The fast industrialization process has led to global challenges in the energy crisis and environmental pollution, which might be solved with clean and renewable energy. Highly efficient ...electrochemical systems for clean‐energy collection require high‐performance electrocatalysts, including Au, Pt, Pd, Ru, etc. Graphene, a single‐layer 2D carbon nanosheet, possesses many intriguing properties, and has attracted tremendous research attention. Specifically, graphene and graphene derivatives have been utilized as templates for the synthesis of various noble‐metal nanocomposites, showing excellent performance in electrocatalytic‐energy‐conversion applications, such as the hydrogen evolution reaction and CO2 reduction. Herein, the recent progress in graphene‐based noble‐metal nanocomposites is summarized, focusing on their synthetic methods and electrocatalytic applications. Furthermore, some personal insights on the challenges and possible future work in this research field are proposed.
Recent progress in the study of graphene‐based noble‐metal nanocomposites is reviewed. Different strategies regarding the synthesis of noble‐metal nanostructures on graphene or its derivatives are presented. Their applications in electrocatalysis including the hydrogen evolution reaction, oxygen reduction reaction, alcohol oxidation reaction, and CO2 reduction reaction are discussed.
Crystal phase, an intrinsic characteristic of crystalline materials, is one of the key parameters to determine their physicochemical properties. Recently, great progress has been made in the ...synthesis of nanomaterials with unconventional phases that are different from their thermodynamically stable bulk counterparts via various synthetic methods. A nanocrystalline material can also be viewed as an assembly of atoms with long-range order. When larger entities, such as nanoclusters, nanoparticles, and microparticles, are used as building blocks, supercrystalline materials with rich phases are obtained, some of which even have no analogues in the atomic and molecular crystals. The unconventional phases of nanocrystalline and supercrystalline materials endow them with distinctive properties as compared to their conventional counterparts. This Review highlights the state-of-the-art progress of nanocrystalline and supercrystalline materials with unconventional phases constructed from multiscale building blocks, including atoms, nanoclusters, spherical and anisotropic nanoparticles, and microparticles. Emerging strategies for engineering their crystal phases are introduced, with highlights on the governing parameters that are essential for the formation of unconventional phases. Phase-dependent properties and applications of nanocrystalline and supercrystalline materials are summarized. Finally, major challenges and opportunities in future research directions are proposed.
Water electrolysis for hydrogen production requires better catalysts to lower the kinetic barrier of the oxygen evolution reaction. Herein, conceptually-new, noble-metal-free, porous, ...atomically-thick sheets are first put forward as an excellent platform to promote the oxygen evolution activity through affording abundant catalytically active sites and enhanced two-dimensional conductivity. As an example, the synthetic porous Co sub(3)O sub(4) atomically-thick sheets with a thickness of 0.43 nm and about 30% pore occupancy afford low-coordinated Co super(3+) atoms to serve as the catalytically active sites, while the obviously increased density of states at the valence band and conduction band edge facilitate fast electron transport along their two-dimensional conducting paths. As a result, the porous, atomically-thick Co sub(3)O sub(4) sheets exhibit an electrocatalytic current up to 341.7 mA cm super(-2), roughly 50-times larger than that of the bulk counterpart and even more strikingly higher than that of most existing reports under similar conditions. This work holds great promise for triggering breakthroughs in the field of electrocatalysis.
