Core-shell Metal Research Articles

ZIF-8@Zn-MOF-74 core–shell metal–organic framework (MOF) with open metal sites: Synthesis, characterization, and gas adsorption performance

In this paper, an efficient hierarchical metal–organic framework (MOF), namely ZIF-8@Zn-MOF-74 with core–shell structure and coordinately open/unsaturated metal sites (OMS) was successfully synthesized. For this purpose, the facile post-synthetic ligand exchange (PSE) method at ambient temperature was applied. In the fabricated core–shell porous structure, the SOD-type ZIF-8 acts as the core, providing molecular sieving features, resulting in greater adsorption selectivity values. On the other hand, Zn-MOF-74 as the shell part, owing to the larger pore size, makes entrance and diffusion of the guest gas molecules more convenient. In addition, due to the presence of OMS in the Zn-MOF-74 structure, a greater adsorption capacity would be achieved. The prepared MOFs were characterized by FESEM, EDS, HRTEM, FTIR, XRD, BET, and TGA analyses, and formation of the core–shell structure was confirmed. The FESEM and HRTEM images demonstrated rather smooth coverage of the core (ZIF-8) with a layer of the shell (Zn-MOF-74). The rather high BET surface area (633.2 m2/g) and total pore volume (0.671 cm3 g−1) of the core–shell structure, make it promising for gas adsorption applications. The gas adsorption measurements were conducted for CO2, N2, H2, O2, CH4, C2H6, C3H8, C2H4, and C3H6 pure gases at 308 K and equilibrium pressures up to 4 bar. It was found that the CO2 adsorption capacity of ZIF-8@Zn-MOF-74 nanoparticles (3.27 mmol g−1) has enhanced ∼63.5 % compared to the pristine ZIF-8 (∼2 mmol/g). The CO2/N2 and CO2/CH4 selectivity values were also increased by 85.4 % and 74.4 %, respectively, that indicates overcoming the trade-off between adsorption capacity and selectivity.

Multi-layer core-shell metal oxide/nitride/carbon and its high-rate electroreduction of nitrate to ammonia.

The electroreduction of nitrate to ammonia is both an alternative strategy to industrial Haber-Bosch ammonia synthesis and a prospective idea for changing waste (nitrate pollution of groundwater around the world) into valuable chemicals, but still hindered by its in-process strongly competitive hydrogen evolution reaction (HER), low ammonia conversion efficiency, and the absence of stability and sustainability. Considering the unique electronic structure of anti-perovskite structured Fe4N, a tandem disproportionation reaction and nitridation-carbonation route for building a multi-layer core-shell oxide/nitride/C catalyst, such as MoO2/Fe4N/C, is designed and executed, in which abundant Fe-N active sites and rich phase interfaces are in situ formed for both suppressing HER and fast transport of electrons and reaction intermediates. As a result, the sample's NO3RR conversion displays a very high NH3 yield rate of up to 11.10 molNH3 gcat.-1 h-1 (1.67 mmol cm-2 h-1) with a superior 99.3% faradaic efficiency and the highest half-cell energy efficiency of 30%, surpassing that of most previous reports. In addition, it is proved that the NO3RR assisted by the MoO2/Fe4N/C electrocatalyst can be carried out in 0.50-1.00 M KNO3 electrolyte at a pH value of 6-14 for a long time. These results guide the rational design of highly active, selective, and durable electrocatalysts based on anti-perovskite Fe4N for the NO3RR.

Effect of flake silver-plated copper particles on the property enhancement of electrically conductive adhesives.

