique was used to prepare nanobiocomposite containing iron nanoparticles coated with collagen. This nanobiocomposite was used as matrix for the synthesis of nanohydroxyapatite. The physicochemical characteristic studies of the nanohydroxyapatite thus formed were carried out using fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction technique to confirm the formation of hydroxyapatite on iron nanoparticle–collagen complex. The results of the above studies supported the formation of iron nanoparticle–collagen–hydroxyapatite composite. The biological studies such as biocompatibility and hemocompatibility were carried out for nanohydroxyapatite using different cell lines and blood sample. The results of biocompatibility and hemolytic assay revealed that the prepared nanobiocomposite was 100 % biocompatible and hemocompatible. This nanobiocomposite may be used for biomedical application such as injectables for targeted delivery and as scaffold for tissue engineering.     

Microwave irradiation assisted rapid synthesis of Fe-Ru bimetallic nanoparticles and their catalytic properties in water-gas shift reaction

Fe-Ru bimetallic nanoparticles were prepared by a microwave irradiation assisted glycol reduction method using poly-N-vinyl-2-pyrrolidone (PVP) as protective agent. The structure and morphology of the nanoparticles were characterized by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDXA) and high-resolution transmission electron microscopy (HRTEM). EDXA and XRD analysis confirmed the presence of Fe and Ru. The bimetallic nanoparticles were subsequently loaded onto an MgAl₂O₄ supporter with K₂O as promoters and used as catalyst for water-gas shift reaction. The results indicated that the FeRu bimetallic nanoparticles exhibit high catalytic activity for water-gas shift reaction due to the synergistic effect between iron and ruthenium. Potassium oxide can enhance the CO selectivity of the catalyst significantly besides increasing the catalyst activity.     

Morphology and surface plasma changes of Au-Pt bimetallic nanoparticles

In this study, we examined the amount-dependent change in morphology in a series of Au-Pt bimetallic nanoparticles synthesized using chemical reduction. The amount of Au precursor was kept constant throughout the experiment. The Au/Pt molar ratio was varied from 1/1 to 1/4 to synthesize Pt shell layers with different thicknesses. We observed a remarkable shift of the surface plasmon band at around 410 nm. By high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometry (EDS), the composition of the shell layer was found to be Pt-enriched Au-Pt alloy. As the concentration of Pt increases, Pt clusters (ca. 1.8 nm in diameter) form a string-like shape on the surface of nanoparticles.     

Green synthesis of silver nanoparticles and biopolymer nanocomposites: a comparative study on physico-chemical,antimicrobial and anticancer activity

The current report was intended towards comparative study of green-synthesized biogenic Rhubarb silver nanoparticles (RS-AgNPs) and chitosan crosslinked silver nanocomposites (CSHD-AgNCs). The physico-chemical characterization was done by UV–visible, FTIR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), EDX, TGA, XRD and zeta potential (\(\zeta \)). The analysis and spectroscopic characterization was done by SEM and TEM and their results reveal that the nanoparticles are spherical in shape, with average size ranges from 5 to 50 nm, and was gathered by face centered cubic (FCC) structure throughout the polymer matrix and stable without any protecting or capping reagents over 450 days. The antimicrobial property of RS-AgNPs and CSHD-AgNCs (\(\zeta = +29.6\) and \(+\)32.8 mV) was evaluated against E. coli and S. aureus and showed an effective inhibitory property. The RS-AgNPs and CSHD-AgNCs were assessed for their anticancer activity against HeLa cell line by MTT method, and it reveals a dose–response activity, time and cell line-dependent cytotoxicity. Based on the results obtained, the RS-AgNPs exhibited higher toxicity over CSHD-AgNCs after 24 h incubation of HeLa cells with different concentrations and is negligible for the aqueous Rhubarb extract. It was concluded that the changes in anticancer activity towards HeLa cells due to biological activity of silver nanoparticles depend on their method of biosynthesis and their physico-chemical nature.     

Silica coated hard-magnetic strontium hexaferrite nanoparticles

Stable colloids of hard magnetic particles are newly developed and very promising materials. Surface functionalization of these particles remains challenging because the particles tend to aggregate during reaction due to strong magnetic interactions. Herein we report on a synthesis of strontium hexaferrite hard magnetic nanoparticles coated with silica by hydrolysis of tetraethoxysilane. As a source of hexaferrite we used stable colloid of plate-like nanoparticles with mean diameter of 40 nm and thickness of 5 nm, which were prepared by a glass-ceramic process. We have shown that to successfully coat each hexaferrite particle individually the hydrolysis conditions should provide heterogeneous nucleation of silica with rate higher than the aggregation rate of the colloidal nanoparticles. The resulting materials represent single crystal hexaferrite cores wrapped in silica shell with mean thickness of 18 and 23 nm depending on synthesis conditions. The obtained core-shell particles can be easily dispersed as stable aqueous colloids. The materials can be used as magnetic sorbents or nanocontainers and, furthermore, they are very promising colloidal building blocks for various magnetically assembled nanostructures.     

Synthesis and characterization of the iron oxide magnetic particles coated with chitosan biopolymer

Magnetic particles are extremely interesting for several biomedical applications; amongst these are therapeutic applications, such as: hyperthermia and release of drugs. The use of magnetic particles to induce hyperthermia in biological tissues is an important factor in cancer therapy. The aim of this study was to prepare and characterize iron oxide magnetic particles coated with biopolymer chitosan, and also to produce ferrofluids from the magnetic particles. The iron oxide magnetic particles (IOMP) were coated with chitosan (CS) by spray-drying method using two IOMP/coating ratios (IOMP/CS = 1.6 and IOMP/CS = 4.5). The magnetic particles were characterized by way of scanning electronic microscopy and energy-dispersive X-ray. The analysis by energy-dispersive X-ray was carried out to determine the chemical composition of particles in samples. The size distribution the iron oxide magnetic particles uncoated and coated were evaluated by the laser diffraction analysis and image analysis, respectively. Amongst the prepared ferrofluids, the sample IOMP/CS = 1.6 proved to be the one that has brought about the best results in therapeutics applications, such as in hyperthermia treatment. This sample was placed within an alternating magnetic field during 40 min, it was observed that 1 °C heated in 3 min and underwent a temperature variation of 7 °C, since it varied from 25 °C to 32 °C. Considering that the experiment would be carried out at body temperature 37 °C, probably, the temperature variation would be very close to the one reported at 25 °C. In such a way, the cancerous cells would reach 44–45 °C and at such temperatures the cancer cells generally perish.     

Three-layer core/shell structure in Au-Pd bimetallic nanoparticles

This paper describes the internal structure of Au-Pd nanoparticles exhibiting newly discovered three-layer core/shell morphology, which is composed of an evenly alloyed inner core, an Au-rich intermediate layer, and a Pd-rich outer shell. By exploitation of spatially resolved imaging and spectroscopic and diffraction modes of transmission electron microscopy (TEM), insights were gained on the composition of each one of the observed three layers, indicating a significant extent of intimate alloy among the monometallic elements.