27Al Solid-state Nuclear Magnetic Resonance Research Articles

Functionalization of mesoporous Al-MCM-41 for indoor humidity control as building humidity conditioning material

This study sought to overcome the high energy consumption of mechanical dehumidifiers by synthesizing humidity control materials using alumino-silicate raw materials extracted from stone sludge and cathode ray tube (CRT) waste panel glass. The structure of the synthesized materials matches that of Mobil Composition of Matter No. 41 (MCM-41) mesoporous molecular sieves, which was subjected to amine functionalization using (3-Aminopropyl) triethoxysilane at various concentrations (2.5, 5, 7.5 vol.%). The resulting materials were characterized using X-ray fluorescence analysis, small angle X-ray diffractometry, Fourier transform infrared spectroscopy, transmission electron microscopy, the Brunauer–Emmett–Teller method, and 27Al solid-state nuclear magnetic resonance spectrometry. Al-MCM-41 molecular sieves with 5.0% grafted amine functional groups presented high specific surface area and high pore uniformity resulting in the highest equilibrium moisture content (39.4 kg/kg). The high thermal and humidity buffer capacity of the proposed material could greatly enhance the comfort of interior spaces without the energy consumption of mechanical dehumidifiers.

A multi-faceted structural, thermodynamic, and spectroscopic approach for investigating ethanol dehydration over transition phase aluminas.

Understanding the role that the surface of a material plays in the mediation of a chemical reaction at the atomic level is paramount to the optimization and improvement of catalytic materials. While this area of research has matured over several decades, few techniques are sensitive enough to directly examine and differentiate the behavior of molecular adsorbates during the course of the chemical reaction with a substrate. In this study, a combined approach which involves structural characterization techniques, volumetric adsorption, temperature programmed desorption, and inelastic neutron scattering (INS) was used to investigate the mechanism of ethanol dehydration on the surface of transition phase aluminas. The alumina samples employed were extensively characterized using X-ray diffraction, solid-state 27Al nuclear magnetic resonance spectroscopy, and thermogravimetric analysis with differential scanning calorimetry. A high-precision volumetric adsorption apparatus was used to characterize the surface area and to controllably dose ethanol onto the surface of the aluminas. A modified temperature programmed desorption (TPD) method which samples the molecular composition of the vapor at discrete temperatures in a closed cell is described. INS results were used to confirm adsorption of ethanol on γ- and θ-alumina and show the reaction of ethanol and subsequent formation of ethylene as a function of temperature. The TPD and INS results affirm that the dehydration reaction and subsequent formation of ethylene on both γ- and θ-aluminas occur rapidly at 300 °C, though ethanol is still observed on θ-alumina indicating fewer active sites. These results demonstrate the value of a multi-faceted characterization approach, featuring INS, towards providing a detailed understanding of the ethanol dehydration mechanism on θ-alumina and further provide the basis for extending this approach to other systems in heterogeneous catalysis and areas where molecule-substrate interactions are poorly understood.

An investigation of Al2O3 induced variations in the structural parameters in strontium borosilicate glasses using solid state NMR.

The physical properties of oxide glasses are crucially dependent on the atomistic structural speciation. In this study, we investigate the variation in the local ordering in the glass network of strontium borosilicate glasses (34.82 SrO, 51.84 B2O3, 13.34 SiO2 in mol%) with a progressive substitution of B2O3 by Al2O3 and estimate the structural parameters: the oxygen packing fraction, and the average network coordination number. The coordination of the network forming cations at various glass compositions is determined using 11B, 27Al, and 29Si solid-state nuclear magnetic resonance (SSNMR). The SSNMR reveals that at the higher substitution of B2O3 by Al2O3 in the glass composition, the coordination network of Al3+ exists predominantly in the 4 coordinated state, the network forming B3+ cations transform from a tetrahedral BO4 to a trigonal BO3 structure, and the Q4 form of silicates is dominant. The average coordination number and the oxygen packing fraction were calculated using the parameters obtained from the SSNMR results, and it is observed that the average coordination number decreases, and the oxygen packing fraction increases on incorporating Al. It is interesting to note that some of the thermophysical properties of these compositions closely follow the pattern shown by the average coordination number and the oxygen packing fraction.

Structure of diopside, enstatite, and magnesium aluminosilicate glasses: A joint approach using neutron and x-ray diffraction and solid-state NMR.

Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and 29Si, 27Al, and 25Mg solid-state nuclear magnetic resonance (NMR) spectroscopy were used to measure the structure of glassy diopside (CaMgSi2O6), enstatite (MgSiO3), and four (MgO)x(Al2O3)y(SiO2)1-x-y glasses, with x = 0.375 or 0.25 along the 50 mol. % silica tie-line (1 - x - y = 0.5) or with x = 0.3 or 0.2 along the 60 mol. % silica tie-line (1 - x - y = 0.6). The bound coherent neutron scattering length of the isotope 25Mg was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline 25MgO. The diffraction results for the glasses show a broad asymmetric distribution of Mg-O nearest-neighbors with a coordination number of 4.40(4) and 4.46(4) for the diopside and enstatite glasses, respectively. As magnesia is replaced by alumina along a tie-line with 50 or 60 mol. % silica, the Mg-O coordination number increases with the weighted bond distance as less Mg2+ ions adopt a network-modifying role and more of these ions adopt a predominantly charge-compensating role. 25Mg magic angle spinning (MAS) NMR results could not resolve the different coordination environments of Mg2+ under the employed field strength (14.1T) and spinning rate (20kHz). The results emphasize the power of neutron diffraction with isotope substitution to provide unambiguous site-specific information on the coordination environment of magnesium in disordered materials.

Unique responses of Cu-SSZ-13 toward phosphorus: Al atoms on zeolite framework versus varied Cu species

Phosphorus (P) poisoning of NH3-SCR catalysts is inevitable in application of NOx abatement of diesel exhaust. The distinct effects on Cu-SSZ-13 of P from different precursors (H3PO4 and (NH4)2HPO4) were figured out and the mechanism was further investigated. P-poisoned Cu-SSZ-13 (Si/Al = 6) catalysts were prepared and characterized using N2 adsorption, X-ray powder diffraction (XRD), scanning electron microscope with energy-dispersive X-ray spectroscopy mapping (SEM-EDX), ammonia temperature-programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature programmed reduction (H2-TPR), electron paramagnetic resonance (EPR) and 27Al solid-state magic angle spinning nuclear magnetic resonance spectroscopies (27Al NMR). Significant enhancement of high-temperature activities (400–600 °C) were observed for the catalysts with P loading of 0.3–0.9 wt%, since the appropriate incorporation enabled to bind P atoms to CuOx in remained framework. However, the high P content of 1.5 wt% resulted in a detrimental effect on framework to induce the accumulation of Cu species. Interestingly, the dominant P from H3PO4 was inclined to directly attack the framework Al leading to more severe dealumination, while the P from (NH4)2HPO4 interacted with Cu2+ to form copper phosphate with more Cu2+ migrating to the surface of the catalyst which promoted the NOx conversation at each active site resulting in the low-temperature catalytic activity unchanged. So, control of the P/Cu and form of P is capable of preventing P poisoning and unlocks the potential of Cu-SSZ-13 in exhaust treatment.

Thermal activation of palygorskite for enhanced fluoride removal under alkaline conditions

Fluoride contamination of groundwater is a global environmental problem. Based on adsorption treatment strategies, magnesium-based materials have shown potential for defluoridation of this water source. In this research, we calcined raw palygorskite (RPAL), a natural magnesium-rich clay, at different temperatures (100–1000 °C), to examine the defluoridation performance. The evolution of the morphology, physical-chemical properties, and crystal structure was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and 27Al and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy. Palygorskite calcined at 200 °C (CP200) had F− uptake of ∼1.6 mg F−/g within a neutral-to-basic pH region of F-contaminated groundwater (e.g., pH 7–9), which is 5–6 times larger than that for RPAL. Additionally, CP200 and CP400 exhibited comparatively greater adsorption performance for fluoride removal compared with activated alumina (AA) under alkaline conditions (e.g., 1.5–3 times at pH ≥ 9). The dependence of fluoride uptake by the calcined samples appeared to be related to major changes in the crystal structure of palygorskite, particularly the dehydration of zeolite waters and partially coordinated water within pores. The exposed > MgOH2 groups at tunnel edges may play an important role in fluoride removal, especially at elevated pH. The higher stability under alkaline conditions and the lower sensitivity to pH compared with AA demonstrated the potential of calcined palygorskite as an effective magnesium-based clay for the remediation of fluoride contamination of groundwater.