Abstract
WEGO (Web Gene Ontology Annotation Plot), created in 2006, is a simple but useful tool for visualizing, comparing and plotting GO (Gene Ontology) annotation results. Owing largely to the ...rapid development of high-throughput sequencing and the increasing acceptance of GO, WEGO has benefitted from outstanding performance regarding the number of users and citations in recent years, which motivated us to update to version 2.0. WEGO uses the GO annotation results as input. Based on GO's standardized DAG (Directed Acyclic Graph) structured vocabulary system, the number of genes corresponding to each GO ID is calculated and shown in a graphical format. WEGO 2.0 updates have targeted four aspects, aiming to provide a more efficient and up-to-date approach for comparative genomic analyses. First, the number of input files, previously limited to three, is now unlimited, allowing WEGO to analyze multiple datasets. Also added in this version are the reference datasets of nine model species that can be adopted as baselines in genomic comparative analyses. Furthermore, in the analyzing processes each Chi-square test is carried out for multiple datasets instead of every two samples. At last, WEGO 2.0 provides an additional output graph along with the traditional WEGO histogram, displaying the sorted P-values of GO terms and indicating their significant differences. At the same time, WEGO 2.0 features an entirely new user interface. WEGO is available for free at http://wego.genomics.org.cn.
The evolution of fractures in overburden is quantitatively investigated to characterize the effect of mining activity. Scale model testing and numerical modeling were used based on the engineering ...geological and mining environments of Panel 11050 in the Quandian Coalmine in Henan Province, China. The maximum vertical displacement is 62.76 m, which is 140 m from the initial mining in the scale model test. Based on the fractal geometric theory, the fractal dimensions of the fractures in the overburden are calculated and visualized. The results reveal that if two coal seams are mined at the same time, the fractal dimension of the fracture network in the overburden increase with the progression of mining, but the rate of increase gradually slows. The relationships between the fractal dimension and the maximum height of the overburden failure and maximum overburden subsidence are nonlinear. The structural characteristics of the overburden are represented by the network of fractures. With increasing distance from the coal seam roof, the mining stress is gradually transferred upward to the overlying strata, and the scale of this stress transfer gradually reduces. The variation in the vertical stress gradually weakens and shows a delayed change with the mining process. The maximum principal stress is compressive stress and is distributed in an “arch” shape. The stress on both sides of the “arch” is high, and the intermediate stress is low. The stress within the “arch” shows an opposite trend.
Abstract
Constructing photocatalytically active and stable covalent organic frameworks containing both oxidative and reductive reaction centers remain a challenge. In this study, ...benzotrithiophene-based covalent organic frameworks with spatially separated redox centers are rationally designed for the photocatalytic production of hydrogen peroxide from water and oxygen without sacrificial agents. The triazine-containing framework demonstrates high selectivity for H
2
O
2
photogeneration, with a yield rate of 2111 μM h
−1
(21.11 μmol h
−1
and 1407 μmol g
−1
h
−1
) and a solar-to-chemical conversion efficiency of 0.296%. Codirectional charge transfer and large energetic differences between linkages and linkers are verified in the double donor-acceptor structures of periodic frameworks. The active sites are mainly concentrated on the electron-acceptor fragments near the imine bond, which regulate the electron distribution of adjacent carbon atoms to optimally reduce the Gibbs free energy of O
2
* and OOH* intermediates during the formation of H
2
O
2
.
Heterostructured, including heterophase, noble-metal nanomaterials have attracted much interest due to their promising applications in diverse fields. However, great challenges still remain in the ...rational synthesis of well-defined noble-metal heterophase nanostructures. Herein, we report the preparation of Pd nanoparticles with an unconventional hexagonal close-packed (2H type) phase, referred to as 2H-Pd nanoparticles, via a controlled phase transformation of amorphous Pd nanoparticles. Impressively, by using the 2H-Pd nanoparticles as seeds, Au nanomaterials with different crystal phases epitaxially grow on the specific exposed facets of the 2H-Pd, i.e., face-centered cubic (fcc) Au (fcc-Au) on the (002)h facets of 2H-Pd while 2H-Au on the other exposed facets, to achieve well-defined fcc-2H-fcc heterophase Pd@Au core–shell nanorods. Moreover, through such unique facet-directed crystal-phase-selective epitaxial growth, a series of unconventional fcc-2H-fcc heterophase core–shell nanostructures, including Pd@Ag, Pd@Pt, Pd@PtNi, and Pd@PtCo, have also been prepared. Impressively, the fcc-2H-fcc heterophase Pd@Au nanorods show excellent performance toward the electrochemical carbon dioxide reduction reaction (CO2RR) for production of carbon monoxide with Faradaic efficiencies of over 90% in an exceptionally wide applied potential window from −0.9 to −0.4 V (versus the reversible hydrogen electrode), which is among the best reported CO2RR catalysts in H-type electrochemical cells.
