Easy preparation of iron oxide nanoparticles [5-and 11-nm maghemite (γ-Fe 2 O 3 ) and 19-nm magnetite (Fe 3 O 4 )] by thermal decomposition of Fe(CO) 5 in the presence of residual oxygen of the system and by consecutive aeration were investigated by TEM/HRTEM, XRD, and Mössbauer spectroscopy. Also, the magnetic properties of the nanoparticles were studied by SQUID magnetometer and optical microscopy. It was suggested that the intermediate iron oxide nanoparticles (before aeration) were formed by the competing processes of oxidation and crystal growth after decomposition of Fe(CO) 5 . At room temperature, the aerated 5-nm particles were superparamagnetic without interaction among the particles, whereas the 19-nm particles were ferrimagnetic. The 11-nm iron oxide nanoparticles were superparamagnetic with some interactions among the particles.

Nanorods as one-dimensional nanostructured materials have attracted much attention due to their peculiar properties, which originate from their high surface area and low dimensionality. [1,2] Recently, much effort has been devoted to the synthesis of various nanorods, including metals, [3,4] oxides, [5±8] and chalcogenides. [9] Among them, metal-oxide nanorods have been shown to possess many interesting properties that make them useful for a wide range of applications such as catalysts, [8,10] electrochromic devices, [11] magnetic storages, [12] lasers, and sensors. [13] Many solution-based syntheses of nanorods have utilized a thermal decomposition reaction of delicate and costly organometallic precursors in mixed surfactants. [3,9] A template-directed synthesis has been studied as an alternative route. [8,14] However, it may contaminate the nanorods by the successive removal process of the template materials. Here, we report a novel and easy route to Fe 2 O 3 nanorods by a sol-gel-mediated reaction of ubiquitous Fe 3+ ions in reverse micelles. A plausible mechanism is proposed for the formation of these nanorods, and it is expected that this synthetic technique can be extended to obtain other metal oxides.The reaction was carried out utilizing a sol±gel reaction inside reverse micelles and followed by crystallization by reflux. This sol±gel reaction, which we utilized here, was first reported by A. E. Gash et al.[ gel in a container. Instead of producing a container-sized monolithic gel, we prepared a countless number of monolithic gel particles inside reverse micelles using the reported sol±gel reaction and water-in-oil type microemulsion stabilized by an oleic acid surfactant. Scheme 1 represents the transformations of materials in a reverse micelle. First, we prepared Fe 2 O 3 monolithic gel particles with a narrow size distribution. This was possible by slow gelation initiated by a proton scavenger inside the reverse micelles. Each reverse micelle acts as a microreactor, which produced a monolithic gel particle in itself. Next, the gel particles were washed with a polar solvent to remove chloride impurities and excess surfactants and then air-dried. Now, each gel particle is composed of a porous network of amorphous Fe 2 O 3 (confirmed by X-ray diffraction (XRD) pattern) and its surface is roughly coated with surfactants. At this stage, scanning electron microscopy (SEM) images of gel particles showed shapeless aggregates and could not give any meaningful information. Then, the gel powder was treated in a highboiling-point solvent with reducing properties while controlling the temperature and the atmosphere, inducing crystallization [16] with a controlled phase depending on the conditions. During crystallization, the partially crystallized monolithic gel particles seem to fuse together in an end-to-end manner and grow into a nanorod. At the same time, a decrease of the particle size by crystallization seems to occur. Figure 1 shows the representative FTIR spectra of Fe 2 O 3 gels and a-Fe 2 O 3 (hematite...

