Shumin Han

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.

Ultrasensitive electrochemical detection of tumor cells based on multiple layer CdS quantum dots-functionalized polystyrene microspheres and graphene oxide - polyaniline composite.

In this work, a novel ultrasensitive electrochemical biosensor was developed for the detection of K562 cell by a signal amplification strategy based on multiple layer CdS QDs functionalized polystyrene microspheres(PS) as bioprobe and graphene oxide(GO) -polyaniline(PANI) composite as modified materials of capture electrode. Due to electrostatic force of different charge, CdS QDs were decorated on the surface of PS by PDDA (poly(diallyldimethyl-ammonium chloride)) through a layer-by-layer(LBL) assemble technology, in which the structure of multiple layer CdS QDs increased the detection signal intensity. Moreover, GO-PANI composite not only enhanced the electron transfer rate, but also increased tumor cells load ratio. The resulting electrochemical biosensor was used to detect K562 cells with a lower detection limit of 3 cellsmL-1 (S/N = 3) and a wider linear range from 10 to 1.0 × 107 cellsmL-1. This sensor was also used for mannosyl groups on HeLa cells and Hct116 cells, which showed high specificity and sensitivity. This signal amplification strategy would provide a novel approach for detection, diagnosis and treatment for tumor cells.

Hydrogen absorption–desorption characteristics of a Gd2Co7-type Sm1.6Mg0.4Ni7 compound

In this paper, we report a new Gd2Co7-type Sm1.6Mg0.4Ni7 compound as a hydrogen storage material with a special hydrogen absorption/desorption process and good hydrogen storage ability. The Gd2Co7-type Sm1.6Mg0.4Ni7 compound absorbs 1.88 wt% H2 within 17 min at 298 K under 10 MPa H2. Meanwhile, the hydrogen absorption speed accelerates to 3.4 min after 20 hydrogenation/dehydrogenation cycles with a 1.44 wt% H2 under 3 MPa H2. Especially, the capacity retention of the compound is 99.3% at the 100th cycle. We found the hydrogen absorption/desorption of the compound undergoes two equilibrium stages, relating to the transformation of H2 between H-solid solution phase and hydride phase with a lower rate and higher enthalpy change at the lower concentration H2 stage, and the direct conversion between H2 and the hydride phase with a higher rate and lower enthalpy change at the higher concentration H2 stage. The two step mode lowers the inner-molecular strain and mismatch in subunit volumes of the compound in hydrogen absorption/desorption, caused by the transformation of H2 at the lower concentration of H2 stage, thus leading to good structural stability and excellent cycling stability. The new insights are expected to provide viable intermetallic materials as high-pressure tank materials for hydrogen storage with nice hydrogen storage properties.

Enhanced H2 sorption performance of magnesium hydride with hard-carbon-sphere-wrapped nickel

Magnesium hydride is regarded as one of the most ideal candidates for hydrogen storage, but its relatively high operating temperatures and slow kinetics always hinder its commercial applications. Herein, we first fabricated hard-carbon-sphere-wrapped Ni (Ni/HCS) via a mild chemical method; subsequently, the as-prepared additive was introduced to fabricate an Mg–Ni/HCS composite by using hydriding combustion synthesis. Hard carbon spheres (HCS) effectively inhibited the agglomeration of hydride particles during hydrogen storage cycling; they could also provide active sites to promote the nucleation of Mg-based hydrides. During the hydriding combustion synthesis procedure, in situ-formed Mg2NiH4 could induce the absorption of MgH2, thus triggering its hydrogen properties. Remarkable enhancement in hydrogen absorption properties of the composite was found. The composite absorbed 6.0 wt% H2 within 5 min at 275 °C; moreover, even at 75 °C, it could still absorb 3.5 wt% H2. Furthermore, it delivered a high reversible hydrogen absorption capacity of 6.2 wt% and excellent rate capability at 350 °C. It was also demonstrated that the composite could release 6.2 wt% H2 at 350 °C within 5 min. A rather low activation energy value (65.9 kJ mol−1) for the dehydrogenation of MgH2 was calculated as compared to that for commercial MgH2 (133.5 kJ mol−1).