First-Principles Study of Microporous Magnets M‑MOF-74 (M = Ni, Co, Fe, Mn): the Role of Metal Centers

A clear understanding of the origin of magnetism in metal–organic frameworks (MOFs) would provide useful insight for tuning the electromagnetic properties of MOFs and finding new applications. In the present study, first-principles calculations show that the open paramagnetic metal sites in three-dimensional porous magnets M-MOF-74 (M = Ni, Co, Fe, Mn) favor high-spin electronic arrangement. Fe- and Co-MOF-74 exhibit ferromagnetic (FM) features and significantly distinct energy gaps between spin-up and spin-down channels in metastable states. After replacement of the Co center with a Ni ion, the FM feature was exhibited for the stable state since the “extra” valence electron was filled in the spin-down 3d bands to shift the Fermi level to higher energy. In contrast, after removal of one valence electron (i.e., replacement of the Fe center with Mn atoms), the energy gap was significantly enlarged and an antiferromagnetic (AFM) feature will be discerned

Optimization of Ag-Coated Polystyrene Nanosphere Substrates for Quantitative Surface-Enhanced Raman Spectroscopy Analysis

The optical properties of Ag-coated polystyrene nanospheres can be varied by changing the vapor deposition angle θ. When θ < 55°, a sharp absorbance spectrum is observed, and for θ > 55°, broad band absorbance is achieved. The difference in optical absorbance is due to the coverage and shape change of the Ag coating on nanospheres with multiple oriented domains, as demonstrated by finite-difference time-domain simulations. The localized surface plasmon resonance of substrates coated at small θ can be tuned closely to the excitation wavelength, and these samples can serve as good surface-enhanced Raman scattering (SERS) substrates. The polystyrene vibrational peak at Δν = 1004 cm^–1, which is inherent to the substrate, can be used as an internal standard. By normalizing the SERS peak of an analyte by this peak intensity, the SERS intensity ratio is independent of the substrate fabrication conditions. Such an internal standard is also shown to be effective for revealing the adsorption kinetics for rhodamine 6G and 4-mercaptophenol. Thus, metal films on polystyrene nanospheres can be a simple platform for quantitative SERS measurements

Monopolar Magnetic MOF-74 with Hybrid Node Ni–Fe

Effects of metal hybridization on the electronic properties of the metal–organic framework (MOF) Fe-MOF-74 with different Ni content are investigated using the first-principles method with the Heyd–Scuseria–Ernzerhof (HSE06) functional. The hybrid Ni–Fe-MOF-74, named as the monopolar magnetic semiconductor (MMS), is a new type of porous polarization material that can be easily converted to a half-metal. On the basis of our investigation of the effects of Ni content and the hybrid node arrangement on the band gap of the MOF, we found that the interchain Ni–Fe–Fe arrangement with a Ni content of 33–50% is likely the most suitable configuration due to the narrowing of the spin-down band gap to ∼0.62–0.91 eV from 1.38 eV of the pristine Fe-MOF-74. Hybrid nodes can provide an effective way to narrow the electronic band gap of MOFs and to allow easy conversion of MOFs to polarization materials. Our computation also suggests that the pure Ni-MOF-74, with a band gap of 2.10 eV, can serve as a good visible-light photocatalyst

Cobalt-Borate Nanoarray: An Efficient and Durable Electrocatalyst for Water Oxidation under Benign Conditions

The development of efficient earth-abundant electrocatalysts for oxygen evolution reaction (OER) under benign conditions is still urgent and challenging. Herein, we report the electrochemical generation of novel Co–Bi nanoarray on carbon cloth (Co–Bi NA/CC) from CoS₂ nanoarray precursor. As a three-dimensional anode, such Co–Bi NA/CC exhibits excellent electrocatalytic performance for OER with the overpotential requirement of 411 mV to drive 10 mA cm^–2. Notably, this electrode also demonstrates outstanding long-term electrochemical durability for 20 h

Catalytic Oxygen Activation on Helical Gold Nanowires

Oxygen activation on one-dimensional (1D) gold nanotube T­(6,0) and nanowire W6-1 was investigated using first principles density functional methods (DFT). It is found that the oxygen adsorption strength on T­(6,0) is unexpectedly weak, whereas W6-1 with inner Au–Au bonds is more active for O₂ adsorption. To further promote the catalyzed oxygen activation, we proposed and evaluated two working strategies, including imposing a small strain along the axial direction and doping alien transition metal (TM) atoms. Specifically, 4% compression or doping Pt atoms can decrease the O₂ dissociation barriers from 0.85 eV to a more desired 0.6 eV. The analysis of electronic structures and charge density difference revealed that the inner Au–TM bond can decrease the filling degree of the Au-d_<i>z</i>2 orbital and, thus, improve the oxygen activity

Characteristics of survey respondents aged >18 years in China, 2003 and 2008.

<p>Characteristics of survey respondents aged >18 years in China, 2003 and 2008.</p

Adjusted RR and 95%CI for 2008 vs. 2003 in chronic disease in the last 6 months in different subpopulations^*.

<p>*Rate ratio for 2008 vs. 2003 adjusted for sex (or residence area), age, minority, marital status, education, and geographic region.</p

Prevalence of smoking, alcohol intake, and physical activity in respondents aged >18 years in China.

<p>*Note: adjusted P value <0.001 for 2008 versus 2003 after adjustment for age, minority, marital status, education, gender (or residence area) and geographic region.</p

Associations of bone mineral density with lean mass, fat mass, and dietary patterns in postmenopausal Chinese women: a 2-year prospective study

Associations of bone mineral density with lean mass, fat mass, and dietary patterns in postmenopausal Chinese women: a 2-year prospective stud

The results from linear mixed model of the primary variables on BMD of the spine, hip, and the total body: 2-year follow-up data.

<p>^*systolic blood pressure</p><p>^#waist-hip-ratio</p><p>The results from linear mixed model of the primary variables on BMD of the spine, hip, and the total body: 2-year follow-up data.</p