Synthesis of BaWO4/NRGO‒g-C3N4 nanocomposites with excellent multifunctional catalytic performance via microwave approach

Novel barium tungstate/nitrogen-doped reduced graphene oxide?graphitic carbon nitride (BaWO₄/NRGO?g-C₃N₄) nanocomposite has been synthesized by a simple one-pot microwave technique. The synthesized nanocomposites are well characterized by diffraction, microscopic and spectroscopic techniques to study its crystal structure, elemental composition, morphological features and optical properties. The material prepared is tested for its performance as an electrocatalyst, photocatalyst and reduction catalyst. The nanocomposite catalyzed the photodegradation of methylene blue (MB) dye in 120 min, reduction of 4-nitro phenol (4-NP) to 4-amino phenol (4-AP) in 60 s, showed an impressive Tafel slope of 62 mV/dec for hydrogen evolution reaction (HER). The observed results suggest that the nanocomposite acts as an efficient multifunctional catalyst. The reported approach provides fundamental insights which can be extended to other metal tungstate-based ternary composites for applications in the field of clean energy and environment in the future.     

Enhanced antibacterial performance of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Ag and MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>–Ag nanocomposites

In this work, we have described the antibacterial activities of Fe₃O₄ nanoparticles with different organic parts, including Humic acid (HA), Nicotinic acid (Nico) and Histidine (His), and the antibacterial activity of MnFe₂O₄ nanoparticles coated with PANI and SiO₂ against different bacteria and some standard antibacterial drugs. The present study revealed that the newly fabricated various Fe₃O₄ and MnFe₂O₄ nanocomposites, when combined with some different organic parts, are superiour antibacterial agents. Also, the synthesized nanocomposites can be easily separated from aqueous solution by magnetic filtration without any contamination of the medium.     

Effect of brazing temperature on microstructure and mechanical properties of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> joints brazed with Ag–Cu–Ti + Mo composite filler

Mo particles have been introduced into Ag–Cu–Ti brazing alloy for the joining of Si₃N₄ ceramic. Effect of brazing temperature on microstructure and mechanical properties of the joints were investigated. The result shows that a continuous reaction layer which is composed of TiN and Ti₅Si₃ was formed at the Si₃N₄/braze interface. The central part of the joint was composed of Ag-based solid solution, Cu-based solid solution, Mo particles, and Cu–Ti intermetallic compounds. By increasing the brazing temperature, both the thickness of the reaction layer and amount of Cu–Ti intermetallic compounds in the joint increased, being beneficial for the joint strength. Whereas, the reaction between Ti and Si₃N₄ ceramic proceeded excessively and more Cu–Ti intermetallic compounds were precipitated in the joint while elevating the brazing temperature to 950 °C, leading to deterioration of the bending strength. The maximal bending strength reached 429.4 MPa at 900 °C for 5 min when the Si₃N₄ ceramic was brazed with Ag–Cu–Ti + Mo composite filler.     

Synthesis and microwave absorption enhancement of yolk–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@C microspheres

Rational design on the microstructure of microwave-absorbing materials is paving the way for upgrading their performances in electromagnetic pollution prevention. In this study, a Fe₃O₄/C composite with unique yolk–shell microstructure (YS-Fe₃O₄@C) is successfully fabricated by a silica-assisted route. It is found that carbon shells in this composite can make up the shortages of Fe₃O₄ microspheres in dielectric loss ability, while they may more or less attenuate the intrinsically magnetic loss of Fe₃O₄ microspheres. The microwave absorption properties of YS-Fe₃O₄@C are evaluated in the frequency range of 2.0–18.0 GHz in terms of the measured complex permittivity and complex permeability. The results demonstrate that YS-Fe₃O₄@C can exhibit much better performance than bare Fe₃O₄ microspheres and individual carbon materials, as well as core–shell Fe₃O₄/C composite (CS-Fe₃O₄@C), where strong reflection loss and wide response bandwidth can be achieved simultaneously. With an absorber thickness of 2.0 mm, the maximum reflection loss is ?73.1 dB at 14.6 GHz and a bandwidth over ?10.0 dB is in the range of 12.3–18.0 GHz. It can be proved that the unique yolk–shell microstructure is helpful to reinforce the dielectric loss ability and create an optimized matching of characteristic impedance in the composite.     

