Fourier-transform infrared and X-ray diffraction analyses of the hydration reaction of pure magnesium oxide and chemically modified magnesium oxide

Inhibition of Reaction Layer Formation on MgO(100) by Doping with Trace Amounts of Iron

Despite extensive research on MgO's reactivity in the presence of CO2 under various conditions, little is known about whether impurities incorporated into the solid, such as iron, enhance or impede hydroxylation and carbonation reactions. The purity of the MgO required for the successful implementation of MgO looping as a direct air capture technology affects the deployment costs. With this motivation, we tested how incorporated iron impacts MgO (100) reactivity and passivation layer formation under ambient conditions by using atomic force microscopy, electron microscopy, and synchrotron-based X-ray scattering. Based on electron microprobe analysis, our MgO samples were 0.5 wt % iron, and Mössbauer spectroscopy results indicated that 70% of the iron is present as Fe(II). We find that even these low levels of iron dopants impeded both the hydroxylation at various relative humidities (10%, 33%, 75%, and >95%) and carbonation in CO2 (33%, 75%, and >95%) on the (100) surface. Crystalline reaction products were formed. Reaction layers on the sample were easily removed by exposing the sample to deionized water for 2 min. Overall, our findings demonstrate that the presence of iron dopants slows the reaction rate of MgO, indicating that MgO without incorporated iron is preferable for mineral looping applications.

Conjugation of PDLA onto MgO microspheres: comparison between solution grafting and melt grafting methods

Magnesium oxide (MgO) is known for its bioactivity and osteoconductivity when incorporated into biodegradable poly(lactic acid) (PLA), whereas the weak interfacial bonding between MgO microspheres (mMPs) and PLA often leads to suboptimal composite properties with uncontrollable functionality. Conjugation of mMPs with PLA may offer a good way to enhance their compatibility. In this study, we systematically investigated two grafting techniques, solution grafting (Sol) and melt grafting (Mel), to decorate poly (D-lactic acid) (PDLA) on mMPs pre-treated by prioritized hydration to obtain Sol MPs and Mel MPs, in order to optimize the grafting efficiency and improve their controllability in the properties including the crystal structure and surface morphology. Meanwhile, the Sol method showed an improved grafting ratio (2.9 times higher) compared to the Mel method. The conjugation of mMPs with PDLA effectively neutralized the rapid pH increase during the degradation of pure mMPs, which could be used for sustainable delivery of the Mg2+ ions. Moreover, the Sol MPs exhibited the lowest degradation rate constant, which could be well fitted by the first-order dynamic model, suggesting a transformation of the mMP degradation mode from bulk degradation to surface degradation. This change in the biodegradation mode was beneficial for decreasing the over-basic effect caused by the quick degradation of pure mMPs, thus extending their application in the development of PDLA/MgO composites towards tissue engineering or regenerative medicine.

Magnesium-Impregnated Membrane Promotes Bone Regeneration in Rat Skull Defect by N-Linked Glycosylation of SPARC via MagT1

Autograft has long been the gold standard for various bone surgeries. Nevertheless, the increasing usage of synthetic implants is taking over the operation rooms due to biosafety and standardized protocols. To fulfill such tremendous needs, a magnesium-impregnated membrane is devised that steadily releases magnesium ions to stimulate osteogenesis. The compatibility of Magnesium oxide (MgO) particles is enhanced through hydration and grafting, characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). With detailed degradation profiles, an in-depth investigation of Magnesium transporter 1 (MagT1) for magnesium intake is carried out and engaging in the N-linked glycosylation by using RNAi and inhibitors. The glycosylation of secreted protein acidic and rich in cysteine (SPARC) affected extracellular secretion and mineral deposition, demonstrated by immunostaining and density-dependent color-SEM (DDC-SEM). Skull defects are treated by implanting magnesium-impregnated membranes in rats and evaluated them by micro-CT and histological exams. This study revealed the compatible integration of grafted magnesium hydroxide (g-MH) particles is the key to functional performance and critical to applicability in vivo; meanwhile, it opens the door to a biological rationale for designing biomimetic materials.