Flavonol-Aluminum Complex Formation: Enhancing Aluminum Accumulation in Tea Plants.

Polyphenol-rich tea plants are aluminum (Al) accumulators. Whether an association exists between polyphenols and Al accumulation in tea plants remains unclear. This study revealed that the accumulation of the total Al and bound Al contents were both higher in tea samples with high flavonol content than in low, and Al accumulation in tea plants was significantly and positively correlated with their flavonol content. Furthermore, the capability of flavonols combined with Al was higher than that of epigallocatechin gallate (EGCG) and root proanthocyanidins (PAs) under identical conditions. Flavonol-Al complexes signals (94 ppm) were detected in the tender roots and old leaves of tea plants through solid-state 27Al nuclear magnetic resonance (NMR) imaging, and the strength of the signals in the high flavonol content tea samples was considerably stronger than that in the low flavonol content tea samples. This study provides a new perspective for studying Al accumulation in different tea varieties.

Mechanical, thermal, and structural investigations of chemically strengthened Na2O–CaO–Al2O3–SiO2 glasses

For a series of conventional soda-lime-silicate glasses with increasing Al2O3content, we investigated the thermal, mechanical, and structural properties before and after K+-for-Na+ion-exchange strengthening by exposure to molten KNO3. The Al-for-Si replacement resulted in increased glass network polymerization and lowered compactness. The glass transition temperature (Tg), hardness (H) and reduced elastic modulus (Er), of the pristine glasses enhanced monotonically for increasing Al2O3content.HandErincreased linearly up to a glass composition with roughly equal stoichiometric amounts of Na2O and Al2O3where a nonlinear dependence on Al2O3was observed, whereasHandErof the chemically strengthened (CS) glasses revealed a strictly linear dependence.Tg, on the other hand, showed linear increase with Al-for-Si for pristine glasses while for the CS glasses a linear to nonlinear trend was observed. Solid-state27Al nuclear magnetic resonance (NMR) revealed the sole presence of AlO4groups in both the pristine and CS glasses.23Na NMR and wet-chemical analysis manifested that all Al-bearing glasses had a lower and near-constant K+-for-Na+ion exchange ratio than the soda-lime-silicate glass. Differential thermal analysis of CS glasses revealed a “blurred” glass transition temperature (Tg) and an exothermic step belowTg; the latter stems from the relaxation of residual compressive stresses. The nanoindentation-derived hardness at low loads and <5 mol% Al2O3showed evidence of stress relaxation for prolonged ion exchange treatment. The crack resistance is maximized for molar ratiosn(M(2)O)/n(Al2O3)≈1for the CS glasses, which is attributed to an increased elastic energy recovery that is linked to the glass compactness.

Relationship between thermal dehydroxylation and aluminium extraction from a low-grade kaolinite: Role of clay chemistry and crystallinity

The presented research investigates the impact of clay crystallinity and iron oxide content on thermal dehydroxylation of kaolinite and thus the impact on aluminium dissolution. Two clay samples with different crystallinity and purity levels (designated low-grade for the impurity rich and disordered kaolin, and high grade for the highly crystalline and relatively pure kaolin) underwent thermal treatment from ambient temperature to 850 °C in 50 °C increments, followed by acid digestion to recover aluminium. Infrared spectroscopy and X-ray diffraction were used to characterise the clays after thermal treatment and following acid digestion to gain insights into the chemistry of the process. Lower temperatures were required to achieve complete thermal dehydroxylation for the low-grade kaolin at 450 °C, in comparison to high-grade kaolin, which was complete at 650 °C. Solid-state 27Al Nuclear magnetic resonance (NMR) highlighted the emergence of Al(IV) at 600 °C and Al(V) at 650 °C, the latter of which corresponded to the complete thermal dehydroxylation of the kaolinite and was the main aluminium species responsible for aluminium dissolution. The iron oxide phases present within the low-grade kaolin resulted in phase transformation to insoluble aluminium spinels at lower temperatures (750 °C), which caused a reduction in the acid solubility of aluminium and iron. However, there were benefits associated with aluminium recovery from the low-grade kaolin, namely, less energy being required to achieve complete thermal dehydroxylation for aluminium dissolution. This finding holds significance for the utilisation of low-grade kaolin by industry, such as for production of new commodities such as high purity alumina.

