Large aqueous aluminum hydroxide molecules

Recent advances in atomic cluster synthesis: a perspective from chemical elements

Despite its potential significance, "cluster chemistry" remains a somewhat marginalized topic within the chemistry field. However, atomic clusters with their unusual and unique structures and properties represent a novel material group situated between molecules and nanoparticles or solid matter, judging from both scientific standpoints and historical backgrounds. Surveying an entire material group, including all substances that can be regarded as a cluster, is essential for establishing cluster chemistry as a more prominent chemistry field. This review aims to provide a comprehensive understanding by categorizing, summarizing, and reviewing clusters, focusing on their constituent elements in the periodic table. However, because numerous disparate synthetic processes have been individually developed to date, their straightforward and uniform classification is a challenging task. As such, comprehensively reviewing this field from a chemical composition viewpoint presents significant obstacles. It should be therefore noted that despite adopting a synthetic method-based classification in this review, the discussions presented herein could entail inaccuracies. Nevertheless, this unorthodox viewpoint unfolds a new scientific perspective which accentuates the common ground between different development processes by emphasizing the lack of a definitive border between their synthetic methods and material groups, thus opening new avenues for cementing cluster chemistry as an attractive chemistry field.

Analyzing Stabilities of Metal-Organic Frameworks: Correlation of Stability with Node Coordination to Linkers and Degree of Node Metal Hydrolysis

Among the important properties of metal-organic frameworks (MOFs) is stability, which may limit applications, for example, in separations and catalysis. Many MOFs consist of metal oxo cluster nodes connected by carboxylate linkers. Addressing MOF stability, we highlight connections between metal oxo cluster chemistry and MOF node chemistry, including results characterizing Keggin ions and biological clusters. MOF syntheses yield diverse metal oxo cluster node structures, with varying numbers of metal atoms (3-13) and the tendency to form chains. MOF stabilities reflect a balance between the number of node-linker connections and the degree of node hydrolysis. We summarize literature results showing how MOF stability (the temperature of decomposition in air) depends on the degree of hydrolysis/condensation of the node metals, which is correlated to their degree of substitution with linkers. We suggest that this correlation may help guide the discovery of stable new MOFs, and we foresee opportunities for progress in MOF chemistry emerging from progress in metal oxo cluster chemistry.

Induced Aggregation, Solvent Regulation, and Supracluster Assembly of Aluminum Oxo Clusters

ConspectusRecent years have witnessed the development of cluster materials as they are atomically precise molecules with uniform size and solution-processability, which are unattainable with traditional nanoparticles or framework materials. The motivation for studying Al(III) chemistry is not only to understand the aggregation process of aluminum in the environment but also to develop novel low-cost materials given its natural abundance. However, the Al-related clusters are underdeveloped compared to the coinage metals, lanthanides, and transition metals. The challenge in isolating crystalline compounds is the lack of an effective method to realize the controllable hydrolysis of Al(III) ions. Compared with the traditional hydrolysis of inorganic Al(III) salts in highly alkaline solutions and hydrolysis of aluminum trialkyl compounds conducted carefully in an inert operating environment, we herein developed an effective way to control the hydrolysis of aluminum isopropanol through an alcoxalation reaction. By solvothermal/low melting point solid melting synthesis and using "ligand aggregation, solvent regulation, and supracluster assembly" strategies, our laboratory has established an organic-inorganic hybrid system of aluminum oxo clusters (AlOCs). The employment of organic ligands promotes the aggregation and slows the hydrolysis of Al(III) ions, which in turn improves the crystallization process. The regulation of the structure types can be achieved through the selection of ligands and the supporting solvents. Compared with the traditional condensed polyoxoaluminates, we successfully isolated a broad range of porous AlOCs, including aluminum molecular rings and Archimedes aluminum oxo cages. By studying ring expansion, structural transformation, and intermolecular supramolecular assembly, we demonstrate unique and unprecedented structural controllability and assembly behavior in cluster science. The advancement of this universal synthetic method is to realize materials customization through modularly oriented supracluster assembly. In this Account, we will provide a clear-cut definition and terminology of "ligand aggregation, solvent regulation, and supracluster assembly". Then we will discuss the discovery in this area by using a strategy, such as aluminum molecular ring, ring size expansion, ring supracluster assembly, etc. Furthermore, given the internal and external pore structures, as well as the solubility and modifiability of the AlOCs, we will demonstrate their potential applications in both the solid and liquid phases, such as iodine capture, the optical limiting responses, and dopant in polymer dielectrics. The strategy herein can be applied to extensive cluster science and promote the research of main group element chemistry. The new synthetic method, fascinating clusters, and unprecedented assembly behaviors we have discovered will advance Al(III) chemistry and will also lay the foundation for functional applications.

