Highly Sensitive Ratiometric Fluorescent Flexible Sensor Based on the RhB@ZIF-8@PVDF Mixed-Matrix Membrane for Broad-Spectrum Antibiotic Detection.

Antibiotics play an essential role in the treatment of various diseases. However, the overuse of antibiotics has led to the pollution of water bodies and food safety, affecting human health. Herein, we report a dual-emission MOF-based flexible sensor for the detection of antibiotics in water, which was prepared by first encapsulating rhodamine B (RhB) by a zeolite imidazolium ester skeleton (ZIF-8) and then blending it with polyvinylidene difluoride (PVDF). The luminescent properties, structural tunability, and flexible porosity of the MOF-based composites were combined with the processability and flexibility of polymers to prepare luminescent membranes. The sensor is capable of dual-emission ratiometric fluorescence sensing of nitrofurantoin (NFT) and oxytetracycline (OTC), exhibiting sensitive detection of fluorescence burst and fluorescence enhancement, respectively, with detection limits of 0.012 µM and 8.9 nM. With the advantages of visual detection, high sensitivity, short detection time, and simplicity, the highly sensitive ratiometric fluorescent flexible sensor has great potential for detecting antibiotics in an aqueous environment. It will further stimulate interest in luminescent MOF-based mixed matrix membranes and their sensing applications.

SnSe Nanosheet Array on Carbon Cloth as a High-Capacity Anode for Sodium-Ion Batteries.

Binder-free electrodes offer a great opportunity for developing high-performance sodium-ion batteries (SIBs) aiming at the application in energy storage devices. Tin selenide (SnSe) is considered to be a promising anode material for SIBs owing to its high theoretical capacity (780 mA h g-1). In this work, a SnSe nanosheet array (SnSe NS) on a carbon cloth is prepared using a vacuum thermal evaporation method. The as-prepared SnSe NS electrode does not have metal current collectors, binders, or any conductive additives. In comparison with the electrode of SnSe blocky particles (SnSe BP), the SnSe NS electrode delivers a higher initial charge capacity of 713 mA h g-1 at a current density of 0.1C and maintains a higher charge capacity of 410 mA h g-1 after 50 cycles. Furthermore, the electrochemical behaviors of the SnSe NS electrode are determined via pseudocapacitance and electrochemical impedance spectroscopy measurements, indicating a faster kinetic process of the SnSe NS electrode compared to that of the SnSe BP. Operando X-ray diffraction measurements prove that the SnSe NS exhibits better phase reversibility than the SnSe BP. After the cycles, the SnSe NS electrode still maintains its particular structure. This work provides a feasible method to prepare SnSe nanostructures with high capacity and improved sodium ion diffusion ability.

Topological insulator Bi2Se3 for highly sensitive, selective and anti-humidity gas sensors.

Chemiresistive gas sensors generally surfer from low selectivity, inferior anti-humidity, low response signal or signal-to-noise ratio, severely limiting the precise detection of chemical agents. Herein, we exploit high-performance gas sensors based on topological insulator Bi2Se3 that is distinguished from conventional materials by robust metallic surface states protected by time-reversal symmetry. In the presence of Se vacancies, Bi2Se3 nanosheets exhibit excellent gas sensing capability toward NO2, with a high response of 93% for 50 ppm and an ultralow theoretical limit of detection concentration about 0.06 ppb at room temperature. Remarkably, Bi2Se3 demonstrates ultrahigh anti-humidity interference characteristics, as the response with standard deviation of only 3.63% can be achieved in relative humidity range of 0-80%. These findings are supported by first-principles calculations, with analyses on adsorption energy and charge transfer directly revealing the anti-humidity and selectivity. This work may pave the way for implementation of exotic quantum states for intelligent applications.

Highly efficient removal of aqueous Hg(II) by FeS micro-flakes.

