Polyhedron Morphology Research Articles

Nonprecious and shape-controlled Co3O4-CoO@Co electrocatalysts with defect-rich and spin-state altering properties to accelerate hydrogen evolution reaction at large current densities over a wide pH range

In this study, efficient HER activity is achieved through the successful preparation of Co3O4-CoO@Co catalysts that are morphology-dependent. It is proposed that the distinctive skeletal polyhedron (SPH) morphology of the Co3O4-CoO@Co catalyst shows outstanding HER performances over the universal pH range. The heterostructure catalyst exhibits a current density of 50 mAcm−2 at an ultra-low overpotential of 28, 62, and 138 mV under 0.5 M H2SO4, 1 M KOH, and 1 M PBS electrolytes, respectively. Experimental and theoretical studies indicate that electron-enriched Co2+ in the CoO site is favorable for H+ cation adsorption and high valence Co3+ in the Co3O4 site is favorable for H2O molecule activation and dissociation in acidic, neutral, and alkaline electrolytes. Benefitting from an empty eg 3d orbital with a strong Jahn–Teller effect, a high density of spin states, and a large number of oxygen vacancies, the SPH-Co3O4-CoO@Co catalyst is demonstrated to provide faster hydrogen evolution reaction.

Shear thickening and hysteresis in dense suspensions: The effect of particle shape

The flow of dense suspension of non-Brownian particles has been considered by various studies affected by their significance in a variety of industries and natural phenomena. In this study, we investigate the effect of polyhedron morphology on shear thickening, shear jamming, and hysteresis characteristics of non-Brownian suspension of acrylate particles. Particles with the same chemical nature and three different shapes of spherical (aspect ratio Γ = 1), elliptical paraboloid (Γ ≈ 1), and boat-shaped (Γ ≈ 3) are fabricated via photopolymerization-based methods. Studied suspensions show the shear-thinning behavior at low shear stresses and shear thickening behavior at the higher range of shear stress. Also, the strength of observed shear thickening is enhanced for the suspensions of polyhedron particles, which can be attributed to the heightened degree of interparticle frictional contacts. Furthermore, it is found that angularity not only shifts the predicted frictionless and frictional jamming packing fractions to lower values but also expands the shear jamming packing fraction range. Finally, a history-dependent hysteresis is observed in all samples due to the different particle spatial structures forming in ascending and descending flow modes. The observed hysteresis loops strongly depend on the volume fraction and diminish near the jamming packing fraction due to the restricted mobility space of particles. In addition, the tumbling of elongated particles also can decrease the hysteresis loop by enhancing viscosity in the ascending flow mode, where the structures are not fully developed.

Promoting the activation of H2O via vacancy defects over metal-organic framework-derived cobalt oxide for enhanced oxygen evolution

Engineering the electronic structures of transition metal oxides via vacancy defects is an efficient approach to enhance their catalytic performances, while facilely creating vacancy defects and deeply exploring the effects still remain challenging. Herein, a facile reduction method was applied to introduce oxygen vacancy defects into metal-organic frameworks (MOFs)-derived cobalt oxide (Co3O4) polyhedron. Using zeolitic imidazolate framework-67 (ZIF-67) as Co source and self-sacrificial template, Co3O4 with polyhedron morphology and porous structure was synthesized, and then oxygen vacancy defects were introduced into the as-prepared Co3O4 through one-step NaBH4 reduction treatment. Strikingly, the obtained electrocatalyst (denoted as Co3O4-x) exhibited a larger current density (112.9 mA cm−2 vs. 1.75 V), a lower overpotential (335 mV at 10 mA cm−2) and a smaller Tafel slope (83 mV dec−1) than the Co3O4, which is even superior to the state-of-the-art IrO2 catalyst. Moreover, experiment results combined with density-functional theory (DFT) calculations revealed that the existence of oxygen vacancies could improve the conductivity, promote the activation of H2O and reduce the potential of potential-limited step (PLS), thus greatly boosting electrocatalytic oxygen evolution reaction (OER) performances. This work reported a strategy for preparing defect-rich OER electrocatalysts, and also provided a deep understanding of the defect effects on catalytic performances.