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The absolute structures of a pair of infinite Na(H2O)4+-connected ε-Keggin-Al13 species (Na-ε-K-Al13) that were inversion structures and mirror images of each other were determined. Single crystals obtained by adding A2SO4 (A = Li, Na, K, Rb, or Cs) solution to NaOH-hydrolyzed AlCl3 solution were subjected to X-ray structure analyses. The statistical results for 36 single crystals showed that all the crystals had almost the same unit cell parameter, belonged to the same F4̅3m space group, and possessed the same structural formula [Na(H2O)4AlO4Al12(OH)24(H2O)12](SO4)4·10H2O. However, the crystals had two inverse absolute structures (denoted A and B), which had a crystallization ratio of 1:1. From Li+ to Cs+, with increasing volume of the cation coexisting in the mother solution, the degree of disorder of the four H2O molecules in the Na(H2O)4+ hydrated ion continuously decreased; they became ordered when the cation was Cs+. Absolute structures A and B are the first two infinite aluminum polycations connected by statistically occupied [(Na1/4)4(H2O)4]+ hydrated ions. The three-dimensional structure of the infinite Na-ε-K-Al13 species can be regarded as the assembly of finite ε-K-Al13 species linked by [(Na1/4)4(H2O)4]+ in a 1:1 ratio. In this assembly, each [(Na1/4)4(H2O)4]+ is connected to four ε-K-Al13 and each ε-K-Al13 is also connected to four [(Na1/4)4(H2O)4]+ in tetrahedral orientations to form a continuous rigid framework structure, which has an inverse spatial orientation between absolute structure A and B. This discovery clarifies that the ε-K-Al13 (or ε-K-GaAl12) species in Na[MO4Al12(OH)24(H2O)12](XO4)4·nH2O (M = Al, Ga; X = S, Se; n = 10-20) exists as discrete groups and deepens understanding of the formation and evolution process of polyaluminum species in forcibly hydrolyzed aluminum salt solution. The reason why Na+ statistically occupies the four sites was examined, and a formation and evolution mechanism of the infinite Na-ε-K-Al13 species was proposed.

Development and validation of a general-purpose ReaxFF reactive force field for earth material modeling

ReaxFF reactive force field bridges the gap between nonreactive molecular simulations and quantum mechanical calculations and has been widely applied during the past two decades. However, its application to earth materials, especially those under high T-P conditions relevant to Earth's interior, is still limited due to the lack of available parameters. Here, we present the development and validation of a ReaxFF force field containing several of the most common elements in Earth's crust, i.e., Si/Al/O/H/Na/K. The force field was trained against a large data set obtained from density functional theory (DFT) calculations, including charges, bond/angle distortion curves, equation of states, ion migration energy profiles, and condensation reaction energies. Different coordination environments were considered in the training set. The fitting results showed that the current force field can well reproduce the DFT data (the Pearson correlation coefficient, Rp, is 0.95). We validated the force field on mineral-water interfaces, hydrous melts/supercritical geofluids, and bulk crystals. It was found that the current force field performed excellently in predicting the structural, thermodynamic, and transport properties of various systems (Rp = 0.95). Moreover, possible applications and future development have been discussed. The results obtained in this study suggest that the current force field holds good promise to model a wide range of processes and thus open opportunities to advance the application of ReaxFF in earth material modeling.

Supracluster Assembly of Archimedean Cages with 72 Hydrogen Bonds for the Aldol Addition Reaction

Clusters that can be experimentally precisely characterized and theoretically accurately calculated are essential to understanding the relationship between material structure and function. Here, we propose the concept of "supraclusters", which aim to connect "supramolecules" and "suprananoparticles" as well as reveal the unique assembly behavior of "supraclusters" with nanoparticle size at the molecular level. The implementation of supraclusters is full of challenges due to the difficulty in satisfying the ordered connectivity of clusters due to their abundant and dispersed hydrogen bonding sites. By solvothermal synthesis under a high catechol (H2 CATs) content, we successfully isolated a series of triangular {Al6 M3 } cluster compounds possessing brucite-like structural features. Interestingly, eight {Al6 M3 } clusters form 72-fold strong hydrogen bonding truncatedhexahedron Archimedean {Al6 M3 }8 supracluster cage (abbreviated as H-tcu). Surprisingly, the solution stability of the H-tcu was further proved by electrospray ionization mass spectrometry (ESI-MS) characterization. Therefore, it is not difficult to explain the reason for assembly of H-tcu into edge-directed and vertex-directed isomers. These porous supraclusters can be obtained by scale-up synthesis and exhibit a noticeable catalysis effect towards the condensation of acetone and p-nitrobenzaldehyde. As an intermediate state of supramolecule and suprananoparticle, the supracluster assembly can enrich the cluster chemistry and bring new structural types.

Observation of alumina nanoparticles generated from aqueous solutions of a "flat" aluminum-13 cluster

Amorphous alumina nanoparticles were synthesized via dynamic processes during the dissolution of aluminum hydroxide by nitric acid, a method commonly used to produce aqueous solutions of aluminum oxide molecular clusters. These particles were characterized by DLS measurements, and corroborated by other solution and solid state analyses. The methods used represent a highly tuneable, facile synthetic pathway that allows for size targeting and scalability for industrial purposes, and provides insight into pH- and temperature-dependent alumina speciation and aggregation.

Oxygen-evolution reaction in the presence of cerium(IV) ammonium nitrate and iron (hydr)oxide: old system, new findings

Solar fuel production by photosynthetic systems strongly relies on developing efficient and stable oxygen-evolution catalysts (OECs). Cerium(IV) ammonium nitrate (CAN) has been the most commonly used sacrificial oxidant to investigate OECs. Although many metal oxides have been extensively investigated as OECs in the presence of CAN, mechanistic studies were rarely reported. Herein, first, Fe(III) (hydr)oxide (FeOxHy) was prepared by the reaction of Fe(ClO4)3 and KOH solution and characterized by some methods. Then, changes in Fe oxide in the presence of CAN during the OER were tracked using in situ Raman spectroscopy, in situ X-ray absorption spectroscopy, in situ visible spectroscopy, and in situ electron paramagnetic resonance spectroscopy. FeOxHy in the presence of CAN and during the OER converted to γ-Fe2O3 and [Fe(H2O)6]3+, and a small amount of oxygen was formed. A maximum turnover frequency and turnover number of 10-6 s-1 and 1.3 × 10-3 mol(O2)/mol(Fe) (for half an hour) in the presence of CAN (0.20 M) and FeOxHy were observed.

