Influence of spatial structure migration of overlying strata on water storage of underground reservoir in coal mine.

Underground reservoir technology for coal mines can realize the coordinated development of coal exploitation and water protection in water-shortage-prone areas. The seepage effect of the floor seriously affects the safety of underground reservoirs under the action of mining damage and seepage pressure. Focusing on the problem of floor seepage in underground reservoirs, a spatial mechanical model of underground reservoirs was established. The main factors affecting the seepage of the surrounding rock were studied. The seepage pressure law in different stages of spatial structure evolution of overlying strata was explored. The results showed that pressure change was the main factor affecting the stability of a reservoir's surrounding rock. The pore space between the broken and fractured rock in the water-flowing fractured zone was the main water storage space, which was directly related to the development of a breaking arch. According to the spatial structure evolution process of the overlying strata, the water storage state of an underground reservoir was divided into two stages and three situations. The seepage pressure was mainly affected by the water pressure and the overlying strata weight. The water pressure was affected by the reservoir head height, and the overlying strata weight was mainly affected by the overlying strata thickness.

Fabrication of Oriented MOF-Based Mixed Matrix Membrane via Ion-Induced Synchronous Synthesis.

Developing a facile strategy for constructing oriented mixed matrix membranes (MMMs) with uniformly dispersed and high-loading metal-organic frameworks (MOFs) is a crucial scientific challenge in probing the enhanced capability and potential applications of MOF-polymer MMMs. Herein, a novel synchronous synthetic method for constructing oriented CuBDC/poly(m-phenylenediamine) (CuBDC/PmPD) MMM with uniform MOF dispersion at high loading at the air-solution interface via the dual function of metal ions is reported. The resulting MMM exhibits excellent separation performance in ion sieving and seawater desalination due to the structural integrity of the proposed membrane and the highly interconnected channels created through the oriented distribution of MOF in a polymer matrix. Such a cutting-edge approach may provide promising insights into the development of advanced MMMs with optimized structure and superior performances.

Fabrication of a Co-Mo-Based Metal-Organic Framework for Growth of Double-Walled Carbon Nanotubes.

Double-walled carbon nanotubes (DWCNTs) make up a unique class of carbon nanotubes (CNTs) that are particularly intriguing for scientific research and are promising candidates for technological applications. A more precise level of control and greater yields can be achieved via catalytic chemical vapor deposition (CCVD), which involves the breakdown of a carbonaceous gas over nanoparticles. The addition of molybdenum to the system can increase the selectivity with regard to the number of walls that exist in the obtained CNTs. As reported herein, we have designed and synthesized a novel Co-Mo-MOF, [Co(3-bpta)1.5(MoO4)]·H2O (where 3-bpta = N,N'-bis(3-pyridyl)terephthalamide), and employed the Co-Mo-MOF as a bimetallic catalyst precursor for the CCVD approach to prepare high-quality DWCNTs. The Co-Mo-MOF was employed after being calcined in N2 and H2 at 1100 °C and decomposing into CoO, CoMoO4, and MoO3. Existing CoMoO4 is unaltered after reduction in H2 at 1100 °C, while CoO and MoO3 are converted into Co0 and MoO2, and more CoMoO4 is created at the expense of Co0 and MoO2 without clearly defining agglomeration. Finally, the interaction between metallic Co particles and C2H4 is what initiates the formation of DWCNTs. In-depth discussion is provided in this paper regarding the mechanism underlying the high selectivity and activity of Co-Mo catalysts in regulating the development and structure of DWCNTs. The DWCNTs also offer excellence performance when they are used as water purification agents and as selective sorbents. This work opens a feasible way to use MOFs as a way to produce MWCNTs, thus blazing a new trail in the field of MOF-derived carbon-based materials.

A Substrate Integrated Waveguide-Based W-Band Antenna for Microwave Power Transmission.

