Synthesis of mesoporous γ-AlOOH@Fe3O4 magnetic nanomicrospheres

Mesoporous γ-AlOOH@Fe₃O₄ magnetic nanomicrospheres were synthesized using superparamagnetic Fe₃O₄ nanoparticles as the core and aluminum isopropoxide (AIP) as the aluminum source. The obtained magnetic nanomicrospheres were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N₂ adsorption–desorption and vibrating sample magnetometry (VSM). The effects of preparation parameters such as hydrolysis time of AIP, concentration of AIP and coating layer number on microspheres were investigated. The results indicated that the mesoporous γ-AlOOH@Fe₃O₄ magnetic nanomicrospheres consisted of a mesoporous γ-AlOOH shell and a Fe₃O₄ magnetic core. The diameter of γ-AlOOH@Fe₃O₄ nanomicrospheres was about 200 nm, the thickness of mesoporous γ-AlOOH shell was about 5 nm and the average pore size was 3.8 nm. The thickness of the mesoporous γ-AlOOH shell could be controlled via layer-by-layer coating times. The formation mechanism of the mesoporous γ-AlOOH shell involved a “chemisorption–hydrolysis” process.     

Fabrication of magnetic nanosized γ-FeNi-coated ceramic core–shell microspheres by heterogeneous precipitation and thermal reduction

Precursors with NiCO₃·2Ni(OH)₂·2H₂O- and Fe₂O₃·nH₂O-coated alumina, graphite and cenosphere were synthesized by precipitation using ferrous sulfate, nickel sulfate, ammonium bicarbonate, alumina, graphite and cenosphere as the main starting materials. Magnetic γ-FeNi-coated alumina, graphite and cenosphere core–shell structural microspheres were subsequently prepared by thermal reduction of the as-prepared precursors at 600 °C for 2 h. Precipitation parameters, e.g. concentration of ceramic micropowders (10 g/L), sulfate solution (0.2 mol/L), rate of adding reactants (3 mL/min) and pH value were optimized by a trial-and-error method. Powders of the precursors and the resulting coating of γ-FeNi with grain size below 40 nm on alumina, graphite and cenosphere microspheres were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The magnetic properties of the nanosize γ-FeNi-coated alumina, graphite and cenosphere microspheres were measured by vibrating sample magnetometer (VSM). The results show that the core–shell structural γ-FeNi-coated ceramic microspheres exhibited higher coercivity than pure γ-FeNi powders, indicating that these materials can be used for high-performance functional materials and devices.     

Preparation and electrochemical performance of carbon-coated LiFePO4/LiMnPO4-positive material for a Li-ion battery

Lithium iron phosphate (LiFePO₄)/lithium manganese phosphate (LiMnPO₄)-positive material was successfully prepared through ball milling and high-temperature sintering using manganese acetate, lithium hydroxide, ammonium dihydrogen phosphate, and ferrous oxalate as raw materials. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, a constant current charge–discharge test, cyclic voltammetry, and electrochemical impedance spectroscopy. The effects of lithium iron phosphate coating were also discussed. Because of its special core–shell structure, the as-prepared LiMn_0.7Fe_0.3PO₄–LiFePO₄–C exhibits excellent electrochemical performance. The discharge capacity reached 136.6 mAh/g and the specific discharge energy reached 506.9 Wh/kg at a rate of 0.1 C.     

Catalytic oxidation of benzene over Ce–Mn oxides synthesized by flame spray pyrolysis

Flame spray pyrolysis (FSP) was utilized to synthesize Ce–Mn oxides in one step for catalytic oxidation of benzene. Cerium acetate and manganese acetate were used as precursors. The materials synthesized were characterized using X-ray diffraction (XRD), N₂ adsorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and H₂-temperature programmed reduction (H₂-TPR) and their benzene catalytic oxidation behavior was evaluated. Mn ions were evidenced in multiple chemical states. Crystalline Ce–Mn oxides consist of particles with size <40 nm and specific surface areas (SSA) of 20–50 m²/g. Raman spectrums and H₂-TPR results indicated the interaction between cerium and manganese oxides. Flame-made 12.5%-Ce–Mn oxide exhibited excellent catalytic activity at relatively low temperatures (T₉₅ about 260 °C) compared to other Ce–Mn oxides with different cerium-to-manganese ratios. Redox mechanism and strong interaction conform to structure analysis that Ce–Mn strong interaction formed during the high temperature flame process and the results were used to explain catalytic oxidation of benzene.     