Effects and mechanisms of Al substitution on the catalytic ability of ferrihydrite for Mn(II) oxidation and the subsequent oxidation and immobilization of coexisting Cr(III)

Al(III)-substituted ferrihydrite existing in natural soils is more common than pure ferrihydrite; however, the effects of Al(III) incorporation on the interaction between ferrihydrite, Mn(II) catalytic oxidation, and coexisting transition metal (e.g., Cr(III)) oxidation remain elusive. To address this knowledge gap, Mn(II) oxidation on synthetic Al(III)-incorporated ferrihydrite and Cr(III) oxidation on the previously formed Fe-Mn binaries were investigated in this study via batch kinetic studies combined with various spectroscopic analyses. The results indicate that Al substitution in ferrihydrite barely changes its morphology, specific surface area, or the types of surface functional groups, but increases the total amount of hydroxyl on the ferrihydrite surface and enhances its adsorption capacity toward Mn(II). Conversely, Al substitution inhibits electron transfer in ferrihydrite, thereby weakening its electrochemical catalysis on Mn(II) oxidation. Thus, the contents of Mn(III/IV) oxides with higher Mn valence states decrease, whereas those of lower Mn valence states increase. Furthermore, the number of hydroxyl radicals formed during Mn(II) oxidation on ferrihydrite decreases. These inhibitions of Al substitution on Mn(II) catalytic oxidation subsequently cause decreased Cr(III) oxidation and poor Cr(VI) immobilization. Additionally, Mn(III) in Fe-Mn binaries is confirmed to play a dominant role in Cr(III) oxidation. This research facilitates sound decision-making regarding the management of Cr-contaminated soil environments enriched with Fe and Mn.

Decomposition of Al13 promoted by salicylic acid under acidic condition: Mechanism study by differential mass spectrometry method and DFT calculation

Decomposition of the polycation Al₁₃O₄(OH)₂₄(H₂O)₁₂⁷⁺ (Al₁₃) promoted by ligand is a vital subject to advance our understanding of natural and artificial occurrence and evolution of aluminum ions, especially in the case of acidic condition that dissolved Al³⁺ species can be released from the Al-bearing substances. However, the microscopic pathway of synchronous proton-promoted and ligand-promoted decomposition process for Al₁₃ is still in the status of ambiguity. Herein, we applied differential mass spectrometry method and DFT calculation to study the initial detailed process of Al₁₃ decomposition under the presence of proton and salicylic acid (H₂Sal). Mass results showed that the mononuclear Al³⁺-H₂Sal complexes dominated the resulting Al species, whereas the monodentate complex Al₁₃HSal⁶⁺ was not observed in the spectra. The difference of decomposition levels between the ligand/Al ratio 0.2 and 0.5 cases revealed that proton and ligand performed synergistic effect in initial Al₁₃ decomposition process, and the proton transfer determined the ring closure efficiency. The ring closure reaction is the prerequisite for the collapse of Al₁₃ structure and detachment of the mononuclear complex. DFT calculations reveal that hydrogen bond plays an important role in inducing the formation of chelated complex accompanying proton transfer. Attachment of protons at the bridging OH^- can elongate and weaken the critical bond between targeted Al³⁺ and µ₄-O^2- resulting from delocalization of electron pairs in the oxygen atom. These results demonstrate the detailed mechanism of Al₁₃ composition promoted by ligand and proton, and provide significant understanding for further application and control of Al₁₃.

From an aluminum oxo cluster to an aluminum oxo cluster organic cage

Presented herein is an example of the conversion of an aluminum oxo cluster (AlOC) to an aluminum oxo cluster organic cage (AlOCOC). We successfully synthesized the first example of an aluminum cluster-based organic cage-Al₁₂ tetrahedral cage via an Al₃ cluster. The use of 4-pyrazolecarboxylic acid plays an important role in the construction of the organic cage. Due to the presence of partially deprotonated ligands, the hydrogen-bonding interactions between the discrete tetrahedra generate porous supramolecular structures. Considering the high porosity and the abundant N-H sites, we further investigated the performance of the material towards iodine capture.

Water-Harvesting Metal-Organic Frameworks with Gigantic Al24 Units and their Deconstruction into Molecular Clusters

In contrast to the vast Al-oxo molecular cluster chemistry, Al-based building units for metal-organic framework (MOF) construction are limited in structural diversity and complexity. Synthesis of single crystalline MOFs based on this "hard" metal is further complicated by the poor reversibility of the Al-organic coordination linkages. Here, a strategy to employ two kinds of linkages with distinct strength-strong Al-carboxylate linkage and weak Cu-pyrazol N linkage-gives FDM-91 (FDM=Fudan Materials) with gigantic Al₂₄ -based units. After replacing the weak moieties with organic linkers post-synthetically, two new stable MOFs with exceptional water harvesting capacity (up to 0.53 g g^-1 ) and outstanding cycling performance are developed. Linkage-selective dissociation of FDM-91 further leads to the isolation of the Al₂₄ molecular clusters. The versatile chemistry performed here to reinforce or deconstruct MOFs provides a new way to make important extended and discrete structures.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