To impart conductivity and improve the shear performance of epoxy resin-based adhesives, a simple, environmentally friendly, and stable method was used to deposit silver on the surface of 5 μm flake copper particles as a conductive filler. The core-shell metal fillers were prepared by utilizing the autocatalytic properties of Cu without adding any reducing agent during the reaction. An epoxy curing agent (MeTHPA) was used as a curing agent for the crosslinking reaction with epoxy resin to form a supporting skeleton of conductive components. The structure of flake plated Cu@Ag particles was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). It was verified that a layer of compact and crystalline silver with a concave-convex characteristic was deposited on the surface of copper particles. This feature has a positive effect on improving the performance of silver-plated copper particles. The results show that the optimal curing condition of flake plated Cu@Ag particle-epoxy composite electrically conductive adhesives (ECAs) was 200 °C for 1 h, the resistivity of flake plated Cu@Ag particle-epoxy composite ECAs with a content of flake plated Cu@Ag particles above 55 wt% was less than 6 × 10-5 Ω m, and the maximum shear strength was 8 MPa. The flake plated Cu@Ag particle-epoxy composite ECAs prepared by this method have excellent properties and have very important application value for advanced electronic devices.

In English

The behavior of the diagonal components of the dielectric tensor and the behavior of the absorption cross-section in the different frequency ranges for the composite cylindrical nanostructures “metallic core – graphene shell” have been studied. In order to obtain the calculation formulas one uses the relations for the longitudinal and transverse components of the dielectric tensors for metallic core and graphene shell, which are determined by Drude model and Cubo model correspondingly. The consideration is carried out in the frameworks of “equivalent” elongated spheroid approach, according to which the defining dimensional parameter is effective aspect ratio, calculated from the condition of the equality of the corresponding axial inertia moments for two-layer cylinder and the “equivalent” elongated spheroid. The numerical results have been obtained for the nanocylinders with the cores of different metals, different radius and with the different number of graphene layers. The variation of amplitude and the variation of the location of extremes of the real and imaginary parts of the transverse component of the dielectric tensor under the increase in radius of the metallic core and the thickness of the graphene shell have been analyzed. It has been shown that the variation of the radius of the core has the significantly greater influence on the properties of the polarizability resonances and absorption cross-section than the variation of the number of graphene layers. The reasons of the presence of two maxima of the absorption cross-section for the metal-graphene cylinders which differ in both amplitude and width and located in infrared, violet and near ultraviolet parts of the spectrum and their relation with the surface plasmonic resonances in the metallic core and with the terahertz plasmons of graphene have been found. The factors which have an effect on amplitude and on the shift of the maxima of the absorption cross-section have been found. The reasons of the different width of maxima, which are located in the different spectral intervals, have been determined.

Covalently connected core–shell NH2-MIL-125@COFs-OH hybrid materials for visible-light-driven CO2 reduction

Herein, the covalently connected core–shell metal–organic frameworks (MOFs)@covalent-organic frameworks (COFs) hybrid materials were successfully constructed by coating the stable COF-OH shell on the NH2-MIL-125 core. The introduction of the NH2-MIL-125 core endowed the hybrid materials with high Brunauer–Emmett–Teller (BET) surface area (SBET) and abundant unsaturated metal sites. And the coating of COF-OH shell endowed the hybrid materials outstanding physicochemical stability and visible-light response, and suitable band gaps. Moreover, the thickness of the COF-OH shell was carefully adjusted according to the feeding amount of NH2-MIL-125. Impressively, the electron transfer pathway in the formed heterostructure was clarified and it was proven that a type-II heterojunction was generated between the MOFs and the COFs. The formed stable CN covalent bonds in the interfacial layer was beneficial to the photogenerated electron transfer and the electron-hole pairs separation, which greatly enhanced the CO2 photocatalytic reduction. The product NH2-MIL-125@COF-3 exhibited the highest CO yield of 22.93 μmol·g−1·h−1, about 2 times higher than NH2-MIL-125 (11.82 μmol·g−1·h−1) and 3 times greater than COF-OH (7.26 μmol·g−1·h−1). This work can provide helpful ideas for the careful design of the novel MOFs@COFs hybrid materials as well as useful exploration for the CO2 photocatalytic reduction.

