CoFe2O4/NiFe2O4 S-scheme composite for photocatalytic decomposition of antibiotic contaminants

Keeping in view of the hazardous application of tetracycline hydrochloride antibiotic, an efficient CoFe₂O₄/NiFe₂O₄ heterojunction photocatalyst has been prepared hydrothermally by combining CoFe₂O₄ and NiFe₂O₄ nanoplates. The CoFe₂O₄/NiFe₂O₄ composite with the improved photocatalytic activity can be employed for removal of tetracycline hydrochloride antibiotic, comparing to the bare CoFe₂O₄ and NiFe₂O₄. The optimized sample 5%-CoFe₂O₄/NiFe₂O₄ shows the high photocatalytic degrading tetracycline with 76.1% removal efficiency in 60 min. These improved photocatalytic activities are attributed to the extended visible light absorption and enhanced charge separation following S-scheme route as confirmed from photoluminescence and electrochemical studies. From the charge trapping experiments, it is confirmed that superoxide radical and holes in the valence band of NiFe₂O₄ with high thermodynamic energies are responsible for the photodegradation of the target pollutant. This work provides sufficient attention towards the preparation of low cost materials for the removal of highly hazardous pollutants being present in water.     

Preparation and properties of MgAl2O4 spinel ceramics by double-doped CeO2 and La2O3

Magnesium aluminate spinel (MgAl₂O₄) ceramics are high-performance and carbon-free materials widely used in both military and civilian fields. However, it is usually challenging to densify during the solid-state sintering process. The excellent properties of some rare earth oxides have been proved to promote the densification of MgAl₂O₄ spinel ceramics. But the mechanism of promoting sintering is not clear. In the present work, MgAl₂O₄ spinel ceramics have been successfully fabricated by co-doping CeO₂ and La₂O₃ via a single-stage solid-state reaction sintering. The effects of addition amounts of CeO₂ and La₂O₃ on phase compositions, microstructures, sintering characteristics, cold compressive strength, and thermal shock resistance of as-prepared MgAl₂O₄ spinel ceramics were systematically investigated. The results show that by co-doping CeO₂ and La₂O₃ can increase the defect concentration due to the lattice distortion. This could promote the movement of Al³⁺ and Mg²⁺ at high temperature, which is beneficial to the formation of more secondary MgAl₂O₄ spinel. t-ZrO₂ with more Ce⁴⁺ filling between spinel grains could prevent the growth of grains and promote the densification, besides the new-formed LaAlO₃ that was mainly distributed along the grain boundary of the MgAl₂O₄ phase, both of which were favorable for the formation of dense microstructure of MgAl₂O₄ spinel materials. At the same time, the formation of more secondary MgAl₂O₄ spinel and sintering densification also improve the mechanical properties of spinel ceramics. La³⁺ will segregate to the spinel grain boundary, preventing grain boundary movement and absorbing the main crack's fracture energy. With 3 wt% CeO₂ and 3 wt% La₂O₃ co-doping, the bulk density of the sample increased from 3.02 g∙cm⁻³ to 3.55 g∙cm⁻³; the apparent porosity decreased from 12.21% to 9.97%; the cold compressive strength increased from 172.88 MPa to 189.54 MPa; and the residual strength retention ratio after thermal shock increased from 84.92% to 89.15%.     

Novel binder-free electrode of NiCo2O4@NiMn2O4 core-shell arrays modified carbon fabric for enhanced electrochemical properties

There is still a great challenge to develop new-style battery-type electrode materials with low resistance, large surface area, and stable microstructures on carbon fabric, which limited the development of flexible devices. In this work, NiCo₂O₄ nanoneedle@NiMn₂O₄ nanosheet core-shell arrays are constructed on the carbon fabric as a high-capacitance and long-life supercapacitor electrode for the first time. Benefiting from this kind of binder-free core-shell microstructure, the CF@NiCo₂O₄@NiMn₂O₄ electrode displays extraordinary specific-capacitance of 539.2 F g⁻¹ at a current density of 2 A g⁻¹, and nearly 93.0% retention of total capacitance even after discharging 5000 cycles. The outstanding properties of the hybrid electrode demonstrate that it is of great potential for flexible supercapacitors and batteries the application.     