The arsenic species in the sulfidic environments: Determination, transformation, and geochemical implications

The species and fate of arsenic (As) are closely related to sulfide (S^-II) in the anaerobic and sulfidic environment. In this work, the mechanisms and kinetics of arsenate (As^V) reduction by S^-II at different pHs, S^-II/As^V molar ratios, and initial As^V concentrations in the absence (or presence) of Al-hydroxide were studied, where the concentrations of various kinds of As species, namely As^V, arsenite (As^III), and thioarsenics (ThioAs) were qualitatively and quantitatively determined by liquid chromatography with atomic fluorescence spectrophotometry. The results showed that under acidic or neutral conditions, ThioAs may act as intermediate(s), where amorphous As₂S₃ precipitate was observed at pH 5 in high S^-II condition. By comparison, at pH 9, As^V was probably directly reduced to As^III with polysulfide as the byproduct. The reaction rate was faster at mildly acidic pH than that of neutral or alkaline pH, as well as in the presence of Al-hydroxide. The findings may give further insights about the role of ThioAs in the biogeochemical cycle of As.

Exploring the In Situ Formation Mechanism of Polymeric Aluminum Chloride-Silica Gel Composites under Mechanical Grinding Conditions: As a High-Performance Nanocatalyst for the Synthesis of Xanthene and Pyrimidinone Compounds

The use of mechanical ball milling to facilitate the synthesis of organic compounds has attracted intense interest from organic chemists. Herein, we report a new process for the preparation of xanthene and pyrimidinone compounds by a one-pot method using polymeric aluminum chloride (PAC), silica gel, and reaction raw materials under mechanical grinding conditions. During the grinding process, polymeric aluminum chloride and silica gel were reconstituted in situ to obtain a new composite catalyst (PAC-silica gel). This catalyst has good stability (six cycles) and wide applicability (22 substrates). The Al-O-Si active center formed by in situ grinding recombination was revealed to be the key to the effective catalytic performance of the PAC-silica gel composites by the comprehensive analysis of the catalytic materials before and after use. In addition, the mechanism of action of the catalyst was verified using density functional theory, and the synthetic pathway of the xanthene compound was reasonably speculated with the experimental data. Mechanical ball milling serves two purposes in this process: not only to induce the self-assembly of silica and PAC into new composites but also to act as a driving force for the catalytic reaction to take place. From a practical point of view, this "one-pot" catalytic method eliminates the need for a complex preparation process for catalytic materials. This is a successful example of the application of mechanochemistry in materials and organic synthesis, offering unlimited possibilities for the application of inorganic polymer materials in green synthesis and catalysis promoted by mechanochemistry.

Structure-Function Correlations in the Mechanism of Action of Key Antiperspirant Agents Containing Al(III) and ZAG Salts

Aluminum hydrolysis chemistry is an important part of modern society because of the dominance of Al(III) as a highly effective antiperspirant active. However, the century-old chemistry centered on aluminum chloride (ACL) is not comprehensive enough to address all of the in vivo events associated with current commercial antiperspirants and their mechanism of action. The present study aims to address the knowledge gap among extensively studied benchmark ACL, its modified version aluminum chlorohydrate (ACH), and a more complex but less explored group of aluminum zirconium chlorohydrate glycine complexes (ZAG salts) toward understanding the mechanism of action under consumer-relevant conditions. ACH, which is the Al source used in the manufacture of ZAG salts, provides a bridge between ACL and ZAG chemistry. High viscosity and gel formation driven by pH and a specific Al(III) salt upon hydrolysis are considered the criteria for building an in vivo occlusive mass to retard or stop the flow of sweat to the skin surface, thus providing an antiperspirant effect. Rheological studies indicated that ACL and aluminum zirconium tetrachlorohydrex glycine (TETRA) were the most efficacious salt actives. Spectroscopic studies, diffraction studies, and elemental analysis suggested that small metal oxide and hydroxide species with coparticipating glycine as well as various polynuclear and oligomeric species are the key to gel formation. At a given pH, the key ingredients (NaCl, urea, bovine serum albumin, and lactic acid) in artificial sweat were found to have little influence on Al(III) salt hydrolysis. The effects of the sweat components were mostly limited to local complex formation and kinetic modification. The in vitro comparative experiments with various Al(III) and ZAG salt systems offer unprecedented insights into the chemistry of different salt types, thus paving the way for engineering more efficacious antiperspirant systems.

27 Al NMR diffusometry of Al13 Keggin nanoclusters

Although nanometer-sized aluminum hydroxide clusters (i.e., ϵ-Al₁₃ , [Al₁₃ O₄ (OH)₂₄ (H₂ O)₁₂ ]⁷⁺ ) command a central role in aluminum ion speciation and transformations between minerals, measurement of their translational diffusion is often limited to indirect methods. Here, ²⁷ Al pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has been applied to the AlO₄ core of the ϵ-Al₁₃ cluster with complementary theoretical simulations of the diffusion coefficient and corresponding hydrodynamic radii from a boundary element-based calculation. The tetrahedral AlO₄ center of the ϵ-Al₁₃ cluster is symmetric and exhibits only weak quadrupolar coupling, which results in favorable T₁ and T₂ ²⁷ Al NMR relaxation coefficients for ²⁷ Al PFGSTE NMR studies. Stokes-Einstein relationship was used to relate the ²⁷ Al diffusion coefficient of the ϵ-Al₁₃ cluster to the hydrodynamic radius for comparison with theoretical simulations, dynamic light scattering from literature, and previously published ¹ H PFGSTE NMR studies of chelated Keggin clusters. This first-of-its-kind observation proves that ²⁷ Al PFGSTE NMR diffusometry can probe symmetric Al environments in polynuclear clusters of greater molecular weight than previously considered.