One-step simple calcination of Ni@C(N) core-shell microspheres: Catalytic reduction of 4-nitrophenol, supercapacitor and electrocatalytic hydrogen production

Ni@C(N) core-shell microspheres have been successfully fabricated through simple thermal decomposition method at different temperature (700, 800 and 900 ℃) in N2 atmosphere. The morphological and structural characterizations of the as-prepared Ni@C(N) samples were explored through a series of technical means, which included X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller method and X-ray photo-electron spectroscopy. The as-prepared materials as multi-function in the fields of catalytic reduction of 4-nitrophenol, supercapacitors and electrocatalytic hydrogen evolution have been also studied in detail. The experimental results showed that Ni@C(N)_700, which calcined at 700 ℃, has the best performance in catalytic and supercapacitor. This study shows that the NH3 atmosphere generated by the pyrolysis of melamine can be used to reduce more metal nanoparticles, which will provide a possibility for the preparation of non-noble metal core-shell nanomaterials with good catalytic and electrochemical activities.

N-Doped Carbon Nanotube Shell Encapsulating the NiFe Metal Core for Enhanced Catalytic Stability in Methanol Oxidation Reaction by the Structural Cooperation Mechanism.

Exploitation of high-efficiency catalysts toward methanol oxidation is a pivotal step to promote the commercialization of direct methanol fuel cells. Herein, a strategy is demonstrated to prepare nitrogen-doped carbon nanotubes with NiFe metal particles (NiFe@N-CNT) as the carrier material of Pt nanoparticles. Combining SEM and TEM, NiFe metal particles are fully encapsulated in N-CNTs, and they form the metal core and carbon nanotube shell structure based on the structural cooperation mechanism. Surprisingly, the as-prepared Pt/NiFe@N-CNT catalyst shows superior catalytic activity (1023 mA mg-1Pt) compared to commercial Pt/C (392 mA mg-1Pt), Pt/Ni@N-CNT (331 mA mg-1Pt), and Pt/Fe@N-CNT (592 mA mg-1Pt). After 1000 cycles, Pt/NiFe@N-CNT maintains the optimal catalytic activity (588 mA mg-1Pt), and its mass activity loss is 42.5%, which is better than those of commercial Pt/C (64.0%), Pt/Ni@N-CNT (67.7%), and Pt/Fe@N-CNT (59.6%) catalysts, indicating that the Pt/NiFe@N-CNT catalyst achieves excellent catalytic activity and stability, which stems chiefly from the homodispersed Pt nanoparticles and the generation of the metal core-carbon nanotube shell based on the structural cooperation mechanism. This study reports the facile construction of a metal core-carbon nanotube shell structure, which intrinsically ameliorates structural collapse of carrier material, thereby improving the catalytic stability of the Pt-based catalyst and broadening the view for design of other desire catalysts in methanol oxidation.

Synthesis, characterization, and gas adsorption performance of an efficient hierarchical ZIF-11@ZIF-8 core–shell metal–organic framework (MOF)

In this paper, the solvent-assisted linker exchange (SALE) technique was successfully applied for the synthesis of porous ZIF-11@ZIF-8 core–shell composite structure metal–organic framework (MOF). The RHO-type ZIF-11 owing to larger cavities along with higher freedom in linker rotation, acts as the core and contributes in adsorption capacity enhancement. On the other hand, the SOD-type ZIF-8 provides greater molecular sieving features due to its lower degree of linker flexibility and thereby results in an improvement of the adsorption selectivity. The morphology and structure of the fabricated MOFs were characterized by XRD, FTIR, FESEM, EDS, TEM, BET, and TGA analyses and formation of the core–shell structure was confirmed. The BET surface area and micropore volume of the synthesized ZIF-11@ZIF-8 MOF were obtained as high as 1023.4 m2/g and 0.435 cm3 g−1, respectively. Gas adsorption measurements were carried out for CO2, N2, CH4, C2H6, and C2H4 gases at 298 and 328 K and equilibrium pressures up to 4 bar. The results revealed a remarkable rise (∼100 %) in CO2 adsorption capacity of ZIF-11@ZIF-8 nanoparticles (8.21 mmol g−1), compared to the pristine ZIF-11 (4.35 mmol g−1) at 298 K. The CO2/N2 and CO2/CH4 adsorption selectivity values were also augmented by 131 % and 92 %, respectively. In addition, the fabricated core–shell MOF, exhibited greater ethane (C2H6) adsorption capacity by ∼ 65 %, along with ethane to ethylene (C2H4) adsorption selectivity enhancement by ∼ 50 %. The higher adsorption capacity values without sacrificing adsorption selectivity suggests that the controlled core–shell MOF structures would be promising candidates for effective separation of CO2 from CH4 and N2 as well as C2H6 from C2H4.