Effect of different MgFe2O4 contents on 3D gel-printed porous TCP–MgFe2O4 composite scaffolds

Magnetic materials have shown significant influence in the process of bone regeneration. In order to combine the bone repairing capability of tricalcium phosphate (TCP) ceramic with magnetic material, porous TCP–MgFe₂O₄ composite scaffolds were successfully prepared by three-dimensional (3D) gel-printing technology, and the effect of different MgFe₂O₄ contents on TCP–MgFe₂O₄ composite scaffolds was studied. The viscosity of printing slurry prepared with polyvinyl alcohol as binder decreased with the increase of shear rate, showing shear thinning. Results show that following with MgFe₂O₄ content increasing from 30 to 70 wt%, the compressive strength of the composite scaffolds increased from 8.45 to 10.58 MPa, the saturation magnetization increased from 3.07 to 7.20 emu/g, and the weight loss rate of degradation in vitro increased from 1.83% to 2.1% after 4 weeks, respectively. Live and dead staining shows that MC3T3-E1 cells had better proliferation on TCP–MgFe₂O₄ composite scaffolds than TCP scaffolds. Compared with pure TCP scaffolds, the addition of MgFe₂O₄ improves the comprehensive performance of scaffolds and meets the application requirements of bone repairing.     

Low dielectric loss ceramics in the Mg4Nb2O9-ZnAl2O4-TiO2 ternary system

This study used a traditional solid-state reaction method to prepare a series of composite ceramics in the 0.7Mg₄Nb₂O₉-(0.3-x)ZnAl₂O₄-xTiO₂ ternary system. Crystalline phases and microstructure of Mg₄Nb₂O₉-ZnAl₂O₄-TiO₂ dielectric ceramic composites were investigated and correlated with the relevant dielectric properties. It was observed that the addition of Ti⁴⁺ substituted Nb⁵⁺ in the Mg₄Nb₂O₉ structure, which promoted the decomposition of Mg₄Nb₂O₉ to form the second phase, Mg₅Nb₄O₁₅, during sintering. The synergistic effect of ZnAl₂O₄-TiO₂ co-doping promoted the Mg₄Nb₂O₉ ceramic densification. The sample (0.7Mg₄Nb₂O₉-(0.3-x)ZnAl₂O₄-xTiO₂) with x = 0.15?0.2 exhibited dielectric constants of 13–14, larger than those of ZnAl₂O₄, Mg₄Nb₂O₉ and Mg₅Nb₄O₁₅, due to the NbO₆ octahedra distortion resulting from the substitution of Al³⁺/Ti⁴⁺ for Nb⁵⁺ in Mg₄Nb₂O₉ and Mg₅Nb₄O₁₅. The long-range order of the NbO₆ octahedra was enhanced by co-doping ZnAl₂O₄ and TiO₂, thereby enhancing the Qxf value. A dielectric constant of 13.1, Qxf value of 366,000 GHz and a τ_f of ?60.8 ppm/°C were obtained from 1300 °C sintered 0.7Mg₄Nb₂O₉-0.15ZnAl₂O₄-0.15TiO₂. These results show that 0.7Mg₄Nb₂O₉-0.15 ZnAl₂O₄-0.15TiO₂ ceramic is a good candidate for microwave electronic device applications.     

