23 research outputs found
Covalent Organic Polymers for Rapid Fluorescence Imaging of Latent Fingerprints
Rapid, simple and highly sensitive identification of latent fingerprints
(LFPs) is an important issue related to national security and recognition
of potential crimes. Here, we synthesize a series of covalent organic
polymers (COPs) with colorful fluorescence (from blue to green, pale
yellow, bright yellow, and red) and further investigate their performance
for fluorescence imaging of LFPs. Results indicate that the COP materials
can be used as fluorescence probes to rapidly visualize the precision
substructure of LFPs within 5 s by simply spraying method, and tunable
fluorescent color makes the COP probes have a high contrast and low
interference for fluorescence imaging of LFPs on different substrates
(including glass slides, paper, aluminum foil, plastic, ironware)
in different backgrounds. We also further reveal the mechanism of
COP probes for fluorescence imaging of LFPs. Importantly, the COP
probes show high stability and could successfully achieve the fluorescence
imaging for LFPs after aged for 45 days or washed by water. In short,
this is the first report on the porous polymers for fluorescence imaging
of LFPs and expected that it can be also applied to the fluorescence
imaging of other fields
Nitrogen and Fluorine-Codoped Porous Carbons as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells
The
severe dependence of oxygen reduction reaction (ORR) in fuel cells
on platinum (Pt)-based catalysts greatly limits the process of their
commercialization. Therefore, developing cost-reasonable non-precious-metal
catalysts to replace Pt-based catalysts for ORR is an urgent task.
Here, we use the composite of inexpensive polyaniline and superfine
polytetrafluoroethylene powder as precursor to synthesize a metal-free
N,F-codoped porous carbon catalyst (N,F-Carbon). Results indicate
that the N,F-Carbon catalyst obtained at the optimized temperature
1000 °C exhibits almost the same onset (0.97 V vs RHE) and half-wave
potential (0.84 V vs RHE) and better durability and higher crossover
resistance in alkaline medium compared to commercial 20% Pt/C, which
is attributed to the good dispersion of fluorine and nitrogen atoms
in the carbon matrix, high specific surface area, and the synergistic
effects of fluorine and nitrogen on the polarization of adjacent carbon
atoms. This work provides a new strategy for in situ synthesis of
N,F-codoped porous carbon as highly efficient metal-free electrocatalyst
for ORR in fuel cells
Nitrogen-Doped Nanoporous Carbons for Selective Separation of Ar/Kr/Xe/Rn Gases: An Experiment-Based Simulation Study
It is still a challenge
to find high-efficiency adsorbents for
the separation of noble gases. In this work, we combine the grand
canonical Monte Carlo (GCMC) simulation and adsorption integral equation
to theoretically characterize the pore size distribution (PSD) of
experimentally synthesized nitrogen-doped nanoporous carbon (Carbon-ZX)
and further predict the selectivity of Carbon-ZX for Xe/Kr, Xe/Ar,
and Rn/N<sub>2</sub> mixtures. Results indicate that the selectivities
of Carbon-ZX for Xe/Kr and Xe/Ar apparently are greater than that
of other MOFs in the same conditions, which also is further confirmed
by Henryâs constant and isosteric adsorption heat. Moreover,
the Carbon-ZX for the Rn/N<sub>2</sub> binary mixture shows the extremely
high selectivity (about 800â1200) in the molar fraction <i>X</i><sub>Rn</sub> < 0.001, which means that Carbon-ZX is
a promising candidate for indoor Rn capture. In short, this work provides
a useful method to characterize the experimentally synthesized nanoporous
materials and further explores their applications in adsorption and
separation
Fluorite TiO<sub>2</sub>(111) Surface Phase for Enhanced Visible-Light Solar Energy Conversion
The
wide band gap of titanium dioxide (TiO<sub>2</sub>) limits its photoactivity
only in the ultraviolet-light region and greatly blocks application
of TiO<sub>2</sub> in solar energy. Finding a pure TiO<sub>2</sub> phase with a band gap around 2.0 eV is a very important issue for
solar energy applications. We use the first-principles calculations
to predict a fluorite TiO<sub>2</sub>(111) surface phase formed on
the reconstructed high-energy rutile TiO<sub>2</sub>(011) surface.
