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/N₂ 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 Henry’s constant and isosteric adsorption heat. Moreover, the Carbon-ZX for the Rn/N₂ binary mixture shows the extremely high selectivity (about 800–1200) in the molar fraction <i>X</i>_Rn < 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 TiO₂(111) Surface Phase for Enhanced Visible-Light Solar Energy Conversion

The wide band gap of titanium dioxide (TiO₂) limits its photoactivity only in the ultraviolet-light region and greatly blocks application of TiO₂ in solar energy. Finding a pure TiO₂ 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 TiO₂(111) surface phase formed on the reconstructed high-energy rutile TiO₂(011) surface. The band gap of the fluorite TiO₂(111) surface phase is about 2.1 eV. We propose that engineering the high-energy surfaces of common TiO₂ to obtain the fluorite TiO₂(111) surface phase at room conditions is a promising method for the preparation of pure TiO₂ materials with visible-light activity

I, N‑Codoping Modification of TiO₂ for Enhanced Photoelectrochemical H₂O Splitting in Visible-Light Region

The donor–acceptor codoping is an effective approach to tune the photoelectrochemical properties of TiO₂. Here, we systematically investigate the effects of (I+N) codoping on the electronic structures and H₂O splitting reactions of anatase TiO₂ by using density functional theory. It is found that the codoping of the stable charge-compensated (I+N) donor–acceptor pair in anatase TiO₂ not only can prevent the recombination of photogenerated electron–hole 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 TiO₂ is desirable for H₂O splitting, and the calculated optical absorption curve of (I+N) codoped TiO₂ verifies that (I+N) codoping can significantly improve visible-light absorption. Moreover, we also calculate the chemical reaction pathways of H₂ generation via H₂O splitting on (I+N) codoped TiO₂ surfaces by using the climbing nudged elastic band (cNEB) method and find that the (I+N) codoping in TiO₂ can efficiently reduce the energy barrier of H₂ production by about 1.0 eV. These findings imply that the (I+N) codoped anatase TiO₂ is a promising visible-light photocatalyst for H₂O splitting

Amino-Functionalized Luminescent Metal–Organic Framework Test Paper for Rapid and Selective Sensing of SO₂ Gas and Its Derivatives by Luminescence Turn-On Effect

Rapid and selective sensing of sulfur dioxide (SO₂) gas has attracted more and more attention because SO₂ not only causes environmental pollution but also severely affects the health of human beings. Here we report an amino-functionalized luminescent metal–organic framework (MOF) material (i.e., MOF-5-NH₂) and further investigate its sensing property for SO₂ gas and its derivatives as a luminescent probe. The results indicate that the MOF-5-NH₂ probe can selectively and sensitively sense SO₂ derivatives (i.e., SO₃^2–) 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-NH₂ into a test paper to achieve the aim of portable detection, and the lower-limit concentration of the test paper for sensing SO₂ in real time was found to be about 0.05 ppm. Moreover, MOF-5-NH₂ 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 “from inorganic to organic” strategy, that is, using tetrakis­(4-bromophenyl)­methane (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 4600–6000 m²/g, 2.0–7.9 g/cm³, and 10–55 Å, 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 CO₂ capture, owing to its extremely high pore volume and accessible surface area

Understanding the Mechanism of Photocatalysis Enhancements in the Graphene-like Semiconductor Sheet/TiO₂ Composites

The electronic properties of monolayer transition-metal dichalcogenide MX₂ (M = Mo and W; X = S and Se) interfaced TiO₂(110) composites were investigated by hybrid density functional theory. In the MX₂/​TiO₂(110) composites, MX₂ serves as an efficient photosensitizer, and the electron–hole pair can, therefore, be easily generated by visible-light irradiation and be effectively separated by the electron injection from MX₂ to TiO₂. This mechanism is quite different from the one of the foreign elements doped TiO₂, in which the electron is directly excited from the midgap impurity states into the CB of TiO₂, leading to an optical absorption edge extending to the visible-light region. Moreover, we reveal that the prerequisite of designing the highly efficient semiconductor–TiO₂ photocatalytic composites is to select the proper semiconductor, which holds the band gap of ∼2.0 eV and generates a built-in potential of 0.3–0.5 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 TiO₂-based heterojunction composites for improving visible-light photocatalysis

Functional Group Modification of Metal–Organic Frameworks for CO₂ Capture

Reducing the anthropogenic emission of CO₂ is currently a top priority due to its global warming effect. Capturing CO₂ by porous materials is a promising approach due to its energetic efficiency and technical feasibility. A promising adsorbent for capturing CO₂ should possess not only large BET specific surface areas (SSAs) but also high heat of adsorption. Since the intrinsic quadrupole moment of the CO₂ molecule exists, introduction of a polar functional group in the framework of porous materials could enhance CO₂ uptake. In this work, we adopt the postsynthetic modification approach to synthesize UMCM-1-NH₂-MA (MA = maleic anhydride) material on the basis of UMCM-1-NH₂ with an extremely high BET SSA of 4064 m² g^–1 and further explore the effects of free acid functionalities and aromatic amino groups on CO₂ capture. The experimental and theoretical results show that, besides amino groups, the polar acidic functionalities also exhibit excellent capability for CO₂ capture. Moreover, our first-principles calculations indicate that the aromatic imino group loses affinity toward CO₂ 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 CO₂ 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 ([C₄mim]­[BF₄]) 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 Stokes–Einstein (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>₂) less than 0.2, most of the water molecules are isolated in the polar cation–anion network in ionic liquids. With the increase of <i>x</i>₂ from 0.2 to 0.8, large water cluster forms and eventually percolates the whole system. When <i>x</i>₂ > 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