Distribution of aluminum and boron in the periodical building units of boron-containing Beta zeolites

Various boron only ([B]-BEA) as well as aluminum- and boron-containing beta zeolites ([Al,B]-BEA) have been prepared and modified by ion exchange of ammonium, sodium, and nickel ions. The zeolite samples have been characterized by 11B, 27Al, and 29Si MAS as well as three of them by 11B and 27Al 3Q-MAS NMR spectroscopy. The quantitative contributions of defect-free Si(nX) (n = 2, 1, 0; X = Al, B) and Si(OH)x (x = 2, 1) sites to the NMR signal intensities were calculated from the various Si/(Al + B) ratios and relative 11B, 27Al, and 29Si NMR signal intensities using the special distribution of aluminum and boron in different periodical building units of the zeolite framework. The boron atoms are sitting exclusively in diagonal positions in the four-membered rings of [B]-BEA zeolites, while the aluminum atoms are situated both in diagonal and lone positions in the four-membered rings of [Al,B]-BEA zeolites. A higher part of boron atoms are positioned in framework-related deformed tetrahedral boron species than in lattice positions in the [B]-BEA than in the [Al,B]-BEA zeolites. All extraframework octahedral aluminum species are transformed back to lattice positions due to ion exchange from the protonated form to ammonium-, sodium-, or nickel-ions containing zeolites. Oppositely, trigonal boron leaves the zeolite structure completely during ion exchange.     

Solid-state 1H and 27Al NMR studies of amorphous aluminum hydroxides

Two kinds of amorphous aluminum hydroxides, a sample precipitated from admixing AlCl3 and NaOH aqueous solutions and the commercial product, were measured by 27Al and 1H solid-state NMR spectroscopy. Pentahedral and tetrahedral coordinations, as well as octahedral coordination of oxygen atoms for aluminum, are observed in 27Al magic angle spinning (MAS) spectra of both amorphous samples. In contrast, octahedral coordination is only observed in gibbsite, bayerite, and boehmite. According to 1H MAS-NMR spectra under conditions of high spinning rate (35 kHz) and high field (14.09 T), free waters and OH groups coupled with aluminum for amorphous samples are observed at approximately 5 and approximately 4.5 ppm, respectively, the latter peak being broader. This is consistent with the differential spectra between spin echo and transfer of populations in double resonance. We conclude that the subunits of AlO4, AlO5, and AlO6 in amorphous aluminum hydroxides are bound through hydrogen bonds with a wide distribution of bonding strength.     

Hydration of Portland cement in the presence of high activity aluminum hydroxides

The effect of highly dispersed amorphous aluminum hydroxides on the hydration of Portland cement was studied by the solid-state ²⁷Al and ²⁹Si NMR spectroscopy. It was established that in the presence of aluminum hydroxides the decrease in the setting time of a cement paste is due to rapid formation of ettringite phase, with contribution of admixture material the main and contribution of aluminum-containing phases at this stage insignificant.     

Hydrogen bonds and local symmetry in the crystal structure of gibbsite

First‐principles quantum mechanical calculations of NMR chemical shifts and quadrupolar parameters have been carried out to assign the ²⁷Al MAS NMR resonances in gibbsite. The ²⁷Al NMR spectrum shows two signals for octahedral aluminum revealing two aluminum sites coordinated by six hydroxyl groups each, although the crystallographic positions of the two Al sites show little difference. The presence of two distinguished ²⁷Al NMR resonances characterized by rather similar chemical shifts but quadrupolar coupling constants differing by roughly a factor of two is explained by different character of the hydrogen bonds, in which the hydroxyls forming the corresponding octahedron around each aluminum site, are involved. The Al‐I site characterized by a C_Q = 4.6 MHz is surrounded by OH? groups participating in four intralayer and two interlayer hydrogen bonds, while the Al‐II site with the smaller quadrupolar constant (2.2 MHz) is coordinated by hydroxides, of which two point toward the intralayer cavities and four OH‐bonds are aligned toward the interlayer gallery. In high‐resolution solid‐state ¹H CRAMPS (combination of rotation and multiple‐pulse spectroscopy) four signals with an intensity ratio of 1:2:2:1 are resolved which allow to distinguish six nonequivalent hydrogen sites reported in the gibbsite crystal structure and to ascribe them to two types of structural OH groups associated with intralayer and interlayer hydrogen bonds. This study can be applied to characterize the gibbsite‐like layer—intergallery interactions associated with hydrogen bonding in the more complex systems, such as synthetic aluminum layered double hydroxides. Copyright © 2010 John Wiley & Sons, Ltd.     

