27Al NMR Research Articles

Catalytic performance and acidic analysis of chloroaluminate ionic liquid with various impurities in the synthesis of multi-octylnaphthalene base oil

The effects of the structure and concentration of impurities on the alkylation of naphthalene with 1-octene catalyzed by chloroaluminate ionic liquid (IL) were investigated. The presence of impurities containing oxygen and nitrogen led to a decrease in the catalytic performance of chloroaluminate IL. As the water concentration increased to 65 mg·g–1, the total selectivity of multi-octylnaphthalene gradually decreased to 42.33%, and the average friction coefficient of the multi-octylnaphthalene base oil gradually increased to 0.201. When the concentration of impurities increased to a critical value, the chloroaluminate IL began to deactivate, leading to a decrease in naphthalene conversion. The critical concentrations for ethanolamine, water, methanol, ether, and diisopentyl sulfide were 33 mg·g–1, 65 mg·g–1, 67 mg·g–1, 87 mg·g–1, and 123 mg·g–1, respectively. Impurities with higher basicity resulted in an earlier onset of chloroaluminate IL deactivation. The changes of Lewis and Brønsted acids in chloroaluminate IL under the influence of impurities were investigated using in situ IR and 27Al NMR spectroscopy. 2,6-dimethylpyridine as an indicator could detect the changes of Brønsted acid in chloroaluminate IL better, but the changes of Lewis acid were not obvious because of the overlap between the characteristic peaks. 2,6-dichloropyridine as an indicator could exclusively detect the changes of Lewis acid in chloroaluminate IL. With the increase in water concentration, the Lewis acid in chloroaluminate IL was continuously consumed and converted into Brønsted acid, and the Lewis acid gradually decreased, while the Brønsted acid showed a change of increasing first and then decreasing.

Acid attack on hydrated cement: effect of organic acids on the degradation process

Owing to their ability to form buffer solutions, the attack of organic acids on concrete structural components can be highly aggressive. This work considers the changes in microstructure, chemical and phase composition in hardened Portland cement paste (hcp) exposed to acetic acid/sodium acetate or citric acid/sodium citrate buffer solutions. The degradation products were investigated using 29Si and 27Al NMR spectroscopy with XRD and ICP-OES. Exposure to acetic acid/sodium acetate at pH 3.9 ≤ pH ≤ 5.5 decalcifies hcp to produce aluminosilica gels (0.1 ≤ Al/Si ≤ 0.3) with Si predominately in Q3/Q4 sites and NBO values (non-bridging oxygen per Si atom) 0.6 ≤ NBO ≤ 0.9. Cross-linking processes causing the formation of the gel from C–A–S–H dreierketten incorporate Al, originally in crystalline phases and C–A–S–H phases. Degradation by citric acid/sodium citrate is governed by the precipitation of expansive calcium citrate which continuously removes degraded surface material. Pore-blocking at the degradation front inhibits acid transport deeper into the material. A new mathematical expression is presented which enables the calculation of NBO for aluminosilica gels of known Al/Si ratio from 29Si NMR spectra despite overlapping signals. The expression was verified by a stochastic computer model based on a Si quartz lattice with substituted Al and vacancies. The model simulated the measured 29Si NMR spectra of aluminosilica gels.

Monitoring the Degradation of Metal‐Organic Framework Drug Nanocarriers by In‐Situ NMR Spectroscopy

AbstractAn accurate characterization methodology is indispensable to design nanoparticle‐based drug delivery system (DDS) adapted to specific diseases and therapies. However, characterization techniques employed to investigate drug release and nanoparticle degradation require separating the nanoparticles from their suspension media, which can lead to artefacts. Therefore, there is a clear need to implement novel versatile in‐situ methods. Here, we report the use of in‐situ NMR spectroscopy to monitor drug delivery processes from MOF nanocarriers, both in solution and in the solid state simultaneously. In‐situ 1H NMR investigation of nanoMIL‐100(Al) suspension in phosphate medium enabled recording the trimesate ligand loss in the solid phase and the ligand release in the liquid phase as a function of time. Simultaneously, 27Al NMR enabled assessing the progressive replacement of carboxylate ligands by phosphates leading to the formation of new aluminum species. Using the same strategy, we also compared the degradation of nanoMIL‐100(Al) loaded with two drug analogs, highlighting an effect of metal‐ligand complexing strength. Furthermore, our in‐situ technique is applicable to studying the reaction of paramagnetic nanoMIL‐100(Fe) in the liquid phase. This work offers an alternative to ex‐situ techniques for understanding the degradation mechanism of MOF nanocarriers and could be an asset for other nanoscale DDSs.