Preparation of nanosized hollow silica spheres from Na2SiO3 using Fe3O4 nanoparticles as templates

Nanosized hollow silica spheres with average diameters from 43 to 70 nm were prepared by removal of Fe₃O₄ templates with hydrochloric acid from silica-coated Fe₃O₄ core–shell composites. The shells of the hollow silica spheres had nanopores with average diameters of 0.92–1.25 nm. When the silica-coated Fe₃O₄ core–shell composites were prepared at a high pH value or with a low mole ratio of Na₂SiO₃ to Fe₃O₄, the resulting hollow silica spheres consisted of highly porous shells. When the silica-coated Fe₃O₄ core–shell composites were prepared with a high mole ratio of Na₂SiO₃ to Fe₃O₄, the resulting hollow silica spheres had large diameters and thick shells. The release rate of herbicide, ammonium glyphosate, could be tuned by using hollow silica spheres with different shell thicknesses.     

Large-scale synthesis of hierarchical MnO2 for benzene catalytic oxidation

Hierarchical sea-urchin-shaped manganese oxide microspheres were synthesized via a facile method based on the reaction between KMnO₄ and MnSO₄ in HNO₃ solution at 50 °C. The average diameter of the microspheres is ∼850 nm. The microspheres consist of a core of diameter of ∼800 nm and nanorods of width ∼50 nm. The nanorods exist at the edge of the core. The Brunauer–Emmett–Teller surface area of the sea-urchin-shaped microspheres is 259.4 m²/g. A possible formation mechanism of the hierarchical sea-urchin-shaped microspheres is proposed. The temperature for 90% conversion of benzene (T_90%) on the hierarchical urchin-shaped MnO₂ microspheres is about 218 °C.     

Preparation of FeCo-, FeNi- and NiCo-alloy coated cenosphere composites by heterogeneous precipitation

Precursors of binary alloy (Fe_1/2Co_1/2, Fe_1/2Ni_1/2, Ni_1/2Co_1/2, hereinafter referred to as FeCo, FeNi, NiCo) coated cenospheres were prepared by heterogeneous precipitation under optimized conditions. Magnetic binary alloy coated cenosphere composites with core–shell structure were subsequently obtained by thermal reduction of the as-prepared precursors at 700 °C for 2 h under H₂/N₂ atmosphere. The results showed that the alloy coatings were uniform and the binary alloy coated cenosphere composites basically retained the spherical morphology, suggesting that the thickness of the alloy coating could be adjusted to fabricate core–shell composites with multilayer structures. The composites exhibited higher coercivity than the pure alloy powders, and could therefore be used for high-performance functional materials and devices.     

Hydrothermal preparation of nanocrystalline ZnO2

A green hydrothermal method was proposed for the synthesis of nanocrystalline ZnO₂, using Zn₅(CO₃)₂(OH)₆ powder and 6 vol% H₂O₂ aqueous solution as the starting materials. Characterization results from X-ray diffraction, Raman, high resolution transmission electron microscopy and selected area electron diffraction revealed that the products synthesized at 80–120 °C for 6–18 h were pure cubic phase ZnO₂ nanocrystals. Room temperature photoluminescence spectra of the as-synthesized ZnO₂ nanocrystals displayed a wide and strong emission band in the visible region of about 525–570 nm upon laser excitation at 325 nm, which may have originated from their surface state and other crystal defects.     

Experimental study of lean flammability limits of methane/hydrogen/air mixtures in tubes of different diameters

Lean limit flames in methane/hydrogen/air mixtures propagating in tubes of internal diameters (ID) of 6.0, 8.9, 12.3, 18.4, 25.2, 35.0, and 50.2 mm have been experimentally studied. The flames propagated upward from the open bottom end of the tube to the closed upper end. The content of hydrogen in the fuel gas has been varied in the range 0–40 mol%. Lean flammability limits have been determined; flame shapes recorded and the visible speed of flame propagation measured. Most of the observed limit flames in tubes with diameters in the range of 8.9–18.4 mm had enclosed shape, and could be characterized as distorted or spherical flame balls. The tendency was observed for mixtures with higher hydrogen content to form smaller size, more uniform flame balls in a wider range of tube diameters. At hydrogen content of 20% or more in the fuel gas, limit flames in largest diameters (35.0 mm and 50.2 mm ID) tubes had small, compared to the tube diameter, size and were “lens”-shaped. “Regular” open-front lean limit flames were observed only for the smallest diameters (6.0 mm and 8.9 mm) and largest diameters (35.0 and 50.2 mm ID), and only for methane/air and (90% CH₄ + 10% H₂)/air mixtures, except for 6 mm ID tube in which all limit flames had open front. In all experiments, except for the lean limit flames in methane/air and (90% CH₄ + 10% H₂)/air mixtures in the 8.9 mm ID tube, and all limit flames in 6.0 mm ID tube, visible flame speeds very weakly depended on the hydrogen content in the fuel gas and were close to- or below the theoretical estimate of the speed of a rising hot bubble. This observation suggests that the buoyancy is the major factor which determines the visible flame speed for studied limit flames, except that last mentioned. A decrease of the lean flammability limit value with decreasing the tube diameter was observed for methane/air and (90% CH₄ + 10% H₂)/air mixtures for tubes having internal diameters in the range of 18.4–50.2 mm. This effect has been attributed to the stronger combined effect of the preferential diffusion and flame stretch in narrower tubes for flames which resemble rising bubble.     