Synthesis and characterization of TiO<Subscript>2</Subscript>–NiO and TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> nanocomposites

TiO₂–NiO and TiO₂–WO₃ nanocomposites were prepared by hydrothermal and surface modification methods. The samples were analyzed using X-ray diffraction, Scanning Electron Microscope images, Transmission Electron Microscope, Energy dispersive analysis, Zeta potential, Electrophoretic mobility and Photocatalysis activity measurement. XRD data sets of TiO₂–NiO, TiO₂–WO₃ powder nanocomposite have been studied for the inclusion of NiO, WO₃ on the anatase-rutile mixture phase of TiO₂ by Rietveld refinement. The cell parameters, phase fraction, the average grain size, strain and bond lengths between atoms of individual phases have been reported in the present work. Shifted positional co-ordinates of individual atoms in each phase have also been observed.     

Synthesis,charge transport studies,and microwave shielding behavior of nanocomposites of polyaniline with Ti-doped γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

This article reports the synthesis, charge transport studies, and microwave shielding properties of polyaniline–Ti-doped γ-Fe₂O₃ nanocomposite. The composite has been prepared by the in situ chemical oxidative polymerization using dodecylbenzenzesulfonic acid as a dopant. These resulting polymer composites have been found thermally stability up to 260 °C with magnetization value of ~10 emu/g. The temperature dependence of electrical conductivity reveals the applicability of Mott’s 3D-VRH model. The composites has shown the shielding effectiveness of 35.64–45.20 dB (>99.99% attenuation) in 12.4–18 GHz (Ku-Band) frequency range. The enhancement of SE has been due to combination of dielectric and magnetic losses leading to decrease in skin depth increase in total (σ_T) conductivity and better matching of input impedance.     

Preparation and microwave absorbing performance of TiO<Subscript>2</Subscript>/ NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> /hollow glass microsphere composite with core–shell structure

Microwave absorbing TiO₂/NiFe₂O₄/HGM composite with core–shell structure was prepared via a facile two-step method. The obtained composite was then investigated by SEM, TEM, XRD, XPS, VSM and a vector network analyzer. The results indicated that HGM was completely coated by NiFe₂O₄ nanospheres after the hydrothermal reaction, and TiO₂/NiFe₂O₄/ HGM composite with core–shell structure was also successfully synthesized. The composite exhibited excellent magnetic performance and microwave absorption capacity. Measurement of VSM suggested that the saturated magnetization values (Ms) of TiO₂/NiFe₂O₄/HGM was 27.79 emu.g^??1. When the frequency was 10.3 GHz, the R _L value of TiO₂/NiFe₂O₄/HGM composite with the thickness of 2.6 mm could reach up to ?20 dB. The obtained composite exhibited excellent microwave absorbing properties, which could be used as a promising EM wave absorber.     

Novel g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> wrapped γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> microspheres heterojunction for efficient photocatalytic application under visible light irradiation

The novel g-C₃N₄ wrapped γ-Al₂O₃ microspheres heterojunction was successfully prepared by a simple hydrothermal process followed by calcination. The photocatalytic performances of the composite were evaluated by the degradation of methyl orange (MO) and rhodamine B (RhB) under visible light irradiation. The obtained Al₂O₃/g-C₃N₄ heterojunction exhibited much higher photocatalytic activity compared to pure g-C₃N₄. The enhanced performance may be mainly attributed to the tight contact between the components of the heterostructure as well as the efficient transfer of photoinduced electrons from the valence band (VB) of g-C₃N₄ to the defect sites of γ-Al₂O₃. The trapping experiment results indicated that the ·O₂ ^? radicals and holes (h⁺) are main active species in the decomposition of MO. This work will provide new ideas for manipulation of high-performance heterojunction for practical photocatalysis applications in water pollution controls.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

Synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powder via PVA assisted sol–gel process

CoFe₂O₄ ferrites were synthesized by sol–gel method, having metal nitrates as precursors and PVA as surfactant, followed by a heat treatment at 960 °C for 2 h. The ultrafine ferrite powders obtained have been characterized by X-ray diffraction, thermal gravimetry, differential scanning calorimetry and room temperature magnetic measurement studies. The morphology of the powder was identified by high resolution-scanning electron microscopy. X-ray diffraction results indicate that the resultant CoFe₂O₄ crystallites consist of spinel phase. Significant differences in magnetic properties of CoFe₂O₄ samples synthesized with various concentrations of PVA were observed. The magnetisation measurements show that when the PVA concentration increased, coercivity initially decreased and then increased where as retentivity and magnetisation decreased. The optimum concentration of PVA for the synthesis of CoFe₂O₄ ferrites is obtained from this investigation. Obviously this material can be used as an efficient candidate for practical recording purpose.     