Can the combination of in situ differential impedance spectroscopy and 27Al NMR detect incongruent zeolite crystallization?

Crystallizing zeolites with isotropic properties is critical to the chemical industry but can be extremely challenging as small deviations in the synthesis conditions can have extreme effects on the final products. Easily implemented in-situ monitoring systems could make a real difference, but very few experimental methodologies cater to the specific needs of applications relying on harsh, hyper-alkaline conditions involving multiphasic systems such as Hydrated Silicate Ionic Liquids. Differential impedance spectroscopy (DIS) promises to enable such studies. It remains highly accurate despite possible electrode degradation or scaling. This study showcases how in-situ differential impedance measurements not only enable reliable detection of crystallization of even minimal amounts of zeolite product but also illustrates how the unique combination of in situ DIS and in situ, 27Al NMR provides insight into complex, incongruent zeolite crystallization processes.

Insights on the effects of carbonates and phosphates on the hydration of magnesia (alumino-)silicate cements

Cements based on magnesium oxide (MgO) and reactive (alumino-)silicates (xSiO2-yAl2O3) have drawn increasing attention owing to their potential to be produced using raw materials with low CO2 emissions. This study examines how the phase assemblages and compressive strengths of magnesia (alumino-)silicate cements are influenced by the addition of sodium hexametaphosphate (NaHMP) and sodium carbonate (Na2CO3). Cement paste samples with a Mg/Si molar ratio of 1.5 and Al/Si molar ratios of 0 and 1.0 were prepared using microsilica (SF) and metakaolin (MK), respectively, and investigated using SEM, TGA, XRD, and 29Si, 27Al, 31P, and 13C MAS NMR. The results showed that the addition of NaHMP and sodium carbonate enhanced the reactivity of the raw materials in the Al-free MgO-SF systems, with magnesium silicate hydrate (M-S-H) being the primary hydrated phase. After 91 days, the degrees of reaction of microsilica were ∼86% and 96% for systems containing 0 and 2.5 wt % Na2CO3, respectively. In contrast, the reactivity of metakaolin in the Al-containing MgO-MK systems was limited to ∼53%, irrespective of Na2CO3 addition, likely due to the excess sodium hexametaphosphate covering the surface of MK. Here, the main reaction products were magnesium aluminosilicate hydrate (M-A-S-H) and hydrotalcite (Mg6Al2CO3(OH)16·4(H2O))-like phases. Despite the MgO-SF systems displaying higher degree of reaction than the MgO-MK systems, the latter exhibited higher compressive strength. Sodium carbonate increased the compressive strength of the MgO-SF systems but decreased that of the MgO-MK systems. Thermodynamic modelling was also carried out and the results generally agreed with the phase formation observed with XRD and solid-state NMR.

Tunable luminescent properties and structure of Sn2+-doped boroaluminate glasses

A series of novel Sn2+ doped boroaluminate glasses were prepared by the traditional melt quenching method in this work. Their glass network structure, luminescent properties, and mechanisms were studied in detail. The main framework of the glass network was dependent on the glass network former (B2O3) and intermediate (Al2O3), and was characterized by the 11B and 27Al NMR spectra. Broadband tunable blue-violet emissions ranging from 320 to 550 nm were realized by regulating the glass network structure through optical basicity. The quantitative relationship between optical basicity and emission/excitation peak positions and intensities, FWHM, and Stokes-Shift of this Sn2+-doped glass were revealed, according to which the luminescent properties of Sn2+ could be modulated and even predicted in the future. This work will enrich our understanding of the luminescent properties of Sn2+ ions and the variations of glass network structure, guiding the design of efficient and tunable luminescent boroaluminate glass.