The band gap of the fluorite TiO<sub>2</sub>(111) surface phase is
about 2.1 eV. We propose that engineering the high-energy surfaces
of common TiO<sub>2</sub> to obtain the fluorite TiO<sub>2</sub>(111)
surface phase at room conditions is a promising method for the preparation
of pure TiO<sub>2</sub> materials with visible-light activity
I, NâCodoping Modification of TiO<sub>2</sub> for Enhanced Photoelectrochemical H<sub>2</sub>O Splitting in Visible-Light Region
The
donorâacceptor codoping is an effective approach to
tune the photoelectrochemical properties of TiO<sub>2</sub>. Here,
we systematically investigate the effects of (I+N) codoping on the
electronic structures and H<sub>2</sub>O splitting reactions of anatase
TiO<sub>2</sub> by using density functional theory. It is found that
the codoping of the stable charge-compensated (I+N) donorâacceptor
pair in anatase TiO<sub>2</sub> not only can prevent the recombination
of photogenerated electronâhole pairs but also can effectively
reduce the band gap to 2.251 eV by forming an intermediate band within
the band gap. The band edge alignment of (I+N) codoped TiO<sub>2</sub> is desirable for H<sub>2</sub>O splitting, and the calculated optical
absorption curve of (I+N) codoped TiO<sub>2</sub> verifies that (I+N)
codoping can significantly improve visible-light absorption. Moreover,
we also calculate the chemical reaction pathways of H<sub>2</sub> generation
via H<sub>2</sub>O splitting on (I+N) codoped TiO<sub>2</sub> surfaces
by using the climbing nudged elastic band (cNEB) method and find that
the (I+N) codoping in TiO<sub>2</sub> can efficiently reduce the energy
barrier of H<sub>2</sub> production by about 1.0 eV. These findings
imply that the (I+N) codoped anatase TiO<sub>2</sub> is a promising
visible-light photocatalyst for H<sub>2</sub>O splitting
Amino-Functionalized Luminescent MetalâOrganic Framework Test Paper for Rapid and Selective Sensing of SO<sub>2</sub> Gas and Its Derivatives by Luminescence Turn-On Effect
Rapid
and selective sensing of sulfur dioxide (SO<sub>2</sub>)
gas has attracted more and more attention because SO<sub>2</sub> not
only causes environmental pollution but also severely affects the
health of human beings. Here we report an amino-functionalized luminescent
metalâorganic framework (MOF) material (i.e., MOF-5-NH<sub>2</sub>) and further investigate its sensing property for SO<sub>2</sub> gas and its derivatives as a luminescent probe. The results
indicate that the MOF-5-NH<sub>2</sub> probe can selectively and sensitively
sense SO<sub>2</sub> derivatives (i.e., SO<sub>3</sub><sup>2â</sup>) in real time by a luminescence turn-on effect with a lower detection
limit of 0.168 ppm and a response time of less than 15 s. Importantly,
the luminescence turn-on phenomenon can be observed by the naked eye.
We also assembled MOF-5-NH<sub>2</sub> into a test paper to achieve
the aim of portable detection, and the lower-limit concentration of
the test paper for sensing SO<sub>2</sub> in real time was found to
be about 0.05 ppm. Moreover, MOF-5-NH<sub>2</sub> also shows good
anti-interference ability, strong luminescence stability, and reusability,
which means that this material is an excellent sensing candidate.
The amino functionalization may also provide a modification strategy
to design luminescent sensors for other atmospheric pollutants
From Inorganic to Organic Strategy To Design Porous Aromatic Frameworks for High-Capacity Gas Storage
Developing
high-capacity gas storage materials is still an important
issue, because it is closely related to carbon dioxide capture and
hydrogen storage. This work proposes a âfrom inorganic to organicâ
strategy, that is, using tetrakisÂ(4-bromophenyl)Âmethane (TBM) to replace
silicon in zeolites, to design porous aromatic frameworks (PAF_XXXs)
with extremely high pore volume and accessible surface area, because
the silicon atom in the silicon-based zeolites and the TBM ligand
have the same coordination manner. Through the adoption of this strategy,
115 organic PAF_XXXs based on the inorganic zeolite structures were
designed. These designed PAF_XXXs have the same topology with the
corresponding matrix zeolites but possess significantly higher porosity
than matrix zeolites. In general, the surface area, pore volume, and
pore size of PAF_XXX are in the ranges of 4600â6000 m<sup>2</sup>/g, 2.0â7.9 g/cm<sup>3</sup>, and 10â55 Ă
, respectively.
In particular, the hydrogen uptake of PAF_RWY reaches 5.9 wt % at
100 bar and 298 K, exceeding the DOE 2015 target (5.5 wt %) for hydrogen
storage. Moreover, PAF_RWY is also a promising candidate for methane
storage and CO<sub>2</sub> capture, owing to its extremely high pore
volume and accessible surface area
Understanding the Mechanism of Photocatalysis Enhancements in the Graphene-like Semiconductor Sheet/TiO<sub>2</sub> Composites
The electronic properties of monolayer
transition-metal dichalcogenide
MX<sub>2</sub> (M = Mo and W; X = S and Se) interfaced TiO<sub>2</sub>(110) composites were investigated by hybrid density functional theory.
