Antioxidant action by gold-PAMAM dendrimer nanocomposites

Gold-dendrimer nanocomposites were prepared in the presence of poly(amidoamine) (PAMAM) dendrimer (generation 3, 3.5, 5, and 5.5) via reduction of HAuCl4 with sodium borohydride. The average particle size of the gold nanoparticles was independent of the dendrimer concentration, ranging between 3.0 and 4.3 nm in diameter. The catalytic activities of the gold-dendrimer nanocomposites upon elimination of hydroxyl radicals formed in an H2O2/FeSO4 system were examined using a spin-trapping method. The gold-dendrimer nanocomposites exhibited high catalytic activities which were hardly affected by the concentration and the generation of the dendrimer except PAMAM dendrimer 3.5. The highest activity for the gold-PAMAM dendrimer 3.5 nanocomposites was 85 times that of ascorbic acid.     

磁性Fe_3O_4@PS@PAMAM-Ag复合催化粒子的制备及其可再生催化性能(英文)

采用聚苯乙烯(PS)包裹Fe3O4磁性纳米粒子,制得Fe3O4@PS复合微球,以此作为磁性载体,通过微球表面的羧基将聚酰胺-胺类树形大分子(PAMAM)连接到磁性载体上,然后使Ag纳米粒子镶嵌在树形分子层中,制得可再生的金属复合催化粒子Fe3O4@PS@PAMAM-Ag.并采用红外光谱、扫描电镜、电感耦合等离子体质谱(ICP-MS)和X射线光电子能谱等方法对复合催化粒子进行了表征,结果表明,树形分子可以较好地分散和稳定金属Ag纳米粒子,所制复合催化粒子表面Ag含量为1.64%,具有较高的催化还原对硝基苯酚的活性.同时,利用外加磁场可以方便快捷地从反应体系中分离出来,继续用于下一次反应中,复合催化粒子循环使用6次后,仍保持完全的催化性能.     

Preparation of PAMAM- and PPI-metal (silver, platinum, and palladium) nanocomposites and their catalytic activities for reduction of 4-nitrophenol

Dendrimer-metal (silver, platinum, and palladium) nanocomposites are prepared in aqueous solutions containing poly(amidoamine) (PAMAM) dendrimers with surface amino groups (generations 3, 4, and 5) or poly(propyleneimine) (PPI) dendrimers with surface amino groups (generations 2, 3, and 4). The particle sizes of the metal nanoparticles obtained are almost independent of the generation as well as the concentration of the dendrimer for both the PAMAM and the PPI dendrimers; the average sizes of silver, platinum, and palladium nanoparticles are 5.6-7.5, 1.2-1.6, and 1.6-2.0 nm, respectively. It is suggested that the dendrimer-metal nanocomposites are formed by adsorbing the dendrimers on the metal nanoparticles. Studies of the reduction reaction of 4-nitrophenol by these nanocomposites show that the rate constants are very similar between PAMAM and PPI dendrimer-silver nanocomposites, whereas the rate constants for the PPI dendrimer-platinum and -palladium nanocomposites are greater than those for the corresponding PAMAM dendrimer nanocomposites. In addition, it is found that the rate constants for the reduction of 4-nitrophenol involving all the dendrimer-metal nanocomposites decrease with an increase in the dendrimer concentrations, and the catalytic activity of dendrimer-palladium nanocomposites is highest.     

