Pristine MgO Research Articles

Effect of calcination temperature on structural, morphological elastic and electrical properties of MgO nanoparticles synthesized by combustion method

This study explores the influence of calcination temperature on the properties of MgO nanoparticles (MgO NPs) synthesized via the solution combustion method. Through X-ray diffraction (XRD) and scanning electron microscopy (SEM), structural and morphological changes were investigated. Elastic and dielectric properties were analyzed using computational tools and impedance spectroscopy. Results show that the prepared nanomaterial is belongs to a cubic system and a space group of F m −3 m. Increasing in the calcination temperature (550 °C and 750 °C) enhances crystallinity, reduces defects, and improves structural uniformity. Elastic properties exhibit notable improvements, with Young's modulus increasing from 356.43 GPa for pristine MgO to 364.6 GPa for MgO calcined at 750 °C. Dielectric studies were conducted in the frequency range from 50 to 5 MHz at room temperature. Dielectric analysis reveals enhanced properties, including increased dielectric constant and AC conductivity with rising temperature. The study emphasizes the pivotal role of calcination temperature in tailoring MgO NPs for diverse applications.

Site dependent strategy for B/C/N homo and heteroatom co-doping in governing the optoelectronic behavior of MgO monolayers

Density functional theory calculations are carried out to investigate the effects of homo- and hetero-type co-doping of B, C and N on structural and electronic properties of MgO monolayers (MLs). The co-doping sites considered here are the possible equivalent and non-equivalent positions of a hexagon in a pristine MgO ML. The planarity of the monolayers is found to be governed by the site selectivity of the dopant atoms as well as the positions of doping. Planar monolayers have a higher likelihood of formation than the non-planar monolayers. In case of non-equivalent doping, the doping atoms always prefer positions that are closer. Stepwise substitution is more likely to occur than simultaneous substitution in formation of the co-doped monolayers. Most of the co-doping combinations introduce magnetism to the pristine MgO ML. Hetero-type monolayers prefer to be in magnetic states and even exhibit higher magnetic moments than homo-type MLs, with a maximum value of 4 μB for B–N co-doping. Almost all the monolayers are semiconducting with significantly reduced band gaps, while few hetero-type monolayers are metallic in nature. The electronic energy band gaps of the monolayers are compatible with the IR and visible regions of the electromagnetic spectrum. The overall tuning of the electronic properties renders the co-doped MgO monolayers effective for applications in spintronics and optoelectronics.

Site selective behaviour of B, C and N doping in MgO monolayers towards spintronic and optoelectronic applications

The electronic, magnetic and optical properties of graphene-like MgO monolayers doped with B, C and N atoms in both Mg and O sites are investigated in the framework of density functional theory. The impurity atoms induce magnetism in the host material irrespective of the sites of substitution. The HSE based hybrid DFT calculations show that the wide electronic band gap semiconducting pristine MgO monolayer becomes metallic due to B and C doping in the Mg site of MgO monolayer system (BMg and CMg). However, rests of the doped monolayers remain semiconducting with appearance of impurity states that lowers their energy band gaps compared to the pristine value. Accordingly, the optical behaviour of the doped systems get tuned making them optically active for a wide spectral range in electromagnetic spectrum starting from infrared to UV region. Therefore, such site selective modulation of electronic and optical properties achieved through substitutional doping in MgO monolayers may be effective for desirable moulding of these materials for spintronic and optoelectronic applications.

Magnetic Properties of C-Implanted and P-Implanted MgO Single Crystal: A Comparative Experimental and First-Principle Study

The magnetic properties were investigated for C- and P-implanted MgO single crystals, which were irradiated by 80 keV C and P ions with the dose of 3 × 1017 ions/cm2. The magnetic properties of pristine MgO were apparently changed by C and P ion implantation. Room temperature ferromagnetism was presented in the C-implanted sample, while the P-implanted sample only displayed paramagnetism at 20 K. For the purpose of clarifying the correlation between the magnetic properties and microstructure, a comparative study was carried out using experimental and theoretical methods in both C and P ion-implanted samples. The defect types were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence, and absorption spectrum. The existence of intrinsic (Mg vacancies, O vacancies) and extrinsic (C-related and P-related) defects were verified by the experimental results. The magnetic properties induced by various single and composite defects were studied by first-principle calculations. The calculation results indicated that the configuration of VMg (Mg vacancy) + CO (C substitute O defect) was a key factor for the inducing ferromagnetic properties in C-implanted MgO. For the case of the P-implanted MgO, the configuration of P-related defects and intrinsic vacancies can only contribute to the total moment value but cannot induce ferromagnetism.