Preparation of Ni–Zn dual-doped polyhedral LiMn2O4 for endurable cycling lithium ion batteries at high rate

Jahn-Teller distortion and manganese dissolution are always the dominant problem of attenuating long cyclic performance and rate capacity of spinel LiMn2O4 cathode materials. Herein, a Ni–Zn dual-doping strategy is proposed to synthesize various LiNi0.05ZnxMn1.95-xO4 (x = 0–0.05) materials via a solid phase combustion method. All the as-prepared Ni–Zn co-doping materials have a good spinel structure with Fd3m space group and present unique polyhedron morphology with exposed (111) facets, which is conductive to relieving the manganese dissolution and Jahn-Teller effect. Moreover, the Ni–Zn co-doping gives rise to the extended Li–O bond and increased cell volume, hence boosting the favorable intercalation and deintercalation kinetics of Li+ ions. Consequently, the optimized LiNi0·05Zn0·02Mn1·93O4 cathode exhibits good electrochemical performance with the initial discharge capacity of 127.30 mAh g−1 and capacity retention of 70% after 1000 cycles at 1 C. At 5 C, an ultra-long cycle stability with a capacity retention of 61% is obtained up to 1800 cycles. Even at the high current rates of 10 C and 20 C, the relatively high first discharge capacities of 106.50 mAh g−1 and 99.40 mAh g−1 are also delivered, respectively. The Ni–Zn co-doping polyhedral LiMn2O4 will provide a solution for developing high-performance cathode materials in lithium ion battery.

Metal-organic frameworks derived interfacing Fe2O3/ZnCo2O4 multimetal oxides as a bifunctional electrocatalyst for overall water splitting

Exploring highly effective, long-lasting, and earth-abundant catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is very important to improve the next-generation water-splitting process. Herein, we report the Fe2O3/ZnCo2O4 heterointerface nanocomposite derived from trimetallic metal-organic frameworks (MOFs), which has been considered a promising electrode catalyst material for overall water splitting, including bifunctional HER and OER performances. However, there is no study being reported yet on the Fe2O3/ZnCo2O4 polyhedron morphology for HER, OER, and overall water-splitting activities. The synergic effect or heterointerface engineering between the Fe2O3 and ZnCo2O4 is advantageous for improved active sites, effective charge transfer, and the long-term stability of the composite. This electrocatalyst shows enhanced HER and OER performances in terms of low overpotential of 44.8 mV and 212 mV to achieve a benchmark current density of 10 mAcm−2. Moreover, the two-electrode water electrolyzer can achieve a current density of 10 mAcm−2 at a small cell voltage of 1.44 V. Our findings in this study can motivate further research to focus on the MOFs-derived trimetallic metal oxide electrocatalysts for next-generation water-splitting devices.

Synthesis, crystal structure, and physical properties of a triangular-lattice magnet K2Co(HPO4)(C2O4)(OH2)⋅H2O

A previously unreported geometrically frustrating cobalt oxalatophosphate, K2Co(HPO4)(C2O4)(OH2)⋅H2O (KCoCP), is solvothermally synthesized and characterized. KCoCP shows a typical two-dimensional (2D) layered structure of [Co(HPO4)(C2O4)(OH2)]2− separated by K+ and H2O, which is isostructural to the previously reported Fe analogue. Specifically, the magnetic Co2+ ions sit on a distorted triangular lattice (TL) and introduce geometrical frustration into the system. The mainstay of the 2D layer [Co(HPO4)(C2O4)(OH2)]2− is cobalt oxalate skeleton with HPO4 and H2O groups staggering on both sides. The Bravais–Friedel–Donnay–Harker (BFDH) theory, which is used to predict the polyhedral morphology and crystal growth faces, indicates a chamfer polyhedron morphology of KCoCP crystal. UV–vis diffuse reflection and electronic structure calculation suggest KCoCP being a semiconductor with an indirect band gap (0.214 ​eV). The absence of long-range magnetic ordering for KCoCP is proved via a combination of magnetic susceptibility and specific-heat measurements down to 1.8 ​K. Thus, KCoCP shows potential to investigate unconventional low temperature physical properties in TL system.