Transformation of Light Alkanes into High-Value Aromatics

This research work is focused on the transformation of light alkane (propane) into high-value aromatics using gallo-alumino-silicate catalysts. Two sets of gallo-alumino-silicates were synthesized for this study. In the first set, the ratio of Ga/(Al+Ga) was modified, while the Si/(Al+Ga) ratio was held constant. In the subsequent set, the Si/(Al+Ga) ratio was adjusted, while maintaining a consistent Ga/(Al+Ga) ratio. This approach aimed to directly assess the impact of each ratio on catalyst performance. The comprehensive characterization of all catalysts was conducted using various instrumental techniques, i.e., BET surface area, XRD, NH3-TPD, 27Al, 71Ga and 29Si MAS NMR, and XPS. A gradual reduction in the percentage of crystallinity and rise in meso-surface area was noticed with a rise in Ga/(Al+Ga) ratio. The total acidity (NH3-TPD) demonstrated a decline as the Si/(Al+Ga) ratio increased, attributed to an overall decline in Al3+ or Ga3+ species. The XPS intensity of the Ga 2p3/2 peak rose in correlation with an elevated ratio of Ga/(Al+Ga), suggesting the formation of extra-framework Ga species. The propane conversion, aromatic yield, and aromatization/cracking ratio exhibited an increase with an increasing Ga/(Al+Ga) ratio, reaching an optimum value of 0.46 before declining. Conversely, an appreciable drop in the conversion of propane and yield of aromatics was detected with the rise in Si/(Al+Ga) ratio, attributing to the decline in acidity. The catalyst having a Ga/(Al+Ga) ration of 0.46 exhibited the highest propane conversion and aromatic yield of 83.0% and 55.0% respectively.

Repulsive Lateral Interaction of Water Molecules at the Initial Stages of Adsorption in Microporous AlPO4-11 According to 27Al NMR and DFT.

Lateral (adsorbate-adsorbate) interactions between adsorbed molecules affect various physical and chemical properties of microporous adsorbents and catalysts, influencing their functional properties. In this work, we studied the hydration of microporous AlPO4-11 aluminophosphate, which has an unusually ordered structure upon adsorption of water vapor, and according to 27Al NMR data, only tetrahedrally or octahedrally coordinated Al sites are present in the AlPO4-11. These 27Al NMR data are consistent with the results of density functional theory (DFT) calculations of hydrated AlPO4-11, which revealed the presence of a strong repulsive lateral interaction at the initial stage of adsorption, suppressing the adsorption of water on neighboring (separated by one -O-P-O- bridge) Al crystallographic sites. As a result, of all the different aluminum sites, only half of the Al1 sites adsorb two water molecules and acquire octahedral coordination.

Lewis Acidic Aluminosilicates: Synthesis, 27Al MQ/MAS NMR, and DFT-Calculated 27Al NMR Parameters.

Porous aluminosilicates are functional materials of paramount importance as Lewis acid catalysts in the synthetic industry, yet the participating aluminum species remain poorly studied. Herein, a series of model aluminosilicate networks containing [L-AlO3] (L = THF, Et3N, pyridine, triethylphosphine oxide (TEPO)) and [AlO4]- centers were prepared through nonhydrolytic sol-gel condensation reactions of the spherosilicate building block (Me3Sn)8Si8O20 with L-AlX3 (X = Cl, Me, Et) and [Me4N] [AlCl4] compounds in THF or toluene. The substoichiometric dosage of the Al precursors ensured complete condensation and uniform incorporation, with the bulky spherosilicate forcing a separation between neighboring aluminum centers. The materials were characterized by 1H, 13C, 27Al, 29Si, and 31P MAS NMR and FTIR spectroscopies, ICP-OES, gravimetry, and N2 adsorption porosimetry. The resulting aluminum centers were resolved by 27Al TQ/MAS NMR techniques and assigned based on their spectroscopic parameters obtained by peak fitting (δiso, CQ, η) and their correspondence to the values calculated on model structures by DFT methods. A clear correlation between the decrease in the symmetry of the Al centers and the increase of the observed CQ was established with values spanning from 4.4 MHz for distorted [AlO4]- to 15.1 MHz for [THF-AlO3]. Products containing exclusively [TEPO-AlO3] or [AlO4]- centers could be obtained (single-site materials). For L = THF, Et3N, and pyridine, the [AlO4]- centers were formed together with the expected [L-AlO3] species, and a viable mechanism for the unexpected emergence of [AlO4]- was proposed.