Theoretical study on the cluster–surface interaction: The case of subnanometer Pt–Re clusters supported on MgO(100)

Bimetallic clusters in gas phase display novel physicochemical properties that are different from those present in their pure metal analogs. When bimetallic clusters are deposited on a substrate, such properties may change depending on the type and strength of the metal–support interaction. Here, we report a theoretical study, based on density functional theory (DFT), for sub-nanometer clusters of Pt–Re on the pristine MgO(100) surface, using the Basin-Hopping DFT algorithm to find the global minima. Then, their structural, energetic, electronic, and vibrational properties are calculated, and a comparison between gas- and supported-phase behavior is performed. It is obtained that the MgO(100) surface has a more relevant effect on the structural and vibrational properties of the Pt–Re bimetallic clusters and pure Pt clusters. For example, the metal–metal bond lengths of the supported clusters increase with respect to those observed in gas phase, also giving rise to red shifts in the corresponding vibrational frequencies. On the other hand, the structural and vibrational properties of pure gas- and supported-phase Re clusters are quite similar. These results are consistent with the adsorption energy calculations indicating a strong interaction between Pt–Re clusters and pure Pt clusters with the MgO(100) surface. Moreover, the metal–support interaction leads to a charge transfer from the metal oxide to the metal clusters and to the hybridization of the d- and s-states of the metal atoms with the p-states of the oxygen atoms present in the substrate. This work contributes to the understanding of the role of the support in bimetallic Pt–Re clusters on metal oxides, which would be of potential interest in the design of novel nanocatalysts.

Photocatalytic water splitting ability of Fe/MgO-rGO nanocomposites towards hydrogen evolution

Photocatalytic water splitting has greatly stimulated as an ideal technique for producing hydrogen (H2) fuel by employing two renewable sources, i.e., water and solar energy. Here, we have adopted a facile hydrothermal approach for the successful synthesis of reduced graphene oxide (rGO) incorporated Fe/MgO nanocomposites followed by thermal treatment at inert atmosphere to investigate their ability for photodegradation and photocatalytic hydrogen evolution via water splitting. Transmission Electron Microscopy images of Fe/MgO-rGO nanocomposite ensured the distribution of Fe/MgO nanoparticles throughout rGO sheets. Notably, all rGO supported nanocomposites, especially the one, thermally treated at 500 °C at Argon (Ar) atmosphere has demonstrated significantly higher photocatalytic efficiency towards the photodegradation of a toxic textile dye, rhodamine B, than pristine MgO and commercially available Degussa P25 titania nanoparticles as well as other composites. Under solar irradiation, Fe/MgO-rGO (500) nanocomposite exhibited 86% degradation of rhodamine B dye and generated almost four times higher H2 via photocatalytic water splitting compared to commercially available P25 titania nanoparticles. This promising photocatalytic ability of the Fe/MgO-rGO(500) nanocomposite can be attributed to the improved morphological and surface features due to heat treatment at inert atmosphere as well as escalated charge carrier separation with increased light absorption capacity imputed to rGO incorporation.

