Al-O Bonds Research Articles

Study of ReaxFF molecular dynamics simulation about chemical reactions mechanisms of magnesium-aluminium spinel polishing

Chemical mechanical polishing (CMP) is the predominant method for finishing hard and brittle materials that are challenging to machine. We proposed replacing the soft polishing pads used in traditional CMP with hard ceramic plate to offer rigid support for polishing magnesia-alumina spinel (MgAl2O4) and to achieve better flatness. However, the chemical reaction mechanisms occurring during the process remain unclear. In this study, we employed ReaxFF molecular dynamics (MD) simulations to investigate the chemical reaction mechanisms between MgAl2O4 and the polishing slurries (ethylene glycol, ethylenediamine, hydrogen peroxide, water) during the polishing process. We found that reactions mostly involved –OH chemisorption. Ethylenediamine (C2H8N2) slurries had the lowest bond order of reactant cations (Ct) with −O and the highest ethylene glycol ((CH2OH)2) Ct-O bonds. Al-O bonds were more common than Mg-O bonds in all slurries. C2H8N2 slurry had the lowest bond energies, aiding material removal. Higher slurry concentrations increased reactant bonding and lowered bond energy, with polishing pressure having minimal effect. Our results clarify the atomic-level chemical mechanisms of MgAl2O4 polishing. This provides a valuable approach for designing chemically reactive polishing slurries and offers theoretical support for the efficient removal of MgAl2O4 materials.

Research on leaching kinetics and reactivity evaluation of copper tailings as precursor for alkali-activated materials

Copper tailings are by-products of copper mining, and because of their rich content of SiO2 and Al2O3, it is considered as a possible raw material for the preparation of geopolymer composites. In this paper, the leaching kinetics and reactivity of reactive elements Si and Al in copper tailings under alkali hydrothermal environment are investigated, and the reasons for the difference in reactivity between copper tailings and granulated blast furnace slag (GBFS), fly ash (FA) are also introduced. The results show that the leached Si and Al in the precursor materials are involved in the formation of N/C-A-S-H. Similar to FA and GBFS, the leaching behavior of reactive elements in copper tailings is mainly controlled by the diffusion behavior through the surface product layer. Additionally, the activation energy of Al in the precursor materials is lower than that of Si, which makes the Al-O bond easier to break in alkaline environment, thus causing the leaching rate of Al in the raw materials to be higher than that of Si. Meanwhile, the activation energies of Si and Al in copper tailings are 69.29kJ/mol and 33.91kJ/mol, respectively, and higher elemental activation energy makes the efficiency of elemental dissolution lower, which is also the main reason for the lower reactivity of copper tailings. This study aims to elucidate the interrelationships between physicochemical properties, leaching behavior and reactivity of copper tailings.

Frustrated Lewis Pairs from Al-E{14} Bonds (E{14}=Ge, Sn, Pb).

The potassium aluminyl K[Al(NON)] ([NON]2-=[O(SiMe2NDipp)2]2-, Dipp=2,6-iPr2C6H3) reacts with group 14 chloroamidinates E{14}(Am)Cl (E{14}=Ge, Sn, Pb. [Am]-=[tBuC(NDipp)2]-) to form (NON)Al-E{14}(Am) Lewis pairs with unsupported Al-E{14} bonds, including the first structurally authenticated Al-Pb bond. Analysis using spectroscopic (NMR, UV-vis and Mössbauer for E{14}=Sn), X-ray diffraction and computational (DFT, QTAIM, TD-DFT) methods conclude an Al-E{14} σ-bond derived from a Lewis basic Al and a Lewis acidic tetrylene, with back-donation from the E{14} s-orbital lone pair donor NBO to acceptor NBOs on Al that are derived from s/p-orbitals. The reaction of the Al-Ge compound with CO2 forms the dioxocarbene (NON)Al(μ-O2C)Ge(Am), whilst under the same conditions the Al-Sn compound reacts with additional CO2 to form the carbonate, (NON)Al(μ-CO3)Sn(Am). Addition of ethene to the Al-E{14} (E{14}=Ge, Sn) compounds introduces an ethylene bridge between the aluminium and group 14 atoms forming a frustrated Lewis pair (FLP). Reaction of the (Al/Ge) FLP with CO2 forms an activation product with new Al-O and Ge-C bonds, whilst reaction with iPrN=C=NiPr proceeds with insertion into the Al-C bond to form an aluminium amidinate.