Catalytic role of Ti dopant in boehmite for the photodegradation of rhodamine B

Research on Chemical Intermediates - Ti(IV) ions were introduced into the layered aluminum hydroxides via the precipitation of Al(NO3)3 solution and Ti(C2H5)4. Catalyst texture and structure were...     

Long-term phosphorus effects on evolving physicochemical properties of iron and aluminum hydroxides

Iron (Fe) and aluminum (Al) hydroxides are highly reactive components in environmental processes, such as contaminant fate and transport. Phosphorus (P) sorption by these components can decrease environmental problems associated with excess accumulation of P in soils. The long-term stability of P sorbed by Fe/Al hydroxides is of major concern. Synthetic Fe and Al hydroxides coprecipitated with P (1:1 metal:P molar ratio) were incubated at 70 degrees C for 24 months to simulate natural long-term weathering processes that could influence the stability of sorbed P. Heat incubation (70 degrees C) of the untreated (no P) Al hydroxides resulted in drastic decreases (within the first month of incubation) in oxalate-Al extractability, specific surface area (SSA), and micropore volume with time. These changes were consistent with the formation of pseudoboehmite. Untreated Fe hydroxides showed no formation of crystalline components following heating (70 degrees C) for 24 months. Much smaller changes in oxalate-Al, P extractability, and SSA values were observed in the P-treated Al particles when compared with the untreated. Phosphorus treatment of both Fe and Al hydroxides stabilized the particle surfaces and prevented structural arrangements toward a long-range ordered phase. Slight reduction in SSA of the P-treated particles was related to dehydration phenomena during heating at 70 degrees C. Monitoring of physicochemical properties of the solids after heating at 70 degrees C for 2 years showed that sorbed P may be stable in the long-term. Understanding long term physicochemical properties may help engineers to optimize the Fe/Al hydroxides performance in several environmental/industrial applications.     

Development of Electroflotation Technology for Extraction of Anionic Surfactants and Nonferrous Metal Ions from Wastewater Produced at Electroplating Industries

Sorption extraction of anionic surfactants NaDDS and NaDBS on freshly formed iron(III) and aluminum(III) hydroxides and on a highly dispersed activated carbon of OU-B brand was experimentally studied. It was shown that NaDDS is the most fully sorbed on Al(OH)₃ and OU-B, whereas on Fe(OH)₃, the maximum sorption is observed for NaDBS. The electroflotation extraction of anionic surfactants and poorly soluble iron(III) and aluminum(III) hydroxides was examined and the influence exerted by the following factors (pH, nature of electrolyte, surfactant concentration) on the degree of extraction of these substances was analyzed. In addition, electroflotation extraction of OU-B in the presence on nonferrous metal hydroxides and surfactants of varied nature from aqueous solutions was performed. The results obtained were used to develop a technological scheme for electroflotation of complex-composition wastewater.     