In vitro antibacterial response of ZnO‐MgO nanocomposites at various compositions

AbstractZnO‐MgO nanocomposites were prepared by a co‐precipitation method and afterward compared with pristine ZnO and MgO accordingly. XRD and EDX spectra were used to confirm the crystal structure and crystallite size of these materials. X‐ray diffraction analysis shows that antibacterial activity of ZnO:MgO composite enhances with crystallite size reduction ~1.34 times in comparison to pristine ZnO or MgO specimens, accompanied by domination of defect generation over defect annihilation activity. Besides, average particle sizes also reduce to ~2 times at 1:3 MgO/ZnO composite in comparison to MgO. The particle size of ZnO was substantially higher due to rod‐like morphology. Moreover, the minimum inhibitory concentration outcomes also show that ZnO‐MgO composites are more effective against gram‐negative pathogens in appropriate ratios (ZnO:MgO) of 1:3 and 3:1 with the concentration of 15,000 µg/ml. Similarly, gram‐positive pathogens were In contrast, ZnO and MgO separately or in 1:1 composite ratio does not prove considerably effective on all the five microbes (required higher >25,000 µg/ml) MIC to counter gram‐negative pathogens. Additionally, lower doses of 3ZnO:1MgO and 1ZnO:3MgO ~5000 µg/ml composite nanoparticles are effective on gram‐positive pathogens. Similarly, 3ZnO:1MgO composition proved highly productive at a much lower concentration, that is, 12500 ≤ X ≤ 15000 to counter gram‐negative pathogens. Besides, 1ZnO:3MgO is effective against gram‐negativepathogens at MIC ranging from 12500 ≤ X ≤ 15000 µg/ml.

Adsorption of SO2 on pristine and defective single-walled MgO nanotubes: a dispersion-corrected density-functional theory (DFT-D) study

The dispersion-corrected density functional theory (DFT-D) has been used to study the interactions of SO2 on the pristine and defective single-walled MgO nanotubes (MgONTs). A geometric optimization was performed for MgONTs and adsorbents/MgONTs. The adsorption energies of SO2 molecules at different layers of MgONTs were considered. The adsorption property of SO2 was analyzed in terms of the adsorption energy, the electron donation (basicity), and the atomic charges on the adsorbed materials. The densities of states (DOS) have been calculated and used for examining the adsorption properties. In addition, the presence of vacancy defects increases the adsorption energies of the SO2molecules. The band gaps of the defective MgONTs are sensitive to SO2 molecules.

Hybrid Functional Study of H-Abstraction from Methane by Li-Doped, Pristine and Stepped MgO(100) and MgO(110) Surfaces

Hydrogen abstraction from CH4 to MgO is a key step in the oxidative coupling of methane. We investigated CH4 activation on Li-doped MgO, MgO(110), and stepped MgO with the density functional theory. Our calculations with hybrid functionals revealed that MgO(110) and stepped MgO are strong candidate as the active site.

Catalytic Dehydration of 1,4‐Butanediol over Mg−Yb Binary Oxides and the Mechanism Study

AbstractIn this study, Mg−Yb binary oxides were synthesized using different MgO concentrations and investigated for the catalytic dehydration of 1,4‐butanediol (BDO) into 3‐buten‐1‐ol (BTO). The physicochemical properties of the catalysts were characterized by N2 physisorption, X‐ray diffraction, Raman spectroscopy, temperature‐programmed techniques, and diffuse reflectance infrared Fourier transform spectroscopy. The Mg−Yb binary oxides exhibited superior catalytic activity and better BTO selectivity compared with the pristine Yb2O3 or MgO. Structures of Mg−O−Yb were generated in the binary oxides via the interchange of Yb or Mg in the MgO or Yb2O3 crystalline phases. Extra basic and acidic sites were formed over the Mg−Yb binary oxides because of the formation of surface defects and the presence of Mg−O−Yb structures, respectively. The acidic as well as basic sites were observed to influence the catalytic performance: BDO reactivity was enhanced by the more acidic sites, while BTO selectivity was favored by the basic sites. The highest BTO yield of 71.1 % was achieved over the Mg7Yb3 catalyst with 90.4 % BDO conversion and 78.6 % BTO selectivity at 350 °C. The in situ DRIFTS results indicated that BDO was first adsorbed on the catalyst and then reacted with the acidic sites to generate butoxides. The β‐H of the surface butoxides was abstracted by the basic oxygen anions to produce aldehyde species, which dissociated to form BTO.

