X.-D. Zhou

Toxicity of Cerium Oxide Nanoparticles in Human Lung Cancer Cells

With the fast development of nanotechnology, the nanomaterials start to cause people’s attention for potential toxic effect. In this paper, the cytotoxicity and oxidative stress caused by 20-nm cerium oxide (CeO2) nanoparticles in cultured human lung cancer cells was investigated. The sulforhodamine B method was employed to assess cell viability after exposure to 3.5, 10.5, and 23.3 μg/ml of CeO2 nanoparticles for 24, 48, and 72 h. Cell viability decreased significantly as a function of nanoparticle dose and exposure time. Indicators of oxidative stress and cytotoxicity, including total reactive oxygen species, glutathione, malondialdehyde, α-tocopherol, and lactate dehydrogenase, were quantitatively assessed. It is concluded from the results that free radicals generated by exposure to 3.5 to 23.3 μg/ml CeO2 nanoparticles produce significant oxidative stress in the cells, as reflected by reduced glutathione and α-tocopherol levels; the toxic effects of CeO2 nanoparticles are dose dependent and time dependent; elevated oxidative stress increases the production of malondialdehyde and lactate dehydrogenase, which are indicators of lipid peroxidation and cell membrane damage, respectively.

Oriented Nanostructures for Energy Conversion and Storage

Recently, the role of nanostructured materials in addressing the challenges in energy and natural resources has attracted wide attention. In particular, oriented nanostructures demonstrate promising properties for energy harvesting, conversion, and storage. In this Review, we highlight the synthesis and application of oriented nanostructures in a few key areas of energy technologies, namely photovoltaics, batteries, supercapacitors, and thermoelectrics. Although the applications differ from field to field, a common fundamental challenge is to improve the generation and transport of electrons and ions. We highlight the role of high surface area to maximize the surface activity and discuss the importance of optimum dimension and architecture, controlled pore channels, and alignment of the nanocrystalline phase to optimize the transport of electrons and ions. Finally, we discuss the challenges in attaining integrated architectures to achieve the desired performance. Brief background information is provided for the relevant technologies, but the emphasis is focused mainly on the nanoscale effects of mostly inorganic-based materials and devices.

Size-induced lattice relaxation in CeO2 nanoparticles

Size-induced lattice relaxation was observed for nanoscale CeO2 single crystals with an average size from 4 to 60 nm. Results showed the finest crystallites exhibited no strain-induced line broadening, while high temperature annealing resulted in larger grain sizes and significant strains. The observed shift in the x-ray diffraction lattice parameters was assumed to be due to the formation of defects on the lattice, specifically oxygen vacancies. Modeling revealed that the oxygen vacancy concentration ([VO••]) was found to be ≈4×1020/cm3 for the 4 nm crystallites, and decreased two orders of magnitude for larger 60 nm single crystals.

Room-temperature homogeneous nucleation synthesis and thermal stability of nanometer single crystal CeO2

Nanometer (about 4∼5 nm) CeO2 single crystals were first synthesized by room-temperature homogeneous nucleation; the size was determined by electron microscopy and specific surfaced area of the particles. Modeling revealed that the surface energy of as-synthesized nanometer single crystals was in the range of 2.8–3.7 J/m2. Crystal growth mechanisms change over the temperature regimes, from boundary diffusion over low-temperature regime (Ea=0.16 eV) to bulk diffusion (Ea=0.50 eV) over high-temperature region.

Effect of the solvent on the particle morphology of spray dried PMMA

The effect of various solvents on the morphology of polymethyl methacrylate (PMMA) particles synthesized by spray drying is examined. It is concluded that the product PMMA particles, derived from the PMMA-acetone dilute solution, have a smaller particle size than those from the PMMA-THF dilute solution. This is due to the stronger PMMA-acetone interaction, since acetone is a good solvent for PMMA, while THF is a poor solvent for PMMA. By controlling the temperature of each section of the tube furnace, the heating rate was adjusted so that both solid and hollow particles could be obtained. When water was added to these dilute solutions, porous or honeycomb particles were produced due to the different evaporation rates of solvent and water. This was a result of a large difference in the solubility parameter values between PMMA and solvent. The strong interaction between PMMA and acetone results in the formation of porous particles while the weak interaction between THF and PMMA produced honeycomb structure particles.

Enthalpies of Formation of LaMO3 Perovskites (M = Cr, Fe, Co, and Ni)

Enthalpies of formation from constituent oxides and elements at 298 K were determined by high-temperature oxide melt solution calorimetry for a group of technologically important perovskites LaMO 3 (M = Cr, Fe, Co, and Ni). The enthalpies of formation of LaCrO 3 and LaFeO 3 from oxides (La 2 O 3 and Cr 2 O 3 or Fe 2 O 3 ) are –70.06 ± 2.79 kJ/mol and –64.58 ± 2.32 kJ/mol, respectively. The enthalpies of formation of LaCoO 3 and LaNiO 3 from oxides (La 2 O 3 and CoO or NiO) and O 2 are −107.64 ± 1.77 kJ/mol and –57.31 ± 2.55 kJ/mol, respectively. All these data are evaluated and found to be consistent with literature values obtained using other methods. The relative stability among these four perovskites decreases in the order of Cr, Fe, Co, Ni.