Understanding of a Ni-Rich O3-Layered Cathode for Sodium-Ion Batteries: Synthesis Mechanism and Al-Gradient Doping.

O3-type NaNi0.8Mn0.1Co0.1O2 (NaNMC811) cathode active materials for sodium-ion batteries (SIBs), with a theoretical high specific capacity (∼187mAhg-1), are in the preliminary exploration stage. This study comprehensively investigates NaNMC811 from multiple perspectives. For the first time, the phase evolution ( - - ) during the solid-state synthesis is systemically investigated, which elucidates in-depth the mechanisms of the thermal sodiation process. Furthermore, an Al-gradient doping of NaNMC811 wassuccessfully implemented through Al2O3 coating on the cathode active material (CAM) precursor. The modified Al-NaNi0.8Mn0.1Co0.1O2 (Al-NaNMC811) exhibits excellent electrochemical dynamics and performance, maintaining a specific capacity above 100mAhg-1 after 100 cycles at 0.1 C (1.5-4.1 V) while providing a promising capacity retention of 63%. Additionally, the material demonstrates excellent rate capabilities, retaining a specific capacity of 107 mAh g-1 at 5 C. Compared to pristine NaNMC811, the modified Al-NaNMC811 is proven to have improved electrochemical kinetics with a higher Na+ diffusion coefficient due to dilated (003) interplanar spacing, and a more stable structure during the electrochemical charge-discharge processes, which is attributed to stronger Al-O bond energy. Understanding phase formations during the synthesis and comprehensive insight in the gradient doping for O3-type NaNMC811 CAMs guides further development of next-generation SIBsmaterials.

Insights of the Multimode Orientation-Dependent Initial Oxidation of Aluminum by First-Principles Theory Calculations.

A fundamental understanding of the oxidation mechanisms of aluminum (Al) alloys is of great importance for its applications in corrosion, catalysis, sensors, etc. In this work, we systematically investigated the first-stage oxidation behaviors of three low-index Al facets with O coverage up to two monolayers (ML) by using density-functional theory (DFT). The large negative adsorption energies indicated favorable oxidation on all three facets. However, distinctive structural and electronic changes induced by the adsorption of oxygen have led to different oxidation modes. More specifically, the oxidation process proceeded by "intercalating" into the subsurface region along the (111) plane out of the (110) facet with spontaneous O ingress into (110) far below one ML, as revealed by the electron density distribution, whereas the oxide ad-layer grew in a "layer-by-layer" mode on Al(111) and (001) facets. Moreover, various Al-O complexes with different atomic coordination numbers (CN), configurations, and sizes may be indicators of the tendency of an Al surface to be oxidized. Besides, the oxide phases formed on (111)/(001) and (110) assembled the Al-O bond distribution within α-Al2O3 and γ-Al2O3, respectively.

Substitution of blast furnace slag by melting furnace slag as active component in green concrete application

Blast furnace slag (BFS), a commonly used substitute for cement clinker, is in large demand and gradually increasing in price. Melting furnace slag (MFS), a by-product of the co-disposal of waste incineration fly ash and metallurgical dust sludge, has potential hydration properties, and its large accumulation also poses a serious threat to the environment. In this study, we focus on the effect of MFS replacing BFS on concrete properties and its hydration mechanism. Results showed that MFS significantly enhanced the compressive strength at the later stage of hydration, and the 28-d compressive strength of MSD concrete was 15.15 % higher than BSD concrete. MFS enriched with a large amount of amorphous silica and alumina played a key role in the hydration process. This is mainly shown as the increase in the fluctuation of Si-O and Al-O bond strengths and the decrease in the energy separation between Ca 2p and Si 2p levels. In addition, the increased substitution of aluminum for silicon in MSD results in the formation of C-A-S-H gels, which are tightly bonded with ettringite to form a composite structure. Subsequent durability assessments indicate that the incorporation of MFS diminishes the permeability to chlorides and sulfates, while also bolstering the concrete’s resistance to carbonation. These findings imply a positive impact on the concrete’s enduring service life.

Revealing the Bro̷nsted Acidic Nature of Penta-Coordinated Aluminum Species in Dealuminated Zeolite Y with Solid-State NMR Spectroscopy.