Effect of milled pegmatite quarry wastes powders on structure, microstructure and mechanical properties of pegmatite-based geopolymers

In this investigation, mechanical activation (MA) of pegmatite quarry wastes was perform via an eccentric vibratory mill to improve the geopolymeric reactivity. The MA at miscellaneous times (0 to 90 min) resulted in different activation degrees of samples with improved the fineness of particle size and specific surface area from 2.974 to 5.311 m2.g− 1. Geopolymer binders were synthesized by partly replacing the pegmatite quarry waste with 12.5 wt% of metakaolin. The activating solution used was a mixture of 10 M NaOH and Na2SiO3 solution with a volume ratio of 1:1. Reaction kinetics, compressive strength, water absorption, chemical (FT-IR, XRD, 27Al and 29Si MAS NMR), and microstructural (SEM/EDS and TEM) analyses were done to characterize the obtained geopolymer binders. The microstructural characterization reveals that undissolved/unreacted particles decreased while the non-bridge particles increased with pegmatite milled. Under SEM/EDS and TEM, fineness of pegmatite particles is highlighted by the formation of more reaction product. As a result, the compressive strength of geopolymer binders improved from 22.3 to 51.6 MPa for 0 to 60 min of milling. From these results, there is feasibility of valorising feldspathic (pegmatite) quarry wastes as alternative aluminosilicate precursors to develop environmentally-friendly geopolymer binders. The resulting binders with high-strength and low water absorption (≤ 8.6%) associated to minimization of CO2-emissions can be used as potential candidate in structural applications.

Catalytic condensation of α-pinene with formaldehyde

While synthesis of hydroxymethyl derivatives of common terpenes by a reaction with formaldehyde (FA) has been commercialized, no open data are available on the preparation of such α-pinene derivatives. Here, an approach for the renewable (–)-α-pinene catalytic utilization by its condensation with FA into a novel terpenoid 8-acetoxy-6-hydroxymethyllimonene is proposed. Both common homogeneous acids and aluminosilicates (halloysite nanotubes pretreated with H3PO4 and HCl, montmorillonite K-10, zeolite H-Beta-25) have been investigated. The solids were characterized by SEM, EDX, 27Al and 29Si MAS NMR, as well as FTIR with pyridine and N2 adsorption–desorption methods. Traditional Lewis and Brønsted acids (ZnCl2, FeCl3, H3PO4 etc.) catalyzed the desired condensation although selectivity did not exceed 24 % in the case of phosphoric acid due to the side reactions, including opening of the α-pinene cyclobutane ring, as well as skeletal rearrangements of its bicyclic structure. On aluminosilicates with a weak to moderate Lewis and Brønsted acidity (45–104 µmol/g), the products of a direct substrate protonation (up to 52.8 %) were predominantly formed. In the presence of strongly acidic H-Beta-25 (301 µmol/g) and phosphoric acid, selectivity to α-pinene addition products with formaldehyde (32.3–35.3 %) and substrate direct protonation (30.0–36.8 %) were comparable. However, with H3PO4 the content of borneol derivatives formed via the Wagner-Meerwein rearrangement was the smallest (13.5 %) giving subsequently the largest selectivity to the desired 8-acetoxy-6-hydroxymethyllimonene. Higher selectivity to the target product was observed at lower reaction temperature and a larger formaldehyde amount. The reaction mechanism has been proposed and elucidated using kinetic and quantum chemical approaches. The developed kinetic model adequately describes the experimental results. The DFT calculations showed that in the presence of H3PO4 there are no significant differences between the energy of the intermediates formed due to formaldehyde addition to α-pinene or its direct protonation. Synthesis of 8-acetoxy-6-hydroxymethyllimonene was performed on 22 g scale. This compound can be considered as a chiral platform for further utilization, including synthesis of heterocyclic compounds.

A novel hydrophobic chitosan-polyaluminum chloride composite flocculant for effectively simultaneous removal of microplastic and antibiotics composite pollution