Washable, stretchable, and reusable core–shell metal nanowire network-based electronics on a breathable polymer nanomesh substrate

Polymer nanofiber-based porous structures, referred to as “breathable devices,” have been recently developed to minimize user discomfort. Although these devices enable conformal integration to the skin with gas permeability, their performance and durability are significantly lower than those of conventional film-based devices. In this study, an ultradurable embedded Ag–Au core–shell nanowire network (AANN) on a nanomesh substrate is fabricated using the intense pulsed light irradiation and electroplating (IPL-EP) process. The AANN is designed to achieve breathability and durability without sacrificing device performance. It can be used in breathable nanomesh electronics and exhibits a low sheet resistance (1.4 Ω sq−1), cycle stability (above 20,000 cycles), stability in chemicals (water-based solutions and highly corrosive H2O2 solution), washability (20 washings), and reusability. Additionally, it is used in reusable conductive electronic textiles, and its applications as a reusable strain sensor for motion detection and wearable heater for thermal therapy are demonstrated. Furthermore, the AANN-based conductive thread exhibits excellent electrical performance (0.3 Ω cm−1) with durability and maintains its electrical characteristics after 50 wash cycles. The proposed process can enable large-scale fabrication of highly durable breathable electronics, electronic textiles, and other biomedical devices.

High synergetic transition metal phosphides@ nitrogen doped porous carbon nanosheets hybrids derived from silk fibroin and phytic acid self-assembly for ultra-high performance lithium storage

Transition metal phosphides (TMPs) have received widespread attention due to their high theoretical specific capacity and fast reaction kinetics. However, their poor conductivity and volume changes during the cycle limited their applications. Herein, we explore a facile and cost-effective way to prepare core–shell-like transition metal phosphides (TMPs: CoP, Ni 2 P, Cu 3 P) nanoparticles embedded into nitrogen doped porous carbon nanosheets (denoted as CoP@NDPCS, Ni 2 P@NDPCS, Cu 3 P@NDPCS) via biological material-driven assembly and self-template strategy. By self-assembled process, the amino and carbonyl groups in silk fibroin can chelate with metal ions, and then phytic acid added undergoes a coordination reaction with the metal components. Subsequently, core-shell TMPs nanoparticles supported by nitrogen doped porous carbon nanosheets were prepared by a one-step high-temperature calcination process. The obtained unique hybrid structure material with enough vacancy space to alleviate volume expansion exhibits ultra-high specific capacity and excellent cycling performance for the anode of lithium-ion batteries. The CoP@NDPCS, Ni 2 P@NDPCS and Cu 3 P@NDPCS electrodes exhibit the reversible capacities of 1014.2, 486.5 and 877 mAh g −1 at the current density of 500 mA g -1 , respectively. The remarkable lithium storage performance of TMP@NDPCS indicates that a reasonable structure designed by biological material-driven is an effective and promising method to enhance the lithium storage of transition metal phosphides. Core-shell transition metal phosphides supported by N-doped porous carbon nanosheets were prepared by one-step high temperature calcination process. The unique hybrid structure materials exhibit ultra-high specific capacity and excellent cycling stability for the anode of lithium-ion batteries, and the reasonable structure design by biological material-driven is very effective and universal method to enhance the lithium storage of transition metal phosphides. • Carbon nanosheets derived from silk fibroin can effectively alleviate the volume expansion of TMPs during the cycling process. • The TMP@NDPCS materials exhibit ultra-high specific capacity and excellent cycling stability for lithium-ion batteries. • The TMP@NDPCS hybrid materials were synthesized by one step phosphating.

