MgO Nanostructures Research Articles

From Heterolytic to Homolytic H2Dissociation on Nanostructured MgO(001) Films As a Function of the Metal Support

It is well-known that the H2 molecule dissociates heterolytically on stepped MgO surfaces with formation of protons bound to O2– anions (OH groups) and hydride ions bound to Mg cations (MgH groups)...

Mesoporous (ZnO)x(MgO)1−x nanoplates: template-free solvothermal synthesis, optical properties, and their applications in water treatment

Mesoporous (ZnO)x(MgO)1-x nanoplates were synthesized from a solution containing zinc acetate and magnesium acetate by a template-free solvothermal synthetic method followed by subsequent calcination. After thermal treatment, the plate-like morphology was retained. The formation of pores was due to thermal decomposition of Mg(OH)2 and the release of H2O. The optical properties of the mesoporous (ZnO)x(MgO)1-x nanoplates had been investigated by UV-vis absorption and cathodoluminescence (CL) emission spectroscopy. The UV-vis absorption spectra showed the band gap variation of the as-prepared samples due to the presence of ZnO in the MgO nanostructures. The CL spectra showed strong broad peaks in the visible range from 450 to 700 nm, indicating significant oxygen vacancy defects on the surface of the (ZnO)x(MgO)1-x nanoplates. Moreover, the samples were evaluated as photocatalysts for the UV-induced degradation of methyl orange (MO) in aqueous solution. The (ZnO)x(MgO)1-x nanoplates showed high photocatalytic performance and thus would be promising candidates for polluted water treatment.

Sonochemical Syntheses of a One‐Dimensional Mg(II) Metal‐Organic Framework: A New Precursor for Preparation of MgO One‐Dimensional Nanostructure

Nanostructure of a MgII metal‐organic framework (MOF), {[Mg(HIDC)(H2O)2]·1.5H2O}n (1) (H3IDC = 4,5‐imidazoledicarboxylic acid), was synthesized by a sonochemical method and characterized by scanning electron microscopy, X‐ray powder diffraction, IR spectroscopy, and elemental analyses. The effect of concentration of starting reagents on size and morphology of nanostructured compound 1 has been studied. Calcination of the bulk powder and nanosized compound 1 at 650°C under air atmosphere yields MgO nanostructures. Results show that the size and morphology of the MgO nanoparticles are dependent upon the particles size of compound 1.

Template‐Free Hydrothermal Synthesis of Mesoporous MgO Nanostructures and Their Applications in Water Treatment

The controlled synthesis of Mg(OH)(2) nanowires and microflowers composed of nanoplates was successfully achieved by a template-free hydrothermal synthetic method. It was found that the reaction medium played a crucial role in the morphological control of the precursor nanostructures. The high polarity of water molecules favored the polar growth of the precursor, resulting in the formation of nanowires with a diameter of 80 nm, whereas a mixed water/ethanol medium with a lower degree of polarity led to the formation of microflowers. Moreover, mesoporous MgO nanostructures could be obtained by further annealing these as-prepared precursors in air at 500 °C for 2 h. During thermal treatment, the wire- and flower-like morphologies were retained. Porosity formation was due to thermal decomposition of Mg(OH)(2) and release of H(2)O. Both the mesoporous MgO nanowires and microflowers showed superior ability of adsorbing the organic dye methyl orange, and thus they are promising candidates for polluted water treatment.

Superb Adsorption Capacity and Mechanism of Flowerlike Magnesium Oxide Nanostructures for Lead and Cadmium Ions

A facile method based on microwave-assisted solvothermal process has been developed to synthesize flowerlike MgO precursors, which were then transformed to MgO by simple calcinations. All the chemicals used (magnesium nitrate, urea, and ethanol) were low cost and environmentally benign. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution TEM, and N(2) adsorption-desorption methods. These flowerlike MgO nanostructures had high surface area and showed superb adsorption properties for Pb(II) and Cd(II), with maximum capacities of 1980 mg/g and 1500 mg/g, respectively. All these values are significantly higher than those reported on other nanomaterials. A new adsorption mechanism involving solid-liquid interfacial cation exchange between magnesium and lead or cadmium cations was proposed and confirmed.