A W-band slot array antenna based on a substrate integrated waveguide (SIW) for microwave power transmission (MPT) is proposed in this paper. By size optimization, the transition from the rectifier element to the antenna is limited to a small size. It realizes a compact arrangement of the radiating slots, which not only improves the aperture efficiency of the antenna but also makes it easy to integrate into a large-scale array. For antenna testing, a coplanar waveguide-SIW-rectangular waveguide transition structure is added at the end of the antenna, and an antenna with this transition structure is processed by PCB printing technology and measured. The measured reflection coefficient is less than -10 dB at 90-96 GHz, the aperture efficiency is greater than 60% at 93.5-94.5 GHz, the maximum gain is 13.2 dB at 93.5 GHz, and the aperture efficiency is 79%. The test results of the antenna show that the antenna has a good performance and can be applied to the MPT system as a rectenna.

A new class of bilayer kagome lattice compounds with Dirac nodal lines and pressure-induced superconductivity.

Kagome lattice composed of transition-metal ions provides a great opportunity to explore the intertwining between geometry, electronic orders and band topology. The discovery of multiple competing orders that connect intimately with the underlying topological band structure in nonmagnetic kagome metals AV3Sb5 (A = K, Rb, Cs) further pushes this topic to the quantum frontier. Here we report a new class of vanadium-based compounds with kagome bilayers, namely AV6Sb6 (A = K, Rb, Cs) and V6Sb4, which, together with AV3Sb5, compose a series of kagome compounds with a generic chemical formula (Am-1Sb2m)(V3Sb)n (m = 1, 2; n = 1, 2). Theoretical calculations combined with angle-resolved photoemission measurements reveal that these compounds feature Dirac nodal lines in close vicinity to the Fermi level. Pressure-induced superconductivity in AV6Sb6 further suggests promising emergent phenomena in these materials. The establishment of a new family of layered kagome materials paves the way for designer of fascinating kagome systems with diverse topological nontrivialities and collective ground states.

A dual-emissive europium-based metal-organic framework for selective and sensitive detection of Fe3+ and Fe2.

A dual-emissive optical material as a ratiometric fluorescent probe has been demonstrated to be remarkably superior in precise and quantitative analyses. Herein, a novel dual-emissive fluorescent probe Eu-BDC-OH was designed and successfully synthesized using Eu3+ and 2-hydroxyterephthalic acid (H2BDC-OH) at room temperature. Eu-BDC-OH has a three-dimensional interpenetrating network structure with a large number of exposed hydroxyl functional groups, providing abundant active sites for molecular recognition. In particular, the as-obtained Eu-BDC-OH serves as a unique fluorescent probe, and the double emission peaks of both the ligand and Eu3+ are completely quenched by Fe3+. However, it is worth noting that the dual emissions of Eu-BDC-OH enable the ratiometric detection of Fe2+, which leads to an increase in ligand emission and a decrease in Eu3+ emission, accompanied by a distinct red to blue color transition. The relative fluorescence intensity ratio (I618 nm/I433 nm) decreased linearly with increasing Fe2+ concentration in the 0-50 µM range with a superior detection limit of 0.32 µM. In this work, a fluorescent probe based on a MOF was developed for the recognition of Fe2+ and Fe3+, providing a promising strategy for the synthesis of novel dual-emission materials by integrating suitable luminescent ligands with lanthanide metal ions.

Synthesis of FeNiCo Ternary Hydroxides through Green Grinding Method with Metal-Organic Frameworks as Precursors for Oxygen Evolution Reaction.

Metal-organic framework (MOF)-derived materials have been widely applied to diversified fields until now due to their flexible processibility. Different kinds of suitable materials can be synthesized by varying MOF templates/precursors and synthesis methods. An appropriate method can skillfully fabricate the materials with excellent performance while meeting the environmentally friendly concept. In this work, a green and flexible grinding method was introduced to synthesize MOF-derived FeNiCo trimetallic materials without solvent-assistance, in which Co-ZIF-L was selected as a sacrificial precursor and Fe3+ and Ni2+ as etchants and dopants. Surprisingly, the as-prepared FeNiCo ternary hydroxides supported on Ni foam (G-FeNi-Co-ZIF-L/NF) showed superior electrocatalytic performance for the oxygen evolution reaction (OER) with a low overpotential of 248 mV at 10 mA cm-2 . This work provides a prospective approach to synthesize various MOF-derived multi-metallic materials, which also opens the door for syntheses of OER electrocatalysts.

Preparation of Superhydrophobic Metal-Organic Framework/Polymer Composites as Stable and Efficient Catalysts.