Synthesis of ternary CoZnAl layered double hydroxide and Co-embedded N-doped carbon nanotube hollow polyhedron nanocomposite as a bifunctional material for ORR electrocatalyst and supercapacitor electrode

The construction of non-precious and high-performance nanomaterial is the current hotspot in oxygen reduction reaction and supercapacitor applications. Herein, a novel composite consisting of a three-metal layered double hydroxide (CoZnAl-LDH) and a ZIF-derived carbon base (Co/NCNHP) is proposed, which is fabricated by the hydrothermal synthesis of CoZnAl-LDH and the in situ loading of Co/NCNHP in different ratios of 10, 20, and 30 %. The synthesized nanomaterials were evaluated by various physical and electrochemical tests. The results manifest that the addition of Co/NCNHP with a carbon nanotube hollow polyhedron morphology to the flower-like CoZnAl-LDH had a remarkable impact on its morphology and properties, such that it elevates the surface area, enhances mass and electron transfer, and improves electrical conductivity of the final product. Based on the results, the CoZnAl-LDH@Co/NCNHP 20 % indicated better electrochemical performance than other synthesized samples. This composite offered excellent ORR catalytic activity with an onset potential of −0.043 V vs. Ag/AgCl in alkaline electrolyte, 4-electrons path selectivity (average electron transfer number = 3.69), and high durability. Furthermore, it exhibited a superior capacitance performance of 869.6 F.g−1 at a current density of 1 A.g−1 and superior cycling stability (92.7 % capacitance retention at 2 A.g−1 after 1000 cycles). Therefore, according to the test results, the final as-prepared nanocomposite possesses a desirable electrochemical performance in both ORR and supercapacitor applications.

Magnetically Controllable Flowerlike, Polyhedral Ag-Cu-Co3O4 for Surface-Enhanced Raman Scattering.

Syntheses of Cu-, Ag-, and Ag-Cu-Co3O4 nanomaterials are of interest for a wide range of applications including electrochemistry, thermal catalysis, energy storage, and electronics. However, Co3O4-based nanomaterials have not been explored for surface-enhanced Raman scattering (SERS). Here, we present Cu-, Ag-, and Ag-Cu-Co3O4 nanomaterials of a hierarchical flower shape comprising two separate phases: a pure Cu or Ag core and multiple Co3O4 branches, in which the optical properties of the core and the magnetic properties of the branches are integrated. In addition, a series of nonmagnetic Cu-dominant Cu-Co-O polyhedra without Co3O4 branches were derived from Cu-Co3O4. The polyhedron morphology can be controlled and transformed among cubes, cuboctahedra, and truncated octahedra by tuning the amounts of ligands and additives to vary the potential energy and growth rate of specific crystal facets. The flowerlike Cu-, Ag-, and Ag-Cu-Co3O4 were characterized for SERS enhancement, showing that Ag-Cu-Co3O4 does not enhance SERS from 4-mercaptobenzoic acid (4-MBA) but dramatically and selectively does so for adsorbed rhodamine 6G. Obviously, the synergy of Ag and Cu within the Co3O4 flower constraint promotes the SERS activity. This type of spinel with not only excellent SERS activity but also ferromagnetism could be of great potential in tandem SERS detection/magnetic separation and related applications.

Optical and mechanical study of size-controlled Cu particles synthesized by electrodeposition

Optical and mechanical properties of size-controlled Cu particles (1.5 µm, 500 nm and 50 nm) fabricated by one-step electrodeposition were studied. First, surface morphology and composition were characterized by SEM and EDS, with crystal structure by TEM, SAED and XRD. Antioxidant ability of 50nm was verified by TGA. In the simple and novel synthesis process, Cu particles of 1.5 µm with polyhedron morphology were firstly synthesized. The increase of current density and addition of potassium ferrocyanide trihydrate played key roles in the grain refinement to 500 nm and 50 nm, respectively. Then, particular focus was given to the improvement of optical and mechanical properties with size reduction, by SERS, UV-Vis and nanoindentation. These properties were gradually enhanced with the decrease of particle size, and Cu particles of 50 nm show the best performance.