We report the systematic control of the morphology of β-NaYF4:Yb,Er/Tm upconversion nanophosphors (UCNPs) from large spheres (37.9 nm) to rods (length = 60.1 nm, width = 21.5 nm) and from rods to hexagonal prisms (length = 48.8 nm, width = 44.0 nm) or small spheres (14.0 nm) by the use of a surfactant, an additive, and lanthanide doping. Increasing the ratio of oleic acid (OA) to 1-octadecene (ODE) caused a decrease in the size of the UCNPs, and increasing the OA/ODE ratio above a critical value caused the particle shape to change from a sphere to a rod. The length-to-width aspect ratio (AR) of upconversion nanorods (UCNRs) was finely manipulated from 1.28 to 2.80. The rounded tips of the UCNRs were flattened by adding Cl(-) ions, and the UCNRs changed to hexagonal prisms with a controllable AR depending on the quantity of Cl(-) ions. Additionally, the morphology of the β-NaYF4-based UCNPs was controlled by lanthanide doping. The size and AR of the UCNRs decreased with Gd(3+) doping, and the UCNRs ultimately transformed into small spheres (14.0 nm) with high monodispersity. Doping with Ce(3+) ions also decreased the AR of the UCNRs from 2.80 to 1.27. In addition, highly transparent polymer composites for 3D volumetric displays were fabricated by blending high-AR β-NaYF4:Yb,Er/Tm UCNRs with polydimethylsiloxane. These composites exhibited bright green and blue upconversion light during excitation with 980 nm light.

c Silver nanoparticles (AgNPs) are considered to be a potentially useful tool for controlling various pathogens. However, there are concerns about the release of AgNPs into environmental media, as they may generate adverse human health and ecological effects. In this study, we developed and evaluated a novel micrometer-sized magnetic hybrid colloid (MHC) decorated with variously sized AgNPs (AgNP-MHCs). After being applied for disinfection, these particles can be easily recovered from environmental media using their magnetic properties and remain effective for inactivating viral pathogens. We evaluated the efficacy of AgNP-MHCs for inactivating bacteriophage X174, murine norovirus (MNV), and adenovirus serotype 2 (AdV2). These target viruses were exposed to AgNP-MHCs for 1, 3, and 6 h at 25°C and then analyzed by plaque assay and real-time TaqMan PCR. The AgNP-MHCs were exposed to a wide range of pH levels and to tap and surface water to assess their antiviral effects under different environmental conditions. Among the three types of AgNP-MHCs tested, Ag30-MHCs displayed the highest efficacy for inactivating the viruses. The X174 and MNV were reduced by more than 2 log 10 after exposure to 4.6 ؋ 10 9 Ag30-MHCs/ml for 1 h. These results indicated that the AgNP-MHCs could be used to inactivate viral pathogens with minimum chance of potential release into environment. With recent advances in nanotechnology, nanoparticles have been receiving increased attention worldwide in the fields of biotechnology, medicine, and public health (1, 2). Owing to their high surface-to-volume ratio, nano-sized materials, typically ranging from 10 to 500 nm, have unique physicochemical properties compared with those of larger materials (1). The shape and size of nanomaterials can be controlled, and specific functional groups can be conjugated on their surfaces to enable interactions with certain proteins or intracellular uptake (3-5).Silver nanoparticles (AgNPs) have been widely studied as an antimicrobial agent (6). Silver is used in the creation of fine cutlery, for ornamentation, and in therapeutic agents. Silver compounds such as silver sulfadiazine and certain salts have been used as wound care products and as treatments for infectious diseases due to their antimicrobial properties (6, 7). Recent studies have revealed that AgNPs are very effective for inactivating various types of bacteria and viruses (8-11). AgNPs and Ag ϩ ions released from AgNPs interact directly with phosphorus-or sulfur-containing biomolecules, including DNA, RNA, and proteins (12-14). They have also been shown to generate reactive oxygen species (ROS), causing membrane damage in microorganisms (15). The size, shape, and concentration of AgNPs are also important factors that affect their antimicrobial capabilities (8,10,13,16,17).Previous studies have also highlighted several problems when AgNPs are used for controlling pathogens in a water environment. First, existing studies on the effectiveness of AgNPs for inactivating viral pathogens in water are limite...