Metal-organic frameworks (MOFs), as a chemical platform, combined with multifunctional polymers are of interest in catalytic applications, which can not only inherit the outstanding properties of the two components but also lead to unique synergistic effects. Nonetheless, most MOFs possess varying degrees of water instability, which limits their real application. Herein, we fabricated highly hydrophobic MOF/polymer composites via a universal post-synthetic polymerization strategy as efficient catalysts. Polyaniline (PANI) was first hybridized with MOFs by vapor deposition polymerization, and then, hydrophobic molecules were grafted to the PANI by a covalent linking process, thereby forming a superhydrophobic MOF/PANI hybrid material (MOF/PANI-shp). The resultant MOF/PANI-shp not only obtains superior moisture/water resistance without significantly disturbing the original features but also exhibits a novel catalytic selectivity in styrene oxidation because of the accessible sites and synergistic effects. Such a synthetic strategy for the MOF/polymer catalyst opens a new avenue for the design of a unique catalyst with outstanding catalytic efficiency, selectivity, and stability.

Enhanced electrochemical performance of MnO2 nanoparticles: graphene aerogels as conductive substrates and capacitance contributors.

An N-doped graphene aerogel (NGA) is used as a reactive container for growing MnO2 nanoparticles via a soaking-hydrothermal strategy. MnO2 nanoparticles pile up on the surface of reduced graphene oxide sheets with crosslinked structures serving as electrical conductors. Importantly, the NGA generates extra capacitance during the electrochemical process, which accomplishes a satisfactory compensation in the physical-chemical properties of MnO2. As a cathodic electrode for Zn-ion batteries, the MnO2/NGA exhibits a specific capacity of 275.8 mA h g-1 and pre-eminent cycling stability with a retention of 93.6% at 3 A g-1 after 1000 cycles. Meanwhile, the proposed electrode also shows a relatively high specific capacitance of 341 F g-1 for a supercapacitor in 1 M Na2SO4. Meanwhile, the long-term cycling stability shows only a slight decrease by 5.1% of the initial capacitance after 5000 continuous cycles at 3 A g-1, which indicates its superior electrochemical stability. Additionally, the assembled asymmetric supercapacitor also shows good electrochemical performance. This work highlights the extensive function of an N-doped graphene aerogel as a promising substrate for enhancing the electrochemical performance of MnO2, which opens the gate for wide potential applications of graphene aerogel composites emphasizing their complementary effects.

Construction of Zn/Ni Bimetallic Organic Framework Derived ZnO/NiO Heterostructure with Superior N-Propanol Sensing Performance.

Bimetallic organic frameworks (Bi-MOFs) have been recognized as one of the most ideal precursors to construct metal oxide semiconductor (MOS) composites, owing to their high surface area, various chemical structures, and easy removal of the sacrificial MOF scaffolds through calcination. Herein, we synthesized Zn/Ni Bi-MOF for the first time via a facile ion exchange postsynthetic strategy, formed a three-dimensional framework consisting of infinite one-dimensional chains that is unattainable through the direct solvothermal approach, and then transformed the Zn/Ni Bi-MOF into a unique ZnO/NiO heterostructure through calcination. Notably, the obtained sensor based on a ZnO/NiO heterostructure exhibits an ultrahigh response of 280.2 toward 500 ppm n-propanol at 275 °C (17.2-fold enhancement compared with that of ZnO), remarkable selectivity, and a limit of detection of 200 ppb with a notable response (2.51), which outperforms state-of-the-art n-propanol sensors. The enhanced n-propanol sensing properties may be attributed to the synergistic effects of several points including the heterojunction at the interface between the NiO and ZnO nanoparticles, especially a one-dimensional chain MOF template structure as well as the chemical sensitization effect of NiO. This work provides a promising strategy for the development of a novel Bi-MOF-derived MOS heterostructure or homostructure with well-defined morphology and composition that can be applied to the fields of gas sensing, energy storage, and catalysis.

Amorphous FeNi-bimetallic infinite coordination polymers as advanced electrocatalysts for the oxygen evolution reaction.

Amorphous bimetallic coordination polymers have been prepared by a mild room temperature solution phase method and utilized as an OER electrocatalyst. Their excellent performance with an overpotential of 228 mV at 10 mA cm-2 and a Tafel slope of 30.3 mV dec-1 exhibits their great potential in the field of the OER.