Valence-induced effects on the electrical properties of NiMn2O4 ceramics with different Ni sources

Spinel-structured NiMn₂O₄ ceramics, with different valence Ni sources, were originally prepared using Ni₂O₃ and NiO as raw materials, and the effects of different valence Ni sources on their electrical properties were first investigated. XRD patterns show that both Ni₂O₃-based and NiO-based NiMn₂O₄ ceramics are single cubic spinel structures. SEM/EDS images indicate that the NiMn₂O₄ ceramics exhibited high density at the experiment-determined sintering temperatures. XPS results and Raman drifts prove that the Ni valence-induced changes in Mn ions at B sites played a significant role in the electrical properties and thermal stability of NiMn₂O₄ ceramics. Compared with NiO-based NiMn₂O₄, the resistivity at 25°C (ρ_25°C) of Ni₂O₃-based NiMn₂O₄ increased dramatically from 3109 to 106958 Ω cm, the thermal constant (B_25/50) increased from 3264 to 4473 K, and the resistance shifts after annealing for 1000 h at 150°C decreased from 0.80% to 0.74%. The investigation of the relationship between the material properties and valence of Ni sources has provided a new and effective way for designing the spinel-structured negative temperature coefficient (NTC) materials by modulating the valence of ions at A sites in the raw materials.     

Preparation and characterisation of closed-pore Al2O3-MgAl2O4 refractory aggregate utilising superplasticity

ABSTRACT

A novel high closed porosity Al₂O₃-MgAl₂O₄ refractory aggregate has been successfully fabricated by utilising superplasticity with Al₂O₃ and MgO as raw materials, SiC as high temperature pore-forming agent. The effects of the addition amounts of MgO and SiC on porosity, sintering behaviours, phase composition, pore size distribution and microstructure of the refractory aggregate have been investigated. The formation mechanism of the closed pore in the refractory aggregate has been discussed. The results showed that the MgO can improve the superplastic deformation ability of Al₂O₃-based ceramic at high temperature. With the content of MgO and SiC increased, the closed porosity and the pore size increased. The oxidation of SiC improved the sinterability of materials at the initial stage of sintering, and then the released gases due to the further oxidation of SiC promoted the formation of closed pores by motivating the superplastic deformation ability of Al₂O₃-based materials.     

Electrochemical performance of quaternary (1-x)ZnMn2O4/(x)MgFe2O4 solid solution as supercapacitor electrode

Novel nano quaternary metals solid solutions from MgFe₂O₄ and ZnMn₂O₄ were synthesized using a sol-gel procedure. The development of a solid solution and the formed phase were examined by phase analysis utilizing the X'Pert High Score Plus program and Fourier transform infrared (FTIR) spectroscopy technique. Rietveld analysis of X-ray diffraction data (XRD), scanning electron microscope (SEM/EDS) and transmission electron microscope (TEM) were applied to determine the lattice parameters, crystallite size, different cations distribution and elemental analysis of the formed solid solutions. The measured dielectric properties of obtained solid solutions are found to be affected by the composition ratio (x). The solid solution (1-x)ZnMn₂O₄/(x)MgFe₂O₄ samples exhibited a ferroelectric–paraelectric transition at ferroelectric Curie temperature (T_c). The different hopping mechanisms in the different samples were also examined. The electrochemical performance was tested and influence of composition ratio (x) on the cathodic and anodic potential was investigated. The specific capacitance (C_s) value of electrodes depended on the composition ratio (x) beside the type of cations forming oxides. The (0.9)MgFe₂O₄/(0.1)ZnMn₂O₄ sample showed the best performance as a supercapacitor material. The outstanding electrochemical property of the (0.9)MgFe₂O₄/(0.1)ZnMn₂O₄ electrode was further confirmed by EIS inspection. The super stability of MgFe₂O₄/ZnMn₂O₄ solid solution could be attributed to the activation of the solid solution materials during the CV cycling and the synergistic effects.     

Effect of preparation method on sinterability and properties of nanocrystalline MgAl2O4 and ZrO2-MgAl2O4 materials