Composite pollution of emerging pollutants such as microplastics (MPs) with small size and antibiotics has brought a great challenge in the fields of water and wastewater treatment. Up to now, the simultaneous removal of MPs and antibiotics by traditional coagulation is still not satisfied. Herein, a novel composite flocculant named hydrophobic chitosan-polyaluminum chloride (Hmcs-PAC) was designed and prepared for efficiently simultaneous removal of polyethylene terephthalate (PET, 10 μm) and tetracycline (TC) from water. Under the optimal preparation conditions (i.e. Basicity = 1 and the weight ratio of Hmcs:Al = 0.5), the Hmcs-PAC exhibited better removal of both PET and TC than PAC and Hmcs under the same dosage, with the maximum removal efficiency of 99.9 % for PET, and 91.5 % for TC, respectively. The PAC was successfully grafted on the Hmcs via Al-N bond, confirmed by FTIR and 27Al NMR. More importantly, the removal of TC in composite PET + TC system was significantly enhanced by above 10 % compared with that in single TC system, which was mainly attributed to the complexes formation of Hmcs-PAC-PET-TC via the PET bridging effect based on 2D Fourier transform infrared correlation spectroscopy (2D-FTIR-COS) and scanning electron microscopy (SEM) analysis. In contrast, the removal of PET in composite system was slightly lower than that in PET single system, possibly due to the competition of TC for the active sites of hydrolysates of Hmcs-PAC. Furthermore, the presence of co-existing ions except CO32− had adverse effect on the coagulation removal, especially for TC. While the increase in temperature, humic acid and anionic surfactant content showed a promotion effect on the removal of PET and TC. Finally, the prepared Hmcs-PAC exhibited a potential removal of composite pollutants from urban sewage. This study can provide a promising flocculant for the effective co-removal of MPs and antibiotics from water and wastewater.

Efficient lithium recovery from electrolytic aluminum slag via an environmentally friendly process: Leaching behavior and mechanism

The electrolytic aluminum industry generates a large amount lithium (Li)-containing electrolytic aluminum slag (EAS) annually, and this can result in severe environmental pollution and wasting of Li resources. This paper proposes a method for recovering Li from the slag using AlCl3 as the leaching agent. The effects of the leaching temperature, AlCl3 concentration, pH, and solid-to-liquid ratio (S/L) on the leaching efficiency of Li+ were systematically examined. The structural transformation during the Li leaching process was revealed by SEM, XRD, 27Al NMR, and XPS analyses. The results indicate that up to 88.3% of Li + can be leached out using 0.85 M of AlCl3 with an S/L of 1:3 at a leaching temperature of 95 °C and pH of 0.5. The addition of AlCl3 played an essential role in the decomposition of cryolite/cryolithionite, ultimately resulting in Al–F fracture and Li+ release in the leaching solution. Moreover, Al3+ enters the interior of the slag to participate in the reconstruction of the chiolite with a low NaF/AlF3 ratio, and reacts with OH− ionized from H2O to form hydroxyl aluminum fluoride species. Fluorine ions were solidified in the leaching residues for subsequent cryolite regeneration. This study not only provides an environmentally friendly process for resource utilization from EAS but also reduces the environmental threat caused by the storage of the hazardous waste.

Al/SBA-15 Mesoporous Material: A Study of pH Influence over Aluminum Insertion into the Framework.

Herein, ordered mesoporous materials like SBA-15 and Al/SBA-15 were prepared using the pH adjustment method. Thus, these materials were developed in different pH of synthesis, from the pH adjustment method using a KCl/HCl solution and varying the Si/Al molar ratio (5, 25, and 75). All the ordered mesoporous materials were characterized by FRX, 27Al NMR, SEM, XRD, N2 adsorption/desorption, and CO2 adsorption. From the applied method, it was possible to obtain SBA-15 and Al/SBA-15 with high mesoscopic ordering based on the XRD patterns, independent of the pH employed. From the chemical composition, the insertion of higher amounts of Al into the synthesis caused a progressive improvement in the structural and textural properties of the ordered mesoporous materials. Thus, the chosen synthesis conditions can lead to different aluminum coordination (tetrahedral and octahedral), which gives these materials a greater potential to be applied. The presence of Al in high amounts provides material with the ability to form micropores. Finally, the proposed method proved to be innovative; low-cost; less aggressive to the environment, with efficient insertion of aluminum in the framework of SBA-15 mesoporous material; and practical, based on only one step.