Oxidative Dehydrogenation of n-Butane Over Vanadium Magnesium Oxide Catalysts Supported on Nano-Structured MgO and ZrO2: Effect of Oxygen Capacity of the Catalyst

Vanadium-magnesium oxide catalysts supported on nano-structured MgO and ZrO2 (Mg3(VO4)2/MgO/ZrO2) were prepared by a wet impregnation method with a variation of Mg:Zr ratio (8:1, 4:1, 2:1, and 1:1). For comparison, Mg3(VO4)2/MgO and Mg3(VO4)2/ZrO2 catalysts were also prepared by a wet impregnation method. The prepared catalysts were applied to the oxidative dehydrogenation of n-butane in a continuous flow fixed-bed reactor. Mg3(VO4)2/MgO/ZrO2 (Mg:Zr = 4:1, 2:1, and 1:1) and Mg3(VO4)2/ZrO2 catalysts showed a stable catalytic activity during the whole reaction time, while Mg3(VO4)2/MgO/ZrO2 (8:1) and Mg3(VO4)2/MgO catalysts experienced a severe catalyst deactivation. Deactivation of Mg3(VO4)2/MgO/ZrO2 (8:1) and Mg3(VO4)2/MgO catalysts was due to their low oxygen mobility. Effect of oxygen capacity (the amount of oxygen in the catalyst involved in the reaction) of the supported Mg3(V04)2 catalysts on the catalytic performance in the oxidative dehydrogenation of n-butane was investigated. Experimental results revealed that oxygen capacity of the catalyst was closely related to the catalytic activity in the oxidative dehydrogenation of n-butane. A large oxygen capacity of the catalyst was favorable for obtaining a high catalytic activity in this reaction. Among the catalysts tested, Mg3(VO4)2/MgO/ZrO2 (4:1) catalyst with the largest oxygen capacity showed the best catalytic performance.

Pore size and surface area control of MgO nanostructures using a surfactant-templated hydrothermal process: High adsorption capability to azo dyes

Dioctylsulfosuccinate sodium surfactant (AOT) was selected as a structure-directing agent to prepare mesoporous MgO adsorbent by a hydrothermal method. The anionic AOT surfactant combines with Mg(OH)2 crystallites to form AOT·Mg(OH)2 micelle colloids by hydrogen bonding and electrostatic attraction to template the mesopores with diameter of 10–20nm in MgO nanoplates The whole process is composed of three stages: nucleation, orientation growth, and porecreating. The results demonstrated that the presence of AOT surfactant was essential to produce the mesopores and to adjust the structural parameters of the nanoplates. Because of their higher specific surface area and porous structure, the MgO materials exhibit a satisfactory adsorptive property to three typical azo dye pollutants, Congo red (471–588mg/g), Methyl orange (∼370mg/g) and Sudan III (∼180mg/g), and good performance for decolorization of low-concentration dyes. The highly adsorption capacities of the adsorbents are ascribed to their mesoporous structures which can provide more interaction sites, facilitate the mass diffusion in pores and help the dye molecules to contact the adsorptive sites more easily. The present work provided an alternative approach for preparation of inorganic adsorbent with controlled porous structures and high adsorption ability for hazardous dyes.

Preparation and hydrogen sorption properties of a nano-structured Mg based Mg–La–O composite

For the first time, a Mg based Mg–La–O hydrogen storage nano-composite was prepared through an arc plasma method followed by passivation in air. XRD, TEM and PCT techniques were used to characterize the phase components, microstructure and hydrogen sorption properties of the nano-composite. It is shown that the Mg–La–O composite is mainly composed of ultrafine Mg, nano-structured MgO and La2O3. TEM analysis shows that those Mg ultrafine particles were covered by MgO and La2O3 nano particles, forming a special core–shell structured metal-oxide composite. Based on the PCT measurements, the hydrogenation and dehydrogenation enthalpies of the composite are determined to be −71.9 kJ/mol H2 and 75.9 kJ/mol H2, respectively. The apparent activation energy for hydrogen adsorption is measured to be 41.98 kJ/mol H2. The results gathered in this study showed that those oxide nano-particles, especially La2O3, can act as channels for the hydrogen sorption of Mg ultrafine particles, leading to the significantly improved hydrogen sorption kinetics over pure Mg ultrafine powders.

Spatial control of magnetic anisotropy for current induced domain wall injection in perpendicularly magnetized CoFeB|MgO nanostructures

Magnetic anisotropy of perpendicularly magnetized CoFeB|MgO films is spatially tailored using depth controlled Ar ion etching with patterned etching masks. Nanowires with patterned etching have significantly reduced coercivity compared to those without the etching. We show that the sign of the anisotropy can be locally changed by partially etching the MgO layer, and as a consequence, 90° domain walls can be created at the boundary of etched/non-etched region. Direct current application to the nanowire can result in moving such 90° domain walls, which can prove as an efficient mean to inject domain walls into perpendicularly magnetized nanowires.