What Is the Active Site for the Oxidative Coupling of Methane Catalyzed by MgO? A Metadynamics-Biased Ab Initio Molecular Dynamics Study

MgO is the best-known catalyst for oxidative coupling of methane (OCM). However, the correlation between the surface characteristics and CH4 activation, the initial step of the OCM process, has not yet been fully understood. In this study, we investigated the mechanism of the CH4 activation step in the OCM on MgO(100), MgO(110), stepped MgO(100), and Li-doped MgO(100) using metadynamics-biased ab initio molecular dynamics calculations. Calculated free-energy surfaces for C–H dissociation indicated that the most stable MgO(100) surface is less active in the C–H dissociation, while the MgO(110), stepped MgO(100), and Li-doped MgO(100) surfaces become more active. The pristine MgO(110) and stepped MgO(100) surfaces showed heterolytic C–H dissociation with H adsorption to surface oxygen and CH3– moiety adsorption on the Mg site, although the reaction energies seem high. On the other hand, homolytic C–H dissociation happens on Li-doped MgO where an H atom adsorbs on O next to the doped Li, leaving CH3 radicals in the gas phase. The present results demonstrated that two representative CH4 activation catalysts, stepped MgO and Li-doped MgO, have two different mechanisms of CH4 activation, the latter of which is energetically more preferable and suitable for efficient OCM.

O2 activation by AuAg clusters on a defective (100)MgO surface

In the present work, we discuss the electronic properties of supported dispersed bimetallic clusters with respect to their size, geometry, and Aun/Agm (n + m = 6) composition. We have studied with supercell-density functional theory calculations the role of the charge transfer from the MgO defective support toward the cluster in the activation of O2 by AunAgm clusters. We first considered gas-phase clusters with different atomic compositions; then, we deposited all of them on a pristine (100)MgO surface and finally on a more realistic (100)MgO F-center. We performed a global and unrestricted search of the (cluster + surface) geometry. The Mexican enhanced genetic algorithm has been used to exhaustively explore the potential energy surface. Our results show that O2 activation depends on the Aun/Agm ratio. It has been found that both metals involved play different and important roles toward (a) the actual O2 dissociation and (b) weakening of the oxygen-cluster bond, which, in turn, may promote the possibility of a catalytic process to take place, such as the oxidation process of CO and NOx among others.

Nucleation and growth of water ice on oxide surfaces: the influence of a precursor to water dissociation.

We have investigated how nucleation and growth processes of ice are influenced by interfacial molecular interactions on some oxide surfaces, such as rutile TiO2(110), TiO2(100), MgO(100), and Al2O3(0001), based on the diffraction patterns of electrons transmitted through ice crystallites under the experimental configuration of reflection high energy electron diffraction (RHEED). The cubic ice Ic grows on the TiO2(110) surface with the epitaxial relationship of (110)Ic//(110)TiO2 and [001]Ic//[11[combining macron]0]TiO2. The epitaxial ice growth tends to be disturbed on the TiO2(110) surface under the presence of oxygen vacancies and adatoms. The result is not simply ascribable to small misfit values between TiO2 and ice Ic lattices (∼2%) because ice grains are formed randomly on TiO2(100). No template effects are identified during ice nucleation on the pristine MgO(100) and Al2O3(0001) surfaces either. The water molecules are chemisorbed weakly on these surfaces as a precursor to dissociation via the acid-base interaction. Such anchored water species act as an inhibitor of epitaxial ice growth because the orientation flexibility of physisorbed water during nucleation is hampered at the interface by the preferential formation of hydrogen bonds.

Ammonia-treated metal oxides as base catalysts for selective isomerization of glucose in water