A highly active and cost-effective tungsten modified Ni-based catalyst for the production of hydrogen via methane dry reforming

Catalyst community requires a low-cost, high-performance catalyst immediately for cost-effective H2 production through dry reforming of methane. Herein, cost-effective 1–9 wt% tungsten oxide-alumina supported Ni catalysts were prepared, examined and characterized by x-ray diffraction, 27Al solid-state nuclear magnetic resonance, X-ray photoelectron spectroscopy, high resolution-transmission electron microscopy and temperature programmed experiments. On 5.0 wt% W incorporation; minimum crystallinity, additional CO2-surface interacting species, maximum oxygen replenishment capacity by CO2, thermally retainable coordinated Al sites and minimum % weight loss pivot optimum hydrogen production 77% H2 yield, minimum deactivation factor −0.9, and maximum rate of hydrogen formation of 1.1301 molH2gcat−1h−1 at 440-min time-on-stream.

Steam Catalytic Cracking of n-Dodecane to Light Olefins over Phosphorous- and Metal-Modified Nanozeolite Y.

Nanozeolite Y was synthesized without a template and modified with phosphorous (P) and metals. P was introduced via impregnation with different weight loadings (0.5, 1, and 2 wt %), while ion exchange was developed to introduce zirconium (Zr) and cobalt (Co). The physicochemical properties of the catalysts were characterized with X-ray diffraction (XRD), N2 adsorption–desorption, temperature-programmed desorption of ammonia (NH3-TPD), and 27Al and 31P solid-state nuclear magnetic resonance (NMR). The parent nanozeolite Y showed an identical XRD pattern to that of a previous study, and the modified nanozeolite Y showed a lower crystallinity. The introduction of P altered tetrahedral Al to an octahedral coordination, which affected the catalyst acidity. Then, the catalyst was evaluated to produce olefins from n-dodecane at 550, 575, and 600 °C. The conversion, gas yield, and olefin yield increased with increasing temperature. The maximum olefin yield (63%) was achieved with the introduction of 1 wt % P with the highest selectivity to ethylene. The Co-modified nanozeolite altered the zeolite structure and exhibited similar activity to the P-modified one. Meanwhile, Zr-modified nanozeolite Y caused excessive metal distribution, blocked the porous structure of the zeolite, and then reduced the catalytic activity.

Improving the mechanical property and water resistance of β-hemihydrate phosphogypsum by incorporating ground blast-furnace slag and steel slag

This research work mainly explored the solid waste cementitious material by incorporating ground blast-furnace slag (GBFS) and steel slag (SS) into the β-hemihydrate phosphogypsum (β-HPG) system. The optimum ratio of GBFS/SS was attempted to be found by referring to the ternary contour design method, and the hydration and hardening mechanism of binary systems of β-HPG -GBFS and β-HPG -SS and ternary system of β-HPG -GBFS-SS was investigated. Contour distributions of the compressive strength of pastes with 60–100% β-HPG, and 0–40% GBFS and SS content at the age of 2 h, 1 d, 7 d, and 28 d were analyzed. The further study focused on the performance change rule of the experimental groups with 60% content of β-HPG under different GBFS/SS ratio. Hydration products of these hardened paste samples were characterized by X-ray diffraction (XRD), thermo-gravimetric analysis (TG), 27Al solid-state nuclear magnetic resonance (27Al-NMR). Hydration heat was used to evaluate the hydration process. Pore structure was verified by mercury injection apparatus (MIP) and scanning electron microscope (SEM). The results showed that in comparison with the pure β-HPG system, the compressive strength was improved greatly, the softening coefficient was increased largely, and the water absorption rate was reduced in the β-HPG-GBFS-SS ternary system. Comprehensive consideration of mechanical property and water resistance, results showed that the test group composed of 60% β-HPG, 30% GBFS and 10% SS was the best experimental scheme, and the reasons behind were discussed in detail. These conclusions were hoped to provide significative guidance for the comprehensive utilization of β-HPG, GBFS and SS.

