Dandan Ke

Phase transformation and cycling characteristics of a Ce2Ni7-type single-phase La0.78Mg0.22Ni3.45 metal hydride alloy

A Ce2Ni7-type single-phase La0.78Mg0.22Ni3.45 alloy has been prepared by zoning annealing of the as-cast sample. It is found that at temperatures below 890 °C, non-super-stacking CaCu5- and MgCu4Sn-type phases disappear and super-stacking Ce5Co19-, Gd2Co7- and Ce2Ni7-type phases remain. The Ce5Co19-type phase can totally transform into the Ce2Ni7-type phase via a peritectic reaction at temperatures of 890–900 °C. At temperatures of 900–950 °C, the Gd2Co7-type phase melts and decomposes into the Ce5Co19-type phase, and the newly formed Ce5Co19-type phase subsequently reacts to form the Ce2Ni7-type phase. The Ce2Ni7-type single phase remains stable even at higher temperatures of 950–975 °C. The single-phase alloy shows a superior discharge capacity, close to 394 mA h g−1, and high electrochemical cycling stability, which can achieve 413 cycles as its discharge capacity reduces to 60% of the maximum value. We found that the capacity attenuation of the single-phase alloy is mainly due to the loss of active material at the alloy surface caused by oxidization of La and Mg, and the pulverization of the alloy is not severe with 100 charge/discharge cycles. The crystal structure of the single-phase alloy can be preserved well. Oxidation of La occurs prior to that of Mg. La hydroxide grows from nano-structured needles to larger-scaled rods then to unformed lamellar hydroxide, whereas the precipitation of Mg forms as irregular lamellae inlaid with hexagonal flakes.

Semiconductor quantum dots surface modification for potential cancer diagnostic and therapeutic applications

Semiconductor Quantum dots (QDs) have generated extensive interest for biological and clinical applications. These applications arise from their unique properties, such as high brightness, long-term stability, simultaneous detection of multiple signals, tunable emission spectra. However, high-quality QDs, whether single or core-shell QDs, are most commonly synthesized in organic solution and surface-stabilized with hydrophobic organic ligands and thus lack intrinsic aqueous solubility. For biological applications, very often it is necessary to make the QDs dispersible in water and therefore to modify the QD surfaces with various bifunctional surface ligands or caps to promote solubility in aqueous media. Well-defined methods have been developed for QD surface modification to impart biocompatibility to these systems. In this review, we summarize the recent progress and strategies of QDs surface modification for potential cancer diagnostic and therapeutic applications. In addition, the question that arose from QD surface modification, such as impact of size increase of QD bioconjugates after surface-functionalization or surface modification on photophysical properties of QDs, are also discussed.