Mode Hybridization in Silicon Core-Gold Shell Nanosphere.

A dielectric core-metal shell nanosphere has attracted scientific and technological interests due to the unique optical resonances arising from the hybridization of surface plasmon modes and cavity modes. The previous studies focus on a low-index dielectric core without its own optical resonances. Here, optical resonances of a core-shell nanosphere with a high refractive index (n≈ 4) core with the lowest order Mie resonances in the visible range are investigated theoretically and experimentally. Scattering and absorption spectra of a core-shell nanosphere for different values of the core refractive index are first analyzed, and there is a transition of the hybridization scheme around n≈ 2. Above the value, a characteristic hybridized mode with strong absorption and weak scattering emerges in the near-infrared range. A core-shell nanosphere composed of a silicon core and a gold shell is prepared, and the resonance modes are studied by single particle scattering spectroscopy and electron energy loss spectroscopy (EELS) in a transmission electron microscope. The core-shell nanospheres exhibit the hybridized modes depending on the core diameter. The hybridized mode as well as the higher order one that is not observable in the scattering spectroscopy is observed in the EELS.

Bimetallic oxide nanoparticles contained hollow spheres with sodium as a core: a promising energy storage advanced structure

The bimetallic oxide nanoparticles as outer shell with sodium entrapped as a core part of a hollow porous core–shell (HoPoCs) can be a promising battery electrode composition. Till now, scientists are struggling to synthesize ternary metal oxide hollow spheres due to the reactions between diverse cations and anions of different metal precursors. Also, the extremely reactive character of sodium prevents it from remaining alone without compound formation is unveiled. Here for the first time, we entrapped sodium and synthesized bimetallic nanoparticles contained outer shell hollowsphere (Na@ZnO@MoO2) successfully by sorption (absorption + adsorption) of two metal precursors (sodium molybdate dihydrate and zinc chloride) in two steps without adding any reaction inhibiting agent. As a result, significantly Na is entrapped as a core and ZnO and MoO2 nanoparticles forming the outer shell of the sphere. ‘Na’ entrapment is confirmed by X-ray photoelectron spectroscopy and high-angle annular dark-field scanning transmission electron microscopy elemental mapping. We employed our sodium entrapped HoPoCs bimetallic oxide nanoparticles sphere (Na@ZnO@MoO2) as a battery anode getting advantages from their structural specialty shows excellent battery properties promising for application in energy storage technologies. The initial specific capacity of these HoPoCs-Na@ZnO@MoO2 sphere is 940 mAh/g (1C), with exceptional stability (790 mAh/g) after 1000 cycles at a current density of 2C) and excellent rate capability. This approach will motivate the synthesis of other superior reactive element entrapped core–shell metal oxides for next-generation rechargeable batteries and other advanced suitable applications like microreactor, protector of explosive materials, and so on.

Preparation of metal–organic framework @molecularly imprinted polymers for extracting strobilurin fungicides from agricultural products

The core–shell metal–organic framework coated with molecularly imprinted polymers (ZIF-8@MIPs) were successfully synthesized by surface imprinting technique, and applied as adsorbents for solid-phase extraction of strobilurin fungicides. The obtained hybrid complex was characterized in detail, and their adsorbing and recognition performance were evaluated. The results showed that ZIF-8@MIPs presented typically core–shell structure with MIP shell (about 20 nm), and exhibited larger adsorption capacity (102.5 mg g−1) and fast adsorption ability (only 5 min). Under the optimized conditions, a sensitive, efficient and reliable method for determining six strobilurin fungicides in different agricultural products based on ZIF-8@MIPs coupling with high performance liquid chromatography-tandem mass spectrometry was established. This method showed good linearity with correlation coefficients higher than 0.9990. With spiked at three different concentration levels in agricultural products (apple, pear, banana, Chinese cabbage, cabbage, cucumber), the good recoveries (83.5–129.0%) with relative standard deviations from 0.5 to 10.2% were obtained. The limit of detections and the limit of quantifications were 0.01–1.12 ng g−1 and 0.03–3.73 ng g−1, respectively. Those results demonstrated good potential application of ZIF-8@MIPs for enriching and separating trace strobilurin fungicides in agricultural samples.