Hydration kinetics and performance of sodium carbonate-activated slag-based systems containing reactive MgO and metakaolin under carbonation

The hydration mechanism and strength development of sodium carbonate-activated slag-based systems mainly depend on the additives used. Although the effects of mineral additives in such systems have been extensively investigated, the effects of Mg2+, Al3+, and Si4+ ions increasing with the addition of reactive MgO (Mg) and metakaolin (Mk) on the hydration mechanism of such systems have not been established yet. This study investigated the hydration kinetics and performance of sodium carbonate-activated ternary blended slag-based binder systems. The hydration mechanism was revealed by isothermal calorimetry and mechanical performance was evaluated with the measurement of compressive strength at different ages up to 56 days. The reaction mechanisms were investigated through X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and 29Si and 27Al solid-state nuclear magnetic resonance (NMR). C-(A)-S-H, Na and Al-enriched C-(N,A)-S-H and hydrotalcite were the main reaction products responsible for the strength development of the samples, accompanied by the minor contribution of other carbonate-containing phases. Partial replacement of slag with Mg and Mk led to high early-age strengths compared to plain samples when Mk was used at 5%. Samples incorporating Mg and Mk achieved similar or higher strengths than ordinary Portland cement-based samples. However, an increase in replacement ratio of Mk beyond 5% led to a significant decrease in compressive strength. Furthermore, the performance of samples under accelerated carbonation was studied. The use of Mg and Mk enhanced carbonation resistance due to enhanced hydrotalcite and C-(N,A)-S-H gel formation, highlighting the potential of using slag-Mg-Mk blends as an alternative binder system.

Generation of Environmentally Persistent Free Radicals on Metal-Organic Frameworks.

Environmentally persistent free radicals (EPFRs) have been recognized as one of the important emerging contaminants with biological toxicity, environmental persistence, and global mobility. Previous studies have identified the catalytic role of surface metal oxides in EPFRs formation and illustrated the metal-dependence of EPFRs by studying on various metal oxide nanoparticles and single crystals. However, there is still lack of an understanding on the formation of EPFRs from the point of view of metal sites. Various factors (e.g., crystalline phases and surface species) of metal oxides are regarded to contribute to the generation of EPFRs, which present profound difficulties for scientists to tease apart the impact of metal type. Herein, a laboratory investigation, in terms of the acidity and oxidation strength of metal cations, was conducted by selecting metal-variable isostructural metal-organic frameworks as material platforms. Specifically, we evaluated EPFRs generation on MIL-100(M) (M = Al, Cr, Fe) from chlorine-substituted phenol vapor and catechol under thermal conditions. It is found that high Lewis acidity of metal sites is crucial for capturing the above two phenolic precursors, activating the O-H bond and promoting EPFRs formation. Radical species with half-life as long as 70 days were generated on MIL-100 rich in 5-fold coordinated Al3+ sites. The unpaired electron spin density donation was further confirmed by using 27Al solid-state nuclear magnetic resonance spectroscopy. Despite their higher oxidation power than Al3+, the exposed Cr3+ and Fe3+ sites show undetectable catalytic activity for the formation of EPFRs, because of their insufficient Lewis acidity. Our results suggest that the surface species rather than Lewis acid sites may be a major contributor to the formation of EPFRs on metal oxides like Fe2O3.

Structural model for amorphous aluminosilicates.

An analytical model is developed for the composition-dependent structure of the amorphous aluminosilicate materials (M2O)x(Al2O3)y(SiO2)1-x-y and (MO)x(Al2O3)y(SiO2)1-x-y, where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. The model is based on a simple set of reactions and contains a single adjustable parameter p (0 ≤ p ≤ 1). The latter is found from 27Al solid-state nuclear magnetic resonance (NMR) experiments in the regime where R = x/y ≥ 1, aided by new experiments on the magnesium and zinc aluminosilicate systems. The parameter p decreases linearly as the cation field strength of M+ or M2+ increases, as per the observation previously made for the degree of aluminum avoidance [Lee et al., J. Phys. Chem. C 120, 737 (2016)]. The results indicate that as the cation field strength increases, there are less fourfold coordinated aluminum atoms to contribute toward the glass network, and Al-O-Al bonds become more prevalent in a progressive breakdown of Loewenstein's aluminum avoidance rule. The model gives a good account of the composition-dependent fraction of non-bridging oxygen (NBO) atoms for R ≥ 1, as assessed from the results obtained from solid-state NMR experiments. An extension of the model to (M2O3)x(Al2O3)y(SiO2)1-x-y glasses leads, however, to an excess of NBO atoms, the proportion of which can be reduced by invoking network-forming fivefold coordinated Al atoms and/or oxygen triclusters. The model provides a benchmark for predicting the structure-related properties of aluminosilicate materials and a starting point for predicting the evolution in the structure of these materials under the extreme conditions encountered in the Earth's interior or in processes such as sharp-contact loading.

