MgO Materials Research Articles

Aluminum-nanosphere-stacked MgNiO metal-semiconductor-metal ultraviolet photodetectors

Because MgO and NiO materials have the same rock-salt cubic structure and similar lattice constants, the MgNiO absorption layers of metal–semiconductor–metal ultraviolet photodetectors (MSM-UVPDs) were deposited by alloying MgO and NiO. To improve the properties of the MgNiO films, the films were annealed at various temperatures. The grain size of 18.5 nm for the as-deposited MgNiO films was improved to 23.4 nm and 24.8 nm for the MgNiO films annealed at 500 °C and 600 °C for 60 min, respectively. For the film-structured MSM-UVPDs with 500 °C-annealed MgNiO films operated at a bias voltage of 5 V, the photoresponsivity, average noise current, noise equivalent power, and specific detectivity were 1.78 × 10−2 A/W, 3.74 × 10−12 A, 2.10 × 10−10 W, and 1.50 × 109 cmHz0.5W−1, respectively. Aluminum (Al) nanospheres were stacked on the film-structured MgNiO MSM-UVPDs. The performance of the resulting Al-nanosphere-stacked MgNiO MSM-UVPDs was improved by increasing the density of the Al nanospheres. With an Al nanosphere density of approximately 2.0 × 107/mm2, when the Al-nanosphere-stacked MgNiO MSM-UVPDs operated at a bias voltage of 5 V, the photoresponsivity, average noise current, noise equivalent power, and specific detectivity were 2.00 × 10−1 A/W, 7.71 × 10−12 A, 3.88 × 10−11 W, and 8.16 × 109 cmHz0.5W−1, respectively. Despite the noise induced by the Al nanospheres, the performance of the Al-nanosphere-stacked MgNiO MSM-UVPDs was better than that of the film-structured MgNiO MSM-UVPDs. The improved detective performance was attributed to the increase in absorbance induced by the surface plasmon resonance and the optical scattering effect of the stacked Al nanospheres.

Magnesium oxide as an efficient catalyst for CO2 fixation and N-formylation reactions under ambient conditions

Chemical fixation of CO2 into fine chemicals is one of the key areas of research today to mitigate greenhouse gas CO2 and its successful utilization as C1 building block. Nanocrystalline MgO has been synthesized by simple precipitation method followed by calcination at 450 °C. The materials are characterized thoroughly by several instrumental tools, which suggested the presence of mesoscopic void space and excellent catalytic activity for the synthesis of organic cyclic carbonates by chemical fixation of CO2 on a wide range of epoxides at atmospheric pressure and room temperature within a short reaction time. Maximum product yields upto 99% for the cyclic carbonates are observed. It also displayed a high catalytic activity in the N-formylation of various amines by using formic acid as reagent (acts both as carbon source and reducing agent) at room temperature with excellent product yields upto 99.5%. This nanocrystalline MgO material showed high recycling efficiency for the cycloaddition of CO2 onto the epoxides and no sign of catalyst deactivation.

Ni-phyllosilicate structure derived Ni–SiO2–MgO catalysts for bi-reforming applications: acidity, basicity and thermal stability

In this work, Ni–SiO2–MgO materials synthesized via Ni-phyllosilicate (PS) intermediates were explored for bi-reforming of methane (BRM) reaction.

Hexamethylene tetramine-assisted hydrothermal synthesis of porous magnesium oxide for high-efficiency removal of phosphate in aqueous solution

Porous magnesium oxide as the adsorbent of phosphate was prepared by hexamethylene tetramine (HMT) assisted hydrothermal method. Various techniques were used to carefully characterize crystallinity structure, morphology, pore structure, and adsorption performance of the prepared MgO samples. The results show that the HMT plays a key role during the formation of pore structure of MgO materials. The BET surface area and pore size were varied as a function of the feeding ratio of HMT and Mg2+ in the synthesis system. When the ratio is equal to 1.2, the obtained MgO sample has the appropriate BET surface area of 181.02m2g−1 and the averaged pore diameter of ca. 10.76nm, which shows the highest adsorption capacity of 236mgg−1 among the prepared samples and the outstanding adsorption performance compared with those reported in the literature. The adsorption of these porous MgO materials matches well the pseudo second order kinetic model and the Freundlich isotherms. Besides, the phosphate anions was adsorbed on MgO to produce magnesium hydrogen phosphate and magnesium phosphate.