Abstract

Nanocrystalline MgAl₂O₄ and ZrO₂-MgAl₂O₄ powders were synthesised by combustion and conventional solid state reaction routes. The synthesised powders were processed, dry pressed, and sintered for 3 h at temperatures ranging from 1550 to 1625°C. The sintered pellets were then characterised in terms of phase (XRD), microstructure (SEM), relative density, apparent porosity, water absorption, hardness, three point bend strength, and fracture toughness. The XRD studies revealed that ZrO₂ was present in tetragonal form in the case of combustion synthesised powders (CSP), whereas in powders obtained by solid state reaction (SSP) it was present in the monoclinic form. This study also revealed that the addition of ZrO₂ improved the mechanical properties of sintered MgAl₂O₄ samples: 20 wt-%ZrO₂-MgAl₂O₄ composites prepared from CSPs and conventional SSPs and sintered at 1625°C for 3 h had fracture toughness of 5·96 and 4·33 MPa m^1/2 and three point bend strength of 269 and 98 MPa respectively. Higher sintered density, the presence of tetragonal zirconia as a major phase, and the finer microstructure are probably responsible for the superior mechanical properties exhibited by sintered CSP materials as compared with the sintered SSPs.     

Liquidus Relations in the Quaternary Subsystem CaAl2O3-CaAl4O7-Ca2Al2SiO7-MgAl2O4

Equilibrium diagrams for the joins CaAl₄O₇-MgAl₂O₄, CaAl₄O₄-Ca₂Al₂SiO₇-MgAl₂O₄, and Ca₂Al₂O₄–Ca₂Al₂SiO₇-MgAl₂O₄ were determined by the classical quenching method and hot stage microscopy. Liquidus relations in the quaternary subsystem are discussed. Two univariant curves are located within the composition tetrahedron. The quaternary invariant point is a peri-tectic. Technological application of results is indicated.     

Thermochemistry of BaSm2O4 and thermodynamic assessment of the BaO–Sm2O3 system

The BaO–Sm₂O₃ system is of interest for the optimization of synthesis of electroceramics. The only systematic experimental study of phase equilibria in the system was performed more than 40 years ago. The reported experimental values of the enthalpy of formation of BaSm₂O₄ are in conflict, and the reported compound Ba₃Sm₄O₉ has never been confirmed. In this work we synthesized BaSm₂O₄ by solid‐state reaction and determined its heat capacity, enthalpy of formation, and phase transitions by differential scanning calorimetry, high‐temperature oxide melt solution calorimetry and ultra‐high‐temperature differential thermal analysis, respectively. We confirmed the existence of Ba₃Sm₄O₉ and its apparent stability from 1873 to 2273 K by X‐ray diffraction on quenched laser‐melted samples but were not able to obtain single‐phase material for calorimetric measurements. The CALPHAD method was used to assess phase equilibria in the BaO–Sm₂O₃ system, using both available literature data and our new measurements. A self‐consistent thermodynamic database and the calculated phase diagram of the BaO–Sm₂O₃ system are provided. This work can be used to model and thus to understand the relationships among composition, temperature, and microstructure for multicomponent systems with BaO and Sm₂O₃.     

Glycine-assisted solution combustion synthesis of NiCo2O4 electromagnetic wave absorber with wide absorption bandwidth

Design of high-performance electromagnetic (EM) wave absorbing materials has been regarded as an effective solution to excessive EM wave interference problem. As a promising candidate, NiCo₂O₄ absorbers have attracted enormous research attentions. However, currently reported morphology-manipulation synthetic methods of NiCo₂O₄ absorbers are time-consuming and require high energy consumption, which inhibit their practical applications. Herein, a more facile and cost-effective solution combustion synthesis was utilized to fabricate NiCo₂O₄ materials. The absorber prepared by using glycine as fuel displayed the best EM wave absorption performance. Impressively, ultra wide absorption bandwidth of 7.44 GHz from 10.56 GHz to 18 GHz could be achieved with relatively thin thickness of 2.1 mm NiCo₂O₄ sample fabricated in this work displayed the widest effective absorption bandwidth (EAB) among reported NiCo₂O₄-based EM wave absorbing materials so far. In view of its simple and low-cost synthetic process and excellent EM wave dissipation capacity, NiCo₂O₄ samples in this work showed great feasibility as practical absorber. In addition, our findings may also provide new sight for facile preparation of other high-performance EM wave absorbers by solution combustion synthesis instead of complex morphology-manipulation routes.     