FeS (mackinawite) is known to be effective in the sorption of aqueous Hg(II). However, FeS nanoparticles are apt to aggregate and easy to be oxidized, which limits their wide applications. Here, we have synthesized FeS micro-flakes which can be uniformly dispersed in water without aggregation. Owing to the good stability and dispersibility, FeS micro-flakes exhibit high efficiency in the removal of Hg(II) from water. The sorption of Hg(II) on the FeS micro-flakes is more consistent with the pseudo-second-order kinetic model and Langmuir model, indicating that the sorption of Hg(II) is mainly monolayer sorption dominated by chemical sorption. The maximum sorption capacity is 2680 mg/g at pH 5.6 and 30 °C, significantly higher than those of FeS nanoparticles and other Hg(II) scavengers. The pH studies indicate that FeS (0.31 g/L) can effectively remove >97.6 % of 200 mg/L Hg(II) in the pH range of 2-12 at 30 °C. Powder X-ray diffraction, elemental and sorption analyses suggest that Hg(II) is removed via chemical precipitation and surface adsorption. This study demonstrates the potential and viability of FeS micro-flakes for efficient removal of aqueous Hg(II).

Capacity-enhanced and kinetic-expedited zinc-ion storage ability in a Zn3V3O8/VO2 cathode enabled by heterostructural design.

Heterostructured double-phase composites are promising electrode candidates for high-performance secondary metal batteries due to their superior capacity and ion transfer kinetics compared with the pristine phase. Herein, a Zn3V3O8/VO2 (ZVO/VO) heterostructure with abundant phase boundaries was designed as the cathode for aqueous zinc-ion batteries (ZIBs). The preparation method is based on a solid pre-intercalation approach, and the Zn content in the ZVO/VO heterostructure can be precisely controlled. The electrochemical performance of ZVO/VO containing different amounts of Zn, pristine ZVO, and VO phases was compared. ZVO/VO showed superior capacity and cycling stability compared to pristine ZVO and VO. The ZVO/VO heterostructure showed a capacity of 328.4 mA h g-1 at 0.3 A g-1 after 200 cycles. The long-term cycling performance of ZVO/VO was evaluated at 3 A g-1, and it delivered a capacity retention of 90.5% after 1000 cycles. The ion storage mechanism of the ZVO/VO electrode was analyzed by ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). This work provides a simple strategy for designing vanadium-based heterostructure composites as advanced cathodes for ZIBs.

NaOH-Intercalated Iron Chalcogenides (Na1-xOH)Fe1-yX (X = Se, S): Ion-Exchange Synthesis and Physical Properties.

The discovery of the (Li1-xFexOH)FeSe superconductor has aroused significant interest in metal hydroxide-intercalated iron chalcogenides. However, all efforts made to intercalate NaOH between FeSe and FeS layers have failed so far. Here we report two NaOH-intercalated iron chalcogenides (Na1-xOH)Fe1-yX (X = Se, S) that were synthesized by a low-temperature hydrothermal ion-exchange method. Their crystal structures were solved through single-crystal X-ray diffraction and refined against powder X-ray and neutron diffraction data. Different from the (Li1-xFexOH)FeX superconductors that crystallize in a tetragonal space group P4/nmm with Z = 2, (Na1-xOH)Fe1-yX belong to an orthorhombic space group Cmma with Z = 4. The structural solution also reveals that there are vacancies in both Na and Fe sites and there are not iron ions in the (Na1-xOH) layer. This is probably why both Fe(II) and Fe(III) species exist in the title compounds, as detected by X-ray photoelectron spectroscopy. Based on magnetization and electrical resistivity measurements, the two compounds were found to be paramagnetic semiconductors. The absence of superconductivity should be closely related to the iron vacancies in the Fe1-yX layer. Theoretical calculations suggest that inducing superconductivity in (Na1-xOH)Fe1-ySe is promising due to the similarity of the electronic structures between stoichiometric (NaOH)FeSe and the (Li1-xFexOH)FeSe superconductor.

Electron energy loss spectroscopy and first-principles study of GaN via Zn doping.

The electronic structure of GaN and GaN:Zn was investigated by electron energy loss spectroscopy and first-principles calculations. In the low-loss spectrum, the interband transitions are assigned to the observed energy loss peaks. After Zn doping, impurity levels are introduced to the density of states and hybrid orbitals of N 2p and Zn 3d are formed around the Fermi level. In the nitrogen K-edge, an additional peak was observed due to the formation of donor defect states. A core-hole effect is believed to be significant for simulation of the N K-edge for both GaN and GaN:Zn.