Advancing Chlorophyll Photostability: Dual Physicochemical Protection via Ce-Doped Hydrotalcite Organic-Inorganic Hybrid Pigments

In pursuit of enhancing the photostability of chlorophyll, a novel organic-inorganic hybrid pigment has been synthesized via a supramolecular intercalation assembly method, incorporating cerium-ion-doped hydrotalcite as the host matrix and chlorophyll as the intercalated guest molecule. This innovative pigment amalgamates the vivid coloration properties of organic dyes with the robust stability characteristic of inorganic substances. Determined from the detailed investigation of the structural evolution of chlorophyll during photodegradation, the dual physicochemical protection mechanism is critical to the advancement of chlorophyll photostability. It leverages the oxygen barrier attributes of the hydrotalcite's laminate structure and the ultraviolet light absorption and scattering capabilities of CeO2 nanoparticles formed in situ. Furthermore, Ce-doping introduces a redox cycle between Ce4+ and Ce3+ ions, which serves as a chemical defense by neutralizing reactive oxygen species that emerge during chlorophyll degradation. This multifaceted approach results in a substantial enhancement of photostability, with the hybrid pigment containing 0.3 Ce doped content, demonstrating a mere 5.90% alteration in reflectance at the 635 nm peak after 250 h of UV-accelerated aging. This breakthrough provides a dual physicochemical protective strategy that not only significantly prolongs the lifespan of chlorophyll pigments but also holds potential for broadening their application scope in various industries, including plastics and coatings, where color fastness and durability are paramount.

Dynamic structural evolution of MgO-supported palladium catalysts: from metal to metal oxide nanoparticles to surface then subsurface atomically dispersed cations

Supported noble metal catalysts, ubiquitous in chemical technology, often undergo dynamic transformations between reduced and oxidized states-which influence the metal nuclearities, oxidation states, and catalytic properties. In this investigation, we report the results of in situ X-ray absorption spectroscopy, scanning transmission electron microscopy, and other physical characterization techniques, bolstered by density functional theory, to elucidate the structural transformations of a set of MgO-supported palladium catalysts under oxidative treatment conditions. As the calcination temperature increased, the as-synthesized supported metallic palladium nanoparticles underwent oxidation to form palladium oxides (at approximately 400 °C), which, at approximately 500 °C, were oxidatively fragmented to form mixtures of atomically dispersed palladium cations. The data indicate two distinct types of atomically dispersed species: palladium cations located at MgO steps and those embedded in the first subsurface layer of MgO. The former exhibit significantly higher (>500 times) catalytic activity for ethylene hydrogenation than the latter. The results pave the way for designing highly active and stable supported palladium hydrogenation catalysts with optimized metal utilization.

Reaction Layer Formation on MgO in the Presence of Humidity

Mineralization by MgO is an attractive potential strategy for direct air capture (DAC) of CO2 due to its tendency to form carbonate phases upon exposure to water and CO2. Hydration of MgO during this process is typically assumed to not be rate limiting, even at ambient temperatures. However, surface passivation by hydrated phases likely reduces the CO2 capture capacity. Here, we examine the initial hydration reactions that occur on MgO(100) surfaces to determine whether they could potentially impact CO2 uptake. We first used atomic force microscopy (AFM) to explore changes in reaction layers in water (pH = 6 and 12) and MgO-saturated solution (pH = 11) and found the reaction layers on MgO are heterogeneous and nonuniform. To determine how relative humidity (R.H.) affects reactivity, we reacted samples at room temperature in nominally dry N2 (∼11-12% R.H.) for up to 12 h, in humid (>95% R.H.) N2 for 5, 10, and 15 min, and in air at 33 and 75% R.H. for 8 days. X-ray reflectivity and electron microscopy analysis of the samples reveal that hydrated phases form rapidly upon exposure to humid air, but the growth of the hydrated reaction layer slows after its initial formation. Reaction layer thickness is strongly correlated with R.H., with denser reaction layers forming in 75% R.H. compared with 33% R.H. or nominally dry N2. The reaction layers are likely amorphous or poorly crystalline based on grazing incidence X-ray diffraction measurements. After exposure to 75% R.H. in air for 8 days, the reaction layer increases in density as compared to the sample reacted in humid N2 for 5-15 min. This may represent an initial step toward the crystallization of the reaction layer. Overall, high R.H. favors the formation of a hydrated, disordered layer on MgO. Based on our results, DAC in a location with a higher R.H. will be favorable, but growth may slow significantly from initial rates even on short timescales, presumably due to surface passivation.