The aluminum ordering in aluminosilicates: a dipolar 27Al NMR spectroscopy study

The spatial ordering of aluminum atoms in CsAl(SiO3)2 and 3Al2O3.2SiO2 was probed by 27Al dipolar solid-state NMR spectroscopy. The 27Al response to a Hahn spin-echo pulse sequence in a series of aluminum-containing model crystalline compounds demonstrates that quantitative 27Al homonuclear dipolar second moments can be obtained to within +/-20% of the theoretical values, if evaluation of the spin-echo response curve is limited to short evolution periods (2t1 < or = 0.10 ms). Additionally, selective excitation of the central transition m = 1/2 --> -1/2 is necessary in order to ensure quantitative results. Restriction of spin exchange affecting the dephasing of the magnetization may decelerate the spin-echo decay at longer evolution periods. Considering these restraints, the method was used to probe the spatial distribution of aluminum atoms among the tetrahedral sites in two aluminosilicate materials. Experimental 27Al spin-echo response data for the aluminosilicates CsAl(SiO3)2 (synthetic pollucite) and 3Al2O3.2SiO2 (mullite) are compared with theoretical data based on (I) various degrees of aluminum-oxygen-aluminum bond formation among tetrahedrally coordinated aluminum atoms (Al(T(d) )-O-Al(T(d) )) and (II) the maximum avoidance of Al(T(d) )-O-Al(T(d) ) bonding. Analysis of the second moment values and resulting echo decay responses suggests that partial suppression of spin exchange among aluminum atoms in crystallographically distinct sites may contribute to the 27Al spin echo decay in 3Al2O3.2SiO2, thus complicating quantitative analysis of the data. Silicon-29 and aluminum-27 magic angle spinning (MAS) NMR spectra of 3Al2O3.2SiO2 are consistent with those previously reported. The experimental 27Al spin-echo response behavior of CsAl(SiO3)2 differs from the theoretical response behavior based on the maximum avoidance of Al-O-Al bonding between tetrahedral aluminum sites in CsAl(SiO3)2. A single unresolved resonance is observed in both the silicon-29 and aluminum-27 MAS spectra of CsAl(SiO3)2.     

Multinuclear solid-state high-resolution and 13C -{27Al} double-resonance magic-angle spinning NMR studies on aluminum alkoxides

A combination of 27Al magic-angle spinning (MAS)/multiple quantum (MQ)-MAS, 13C-1H CPMAS, and 13C-{27Al} transfer of population in double-resonance (TRAPDOR) nuclear magnetic resonance (NMR) were used for the structural elucidation of the aluminum alkoxides aluminum ethoxide, aluminum isopropoxide, and aluminum tertiarybutoxide. Aluminum alkoxides exist as oligomers with aluminum in different coordinations. High-resolution 27Al MAS NMR experiments with high-spinning speed distinguished the aluminum atoms in different environments. The 27Al MAS NMR spectrum gave well-resolved powder patterns with different coordinations. Z-filter MQ-MAS was performed to obtain the number and types of aluminum environments in the oligomeric structure. 13C-1H CPMAS chemical shifts resolved the different carbon species (-CH3, =CH2, =CH-, and =C=) in the structures. 13C-{27Al} TRAPDOR experiments were employed to obtain relative Al-C dipolar interactions and to distinguish between terminal and bridging alkoxides in the crystallographic structures. The complete characterization of selected aluminum alkoxides using advanced NMR methods has evidenced the tetrameric structure for aluminum isopropoxide and the dimeric structure for aluminum tertiary-butoxide, as reported in the literature, and proposed a polymeric structure for aluminum ethoxide.     

羟基铝溶液及铝交联蒙脱土的研究

本文用(27)~Al NMR法和8-羟基喹啉萃取法分别研究了羟基铝溶液中十三聚铝含量的变化规律,还用X-射线衍射法研究了铝交联蒙脱土d_(001)的变化。研究结果表明,铝离子的聚合情况主要由羟铝比决定,而浓度影响不大。随着羟铝比的增加,溶液中单核铝离子含量减少,十三聚铝离子相对含量增加,所得铝交联蒙脱土的d_(001)也随之增大。参照这些变化规律、控制羟基铝溶液的组成,可以制备各种层柱状铝交联蒙脱土复合物。     

High-pressure delta-Al(OH)3 and delta-AlOOH phases and isostructural hydroxides/oxyhydroxides: new structural insights from high-resolution 1H and 27Al NMR