Intramolecular modulation of iron-based metal organic framework with energy level adjusting for efficient photocatalytic activity

Efficient photocatalytic activity is always pressingly expected for photocatalytic technology on removing organic water contaminations. Modulating the intrinsic electronic properties is one of the most effective approaches to improve photocatalytic efficiency. Herein, we developed a promising photocatalyst through modulation electronic properties of iron-based metal organic framework by sulfur (S-MIL-53(Fe)), in which the sulfur particles were intramolecularly in-suite inserted into MIL-53(Fe) through annealing treatment process. The constructed S3-MIL-53(Fe) crystal with regular spindle-shaped polyhedron morphology exhibited superior higher apparent quantum efficiency (AQE) of 27.82% which was over 30 times than that of pure MIL-53(Fe) (0.903%) indicating the significantly enhanced photoactivity. A computational study was conducted to reveal the electronic structure changes and the resulted charge transfer induced by the sulfur modulation. The experimental and computational analyses suggest that intramolecular modulation MIL-53(Fe) with sulfur to engineer band structure for promoting charge transfer is a promising approach to improve the photocatalytic efficiency.

Copper-based composites derived from metal-organic frameworks on carbohydrates-rich corncobs as efficient catalysts for organic compounds removal

It is of great significance to exploit environmentally friendly, efficient and economical catalysts for dealing with wastewater and other aquatic environments. In this study, a series of P-doped Cu/Cu2O/C heterostructures were obtained by controlled calcination of corncobs supported Cu-MOF in different temperature. Comprehensive structural characterizations indicate the polyhedron morphology and high porosity of HKUST-1-P@corncob-400. The composites were further explored as an efficient catalyst for catalytic reduction of 4-nitrophenol (4-NP). Remarkably, HKUST-1-P@corncob-400 could efficiently catalyze the reduction of 4-NP, and the reduction could be finished within 90 s with a 4-aminophenol (4-AP) selectivity of >99%, demonstrating the excellent performance of Cu-based catalysts for 4-NP reduction. The application scope could be further expanded to the catalytic reduction of ofloxacin and a conversion of 95.7% could be achieved within 10 min. Reproducibility studies and characterizations comprehensively demonstrate the promising potential of HKUST-1-P@corncob-400 acting as efficient catalyst for the reductive removal of environmental pollutants. This work provides a facile strategy for the fabrication of highly active catalysts for high-performance environmental purification, and the employment of renewable bioresources and functional MOFs represents a promising strategy for design and synthesis of highly active catalysts towards various advanced applications.

Enhanced photocatalytic H2/H2O2 production and tetracycline degradation performance of CdSe quantum dots supported on K, P, N-co-doped hollow carbon polyhedrons

A K, P, N-co-doped hollow carbon polyhedron (KPN-HCP) was prepared by two-step calcination of triphenylphosphine@ZIF-8, which was then used to modify CdSe quantum dots (QDs). The effect of the dopants on the photocatalytic activity of CdSe QDs for H2/H2O2 production and tetracycline degradation was investigated. Through post-calcination in KCl-LiCl, the hollow polyhedron morphology was retained in KPN-HCP, and the graphitization degree increased. The introduction of P atoms followed by K+ doping could significantly enhance light harvesting, and accelerate electrons transfer from CdSe QDs to HCP. The H2 evolution rate and apparent rate constant of TC degradation for CdSe/KPN-HCP were 39.9- and 7.5-fold larger than those for CdSe QDs, respectively. The yield of H2O2 for CdSe/KPN-HCP in water was 900.0 μmol g−1 after 60 min. This work provides new insights for design of QD-based photocatalysts with high photocatalytic H2/H2O2 evolution, and tetracycline degradation activity.

