Hollow MgO Research Articles

Preparation of hollow MgO nanosorbents via the templating method and study of their adsorption mechanism

The treatment of dye-containing wastewater has been a concern in recent years. Herein, we used laboratory-waste-skimmed cotton as a biotemplate and successfully synthesized MgO hollow tubular nanosorbents via a mild microwave solvent-thermal method. In adsorption experiments, the response surface methodology and Box–Behnken design were used to optimize and determine the optimal Mg(OAc)2 concentration (0.4 mol/L), skimmed cotton template mass (0.4 g), and calcination temperature for Congo red adsorption (600 °C). The adsorption process was comprehensively analyzed from thermodynamic and kinetic perspectives. Results showed that the adsorption process of MgO-urea template (MgO-UT) hollow nanosorbent conforms to the Dubinin–Radushkevich equation of the ion-exchange adsorption process and follows the pseudo-second-order kinetic model. The maximum amount of Congo red adsorbed by MgO-UT hollow nanosorbent is 3511.35 mg/g, demonstrating its excellent adsorption effect. Therefore, MgO hollow tubular nanosorbents prepared using biological templates can be used as novel organic dye adsorbents.

Co-axial electrospun hollow MgO nanofibers for efficient removal of fluoride ions from water

Porous and hollow metal oxide nanomaterials receive more attraction towards adsorption of various contaminates from water due to extremely high surface area. Co-axial electrospinning is an advance method to easily fabricate long length hollow nanotubes/nanofibers. Herein, hollow MgO nanofibers were synthesized using co-axial electrospinning method followed by post annealing. The co-axial electrospinning was performed by maintaining applied voltage (15 kV), needle tip to collector distance (12 cm) and flow rate of core and shell solutions (0.3 and 0.5 mL/h respectively). The formation, morphologies, bonding and surface area of the prepared nanofibers was analysed by XRD, FESEM, TEM and BET analytical techniques. The inner pore diameter of hollow MgO nanofibers was 32 nm. The surface area was found to be 527 m2/g which is much higher as compared to solid MgO nanofibers. The prepared hollow MgO nanofibers were used for the adsorption of fluoride ions from water. The effect of dose, contact time, pH and concentration were analysed. The fluoride adsorption process follows Pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of hollow MgO was found to be 294 mg/g which is almost three-time greater than that of solid MgO nanofibers (92 mg/g). All the co-existing ions have showed negligible effect on fluoride adsorption except CO32- and PO43- ions. The adsorption energy of fluoride adsorbed MgO was calculated. The adsorption energy is found to be − 6.9004 eV. The negative value of adsorption energy indicates the feasibility of adsorption process.

Synthesis of Ag nanoparticle-decorated MgO hollow spheres for enhancing photocatalytic activity

Ag nanoparticle-decorated MgO hollow spheres and MgO hollow spheres were fabricated by a facile hydrothermal method using Ag@carbon and carbon microspheres as templates, respectively. The obtained products were identified by several characterization techniques. The photocatalytic activities of the prepared samples were evaluated by degradation of RhB dye in an aqueous medium. After 120 min of UV illumination, above 98% of Rhodamine B was degraded in the presence of MgO/Ag hollow spheres, while only 48% is degraded within the same time using MgO hollow spheres. The higher specific surface area of MgO/Ag hollow spheres with respect to MgO hollow spheres along with its longer photogenerated charge carrier lifetime cause MgO/Ag hollow spheres to exhibit superior RhB dye photodegradation activity in comparison to MgO hollow spheres. The presence of Ag in MgO/Ag hollow spheres creates a Schottky junction between silver and magnesium oxide, resulting in efficient charge separation and enhancing the rate of photocatalytic reactions.

Efficient Treatment of Phenol Wastewater by Catalytic Ozonation over Micron-Sized Hollow MgO Rods.

Phenol is a nocuous water pollutant that threatens human health and the ecological environment. CoOx-doped micron-sized hollow MgO rods were prepared for the treatment of phenol wastewater by catalytic ozonation. Magnesium sources, precipitants, initial precursor concentration, Co/Mg molar ratio, and catalyst calcination temperature were optimized to obtain the best catalysts. Prepared catalysts were also well characterized by various methods to analyze their structure and physical and chemical properties. In this process, CoOx/MgO with the largest large surface area (151.3 m3/g) showed the best catalytic performance (100 and 79.8% of phenol and chemical oxygen demand (COD) removal ratio, respectively). The hydrolysis of CoOx/MgO plays a positive role in the degradation of phenol. The catalytic mechanism of the degradation of O3 to free radicals over catalysts has been investigated by in situ electronic paramagnetic resonance (EPR). The catalyst can be reused at least five times without any activity decline. The prepared CoOx/MgO catalyst also showed excellent catalytic performance for removal and degradation of ciprofloxacin, norfloxacin, and salicylic acid.

