A multifunctional architecture for biomedical applications has been developed by deliberately combining the useful functions of superparamagnetism, luminescence, and surface functionality into one material. Good control of the core-shell architecture has been achieved by employing a sol-gel synthesis. Superparamagnetic iron oxide nanoparticles are first coated with silica to isolate the magnetic core from the surrounding. Subsequently, the dye molecules are doped inside a second silica shell to improve photostability and allow for versatile surface functionalities. The architecture has been characterized by transmission electron microscopy, UV-vis absorption and emission spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and magnetometry. The hybrid nanoparticles exhibit improved superparamagnetic behavior over the as-received nanoparticles with a significant decrease in the blocking temperature. The architecture shows emission properties similar to those of the free dye molecules, suggesting that the first silica shell successfully prevents luminescence quenching by minimizing dyemagnetic core interactions.

No abstract

Open single-walled carbon nanotubes (SWNTs) are attractive as potential storage media for hydrogen gas. The present paper investigates the micropore structure of HiPco SWNTs samples, as studied by nitrogen and argon adsorption technique at low pressures. The proportion of open SWNT is estimated with the Horvath−Kawazoe method. The results show that as-prepared samples may contain as much as 40% open SWNTs, whereas the oxidative purification process reduces this amount significantly. X-ray diffraction and Raman spectroscopy show that the Horvath−Kawazoe method is reliable for estimating the diameter of open SWNTs. In addition, the Horvath−Kawazoe method appears to be sensitive to species adsorbed in the outer grooves.

Current processes to manufacture nanotubes at commercial scales are unfortunately imperfect and commonly generate undesirable byproducts. After manufacturing, purification is necessary and is a rate and cost determining step in advancing the development of commercial products based on nanotubes. Boron nitride nanotubes (BNNTs) produced without metal catalysts from high-temperature processes are known to contain a significant amount (e.g., 50 wt %) of various boron derivatives. Herein we report a simple yet efficient and scalable process to purify these types of BNNT materials at commercial scales, from a few grams to hundreds of grams, at purity over 85 wt % in a single step. The process relies on a vertically mounted flow tube reactor and scrubber system that can be operated under pure or diluted chlorine gas flow at temperatures up to 1100 °C. The main chemical reactions driving the purification are the conversion of boron and BN derivatives into BCl3 and HCl, which are removed as gaseous species, while pristine BNNTs are left behind. The preferential etching of impurities over pristine BNNTs shows the extreme chemical resistance of BNNTs in this harsh environment and opens up new applications for this nanomaterial. The process has been examined at various temperatures, up to 1050 °C, and the resulting materials display improved BNNT purity and quality across a range of imaging and spectroscopic assessments. The recommended temperature to optimize quality with yield is 950 °C, although higher quality material is obtained at a higher temperature.