Zeolites Derived from Natural Kaolinite for CO2 Adsorption

This manuscript deals with the synthesis of different types of zeolites from natural kaolinite samples for CO2 adsorption. A zeolite A was prepared from kaolinite by means of an alkaline fusion process, followed by hydrothermal treatment, whereas a highly crystalline zeolite X was synthesized by optimizing the previously mentioned synthetic procedure. In detail, the SiO2/Al2O3 molar ratio in the preliminary mixture was modified with the addition of a secondary silicon source (sodium silicate) in order to obtain the one required for zeolites X. The physicochemical properties of the pristine clay and of the different zeolites were investigated by means of a multi-technique approach, including XRPD; SEM-EDX; 23Na, 27Al and 29Si MAS NMR spectroscopy; and N2 physisorption analysis at 77 K. Since the Si and Al molar ratios and reactivities are key parameters for the synthesis of zeolites, these aspects, primarily related to the use of a naturally occurring aluminosilicate as the raw material, have been investigated for their correlation with the physicochemical properties of the synthetic products. Moreover, by means of a custom-built volumetric apparatus, the CO2 adsorption capacity of the resulting zeolites at low gas pressures (<1 bar) and at 25 °C was assessed.

Theoretical Insights into the 27Al NMR Parameters of Binary Aluminosilicate Glass and Their Relationship to the Atomic and Electronic Structure

Theoretical Insights into the ²⁷Al NMR Parameters of Binary Aluminosilicate Glass and Their Relationship to the Atomic and Electronic Structure

Synthesis of impregnants for dispenser cathodes via homogeneous-lyophilization: Phase structure, optical response and emission property of four aluminates

Dispenser cathodes are the most widely used electron emission source in vacuum electron devices. The impregnant is the source for producing active substances in the dispenser cathodes, which play an irreplaceable role. However, impregnants’ phase structure and optical response properties have yet to be systematically investigated. Herein, four aluminates were prepared as impregnants via homogeneous-lyophilization followed by calcination. Due to the unique preparation process, the elemental distribution of aluminates is exceptionally uniform. Based on the first-principles DFT calculations, the primary phases of the two aluminates 532 and 411 were confirmed to be (Ba0.61Ca0.39)3Al2O6 (P213) and (Ba0.75Ca0.25)4Al2O7 (Cmca). At the same time, α-Ba2ScAlO5 and β-Ba2ScAlO5 are the only phases of aluminates 411-0.75Sc and 411-1.25Sc, respectively. XPS confirmed two chemical states of Ba and Sc in the aluminates. FT-IR and 27Al NMR indicate that the aluminum-oxygen skeleton in all aluminates exists mainly as [AlO4] tetrahedrons, accompanied by a small amount of distorted [AlOx] (x = 5, 6) polyhedrons. The UV–visible light absorption capacity, band gap and intra-structural electron transfer capacity of all aluminates are determined by UV–Vis DRS and PL spectra. The dispenser cathodes impregnated with aluminates 532 and 411 have zero-field current densities of 5.3 A/cm2 and 14.3 A/cm2 at 1100°Cb, respectively. The dispenser cathodes impregnated with aluminate containing scandium have different space-charge-limited current densities, i.e., 29.48 A/cm2 for 411-0.75Sc and 13.66 A/cm2 for 411-1.25Sc at 1000°Cb. This work will provide more options for synthesizing and applying impregnants.

Metal ion effect on pore size reduction in Mesoporous Aluminosilicate in the presence of TETA as a template and its catalytic performance of CO2 decomposition at lower temperature

AbstractMesoporous AlSiO4‐33 and Co2+ incorporated Co‐AlSiO4‐15 catalysts are synthesized at room temperature using Triethylenetetramine (TETA) as a template for the purpose of CO2 decomposition. The prepared materials are characterized by FT‐IR, XRD, UV‐DRS, BET, TGA, 27Al NMR and TEM. Based on XRD data, the materials are crystalline in nature. The mesoporosity of the materials with pore sizes of 33 nm (AlSiO4) and 15 nm (Co‐AlSiO4) are confirmed by BET analysis. Consequently, we designated AlSiO4 and Co‐AlSiO4 as AlSiO4‐33 and Co‐AlSiO4‐15. This lowered diameter value for Co‐AlSiO4‐15 may be due to the octahedral coordination of Co2+ ion. In the tetrahedral aluminosilicate framework, the template directs the Co2+ towards octahedral coordination. Due to the octahedral coordination, the bond angle between Si−O−Co is reduced. Due to this reduction, the pore size reduced from 33 nm (AlSiO4‐33) to 15 nm (Co‐AlSiO4‐15). These two catalysts are applied for CO2 decomposition. AlSiO4‐33 is active at 100 °C while Co‐AlSiO4‐6 is active at 150 °C. Co‐AlSiO4‐15 has produced more oxygen than AlSiO4‐33. It may be due to the Co‐AlSiO4‐15 has more bronsted acidic sites than the AlSiO4‐33. Co‐AlSiO4‐15 is reduced the activation energy 67 % while AlSiO4‐33 is reduced 78 % for CO2 decomposition at lower temperatures compare to conventional methods.