Metal organic framework derived iron-nitrogen doped porous carbon support decorated with cobalt and iron as efficient nanocatalyst toward oxygen reduction reaction

Two porous carbon supports as N-doped carbon (NC) and Fe/N-co-doped carbon (Fe-NC), are obtained from ZIF-8 (zeolitic imidazolate framework) and Fe@ZIF-8, respectively, through the pyrolysis process. They are then decorated with transition metals using a modified polyol method to precipitate Fe, Co, and Fe–Co nanoparticles. The as-prepared catalysts are characterized by different physicochemical, morphological, and electrochemical characterization methods. Field emission scanning electron microscopy images show well-defined preserved polyhedron morphology for all prepared catalysts. Transmission electron microscopy images confirm a uniform distribution of metal nanoparticles through the surface of the supports. X-ray photoelectron spectroscopy results illustrate the existence of high content of graphitic and pyridinic nitrogen. Oxygen reduction reaction (ORR) results show the prepared support, which is in-situ doped with iron (Fe-NC), has better ORR performance than NC support. The results also display Co and Fe nanoparticles' coincident precipitation on the supports can improve ORR. This finding indicates both in-situ and ex-situ metal doping can be beneficial for good ORR performance. The optimum catalyst (Fe–Co/Fe-NC) illustrates enhanced ORR activity and stability with onset potential ~0.9VRHE in 0.1 M HClO4. Superior performance is associated with a synergistic effect between small and uniform dispersion of Co and Fe nanoparticles and appropriate nitrogen content.

Excitation-induced tunable luminescent properties of polyhedral CaMoO4 microcrystallites

Polyhedral CaMoO4 microcrystallites with excitation-induced tunable luminescent characteristics were successfully synthesized by a hydrothermal method. Polyhedral morphologies with different shapes and exposed facets were observed for the samples prepared at different temperatures. Sharp-vertex polyhedron was obtained at 140 °C due to the increase of (001) surface energy and the sample exhibited the strongest PL emission intensity due to its regular polyhedron morphology. Green and blue light emissions were observed separately under different excitation wavelengths in single CaMoO4 microcrystallites, which can be attributed to the charge transfer transitions within the [MoO4]2− complex and the shallow defects in the bandgap, respectively. The excitation-induced tunable luminescent characteristics make it to be a promising inorganic single-emitting component for optical applications.

Synergistic effects of flake-like ZnO/SnFe2O4/nitrogen-doped carbon composites on structural stability and electrochemical behavior for lithium-ion batteries

In order to improve the electrochemical performance and relieve volume expansion of pure SnFe2O4 anode for lithium-ion batteries (LIBs), we synthesized a novel ZnO/SnFe2O4/nitrogen-doped carbon composites (ZSFO/NC) with flake-like polyhedron morphology by using ZIF-8 as a sacrificial template. Remarkably, it exhibited an initial charge/discharge capacities of 1078.3/1507.5 mAh g−1 with a high initial coulombic efficiency (ICE) of 71.2%, and maintained a steady charge/discharge capacities of 1495.7/1511.8 mAh g−1 at 0.2 A g−1 after 300 cycles. The excellent rate performance of 435.6 mAh g−1 at a higher current density of 10.0 A g−1 and superior reversible capacity of 532.3/536.2 mAh g−1 after 500 cycles at 2.0 A g−1 were obtained. It revealed that the nitrogen-doped carbon matrix and peculiar structure of ZSFO/NC not only effectively buffered large volume expansion upon (de)lithiation through the synergistic interface action between ZnO, SnFe2O4 and NC, but also improved capacity of the composite by large contribution of surface pseudo-capacitance. The excellent charge–discharge performance showed that ZSFO/NC composite has a great potential for LIBs due to the synergistic effect of the multi-components.

