Laifeng Li

Low-temperature negative thermal expansion of the antiperovskite manganese nitride Mn3CuN codoped with Ge and Si

We have synthesized antiperovskite manganese nitrides Mn3(Cu0.6SixGe0.4−x)N, (x=0–0.2) and investigated their negative thermal expansion (NTE) in the temperature range of 80–300 K. We found that the transition temperature of NTE moves toward lower temperature region and as well the NTE operation-temperature window (ΔT) becomes broader with increasing Si content. Typically, the giant low-temperature NTE coefficient identified in Mn3(Cu0.6Si0.15Ge0.25)N reaches as large as −16×10−6 K−1, and its ΔT reaches as wide as 100 K. The magnetic properties of these compounds were measured and correlated with the broadened NTE operation-temperature window. The present discovery highlights the potential applications of NTE materials in cryogenic engineering.

Giant Negative Thermal Expansion in NaZn13-Type La(Fe, Si, Co)13 Compounds

La(Fe, Si)13-based compounds are well-known magnetocaloric materials, which show a pronounced negative thermal expansion (NTE) around the Curie temperature but have not been considered as NTE materials for industrial applications. The NaZn13-type LaFe13-xSix and LaFe11.5-xCoxSi1.5 compounds were synthesized, and their linear NTE properties were investigated. By optimizing the chemical composition, the sharp volume change in La(Fe, Si)13-based compounds was successfully modified into continuous expansion. By increasing the amount of Co dopant in LaFe11.5-xCoxSi1.5, the NTE shifts toward a higher temperature region, and also the NTE operation-temperature window becomes broader. Typically, the linear NTE coefficient identified in the LaFe10.5Co1.0Si1.5 compound reaches as much as -26.1 × 10(-6) K(-1), with an operation-temperature window of 110 K from 240 to 350 K, which includes room temperature. Such control of the specific composition and the NTE properties of La(Fe, Si)13-based compounds suggests their potential application as NTE materials.

Hepatic cytochrome P450s metabolize aristolochic acid and reduce its kidney toxicity

Cytochrome P450s metabolize the naturally occurring nephrotoxin aristolochic acid. Using liver-specific cytochrome P450 reductase-null mice we found that a low but lethal dose of aristolochic acid I was ineffective in wild-type mice. Induction of hepatic CYP1A by 3-methylcholanthrene pretreatment markedly increased the survival rate of wild type mice given higher doses and these mice were protected from aristolochic acid I-induced renal injury. Clearance of aristolochic acid I in null mice was slower compared to control and the 3-methylcholanthrene-pretreated wild type mice. The levels of aristolochic acid I in the kidney and liver were much higher in null mice but much lower in 3-methylcholanthrene-treated compared to control wild type mice. Hepatic microsomes from 3-methylcholanthrene-treated wild type mice had greater activity compared to untreated mice. Finally, aristolochic acid I was more cytotoxic than its major metabolite aristolactam I and this cytotoxicity was decreased in human renal tubular epithelial HK2 cells in the presence of a reconstituted hepatic microsome-cytosol (S9) system. These results indicate that hepatic P450s play an important role in metabolizing aristolochic acid I into less toxic metabolites and thus have a detoxification role in aristolochic acid I-induced kidney injury.

Thermoelectric performance of SnS and SnS–SnSe solid solution

Solid solution is a potential way to optimize thermoelectric performance for its low thermal conductivity compared to those of the constituent compounds because of the phonon scattering from disordered atoms. Tin(II) sulfide (SnS) shows analogous band structure and electrical properties with tin selenide (SnSe), which was the motivation for investigating the thermoelectric performance of SnS and SnS–SnSe solid solution system. SnS compound and SnS1−xSex (0 < x < 1) solid solution were fabricated using the melting method and they exhibited anisotropic thermoelectric performance along the parallel and perpendicular to the pressing directions. For the SnS compound, the maximum zT∥ value is 0.19 at 823 K along the parallel to pressing direction, which is higher than that along the perpendicular to the pressing direction (zT⊥ = 0.16). The zT values of SnS0.5Se0.5 and SnS0.2Se0.8 were higher than those of the SnS compound and a maximum zT value of 0.82 was obtained for SnS0.2Se0.8 at 823 K, which is more than four times higher than that of SnS.