Synthesis, photoluminescence, and adsorption of CdS/dendrimer nanocomposites

CdS/dendrimer nanocomposites can be synthesized from methanolic Cd(2+) and S(2-) with amine-terminated polyamidoamine dendrimers of generation 8 (G8NH(2)) as stabilizers. By controlling the preparation conditions, nanoparticles with diameters < or = 2 nm can be obtained with a narrow size distribution. They show blue photoluminescence at approximately 450 nm. We studied the effects of various additives on the photoluminescence and elucidated its mechanism. Stable aggregates of two to three G8NH(2) molecules with several CdS nanoparticles form; the particles are located at the surface of the G8NH(2) molecules. The adsorption of the CdS/G8NH(2) nanocomposites on flat substrate surfaces is determined by the substrate chemistry. The hydrophilic nature of G8NH(2) results in weak affinity to graphite but strong affinity to hydroxy-terminated substrates such as mica, oxidized silicon wafers, and carboxylate-terminated monolayers. Patterning of nanocomposites on these hydrophilic substrates is achieved by the microcontact printing method. We propose to use only one molecule, a large dendrimer, to control the nanoparticle formation and also the immobilization of the synthesized nanoparticle/dendrimer composites.     

Morphological change of gold-dendrimer nanocomposites by laser irradiation

Gold-dendrimer nanocomposites are prepared in aqueous solutions in the presence of poly(amidoamine)dendrimers (PAMAM) (generation 3 and 5) or poly(propyleneimine)dendrimers (PPI) (generation 3 and 4) by wet chemical NaBH(4) method. Thus prepared gold-dendrimer nanocomposites are irradiated by laser at 532 nm. UV-vis absorption spectroscopy and transmission electron microscopy reveal that the gold nanoparticles grow with the laser irradiation time as well as the fluence of the laser; in particular, the gold nanoparticles prepared at lower concentrations of PAMAM dendrimer as well as lower generations of PAMAM grow significantly. On the other hand, in the case of PPI dendrimers, the gold nanoparticles hardly grow by irradiation. In addition, dynamic light-scattering measurements show that the laser irradiation markedly promotes the association of the gold-PAMAM G3 dendrimer nanocomposites compared to that of the gold-PAMAM G5 dendrimer nanocomposites, while the sizes of association for the gold-PPI G3, G4 dendrimer nanocomposites hardly change by laser irradiation.     

PAMAM树形分子与Cd2＋的配位作用研究及CdS/PAMAM纳米复合材料的制备与表征

CdS半导体纳米簇具有独特的光、电性能, 如何制备均匀分散的、能够稳定存在的CdS纳米簇是目前的研究热点之一. 以聚酰胺-胺(PAMAM)树形分子为模板, 原位合成了CdS纳米簇. 首先用UV-Vis分光光度法研究了与树形分子的配位机理, 得出G4.5和G5.0的平均饱和配位数分别为16和34, 并发现在G4.5PAMAM树形分子中Cd^2＋主要与最外层叔胺基配位, 在G5.0PAMAM树形分子中Cd^2＋主要与最外层伯胺基配位. 酯端基的G4.5的模板作用要明显优于胺端基的G5.0. 通过改变Cd^2＋与G4.5树形分子的摩尔比可以得到不同粒径的CdS纳米簇. 溶液的pH值对CdS纳米簇影响很大, pH在7.0左右制备的CdS纳米簇粒径小而均匀, 且溶液稳定性高. 用UV-Vis分光光度计和TEM对CdS纳米簇的大小和形貌进行了表征. 结果表明TEM观测CdS纳米簇的粒径要大于用Brus公式的估算值.     

树形大分子/金属配合物及其纳米复合材料的制备与性能研究进展

树形大分子是具有确定代数和末端基的蓬勃发展的新型合成高分子。大量具有不同的中心核、支链和末端基团的树形大分子已经被合成和应用于不同的领域,其功能化和应用是目前树形大分子研究领域的热点。本文综述了树形大分子/金属配合物及其纳米复合材料的制备与性能的研究进展,重点介绍了树形大分子/金属配合物材料和树形大分子/金属纳米复合材料的制备与性能研究的最新进展。     

Polymer‐Supported Bimetallic Ag@AgAu Nanocomposites: Synthesis and Catalytic Properties

