Size-controlled synthesis of monodisperse core/shell nanogels

Small, monodisperse nanogels (∼50-nm radius) were synthesized by free-radical precipitation polymerization and were characterized using a suite of light scattering and chromatography methods. Nanogels were synthesized with either N-isopropylacrylamide or N-isopropylmethacrylamide as the main monomer, with acrylic acid or 4-acrylamidofluorescein as a comonomer and N,N′-methylenebis(acrylamide) as a cross-linker. By varying the surfactant and initiator concentrations, particle size was controlled while maintaining excellent monodispersity. An amine-containing shell was added to these core particles to facilitate subsequent bioconjugation. Successful conjugation of folic acid to the particles was demonstrated as an example of how such materials might be employed in a targeted drug delivery system.     

Low-temperature synthesis and growth mechanism of uniform nanorods of bismuth sulfide

A low-temperature solution-phase method has been demonstrated for the synthesis of uniform nanorods of Bi₂S₃ with diameter of 18 nm and length of below 200 nm. Transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and X-ray diffraction (XRD) studies revealed that these nanorods were grown from a colloidal dispersion of amorphous Bi₂S₃ particles, which was first formed through a thermal reaction between Bi-thiol complexes Bi(SC₁₂)₃ and thioacetamide (TAA) in a pure dodecanethiol (C₁₂SH) solvent at a temperature of 95 °C. Based on these studies, the growth mechanism of Bi₂S₃ nanorods was properly proposed.     

Controlled synthesis, growth mechanism, and properties of monodisperse CdS colloidal spheres

Highly monodisperse submicrometer CdS colloidal spheres (CSCS) with a controllable and tunable size (between 80 and 500 nm) have been synthesized through a facile solvothermal technique. Owing to the controllability of the reaction process, the growth mechanism of the colloidal spheres has been elucidated in detail. The whole growth process can be summarized as homogenous and slow nucleation of nanocrystals, formation of "cores" through 3D-oriented attachment of nanocrystals, and further surface-induced growth to monodisperse colloidal spheres through in situ formation and random attachment of additional nanocrystals. It has been demonstrated that the obtained CSCS colloidal particles are able to be assembled into films which show characteristic stop band gaps of photonic crystals. By using the CSCS as a template, Ag2S, Bi2S3, Cu2S, HgS, and Sb2S3 colloidal spheres, which are difficult to obtain directly, have also been prepared successfully through ion exchange.     

Size-controlled and monodisperse enzyme-encapsulated chitosan microspheres developed by the SPG membrane emulsification technique

The amphiphilic gradient copolymers of 2,2,2-trifluoroethyl methacrylate (TFEMA) and acrylic acid (AA) have been synthesized by using amphiphilic RAFT agent via emulsifier-free emulsion polymerization with a starved feed method of adding TFEMA. Different cosolvents are added into polymerization system to inhibit AA's homopolymerization of in aqueous phase. RAFT polymerization kinetics under different reaction conditions are discussed in detail. (1)H NMR results indicate that the obtained copolymer has a chain structure with AA segments gradually changing to TFEMA segments. The copolymer latexes exhibit good pH stability (pH value from 5 to 14) and Ca(2+) stability. The self-assembly behavior of gradient copolymers in selective solvents are observed and studied by transmission electron microscopy. All the copolymers can form spherical micelles, but the homogeneity and size of micelles are different.     

Solventless synthesis of monodisperse Cu2S nanorods, nanodisks, and nanoplatelets

Cu(2)S nanocrystals with disklike morphologies were synthesized by the solventless thermolysis of a copper alkylthiolate molecular precursor. The nanodisks ranged from circular to hexagonal prisms from 3 to 150 nm in diameter and 3 to 12 nm in thickness depending on the growth conditions. High resolution transmission electron microscopy (HRTEM) revealed the high chalcocite (hexagonal) crystal structure oriented with the c-axis ([001] direction) orthogonal to the favored growth direction. This disk morphology is thermodynamically favored as it allows the extension of the higher energy [100] and [110] surfaces with respect to the [001] planes. The hexagonal prism morphology also appears to relate to increased C-S bond cleavage of adsorbed dodecanethiol along the more energetic [100] facets relative to [001] facets. Monodisperse Cu(2)S nanodisks self-assemble into ribbons of stacked platelets. This solventless approach provides a new technique to synthesize anisotropic metal chalcogenide nanostructures with shapes that depend on both the face-sensitive thermodynamic surface energy and the surface reactivity.     