The inevitable dealumination process of zeolite Y is closely related to ultrastabilization, enhanced Bro̷nsted acidity, and deactivation throughout its life cycle, producing complex aluminum and acidic hydroxyl species. Most investigations on dehydrated zeolites have focused on the Bro̷nsted acidity of tetra-coordinated Al (Al(IV)) and Lewis acidity associated with tricoordinated Al (Al(III)) sites, which has left the penta-coordinated Al (Al(V)) in dealuminated zeolites scarcely discussed. This is largely due to the oversimplified view of detectable Al(V) as an exclusively extra-framework species with Lewis acidity. Here we report the formation of Bro̷nsted acidic penta-coordinated Al species (Al(V)-BAS) in the dealumination process. Two-dimensional (2D) through-bond and multiquantum 1H-{27Al} correlation solid-state NMR experiments demonstrate the presence of a bridging Si-OH-Al(V) structure in dealuminated Y zeolites. Different from the conventional belief that water attack leads to the breaking of zeolite framework Al-O bonds in the initial stage of zeolite dealumination, the observed Al(V) as a dealumination intermediate is directly correlated with a BAS pair because of the direct dissociation of water on the framework tetrahedral aluminum (Al(IV)), thus bypassing the cleavage of Al-O bonds. 1H double-quantum solid-state NMR experiments and theoretical calculations provide further evidence for this mechanism, whereas pyridine adsorption experiments confirm stronger acidity of Al(V)-BASs than the traditional bridging hydroxyl groups associated with Al(IV). We were also able to detect the Al(V)-BAS site from dealuminated SSZ-13 zeolite with CHA topology, suggesting that its creation is not specific to the framework structure of zeolites.

Synergistic hydration mechanism of steel slag-metakaolin based on ionic dissolution properties combined with industrial CT analysis

Replacing cement with solid waste materials is a key approach to preserving natural resources and mitigating carbon dioxide emissions. In this research, we explored elemental complementation as an eco-friendly and low-carbon approach to develop composite cementitious materials (CCMs) by partially substituting cement with steel slag (SS) and metakaolin (MK), thereby overcoming the low reactivity of SS and facilitating its broader application. We scrutinized the synergistic effects of SS-MK CCMs on parameters such as solubility, water demand, setting time, compressive strength, the formation of hydration products, and microstructure. Employing a suite of analytical techniques, including Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), measurement of hydration heat, and X-ray computed tomography. The findings revealed that the alkaline environment produced by SS-cement powder promoted the breakdown of Si-O and Al-O bonds within MK, facilitating both the early hydration process and the development of strength.MK compensates for the lack of strength caused by the slow hydration of SS in the early stage, while the SS accelerated a pozzolanic reaction of MK, leading to a 28d compressive strength of 54.77 MPa for the composite, while the 28d strength of SS20 was 39.74 MPa; MK effectively utilized portlandite, enhancing the hydration of SS and increasing the production of calcium silicate hydrate, which optimized the pore structure and improved sphericity. Furthermore, the SS-MK CCMs addressed the issues of f-CaO excess and prolonged setting times in the SS-cement system, while also ameliorating the high calcium demand and reduced fluidity in the MK-cement system. Additionally, its lower cumulative heat release from hydration enhances the material’s volumetric stability. This study presents a strategy for the large-scale application of SS and contributes to the value-added, eco-friendly use of industrial solid wastes.

Investigation into the hydrogen inhibition mechanism of Platycladus orientalis leaf extract as a biodegradation inhibitor for waste aluminum-silicon alloy dust in wet dust collectors

This study investigates the risk of hydrogen explosion caused by waste metal dust encountering water in wet dust collectors. It proposes using renewable plant extracts to suppress hydrogen evolution from aluminum-silicon (Al-Si) alloy dust, aiming to achieve intrinsically safer production. Platycladus orientalis leaf extract (POLE) was prepared using water as a solvent. Hydrogen inhibition experiments, material characterization, and theoretical calculations were conducted to evaluate the effect of POLE on waste Al-Si dust. The inhibition experiments demonstrated that POLE exhibits excellent inhibitory performance. At a POLE concentration of 2.0 g/L, the hydrogen inhibition efficiency reaches 97.71 % after 22 h, with a reaction rate constant of 8.9708 × 10−5, approaching zero. This efficiency remained stable over 5 days. POLE formed a uniform, dense protective film on the Al-Si dust surface, with a contact angle of 99.23°. FTIR spectra revealed absorption peaks corresponding to POLE functional groups and Al-O bonds, indicating that successfully adsorption of POLE through both physical and chemical interactions. Finally, theoretical calculations were performed to further explain the hydrogen inhibition mechanism of POLE, supplementing and confirming the characterization data. This study inhibited hydrogen production from waste dust, offering a new approach to enhancing the hydrogen production rate from recycled Al scraps.