Transition from Ferromagnetic Semiconductor to Ferromagnetic Metal with Enhanced Curie Temperature in Cr2Ge2Te6 via Organic Ion Intercalation.

Magnetism in the two-dimensional limit has become an intriguing topic for exploring new physical phenomena and potential applications. Especially, the two-dimensional magnetism is often associated with novel intrinsic spin fluctuations and versatile electronic structures, which provides vast opportunities in 2D material research. However, it is still challenging to verify candidate materials hosting two-dimensional magnetism, since the prototype systems have to be realized by using mechanical exfoliation or atomic layer deposition. Here, an alternative manipulation of two-dimensional magnetic properties via electrochemical intercalation of organic molecules is reported. Using tetrabutyl ammonium (TBA+), we synthesized a (TBA)Cr2Ge2Te6 hybrid superlattice with metallic behavior, and the Curie temperature is significantly increased from 67 K in pristine Cr2Ge2Te6 to 208 K in (TBA)Cr2Ge2Te6. Moreover, the magnetic easy axis changes from the ⟨001⟩ direction in Cr2Ge2Te6 to the ab-plane in (TBA)Cr2Ge2Te6. Theoretical calculations indicate that the drastic increase of the Curie temperature can be attributed to the change of magnetic coupling from a weak superexchange interaction in pristine Cr2Ge2Te6 to a strong double-exchange interaction in (TBA)Cr2Ge2Te6. These findings are the first demonstration of manipulation of magnetism in magnetic van der Waals materials by means of intercalating organic ions, which can serve as a convenient and efficient approach to explore versatile magnetic and electronic properties in van der Waals crystals.

Applicability of Yielding-Resisting Sand Column and Three-Dimensional Coordination Support in Stopes.

In view of the existing problems of stope roadways, which are difficult to maintain under the influence of high ground and mining-induced stresses, the structural characteristics and movement regularities of stopes surrounding rocks were analysed. Through the construction of a three-dimensional mechanical model of the coordination support of a stope, the adaptability index of the support in stope is presented, and its mechanism of operation is expounded. Yielding-resisting sand column (YRSC) sidewall-support technology with satisfactory compressibility and supporting strength was developed. The structure and actual mechanical properties of the YRSC were investigated through laboratory experiments, and the optimum ratio of filling materials was obtained. The good applicability of the load and deformation adaptability index of the three-dimensional coordination support in the stope and YRSC sidewall-support technology were demonstrated in practice at the No. 12306 working face of the Dongda coal mine. It was shown that the designed carrying capacity and compression of the sand columns satisfied the site requirements. The actual stress and deformation of the YRSC exhibited three stages: Slow growth at the initial stage, a large increase in the medium term, and a stable trend at the end. The adaptability index of the three-dimensional coordination support in the stope considers all bearing structure units of the stope as an interconnected whole, and the stability conditions of the stope roadway can be quantitatively described. The supporting effect of the YRSC is remarkable and can be applied to the construction of tunnels, bridge systems and other engineering fields.

Absence of van der Waals Gap in Ternary Thorium Nitride ThNF and ThNCl.

Two kinds of ternary thorium nitride compounds, ThNF and ThNCl, are synthesized. Via the refinement of X-ray diffraction patterns, the accurate crystal structure of the two compounds is solved. Although ThNF and ThNCl share a similar structure with MNX (M = Ti, Zr, Hf; X = Cl, Br) compounds, the interaction between adjacent ThNF and ThNCl layers is not a van der Waals gap. For ThNF, the strong electronegativity of F ions leads to the bonding of Th to the F both in the nearest neighbor layer and the next nearest neighbor layer, which results in the absence of a van der Waals gap between ThNF layers. However, for ThNCl, the reason for the absence of a van der Waals gap could be attributed to the large Th-Cl bond length due to the partially covalent Th-Cl bond as well as the flat ThN layer. It is the absence of van der Waals gap that results in the failure of intercalating cations into ThNF and ThNCl. Our result reveals the reason for unsuccessful intercalation in ThNF and ThNCl, thereby providing a deeper understanding for the interlayer interaction in ternary layer structures in metal nitride halides.