Deactivation studies of bimetallic AuPd nanoparticles supported on MgO during selective aerobic oxidation of alcohols

Here we report the synthesis and characterisation of high surface area MgO prepared via the thermal decomposition of various magnesium precursors (MgCO3, Mg(OH)2 and MgC2O4). Bimetallic gold-palladium nanoalloy particles were supported on these MgO materials and were tested as catalysts for the solvent-free selective aerobic oxidation of benzyl alcohol to benzaldehyde. All these catalysts were found to be active and very selective (>97%) to the desired product (benzaldehyde). However, MgO prepared via the thermal decomposition of magnesium oxalate displayed the highest activity among all the magnesium oxide supports tested. Attempts were made to unravel the reasons for the deactivation of these catalysts using different characterisation techniques namely in situ XRD, XPS, ICP-MS, TEM, and TGA-MS. From the data obtained, it is clear that MgO undergoes phase changes from MgO to Mg(OH)2 and MgCO3 during catalyst preparation as well as during the catalytic reaction. Besides phase changes, strong adsorption of reactants and products on the catalyst surface, during the reaction, were also observed and washing the catalyst with organic solvents did not completely remove them. The phase change and catalyst poisoning were reversed through high temperature heat treatments. However, these processes led to the sintering of the metal nanoparticles. Moreover, substantial leaching of the support material (MgO) was also observed during the reaction. These latter two processes led to the irreversible deactivation of AuPd nanoparticles supported on MgO catalyst during the solvent-free selective aerobic oxidation of alcohols. Among the three different MgO supports studied in this article, an inverse correlation between the catalytic activity and Mg leaching has been observed. This article reports a deeper understanding of the mode of deactivation observed in metal nanoparticles supported on MgO during liquid phase reactions.

Influence of phonon focusing on the Knudsen flow of phonon gas in single-crystal nanofilms of spintronic materials

Influence of the anisotropy of elastic energy on the phonon transport has been investigated in single- crystal nanofilms of Fe, Cu, MgO, InSb, and GaAs materials used for spintronic instruments and devices in the Knudsen flow regime of phonon gas. The dependences of the lattice thermal conductivity and lengths of free paths of phonons for all acoustic modes on the geometric parameters of the films have been considered for low temperatures with the dominance of the diffuse scattering of phonons at the boundaries. Physical aspects of the propagation of phonon modes in the films have been analyzed. It has been shown that the anisotropy of phonon transport in single-crystal films is due to the features of the propagation of phonon modes in elastically anisotropic films with a different relationship of the geometric parameters. The directions of heat flow and orientations of the film planes that yield the maximum and minimum thermal conductivity of phonons in film planes have been determined.

Influence of the strong field in enhancing, electronic magnetic and optical properties of Mn-doped MgO

The local spin density approximation with Hubbard-like coulomb term based on first principles calculations are used to investigate a substitute doping of transition metal Mn in MgO. Under the crystal field theory and according to the intensity of the ligand field, the d4-d8 transition elements can have two possible configurations such as the case of Mn(d5), in its low spin configuration that represents a strong field, the Mn+2 doped MgO material has a half-metallic character in the two proposed studies approximations: the local spin density approximation (LSDA) and (LSDA+U), a character that will enable to change the magnetic, electronic and optical properties., This result is supported by the sp-d exchange mechanism calculation confirming that the coupling between impurity and ligand is completely ferromagnetic. The material has a magnetic moment of about 1 μB, mainly due to the Mn impurity of around 95% in LSDA+U case. In optical propriety the material shows a slight spin polarization and reduction of band gap of around 5% with strong filed in LSDA+U case.

Effect of phonon focusing on Knudsen flow of phonon gas in single-crystal nanowires made of spintronics materials

Effect of anisotropy of elastic energy on the phonon propagation in single-crystal nanowires made of Fe, Cu, MgO, InSb, and GaAs materials that are used to fabricate spintronics devices in the regime of the Knudsen flow of phonon gas has been studied. A new method of analyzing the focusing of quasi-transverse modes has been suggested, which made it possible to determine the average values of the densities of phonon states in the regions of focusing and defocusing slow and fast quasi-transverse modes. The effect of phonon focusing on the anisotropy of heat conductivity and lengths of the phonon free paths has been analyzed for all acoustic modes that exist in spintronics nanostructures. It has been shown that for all the nanowires investigated the angular dependences of the free paths of fast and slow transverse modes in the {100} and {110} planes correlate with the angular dependences of the densities of phonon states for these modes. Directions of the heat flux that ensure the maximum and minimum phonon heat conductivity in the nanowires have been determined.