A novel technology for lithium extraction through low-temperature synergistic roasting of α-spodumene with lepidolite

α-Spodumene and lepidolite have garnered significant attention because of the booming market of lithium (Li) salts. However, α-spodumene requires a high-temperature phase transition step at ≥1050 °C, and lepidolite needs a large amount of sulfate to extract Li. The economic and environmental benefits of these processes need to be improved. Herein, an innovative scheme, low-temperature synergistic roasting of α-spodumene with lepidolite, was proposed to efficiently extract Li. The conditions for phase transition roasting, acid baking, and water leaching were sequentially optimized. The mechanisms underlying the synchronous phase transition of α-spodumene and lepidolite were studied using various characterization methods. Results indicated that lepidolite lowers the transition temperature of spodumene from the α-phase to the β-phase by 150 °C. During the synergistic roasting, fluorine escapes from the lepidolite lattice and attacks SiO, AlO, and LiO bonds within the α-spodumene lattice. Under optimal conditions, 97.60 % of the Li was extracted, while the leaching ratios of Na, K, Al, and Si were only 50.96 %, 10.96 %, 5.75 %, and 0.30 %, respectively. Current scheme is a promising low-carbon technology that synchronously achieves the low-temperature phase transition of α-spodumene and additive-free Li extraction from lepidolite, offering superior economics, environmental benefits, and practicality compared with the existing methods.

H2O-based atomic layer deposition mechanism of aluminum oxide using trimethylaluminum

As a nanofabrication technology, atomic layer deposition (ALD) has been widely used in the fields of displays, microelectronics, nanotechnology, catalysis, energy and coatings. It demonstrates excellent conformality, large-area uniformity and precise control of the sub-monolayer film. Al2O3 ALD using trimethylaluminum (TMA) and water (H2O) as precursors is the most ideal ALD model system. In this work, the reactions of TMA and H2O with the surface have been investigated using density functional theory (DFT) calculations in order to obtain more information on the reaction mechanism of the complicated H2O-based ALD of Al2O3. In the TMA reaction, the methyl ligands can be eliminated and new Al-O bonds can be formed via ligand exchange reactions. In the H2O reaction, the methyl ligand on the surface can be further eliminated and new AlO bonds can be formed. Meanwhile, the coupling reactions between the surface methyl and hydroxyl groups can further form new AlO bonds and release CH4 or H2O to densify the Al2O3 film. These complicated reaction mechanisms of Al2O3 H2O-based ALD can provide theoretical guidance for the precursor design and ALD growth of other oxides and aluminum-based compounds.

Al Impurity Upcycled High-Voltage Cathodes from Spent LiCoO2 Batteries.

Al impurity is among the most likely components to enter the spent lithium-ion battery (LIB) cathode powder due to the strong adhesion between the cathode material and the Al current collector. However, high-value metal elements tend to be lost during the deep removal of Al impurities to obtain high-purity metal salt products in the conventional hydrometallurgical process. In this work, the harmful Al impurity is designed as a beneficial ingredient to upcycle high-voltage LiCoO2 by incorporating robust Al-O covalent bonds into the bulk of the cathode assisted with Ti modification. Benefiting from the strong Al-O and Ti-O bonds in the bulk, the irreversible phase transitions of the upcycled R-LCO-AT have been significantly suppressed at high voltages, as revealed by in situ XRD. Moreover, a Li+-conductive Li2TiO3 protective layer is constructed on the surface of R-LCO-AT by pinning slow-diffusion Ti on the grain boundaries, resulting in improved Li+ diffusion kinetics and restrained interface side reactions. Consequently, the cycle stability and rate performance of R-LCO-AT were significantly enhanced at a high cutoff voltage of 4.6 V, with a discharge capacity of 189.5 mAhg-1 at 1 C and capacity retention of 92.9% over 100 cycles at 4.6 V. This study utilizes the detrimental impurity element to upcycle high-voltage LCO cathodes through an elaborate bulk/surface structural design, offering a strategy for the high-value utilization of spent LIBs.

