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.     

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.     

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.     

低代端酯基PAMAM树形分子存在下银纳米颗粒的制备

在低代端酯基PAMAM树形分子(G1.5-COOCH₃)存在时，用氢气还原AgNO₃制备出银纳米颗粒。用透射电子显微镜(TEM)，电子衍射(ED)，紫外-可见吸收光谱(UV-Vis)和红外光谱(FT-IR)对所制备的银纳米颗粒进行了表征。实验结果表明，当用氢气作为还原剂时，以低代树形分子为保护剂，通过优化还原条件，可成功制备尺寸稳定、均一的银纳米颗粒，其粒径为2.9±0.5 nm，且所制备的银纳米颗粒的粒径分布较窄。根据树形分子的理论尺寸与制备的银纳米颗粒的粒径关系，可推断出大多数的银纳米颗粒是由多个树形分子所包围而稳定存在。     

Synthesis of iron oxide-based magnetic nanomaterials and composites

Various properties of spinel iron oxide nanoparticles are reviewed in relation to the control of the particle size and the control of their dispersion in a variety of matrices. The deep knowledge of the different synthesis parameters and the interfacial oxide–solution characteristics allow us to prepare a large variety of materials like calibrated nanoparticles and inorganic or hybrid nanocomposites.     

Synthesis of P(MBA-co-MAA) microsphere-grafted PAMAM dendrimers and their application as supporters for gold nanoparticles

Poly(N,N′-methylenebisacrylamide-co-acrylic acid) microsphere-supported polyamidoamine (PAMAM) dendrimers up to third generation (G) were grown onto the surface as well as the gel-layer of P(MBA-co-MAA) microspheres by a divergent method. The P(MBA-co-MAA) supported PAMAM dendrimers were used as heterogeneous stabilizers for the gold nanoparticles by an in situ reduction of HAuCl₄ via the efficient coordination interaction between the amino groups of the supported PAMAM dendrimers and the gold atoms. The effects of the generations of the P(MBA-co-MAA) supported PAMAM dendrimer on the loadings and the catalytic activity of the heterogeneous Au nanoparticles were systematically investigated with the reduction of 4-nitrophenol to 4-aminophenol as a model reaction.     

Structure modifications during thermal processing of silicon alkoxyde derived silica-iron oxide nanocomposites

The effects of iron concentration in the matrix structure of monolithic γ-Fe₂O₃/SiO₂ nanocomposites with different thermal processing have been studied by means of X-ray diffraction, Fourier transform infrared spectroscopy, temperature programmed decomposition-mass spectrometry and thermogravimetric analysis. The chemical changes occurring during the formation and subsequent growth of iron oxide nanoparticles, have been found to modify the formation process of alkoxysilane derived xerogels as a consequence of the competition for water molecules in the reaction medium. Specifically, the water releasing from the xerogels is shifted towards higher temperatures as a consequence of Fe³⁺ aquocomplexes formed in early stages of the synthesis. The iron content is also associated with changes in the polycondensation of the silica matrix and in the performance of chemical additives used to preserve the mechanical properties of the studied nanocomposites. These modifications extend to the thermal processing of samples, hindering the decomposition and subsequent removal of residues.     

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.     

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.     

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.     

Bifunctional electroactive nanostructured membranes

The advent of techniques based upon the spontaneous assembly of different materials with control over molecular architecture has afforded the fabrication of composite thin films for many nanotechnological applications. The layer-by-layer technique (LbL), in particular, has largely been used in the molecular level processing of nanohybrid systems in the form of multilayers, owing to its low cost and experimental simplicity. In this study we describe the fabrication of a novel, bifunctional film containing platinum nanoparticles/polyamidoamine (PAMAM) dendrimers. Pt nanoparticles were chemically synthesized/stabilized in the presence of PAMAM dendrimers and incorporated in LbL films in conjunction with nickel tetrasulfonated phthalocyanine (NiTsPc). A metallophthalocyanine was chosen because of its well-defined redox activity. Indium tin oxide (ITO)-covered glass plates were used as substrates for film deposition. The nanocomposites displayed high electrocatalytic activity toward dopamine and hydrogen peroxide molecules, two compounds with dissimilar chemical properties.     