Spark Plasma Sintered Bulk Nanocomposites of Bi2Te2.7Se0.3 Nanoplates Incorporated Ni Nanoparticles with Enhanced Thermoelectric Performance.

Bi2Te3-based compounds are important near room temperature thermoelectric materials with commercial applications in thermoelectric modules. However, new routes leading to improved thermoelectric performance are highly desirable. Incorporation of superparamagnetic nanoparticles was recently proposed as a means to promote the thermoelectric properties of materials, but its feasibility has rarely been examined in mainstream thermoelectric materials. In this study, high quality single-crystalline Bi2Te2.7Se0.3 nanoplates and Ni nanoparticles were successfully synthesized by solvothermal and thermal decomposition methods, respectively. Bulk nanocomposites consisting of Bi2Te2.7Se0.3 nanoplates and superparamagnetic Ni nanoparticles were prepared by spark plasma sintering. It was found that incorporation of Ni nanoparticles simultaneously increased the carrier concentration and provided additional scattering centers, which resulted in enlarged electric conductivities and Seebeck coefficients. The greatly improved ZT was achieved due to the increase in power factor. Spark plasma sintered bulk nanocomposites of Bi2Te2.7Se0.3 nanoplates incorporated by 0.4 mol %Ni nanoparticles (in molar ratio) showed a figure-of-merit ZT of 0.66 at 425 K, equivalent to 43% increase when compared to pure Bi2Te2.7Se0.3 nanoplates. The results revealed that incorporation of magnetic nanoparticles could be an effective approach for promoting the thermoelectric performance of conventional semiconductors.

Bifunctional Ag/C3N4.5 composite nanobelts for photocatalysis and antibacterium.

Multiple functions can be achieved in carbon nitride-based composite nanomaterials by tuning their components and structures. Here, we report on a large-scale synthesis of novel bifunctional Ag/C3N4.5 composite nanobelts (CNBs) with efficient photocatalytic and antibacterial activity. The Ag/C3N4.5 CNBs were synthesized in high yield by a two-step route including a homogeneous precipitation process and a subsequent calcination treatment. The structural, morphological, compositional, and spectroscopic characterizations revealed that the Ag/C3N4.5 CNBs are composed of N-deficient melem ultrathin nanobelts and crystalline Ag nanoparticles attached to the surface of the nanobelts with good contact. The band gap of the Ag/C3N4.5 CNBs is determined to be about 3.04 eV. The efficient photocatalytic and antibacterial activities of the composite nanomaterials are verified by testing the degradation of Rhodamine B (RhB) and the inhibition zone to bacterium E. coli. The work provides a facile route to bifunctional carbon nitride-based composites with potential applications in the fields of the environment and biology.

Bi-Assisted CdTe/CdS Hierarchical Nanostructure Growth for Photoconductive Applications.

We developed a method to control the structure of CdTe nanowires by adopting Bi-mixed CdTe powder source to a catalyst-assisted chemical vapor deposition, which allowed us to fabricate CdTe/CdS hierarchical nanostructures. We demonstrated that diverse nanostructures can be grown depending on the combination of the Bi powder and film catalysts. As a proof of concepts, we grew CdTe/CdS branched nanowires for the fabrication of photodetectors. The hierarchical nanostructure-based photodetectors showed an improved photoresponsivity compared to the single CdTe nanowire (NW)-based photodetector. Our strategy can be a simple but powerful method for the development of advanced optoelectronic devices and other practical applications.

Direct Transformation from Graphitic C3N4 to Nitrogen-Doped Graphene: An Efficient Metal-Free Electrocatalyst for Oxygen Reduction Reaction.