Supported noble bimetallic nanomaterials have attracted great interest owing to their applications in catalysis. Herein, polystyrene‐supported Ag@AgAu bimetallic nanocomposites were synthesized by using a seed‐growth route. The size and degree of coverage of the Ag@AgAu NPs could be controlled by changing the experimental parameters. SEM, TEM, STEM, EDS, and XPS analysis was used to characterize the morphology, structure, and composition of these nanocomposites. We found that the bimetallic nanoparticles on the polystyrene beads had a core–shell structure that was comprised of a Ag core and a AgAu alloy shell. The optical properties of the nanocomposites were also studied by UV/Vis/NIR spectroscopy, which indicated that the localized surface plasmon resonance (LSPR) absorptions of the nanocomposites could be tailored over a large scale from 450 nm to 950 nm. The catalytic properties of the nanocomposites were studied by using the reduction of 4‐nitrophenol (4‐NP) by NaBH₄ as a model system. The results showed that the catalytic activity of the polystyrene‐supported Ag@AgAu bimetallic nanocomposites was remarkably superior to that of polystyrene‐supported monometallic Ag and Au nanocomposites with the same nanoparticle size. In addition, an investigation of the recycling catalytic activity of the PS‐Ag@AgAu nanocomposites revealed that the catalyst possessed good stability. The enhancement of the catalytic activity was proposed to be due to the ligand and strain effects between Ag and Au.     

Effect of dendrimer modified montmorillonite on structure and properties of EPDM nanocomposites

The purpose of this work was to study the effect of dendrimer modified clay minerals on the structure and properties of ethylene-propylene-diene monomer (EPDM) nanocomposites.Flame-retardant and dendrimer modified organic montmorillonite (FR-DOMt) was successfully prepared by Na⁺-montmorillonite, tetrahydroxymethyl phosphonium chloride (THPC), N, N-dihydroxyl-3-aminomethyl propionate, and boric acid. This dendritic type of organoclay (OC) was used in preparation of EPDM/FR-DOMt nanocomposites. The properties of these nanocomposites were studied. The dispersion status of the layered silicates in EPDM was revealed by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD and TEM results showed that FR-DOMt was exfoliated in the EPDM matrix when 10 phr of FR-DOMt was incorporated. The mechanical behavior, thermal stability, and flame retardance of the samples were examined. The experimental data demonstrated that the EPDM hybrids owned an improved tensile strength and elongation at break. In addition, the nanocomposites exhibited higher thermal stability and flame retardance than that of unfilled EPDM matrix.     

Comparison of PAMAM-Au and PPI-Au nanocomposites and their catalytic activity for reduction of 4-nitrophenol

Dendrimer-Au nanocomposites are prepared in aqueous solutions using poly(amidoammine)dendrimers (PAMAM) (generation 2, 3, and 5) and poly(propyleneimine)dendrimers (PPI)(generation 2, 3, and 4) by wet chemical NaBH(4) method. The Au nanoparticles thus obtained are 2-4 nm in diameter for both dendrimers and no generation dependence on the particle size is observed, whereas the generations of the dendrimers are increased as stabilization of Au-nanoparticles is achieved with lower dendrimer concentrations. Studies of the reduction reaction of 4-nitrophenol using these nanocomposites show that the rate constants for the PAMAM dendrimers (generations 2 and 3) are higher than those for the PPI dendrimers (generations 2 and 3), while a distinct difference in the rate constants is not seen for the PAMAM dendrimer (generation 5) or the PPI dendrimer (generation 4). In addition, the rate constants for the reduction of 4-nitrophenol involving all the dendrimers decrease with increases in dendrimer concentrations.     