Sensitive and selective magnetic dispersive microextraction of diazinon from urine samples by molecularly imprinted polymer based on core–shell metal–organic frameworks

A core–shell magnetic metal–organic framework (Fe3O4 SiO2/ PAEDTC@ MIL- 101 (Fe)) was synthesized as the substrate and then covered with a surface molecularly imprinted polymer (MIP) layer. Next, Fe3O4 SiO2/ PAEDTC@ MIL- 101 (Fe) @ MIP was characterized by XRD, FT-IR, BET, VSM, TEM, and FE-SEM techniques and applied for selective, fast, and sensitive magnetic dispersive solid-phase microextraction (M-DµSPE) of diazinon from urine samples by the GC- FID detection method. The key experimental variables affecting M-DµSPE were studied and optimized by central composite design (CCD). Under optimum conditions (5 mL; sample at pH: 7.0, the mass of solid sorbent; 6 mg, extraction time; 4 min, acetonitrile as an eluent solvent; 1.5 mL, and desorption time; 3 min, and then reconstituted with 100 µL of methanol), the proposed method exhibits high sensitivity with limits of detection and quantification of 0.005 and 0.017 ng mL−1, respectively. Excellent extraction recovery (98.5 %), wide linearity range (0.02–200000 ng mL−1, R2 > 0.992), high enrichment factors (47–53), and satisfactory precision (<6.3 % RSD) were achieved. The MIP- MOF@ M-DµSPE -GC-FID method can be used with high precision and wide linearity to extract and analyze trace levels of diazinon in real urine samples.

Carbon-encapsulated metallic Co nanoparticles for Fischer-Tropsch to olefins with low CO2 selectivity

Tuning Fischer-Tropsch synthesis products of metallic Co-based catalysts from paraffins to value-added olefins chemicals attracts great attention but remains challenging. Herein, we succeed in designing the carbon layers confined cobalt metal core-shell nanocatalyst (Co@C) via a reduction-carburization-pyrolysis (RCP) pretreatment of Co/SiO2, which exhibits highly efficient for Fischer-Tropsch to olefins (FTO) with negligible Water-Gas-Shift activity. At 250 °C and 5 bar, 56.4 % of olefins selectivity and limited CO2 selectivity (5.8 %) are achieved for Mn-promoted Co@C nanocatalyst with at least 200 h of stability running. The electronic effect of carbon layers and Mn promoter as well as the confinement structure tailor the local chemical environment and weaken the hydrogenation ability of Co metal sites, thus improving the selectivity toward olefins while largely reducing the formation of CH4 and CO2. This work develops an effective strategy for the rational design of highly active and stable metallic Co-based FTO catalysts with high carbon efficiency.

Rapid Screening of Lipase Inhibitors in Scutellaria baicalensis by Using Porcine Pancreatic Lipase Immobilized on Magnetic Core–Shell Metal–Organic Frameworks

As for ligand fishing, the current immobilization approaches have some potential drawbacks such as the small protein loading capacity and difficult recycle process. The core–shell metal–organic frameworks composite (Fe3O4-COOH@UiO-66-NH2), which exhibited both magnetic characteristics and large specific surface area, was herein fabricated and used as magnetic support for the covalent immobilization of porcine pancreatic lipase (PPL). The resultant composite Fe3O4-COOH@UiO-66-NH2@PPL manifested a high loading capacity (247.8 mg/g) and relative activity recovery (101.5%). In addition, PPL exhibited enhanced tolerance to temperature and pH after immobilization. Then, the composite Fe3O4-COOH@UiO-66-NH2@PPL was incubated with the extract of Scutellaria baicalensis to fish out the ligands. Eight lipase inhibitors were obtained and identified by UPLC-Q-TOF-MS/MS. The feasibility of the method was further confirmed through an in vitro inhibitory assay and molecular docking. The proposed ligand fishing technique based on Fe3O4-COOH@UiO-66-NH2@PPL provided a feasible, selective, and effective platform for discovering enzyme inhibitors from natural products.