Effect of Al2O3 on the molten slag microstructure information by molecular dynamics simulation and experimental analysis

The metallurgical properties of blast furnace slag changed when high alumina iron ore was used extensively due to the resulting changes of the molten slag microstructure. In the study, based on typical CaO–MgO–SiO2–Al2O3 slag systems with different w(Al2O3) content, molecular dynamics simulation was used to calculate the microstructural properties of particles in the high-temperature slag system, such as bond length, partial radial distribution function, coordination numbers, and diffusion coefficient. In addition, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and 27Al solid-state magic angle spinning nuclear magnetic resonance (27Al SS MAS NMR) were used to detect and analyze the samples. The comprehensive calculations and experimental results show that increasing w(Al2O3) can enhance the structural stability of each ion pair, and the strength of the structural stability is such that Si–O > Al–O > Mg–O > Ca–O. The self-diffusion coefficients are as follows: Mg2+ > Ca2+ > Al3+ > Si4+, which leads to the transformation of the [SiO4]4−(Q0), [Si2O7]6−(Q1) and [Si2O6]4−(Q2) structural units to [Si2O5]2−(Q3). The degree of polymerization of slag increased as well as the stability of the structural units. Moreover, the coordination of Al will change from the [AlO6]9−octahedral structure of six-coordinated Al to the [AlO5]7−pentahedral structure of five-coordinated Al and the [AlO4]5−tetrahedral structure of four-coordinated Al. It was also found that the content of non-bridge oxygen in the whole slag system decreased continuously, leading to the increasing degree of polymerization of slag, and the experimental results were consistent with the molecular dynamics calculation.

Rechargeable Aluminum-chalcogen Batteries: Molecular-Level Mechanistic Insights & Scientific Perspectives

Rechargeable aluminum metal batteries have recently garnered significant interest due to its low cost, earth abundance, inherent safety, and high volumetric and gravimetric capacities. Commercialization of rechargeable aluminum battery systems has been limited due to the small number of (i) electrolytes that enable reversible electrodeposition of Al metal and (ii) positive electrode materials that are (electro)chemically within those electrolytes while providing high capacity and cycle life. Metal-chalcogen (e.g., sulfur, selenium) batteries are among the most promising candidates for low-cost, high-energy-density electrochemical energy storage systems; however, to date, rechargeable aluminum-chalcogen batteries have seldom been explored scientifically or technologically.Here, rechargeable aluminum-sulfur (Al-S) and aluminum-selenium (Al-Se) cells were prepared with a chloroaluminate ionic liquid electrolyte (AlCl3:[EMIm][Cl], molar ratio of 1.5:1) and their electrochemical reaction mechanisms and products were studied at a molecular-level with solid-state nuclear magnetic resonance (NMR) spectroscopy. Galvanostatic cycling of both Al-S and Al-Se cells showed similar initial capacities and overpotentials to previously reported systems. For Al-S systems, the higher specific capacity upon charge, compared to discharge, points towards either an unwanted side reaction or deleterious polysulfide-shuttle-like behavior. This phenomenon is heavily prevalent at low current densities and affects reversibility. For Al-Se systems, two different reaction mechanisms that have been previously reported were found to be dependent on the applied current density and the crystallinity of the selenium. We were able to consolidate both reaction mechanisms during a single charge/discharge step, significantly increasing specific capacity and energy density. For both Al-S and Al-Se systems, significant capacity fade was also observed over multiple galvanostatic cycles. Solid-state 27Al single-pulse magic-angle-spinning (MAS) NMR spectra acquired on sulfur electrodes cycled to different states-of-charge reveal the presence of both solid and liquid discharge products. Solid-state 2D 27Al{27Al} multiple-quantum (MQ-)MAS measurements reveal the amorphous nature of the solid discharge product, while 2D 27Al{27Al} exchange spectroscopy (EXSY) NMR spectra reveal chemical exchange between electrolyte-soluble sulfur species coordinating with AlCl4 - and Al2Cl7 - after discharge. For Al-Se systems, solid-state 27Al and 77Se single-pulse MAS NMR measurements also reveal liquid-state reaction products in the electrolyte, leading to loss of active material from the cathode, while revealing compositional changes in the selenium electrode. Scientific perspectives on these aluminum-chalcogen battery chemistries will be discussed. This work also highlights the importance that molecular-level analytical tools, such as solid-state NMR spectroscopy, can have in clarifying electrochemical mechanisms in emerging electrochemical systems.