Facile Synthesis of Hollow MgO Spheres and Their Fluoride Adsorption Properties

In the present work, the hollow MgO spheres were synthesized through a facile wet-chemistry method. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrum are employed to characterize the as-prepared sample. Those results indicate that the average size of the as-prepared MgO hollow spheres is about 2 μm. Also, the MgO hollow spheres have the polycrystalline and porous structure, which would provide large specific surface area and plenty active sites for fluoride adsorption. The adsorption properties of the MgO hollow spheres towards fluoride are investigated. The fluoride adsorption kinetics of the MgO hollow spheres fits well the pseudo-second-order model. Also, the kinetic data revealed that the fluoride adsorption was rapid, more than 83% of fluoride could be removed within 40 min. The fluoride adsorption capacity of the hollow MgO spheres is larger than 182.4 mg/g at a pH of 7.0. The as-prepared products maintain excellent adsorption performance in the pH range of 3–11. In addition, the adsorption mechanism also has been discussed. From the FTIR results, a hydroxyl and carbonate coexchange mechanism is proposed. It is believed that the hollow MgO spheres are a potential candidate for fluoride removal.

Synthesis of hollow Al-doped MgO spheres via a sacrificial templating method for enhanced CO2 adsorption

This paper presented the effect of the concentration of Mg(NO3)2·6H2O solution and Al doping on the structure, morphology and CO2 adsorption performances of MgO spheres. MgO-based spheres were synthesized through a sacrificial templating method using glucose-derived carbon spheres as the template and Mg(NO3)2·6H2O and Al(NO3)3·9H2O as precursors, and characterized by SEM, XRD, TEM, N2 adsorption/desorption, FT-IR and particle size analysis, respectively. The results demonstrated that hollow MgO spheres were formed with multiple shells, and the concentration of Mg2+ affected the crystallite size and average particle size. With Al incorporation, the crystallite size and average particle size of Mg/Al-10 was obviously reduced, which further influenced alkaline adsorption active sites and internal diffusion of CO2 molecules. As such, the adsorption capacity of the Al-doped adsorbent was greatly improved, for the tiny MgO nanocrystals can provide many more alkaline adsorption active sites and thus significantly advancing CO2 adsorption, while the small average particle size can shorten the diffusion distance of CO2 and increase the contact between the adsorbent and CO2. This work provided the inspiration of MgO-based adsorbent for promoting CO2 adsorption.

Synthesis of hierarchical flower-shaped hollow MgO microspheres via ethylene-glycol-mediated process as a base heterogeneous catalyst for transesterification for biodiesel production

Hierarchical flower-shaped hollow MgO (f-MgO) spheres were synthesized through an ethylene-glycol-mediated polyol process via hydrothermal reactions. The structure of f-MgO originates from intermediate flower-shaped Mg glycolate through the Ostwald ripening process. The surface of f-MgO consists of uniform petal-like nanosheets that provide high surface area and excellent accessibility to catalytic sites. Also, the f-MgO microsphere can prevent aggregation and stacking problems of nanosheets and control a surface area for catalytic activity. The morphology and structure of f-MgO were investigated using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The density of basic catalytic sites was derived from CO2-temperature-programmed desorption measurements. The f-MgO exhibits a basic site density of 0.5134 mmol/g, which is much higher than that of commercial MgO (c-MgO, 0.0288 mmol/g). Experimental results for the fatty acid methyl ester revealed that the catalytic strength of f-MgO as a heterogeneous catalyst for biodiesel production is greater than that of c-MgO. The maximum biodiesel conversion efficiency of f-MgO from canola oil is 93.4%, which is greater than the value of 91.4% for c-MgO.

Facile synthesis of hollow mesoporous MgO nanospheres as ultra-high performance and reusable adsorbent

A facile approach for fabrication of hollow mesoporous MgO nanospheres (HMMN) has been demonstrated. The employed protocol involves the coating of carbon spheres template with MgO nanoparticles, followed by the calcination in presence of air to remove the carbon core at elevated temperature. Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) have been used to characterize the sample. Brunauer-Emmett-Teller (BET) method reveals the specific surface area and the average pore diameter of hollow spheres as 55.1 m2/g and 8.19 nm, respectively. The composite exhibits excellent adsorptive capacity toward Congo red (CR) at room temperature. The adsorption reaches equilibrium within 70 min with the maximum adsorption capacity of 5000 mg/g which is, to the best of our knowledge, the highest reported value. Additionally, the regeneration by calcination shows that adsorbent has high adsorption performance and superb reusability.