树状大分子/金属（化合物）纳米复合材料*

本文综述了一类新的有机/无机杂化材料——树状大分子/金属（化合物）纳米复合材料的研究进展。该杂化纳米材料由树状大分子内或树状大分子间螯合金属离子通过还原生成相应的零价金属纳米粒子或与阴离子反应生成金属化合物的方法制备。其中树状大分子内复合物粒子体积与原树状大分子内负载的金属离子数量有关,树状大分子间复合物粒子体积与树状大分子的浓度和代数有关。     

Catalytic activity of nanoalloys from gold and palladium

We present a quantitative study of the catalytic activity of well-defined faceted gold-palladium nanoalloys which are immobilized on cationic spherical polyelectrolyte brushes. The spherical polyelectrolyte brush particles used as carriers for the nanoalloys consist of a solid polystyrene core onto which cationic polyelectrolyte chains of 2-aminoethyl methacrylate are attached. Au/Pd nanoalloy particles with sizes in the range from 1 to 3 nm have been generated which are homogeneously distributed on the surface of the spherical polyelectrolyte brushes. The reduction of 4-nitrophenol has been chosen as a well-controlled model reaction allowing us to determine the catalytic activity of the nanoalloys as a function of the Au/Pd composition. The adsorption behavior was studied by Langmuir-Hinshelwood kinetics. We find a pronounced maximum of the catalytic activity at 75 molar % Au. A comparison of gold, platinum, palladium and gold-palladium alloy nanoparticles is made in terms of Langmuir-Hinshelwood kinetics. Density functional calculations for Au/Pd clusters with up to 38 atoms show that the density of states at the Fermi level increases with increasing Pd content, and that the highest occupied orbitals are associated with Pd atoms. The calculations confirm that small changes in the atomic arrangement can lead to pronounced changes in the particles' electronic properties, indicating that the known importance of surface effects is further enhanced in nanoalloys.     

以聚酰胺-胺树形分子为模板制备AgI纳米簇

本文以聚酰胺-胺(PAMAM)树形分子为模板,原位制备AgI纳米簇.系统地研究了AgI纳米簇制备过程中各种反应条件如树形分子端基、反应时间、Ag⁺与PAMAM摩尔比等对AgI纳米簇粒径的影响,分别用紫外-可见光谱、荧光光谱、透射电镜等对所制备的纳米簇进行表征.在相同的条件下,以G4.5-COOH₃为模板较以G5.0-NH₂为模板制备的AgI纳米簇粒径小、分布均匀,这主要取决于G4.5-COOCH₃PAMAM树形分子所起的“内模板”作用.G4.5-COOH₃树形分子浓度为1×10^-5mol/L,Ag⁺与树形分子摩尔比为30:1时所制备的AgI纳米簇的粒径分布均匀、稳定性好,室温避光可稳定存在两个月以上.     

Preparation of gold-, gold/silver-dendrimer nanocomposites in the presence of benzoin in ethanol by UV irradiation

Gold- and gold/silver-dendrimer nanocomposites have been synthesized by UV irradiation of their salts dissolved in ethanol containing dendrimers. As dendrimers, poly(amidomaine) PAMAM dendrimers and poly(propyleneimine) PPI dendrimers of various generations were used. The photoreduction of their salts is greatly accelerated by using benzoin as a photoinitiator. The sizes of gold in the nanocomposites are affected by the concentration of benzoin as well as the concentration of dendrimers, but are hardly changed with the kind of dendrimers. For gold/silver-dendrimer nanocomposites, the absorption spectra of gold/silver nanoparticles in the nanocomposites are very similar to the theoretical spectra of gold/silver alloy nanoparticles, suggesting the formation of gold/silver alloy nanoparticles. From the comparison of TEM and DLS measurements, it is found that the metal-dendrimer nanocomposites consist of metal nanoparticles covering by dendrimer molecules.     