Low-temperature and ultrafast dual-powder spark plasma sintering of (W,Ti)C cermets with the addition of metal core-shell nanopowder

Nickel-coated molybdenum metal core-shell (Mo@Ni) nanopowder was prepared by a heterogeneous nucleation–thermal reduction method and then used as the metal binder phase in (W,Ti)C ceramic materials. (W,Ti)C/Mo@Ni/Co cermet was prepared by dual-power spark plasma sintering. The effects of sintering rate and sintering temperature on the microstructure and mechanical properties of (W,Ti)C/Mo@Ni/Co cermets were investigated. Results showed that when the sintering rate was 400 °C/min and the sintering temperature was 1325 °C, the (W,Ti)C/Mo@Ni/Co tool material had the best comprehensive mechanical properties, with a Vickers hardness of 17.44 ± 0.23 GPa, a fracture toughness of 11.27 ± 0.46 MPa·m1/2, and a flexural strength of 1450.23 ± 23 MPa. The core-shell structure of Mo@Ni made full use of the solid solution characteristics of the MoNi binary alloy and produced a solid solution in situ without liquid phase diffusion, which accelerated the sintering rate. The use of Mo nanopowder took advantage of its small-size effects and high surface energy, which reduced the temperature at which the solid solution effect began and reduced the sintering temperature. The combination of these two aspects was used to prepare a (W,Ti)C cermet with good strength and toughness by low-temperature rapid sintering. Low-temperature and ultrafast sintering are helpful to reduce the energy consumption in the preparation of cermets.

Development of Core-Shell Rh@Pt and Rh@Ir Nanoparticle Thin Film Using Atomic Layer Deposition for HER Electrocatalysis Applications

The efficiency of hydrogen gas generation via electrochemical water splitting has been mostly limited by the availability of electrocatalyst materials that require lower overpotentials during the redox reaction. Noble metals have been used extensively as electrocatalysts due to their high activity and low overpotentials. However, the use of single noble metal electrocatalyst is limited due to atomic aggregation caused by its inherent high surface energy, which results in poor structural stability, and, hence, poor electrocatalytic performance and long-term stability. In addition, using noble metals as electrocatalysts also causes the cost to be unnecessarily high. These limitations in noble metal electrocatalysts could be enhanced by combining two noble metals in a core-shell structure (e.g., Rh@Ir) as a thin film over a base substrate. This could significantly enhance electrocatalytic activity due to the following: (1) the modification of the electronic structure, which increases electrical conductivity; (2) the optimization of the adsorption energy; and (3) the introduction of new active sites in the core-shell noble metal structure. The current state-of-the-art employs physical vapor deposition (PVD) or other deposition techniques to fabricate core-shell noble metals on flat 2D substrates. This method does not allow 3D substrates with high surface areas to be used. In the present work, atomic layer deposition (ALD) was used to fabricate nanoparticle thin films of Rh@Ir and Rh@Pt in a core-shell structure on glassy carbon electrodes. ALD enables the fabrication of nanoparticle thin film on three-dimensional substrates (a 2D functional film on a 3D substrate), resulting in a significantly increased surface area for a catalytic reaction to take place; hence, improving the performance of electrocatalysis. The Rh@Pt (with an overpotential of 139 mV and a Tafel slope of 84.8 mV/dec) and Rh@Ir (with an overpotential of 169 mV and a Tafel slope of 112 mV/dec) core-shell electrocatalyst exhibited a better electrocatalytic performances compared to the single metal Rh electrocatalyst (with an overpotential of 300 mV and a Tafel slope of 190 mV/dec). These represented a 54% and a 44% improvement in performance, respectively, illustrating the advantages of core-shell thin film nanostructures in enhancing the catalytic performance of an electrocatalyst. Both electrocatalysts also exhibited good long-term stability in the harsh acidic electrolyte conditions when subjected to chronopotentiometry studies.