Synthesis of Hierarchical Flower-Shaped Hollow Mgo Microspheres Via Ethylene-Glycol-Mediated Process as a Base Heterogeneous Catalyst for Transesterification for Biodiesel Production

Synthesis of Hierarchical Flower-Shaped Hollow Mgo Microspheres Via Ethylene-Glycol-Mediated Process as a Base Heterogeneous Catalyst for Transesterification for Biodiesel Production

Facile synthesis of hollow mesoporous MgO spheres via spray-drying with improved adsorption capacity for Pb(II) and Cd(II).

Spherical-like MgO nanostructures have been synthesized efficiently via spray-drying combined with calcination using magnesium acetate as magnesium source. The products were characterized by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and the specific surface areas were calculated using the Brunauer-Emmett-Teller (BET) method. The obtained spherical-like MgO nanostructures exhibit uniform pore sizes (7.7nm) and high specific surface areas (180m2g-1). The adsorption kinetics and isotherm data agree well with pseudo-second-order model and Langmuir model, indicating the monolayer chemisorption of heavy metal ions. The spherical-like MgO nanostructures exhibited high adsorption performance for Pb(II) and Cd(II) ions, and the maximum adsorption capacities were up to 5214mgg-1 and 4187mgg-1, respectively. These values are much higher than those reported MgO-based adsorbents. Moreover, in less than 10min, Pb(II) and Cd(II) ions in solution can be almost removed, which means that the spherical-like MgO possesses a high adsorption rate. XRD and FTIR analysis revealed the adsorption mechanism of Pb(II) and Cd(II) ions on MgO, which was mainly due to hydroxyl functional groups and ion exchange between Mg and heavy metal ions on the surface of MgO. These favorable performances recommend that the synthesized spherical-like MgO nanostructures would be a potential adsorbent for rapid removal of heavy metal ions from wastewater.

Preparation and Characterization of Nanostructured Hollow MgO Spheres.

Nanostructured hollow MgO microspheres were prepared by the template method. First, D-Anhydrous glucose was polymerized by the hydrothermal method to form a template. Second, a colorless solution was obtained by mixing magnesite with hydrochloric acid in a 1:2 proportion and heating in an 80 °C water bath for 2 h. Finally, the template from the first step was placed in the colorless solution, and the resulting precipitate was calcined at 550 °C for 2 h. The phase composition and microstructure of the calcined samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results indicated that the main crystal is periclase. The SEM results indicates that the template carbon microsphere surface is smooth, and the its size is uniform and concentrated in the range of 100–200 nm. The diameters of the samples range from 60 to 90 nm, which is smaller than the size of the carbon microsphere. The TEM results indicates that the sample is hollow with a shell thickness of about 6–10 nm. The specific surface area of the calcined hollow sphere is 59.5 m²·g−1.

Comments on \u201dEvidence of the hydrogen release mechanism in bulk MgH2\u201d

The effect of an electron beam induced dehydrogenation of MgH2 in the transmission electron microscope (TEM) is largely underestimated by Nogita et al., and led the authors to a misinterpretation of their TEM observations. Firstly, the selected area diffraction (SAD) pattern is falsely interpreted. A re-evaluation of the SAD pattern reveals that no MgH2 is present in the sample, but that it rather consists of Mg and MgO only. Secondly, the transformation of the sample upon in-situ heating in the TEM cannot be ascribed to dehydrogenation, but is rather to be explained by the (nanoscale) Kirkendall effect, which leads to the formation of hollow MgO shells without any metallic Mg in their cores. Hence, the conclusions drawn from the TEM investigation are invalid, as the authors apparently have never studied MgH2.

Synthesis and Absorption Performance of Acrylic Ester and Hollow Fiber MgO Nanoparticle Resin Composite

ABSTRACTA new resin composite was prepared through traditional suspension polymerization and used as an adsorbent to remove oil from wastewater. Biomorphic hollow fiber MgO was prepared by template-directed synthesis using cotton as template first. Then the samples were characterized by X-ray diffraction, scanning electron microscope, and thermogravimetric differential thermal analysis. Kinetic characterization of the absorption process was also investigated. In addition, the composite showed excellent oil absorbency and could be reused for at least six times while keeping high oil absorbency.