First Principles Calculation of Adsorption of Water on MgO (100) Plane

The hydration reaction seriously affects the quality and performance of MgO-based products. The final analysis showed that the problem is the surface hydration of MgO. By studying the adsorption and reaction of water molecules on the surface of MgO, we can understand the nature of the problem from the root cause. In this paper, first-principles calculations are performed on the crystal plane of MgO (100) to study the influence of the different orientation, sites and coverage of water molecules on the surface adsorption. The results show that the adsorption sites and orientations of monomolecular water has no effect on the adsorption energy and adsorption configuration. The adsorption of monomolecular water is unstable, with almost no charge transfer, belonging to the physical adsorption, which implies that the adsorption of monomolecular water on MgO (100) plane will not lead to the dissociation of water molecule. When the coverage of water molecules exceeds 1, water molecules will dissociate, and the population value between Mg and O_s-H will increase, leading to the formation of ionic bond. The density of states of O p orbital electrons changes greatly, which plays an important role in surface dissociation and stabilization.

A First-Principles Study on the Hydration Behavior of (MgO)n Clusters and the Effect Mechanism of Anti-Hydration Agents

Magnesia-based refractory is widely used in high-temperature industries; its easy hydration is, however, a key concern in refractory processing. Understanding the hydration mechanism of MgO will help in solving its hydration problem. Herein, the hydration behavior of (MgO)n (n = 1–6) at the molecular level and the effect mechanisms of several anti-hydration agents on the hydration of (MgO)4 were investigated with first-principles calculations. The results indicated that the following: (1) The smaller the (MgO)n cluster size, the more favorable the hydration of MgO and the tendency to convert into Mg(OH)2 crystal; (2) Anti-hydration agents can coordinate with the unsaturated Mg atom of (MgO)4 to form a bond, increasing the coordination number of Mg, thus reducing its activity when reacting with H2O; (3) The greater the number of −COOH groups and the longer the chain length in the anti-hydration agents, the better its effect of inhibiting the hydration of MgO. These findings could enhance the understanding of the mechanism of hydration of MgO and provide theoretical guidance for the design of novel anti-hydration agents.

Hydration of LiOH and LiCl-Near-Infrared Spectroscopic Analysis

The hydration behavior of LiOH, LiOH·H2O, and LiCl was observed by near-infrared (NIR) spectroscopy. Anhydrous LiOH showed two absorption bands at 7340 and 7171 cm-1. These NIR bands were assigned to the first overtone of surface hydroxyls and interlayer hydroxyls of LiOH, respectively. LiOH·H2O showed two absorption bands at 7137 and 6970 cm-1. These NIR bands were assigned to the first overtone of interlayer hydroxyls and H2O molecules coordinated with Li+, respectively. The interlayer OH- and the coordinated H2O of LiOH·H2O were not modified even when the LiOH·H2O was exposed to air. In contrast, anhydrous LiOH was slowly hydrated for several hours, to form LiOH·H2O under ambient conditions (RH 60%). Kinetic analysis showed that the hydration of the interlayer OH- of LiOH proceeded as a second-order reaction, indicating the formation of intermediate species-[Li(H2O) x (OH)4]3- (x = 1 or 2). However, the hydration of the LiOH surface did not follow a second-order reaction because the chemisorption of H2O molecules onto the defect sites of the LiOH surface does not need to crossover the energy barrier. Furthermore, we succeeded in observing the hydration of deliquescent LiCl, including the formation of LiCl solution for several minutes by NIR spectroscopy.