NiFe2O4/SiO2 nanostructures as a potential electrode material for high rated supercapacitors

Engineered materials are crucial for the higher efficiency of supercapacitors. Current work presents roughly shaped spherical NiFe₂O₄ nanoparticles dispersed in the SiO₂ matrix NiFe₂O₄/SiO₂ as a newfangled electrode material for supercapacitors with remarkable performance. Designing the NiFe₂O₄/SiO₂ nanostructure with a sol-gel method followed by the Stober method to grow silica has instigated NiFe₂O₄/SiO₂ as dynamic material with higher electrochemical activity. Physicochemical aspects of NiFe₂O₄/SiO₂ nanostructures are evaluated using Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical activity is evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) representing the comparable efficiency and reversibility of the electrode materials. The prepared electrode shows a capacitance of 925 F/g (154.1 mAh/g or 555 C/g) at 1 A/g, with 95.5% capacitance retention after 5000 cycles at 20 mA/cm². The improved electrochemical performance of the NiFe₂O₄/SiO₂ electrode can be subjected to prompt diffusion process provided by NiFe₂O₄/SiO₂ and enhanced redox reactions owing to the high surface area. The mentioned features decrease the total impedance of the electrodes as suggested by electrochemical impedance spectroscopy (EIS).     

(Sb2O3/Sb2O5)-doped SnO2–Co3O4–Cr2O3 varistors: The Sb2O4 in-situ formation and its influence over the electrical and microstructural properties

The present study aimed to systematically study the transitions and consequential effects of antimony oxide (Sb₂O₃ or Sb₂O₅) additions over the properties of a SnO₂-based varistor system. High energy ball-milling and conventional sintering were used to obtain the samples with the following molar composition: (98.95-X)% SnO₂ - 1% Co₃O₄ - 0.05% Cr₂O₃ - X% Sb₂O₃/Sb₂O₅ where X = 0, 0.05, 0.1, 0.2 and 0.4 mol%. The thermal analysis suggested the in-situ formation of Sb₂O₄ at ~450 °C from Sb₂O₃ or Sb₂O₅ during the sintering of mixed oxides. SEM, XRD, and electrical analysis revealed similar results by using Sb₂O₃ or Sb₂O₅; the addition of 0.05 mol% antimony oxide provides the foremost properties. The transition equations from Sb₂O₃ or Sb₂O₅ to Sb₂O₄ demonstrate equivalency in the amount of Sb₂O₄ formed. That fact, besides the results obtained, were used to discuss a reasonable route for Sb³⁺ and Sb⁵⁺ incorporation within the SnO₂ lattice.     

Sintering behavior and microwave dielectric characteristics of BaO–Sm2O3–4TiO2 ceramics with B2O3 and BaB2O4 addition

We studied the low temperature sintering and the reaction in BaO–Sm₂O₃–4TiO₂ ceramics with boron-based additives for the application to microwave dielectric devices. The amount of the boride glasses of B₂O₃ and BaB₂O₄ was varied from 1 to 10 wt.% and the green compacts were sintered in the temperature range of 900–1200 °C for 2 h. When B₂O₃ was added, second phases of Sm₂Ti₂O₇, BaTi(BO₃)₂, Ba₂Ti₉O₂₀, and TiO₂ were formed, while BaB₂O₄ addition resulted in the formation of BaSm₂Ti₄O₁₂ single phase without second phases. On the basis of these results, it is regarded that the B₂O₃ is a reactive glass and the BaB₂O₄ is a non-reactive glass. The second-phase development, sintering behavior and microwave dielectric characteristics of BaO–Sm₂O₃–4TiO₂ ceramics were examined.     

A Novel Catalyst Pt/CoAl2O4/Al2O3 for Combination CO2 Reforming and Partial Oxidation of CH4

Pt/CoAl₂O₄/Al₂O₃, Pt/CoO_x/Al₂O₃, CoAl₂O₄/Al₂O₃ and CoO_x/Al₂O₃ catalysts were studied for combination CO₂ reforming and partial oxidation of CH₄. The results indicate that Pt/CoAl₂O₄/Al₂O₃ is the most effective, and XRD results indicate that Pt species are well dispersed over the Pt/CoAl₂O₄/Al₂O₃. High dispersion is related to the presence of CoAl₂O₄, formed during calcining at high temperature before Pt addition. In the presence of Pt, CoAl₂O₄ in the catalyst could be reduced partially at 973 K. Based on these results, it appears that zerovalent platinum with high dispersion and zerovalent cobalt resulting from CoAl₂O₄ reduction are responsible for high activity in the Pt/CoAl₂O₄/Al₂O₃ catalyst.     