The new life of traditional water treatment flocculant polyaluminum chloride (PAC): a green and efficient micro–nano reactor catalyst in alcohol solvents

Polyaluminum chloride (PAC) is an inorganic polymer material that has the advantages of a simple preparation process and special electronic structure. It is considered to be the most efficient and widely used flocculation material for water treatment. In this work, PAC has been used as a Lewis acid catalyst in interdisciplinary fields because of its polynuclear Al–O cation structure. Further, its catalytic mechanism in green organic synthesis has been studied in detail by using the multicomponent Biginelli reaction as the probe. The effect of solvent on the self-assembly and aggregation process of PAC materials was investigated using optical microscopy, UV-Vis spectrophotometry, particle size analysis, XPS, IR, SEM and HR-TEM. The results show that the PAC materials have different morphological characteristics in different solvents. The Al–O–Al cations were transformed in the ethanol solvent to form new multi-nuclear cation aggregates Al_b, which could be used as inorganic micro–nano reactors with unique synergistic catalysis in catalytic reactions. This is the first time the role of PAC in the Biginelli reaction has been analyzed with a liquid in situ infrared instrument, which provided favorable evidence for the speculated reaction mechanism. The PAC–ethanol system is, therefore, considered to be a green, efficient (best yield >99%), economic and recyclable catalyst for catalyzing organic synthesis reactions. The development and utilization of PAC materials in organic synthesis will bring new vitality to this cheap material, which is widely used in industries.

The polyaluminum chloride–ethanol micro–nano reactor is a green, efficient, easy-to-handle and economical catalyst for catalyzing organic synthesis reactions.

Vanadium-substituted polycationic Al-oxo cluster in a porous ionic crystal exhibiting Lewis acidity

A vanadium-substituted polycationic Al-oxo cluster (Al28V4) in an all-inorganic porous ionic crystal exhibits Lewis acidity.

Deprotonation and aggregation of Al13 under alkaline titration: A simulating study related to coagulation process

Unraveling the transformation of coagulants and their interaction with contaminants at the micro-level is vital to advancing our understanding of the coagulation mechanism. To the best of our knowledge, the coagulation effectiveness of [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ (Al₁₃), regarded as the dominant species in polyaluminum chloride (PACl), is highly related to its aggregation characteristic, but the detailed process of Al₁₃ aggregation in coagulation time scale was not well studies. Here we systematically studied the deprotonation and aggregation processes of Al₁₃ by alkaline titration to simulate the reaction in coagulation case. By reacting with OH^-, Al₁₃ can continuously lose protons regardless of pH until its positive charge was well neutralized. The initial Al₁₃ aggregates (Al₁₃agg) appeared at B of 2.70 and large Al₁₃agg was generated by coalescence of small initial Al₁₃agg. Most Al₁₃ polycations kept their main structure unchanged during aggregation and part was decomposed into monomers or oligomers. Density functional theory (DFT) results reveal that Al₁₃ becomes unstable after deprotonation, but the aggregation of Al₁₃ bridged by Al monomers can stabilize the polycations. Al₁₃ needs to be hydrolyzed before interacting with colloidal particles, but particles can promote the aggregation of Al₁₃ by weakening the repulsion force between the polymers. Strong and compact flocs can be generated induced by in-situ aggregation of Al₁₃ in neutral and alkaline conditions. This study can provide a deep understanding about the role of Al₁₃agg in removing particles and instruct the development of new efficient coagulants against the various water qualities.

Dendritic growth of protein gel in the course of sweat pore plugging by aluminium salts under physiological conditions

Are aluminium ions unavoidable in antiperspirants? To answer this question, we present confocal microscopy images of dendritic plugs appearing in sweat flowing across a microfluidic channel in the presence of aluminium salts. By comparing with numerical simulations, we identify the mechanisms forming this structured protein gel inside the pore.

Structure and solvation dynamics of the hydroxide ion in ice-like water clusters: a CCSD(T) and car-parrinello molecular dynamics study

Using MP2, CCSD(T) electronic structure theory and ab initio molecular dynamics simulations, we explore the structure, solvation dynamics and vibrational spectra of OH^-(H₂O)_n clusters. Our study reports new cubic and fused cubic global minima structures of OH^-(H₂O)_n for n = 8-26 with surface and interior solvation arrangements. In the case of OH^-(H₂O)₂₆, we show that MP2 and CCSD(T) calculations predict global minima structures with the hydroxide ion occupying the interior region of a densely packed cubic cluster that is secured by ionic hydrogen bonds. More importantly, results from ab initio molecular dynamics simulations of OH^-(H₂O)₂₆ demonstrate that the hydroxide ion remains in the cluster interior and hexa-coordinated, irrespective of the temperature, up to around 175 K, then incrementally transitions from a surface-exposed penta- (170-200 K), to a tetra- (225 K) to a tri-coordinated OH^-(H₂O)₃ structure at 300 K. Building on our temperature-dependent vibrational power spectra, we are also able to disentangle structure and temperature effects on individual spectral contributions arising from water molecules located in the inner and outer shell of OH^-(H₂O)₂₆. Some of these theoretical results provide valuable guidance for the interpretation of IRMPD spectra of small hydroxide-water clusters, but there are also several intriguing implications of these results, in particular, for the solvation of the OH^- ion at the surface of water nanodroplets and aqueous interfaces.