Surfactant-driven direct synthesis of a hierarchical hollow MgO nanofiber–nanoparticle composite by electrospinning

A single step synthesis of hierarchical MgO nanoparticle–nanofiber composite using surfactant driven electrospinning.

Excellent fluoride removal properties of porous hollow MgO microspheres

Porous hollow MgO microspheres were synthesized and characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption isotherms. The removal properties of the MgO microspheres towards toxic fluoride were investigated, including adsorption kinetics, adsorption isotherms, and influences of pH and coexisting anions. The adsorption capacity was larger than 120 mg g−1 at a pH of 7.0. The effects of anions on fluoride removal were also investigated. The results indicated that phosphate was the greatest competitor of fluoride for adsorptive sites. In addition, the removal mechanism was revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The reaction of MgO and water molecules resulted in the formation of Mg(OH)2. The excellent adsorption properties towards fluoride resulted from the surface reaction between the generated Mg(OH)2 and fluoride in solution.

Microstructure and morphology changes in MgH2/expanded natural graphite pellets upon hydrogen cycling

Compacted mixtures based on ball-milled magnesium hydride (MgH2) have gained significant research interest as suitable materials for hydrogen storage tanks. The issue related to their stability during practical service conditions is one of paramount relevance. In this work, we investigate the microstructure and morphology of pellets obtained by the compaction of ball-milled MgH2/Nb2O5 powders mixed with expanded natural graphite. The pellets are subjected to repeated hydrogen sorption cycles to measure hydrogen storage properties and its stability with cycling. Moreover, the effect of air-exposure on the hydrogen sorption behavior is studied. Electron microscopy observations of as-prepared and cycled pellets point to a dramatic modification of the material's microstructure upon repeated hydrogen cycling. In particular, the appearance of MgH2 particles depleted of the Nb2O5 catalyst and the formation of hollow MgO shells are highlighted. These findings are discussed by a simple model which takes into account the basic mechanisms intervening during the metal-hydride transformation in the pellet.

Fabrication and formation mechanism of hollow MgO particles by pulsed excimer laserablation of Mg in liquid

We report on the formation of hollow MgO particles by excimer laserablation of bulk Mg in water and aqueous solutions of sodium dodecylsulfate (SDS) and sodium citrate (SC). Lamellar nanostructures ofMg(OH)2 also formed in water, but the formation could be avoided by the addition of SDS or SC.Laser ablation produced not only Mg species that were oxidized into MgO andMg(OH)2 in water, but also cavitation bubbles. The bubble interfaces trapped the MgO nanoparticlesto decrease the surface free energy of the system, finally resulting in hollow particles.

Formation and Stability of Hollow MgO Nanoshells

High temperature annealing of gas phase synthesized Mg nanoparticles surrounded by an MgO shell leads to formation of hollow MgO nanoshells due to the evaporation assisted Kirkendall effect. Under electron beam exposure in TEM, the (220) MgO facets reduce their high surface energy by forming cube facets, which is followed by nanoshell size reduction and collapse within a few minutes. However, in ambient conditions the nanoshells remain stable for significant periods of time and further degrade by becoming filled with carbon while lossing any MgO identity. Finally, in moderate low vacuum they remained stable for months indicating promise for applications.

Large scaled hexagonal prismatic sub-micro sized Mg crystals by a vapor–liquid–solid process

Large scaled hexagonal prismatic sub-micro sized Mg crystals were grown by a vapor-liquid-solid process, and found to be sensitive to electron beam irradiation in transmission electron microscope imaging, making hollow prismatic MgO boxes.

Hollow MgO Nanotube Arrays by Using ZnO Nanorods as Templates

AbstractA newly developed solid–gas chemical reaction route has been demonstrated to fabricate MgO nanotube arrays by using prefabricated ZnO nanorods as templates. The formation process involves the Kirkendall effect, in which the out‐diffusion of the ZnO core material through the MgO shells is faster than the in‐diffusion of the vapor‐phase Mg atoms, resulting in the formation of Kirkendall voids, which eventually induces hollow MgO nanotubes. The dimensions and sizes of the obtained MgO nanotubes can be controlled by employing suitable ZnO templates. Other types of complex hollow MgO architectures with different aspect ratios can be further manipulated and fabricated by this method, depending on the morphologies of the starting ZnO nanostructures used as templates. These hollow MgO architectures with high surface‐to‐volume ratios may have promising applications in catalysis, drug delivery, nano‐optics, nanoreactors, and active material encapsulation.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)