In order to shed light on the proton distributions and order/disorder in high-pressure delta-Al(OH)3 and delta-AlOOH phases, two-dimensional, high-resolution 1H CRAMPS (FSLG)-MAS NMR and 27Al 3QMAS NMR spectra have been obtained. For delta-Al(OH)3, the 1H CRAMPS-MAS NMR revealed two peaks with an intensity ratio close to 2:1. The 27Al MAS and 3QMAS NMR suggest a single Al site with a well-defined local structure. For delta-AlOOH, the 1H and 27Al NMR indicate the presence of a single H and Al site each. These results are consistent with crystal structures refined from X-ray diffraction. For comparison, 1H MAS and CRAMPS-MAS NMR spectra were also obtained for several other hydroxides/oxyhydroxides, including In(OH)3 and InOOH that have similar structures to delta-Al(OH)3 and delta-AlOOH, respectively. These data not only provide additional insights into the proton distributions in these important crystal structure classes but also together provide a better defined quantitative correlation between 1H chemical shift and hydrogen-bonding O...O distance.     

Towards guest-zeolite interactions: an NMR spectroscopic approach

Guest(metal)-zeolite interactions in a two component heterogeneous catalyst have been investigated by high-field and high-speed (27)Al MAS NMR, and two-dimensional (27)Al MQ MAS NMR experiments as well as ab initio DFT methods. It was established that strong interactions between guest and zeolite occur in a metal/zeolite system, with the metal anchored to the tetrahedral aluminum framework site through two oxygen bridges. It disturbs the tetrahedral environment of associated aluminum framework, changing AlO(4) geometry from near T(d) to C(2v); this enables us to resolve this species from the undisturbed aluminum framework species in high-field (27)Al MAS NMR and two-dimesional (27)Al MQ MAS NMR experiments.     

The role of the trivalent metal in an LDH: Synthesis, characterization and fire properties of thermally stable PMMA/LDH systems

Two layered double hydroxides (LDHs), calcium aluminum undecenoate (Ca₃Al) and calcium iron undecenoate (Ca₃Fe), have been prepared by the co-precipitation method. XRD analysis of these LDHs reveals that they are layered materials and FT-IR and TGA confirmed the presence of the undecenoate anions in the material produced. The PMMA composites were prepared by bulk polymerization and the samples were characterized by XRD, TEM, TGA and cone calorimetry. Both additives greatly enhance the thermal stability of PMMA, while the calcium aluminum LDH gives better results when the fire properties were examined using the cone calorimeter.     

Pro-oxidant activity of aluminum: stabilization of the aluminum superoxide radical ion

The pro-oxidant activity of aluminum, a nonredox metal, through superoxide formation is studied by theoretical methods, determining the ESR g-tensor values of O2(?–) with a variety of metals and the reaction energies for Al3+ superoxide affinity in solution. First, the intrinsic ability of aluminum to induce a splitting of the πg levels is compared to that of other significant biological metals, such as Na+, K+, Mg2+, and Ca2+. Additional properties such as bond lengths, ionization potentials, and electron affinities are also determined, and the coherency with the trends observed from ESR g-tensor values is analyzed. As it corresponds to the high charge and its small size, there is a strong interaction between Al3+ and the superoxide. We predict that this strong inherent interaction remains when aluminum is microsolvated. Finally, we analyze the possibility of Al3+ superoxide formation in solution, leading to the conclusion that substitution of the first coordination shell water molecules is plausible, but not of hydroxides. This points to the possibility of Al3+ superoxide formation in solution, which would be pH-dependent. Taking into account the earlier established linear relationship between metal–superoxide interactions and promoting effects in electron-transfer reactions, our work reinforces the idea that the presence of aluminum in biological systems could lead to an important pro-oxidant activity through a superoxide formation mechanism.     