Various metal oxides (MgO, Al2O3, SiO2, TiO2, ZrO2, Nb2O5, and CeO2) were treated with NH3 for incorporating nitrogen into the structure of metal oxides. The pristine and NH3-treated metal oxides were used as solid base catalysts for isomerization of glucose to f7ructose in water. SiO2 and Nb2O5 showed a large increment of nitrogen content by the treatment with NH3. FT-IR study on NH3-treated SiO2 revealed that NH3 reacted with terminal silanol groups and siloxane bonds to form Si-NH2 and Si-NH-Si groups. Meanwhile, nitrogen was incorporated into bulk crystal of Nb2O5, causing amorphization of the crystal. Of all the samples, pristine and NH3-treated MgO showed highest catalytic activity for the isomerization of glucose. However, the selectivity to fructose was low due to subsequent reactions of formed fructose. Catalytic activity of Al2O3 and SiO2 was increased by the treatment with NH3, while that of the other metal oxides was not affected. Particularly, the catalytic activity of SiO2 emerged after the treatment with NH3 and was enhanced by increasing the temperature for the treatment up to 800 °C. While fructose was consumed by subsequent reactions over MgO, decreasing the selectivity, such reactions of fructose were not noticeable over NH3-treated SiO2. Consequently, NH3-treated SiO2 showed higher selectivity to fructose and gave higher carbon balance than MgO.

Homolytic cleavage of water on magnesia film promoted by interfacial oxide−metal nanocomposite

The atomic−scale insights into the interaction of water with oxide surface are essential for elucidating the mechanism of physiochemical processes in various scientific and practical fields, since the water is ubiquitous and coats multifarious material surface under ambient conditions. By utilizing van der Waals density functional calculations, herein we report for the first time the energetically and dynamically favorable homolytic dissociative adsorption behavior of water over MgO(001) films deposited on metal substrate. The water adsorption on pristine MgO(001) is quite weak and the heterolytic dissociation is the only fragmentation pathway, which is highly endothermic with large activation barrier of 1.167 eV. The binding strengths for the molecular and dissociative adsorption configurations of water on MgO/Mo(001) are significantly larger than corresponding configurations on bare MgO(001). The homolytic dissociative adsorption energy of water on monolayer oxide is calculated to be −1.231 eV, which is even larger than all the heterolytic dissociative adsorption states. The homolytic dissociative adsorption structure could be obtained by transformation reaction from heterolytic dissociative adsorption structure, presenting activation barriers 0.733, 1.103, 1.306, 1.571, and 1.849 eV for reactions on 1–5 ML films. With the increase of the oxide thickness, the homolytic dissociative adsorption energy decreases promptly, indicating the nanoscale of oxide film play a crucial role during water splitting. Ab initio molecular dynamics (AIMD) simulations were performed to confirm the stability of the ultrathin oxide films and the homolytic fragmentation configuration of water on the hybrid surface. Electronic properties are characterized to interpret the enhancement of chemical reactivity and properties of insulating oxide toward homolytic fragmentation of water.

Aldol Condensation of Cyclopentanone on Hydrophobized MgO. Promotional Role of Water and Changes in the Rate-Limiting Step upon Organosilane Functionalization

Aldol condensation is a key C—C coupling reaction for upgrading of biomass-derived oxygenates to fuels and chemicals. Here, we investigate the effects of added water on the condensation of cyclopentanone (CPO) on hydrophobized MgO catalysts. We have found that the role of water strongly depends on the degree of hydrophobic functionalization of the MgO surface. That is, on a nonfunctionalized (hydrophilic) high-surface-area MgO catalyst, the rate decreases with the addition of water, mostly due to active site blockage. By contrast, on MgO hydrophobized via silylation with octadecyltrichlorosilane (OTS), the rate actually increases with added water. A concomitant change in kinetics is observed from the pristine (hydrophilic) MgO to the hydrophobized sample. Specifically, on the hydrophilic sample, the reaction is first-order, as expected if the rate-limiting step is the formation of an enolate intermediate via α-H abstraction at a basic site, as widely reported in previous literature. By contrast, on the hy...

Controlling the porosity and crystallinity of MgO catalysts by addition of surfactant in the sol-gel synthesis

Abstract This study presents an easy route to induce pore formation, increase the specific surface area and control the crystallite size of magnesium oxides obtained using the sol-gel method with addition of Pluronic P123 surfactant. The structural characteristics of the materials were evaluated using X-ray diffraction, N2 physisorption isotherms, mercury intrusion porosimetry, scanning electron microscopy and CO2 temperature programmed desorption. The catalytic properties were assessed using the Knoevenagel condensation reaction. The results showed a systematic decrease of the magnesium oxide crystallinity with increased concentration of the surfactant used in the synthesis. This was associated with increase of the magnesium oxide BET area from 2 m2/g to over 50 m2/g, as well as the formation of pores in the macropore region, as confirmed by microscopy images. In addition, the surface modification resulted in CO2 chemisorption increasing from 378 μmol/g, for the pristine MgO sample, to 1529 μmol/g, for the porous sample, accompanied by an increase in the concentration of strong basic sites. The most porous sample presented the highest catalytic activity in the Knoevenagel condensation reaction.