Isomeric effects on the acidity of Al13 Keggin clusters in porous ionic crystals

We demonstrate a facile synthesis method of a porous ionic crystal (PIC) composed of the little-known δ-Keggin-type cationic polyoxoaluminum cluster ([δ-Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺, δ-Al₁₃) with an oppositely-charged polyoxometalate, which enabled us to investigate the activity as a solid acid. The δ-Al₁₃ based PIC exhibited much higher activity in pinacol rearrangement, a typical acid-catalyzed reaction, than the PIC based on the well-known and thermodynamically stable rotational isomer (ε-Al₁₃). This work is a rare example of rotational isomers of polyoxoaluminum clusters exhibiting remarkably different catalytic activities.

Pre-aggregation of Al13 in optimizing coagulation for removal of humic acid

The effective removal of humic acid (HA) by coagulation has been extensively investigated for water treatments. However, the limitations of pH variation and excessive residual aluminum issues were still factors needed to be considered. In this study, to investigate the coagulation mechanism for removing HA by Al₁₃ and optimize Al₁₃ operation for removing HA, Al₁₃ and preformed Al₁₃ aggregates (Al₁₃agg) were applied to remove HA at different pH conditions. The results showed that preformed Al₁₃agg exhibited superior HA removal performance than Al₁₃ due to its wide pH range and low residual Al level. During coagulation, Al₁₃ and Al₁₃agg interacted with HA in their original status, but the DSlope_325-375 difference implied that the complexation capacity between HA and Al₁₃agg was stronger than Al₁₃. The new peaks of HPSEC representing larger molecular weight substances were formed under acidic and neutral conditions, which indicated that HA firstly aggregated into larger complexed molecules by interacting with Al₁₃ or its hydrolysates and was subsequently removed by forming large flocs which was completely different from Al₁₃agg situation. Therefore, the different coagulation mechanisms played the roles in HA removal for Al₁₃ and Al₁₃agg which were studied in this paper. It was believed that the complexation and charge neutralization effects dominated coagulation process for Al₁₃ while sweep flocculation and adsorption coagulation were main driving force for Al₁₃agg in HA removing. This work provides significant understanding of HA removal by Al₁₃ and Al₁₃agg coagulation, which can help to design and optimize the high efficiency coagulant based on Al polycations.

Snapshots of Ce70 Toroid Assembly from Solids and Solution

Crystallization at the solid-liquid interface is difficult to spectroscopically observe and therefore challenging to understand and ultimately control at the molecular level. The Ce₇₀-torroid formulated [Ce^IV₇₀(OH)₃₆(O)₆₄(SO₄)₆₀(H₂O)₁₀]^4-, part of a larger emerging family of M^IV₇₀-materials (M = Zr, U, Ce), presents such an opportunity. We elucidated assembly mechanisms by the X-ray scattering (small-angle scattering and total scattering) of solutions and solids as well as crystallizing and identifying fragments of Ce₇₀ by single-crystal X-ray diffraction. Fragments show evidence for templated growth (Ce₅, [Ce₅(O)₃(SO₄)₁₂]^10-) and modular assembly from hexamer (Ce₆) building units (Ce₁₃, [Ce₁₃(OH)₆(O)₁₂(SO₄)₁₄(H₂O)₁₄]^6- and Ce₆₂, [Ce₆₂(OH)₃₀(O)₅₈(SO₄)₅₈]^14-). Ce₆₂, an almost complete ring, precipitates instantaneously in the presence of ammonium cations as two torqued arcs that interlock by hydrogen boding through NH₄⁺, a structural motif not observed before in inorganic systems. The room temperature rapid assemblies of both Ce₇₀ and Ce₆₂, respectively, by the addition of Li⁺ and NH₄⁺, along with ion-exchange and redox behavior, invite exploitation of this emerging material family in environmental and energy applications.

Synthesis, Structures, and Fluorescence Properties of Dimeric Aluminum Oxo Clusters

Aluminum is an important component for luminescence. However, the fluorescent aluminum complex with unambiguous structural information is still limited. Herein, we report a series of fluorescence aluminum oxo clusters (AlOCs). By introducing an additional coordination site to the aromatic conjugation ligand, cluster nuclearity increment and fluorescence variation are observed. Al₈(OH)₂(μ₄-O)₂(1-NA)₂(OEt)₁₆ (AlOC-41, 1-NA = 1-naphthoic acid, OEt = ethanol) is made up of two tetrahedral subunits. By introducing an additional coordination site to the aromatic conjugation ligand, we isolate a high nuclearity compound Al₁₀(μ₃-O)₂(3-HNA)₂(OEt)₂₂ (AlOC-47, 3-HNA = 3-hydroxy-2-naphthoic acid). Correspondingly, their luminescence performance is different (blue fluorescence in AlOC-41 and green in AlOC-47). Present herein is a platform to illustrate the relationship between synthesis, structure, and fluorescence properties.