Templated nucleation of hybrid iron oxide nanoparticles on polysaccharide nanogels

Novel organic–inorganic hybrid nanoparticles consisting of polymer–hydrogel nanoparticles (nanogels) and iron oxide were developed for potential biomedical applications. Hybrid nanoparticles were prepared by a simple procedure using polysaccharide nanogels as a reactive site for iron oxide formation. The hybrid nanoparticles have a narrow size distribution with a diameter of approximately 30 nm and show high colloidal stability. These nanohybrid particles could be used as a contrast medium for magnetic resonance imaging or for magnetic hyperthermia therapy.     

Dependence of Property of Silver Nanoparticles within Dendrimer-template on Molar Ratios of Ag+ to PAMAM Dendrimers

G5.0‐OH PAMAM dendrimers were used to prepare fluorescent silver clusters with weaker ultraviolet irradiation reduction method, in which the molar ratio of Ag⁺ to PAMAM dendrimers was the key factor to determine the geometry and properties of silver nanoparticles. The results showed that because of G5.0‐OH PAMAM dendrimers as strong encapsulatores, when the molar ratios of Ag⁺ to PAMAM dendrimers was smaller than 5, the obtained Ag_n clusters (n<5) had line structures and "molecular‐like" properties, which were highly fluorescent and quite stable in aqueous solution. Whereas when the molar ratios were between 5 and 8, the obtained Ag_n clusters were 2D structures and their fluorescence was weaker. When the molar ratio was larger than 8, the structure of silver nanoparticles was 3D and no fluorescence was observed from the obtained silver nanoparticles.     

Nonaqueous synthesis and characterization of capped α-Fe2O3 nanoparticles from iron(III) hydroxy-oleate precursor

The synthesis of capped α-Fe₂O₃ nanoparticles from thermal treatment of iron (III) hydroxy-oleate in boiling organic solvents around 250 °C with retention of the integrity of the oleate units during the reaction process is reported. The formation of capped iron oxide particles is accomplished under aerobic conditions while the solvents used in the synthesis have strong influence on the nature and morphology of nanoparticles. These nanoparticles are studied by means of X-ray powder diffraction, IR and XPS while the morphology and particle size of nanocrystals are evaluated using SEM and TEM analysis suggesting the formation of monocrystalline α-Fe₂O₃ particles having cubical and spherical morphologies with sizes ranging from 20 to 30 nm. This organophilic material with oleate capping around the surfaces can be readily dispersed in organic solvents thus forming organosols. These organosols exhibit band-edge emission photoluminescence band both in toluene as well as in solid state while FT-IR analysis reveals formation oleate capped nanoparticles The XPS data indicate ferric state having doublet from Fe 2p_3/2 and Fe 2p_1/2 core-level electrons.     

水热法制备聚苯胺及其铁氧化物纳米复合材料

利用水热法与无模板自组装法相结合, 以三氯化铁为氧化剂、 掺杂剂和反应物, 制备了聚苯胺及其铁氧化物纳米复合材料. 结果表明, 通过改变三氯化铁的浓度可以调控产物的微观结构和组成. 当三氯化铁的浓度≤0.13 mol/L时, 产物组成为未掺杂的低聚苯胺与α-Fe₂O₃的复合纳米材料, 其微观结构为纳米颗粒组装成的椭球体和准立方体; 当三氯化铁的浓度≥0.20 mol/L时, 产物组成为掺杂态聚苯胺, 其微观结构为纳米片层结构组装成的微米级大丽花球; 并且产物的粒径随三氯化铁浓度的增大而增大. 利用扫描电子显微镜、 红外光谱、 紫外-可见光谱、 X光电子能谱及X射线衍射等手段对产物的微观结构和组成进行了表征, 并探讨了产物的形成机理.     

New insights into the structure of PAMAM dendrimer/gold nanoparticle nanocomposites

In this work, we have employed a suite of complementary analytical techniques to shed light on the nanocomposite structures formed during gold nanoparticles (AuNPs) synthesis in the presence of poly(amidoamine) (PAMAM) dendrimers. Nanocomposites of AuNPs and either fourth or eighth generation amine-terminated PAMAM dendrimers (G4 or G8) were prepared. The size distributions of AuNPs and the nanocomposites were determined by transmission electron microscopy. Atomic force microscopy phase imaging and neutral impact collision ion scattering spectroscopy (NICISS) were utilized for the first time to investigate and compare nanocomposite structures formed from G4 and G8. Our results suggest that G4 stabilized the AuNP by capping the AuNP particle surface but that a certain fraction of the gold surface was still barely covered. In contrast, the metal nanoparticle surface was completely covered by G8. In addition, NICISS results provided evidence that nanocomposites deformed when being deposited directly onto a substrate.     