The thermoelectric performance of anisotropic SnSe doped with Na

Lead-free polycrystalline SnSe is a promising thermoelectric compound consisting of earth-abundant elements. However, the poor electrical transport property for low intrinsic defect concentration (3 × 1017 cm−3) limits the usage of the stoichiometric SnSe compound. In this work, Na2Se as an acceptor was doped into SnSe in order to optimize the electrical transport properties, especially to increase the carrier concentration. As a result, the carrier concentrations increased and saturated at about 1.0 × 1019 cm−3 for Na0.01Sn0.99Se at 300 K, and a maximum power factor of 0.48 mW m−1 K−2 was obtained. A maximum zT value of 0.75 was obtained at 823 K for Na0.01Sn0.99Se along the direction perpendicular to the sintering pressure, which is 25% higher than that (0.6) of the undoped SnSe compound.

Near-Zero Thermal Expansion and High Ultraviolet Transparency in a Borate Crystal of Zn4B6O13

Intrinsic isotropic near-zero thermal expansion is discovered in borate crystal Zn4 B6 O13 with high transparency in the ultraviolet region. First-principles calculations demonstrate that the very low thermal expansion originates mainly from the invariability of the solid [B24 O48 ] truncated octahedra that are fixed by the [Zn4 O13 ] clusters in the ZBO structure.

The shape effect of mesoporous silica nanoparticles on intracellular reactive oxygen species in A375 cells

Mesoporous silica nanoparticles (MSNs) have attracted great attention in various biomedical applications. However, a detailed mechanism of intracellular behavior, such as reactive oxygen species (ROS), induced by MSNs, has been still paid little consideration to date. In this study, we first found that MSNs with different aspect ratios (1, 2, and 4) could decrease the intracellular ROS level in serum-free media, whereas the introduction of serum proteins could upregulate and display shape-dependent behavior. The ROS regulation mechanism by particle shapes in A375 cells was then analyzed by examining the endocytosis amount of MSNs, the mitochondrial damage, and the ROS-scavenging ability. These results indicated that the particle shapes play significant roles in regulating endogenous ROS. We envisage that the complete oxidative stress study of different shaped MSNs would provide important guidelines when considering the overall toxicity of these nanocarriers in biomedical applications.

Facile preparation of ellipsoid-like MCM-41 with parallel channels along the short axis for drug delivery and assembly of Ag nanoparticles for catalysis

In this study, ellipsoid-like MCM-41 nanoparticles with parallel channels along the short axis were prepared by using a surfactant mixture of cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzenesulfonate (SDBS) as a template. This particulate system shows high drug loading capacity, a sustained release profile and efficient assembly of Ag nanoparticles for 4-nitrophenol reduction.

Controlled fabrication of highly conductive three-dimensional flowerlike poly (3,4-ethylenedioxythiophene) nanostructures

Poly(3,4-ethylenedioxythiophene) (PEDOT) with three-dimensional (3D) flowerlike nanostructures was fabricated by chemical oxidation polymerization in a ternary phase system, which was composed of the surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT), aqueous FeCl3 solution and p-xylene. This kind of 3D flowerlike PEDOT formed by nanofibers was prepared by controlling the molar ratio of water (used to dissolve FeCl3) to the surfactant, AOT. This molar ratio is defined as N which equals nH2O/nAOT. In particular, both the conductivity and specific surface area increased with the molar ratio, N, increasing. The room temperature conductivity of the synthesized PEDOT reached a relative high value of 137 S cm−1. Moreover, the novel 3D flowerlike nanostructures endow a high specific surface area of around 46 m2 g−1. The measurements of UV-visible spectroscopy (UV-vis) and X-ray photoelectron spectroscopy (XPS) indicate that the doping level played a key role in improving conductivity of PEDOT. This study is significant to the potential applications of PEDOT on supercapacitors, sensors, actuators, transistors, and so on.

Roles of particle size, shape and surface chemistry of mesoporous silica nanomaterials on biological systems

The successful application of mesoporous silica nanomaterials (MSNs) in biomedical fields requires careful consideration of their spatial dimensions, biofunctionality, specific cellular uptake efficiency, biocompatibility and targeting delivery efficacy. A deep understanding of the interactions between MSNs and biological systems is thus of significant importance. To this end, over the past few decades, studies aimed at synthesis of MSNs with controlled size, shape and surface chemistry properties and exploring the roles of these properties on in vitro and in vivo biological performance have been conducted. These studies provide new and foundational information for engineering the next generation of mesoporous silica-based nanoscale devices. This review highlights the current progress on the controlled synthesis of size, shape and surface chemistry tuneable MSNs, emphasises the roles of size, shape and surface chemistry on biological systems with a special focus on the direct comparison studies, and discusses the emerging design paradigm for building mesoporous silica-based particulate systems.