Real time observation of the interaction between aluminium salts and sweat under microfluidic conditions

Aluminium salts such as aluminium chlorohydrate (ACH) are the active ingredients of antiperspirant products. Their mechanism of action involves a temporary and superficial plugging of eccrine sweat pores at the skin surface. We developed a microfluidic system that allows the real time observation of the interactions between sweat and ACH in conditions mimicking physiological sweat flow and pore dimensions. Using artificial sweat containing bovine serum albumin as a model protein, we performed experiments under flowing conditions to demonstrate that pore clogging results from the aggregation of proteins by aluminium polycations at specific location in the sweat pore. Combining microfluidic experiments, confocal microscopy and numerical models helps to better understand the physical chemistry and mechanisms involved in pore plugging. The results show that plugging starts from the walls of sweat pores before expanding into the centre of the channel. The simulations aid in explaining the influence of ACH concentration as well as the impact of flow conditions on the localization of the plug. Altogether, these results outline the potential of both microfluidic confocal observations and numerical simulations at the single sweat pore level to understand why aluminium polycations are so efficient for sweat channel plugging.

Kinetics of ion release from a conventional glass-ionomer cement

Release kinetics for sodium, silicon, aluminium, calcium and phosphorus from conventional glass-ionomer dental cement has been studied in neutral and acid conditions. Specimens (6 mm height × 4 mm diameter) were made from AquaCem (Dentsply, Konstanz, Germany), 6 per experiment. They were matured (37 °C, 1 h), then placed in 5 cm3 storage solution at 20-22 °C. In the first experiment, deionised water, changed daily for 28 days, was used. In the second, deionised water, changed monthly for 21 months, was used. In the third, lactic acid (20 mmol dm-3, pH: 2.7 ± 0.1), changed monthly for 21 months was used. After storage each solution was analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Results showed that in neutral conditions, no calcium was released, but in acid, significant amounts were released. The other elements (Na, Al, Si and P) were released in neutral as well as acid conditions, with greater amounts in acid. More frequent changes of water gave greater release. In neutral conditions, release over 21 months followed the equation: [E]c = [E]1t/(t + t½) + β√t ([E]c is the cumulative release of the element). In acid conditions, this became: [E]c = [E]1t/(t + t½) + αt. Hence release of all elements was shown to occur in two steps, a rapid initial one (half-life: 12-18 h) and a longer second one. In neutral conditions, the longer step involves diffusion; in acid it involves erosion. These patterns influence the material's bioactivity.

Aluminium nanorings: configuration deformation and structural transformation

Present herein is the first example of aluminium nanoring assembly by fatty acids. And the auxiliary alcohol sites can be modified either by monohydric alcohols (AlOC-33 to AlOC-35) or diols (AlOC-36 to AlOC-38). The monohydric alcohol modified ten-membered aluminium (Al10) rings are coplanar, while the diol modified ones possess a saddle-shaped configuration. Interestingly, the diol modified Al10 ring (AlOC-36) can convert into a coplanar ring (AlOC-33-B). AlOC-33-B possesses a similar molecular structure but a different supramolecular structure with AlOC-33. The structural transformation is confirmed to be a thermodynamically spontaneous process through density-functional theory (DFT) calculations.

Aluminum-Substituted Keggin Germanotungstate [HAl(H2O)GeW11O39]4-: Synthesis, Characterization, and Antibacterial Activity

We report on the new monosubstituted aluminum Keggin-type germanotungstate (C₄H₁₂N)₄[HAlGeW₁₁O₃₉(H₂O)]·11H₂O ([Al(H₂O)GeW₁₁]^4–), which has been synthesized at room temperature via rearrangement of the dilacunary [γ-GeW₁₀O₃₆]^8– polyoxometalate precursor. [Al(H₂O)GeW₁₁]^4– has been characterized thoroughly both in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by cyclic voltammetry (CV) ¹⁸³W, ²⁷Al NMR and UV–vis spectroscopy. A study on the antibacterial properties of [Al(H₂O)GeW₁₁]^4– and the known aluminum(III)-centered Keggin polyoxotungstates (Al-POTs) α-Na₅[AlW₁₂O₄₀] (α-[AlW₁₂O₄₀]^5–) and Na₆[Al(AlOH₂)W₁₁O₃₉] ([Al(AlOH₂)W₁₁O₃₉]^6–) revealed enhanced activity for all three Al-POTs against the Gram-negative bacterium Moraxella catarrhalis (minimum inhibitory concentration (MIC) up to 4 μg mL^–1) and the Gram-positive Enterococcus faecalis (MIC up to 128 μg mL^–1) compared to the inactive Al(NO₃)₃ salt (MIC > 256 μg mL^–1). CV indicates the redox activity of the Al-POTs as a dominating factor for the observed antibacterial activity with increased tendency to reduction, resulting in increased antibacterial activity of the POT.

We report on the synthesis and thorough characterization of the new monosubstituted aluminum germanotungstate (C₄H₁₂N)₄[HAlGeW₁₁O₃₉(H₂O)]·11H₂O ([Al(H₂O)GeW₁₁]⁴⁻), which has been subjected to an antibacterial study including the previously reported α-Na₅[AlW₁₂O₄₀] and Na₆[Al(AlOH₂)W₁₁O₃₉]. All three aluminum-substituted polyoxotungstates (Al-POTs) revealed enhanced activity against Moraxella catarrhalis and Enterococcus faecalis compared to the inactive Al(NO₃)₃ salt. On the basis of cyclic voltammetry studies, the redox activity of the POTs is suggested to have an impact on their overall antibacterial activity.