Synthesis of ternary rGO–ZnO–Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposites and their application for visible light photocatalytic degradation of dyes

The rGO–ZnO–Fe₃O₄ nanocomposites were synthesized by a simple, economical and environmentally benign solvothermal method. The morphology, structure and photocatalytic activity of rGO–ZnO–Fe₃O₄ nanocomposites were characterized, and the effects of the preparation conditions were analyzed. The 25 mg of rGO–ZnO–Fe₃O₄ nanocomposites performed efficient photocatalytic activity for the degradation of 25 mL of 4.79 mg/L Rhodamine B under both ultraviolet and visible light irradiation. The nanocomposites could be easily retrieved from the wastewater by extra magnetic field due to the presence of magnetic Fe₃O₄ nanoparticles. After the degradation experiment was carried out five times, the degradation ratio is still close to 90% after irradiation after 5 cyclic, indicating that the rGO–ZnO–Fe₃O₄ nanocomposites have high stability for reuse. Therefore, the prepared rGO–ZnO–Fe₃O₄ nanocomposites may be a promising potential material for wastewater treatment.     

Fabrication of stable Ni–Al<Subscript>4</Subscript>Ni<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> superhydrophobic surface on aluminum substrate for self-cleaning,anti-corrosive and catalytic performance

A stable Ni–Al₄Ni₃–Al₂O₃ superhydrophobic surface (SHS) was fabricated on aluminum (Al) substrate via etching, subsequent replacement deposition and then annealing. The water contact angle of the SHS could reach to 155°, and the water sliding angle was less than 2°. The morphology and chemical composition of the samples were characterized using scanning electron microscopy, X-ray diffraction pattern, energy-dispersive spectroscopy and X-ray photoelectron spectroscopy. Anti-corrosion behaviors of the samples were investigated via Tafel extrapolation and electrochemical impedance, and the SHS showed a better corrosion resistance than that of pure Al. In addition, when the water drops impinged on the SHS, the drops could fully bounce, exhibiting exquisite self-cleaning property. The catalytic property of the samples was evaluated by the reduction of 4-nitrophenol (4-NP) at room temperature, in which the SHS served as the hydrogen generator as well as a catalyst. The degradation rate of 4-NP at the existence of the superhydrophobic samples in NaOH aqueous solution was 97%. And the reaction rate constant of 4-NP at the existence of the superhydrophobic samples was 9.51 × 10^?2 s^?1, which was about twice as large as that at the existence of pure Al. This work offers an effective strategy to fabricate SHSs and expands industrial applications for Al and its alloys.     

Synthesis of LaB<Subscript>6</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite powders via ball milling-assisted annealing

In this study, LaB₆–Al₂O₃ nanocomposite powders were synthesized via ball milling-assisted annealing process starting from La₂O₃–B₂O₃–Al powder blends. High-energy ball milling was conducted at various durations (0, 3, 6 and 9 h). Then, the milled powders were annealed at 1200 °C for 3 h under Ar atmosphere in order to obtain LaB₆ and Al₂O₃ phases as reaction products. X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) and transmission electron microscopy (TEM) techniques were utilized to carry out microstructural characterization of the powders. No reaction between the reactants was observed in the XRD patterns of the milled powders, indicating that high-energy ball milling did not trigger any chemical reactions even after milling for 9 h. LaAlO₃ and LaBO₃ phases existed in the annealed powders which were milled for 0, 3 and 6 h. LaBO₃ phase was removed after HCl leaching. 9-h milled and annealed powders did not exhibit any undesired phases such as LaAlO₃ and LaBO₃ after leaching step, and pure nanocrystalline LaB₆–Al₂O₃ composite powders were successfully obtained. TEM analyses revealed that very fine LaB₆ particles (~?100 nm) were embedded in coarse Al₂O₃ (~?500 nm) particles.     