Synthesis of core-shell structured metal oxide@covalent organic framework composites as a novel electrochemical platform for dopamine sensing

In this work, a novel core-shell structured CuO@TAPB-DMTP-COF composites were synthesized by encapsulating CuO nanorods into TAPB-DMTP-COF host matrix. The structural properties of the composites were revealed by X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), and Transmission electron microscopy (TEM). Subsequently, the CuO@TAPB-DMTP-COF composites were immobilized on the glass carbon electrode (GCE) surface to fabricate an electrochemical sensor for dopamine detection. CuO functions as a highly catalytic active substance to accelerate the charge transfer rate of the reaction, while TAPB-DMTP-COF with a large electroactive surface area enhances the adsorption ability of the modified electrode toward the target molecules. The main parameters during the analytical procedure were investigated in detail, and the analytical performance was improved significantly due to the synergistic effects of CuO and TAPB-DMTP-COF. Under the optimal conditions, the dopamine peak responses are linear in a wide range from 0.07 to 800 μM, and the detection limit is as low as 0.023 μM. Furthermore, the dopamine sensor also exhibits good repeatability, stability, and accurate detection ability in actual samples. This study will expand the application of organic porous material based composites in ultra-sensitive electrochemical bioanalysis.

Simulated Leaching of Foliar Applied Copper Bactericides on the Soil Microbiome Utilizing Various Beta Diversity Resemblance Measurements.

ABSTRACTCopper bactericides are routinely used to control Xanthomonas perforans (XP), causal agent of bacterial spot of tomato. Given the widespread tolerance to copper in XP strains in FL, USA, nanotechnology-based elemental composites have gained interest for their potential applications in agriculture in part due to their enhanced antimicrobial properties and toxicity to copper-tolerant strains. However, little is known about the potential impact of conventional copper bactericides as well as nano-based elemental composites on soil microbial communities, as determined by high-throughput sequencing of the 16S rDNA. We compared the effects of 2 and 200 μg/mL of core-shell (CS), a metallic copper composite, and a conventional copper bactericide + mancozeb (Cu+Man) on the soil microbiome. These treatments were compared to three controls, the microbial profile of the soil prior to application of copper products, a water application, and spiking the soil with a soilborne phytobacterium, Ralstonia solanacearum (RS). The RS treatment was included to determine if downstream analysis could detect the artificial inoculation. Utilizing multiple β diversity measurements, each emphasizing various tenets of ecology, provided a greater perspective of the effects the treatments had on the microbiome. Analysis of HTS data revealed that the two treatments containing field applied rates of metallic copper, CS 200 and Cu+Man, had the largest impact on the soil microbiome at seven-days posttreatment compared to water. However, we simulated field applied rates of CS 200 entering the soil by treating soil with CS 2 and determined this concentration had a negligible effect on the soil microbiome.IMPORTANCE Nanotechnology-based elemental composites have gained popularity for their potential applications in plant disease management due to their enhanced antimicrobial properties. However, little is known about their potential impact on the environment. Foliar applications of nano metallic composites upon leaching into the soil have the potential to impact soil microbial populations that in turn influence soil health. Utilizing multiple β diversity measurements, high-throughput sequencing analysis revealed that field applied rates of metallic copper (200 μg/mL) from an advanced copper composite (core-shell [CS]) and a conventional copper bactericide in combination with mancozeb had the largest impact on the soil microbiome compared to water and nontreated control. To simulate leaching from the leaf surface, a lower concentration (2 μg/mL) of CS was also applied to the soil and had a negligible effect on the soil microbiome. Thus, field applied rates of CS may have a minimal effect on soil microbial communities.