Carbon-based nanomaterials provide an attractive perspective to replace precious Pt-based electrocatalysts for oxygen reduction reaction (ORR) to enhance the practical applications of fuel cells. Herein, we demonstrate a one-pot direct transformation from graphitic-phase C3N4 (g-C3N4) to nitrogen-doped graphene. g-C3N4, containing only C and N elements, acts as a self-sacrificing template to construct the framework of nitrogen-doped graphene. The relative contents of graphitic and pyridinic-N can be well-tuned by the controlled annealing process. The resulting nitrogen-doped graphene materials show excellent electrocatalytic activity toward ORR, and much enhanced durability and tolerance to methanol in contrast to the conventional Pt/C electrocatalyst in alkaline medium. It is determined that a higher content of N does not necessarily lead to enhanced electrocatalytic activity; rather, at a relatively low N content and a high ratio of graphitic-N/pyridinic-N, the nitrogen-doped graphene obtained by annealing at 900 °C (NGA900) provides the most promising activity for ORR. This study may provide further useful insights on the nature of ORR catalysis of carbon-based materials.

Black and yellow anatase titania formed by (H,N)-doping: strong visible-light absorption and enhanced visible-light photocatalysis.

Black and yellow anatase TiO2 doped with hydrogen and nitrogen elements annealed under a N2/Ar/air atmosphere are produced. More interestingly, one kind of black TiO2 has excellent performance for degradation of methylene blue under visible-light irradiation but photodegradation of the other is quite limited.

High-performance photoconductive channels based on (carbon nanotube)-(CdS nanowire) hybrid nanostructures.

A photoconductive channel based on hybrid nanostructures comprising carbon nanotubes (CNTs) and CdS nanowires is fabricated by a directed assembly strategy and catalyst-assisted chemical vapor deposition (CVD). The photoconductive channels simultaneously exhibit large photocurrent and fast response speed. Furthermore, it can be easily applied to surfaces that are not flat, such as a glass tube. This is a simple but efficient strategy for various optoelectronic applications.

Metallic nanowire-graphene hybrid nanostructures for highly flexible field emission devices.

We report a simple but efficient method to prepare metallic nanowire-graphene (MN-G) hybrid nanostructures at a low temperature and show its application to the fabrication of flexible field emission devices. In this method, a graphene layer was transferred onto an anodic alumina oxide template, and vertically aligned Au nanowires were grown on the graphene surface via electrodeposition method. As a proof of concept, we demonstrated the fabrication of flexible field emission devices, where the MN-G hybrid nanostructures and another graphene layer on PDMS substrates were utilized as a cathode and an anode for highly flexible devices, respectively. Our field emission device exhibited stable and high field emission currents even when bent down to the radius of curvature of 25 mm. This MN-G hybrid nanostructure should prove tremendous flexibility for various applications such as bio-chemical sensors, field emission devices, pressure sensors and battery electrodes.

Facile route to nitrides: transformation from single element to binary and ternary nitrides at moderate temperature through a new modified solid-state metathesis.

In this article, we report a new modified solid-state metathesis pathway to synthesize nitrides using Li(3)N as a nitrification reagent to transform single element to nitrides. In this process, not only binary (including mono- and multinitrides) but also ternary nitrides can be approached by varying the molar ratio of Li(3)N to a single element. A possible two-step reaction mechanism for Li(3)N and single elements was proposed. This study provides a promising route to meet the increasing demand in energy savings and environmental protection for materials synthesis.

Observation of glassy ferromagnetism in Al-doped 4H-SiC.

Glassy ferromagnetism is observed in diluted magnetic semiconductor Al-doped 4H-SiC. We propose a possible explanation for the origin of ferromagnetism order that is the coeffect of sp(2)/sp(3) configuration along with the structural defects. This result unambiguously demonstrates the existence of intrinsic ferromagnetism order in nonmagnetic sp systems.

Route to GaN and VN assisted by carbothermal reduction process.

A route to prepare nitrides, such as GaN, VN, and other nitrides, is reported. The reaction pathway involves a two-step process by using the as-synthesized a-C3N3.69 as precursor. The route is so potent that a series of nitrides can be directly synthesized from their oxides at moderate temperatures. A striking feature of this method lies in that a-C3N3.69 is found to play double roles as both carbonizing and nitridizing agent in these reactions. These results will greatly deepen our understandings of the mechanism for solid-state metathesis reactions.