Near monodisperse TiO2 nanoparticles and nanorods

Highly crystalline, near monodisperse TiO2 nanoparticles, nanorods and their metal-ion-doped (Sn4+, Fe3+, Co2+, and Ni2+, etc.) derivatives have been prepared by well-controlled solvothermal reactions. Through adjusting the reaction parameters, such as reaction temperature, duration, and concentration of the reactants, the size, shape, and dispersibility of the products can be controlled. A possible reaction mechanism can be proposed based on experimental evidence.     

Structural characteristics and growth of pentagonal silver nanorods prepared by a surfactant method

The crystal structure and growth mechanism of silver nanorods prepared by a seed-mediated surfactant method using the cationic surfactant cetyltrimethylammonium tosylate (CTAT) and its wormlike micelles are characterized by conventional and high-resolution transmission electron microscopy. Depending on the nanorod orientations, two types of electron diffraction patterns are obtained from a truncated decahedral structure consisting of five crystal units packing along [111] twining planes with five [111] planes on each end and five circumferential [001] side surfaces parallel to a <110> longitudinal direction. High-resolution images of the nanorods and the corresponding Fourier transform patterns confirm the results from the morphological and diffraction analyses. The silver nanorods grow only from multiply twinned decahedral seeds, and the high selectivity of surfactant attachment results in a barrier to the transfer of silver atoms from the solution to the circumferential [100] planes. Blockage of circumferential growth causes the aspect ratio of the rod to grow.     

Size-controlled synthesis of SnO2 nanoparticles using reverse microemulsion method

Tin oxide nanoparticles were prepared using an ionic surfactant (sodium dodecyl sulfate) and tin (IV) chloride as an inorganic precursor via the reverse microemulsion method. The size of the nanoparticles is controlled by variation of water-to-surfactant ratio. Eliminating of surfactant in prepared nanoparticles was confirmed by the infrared spectroscopy after sequential calcinations. Transmission electron microscopy, surface area, pore volume, average pore diameter, pore size distribution and X-ray diffraction results were used for evaluation of size distribution, shape and structure of prepared SnO₂ nanoparticles. Transmission electron micrographs confirmed that the obtained materials are spherical nanoparticles. The X-ray diffraction results show the crystalline phases of all samples are SnO₂ with tetragonal structured crystal. In addition, the X-ray diffraction and transmission electron microscopy data showed that the size of SnO₂ nanoparticles decreased with decreasing the water-to-surfactant ratio.     

Size-controlled synthesis and characterization of quantum-size SnO2 nanocrystallites by a solvothermal route

By using ethylenediamine as both an alkali and ligand, quantum size SnO₂ nanocrystallites were synthesized with a solvothermal route. The transmission electron micrographs (TEM) were employed to characterize the morphologies of the products. The crystal sizes of the as-synthesized SnO₂ were ranged form 2.5 to 3.6 nm. The crystal structure and optical properties of the products were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, optical absorption spectra, photoluminescence and Raman spectra. Anisotropic growth of the SnO₂ nanocrystallites was observed by altering the solvent from water to ethanol. The SnO₂ nanocrystal showed apparent quantum confinement effects. Finally, the mechanism for the formation of quantum size SnO₂ was also discussed.     

Size-controlled synthesis of magnetite nanoparticles

Monodisperse magnetite nanoparticles have been synthesized by high-temperature solution-phase reaction of Fe(acac)3 in phenyl ether with alcohol, oleic acid, and oleylamine. Seed-mediated growth is used to control Fe3O4 nanoparticle size, and variously sized nanoparticles from 3 to 20 nm have been produced. The as-synthesized Fe3O4 nanoparticles have inverse spinel structure, and their assemblies can be transformed into gamma-Fe2O3 or alpha-Fe nanoparticle assemblies, depending on the annealing conditions. The reported procedure can be used as a general approach to various ferrite nanoparticles and nanoparticle superlattices.     

二苯胺磺酸钠还原法制备粒径可控的金纳米粒子

采用二苯胺磺酸钠还原四氯合金酸的方法,在室温条件下,用SDS(十二烷基硫酸钠)、SDBS(十二烷基苯磺酸钠)作表面活性剂,成功地合成了金纳米粒子.分别讨论了还原剂二苯胺磺酸钠、表面活性剂(SDS、SDBS)及四氯台金酸的浓度等对金纳米粒子的粒径和形貌的影响.通过控制反应条件,可以合成出平均粒径大约为10、14、30、36nm的金纳米粒子.利用透射电镜(TEN)、紫外-可见(UV-Vis)吸收光谱对金纳米粒子进行了表征.研究结果表明不同的SDS或SDBS/HAuCl4的摩尔比,对金纳米粒子的尺寸大小有影响.     