Wear resistance of electrodeposited Ni–B and Ni–B–Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite coatings

The wear resistance of electrodeposited (ED) Ni–B and Ni–B–Si₃N₄ composite coatings is compared. The effect of incorporation of Si₃N₄ particles in the ED Ni–B matrix on the surface morphology, structural characteristics and microhardness has been evaluated to correlate the wear resistance. The wear mechanism of ED Ni–B and Ni–B–Si₃N₄ composite coatings appears to be similar; both involve intensive plastic deformation of the coating due to the ploughing action of the hard counter disc. However, the extent of wear damage is relatively small for ED Ni–B–Si₃N₄ composite coatings.     

Effect of Ca doping on the performance of CeO<Subscript>2</Subscript>–NiO catalysts for CH<Subscript>4</Subscript> catalytic combustion

Methane catalytic combustion was carried out over the Ce_0.9–xNi_0.1Ca_xO_δ (0 < x ≤ 0.3) catalysts prepared by a citric acid complexation–combustion method. When x ≤ 0.1, the presence of Ca can enhance the surface area and reduce the crystalline size, and improve the reduction of the dispersed NiO species in catalyst, resulting in an improvement of the catalytic activity of Ce_0.9–xNi_0.1Ca_xO_δ. The XRD and Raman results show that Ce_0.9–xNi_0.1Ca_xO_δ (x ≤ 0.1) solid solution can form by Ni and Ca incorporation in the CeO₂ lattices. TEM and etching results reveal that part of Ni disperses well on the surface of Ca-doped sample. FT-IR testing shows that with an increase in Ca amount (x > 0.1), more carbonate species (mainly carbonate calcium) can form on the catalyst surface, which would severely debase the catalytic activity of Ce_0.9–xNi_0.1Ca_xO_δ.     

Preparation,structure and microwave dielectric properties of 3MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–3TiO<Subscript>2</Subscript> ceramics

3MgO–Al₂O₃–3TiO₂ (MAT) ceramics were prepared by a conventional solid-state reaction method. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and network analyzer. MAT ceramics contained the coexistence of three phases, including MgAl₂O₄, MgTiO₃ and MgTi₂O₅. The ceramics sintered at 1350 °C for 4 h presented excellent comprehensive performances with relative permittivity (ε _r ) of 15.4, quality factor (Q × f) of 91,000 GHz and temperature coefficient of resonant frequency (τ _f ) about ?55.1 ppm/°C.     

Synthesis of bulk nanocrystalline HfB<Subscript>2</Subscript> from HfCl<Subscript>4</Subscript>–NaBH<Subscript>4</Subscript>–Mg ternary system

This study reports on the synthesis and consolidation of pure HfB₂ powders starting from HfCl₄–NaBH₄–Mg blends via autoclave processing, annealing and purification followed by pressureless sintering (PS, with 2 wt% Co aid) or spark plasma sintering (SPS). During autoclave reactions conducted at 500 °C for 12 h under autogenic pressure, excess amounts of NaBH₄ were utilized to investigate its effects on the reaction products and mechanism. A subsequent washing (with distilled water), annealing (at 750, 1000 and 1700 °C) and acid leaching (HCl) were applied on the as-synthesized products. Pure HfB₂ powders with an average particle size of 145 nm were obtained after autoclave synthesis in the presence of 200 wt% excess NaBH₄, washing, annealing at 1000 °C for 3 h and 6 M HCl leaching. SPS sample has higher relative density and microhardness values (94.18% and 20.99 GPa, respectively) than those of PS sample (90.14% and 14.85 GPa). Relative wear resistance was improved considerably (8.2 times) by employing SPS technique.     

Synthesis and Structure of Mixed-Cation Salts with [PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the composition NaM₂[PuO₄(OH)₂]·4H₂O, where M = Rb (I) and Cs (III), and NaRb₅[PuO₄(OH)₂]₂·6H₂O (II) were synthesized and structurally characterized. The central Pu atom in [PuO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with oxygen atoms of hydroxide ions in apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb⁺ cations with 10- and 12-vertex coordination polyhedra (CPs), and in the structure of II, three independent Rb⁺ cations with the 12-, 11-, and 13-vertex CPs. In the structure of III, the Cs⁺ cation has a 12-vertex CP. Frameworks of large Rb⁺ or Cs⁺ cations can be distinguished in the structure. The CPs of the Pu and Na atoms (I, III) sharing a common edge or the isolated CPs of the Pu and Na atoms (II) are incorporated in these frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [PuO₄(OH)₂]^3– anions.