Synthesis, characterization, and intracellular uptake of carboxyl-terminated poly(amidoamine) dendrimer-stabilized iron oxide nanoparticles

We report the synthesis and characterization of a group of carboxyl-functionalized poly(amidoamine) (PAMAM) dendrimers of generation 3 (G3) that were used for the stabilization of superparamagnetic iron oxide (Fe(3)O(4)) nanoparticles (NPs). Folic acid (FA) molecules were conjugated onto the dendrimer surfaces in an attempt to achieve specific targeted imaging of tumor cells that overexpress FA receptors using dendrimer-stabilized Fe(3)O(4) NPs. Fe(3)O(4) NPs were synthesized using controlled co-precipitation of Fe(ii) and Fe(iii) ions and the formed dendrimer-stabilized Fe(3)O(4) NPs were characterized using transmission electron microscopy (TEM) and polyacrylamide gel electrophoresis (PAGE). The intracellular uptake of dendrimer-stabilized Fe(3)O(4) NPs was tested in vitro using KB cells (a human epithelial carcinoma cell line) that overexpress FA receptors. It appears that carboxyl-terminated PAMAM dendrimer-stabilized Fe(3)O(4) NPs can be uptaken by KB cells regardless of the repelling force between the negatively charged cells and the negatively charged particles. In the presence of a large amount of carboxyl terminal groups on the dendrimer surface, the receptor-mediated endocytosis of Fe(3)O(4) NPs stabilized by FA-modified dendrimers was not facilitated. It implies that the surface charge of dendrimer-stabilized magnetic iron oxide NPs in biological medium is an important factor influencing their biological performance.     

Preparation and characterization of Fe3O4@SiO2/APTPOSS core–shell composite nanomagnetics as a novel family of reusable catalysts and their application in the one‐pot synthesis of 1,3‐thiazolidin‐4‐one derivatives

Octakis[3‐(3‐aminopropyltriethoxysilane)propyl]octasilsesquioxane (APTPOSS) as a polyhedral oligomeric silsesquioxane derivative was prepared and used as a pioneer reagent to obtain a novel core–shell composite using magnetic iron oxide nanoparticles as the core and the inorganic–organic hybrid polyhedral oligomeric silsesquioxane as the shell. Fe₃O₄@SiO₂/APTPOSS were confirmed using Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, dynamic light scattering, thermogravimetric analysis, X‐ray diffraction and vibrating sample magnetometry. The inorganic–organic hybrid polyhedral oligomeric silsesquioxane magnetic nanoparticles were used as an efficient new heterogeneous catalyst for the one‐pot three‐component synthesis of 1,3‐thiazolidin‐4‐ones under solvent‐free conditions. Moreover, these nanoparticles could be easily separated using an external magnet and then reused several times without significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Air and water free solid-phase synthesis of thiol stabilized au nanoparticles with anchored, recyclable dendrimer templates

Solid-phase synthetic templates for Au nanoparticles were developed using Merrifield resins and polyamidoamine (PAMAM) dendrimers. This synthetic scheme affords the opportunity to prepare metal nanoparticles in the absence of air and water, and it does not necessitate phase transfer agents that can be difficult to remove in subsequent steps. Amine-terminated generation 5 PAMAM (G5NH2) dendrimers were grafted to anhydride functionalized polystyrene resin beads and alkylated with 1,2-epoxydodecane to produce G5C12anch. The anchored dendrimers bound both CoII and AuIII salts from toluene solutions at ratios comparable to those of solution phase alkyl-terminated PAMAM dendrimers. The encapsulated AuIII salts could be reduced with NaBH4 to produce anchored dendrimer encapsulated nanoparticles (DENs). Treatment of the anchored DENs with decanethiol in toluene extracted the Au nanoparticles from the dendrimers as monolayer protected clusters (MPCs). After a brief NaCN etch, the anchored dendrimers were readily recycled and a subsequent synthesis of decanethiol Au MPCs was performed with comparable MPC yield and particle size distribution.     

Chiral dendrimer encapsulated Pd and Rh nanoparticles

The synthesis of a series of chiral PAMAM dendrimers and the formation of chiral dendrimer encapsulated metal nanoparticles are described.