Bimetallic Dendrimer-encapsulated Nanoparticle Catalysts

Bimetallic dendrimer-encapsulated nanoparticles (DENs) have been receiving a significant amount of attention due to their promising properties, unique characteristics, and novel applications in catalysis and other advanced “nano-” science and technology areas. Bimetallic DENs catalysts, as reviewed here, have shown a higher catalytic activity than the monometallic DENs in various catalytic systems. In this review, a general background for the dendrimer is first presented, which is then followed by an introduction of two major routes that are most often adopted in the preparation of dendrimers: divergent method and convergent method. Then, recent research advances in the synthesis, characterization, and catalytic applications of bimetallic DENs are summarized and highlighted in this article. A conclusion is then provided.     

Thermal decomposition of generation-4 polyamidoamine dendrimer films: decomposition catalyzed by dendrimer-encapsulated Pt particles

The thermal decomposition of hydroxyl-terminated generation-4 polyamidoamine dendrimer (G4OH) films deposited on Au surfaces has been compared with decomposition of the same dendrimer encapsulating an approximately 40-atom Pt particle (Pt-G4OH). Infrared absorption reflection spectroscopy studies showed that, when the films were heated in air to various temperatures up to 275 degrees C, the disappearance of the amide vibrational modes occurred at lower temperature for the Pt-G4OH film. Dendrimer decomposition was also investigated by thermogravimetric analysis (TGA) in both air and argon atmospheres. For the G4OH dendrimer, complete decomposition was achieved in air at 500 degrees C, while decomposition of the Pt-G4OH dendrimer was completed at 400 degrees C, leaving only platinum metal behind. In a nonoxidizing argon atmosphere, a greater fraction of the G4OH decomposed below 300 degrees C, but all of the dendrimer fragments were not removed until heating above 550 degrees C. In contrast, Pt-G4OH decomposition in argon was similar to that in air, except that decomposition occurred at temperatures approximately 15 degrees C higher. Thermal decomposition of the dendrimer films on Au surfaces was also studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum conditions. Heating the G4OH films to 250 degrees C during the TPD experiment induced the desorption of large dendrimer fragments at 55, 72, 84, 97, 127, 146, and 261 amu. For the Pt-G4OH films, mass fragments above 98 amu were not observed at any temperature, but much greater intensities for H(2) desorption were detected compared to that of the G4OH film. XPS studies of the G4OH films demonstrated that significant bond breaking in the dendrimer did not occur until temperatures above 250 degrees C and heating to 450 degrees C caused dissociation of C=O, C-O, and C-N bonds. For the Pt-G4OH dendrimer films, carbon-oxygen and carbon-nitrogen bond scission was observed at room temperature, and further decomposition to atomic species occurred after heating to 450 degrees C. All of these results are consistent with the fact that the Pt particles inside the G4OH dendrimer catalyze thermal decomposition, allowing dendrimer decomposition to occur at lower temperatures. However, the Pt particles also catalyze bond scission within the dendrimer fragments so that decomposition of the dendrimer to gaseous hydrogen is the dominant reaction pathway compared to desorption of the larger dendrimer fragments observed in the absence of Pt particles.     

Synthesis of polyamidoamine dendrimer (PAMAM/CuS/AA) nanocomposite and its application in the removal of Isma acid fast yellow G Dye

The adsorption of Isma acid fast yellow G dye was studied using polyamidoamine (PAMAM)/Copper sulfide (CuS)/AA nanocomposite containing different amounts of CuS by batch technique. PAMAM dendrimer/CuS/AA nanocomposites were synthesized via gamma irradiation cross‐linking method with the aid of sonication. The nanocomposites were characterized by Fourier‐transform infrared, X‐ray diffraction, transmission electron microscope, energy dispersive spectroscopy X‐ray, thermal gravimetric analysis, ultraviolet‐visible, and fluorescence spectroscopy. The size of the CuS nanoparticles was formed in the range of 12–19 nm. The adsorption capacity of the nanocomposites was evaluated as a function of initial dye concentration, pH, adsorbent dosage, and time. It was verified that the adsorption rate fits a pseudo‐second‐order kinetics for initial Isma acid fast yellow G dye concentrations. Results indicated that the adsorption of Isma acid fast yellow G dye fitted well to the Langmuir model. Our results demonstrate that the PAMAM dendrimer/CuS/AA nanocomposite is very promising for removing organic dyes from wastewater. Copyright © 2015 John Wiley & Sons, Ltd.     