A novel method for fast and continuous preparation of superfine titanium dioxide nanoparticles in microfluidic system

Previously we had developed a microfluidic system that can be easily fabricated by bending a stainless-steel tube into large circular loops. In this study, a fast and continuous preparation method for superfine TiO₂ nanoparticles (TiO₂-NPs) was developed for the aforementioned microfluidic system. The proposed method can yield anatase TiO₂ in 3.5 min, in contrast to the traditional hydrothermal reaction method, which requires hours or even days. Different reaction conditions, such as reaction temperature (120–200 °C), urea concentration (20–100 g/L), and tube length (5–20 m) were investigated. X-ray diffraction and Brunauer–Emmett–Teller analysis indicate that the as-prepared TiO₂-NPs have crystalline sizes of 4.1–5.8 nm and specific surface areas of 250.7–330.7 m²/g. Transmission electron microscopy images show that these TiO₂-NPs have an even diameter of approximately 5 nm. Moreover, because of their small crystalline sizes and large specific surface areas, most of these as-prepared TiO₂-NPs exhibit considerably better absorption and photocatalytic performance with methylene blue than commercial P5 TiO₂ does.     

Functionalized TiO2@ZrO2@Y2O3 ：Eu3＋ core-multishell microspheres and their photoluminescence properties

TiO2@ZrO2@Y2O3 ：Eu3＋ composite particles with a core-multishell structure were synthesized through the combination of a layer-by-layer （LBL） self-assembly method and a sol-gel process. The obtained sam- ples were characterized with scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and fluorescence spectropho- tometry. The results showed that the composite particles had a core-multishell structure, spherical morphology, and a narrow size distribution. The presence of a ZrO2 layer on the TiO2 core can effec- tively prevent the reaction between the TiO2 core and a Y203 shell; the temperature for the reaction between the TiO2 core and the Y203 shell in the TiO2@ZrO2@Y2O3 ：Eu core-multishell phosphor can be elevated by 300 ℃ compared to that for TiO2@ZrO2：Eu. Upon excitation of the core-multishell particles in the ultraviolet （254 nm）, the Eu3＋ ion in the Y2O3 ：Eu3＋ shell shows its characteristic red emission （611 nm, 5D0→7F2）, and the photoluminescence （PL） intensity of the phosphor with the core-multishell structure was obviously greater than that of the core-shell TiO2@Y2O3 ：Eu phosphor.     

Advanced microemulsion synthesis and characterization of wollastonite (CaSiO3)/polystyrene one-dimensional nanorods with core–shell structures

In this work, one-dimensional core–shell nanorods (CSNRs; 185–250 nm wide and 1–1.5 μm long) consisting of triethoxyvinylsilane-modified wollastonite (CaSiO₃) nanorods (MWNRs) as a core and polystyrene as a shell with uniform size were successfully synthesized using an advanced microemulsion technique. The effect of varying the surfactant cetyltrimethylammonium bromide (producing CSNRs_CTAB) or sodium dodecyl sulphate (producing CSNRs_SDS) upon the size and morphology of the CSNRs was investigated by field-emission scanning electron microscopy (FE-SEM). X-ray diffractometry and Fourier transform infrared spectrophotometer revealed the existence of a strong interaction between the MWNRs and polystyrene, which implies that the polymer chains were successfully grafted onto the surface of the MWNRs. The CSNRs were blended with polypropylene by melt processing, and the effect of the CSNRs upon the morphological properties of the polypropylene matrix was investigated by FE-SEM and atomic force microscopy. It was observed that the polystyrene chains that grafted onto the CaSiO₃ nanorods interfered with the aggregation of CaSiO₃ nanorods in the polypropylene matrix and thus improved the compatibility of the CaSiO₃ nanorods with the polypropylene matrix. Furthermore, the compatibility of CaSiO₃ nanorods with polypropylene of CSNR_SDS/polypropylene was superior to that of CSNR_CTAB/polypropylene.     