•A one-step and DNA amplification-free magnetic DNA sensor is presented.•The proposed magnetic DNA sensor can detect L. monocytogenes as low as 50 CFU/mL.•The sensor combines DNA hybridization ...reaction and magnetic signal readout.•MNP-mediated magnetic signal amplification is an high-efficiency modality.
Early screening of L. monocytogenes in ready-to-eat food can prevent and control its harmful effects. In this study, we propose a highly sensitive magnetic DNA sensor based on nucleic acid hybridization reaction and magnetic signal readout. We design the L. monocytogenes specific probe1 and probe2 and label them on the 30 and 250 nm magnetic nanoparticles, respectively. The hybridization reaction between the magnetic probes and DNA of L. monocytogenes could form a sandwich nanocomplex. After magnetic separation, the unbound MNP30–probe2 can act as the transverse relaxation time (T2) signal readout probe. This assay allows the one-step detection of L. monocytogenes as low as 50 CFU/mL within 2 h without DNA amplification, and the average recovery in the spiked ham sausage samples can reach 92.6%. This system integrates the high sensitivity of magnetic sensing and high efficiency of hybridization reaction, providing a promising detection platform for pathogens.
Organic optoelectronic functional materials featuring circularly polarized emission and persistent luminescence represent a novel research frontier and show promising applications in data encryption, ...displays, biological imaging, and so on. Herein, we present a simple and universal approach to achieve circularly polarized organic phosphorescence (CPP) from amorphous copolymers by the incorporation of axial chiral chromophores into polymer chains via radical cross-linked polymerization. Our experimental data reveal that copolymers (R/S)-PBNA exhibit a maximum CPP efficiency of 30.6% and the largest dissymmetric factor of 9.4 × 10–3 and copolymers (R/S)-PNA show the longest lifetime of 0.68 s under ambient conditions. Given the CPP property of these copolymers, their potential applications in multiple information encryption and displays are demonstrated, respectively. These findings not only lay the foundation for the development of amorphous polymers with superior CPP but also expand the outlook of room-temperature phosphorescent materials.
Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with tailor-made structures and functionalities. To facilitate their utilization for advanced applications, it ...is crucial to develop a systematic approach to control the properties of COFs, including the crystallinity, stability, and functionalities. However, such an integrated design is challenging to achieve. Herein, we report supramolecular strategy-based linkage engineering to fabricate a versatile 2D hydrazone-linked COF platform for the coordination of different transition metal ions. Intra- and intermolecular hydrogen bonding as well as electrostatic interactions in the antiparallel stacking mode were first utilized to obtain two isoreticular COFs, namely COF–DB and COF–DT. On account of suitable nitrogen sites in COF–DB, the further metalation of COF–DB was accomplished upon the complexation with seven divalent transition metal ions M(II) (M = Mn, Co, Ni, Cu, Zn, Pd, and Cd) under mild conditions. The resultant M/COF–DB exhibited extended π-conjugation, improved crystallinity, enhanced stability, and additional functionalities as compared to the parent COF–DB. Furthermore, the dynamic nature of the coordination bonding in M/COF–DB allows for the easy replacement of metal ions through a postsynthetic exchange. In particular, the coordination mode in Pd/COF–DB endows it with excellent catalytic activity and cyclic stability as a heterogeneous catalyst for the Suzuki–Miyaura cross-coupling reaction, outperforming its amorphous counterparts and Pd/COF–DT. This strategy provides an opportunity for the construction of 2D COFs with designable functions and opens an avenue to create COFs as multifunctional systems.
PDF