Removal characteristics and mechanism of microplastics and tetracycline composite pollutants by coagulation process

Water composite pollution is an increasingly severe challenge in the field of water treatment. Especially, microplastic is an emerging concerned pollutant in recent years for its persistent eco-environmental influence. Therefore, investigating the composite pollution effect and developing effective removal technology surrounding microplastic is an urgent task for future need. In this aspect, the removal of composite pollutants, microplastics (PET/weathered PET) and tetracycline (TC), was procedurally studied by coagulation with AlCl3. Based on the analysis of variance (ANOVA) and correlation of experimental data, the characterization of fourier transform infrared spectroscopy (FTIR), solid-state 27Al nuclear magnetic resonance (27Al NMR), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) computation, the removal mechanism for coagulation was well discussed and proposed. It shows that the removal performance of individual PET and TC were mainly influenced by coordination reaction in forming Al-PET and Al-TC, corresponding to the removal rate of 100% and 28%, respectively. Charge neutralization and sweeping flocculation played an auxiliary role for PET removal. However, the weathered PET (WPET) exhibited worse removability (92%) than PET due to a sharp decrease in the hydrodynamic diameter of WPET. The poor removal of TC was induced by the formation of Al-TC which was difficult to transform into solid flocs. In regard to composite pollutants, the removal rate of PET was significantly decreased (91%) due to the low activity of TC in forming flocs and the complexation competition, while the removal of TC was greatly enhanced (41%). In this process of multilayered reaction among PET, TC and Al3+, Al3+ preferentially interacted with TC to form Al-TC, which was subsequently combined to PET to form the ternary complexes PET-Al-TC, thus realizing the transformation from dissolved TC complexes to solid TC composites. This work is of great significance in understanding the interaction mechanism of composite pollutants in coagulation process.

Development and validation of an analytical methodology for quantification of Al in alumina-based materials by 27Al Solid-state nmr

In this work, a simple protocol for counting the Al spins present in diamagnetic materials used as carriers and catalysts based on 27Al solid-state nuclear magnetic resonance using routine 4 mm rotors was developed and validated. The acquisition parameters were optimized, and validation tests were performed using a standard sample of γ-alumina with a known aluminium concentration. The validation results indicated that solid-state NMR can be used for the quantification of quadrupolar aluminium (mmol Al.g-1 material) in diamagnetic materials by employing non-special tools with satisfactory results, similar to the NMR quantitative analysis of dipolar nuclei in solids.

Formation and Location of Pt Single Sites Induced by Pentacoordinated Al Species on Amorphous Silica-Alumina.

Alumina and its mixed oxides are popular industrial supports for emerging supported metal catalysts. Pentacoordinated Al (AlV) species are identified as key surface sites for anchoring and stabilizing metal single-site catalysts; however, AlV is rare in conventional amorphous silica-alumina (ASA). Recently, we have developed AlV-enriched ASA, which was applied as a support for the synthesis of Pt single-site catalysts in this work. Each preparation stage and the interaction between Pt and surface Al species were explored by 1H and 27Al solid-state nuclear magnetic resonance spectroscopy, and the formation of the dominant Pt single sites on the surface of AlV-enriched ASA was confirmed by high-angle annular dark-field imaging scanning transmission electron microscopy and energy dispersive spectroscopy line scanning. On the surface of supports without a significant AlV population (Pt/Al2O3 and Pt/SiO2), mainly Pt nanoparticles were formed. This indicates that AlV contributes to the strong metal-support interaction to stabilize the Pt single sites on Pt/ASA, which was characterized by diffuse reflectance infrared Fourier transform spectroscopy combined with CO adsorption, X-ray photoelectron spectroscopy, and electron energy loss spectroscopy. Pt single sites supported on AlV-enriched ASA exhibit excellent chemoselectivity in the hydrogenation of C═O groups, affording 2-3-fold higher yields compared to those of Pt nanoparticles supported on Al2O3 and SiO2.