The advantages of clay mineral modification methods for enhancing adsorption efficiency in wastewater treatment: a review

This review discusses the recent trends in the research over the last 30 years to use clay minerals in natural and modified forms for removing different toxic organic/inorganic pollutants. The natural and modified forms of clay minerals have an exceptional ability to remove different contaminants. However, the modification methods can improve the clay mineral adsorption properties that consequently increase more adsorption sites and functional groups to adsorb different environmental pollutants. This review shows the importance of modification methods and more extension of novel clay preparation based on nanotechnology which could raise the control of pollution. The syntheses of functionalized clays such as pillared clays and porous clay heterostructures introduce the new class of heterostructure materials with high adsorption capacity, capability, and selectivity. Due to the acceptable properties of heterostructure materials including high specific surface area, thermal and mechanical stability, and the existence of multifunctional groups to selective adsorption, this review collects more literature of research related to environmental protection issues. However, it is expected much attention to get a better understanding of the adsorption mechanism, regeneration, and recovery process of these materials.

The Surface Chemistry of Metal Oxide Clusters: From Metal-Organic Frameworks to Minerals

Many metal-organic frameworks (MOFs) incorporate nodes that are small metal oxide clusters. Some of these MOFs are stable at high temperatures, offering good prospects as catalysts-prospects that focus attention on their defect sites and reactivities-all part of a broader subject: the surface chemistry of metal oxide clusters, illustrated here for MOF nodes and for polyoxocations and polyoxoanions. Ligands on MOF defect sites form during synthesis and are central to the understanding and control of MOF reactivity. Reactions of alcohols are illustrative probes of Zr₆O₈ node defects in UiO-66, characterized by the interconversions of formate, methoxy, hydroxy, and linker carboxylate ligands and by catalysis of alcohol dehydration reactions. We posit that new reactivities of MOF nodes will emerge from incorporation of a wide range of groups on their surfaces and from targeted substitutions of metals within them.

Sulfate ion in raw water affects performance of high-basicity PACl coagulants produced by Al(OH)3 dissolution and base-titration: Removal of SPAC particles by coagulation-flocculation, sedimentation, and sand filtration

Many PACl (poly-aluminum chloride) coagulants with different characteristics have been trial-produced in laboratories and commercially produced, but the selection of a proper PACl still requires empirical information and field testing. Even PACls with the same property sometimes show different coagulation performances. In this study, we compared PACls produced by AlCl₃-titration and Al(OH)₃-dissolution on their performance during coagulation-flocculation, sedimentation, and sand filtration (CSF) processes. The removal targets were particles of superfine powdered activated carbon (SPAC), which are used for efficient adsorptive removal of micropollutants, but strict removal of SPAC is required because of the high risk of their leakage after CSF. PACls of high-basicity produced by AlCl₃-titration and Al(OH)₃-dissolution were the same in terms of the ferron assay and colloid charge, but their performance in CSF were completely different. High-basicity Al(OH)₃-dissolution PACls formed large floc particles and yielded very few remaining SPAC particles in the filtrate, whereas high-basicity AlCl₃-titration PACls did not form large floc particles. High-basicity PACls produced by Al(OH)₃-dissolution were superior to low-basicity PACl in lowering remaining SPAC particles by the same method because of their high charge neutralization capacity, although their floc formation ability was similar or slightly inferior. However, high-basicity Al(OH)₃-dissolution PACl was inferior when the sulfate ion concentration in the raw water was low. Sulfate ions were required in the raw water for high-basicity PACls to be effective in floc formation. In particular, very high sulfate concentrations were required for high-basicity AlCl₃-titration PACls. The rate of hydrolysis, which is related to the polymerization of aluminum species, is a key property, besides charge neutralization capacity, for proper coagulation, including formation of large floc particles. The aluminum species in the high-basicity PACls, in particular that produced by AlCl₃-titration, was resistant to hydrolysis, but sulfate ions in raw water accelerated the rate of hydrolysis and thereby facilitated floc formation. Normal-basicity Al(OH)₃-dissolution PACl was hydrolysis-prone, even without sulfate ions. Aluminum species in the high-basicity AlCl₃-titration PACl were mostly those with a molecular weight (MW) of 1-10 kDa, whereas those of high-basicity Al(OH)₃-dissolution PACls were mostly characterized by a MW > 10 kDa. Normal-basicity Al(OH)₃-dissolution PACl was the least polymerized and contained monomeric species.

Interaction of Polyoxometalates and Nanoparticles with Collector Surfaces—Focus on the Use of Streaming Current Measurements at Flat Surfaces

Streaming current measurements were used to study the interaction of polyoxometalates (POMs) and nanoparticles (NPs) with flat surfaces as an alternative, innovative approach to infer POM and NP properties of potential sparse material in terms of charge and magnitude. With respect to POMs, the approach was able to reveal subtle details of charging properties of +7 vs. +8 charge at very low POM concentrations. For NPs, the sign of charge and even the zeta-potential curve was retrieved. Concerning NPs, mutual interaction between TiO2 and SiO2 surfaces was studied in some detail via macroscopic measurements. Post-mortem analysis of samples from electrokinetic studies and separate investigations via AFM and HRTEM verified the interactions between TiO2 NPs and SiO2 collector surfaces. The interactions in the SiO2/TiO2 system depend to some extent on NP morphology, but in all our systems, irreversible interactions were observed, which would make the studied types of NPs immobile in natural environments. Overall, we conclude that the measurement of streaming currents at flat surfaces is valuable (i) to study NP and POM collector surface interactions and (ii) to simultaneously collect NPs or POM (or other small mobile clusters) for further (structural, morphological or release) investigations.