In-depth characterization of phosphate intercalated Mg Al Layered double hydroxides and study of the PO4 release properties.

Slow-release fertilizers (SRFs) form the core of innovative strategies in sustainable agriculture. Layered Double Hydroxides (LDH), known for their high capacity to sequester plant nutrients, especially phosphate, are emerging as promising candidates for SRF synthesis. The phosphate release properties of MgAl LDH (with a targeted Mg/Al ratio of 2.0) intercalated with HPO42- anions were assessed in various aqueous environments. A comprehensive analysis, including in-depth chemical and structural characterizations (ICP-OES, XRD, PDF, 27Al NMR, 31P NMR, FTIR, SEM) of the as-prepared phase unveiled a more intricate composition than anticipated for a pure or ideal Mg2Al-HPO4 LDH, encompassing an excess of intercalated phosphate in conjunction with K+. Beyond the intercalated phosphate, solid state 31P NMR speciation identified multiple HxPO4(-3+x) environments, indicating a portion of the phosphate reacting with intralayer Mg2+ to form K-struvite. Additionally, some phosphates were adsorbed onto the surface of amorphous aluminum hydroxide, a side phase formed during MgAl coprecipitation. The phosphate release demonstrated rapid kinetics, occurring within 6 days. Moreover, the released phosphate increased significantly when reducing the Solid/Liquid (S/L) ratio (58%) and further increasing in the presence of carbonate ions (90%). The released phosphate varied from 12% to 90% under different release conditions, transitioning from water to a 3.33 mM NaHCO3 aqueous solution at a low S/L ratio (from 20 mg LDH per mL to 0.02 mg LDH per mL). The simultaneous release of K+, Mg2+, Al3+ indicated the complete dissolution of the K-struvite and partial dissolution of phosphate intercalated MgAl LDH. These results enhanced our understanding of the mechanism governing phosphate release from MgAl LDH, paving the way for potential phosphate recovery by LDH or for the development of LDH-based SRFs.

Densification of sodium and magnesium aluminosilicate glasses at ambient temperature: structural investigations by solid-state nuclear magnetic resonance and molecular dynamics simulations.

Sodium and magnesium aluminosilicate glasses with compositions 20Na2O-20Al2O3-60SiO2 (NAS) and 20MgO-20Al2O3-60SiO2 (MAS) were subjected to a 12 and 25 GPa compression and decompression at room temperature, resulting in density increases from 3.7% to 5.3% (NAS) and from 8.2 to 8.4% (MAS), respectively. The pressurization at 25 GPa was done on 17O-enriched glasses, to facilitate characterization by 17O NMR. The structural changes associated with this process have been investigated by solid state 29Si, 27Al, 23Na, 25Mg, and 17O magic-angle spinning NMR and compared with the situation in thermally relaxed glasses and/or glasses prepared at ambient pressure. While in the Na aluminosilicate glass only subtle structural changes were observed in a sample densified at 12 GPa, the average coordination number of Al 〈CN(Al)〉 increases moderately from 4.00 to 4.26 by pressurization at 25 GPa. In the Mg-based system, 〈CN(Al)〉 increases from 4.34 to 4.57 to 4.83 in the sequence 10-4 GPa → 12 GPa → 25 GPa. The experimental result at 25 GPa was qualitatively confirmed by molecular dynamics (MD) simulations. Overall, pressurization results in more positive 29Si and 17O chemical shifts, most likely reflecting a reduction in the Si-O-Si and Si-O-Al bonding angles in the pressurized glasses. Furthermore, the results are also consistent with either an increased number of non-bridging O-atoms upon pressurization, or a larger number of Si-O-Al or Al-O-Al linkages. The significantly higher sensitivity of MAS, compared to NAS glass, to an increase in 〈CN(Al)〉 upon pressurization, provides a good structural rationale for its significantly higher crack initiation resistance.