Novel one-step synthesis of silica nanoparticles from sugarbeet bagasse by laser ablation and their effects on the growth of freshwater algae culture

Scientific research involving nanotechnology has grown exponentially and has led to the development of engineered nanoparticles (NPs). Silica NPs have been used in numerous scientific and technological applications over the past decade, necessitating the development of efficient methods for their synthesis. Recent studies have explored the potential of laser ablation as a convenient way to prepare metal and oxide NPs. Due to its high silica content, low cost, and widespread availability, sugarbeet bagasse is highly suitable as a raw material for producing silica NPs via laser ablation. In this study, two different NP production methods were investigated: laser ablation and NaOH treatment. We developed a novel, one-step method to produce silica NPs from sugarbeet bagasse using laser ablation, and we characterized the silica NPs using environmental scanning electron microscopy (ESEM), energy dispersive spectrometry (EDS), dynamic light scattering (DLS), transmission electron microscopy (TEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR–FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. EDS analysis and XPS confirmed the presence of silica NPs. The NPs produced by laser ablation were smaller (38–190 nm) than those produced by NaOH treatment (531–825 nm). Finally, we demonstrated positive effects of silica NPs produced from laser ablation on the growth of microalgae, and thus, our novel method may be beneficial as an environmentally friendly procedure to produce NPs.     

Capuli cherry-mediated green synthesis of silver nanoparticles under white solar and blue LED light

In this article, the Capuli (Prunus serotina Ehrh. var. Capuli) cherry extract was used for the synthesis of silver nanoparticles (AgNPs) in the presence of white/visible solar and blue light-emitting diode (LED) light. For the characterization of the extract and the AgNPs, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy were employed, along with hydrodynamic particle size analysis, transmission electron microscopy and X-ray diffraction. The Ag nanospheres obtained using white light were 40–100 nm in diameter and exhibited an absorption peak at λ_max = 445 nm, whereas those obtained using blue LED light were 20–80 nm in diameter with an absorption peak at λ_max = 425 nm. Thermal analysis revealed that the content of biomolecules surrounding the AgNPs was about 55–65%, and it was also found that blue LED light AgNPs (56.28%, 0.05 mM) had a higher antioxidant efficacy than the white solar light AgNPs (33.42%, 0.05 mM) against 1,1-diphenyl-2-picrylhydrazyl. The results indicate that obtaining AgNPs using a blue LED light may prove to be a simple, cost-effective and easily reproducible method for creating future nanopharmaceuticals.     

Magnetic and electrochemical behavior of rhombohedral α-Fe2O3 nanoparticles with (1 0 4) dominant facets

Uniform rhombohedral α-Fe₂O₃ nanoparticles, ～60 nm in size, were synthesized via a triphenylphosphine-assisted hydrothermal method. Scanning electron micrograph (SEM) and transmission electron micrograph (TEM) analyses showed that the as-synthesized rhombohedral nanoparticles were enclosed by six (1 0 4) planes. The concentration of triphenylphosphine played an important role in morphological evolution of the α-Fe₂O₃ nanoparticles. The as-prepared rhombohedral nanoparticles possessed remanent magnetization M_r of 2.6 × 10^?3 emu/g and coercivity H_C of 2.05 Oe, both lower than those of other α-Fe₂O₃ particles with similar size, indicating their potential applications as superparamagnetic precursor materials. Furthermore, these rhombohedral α-Fe₂O₃ nanoparticles exhibited good sensor capability toward H₂O₂ with a linear response in the concentration range of 2–20 mM.     

Fabrication of nano-sized Ca(OH)2 with excellent adsorption ability for N2O4

Uniform nano-sized calcium hydroxide (Ca(OH)₂) monocrystal powder was synthesized from calcium oxide in a surfactant solution via a digestion method by decreasing the surface tension of the reaction system to control the growth of crystalline Ca(OH)₂. The Ca(OH)₂ monocrystal powder samples were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and Fourier transform-infrared spectroscopy (FT-IR). The NO_x adsorption ability of the samples was evaluated, and the influence of various types and concentrations of surfactants on powder agglomeration and then the specific surface area in the precipitation process were studied. The specific surface area of the samples was found as high as 58 m²/g and 92 m²/g and the particle size, 300–400 nm and 200–300 nm in the presence of 10 wt% PEG600 and 0.086 mL/L SDS at a reaction time of 5 h, respectively. The product has an exceptionally strong adsorption ability for NO_x, which makes it a highly promising adsorbent for emission control and air purification.     