Synthesis and characterization of Pt-Ti4O7 microelectrode arrays

The synthesis of Pt-Ti₄O₇ microelectrode arrays is achieved from mixtures of TiO₂ and Ti₂O₃ powders plus Pt particles by a thermal procedure commonly used in solid-state chemistry. Data obtained for the Pt-Ti₄O₇ materials by X-ray diffractometry and scanning electron microscopy are consistent with the existence of heterogeneous mixtures of Pt particles imbedded within the conductive Ti₄O₇ matrices. Rotated disc electrodes (RDEs) constructed from pure Pt and from the Pt-Ti₄O₇ materials are compared on the basis of their voltammetric and amperometric response for I^– and H₂O₂ in 0.10m H₂SO₄. The observed enhancement of current densities for the Pt-Ti₄O₇ RDEs is rationalized on the basis of the behaviour expected for microelectrode arrays.     

Ni@NiCo2O4 core/shells composite as electrode material for supercapacitor

A novel Ni@NiCo₂O₄ core/shells structure consisting of the Ni microspheres skeletons and nanosheet-like NiCo₂O₄ skins was designed and investigated as the electrochemical electrode for supercapacitor. Due to the unique architecture with Ni microspheres as the highly conductive cores improving the electrical conductivity of electrode and external nanosheet-like NiCo₂O₄ shells as the efficient electrochemical active materials facilitating the contact between the electrode and electrolyte, the as-prepared Ni@NiCo₂O₄ exhibited excellent electrochemical performance with high specific capacity of 597 F g⁻¹ (1 A g⁻¹) as well as remarkable capacitance retention of 96% (3000 cycles). These impressive results pave the way to design high-performance electrode materials for energy storage.     

Synthesis and characterization of MgAl2O4 micro-rods by a molten salt method

Large amounts of MgAl₂O₄ micro-rods were successfully synthesized using the molten-salt technology. The effect of KCl contents on the formation of MgAl₂O₄ micro-rods was investigated. The structure and morphology of MgAl₂O₄ were investigated by means of powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy, respectively. The experimental results showed that the contents of KCl significantly influenced the formation of MgAl₂O₄ micro-rods. MgAl₂O₄ micro-rods could be prepared at 1150 °C with a weight ratio of 100:1 between the salt and the starting materials. The formation of MgAl₂O₄ micro-rods could be suggested to be due to the inhomogeneous nucleation and orientated growth perpendicularly to the surfaces of Al₂O₃ grains. An impedance-type humidity sensor was finally fabricated based on the as-prepared MgAl₂O₄ micro-rods. According to tests of the humidity performance, MgAl₂O₄ micro-rods might be suitable for high-performance humidity sensors.     

NiCo2O4 arrays nanostructures on nickel foam: Morphology control and application for pseudocapacitors

The design of electrode materials with desirable morphology is of great importance and challenge to fabricate high-performance supercapacitors. In this work, NiCo₂O₄ nanopetal, nanosheet, nanoneedle and nanorod arrays on nickel foam have been synthesized through a facile hydrothermal method. The morphologies of NiCo₂O₄ arrays can be easily controlled by adjusting the kinds of alkali source and the addition of NH₄F. The electrochemical results show that the NiCo₂O₄ nanoneedles electrode has the optimal electrochemical performance among four samples, demonstrating its promising application potential for high performance supercapacitors. This investigation about morphology control of NiCo₂O₄ electrode materials and the relationship between the morphologies and corresponding electrochemical performances provides strategies to enhance the performance of supercapacitor electrodes.