Characterization of framework and extra-framework aluminum species in non-hydrated zeolites Y by 27Al spin-echo, high-speed MAS, and MQMAS NMR spectroscopy at B0 = 9.4 to 17.6 T

27Al spin-echo, high-speed MAS (nu(rot) = 30 kHz), and MQMAS NMR spectroscopy in magnetic fields of B0 = 9.4, 14.1, and 17.6 T were applied for the study of aluminum species at framework and extra-framework positions in non-hydrated zeolites Y. Non-hydrated gamma-Al2O3 and non-hydrated aluminum-exchanged zeolite Y (Al,Na-Y) and zeolite H,Na-Y were utilized as reference materials. The solid-state 27Al NMR spectra of steamed zeolite deH,Na-Y/81.5 were found to consist of four signals. The broad low-field signal is caused by a superposition of the signals of framework aluminum atoms in the vicinity of bridging hydroxyl protons and framework aluminum atoms compensated in their negative charge by aluminum cations (delta(iso) = 70 +/- 10 ppm, C(QCC) = 15.0 +/- 1.0 MHz). The second signal is due to a superposition of the signals of framework aluminum atoms compensated by sodium cations and tetrahedrally coordinated aluminum atoms in neutral extra-framework aluminum oxide clusters (delta(iso) = 65 +/- 5 ppm, C(QCC) = 8.0 +/- 0.5 MHz). The residual two signals were attributed to aluminum cations (delta(iso) = 35 +/- 5 ppm, C(QCC) = 7.5 +/- 0.5 MHz) and octahedrally coordinated aluminum atoms in neutral extra-framework aluminum oxide clusters (delta(iso) = 10 +/- 5 ppm, C(QCC) = 5.0 +/- 0.5 MHz). By chemical analysis and evaluating the relative solid-state 27Al NMR intensities of the different signals of aluminum species occurring in zeolite deH,Na-Y/81.5 in the non-hydrated state, the aluminum distribution in this material was determined.     

Structural characterization of MAO and related aluminum complexes. 1. Solid-state (27)Al NMR with comparison to EFG tensors from ab initio molecular orbital calculations.

Experimental and ab initio molecular orbital techniques are developed for study of aluminum species with large quadrupole coupling constants to test structural models for methylaluminoxanes (MAO). The techniques are applied to nitrogen- and oxygen-containing complexes of aluminum and to solid MAO isolated from active commercial MAO preparations. (Aminato)- and (propanolato)aluminum clusters with 3-, 4-, and 6-coordinate aluminum sites are studied with three (27)Al NMR techniques optimized for large (27)Al quadrupole coupling constants: field-swept, frequency-stepped, and high-field MAS NMR. Four-membered (aminato)aluminum complexes with AlN(4) coordination yield slightly smaller C(q) values than similar AlN(2)C(2) sites: 12.2 vs 15.8 MHz. Planar 3-coordinate AlN(2)C sites have the largest C(q) values, 37 MHz. In all cases, molecular orbital calculations of the electric field gradient tensors yields C(q) and eta values that match with experiment, even for a large hexameric (aminato)aluminum cage. A D(3d) symmetry hexaaluminum oxane cluster, postulated as a model for MAO, yields a calculated C(q) of -23.7 MHz, eta = 0.7474, and predicts a spectrum that is too broad to match the field-swept NMR of methylaluminoxane, which shows at least three sites, all with C(q) values greater than 15 MHz but less than 21 MHz. Thus, the proposed hexaaluminum cluster, with its strained four-membered rings, is not a major component of MAO. However, calculations for dimers of the cage complex, either edge-bridged or face-bridged, show a much closer match to experiment. Also, MAO preparations differ, with a gel form of MAO having significantly larger (27)Al C(q) values than a nongel form, a conclusion reached on the basis of (27)Al NMR line widths in field-swept NMR spectra acquired from 13 to 24 T.     