In situ synthesis of CNTs/Fe–Ni/TiO2 nanocomposite by fluidized bed chemical vapor deposition and the synergistic effect in photocatalysis

Carbon nanotube (CNTs)/Fe–Ni/TiO₂ nanocomposite photocatalysts have been synthesized by an in situ fluidized bed chemical vapor deposition (FBCVD) method. The composite photocatalysts were characterized by XRD, Raman spectroscopy, BET, FESEM, TEM, UV–vis spectroscopy, and XPS. The results showed that the CNTs were grown in situ on the surface of TiO₂. Fe(III) in TiO₂ showed no chemical changes in the growth of CNTs. Ni(II) was partly reduced to metal Ni in the FBCVD process, and the metal Ni acted as a catalyst for the growth of CNTs. The photocatalytic activities of CNTs/Fe–Ni/TiO₂ decreased with the rise of the FBCVD reaction temperature. For the sample synthesized at low FBCVD temperature (500 °C), more than 90% and nearly 50% of methylene blue were removed under UV irradiation in 180 min and under visible light irradiation in 300 min, respectively. The probable mechanism of synergistic enhancement of photocatalysis on the CNTs/Fe–Ni/TiO₂ nanocomposite is proposed.     

Hydrothermal synthesis of Mn-Zn ferrites from spent alkaline Zn-Mn batteries

Nanocrystalline Mn-Zn ferrites （Mno.GZno.4Fe204） with particle size of 12 nm were synthesized hydrotherreally using spent alkaline Zn-Mn batteries, and accompanied by a study of the influencing factors. The nanocrystals were examined by powder X-ray diffraction （XRD） for crystalline phase identification, and scanning electron microscopy （SEM） for grain morphology. The relationship between concentration of Fe（II）, Mn（II）, and Zn（II） and pH value was obtained through thermodynamic analysis of the Fe（II）-Mn（II）-Zn（II）-NaOH-H2O system. The results showed that all ions were precipitated completely at a pH value of 10-11. The optimal preparation conditions are： co-precipitation pH of 10.5, temperature of 200 ℃ and time of 9 h.     

Effect of magnetic field on 3D flow and heat transfer during solidification from a melt

We present the effect of a magnetic field on three-dimensional fluid flow and heat transfer during solidification from a melt in a cubic enclosure. The walls of the enclosure are considered perfectly electrically conducting and the magnetic field is applied separately in three directions. The finite-volume method with enthalpy formulation is used to solve the mathematical model in the solid and liquid phases. The results obtained by our computer code are compared with the numerical and experimental data found in the literature. For Gr = 5 × 10⁵ and Ha = 0, 25, 50, 75, and 100 (where Gr and Ha are the Grashof and Hartmann numbers, respectively), the effects of magnetic field on flow and thermal fields, and on solid/liquid interface shape are presented and discussed. The interface is localized with and without magnetic field. The results show a strong dependence between the interface shape and the intensity and orientation of magnetic field. When the magnetic field is applied along the X-direction, the magnetic stability diagrams (V_max–Ha) and (Nu_avg–Ha) show the strongest stabilization of the flow field and heat transfer.     

“Magnetic-ribs” in fully developed laminar liquid–metal channel flow

This paper documents the numerical investigation of the effects of non-uniform magnetic fields, i.e. magnetic-ribs, on a liquid–metal flowing through a two-dimensional channel. The magnetic ribs are physically represented by electric currents flowing underneath the channel walls. The Lorentz forces generated by the magnetic ribs alter the flow field and, as consequence, the convective heat transfer and wall shear stress. The dimensionless numbers characterizing a liquid–metal flow through a magnetic field are the Reynolds (Re) and the Stuart (N) numbers. The latter provides the ratio of the Lorentz forces and the inertial forces. A liquid–metal flow in a laminar regime has been simulated in the absence of a magnetic field (Re_H = 1000, N = 0), and in two different magnetic ribs configurations for increasing values of the Stuart number (Re_H = 1000, N equal to 0.5, 2 and 5). The analysis of the resulting velocity, temperature and force fields has revealed the heat transport phenomena governing these magneto-hydro-dynamic flows. Moreover, it has been noticed that, by increasing the strength of the magnetic field, the convective heat transfer increases with local Nusselt numbers that are as much 27.0% larger if compared to those evaluated in the absence of the magnetic field. Such a convective heat transfer enhancement has been obtained at expenses of the pressure drop, which increases more than twice with respect to the non-magnetic case.