Large-area spray deposited Ta-doped SnO2 thin film electrode for DSSC application

Large-area (10 × 10 cm2) Ta-doped SnO2 (TTO) thin film was deposited by a facile spray pyrolysis method. The crystallinity, phase purity, and texture properties of the film are studied using XRD analysis. The XPS study confirmed the charge state of Sn to be in 4+, O1s in 2−, and Ta to be in 5+ state. A homogeneous polyhedron morphology was witnessed owing to the Ta dopant effect. The TTO film was highly transparent in the visible to near infrared region (NIR) with an average transmittance value of 81% at 550 nm. The TTO film was having a free carrier concentration of 5.42 × 1021 cm−3 and mobility of 41.7 cm2/Vs. The 4 wt% Ta doped SnO2 electrode exhibits a low sheet resistance of 26 Ω/□ and a high figure of merit value of 6.15 × 10−3 Ω−1. The resistance stability of sheet resistance was fairly good up to 400 °C indicating suitability of the TTO electrode to serve as conducting photoanode/counter electrode in dye-sensitized solar cell (DSSC) device. The DSSC device fabricated with the TTO electrode exhibited appreciable efficiency of 3.26% which is attributed to the enhanced electrical and optical properties by way of doping with Ta element.

Rhombic dodecahedron-like CoMoO4/C composite: A facile construction and excellent electrochemical performances for lithium-ion batteries

The design of an unique micro/nanoscale structure and the composite construction with conductive materials are the two effective means to improve the electrochemical energy storage for transition metal oxides anode. However, the rational design and controllable synthesis of complex ternary transition metal oxide (such as CoMoO4) composite with polyhedron morphology is still a challenge. Herein, we report a facile and effective strategy to synthesize rhombic dodecahedron-like (denoted as RD-like) CoMoO4/C composite, which involves the initial pre-reaction between the newly made ZIF-67 with H2MoO4 in ethanol and the subsequent calcination for the resultant precursor powders in air. It is found that the calcination temperature plays a key role in determining the microstructures and the content of the generated activated carbon. Below 400 °C, the CoMoO4/C composite cannot be derived, whereas the perfect and regular RD morphology for CoMoO4/C composite also cannot be acquired over 500 °C. Moreover, a plausible mechanism for the construction of RD-like CoMoO4/C composite has also been proposed and explained. Benefiting from its unique structural merits and the significant synergistic effect of the in-situ composite activated carbon, the obtained RD-like CoMoO4/C composite at 500 °C displays outstanding electrochemical performances with high reversible capacity (532.5 mAh g−1/500th cycle at 1C), excellent cycling stability and better rate capability when it tested as anode materials for lithium-ion batteries. It is conceivable that this three-in-one strategy can be extended to design and construct other cobalt-based oxyacid/C composites with unique polyhedron morphology, and markedly boost their electrocehmical performaces.

Structural characterization, dielectric, magnetic and optical properties of double perovskite Bi2FeMnO6 ceramics

Double perovskite Bi2FeMnO6 (BFMO) oxides are promising candidate for single-phase multiferroic system. However, up to date only a limited works are carried out to synthesize the BFMO ceramics, and most of them have the issues of impure phases. In this work, we report on the structural, dielectric, magnetic, and optical properties of single-phase BFMO ceramics synthesized by solid-state reaction method. The BFMO ceramics crystallized in a rhombohedral structure with R3c space group, and their grains exhibited polyhedron morphology with average size of 15.0 µm. X-ray energy dispersive spectroscopy revealed the ceramic grains with atomic ratio of Bi:Fe:Mn equal to 2.0:1.16:0.90. XPS spectra of Fe 2p and Mn 2p core levels confirm the mixed chemical valence states of Fe (Fe2+ and Fe3+) and Mn (Mn3+ and Mn4+) in the BFMO ceramics. O 1s XPS spectra reveal the oxygen existing in the forms of lattice oxygen and oxygen vacancies while bismuth is present as Bi3+. Dielectric measurements demonstrate that the BFMO ceramics have much high dielectric constant (in the order of 104) in the frequency below 102 Hz but decrease fast with increasing the frequency. The same phenomenon appeared for the dielectric loss. A dielectric relaxation behavior with activation energy of 0.34 eV was observed in the BFMO ceramics, which was due to the thermal motion of the oxygen vacancies. The BFMO ceramics exhibit antiferromagnetic nature but a weak ferromagnetic behavior at 2 K. Sharp cusp peaks were observed in the zero-field-cooling (ZFC) curves and bifurcations between the field-cooling (FC) and ZFC curves were observed. Both of them shifted to low temperature as increasing the external applied magnetic field, indicating a spin-glass like behavior in the system. UV–Vis absorption spectra demonstrated a broad absorption peak in the wavelength range of 300–800 nm and a direct optical band gap of ~1.23 eV for the BFMO ceramics. Such narrow optical band gap as well as the high dielectric constant at room temperature enable the BFMO ceramics to be promising candidate used for solar cells, sensors, bolometer and optoelectronic devices.

