15 research outputs found
First-Principles Study of Microporous Magnets MāMOF-74 (M = Ni, Co, Fe, Mn): the Role of Metal Centers
A clear understanding of the origin
of magnetism in metalāorganic 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 āextraā
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 Īø. When Īø
< 55Ā°, a sharp absorbance spectrum is observed, and for Īø
> 55Ā°, 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 Īø 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 ĪĪ½ = 1004 cm<sup>ā1</sup>,
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 NiāFe
Effects
of metal hybridization on the electronic properties of the metalāorganic
framework (MOF) Fe-MOF-74 with different Ni content are investigated
using the first-principles method with the HeydāScuseriaāErnzerhof
(HSE06) functional. The hybrid NiāFe-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
NiāFeāFe arrangement with a Ni content of 33ā50%
is likely the most suitable configuration due to the narrowing of
the spin-down band gap to ā¼0.62ā0.91 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
CoāBi nanoarray on carbon cloth (CoāBi NA/CC) from CoS<sub>2</sub> nanoarray precursor. As a three-dimensional anode, such CoāBi
NA/CC exhibits excellent electrocatalytic performance for OER with
the overpotential requirement of 411 mV to drive 10 mA cm<sup>ā2</sup>. 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
TĀ(6,0)
and nanowire W6-1 was investigated using first principles density
functional methods (DFT). It is found that the oxygen adsorption strength
on TĀ(6,0) is unexpectedly weak, whereas W6-1 with inner AuāAu
bonds is more active for O<sub>2</sub> 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 O<sub>2</sub> 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 AuāTM
bond can decrease the filling degree of the Au-d<sub><i>z</i></sub>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<sup>*</sup>.
<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><sup>*</sup>systolic blood pressure</p><p><sup>#</sup>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