Transient Cataluminescence on Flowerlike MgO for Discrimination and Detection of Volatile Organic Compounds

Methodologies for simple and rapid identification of gas compounds are needed in the fields of environmental and security. Here, a new and simple method for the discrimination of gas compounds was designed through an interesting transient cataluminescence (TRCTL) phenomenon on the highly efficient MgO materials. The flowerlike MgO with high CTL activity was controllably synthesized via a facile and time-saving aqueous precipitation route and characterized by scanning electron microscopy, powder X-ray diffractometry, high-resolution transmission electron microscopy, and N2 adsorption measurements, etc. With flowerlike MgO working as the sensing material, the newly developed CTL gas sensor exhibited highly active, ultrafast, and characteristic responses toward many analytes; the TRCTL curves thus were obtained and 10 VOCs have been successfully identified. Parallel experimental results show that the controllable synthesis of flowerlike MgO can greatly enhance the discrimination capacities for VOCs. Further, the TRCTL of CHCl3 and C2H5OC2H5 were taken as typical examples to illustrate the possible sensing mechanism, which could contribute to explaining processes of catalytic oxidations. We expect this novel TRCTL concept will be of practical importance for applications including gas detection, gas discrimination, and research of chemical kinetics processes.

Processing of low-fired glass-free Li2MgTi3O8 microwave dielectric ceramics

An approach in which the raw materials of Li2CO3, MgO and TiO2 were ball milled before mixing (abbreviated as LMT2) was reported. For the traditional ceramic technique (abbreviated as LMT1), the raw materials of Li2CO3, MgO and TiO2 were directly used without further processing. The powders from LMT2 tended to be smaller and uniform and the ceramics exhibited higher densities than that of LMT1, which significantly lowered the sintering temperature from 1075 °C to 925 °C. LMT2 ceramics sintered at 925 °C exhibited good microwave dielectric performance with εr = 27.0, Q × f = 58,480 GHz (at ∼ 5.8 GHz), τf = 0.45 ppm/°C. Moreover, LMT2 ceramic was found to be chemically compatible with Ag. The results indicate that the pretreatment of raw materials is a relatively simple and particularly effective method to obtain glass-free Li2MgTi3O8 LTCC ceramics.

Understanding of the field evaporation of surface modified oxide materials through transmission electron microscopy and atom probe tomography

Understanding of triggering the field evaporation of surface ions on the non-conductive materials enables improvement in the mass resolution in laser-pulsed atom probe tomography. This study addresses the influence of surface modification through metallic-capped layers, such as Co, Ni, and Ag, with surrounding bulk MgO tips on the physical mechanisms responsible for field evaporation and on the mass resolving power compared to uncapped bulk MgO. In particular, the field evaporation on the surface regions of Ag-capped bulk MgO tips during analysis was extensively observed by transmission electron microscopy to confirm the overall evaporation sequences occurring at the tip surface. We found that the introduction of such capping layers, especially for Ag-capping, controls both symmetric tip geometry at the surface of the specimens and the mass resolving power of ion species consisting of MgO materials. This implies the improvements in the symmetries of local field distributions and the isotropy of thermal heating across the tip surface. It reveals that Ag-capping with high thermal diffusivity promotes the compositional uniformities between the laser illumination side and the opposite side for MgO samples as well as the reduced fraction of multiple events for oxygen ions between both sides. Moreover, a variation in the thickness of the Ag-capping layer is an additional factor governing a thermal-assisted mechanism of MgO evaporation. Based on our findings, homogeneous thermal heat transfer for MgO emission along the tip axis by Ag-capping layers may be significant in potential methods for improvement.

Bimodal Mesoporous Carbon-Coated MgO Nanoparticles for CO2 Capture at Moderate Temperature Conditions

Bimodal mesoporous carbon supported MgO (MgOMC) materials were prepared to provide a candidate for trapping CO2 in flue gas at high temperature by an impregnation method. Textural properties of MgOMC were characterized by X-ray diffraction, N2 adsorption/desorption isotherm, scanning electron microscopy, transmission electron microscopy and an element mapping method, and their CO2 adsorption behaviors in both pure CO2 and 10 vol % CO2 simulated flue gas were evaluated by a thermal gravimetric method at ambient temperature. Effects of MgO content in composite and calcination temperature on CO2 adsorption capacity were studied. Results showed that MgOMC samples with high content of basic MgO sites and well-developed porous structure exhibit high CO2 uptakes at 75 °C, rapid adsorption kinetics, excellent CO2 selectivity in flue gas and good regenerability under mild temperature below 300 °C, indicating their potential application in the CO2 capture from flue gas.