Facile synthesis of nitrogen-doped cobalt/cobalt oxide/carbon/reduced graphene oxide nanocomposites for electromagnetic wave absorption

Electromagnetic wave absorption materials with strong absorption, thin thickness, broad bandwidth and low filler loading are highly desirable in the field of electromagnetic absorption. In this work, graphene oxide (GO) was firstly used as a template for growth of cobalt, zinc–zeolitic imidazolate frameworks (Co, Zn–ZIFs), and then nitrogen-doped cobalt/cobalt oxide/carbon/reduced graphene oxide (Co/CoO/C/RGO) nanocomposites were further constructed by the high-temperature pyrolysis strategy. Results of morphology observations demonstrated that numerous carbon frameworks with a slightly contracted polyhedron morphology were anchored on the crumpled surfaces of sheet-like RGO. Moreover, well-constructed structure of RGO loaded with carbon nanotubes wrapping carbon frameworks was observed, and considerable nitrogen atoms had been in situ doped into the porous carbon matrix of attained nanocomposites. Furthermore, the influences of filler loadings, calcination temperature, and addition of GO on the electromagnetic parameters and absorption performance of obtained nanocomposites were investigated. Results revealed that the addition of GO notably strengthened the electromagnetic absorption performance. Remarkably, the percolation transition was observed in the filler loading range of 20–25 wt%. The as-synthesized nanocomposite under 700 °C calcination treatment exhibited superior electromagnetic absorption performance with an optimal reflection loss of −63.0 dB and effective absorption bandwidth of 4.0 GHz (12.2–16.2 GHz) at a thin matching thickness of merely 1.6 mm and filler loading as low as 25 wt%. In addition, the underlying electromagnetic absorption mechanisms were proposed. This work provided a facile strategy for fabricating the carbon-based magnetic composites derived from metal–organic frameworks as light weight and high-performance electromagnetic absorption materials.

Enhancing the performance of aluminium by chromium oxide

The present study deals with the effect of chromium oxide (Cr2O3) addition in the commercially pure Al to observe its effect on mechanical performance. The Cr2O3 powder reacted with molten Al at the 850 °C temperature and formed hybrid composites with different reinforcement particles. The composites so produced were subjected to different studies such as x-ray diffraction (XRD), optical microscopy, electron-microscopy with energy-dispersive spectroscopy (EDS), tensile testing and hardness evaluation. Results of XRD and EDS indicated that the particles of Al7Cr and Al2O3 were formed by the chemical reaction between Cr2O3 and Al. The Al7Cr particles were present in polyhedron and faceted morphology in a size range of 15–55 μm, whereas, Al2O3 particles showed the polyhedron morphology in a size range of 3–17 nm. Optical microscopy showed that the grain size of Al was refined by the formation of Al7Cr and Al2O3 particles and it continuously decreased with the increase in amount of particles. Strength parameters and hardness were improved with formation of reinforcement particles. Maximum improvement in mechanical properties was obtained in the case of HAMC3 (Hybrid Aluminium Matrix Composite3) composite with approximately 13 wt% of Cr2O3. Strengthening mechanisms and fractography were also studied and correlated with the microstructure and mechanical properties of the composites.