Mechanical and microstructural characterization of one-part binder incorporated with alkali-thermal activated red mud

The traditional production of silicate cement is associated with substantial carbon emissions and environmental degradation. In contrast, cementless alkali-activated binders, derived from solid waste and industrial byproducts, have garnered significant interest for their reduced material costs, energy efficiency, and environmental benefits. This research investigates the application potential of an advanced mixture of anhydrous sodium silicate and red mud in one-part alkali-activated binders. It is assessed through various analytical techniques, including compressive strength, X-ray diffraction, fourier transform infrared, thermogravimetric analysis, digital image correlation, and scanning electron microscopy with energy dispersive spectroscopy. Findings demonstrate that the synergy between red mud and anhydrous sodium silicate markedly enhances the early strength of one-part alkali-activated binders incorporated with alkali-thermal activation. The increment in sodium silicate content is pivotal for bolstering binder performance. A 40 % red mud admixture results in a compressive strength of 40 MPa, achieving an optimal carbon-to-strength ratio. The inclusion of polypropylene fiber significantly influences the mode of compression failure in alkali-activated binders. Alkali-thermal activation of red mud elevates the levels of active silicon and aluminum, markedly augmenting the reactive silica and aluminum content. This modification fosters the disintegration and reorganization of Si-O and Al-O bonds in silica-aluminum materials, culminating in a denser structure. This structure is characterized by the generation of amorphous ((N, C)-A-S-H) gels, contributing to the material's enhanced properties.

A synergistic modification strategy for enhancing the cycling stability and rate capacity of single-crystal nickel-rich cathode materials

Ni-rich layered LiNi0.8Co0.1Mn0.1O2 (NCM811) is considered to be one of the most promising cathode materials due to its advantages of high specific capacity, lower cost and environmental friendliness. However, the relatively high nickel content in the LiNi0.8Co0.1Mn0.1O2 layered cathode materials leads to the instability of the internal structure and surface of the materials during long-term cycling, which results in the deterioration of electrochemical performance. In this study, single-crystal NCM811 (SNCM811) was prepared using a convenient solid-state method. By doping Al into SNCM811 (SNCMAl) and purposefully low-temperature surface treatment with a small amount of LiPF6, a Ni-rich single-crystal NCM811 modified by both Al bulk doping and LiF surface coating (SNCMAl@LiF) was obtained. The reversible capacity of SNCMAl@LiF with a cutoff voltage of 2.7–4.3 V at 0.1C is 200.3 mAh·g−1. And the capacity retention of the single-crystal cathode materials is 92.4 % with capacity of 171.07 mAh·g−1 after 100 cycles at 1C. Even at high rate of 10C, the discharge specific capacity maintains 148.8 mAh·g−1, demonstrating excellent electrochemical performance. The dual-modified single-crystal material has the lowest potential difference and electrochemical impedance without intragranular cracks and crystal slips after 100 cycles. Stronger AlO bond in single crystals reduced the degree of cation mixing and maintained the stability of the layered structure. LiF-modified surface can promote the transfer of Li+, maintain the stability of the electrode/electrolyte interface and then improve the electrochemical performance of cathode materials. Al-doping and LiF-coating provides a guidance on how to enhance the electrochemical performance of Ni-rich single-crystal cathode materials.

Unraveling the structural and vibrational response of Zharchikhite to pressure (II): Insights from first principles calculations