Investigation of the optical properties of Mg(OH)2 and MgO nanostructures obtained by microwave-assisted methods

Two simple methods for the synthesis of Mg(OH)2 nanostructures, MgO nanoflakes and MgO/Mg(OH)2 nanocomposite using a conventional microwave oven are reported. The first method includes the preparation of Mg(OH)2 by a simple reaction of magnesium powder with deionized water under microwave radiation. The second approach relates to the transformation of Mg(OH)2 to MgO nanoflakes and grass-like nanostructures by rapid microwave hybrid heating using a SiC-based composite susceptor. The as-synthesized samples have been characterized by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) The optical properties of the samples are investigated using UV–visible spectroscopy to study the reflective index and optical dielectric constant.

Porous Hierarchically Micro-/Nanostructured MgO: Morphology Control and Their Excellent Performance in As(III) and As(V) Removal

Porous micro-/nanostructured MgO were successfully synthesized through a facile method. Flower-like and nest-like micro-/nanostructured MgO were obtained by adjusting the concentration of precipitant. When tested as adsorbent in arsenic removal, the as-prepared micro-/nanostructured MgO were effective for both As(III) and As(V) removal, particularly the As(III). The adsorption capacities of these micro-/nanostructured MgO for As(III)/As(V) are much higher than those reported for other micro-/nanostructured metal oxides. The adsorption kinetics and adsorption mechanism for As(III) and As(V) onto micro-/nanostructured MgO were also investigated. The high uptake capability of the as-prepared micro-/nanostructured MgO make it a potentially attractive adsorbent for the removal of both As(III) and As(V) from water.

Properties and rapid consolidation of nanostructured MgO–MgAl 2O 4 composites

The rapid sintering of nanostructured MgO–MgAl 2O 4 composites was investigated with a high-frequency induction heated sintering process. The advantage of this process is that it allows for very quick densification to near theoretical density and prohibits grain growth in nanostructured materials. Highly dense nanostructured MgO–MgAl 2O 4 composites were produced with simultaneous application of 80 MPa pressure and an induced output current of total power capacity (15 kW) within 2 min. The sintering behaviors, grain sizes and mechanical properties of MgO–MgAl 2O 4 composites were investigated.

MgCO3·3H2O and MgO complex nanostructures: controllable biomimetic fabrication and physical chemical properties

In this paper, we report a method of biomimetic synthesis of MgCO(3)·3H(2)O and MgO Viburnum opulus-like complex nanostructures with superhydrophobicity and adsorption properties. The MgCO(3)·3H(2)O complex nanostructures can be obtained by changing experimental parameters, including concentrations of reactants (dextran and MgCl(2)), molar ratios of reactants, and reaction time. The phase structure of as-synthesized samples was characterized by X-ray diffraction (XRD). The morphology and structure are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. The MgCO(3)·3H(2)O complex nanostructures exhibited superhydrophobicity, due to their unique superstructures, and was proved by the contact angle (CA) measurement. We also show that a simple calcination of these unusually shaped MgCO(3)·3H(2)O results in spontaneous formation of MgO complex nanostructures while the unique shape can be maintained, and the as-synthesized MgO nanostructures show excellent adsorption property. These unique structures and properties will open up a wide range of potential applications in material and environmental protection.

Exciton-Driven Highly Hyperthermal O-Atom Desorption from Nanostructured CaO

We report qualitatively new highly hyperthermal (HHT) oxygen atom emission from nanostructured CaO excited by 6.4 eV nanosecond laser pulses. The kinetic energy distribution of emitted O-atoms peaks at 0.7 eV, which is over 4 times greater than previously observed. Excitation of MgO and CaO nanostructures with UV laser pulses is known to result in thermal and hyperthermal emission of oxygen atoms when photons with energies above and below the band gap, respectively, are used. The highly energetic atomic desorption we observe, following bulk excitation, challenges the conventional view that bulk excitation can only induce thermal desorption. Using density functional theory and an embedded cluster method, we propose a mechanism for this HHT feature based on the interaction of surface holes with bulk excitons. These experimental and theoretical results suggest that specific atomic desorption mechanisms in wide-bandgap materials can be controlled by selective electronic excitation of not only the surface but also the bulk of these materials.