In the MX<sub>2</sub>/âTiO<sub>2</sub>(110) composites, MX<sub>2</sub> serves as an efficient photosensitizer, and the electronâhole
pair can, therefore, be easily generated by visible-light irradiation
and be effectively separated by the electron injection from MX<sub>2</sub> to TiO<sub>2</sub>. This mechanism is quite different from
the one of the foreign elements doped TiO<sub>2</sub>, in which the
electron is directly excited from the midgap impurity states into
the CB of TiO<sub>2</sub>, leading to an optical absorption edge extending
to the visible-light region. Moreover, we reveal that the prerequisite
of designing the highly efficient semiconductorâTiO<sub>2</sub> photocatalytic composites is to select the proper semiconductor,
which holds the band gap of âŒ2.0 eV and generates a built-in
potential of 0.3â0.5 eV in the composite, as a photosensitizer,
which can be also considered as a fundamental criteria to screen the
suitable semiconductor and further to design the TiO<sub>2</sub>-based
heterojunction composites for improving visible-light photocatalysis
Functional Group Modification of MetalâOrganic Frameworks for CO<sub>2</sub> Capture
Reducing the anthropogenic emission of CO<sub>2</sub> is currently
a top priority due to its global warming effect. Capturing CO<sub>2</sub> by porous materials is a promising approach due to its energetic
efficiency and technical feasibility. A promising adsorbent for capturing
CO<sub>2</sub> should possess not only large BET specific surface
areas (SSAs) but also high heat of adsorption. Since the intrinsic
quadrupole moment of the CO<sub>2</sub> molecule exists, introduction
of a polar functional group in the framework of porous materials could
enhance CO<sub>2</sub> uptake. In this work, we adopt the postsynthetic
modification approach to synthesize UMCM-1-NH<sub>2</sub>-MA (MA =
maleic anhydride) material on the basis of UMCM-1-NH<sub>2</sub> with
an extremely high BET SSA of 4064 m<sup>2</sup> g<sup>â1</sup> and further explore the effects of free acid functionalities and
aromatic amino groups on CO<sub>2</sub> capture. The experimental
and theoretical results show that, besides amino groups, the polar
acidic functionalities also exhibit excellent capability for CO<sub>2</sub> capture. Moreover, our first-principles calculations indicate
that the aromatic imino group loses affinity toward CO<sub>2</sub> significantly, compared with the aromatic amino group. In short,
we believe that incorporating polar acidic functionalities into the
porous materials could be an alternatively suitable approach for enhancing
CO<sub>2</sub> capture
Local Structure Evolution and its Connection to Thermodynamic and Transport Properties of 1-Butyl-3-methylimidazolium Tetrafluoroborate and Water Mixtures by Molecular Dynamics Simulations
Our recently developed improved united atom force field
shows a good quality to reproduce both the static and transport properties
of neat ionic liquids (ILs). Combined with the TIP4P-Ew water model,
the force field is used to simulate the mixture of 1-butyl-3-methylimidazolium
tetrafluoroborate ([C<sub>4</sub>mim]Â[BF<sub>4</sub>]) and water without
further optimization to adjust any cross parameters. Liquid densities
of the mixture are well predicted over the entire concentration range
at temperatures from 298.15 to 353.15 K. Simulations also reproduce
the positive values of excess volumes and excess enthalpies, as well
as their increase with temperature. The simulated viscosities are
in good agreement with experimental values, especially in the water-rich
region. We found three distinct regions by analyzing the concentration
dependent self-diffusion coefficients via StokesâEinstein (SE)
relation, indicating the mixture experiences significant microheterogeneity
with the adding of water. This observation is well connected to the
structure features obtained in simulations, such as radial distribution
functions (RDFs), spatial distribution functions (SDFs) and water
clustering analysis. At the water mole fraction (<i>x</i><sub>2</sub>) less than 0.2, most of the water molecules are isolated
in the polar cationâanion network in ionic liquids. With the
increase of <i>x</i><sub>2</sub> from 0.2 to 0.8, large
water cluster forms and eventually percolates the whole system. When <i>x</i><sub>2</sub> > 0.8, ionic liquids show a moderate degree
of aggregation (with maximum around 0.9 to 0.95) before the cations
and anions are fully dissolved in water