Cytotoxicity and cell membrane depolarization induced by aluminum oxide nanoparticles in human lung epithelial cells A549

The cytotoxicity of 13 and 22 nm aluminum oxide (Al2O3) nanoparticles was investigated in cultured human bronchoalveolar carcinoma-derived cells (A549) and compared with 20 nm CeO2 and 40 nm TiO2 nanoparticles as positive and negative control, respectively. Exposure to both Al2O3 nanoparticles for 24 h at 10 and 25 µg mL−1 doses significantly decreased cell viability compared with control. However, the cytotoxicity of 13 and 22 nm Al2O3 nanoparticles had no difference at 5–25 µg mL−1 dose range. The cytotoxicity of both Al2O3 nanoparticles were higher than negative control TiO2 nanoparticles but lower than positive control CeO2 nanoparticles (TiO2 < Al2O3 < CeO2). A real-time single cell imaging system was employed to study the cell membrane potential change caused by Al2O3 and CeO2 nanoparticles using a membrane potential sensitive fluorescent probe DiBAC4(3). Exposure to the 13 nm Al2O3 nanoparticles resulted in more significant depolarization than the 30 nm Al2O3 particles. On the other hand, the 20 nm CeO2 particles, the most toxic, caused less significant depolarization than both the 13 and 22 nm Al2O3. Factors such as exposure duration, surface chemistry, and other mechanisms may contribute differently between cytotoxicity and membrane depolarization.

Crystal and electronic structures of LiNH2

The crystal structure of LiNH2 was reinvestigated using powder neutron diffraction with high sensitivity. The compound crystallizes in the tetragonal space group I4¯ with lattice parameters a=b=5.03442(24)A,c=10.25558(52)A. It is found that H atoms occupy 8g1(0.2429, 0.1285, 0.1910) and 8g2 (0.3840, 0.3512, 0.1278) sites. The bond lengths between the nearest nitrogen and hydrogen atoms are 0.986 and 0.942 A, respectively. The bond angle between H–N–H is about 99.97°. These results are significantly different from those of previous experiments. The electronic structure was calculated according to the revised structural data. The calculated density of states and charge density distribution show strong ionic characteristics between the ionic Li+ cation and the covalent bonded [NH2]− anion.

Magnetic and structural studies of the Verwey transition in Fe3−δO4 nanoparticles

Stoichiometric and cation-deficient magnetite Fe3−δO4 and γ-Fe2O3 particles have been prepared by the chemical method followed by heat treatments. The magnetic and structural properties were studied using neutron diffraction, magnetic measurements, and Mossbauer spectroscopy. Charge ordering of Fe3+ and Fe2+ and lattice distortion are not observed below the Verwey transition temperature in the stoichiometric and cation-deficient magnetite. It is found that the lattice parameter and the Verwey transition temperature decrease as the cation vacancy increases. The Verwey transition almost disappears in the Fe3−δO4 sample with δ=0.066. Mossbauer spectra show that the ratio of Fe3+/Fe2.5+ in stoichiometric magnetite can be modified by heat treatment. The Fe vacancies on the B sites change the nature of the Verwey transition. No cation vacancy ordering is observed for γ-Fe2O3, due to the small amount of cation vacancies in the compound.Stoichiometric and cation-deficient magnetite Fe3−δO4 and γ-Fe2O3 particles have been prepared by the chemical method followed by heat treatments. The magnetic and structural properties were studied using neutron diffraction, magnetic measurements, and Mossbauer spectroscopy. Charge ordering of Fe3+ and Fe2+ and lattice distortion are not observed below the Verwey transition temperature in the stoichiometric and cation-deficient magnetite. It is found that the lattice parameter and the Verwey transition temperature decrease as the cation vacancy increases. The Verwey transition almost disappears in the Fe3−δO4 sample with δ=0.066. Mossbauer spectra show that the ratio of Fe3+/Fe2.5+ in stoichiometric magnetite can be modified by heat treatment. The Fe vacancies on the B sites change the nature of the Verwey transition. No cation vacancy ordering is observed for γ-Fe2O3, due to the small amount of cation vacancies in the compound.

Charge disproportionation and ordering in La1/3Sr2/3FeO3-δ

The perovskite La1/3Sr2/3FeO3−δ was investigated by neutron diffraction, magnetic and Mossbauer spectroscopy measurements. La1/3Sr2/3FeO3−δ undergoes magnetic ordering at T = 190–200 K accompanied by charge disproportionation. Magnetic peaks due to charge ordering are observed below 200 K. The charge ordering is gradually developed below 200 K along with a charge disproportionation, 2Fe4+ Fe3+ + Fe5+. La1/3Sr2/3FeO3−δ shows an antiferromagnetic structure at low temperature. Magnetic moments of about 3 and 1.3 μB were obtained from the neutron diffraction data refinement for Fe3+ and Fe5+ at 15 K, respectively, which suggest that both Fe ions are in a low spin state. These values are significantly lower than those reported by Battle et al for La1/3Sr2/3FeO2.98. Mossbauer spectra indicate that full charge ordering might be reached below 20 K with no Fe4+.