Ex Situ and Operando Studies on the Role of Copper in Cu-Promoted SiO2–MgO Catalysts for the Lebedev Ethanol-to-Butadiene Process

Dehydrogenation promoters greatly enhance the performance of SiO2–MgO catalysts in the Lebedev process. Here, the effect of preparation method and order of addition of Cu on the structure and performance of Cu-promoted SiO2–MgO materials is detailed. Addition of Cu to MgO via incipient wetness impregnation (IWI) or coprecipitation (CP) prior to wet-kneading with SiO2 gave similar butadiene yields (∼40%) as when Cu was added to the already wet-kneaded catalyst. In contrast, the catalyst prepared by impregnation of Cu on SiO2 first proved to be the worst catalyst of the series. TEM, XRD, and XPS analyses suggested that, for all catalyst materials, Cu2+ forms a solid solution with MgO. This was confirmed by UV–vis, XANES, and EXAFS data, with Cu being found in a distorted octahedral geometry. As a result, the acid–base properties, as determined by Pyridine- and CDCl3–IR as well as NH3-TPD, are modified, contributing to the improved performance. Operando XANES and EXAFS studies of the evolution of the copper ...

Catalytic performance of MgO with different exposed crystal facets towards the ozonation of 4-chlorophenol

This study aims to provide a direction to tailor catalytic activity of catalyst by selectively exposing a crystal facet. Herein three sheet-like MgO materials with the primarily exposed crystal facet of (111), (110), (200) were prepared, respectively. Results show that the catalytic ozonation on each MgO substantially enhanced the removal of 4-chlorophenol and total organic carbon when compared with ozonation alone or that on traditional MgO. The pseudo first-order reaction constant of 4-chlorophenol removal in ozonation catalyzed by MgO(111), MgO(110), MgO(200) is 4.8, 2.5, 3.1 times higher than that in the single ozonation, respectively. When different dosage but the same surface area of MgO was applied, their catalytic activities changed as MgO(111)>MgO(110)>MgO(200). It indicates that the catalytic activity significantly depends on the crystal facet besides the surface area. That is because the drawbacks, such as edges, steps, and kinks, on each facet decreased in the order of (111)>(110)>(200). CO2-TPD and zeta potential measurement show that the drawbacks caused more and stronger surface basic groups in the form of hydroxyl and isolated oxygen due to the availability of more unsaturated coordination sites. These active basic centers make the easy formation of basic microenvironment near MgO particles and thus favor the ozonation. Finally, the catalytic mechanism was explored and compared by evaluating the ozone decomposition, qualitatively and quantitatively identifying hydroxyl radicals, and determining the ozone utilization efficiency. It reveals that MgO with more surface basic groups can enhance the transformation rate of ozone to hydroxyl radicals more efficiently. All these results show that MgO is a very potential ozonation catalyst and the catalytic activity can be tailored by exposing crystal facet with more drawbacks.

Influence of acid–base properties on the Lebedev ethanol-to-butadiene process catalyzed by SiO2–MgO materials

The preparation method greatly influences morphology, acid–base properties and performance of SiO2–MgO catalysts. Wet-kneaded catalysts possess an improved distribution, proximity and strength of acidic-basic sites, thus leading to higher butadiene yields.

Dielectric properties and electrical conductivity of MgO synthesized by chemical precipitation and sol-gel method

MgO Powders were synthesized via simple chemical precipitation (SPC) and sol-gel process (SG). The electrical behavior of these powders was determined by complex impedance spectroscopy using an alternative current conductivity at various temperatures and frequencies. For MgO elaborated by SG, the activation energy is 1.49 eV while MgO prepared by SPC, this energy is equal to 0.39 and 4.13 eV. The structural properties of MgO powders were analyzed by X-ray diffraction and FT-IR spectroscopy. The results show that the cristallites size was 28.4 nm for MgO SPC and 42.5 nm for MgO SG. Others methods such DTA, TGA, BET and SEM were used to characterized MgO materials.

Eco‐Friendly Catalytic Systems Based on Carbon‐Supported Magnesium Oxide Materials for the Friedländer Condensation

AbstractCarbon‐supported MgO materials are excellent and sustainable catalysts for the synthesis of N‐containing heterocyclic compounds by the Friedländer condensation under mild, solvent‐free conditions. The results reported herein indicate that MgO is the most active catalytic species that accelerates the reaction compared with the catalytic behavior observed for the carbon material Norit RX3. On the basis of DFT calculations, a reaction mechanism that involves dual activation of the reacting structures by the catalyst is proposed.