Investigation of thermal behaviour of hybrid nanostructures based on Fe2O3 and PAMAM dendrimers

Dendrimers or biofunctionalized dendrimers can be assembled onto magnetic iron oxide nanoparticles to stabilize or functionalize inorganic nanoparticles. Carboxylated poly(amidoamine) PAMAM dendrimers (generation 4.5) have been used for the synthesis of iron oxide nanoparticles, resulting nanocomposites with potential biomedical applications. The present paper aims to systematically investigate the thermal behaviour of nanostructured hybrids based on ferric oxide and PAMAM dendrimers, by differential scanning calorimetry (DSC) technique. The novelty consists both in synthesis procedure of hybrid nanostructures as well as in DSC approach of these nanocomposites. For the first time, we propose a new method to prepare Fe₂O₃??dendrimer nanocomposite, using soft chemical process at high pressure. Commercial PAMAM dendrimers with carboxylic groups on its surface were used. When high pressure is applied, polymeric structures suffer morphological changes leading to hybrid nanostructures' formation. In the same time, crystallinity of inorganic nanoparticles is provided. DSC results showed an increase in thermal stability of composites as compared to commercial dendrimers. This could be due to the formation of strong interactions between ferric oxide and carboxyl groups, as confirmed by Fourier transform infrared spectroscopy. Electron microscopy analysis (SEM/EDX) and size measurements were performed to demonstrate the existence of nanosized particles.     

Effects of various thiol molecules added on morphology of dendrimer-gold nanocomposites

Interactions between poly(amidoamine) dendrimer (PAMAM)-gold nanocomposites and alkanethiols and between the former nanocomposites and thiol-modified poly(amidoamine) dendrons in ethyl acetate were investigated by adding alkanethiols, such as 1-propanethiol and 1,3-propanedithiol, and thiol-modified poly(amidoamine) dendrons, generations 0.5 and 2.5 (G0.5-SH and G2.5-SH). The PAMAM dendrimers with surface methyl ester groups used were generations 1.5 and 5.5 (G1.5 and G5.5). The mean particle sizes of PAMAM-gold nanocomposites were about 2.1 for G1.5 and 2.4 nm for G5.5. In both nanocomposite systems where 1-propanethiol and 1,3-propanedithiol were added, the mean particle size was about 4 nm, twice that of the systems where these thiols were not added. Increasing the addition of 1,3-propanedithiol made the average particle size smaller for both nanocomposites systems. To compare with alkanethiol, thiol-modified poly(amidoamine) dendron with a highly branched structure on one side was synthesized. Using G2.5-SH as a protective agent, dendron-gold nanocomposites with mean diameters of 3 to 4 nm were obtained. The difference in particle size was seen only when the combination of PAMAM-gold nanocomposites and thiol-modified dendron was less sterically dense, modified dendron (G0.5-SH). The mechanisms for morphology changes in the dendrimer-gold nanocomposites by the addition of these thiols are discussed.     

含树枝状大分子PAMAM的苯乙烯乳液聚合

将树枝状大分子PAMAM (4 5代 )作为种子 ,以苯乙烯为代表性单体进行乳液聚合 .研究结果表明 ,加入树枝状大分子PAMAM时 ,所制得的聚合物乳液粒子平均粒径在 30～ 5 0nm之间 ,小于 10 0nm ,且大小分布均匀 ;所制备的聚合物在 16 70cm- 1 左右处出现酰胺的特征吸收峰 ,在 330 0cm- 1 左右处出现N—H伸缩振动特征峰 ;说明树枝状大分子PAMAM起到种子的作用 ,所制备的聚合物含树枝状大分子PAMAM .