Size-controlled synthesis of orderly organized cube-shaped lead sulfide nanocrystals via a solvothermal single-source precursor method

Monodisperse cube-shaped lead sulfide (PbS) nanocrystals were successfully synthesized by virtue of a solvothermal single-source precursor method at mild reaction conditions. These resulted PbS nanocrystals have the average size in a range of 10 nm and a uniform cubic shape, shown by TEM and HRTEM, respectively. Due to their narrow size distribution, orderly self-organized arrays on a large scale can be easily obtained. Experimental results indicate that several factors, such as coordinating ability of the solvent, carbon number of the substitute alkyls (n), reaction temperature, and concentration of the precursor, play key roles in the final size and size distribution of PbS nanocrystals. This finding will enhance our understanding for the formation mechanism of nanostructured materials with special shapes.     

Size-controlled synthesis and characterization of thiol-stabilized gold nanoparticles

Size-controlled synthesis of nanoparticles of less than a few nanometers in size is a challenge due to the spatial resolution limit of most scattering and imaging techniques used for their structural characterization. We present the self-consistent analysis of the extended x-ray absorption fine-structure (EXAFS) spectroscopy data of ligand-stabilized metal nanoclusters. Our method employs the coordination number truncation and the surface-tension models in order to measure the average diameter and analyze the structure of the nanoparticles. EXAFS analysis was performed on the two series of dodecanethiol-stabilized gold nanoparticles prepared by one-phase and two-phase syntheses where the only control parameter was the gold/thiol ratio xi, varied between 6:1 and 1:6. The two-phase synthesis resulted in the smaller particles whose size decreased monotonically and stabilized at 16 A when xi was lowered below 1:1. This behavior is consistent with the theoretically predicted thermodynamic limit obtained previously in the framework of the spherical drop model of Au nanoparticles.     

Large-scale, surfactant-free, hydrothermal synthesis of lithium aluminate nanorods: optimization of parameters and investigation of growth mechanism

Lithium aluminate nanorods were successfully synthesized from Al2O3 nanoparticles and lithium hydroxide by a simple, large-scale hydrothermal process without any surfactant or template. The various reaction parameters were optimized to achieve the maximum yield. The as-obtained nanorods had orthorhombic beta-lithium aluminate structure with edges in the range of 40-200 nm and lengths of 1-2 mum confirmed by SEM, TEM, XRD, and NMR. Upon calcination at 1273 K for 12 h it transformed to gamma-lithium aluminate, yet maintained the initial morphology, demonstrating the thermal stability. The ratio of lithium hydroxide to aluminum oxide showed a significant effect on the morphology as Li/Al = 1 gives "microroses", whereas Li/Al = 3 and Li/Al = 15 gave "microbricks" and "nanorods", respectively. Investigation of the mechanism showed that the nanorods were formed via a "rolling-up" mechanism. As we used all-inorganic raw materials and a simple synthetic procedure under mild conditions, the scale-up of this process for large-scale production should be very easy.     

Size-controlled synthesis of highly water-soluble silver nanocrystals

We describe a modified polyol process for the synthesis of silver nanocrystals with uniform sizes ranging from several nanometers to 20 nm. The use of polyacrylic acid, in place of polyvinylpyrrolidone in the conventional polyol process, significantly limits the growth of silver nanocrystals, prevents the interparticle aggregation and fusion, and leads to a uniform population of samples with high water solubility. The size of nanocrystals can be conveniently tuned by controlling the reaction time, the concentration and chain length of the polymeric surfactants, and the reaction temperature. Uniform silver nanocrystals within sizes below 20 nm are preferred candidates over larger particles for applications where high density of optical absorption is required, for example, for photothermal conversion in cancer therapy.     

One-dimensional BiPO4 nanorods and two-dimensional BiOCl lamellae: fast low-temperature sonochemical synthesis,characterization, and growth mechanism

Regular BiPO4 nanorods, for the first time, and BiOCl lamellae have been successfully synthesized via a facile sonochemical method in a surfactant/ligand-free system under ambient air. The as-prepared products are characterized by XRD, TEM, SAED, FE-SEM, HRTEM, and Raman spectroscopy. The effects of pH and ultrasound irradiation on the phase and morphology of the products are studied and the sonochemical formation mechanisms of 1D and 2D structures are discussed. TEM data from samples made after different reaction times suggest an ultrasound-induced nucleation and an oriented-attachment growth mechanism.     

Synthesis, optical properties, and growth mechanism of blue-emitting CdSe nanorods

Blue-emitting, cubic phase CdSe nanorods with an approximate diameter of 2.5 nm and lengths up to 12 nm have been synthesized at low temperature (100 degrees C) in a single surfactant using a single-source molecular precursor. Transmission electron microscopy and dynamic light scattering measurements indicate that the nanorods are formed from self-assembly of isotropic nanoclusters. Anisotropic growth in a single surfactant appears to be favored when growth occurs below the thermal decomposition temperature of the single-source precursor.