Mechanically activated synthesis of single crystalline MgO nanostructures

One-dimensional (1D) MgO structures were successfully synthesized via carbothermic reduction of mechanically activated mixture of MgO and graphite. Mechanical activation of source materials before carbothermic reduction can substantially enhance the formation of MgO products at a temperature (1000 °C) relatively lower than that required in previous approaches (≥1200 °C). However, the morphology of MgO formed is dependent on the degree of mechanical activation and the condition of the subsequent carbothermic reduction. Two distinctive morphologies were found for MgO products synthesized using our method: single crystalline nanorods with rectangular cross-sections whose diameters range from 50 to 100 nm, and microfibers (∼5 μm in diameter) with and without branching. The synthesized products were systematically studied by XRD, SEM, TEM, and EDS. The results show that the nucleation and growth process of these morphologies seem to be a vapor–solid mechanism.

Toughening and hardening in double-walled carbon nanotube/nanostructured magnesia composites

Dense double-walled carbon nanotube (DWCNT)/nanostructured MgO composites were prepared using an in situ route obviating any milling step for the synthesis of powders and consolidation by spark-plasma-sintering. An unambiguous increase in both toughness and microhardness is reported. The mechanisms of crack-bridging on an unprecedented scale, crack-deflection and DWCNT pullout have been evidenced. The very long DWCNTs, which appear to be mostly undamaged, are very homogeneously dispersed at the grain boundaries of the matrix, greatly inhibiting the grain growth during sintering. These results arise because the unique microstructure (low content of long DWCNTs, nanometric matrix grains and grain boundary cohesion) provides the appropriate scale of the reinforcement to make the material tough.

Syntheses and characterization of Mg(OH) 2 and MgO nanostructures by ultrasonic method

Magnesium hydroxide nanostructures have been synthesized by the reaction of magnesium acetate with sodium hydroxide via sonochemical method. Reaction conditions such as the Mg 2+ concentration, aging time and the ultrasonic device power show important roles in the size, morphology and growth process of the final products. The magnesium oxide nanoparticles have been prepared by calcination of magnesium hydroxide nanostructures at 400 °C. The magnesium hydroxide and magnesium oxide nanostructures were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermal gravimetric (TG) and differential thermal analyses (DTA).

Synthesis, characterization and optical properties of Mg(OH) 2 micro-/nanostructure and its conversion to MgO

Magnesium hydroxide (Mg(OH) 2) micro- and nanostructures have been synthesized by a single step hydrothermal route. Surface morphology analysis reveals the formation of micro- and nanostructures with varying shape and size at different synthesis conditions. Structural investigations by X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that the synthesized material is Mg(OH) 2 with hexagonal crystal structure. An optical band gap of 5.7 eV is determined for Mg(OH) 2 nanodisks from the UV–vis absorption spectrum. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of Mg(OH) 2 nanodisks at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancies in the material. Furthermore, Mg(OH) 2 has been converted to MgO by calcination at 450 °C. Optical studies of the MgO nanodisks have shown an optical band gap of 3.43 eV and a broadband PL emission in the UV region. Mg(OH) 2 and MgO nanostructures with wide-band gap and short-wavelength luminescence emission can serve as a better luminescent material for photonic applications.

MgO polyhedral nanocages and nanocrystals based glucose biosensor

MgO polyhedral nanocages and nanocrystals, synthesized by non-catalytic simple thermal evaporation process, were used to fabricate high-sensitive amperometric glucose biosensor which showed a high and reproducible sensitivity of 31.6 μA μM −1 cm −2 with a response time less than 5 s, linear dynamic range from 1.0 to 9.0 μM and correlation coefficient of R = 0.9993. The detection limit of fabricated biosensor (based on S/ N ratio = 3) was estimated to be 68.3 ± 0.02 nM. To the best of our knowledge, this is the first report which demonstrates the use of MgO nanostructures for the fabrication of glucose biosensor; hence, this work opens a new way to utilize MgO nanostructures as an efficient electron mediator to fabricate efficient glucose biosensors.

Novel surfactant-free synthesis of MgO nanoflakes

A new and an environmentally benign route have been developed for the synthesis of MgO nanoflakes, which does not require any additives, surfactants and substrates. The technique is based on a very simple reaction of magnesium powder and water at temperature of 100 °C. The formation of MgO nanostructures by the reaction of metals with water is suggested to occur due to the decomposition of magnesium hydroxide at higher temperature and higher pressure. The MgO nanoflakes have an average width of 40 nm, thickness of 20 nm and length up to 1 μm. Compared with other methods, the present method is fast, economical, low temperature and free of pollution which will make it suitable for large scale production. Moreover, the technique does not require any sophisticated equipments and as such can be extended to the other metal oxides.