Time-resolved analysis of hydrolytic aluminum species in the formation of the tridecamer using electrospray ionization mass spectrometry

The time-resolved analysis of neutralized aluminum solution was conducted by electrospray ionization mass spectrometry (ESI-MS) for the speciation of aluminum. Using this technique, the behavior of each aluminum species in a 'short-term' (on the order of minutes) reaction time could be observed. Partially neutralized aluminum solutions (R = [OH(-)](add)/[Al(3+)](T) = 0-3) were adopted to elucidate the formation mechanisms of aluminum species, some of which are industrially and geochemically important. The behavior of the species in the solution at R = 1.5 was dependent on aging time for the first 24 h, while solutions at R = 0 and 3 were quickly equilibrated. At R = 1.5, the time lag for the gradual formation of aluminum tridecamer and the sudden decrease of monomer indicates the presence of an intermediate species: the pentamer. In the concentrated aluminum solution ([Al(3+)] = 1 mol/L) at R = 1.3, where the tridecamer was absent, the hexamer was observed instead of the tridecamer. This hexamer was decomposed to the monomer by dilution, and then the formation of the tridecamer was observed. Two reaction pathways exist for the formation of the hexamer and tridecamer, and the pentamer is proved to be a key to the formation of both the tridecamer and the hexamer. The tridecamer and hexamer, which are detected by nuclear magnetic resonance ((27)Al NMR) and potentiometric titration, respectively, were simultaneously observed by ESI-MS. This indicates that ESI-MS complements conventional techniques such as (27) Al NMR and potentiometric titration for the speciation of aluminum, and can offer detailed information on the dynamics of aluminum species.     

Studies on fluoride adsorption capacities of amorphous Fe/Al mixed hydroxides from aqueous solutions

This study evaluated the effectiveness of amorphous iron and aluminum mixed hydroxides in removing fluoride from aqueous solutions. A series of mixed Fe/Al samples were prepared at room temperature by co-precipitating Fe and Al mixed salt solutions at pH 7.5. The compositions (Fe:Al molar ratio) of the oxides were varied as 1:0, 3:1, 2:1, 1:1 and 0:1 and the samples were characterized by XRD, BET surface area and pH_ZPC. The XRD studies indicated the amorphous nature of the samples and Al(III) incorporation on Fe(III) hydroxides. Batch adsorption studies for fluoride removal on these materials showed that the adsorption capacities of the materials were highly influenced by solution pH, temperature and initial fluoride concentration. The rate of adsorption was fast and equilibrium was attained within 2 h. The adsorption followed first-order kinetics with intraparticle diffusion as the rate determining step for all the samples. The experimental data fitted well to both Langmuir and Freundlich adsorption isotherms. All samples exhibited very high Langmuir adsorption capacities; the sample with molar ratio 1 has shown maximum adsorption capacity of 91.7 mg/g. The thermodynamic parameters were determined to study the feasibility of the adsorption process.     

Coordination Structure of Aluminum in Magnesium Aluminum Hydroxide Studied by ^27Al NMR

The coordination structure of aluminum in magnesium aluminum hydroxide was studied by ^27Al NMR.The result showed that tetrahedral aluminum (Al^IV) existed in magnesium aluminum hydroxide,and the contents of Al^TV increased with the increase of the ratio of Al/Mg and with the peptizing temperature.Al^IV originated from the so-called Al13 polymer with the structure of one Al tetrahedron surrounded by twelve Al octahedrons.     

Study on chemical speciation in aluminum chloride solution by ESI-Q-MS

AlCl(3) solution was analyzed at concentrations from 0.02 to 100 mM using an electrospray ionization quadrupole mass spectrometer (ESI-Q-MS), and the dissolution state of aluminum ions is discussed. Results obtained using ESI-Q-MS were consistent with those obtained using (27)Al nuclear magnetic resonance ((27)Al NMR). Aluminum species existed mainly as positively charged monomeric aluminum hydroxide coordinated with several water molecules in solution. The complexation of chloride ions by aluminum ions differed between the positive and negative ion modes. Chemical reactions that partially modified chemical forms of species through ESI-Q-MS measurement were also observed. In the same aluminum chloride solution, using ESI-TOF-MS and ESI-Q-MS/MS studies, the disagreement of the reports is discussed. It is concluded that ESI-TOF-MS might show also the gas-phase reaction in the mass spectrometer but the dissolution state of aluminum species can be shown by ESI-Q-MS.