Electric-field-controlled superconductor-ferromagnetic insulator transition.

Superconductivity beyond electron-phonon mechanism is always twisted with magnetism. Based on a new field-effect transistor with solid ion conductor as the gate dielectric (SIC-FET), we successfully achieve an electric-field-controlled phase transition between superconductor and ferromagnetic insulator in (Li,Fe)OHFeSe. A dome-shaped superconducting phase with optimal Tc of 43 K is continuously tuned into a ferromagnetic insulating phase, which exhibits an electric-field-controlled quantum critical behavior. The origin of the ferromagnetism is ascribed to the order of the interstitial Fe ions expelled from the (Li,Fe)OH layers by gating-controlled Li injection. These surprising findings offer a unique platform to study the relationship between superconductivity and ferromagnetism in Fe-based superconductors. This work also demonstrates the superior performance of the SIC-FET in regulating physical properties of layered unconventional superconductors.

Magnetic-field enhanced high-thermoelectric performance in topological Dirac semimetal Cd3As2 crystal.

Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit (ZT) in three-dimensional Dirac semimetal Cd3As2 crystal. It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in Cd3As2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.

Magnetic field-induced electronic phase transition in the Dirac semimetal state of black phosphorus under pressure.

Different instabilities have been confirmed to exist in the three-dimensional (3D) electron gas when it is confined to the lowest Landau level in the extreme quantum limit. The recently discovered 3D topological semimetals offer a good platform to explore these phenomena due to the small sizes of their Fermi pockets, which means the quantum limit can be achieved at relatively low magnetic fields. In this work, we report the high-magnetic-field transport properties of the Dirac semimetal state in pressurized black phosphorus. Under applied hydrostatic pressure, the band structure of black phosphorus goes through an insulator-semimetal transition. In the high pressure topological semimetal phase, anomalous behaviors are observed on both magnetoresistance and Hall resistivity beyond the relatively low quantum limit field, which is demonstrated to indicate the emergence of an exotic electronic state hosting a density wave ordering. Our findings bring the first insight into the electronic interactions in black phosphorus under intense field.

Effect of sulfonic acid containing mesogens on liquid-crystalline behavior of polysiloxane-based polymers.

A series of liquid-crystalline polysiloxanes synthesized by cholest-5-en-3-ol (3beta)-10-undecenoate and 4'-octanoyloxy-biphenyl-4-yl 4-allyloxy-3-sulfo-benzoate were prepared in a one-step reaction with sulfonic acid group contents ranging between 0 and 2.73 wt %. All the polymers displayed smectic mesophases with a large temperature range for the mesophases. With an increase of sulfonic acid containing mesogens in the polymers, the temperature of the glass transition did not change greatly, while the temperature of the clear point decreased. The hydrogen-bonding mesogen aggregates in the domains disturb the liquid-crystalline molecular mobility and orientation, leading to a decrease in temperature from the mesophase to the isotropic transition. Unlike the polymers containing lower sulfonic acid mesogens, some polymers showed a dendritic texture of the SmB* phase, indicating that the sulfonic mesogens enhanced the rigid moieties of the supermolecular structure of the liquid-crystalline phases. All the polymers displayed sharp and strong peaks at low angles around 2theta approximately 2.6 degrees and broad peaks at wide angles around 2theta approximately 17 degrees in X-ray measurements. The intensity of the strong peak at low angles in the X-ray profiles decreased with an increase of sulfonic acid mesogens in the polymer systems.

Optical characterization of polymer liquid crystal cell exhibiting polymer blue phases.

The optical properties of polymer liquid crystal cell exhibiting polymer blue phases (PBPs) have been determined using ultraviolet-visible spectrophotometry, polarizing optical microscopy (POM), differential scanning calorimetry (DSC), X-ray measurements, FTIR imaging and optical rotation technique. PBPs are thermodynamically stabile mesophases, which appear in chiral systems between isotropic and liquid crystal phases. A series of cyclosiloxane-based blue phase polymers were synthesized using a cholesteric LC monomer and a nematic LC monomer, and some of the polymers exhibit PBPs in temperature range over 300 degrees in cooling cycles. The unique property based on their structure and different twists formed and expect to open up new photonic application and enrich polymer blue phase contents and theory.