Steering reduction and decomposition of peroxide compounds by interface interactions between MgO thin film and transition-metal support

The detection, removal and reduction of hydrogen peroxide and organic peroxides is of significant importance for its increasing application in the areas of environment, food, electrochemistry and clinical laboratory. Herein the dissociative adsorption behavior of H2O2 and organic peroxides on ultrathin magnesia (0 0 1) films deposited on transition metal is uncovered for the first time by employing periodic density-functional theory calculations with van der Waals corrections. Splitting of H2O2 on bulk MgO(0 0 1) is highly endothermic process with activation barrier 1.85 eV, indicating it is extraordinarily difficult to dissociate H2O2 on pristine MgO(0 0 1). The H2O2 is dissociated smoothly and reduced to surface hydroxyls on MgO(0 0 1)/TM, and the dissociative adsorption energies of all the considered fragmentation configurations are substantially negative, demonstrating dissociation and reduction of H2O2 is thermodynamically favorable. The mechanism of reactivity enhancement for energetically and dynamically favorable decomposition of H2O2 on supported magnesia is elucidated by characterizing the geometric structures and electronic properties. The fragmentation and reduction of diethyl peroxide and peroxyacetone are also studied to reveal the catalytic activity of ultrathin magnesia toward splitting organic peroxides. The results are wished to provide useful clue for detecting and reducing hydrogen peroxide and organic peroxides by employing oxide-metal hybrid nanostructure.

Tuning the electronic and chemisorption properties of hexagonal MgO nanotubes by doping – Theoretical study

Oxide materials offer a wide range of interesting physical and chemical properties. Even more versatile behavior of oxides is seen at the nanoscale, qualifying these materials for a number of applications. In this study we used DFT calculations to investigate the physical and chemical properties of small hexagonal MgO nanotubes of different length. We analyzed the effect of Li, B, C, N, and F doping on the properties of the nanotubes. We find that all dopants favor the edge positions when incorporated into the nanotubes. Doping results in the net magnetization whose value depends on the type of the impurity. Using the CO molecule as a probe, we studied the adsorption properties of pristine and doped MgO nanotubes. Our results show that the dopant sites are also the centers of significantly altered chemical reactivity. While pristine MgO nanotubes adsorb CO weakly, very strong adsorption at the dopant sites (B-, C-, and N-doped nanotubes) or neighboring edge atoms (F- and Li-doped nanotubes) is observed. Our results suggest that impurity engineering in oxide materials can be a promising strategy for the development of novel materials with possible use as selective adsorbents or catalysts.

Nonlinear optical, IR and orbital properties of Ni doped MgO nanoclusters: A DFT investigation

Abstract In the present study, density functional theory calculations have been performed to explore the changes in the electronic properties of Mg12O12 nanocluster through exohedral doping with nickel. The changes in zero-point Energies (ΔZPE), thermal Energies (ΔE), thermal Enthalpies (ΔH), and thermal Free Energies (ΔG) of all positions are also calculated and compared with interaction energies. The HOMO-LUMO gaps of Ni-doped MgO nanocages are reduced significantly mainly due to the increase in the energies of HOMO. The Ni atom profoundly increases the polarizability (α) and first hyperpolarizabilities (βo) of MgO nanocluster however, a position dependent effect is observed. The value of α (and βo) changed from 219 (0.3) au for pristine MgO to 261 (1061), 263 (1122), and 262 (1240) au for positions P1, P2, and P3, respectively. These interesting results will be beneficial for the potential use of the MgO nanocluster in novel electronic and high-performance NLO materials.