The halide mineral Zharchikhite with the chemical formula AlF(OH)2 is studied using first-principles methods of density functional theory with the local functional VBH, generalized gradient functionals PBE, BLYP, PBEsol, with an empirical dispersion correction in the form of D3(BJ) PBE-D3, BLYP-D3, global hybrid functionals PBE0, B3LYP, PBEsol0, hybrid functionals with range separation HSE06, SC-BLYP. It is shown that all functionals overestimate O-H and underestimate O-H∙∙∙O distances. The best values are provided by SC-BLYP, B3LYP. The bulk modulus, determined from the Birch-Murnaghan equation of state, is 72.32 GPa. The axes compress unevenly and the fastest is the longest one with a modulus of 217.3 GPa. The linear compressibility modulus of the Al-F bond has a similar value and is twice as large for the Al-O bond. Under pressure, the lengths of H∙∙∙O hydrogen bonds decrease faster and, conversely, O-H bonds slowly increase. Also, at a rate of 0.289°/GPa, the monoclinic angle also increases with pressure. The spectra of infrared absorption and Raman scattering of light have been calculated, in which vibrations of Al-F and Al-O atoms were actived in the region up to 600 cm−1; above 700 cm−1 there are translational vibrations of O-H with a dominant contribution of H1 (Au symmetry) or H2 (Bu symmetry) and above 3200 cm−1 100 % hydrogen atoms. For them, with increasing pressure, the wave numbers decrease and the Grüneisen parameters change from −0.36 to −0.54. The large value of the derivative dν/dP can be used to solve the inverse problem - finding the pressure P from the known wave number ν(P).

Influence of FexOy and Al2O3 Contents on the Thermal Stability of Iron Ore-Waste Fibers: Key Mechanisms and Control.

Traditional rock wool fibres are susceptible to crystallization and pulverization. To mitigate this, glass fibres were produced from iron ore waste (IOW). When the ratio of Fe2+ and Fe3+ is 1:3 and the Al2O3 content is 10 wt.%, increasing the FexOy content enhances the thermal stability.At an FexOy content of 17-19% and an Al2O3 content of 10-13%, the glass transition temperature (Tg) peaked. Increasing the FexOy content from 10% to 20% enhanced the stability of Si-O and Al-O bonds and increased bridged oxygen, stabilizing the structure. Here, Fe2+ balances structural charges, while Fe3+ replaces some Al atoms in the network. When the Al2O3 content is 10-13% and the FexOy content is 17-19%, the thermal stability of the IOW rock glass reaches its optimal level. At 20% FexOy content, the structure becomes three-dimensional and cyclic, increasing polymerization. Consequently, incorporating FexOy alongside a 10% Al2O3 content improves thermal stability, supporting the development of high-stability rock wool from IOW. This approach also enhances the refractory properties of rock wool fibres within the FexOy-Al2O3-SiO2-MgO-CaO system.

Influence mechanism of leaching agent anions on the leaching of aluminium impurities in ionic-type rare earth ores: A DFT simulation combined with experimental verification

The aluminium impurity present during the leaching process of ionic-type rare earth ores increases the complexity and cost of the subsequent dealumination procedure, causing the loss of rare earth elements. Understanding the interactions between minerals and impurities is crucial for grasping interfacial reactions. However, the mechanism by which anions influence the adsorption behaviour of Al3+ remains unclear. This study examined the impact mechanisms of four typical leaching agent anions (SO42-, Cl-, NO3–, and CH3COO–) on the interaction between Al3+ and the kaolinite (001) surface using density functional theory (DFT). According to DFT calculations, the order of adsorption energy of Al3+ on the kaolinite (001) surface in the presence of anions is as follows: Al3+ < Al3+ in aluminium sulfate < Al3+ in aluminium chloride < Al3+ in aluminium nitrate < Al3+ in aluminium acetate. The adsorption strength of Al3+ on the kaolinite (001) surface is weakened to varying degrees by the presence of anions. Specifically, under the influence of acetate anions, it is difficult for Al3+ to adsorb and form bonds on the kaolinite (001) surface. In contrast, Al3+ can still adsorb mainly through Al-O ionic bonds under the influence of the other three anions. The density of states analysis showed that the 3p orbitals of Al atoms and the 2p orbitals of O atoms primarily contribute to the Al-O bond near the Fermi energy level. Experimental results from adsorption capacity tests, microcalorimetry, and zeta potential measurements support the DFT simulations, indicating that Al2(SO4)3 is the most easily adsorbed on the kaolinite surface, followed by AlCl3 and Al(NO3)3, with (CH3COO)3Al being the most difficult to adsorb. Column leaching tests further verified that adding CH3COO– to the leaching agent solution at pH > 4.5 can inhibit the leaching of aluminium impurities, enabling the efficient separation of rare earth elements from aluminium impurities, and reducing the aluminium content in the leachate.