Yb-Fiber-Laser-Pumped Ultrafast Frequency Conversion Sources From the Mid-Infrared to the Ultraviolet

We describe the development of versatile, practical, and high-power ultrafast optical sources based on second-order nonlinear frequency conversion in bulk materials pumped by the mode-locked Yb-fiber laser at 1064 nm, and covering spectral regions from the near- to mid-infrared (mid-IR) to the visible and ultraviolet (UV). By exploiting synchronously-pumped optical parametric oscillators (SPOPOs) based on quasi-phase-matched nonlinear materials of MgO:PPLN and MgO:sPPLT, in combination with internal and external single-pass harmonic generation in birefringent crystals of BiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and β-BaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , we have generated tunable picosecond pulses in spectral regions from above ~4 μm in the mid-IR, into the visible, and down to 317 nm in the UV. The demonstrated sources can deliver average output powers of up to 11.7 W in the near- to mid-IR, 3.5 W in the visible, and 30 mW in the UV, in picosecond pulses at ~80 MHz repetition rate, with high passive stability, excellent output characteristics, and the potential for further power scaling with increased fiber laser pump power. The described sources represent an effective approach for the extension of fiber laser technology across the entire wavelength range from the UV to mid-IR spectrum, and ultimately the THz spectral range.

Yb-Fiber-Laser-Pumped Continuous-Wave Frequency Conversion Sources from the Mid-Infrared to the Ultraviolet

We describe a wide range of versatile, practical and high-power sources of coherent continuous-wave (cw) radiation from the near- to mid-infrared (mid-IR) to the visible and ultraviolet (UV) developed in our laboratory by exploiting second-order nonlinear frequency conversion in novel quasi-phase-matched (QPM) and birefringent materials pumped by the Yb-fiber laser at 1064 nm. By exploiting optical parametric oscillators in combination with internal and external single-pass harmonic generation in QPM nonlinear materials of MgO:PPLN and MgO:sPPLT, and birefriengent crystal of BiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , we have generated stable, high-power cw radiation covering broad spectral regions from ~4 μm in the mid-IR, to 532 nm in the visible, down to 355 nm in the UV. The developed sources can deliver total output powers of up to 17.5 W in the near- to mid-IR, 13 W in the visible, and 68 mW in the UV, at exceptional efficiencies, with excellent passive stability, high spectral and spatial beam quality, in compact, portable and practical design. We also demonstrate successful realization of cw fiber-laser-pumped Ti:sapphire lasers enabled by the development of simplified high-power cw green sources at 532 nm. The described techniques represent a highly versatile, practical, and effective approach for the extension of fiber laser technology across the entire UV to mid-IR spectrum, and ultimately the THz spectral range, also offering the potential for further power scaling with the increase in the fiber laser pump power.

Effect of Mn&lt;sup&gt;2+&lt;/sup&gt; Additive on the Sinterability and Dielectric Properties of Ba&lt;sub&gt;0.55&lt;/sub&gt;Sr&lt;sub&gt;0.4&lt;/sub&gt;Ca&lt;sub&gt;0.05&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt;-MgO Composite Ceramics

Ba0.55Sr0.4Ca0.05TiO3-MgO (BSCTM) with Mn2+additive composite ceramics were prepared by the conventional solid state method with BaCO3, SrCO3, CaCO3, MgO and MnCO3as raw materials and B2O3and Li2CO3as sintering agent. The influence of the MnCO3additive on the sinterability and dielectric properties of BSCTM composite ceramics are investigated. The morphologies were analysized by scanning electron microscopy (SEM). The dielectric constant and dielectric loss of ceramics were measured by LCR meter at 1 kHz and 1 MHz. The temperature dependences of dielectric constant were measured by high-low temperature incubator tank and LCR meter at 1 MHz and a temperature range from-55 to 125 °C. The dielectric tunabilities were tested by C-T-V converter and LCR meter at 1 MHz and room temperature (25 °C). SEM results showed that BSCTM ceramics became more compact with the increase of Mn2+content, because Mn2+helped to form more oxygen vacancies for accelerating densification process. The addition of Mn2+largely reduced the dielectric loss while had little effect on dielectric constant. The dielectric constant and dielectric loss of 0.5mol% Mn2+doped BSCTM ceramics were 222 and 0.001, respectively. The dielectric tunability increased at first and then decreased with the increase of Mn2+content. The tunability of 0.5mol% Mn2+doped BSCTM ceramics were 4.04% under a DC electric field of 8.2 kV/cm.