Enhanced Co3O4 Nanoflakes Reactivity via Integrated Al-Doping and Metal Vacancy Engineering for Large Capacity Li-CO2 Batteries

Rechargeable Li-CO2 batteries are well-regarded for their high-energy, environmental friendliness, and resourceful use of CO2, but suffer from poor cycle reversibility. Herein, Al-doped Co3O4 nanoflakes featuring abundant metal vacancies (V-ACO/CC) were synthesized via a facile approach employing Al ions as both a dopant and sacrificial agents, which serve as high-efficient cathode catalyst for Li-CO2 batteries. Experiment results demonstrate that the incorporation of Al doping and metal vacancies modulates the electronic structure of Co-center and optimizes the growth path of discharge product. The cation vacancies generated by the sacrificed part of the Al atoms change the local charge distribution, strengthen the affinity of CO2 and reaction intermediates and facilitate the reversible decomposition of discharge products. Concurrently, the formation of covalent Al-O bonds by the remaining Al species reinforces the stability of nanostructures. Notably, the V-ACO/CC-based LCBs exhibit enhanced CO2 conversion kinetics, as evidenced by a high specific capacity (12.06 mAh cm−2 at 0.05 mA cm−2), fast rate capability and impressive stability (over 420 cycles under 0.1 mA cm−2).

Analysis of calcination activation modified coal gangue and its acid activation mechanism

Acid activation and utilization of coal gangue is of great significance for effective treatment of bulk solid waste in the environment. However, most gangue is quite inert and requires calcination to induce acid activation. In this paper, coal gangue was calcined, and the optimal calcination temperature for activation of the coal gangue acid was explored. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetry/thermal differential analysis (TG/DTG) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the crystal structures of the gangue samples formed at different calcination temperatures, which showed that increases in the amorphous content and structural degradation of the coal gangue samples occurred during calcination. The solubility of silicon and aluminum in acid solution was demonstrated with inductively coupled plasma optical emission spectroscopy (ICP‒OES). XRD and TG/DTG were used to characterize the acid activation products formed at different calcination temperatures. The results show that with the increase of calcination temperature, the compressive strength first increases and then decreases, and reached the maximum value at 650 °C; the compressive strengths at 7 d, 28 d and 90 d were 1.32 MPa, 3.22 MPa and 5.14 MPa. At 650 °C, the kaolinite in the gangue was converted into metakaolin, the aluminum-oxygen octahedra had the hydroxyl groups removed, the silicon-oxygen tetrahedra were depolymerized, the absorption bands for Si–O, Si–O–Al and Al–O bonds were broadened, the Al2p and Si2p binding energies were reduced, the splitting were increased, and more Al dissolved in the acid solution, so it has the highest acid reactivity.

Low temperature phase transition mechanism of amorphous Al-oxalate to nano α-alumina

α-Alumina (α-Al2O3), widely used as a raw material or production in advanced manufacturing industry, has attracted much attention in terms of its preparation temperature. A simple dissolution-evaporation-precipitation process was employed to obtain the amorphous Al-oxalate (AAO) precursor, serving as the starting material for the low temperature preparation of nano α-Al2O3. The crystalline structure and thermal behavior of the AAO were compared with commercially available aluminum hydroxide (Al(OH)3) powder using the X-ray powder diffraction (XRD) instrument, the thermal gravity analysis and differential scanning calorimetry (TG-DSC). The phase transition mechanism of AAO was investigated by the fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), and 27Al magic angle spinning nuclear magnetic resonance (27Al-MAS-NMR). The DSC results indicated that AAO underwent a phase transformation at 982 °C. The α-alumina diffraction peaks appeared in AAO at 1000 °C, while α-Al2O3 phase was observed for Al(OH)3 at 1200 °C. Furthermore, an absorption peak at 452 cm−1, corresponding to Al–O bond in α-alumina was detected at 1000 °C. The proposed low-temperature preparation mechanism of α-alumina from AAO is as follows: four coordination Al-oxalate species entities coexist within the AAO sample; with increasing temperature, organic acid functional groups oxidize and volatilize, resulting in the formation of tetra-coordinate [AlO4], penta-coordinate [AlO5], and hexa-coordinate [AlO6] atomic groups; these atomic clusters further polymerize to form a structurally dense α-alumina crystal at the nano-scale (∼50 nm) at around 1000 °C. The experimental findings present a novel approach and method for the low-temperature preparation of nano-sized alumina powder. Additionally, a feasible theoretical reference for the low-temperature phase transition mechanism of amorphous Al-oxalate was provided.