The structural origin of the efficient photochromism in natural minerals.

SignificanceNatural photochromic minerals have been reported by geologists for decades. However, the understanding of the photochromism mechanism has a key question still unanswered: What in their structure gives rise to the photochromism's reversibility? By combining experimental and computational methods specifically developed to investigate this photochromism, this work provides the answer to this fundamental question. The specific crystal structure of these minerals allows an unusual motion of the sodium atoms stabilizing the electronic states associated to the colored forms. With a complete understanding of the photochromism mechanism in hand, it is now possible to design new families of stable and tunable photochromic inorganic materials-based devices.

Effect of zeolites on the reduction of the ecotoxicity of carbamazepine in the environment.

In this study, the impact of calcination of zeolites on the ecotoxicity of carbamazepine solutions in two matrices, water and synthetic sewage, was assessed. Two types of zeolites were tested: natural zeolite, in the form of a zeolite rock consisting mainly of clinoptilolite, and a synthetic zeolite type 5 A. Additionally, zeolites were calcined at a temperature of 200 °C. The kinetics of carbamazepine adsorption in aqueous solutions and in synthetic sewage matrix was determined. Higher adsorption capacity was obtained for carbamazepine aqueous solutions as well as zeolites after the calcination process. Considering type of zeolite, the highest and fastest uptake of carbamazepine was observed for natural zeolite after calcination. In the case of ecotoxicity, carbamazepine solutions before adsorption was the most toxic towards Raphidocelis subcapitata, next Aliivibrio fischeri and Daphnia magna, regardless to the matrix type. The differentiation in toxicity regarding the type of matrix was observed, in the case of algae and bacteria, higher toxicity was demonstrated by carbamazepine solutions in the water matrix, while in the case of crustaceans-the sewage matrix. After the adsorption process, the toxicity of carbamazepine solutions on zeolites decreased by 34.5-60.9 % for R. subcapitata, 33-39 % for A. fischeri and 55-60 % for D. magna, thus confirming the effectiveness of the proposed method of carbamazepine immobilization.

Extraordinary Acceleration of an Electrophilic Reaction Driven by the Polar Surface of 2D Aluminosilicate Nanosheets.

To increase chemical reaction rates, general solutions include increasing the concentration/temperature and introducing catalysts. In this study, the rate constant of an electrophilic metal coordination reaction is accelerated 23-fold on the surface of layered aluminosilicate (LAS), where the reaction substrate (ligand molecule) induces dielectric polarization owing to the polar and anionic surface. According to the Arrhenius plot, the frequency factor (A) is increased by almost three orders of magnitude on the surface. This leads to the conclusion that the collision efficiency between the ligands and metal ions is enhanced on the surface due to the dielectric polarization. This is surprising because one side of the ligand is obscured by the surface, so the collision efficiency is expected to be decreased. This unique method to accelerate the chemical reaction is expected to expand the range of utilization of LASs, which are chemically inert, abundant, and environmentally friendly. The concept is also applicable to other metal oxides which have polar surfaces, which will be useful for various chemical reactions in the future.

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite-Water Interface by Adsorption of Rb+ and Halides (Cl- , Br- , I- ) at High Salinity.

Classical electric double layer (EDL) models have been widely used to describe ion distributions at charged solid-water interfaces in dilute electrolytes. However, the chemistry of EDLs remains poorly constrained at high ionic strength where ion-ion correlations control non-classical behavior such as overcharging, i. e., the accumulation of counter-ions in amounts exceeding the substrate's surface charge. Here, we provide direct experimental observations of correlated cation and anion distributions adsorbed at the muscovite (001)-aqueous electrolyte interface as a function of dissolved RbBr concentration ([RbBr]=0.01-5.8 M) using resonant anomalous X-ray reflectivity. Our results show alternating cation-anion layers in the EDL when [RbBr]≳100 mM, whose spatial extension (i. e., ~20 Šfrom the surface) far exceeds the dimension of the classical Stern layer. Comparison to RbCl and RbI electrolytes indicates that these behaviors are sensitive to the choice of co-ion. This new in-depth molecular-scale understanding of the EDL structure during transition from classical to non-classical regimes supports the development of realistic EDL models for technologies operating at high salinity such as water purification applications or modern electrochemical storage.

Highly Cooperative CO2 Adsorption via a Cation Crowding Mechanism on a Cesium-Exchanged Phillipsite Zeolite.

An understanding of the CO2 adsorption mechanisms on small-pore zeolites is of practical importance in the development of more efficient adsorbents for the separation of CO2 from N2 or CH4 . Here we report that the CO2 isotherms at 25-75 °C on cesium-exchanged phillipsite zeolite with a Si/Al ratio of 2.5 (Cs-PHI-2.5) are characterized by a rectilinear step shape: limited uptake at low CO2 pressure (PCO2 ) is followed by highly cooperative uptake at a critical pressure, above which adsorption rapidly approaches capacity (2.0 mmol g-1 ). Structural analysis reveals that this isotherm behavior is attributed to the high concentration and large size of Cs+ ions in dehydrated Cs-PHI-2.5. This results in Cs+ cation crowding and subsequent dispersal at a critical loading of CO2 , which allows the PHI framework to relax to its wide pore form and enables its pores to fill with CO2 over a very narrow range of PCO2 . Such a highly cooperative phenomenon has not been observed for other zeolites.

Structural characterization of interfaces in silica core-alumina shell microspheres by solid-state NMR spectroscopy.

Atomic-scale description of surfaces and interfaces in core-shell aluminosilicate materials is not fully elucidated, partially due to their amorphous character and complex mechanisms that govern their properties. In this paper, new insights into nanostructured core-shell aluminosilicates have been demonstrated, by using different solid-state NMR methods, i.e 29Si, 29Si cross-polarization (CP), 27Al, 27Al triple-quantum (3Q), and 1H-27Al heteronuclear correlation (HETCOR) MAS NMR. For this purpose, nanostructured silica core-alumina shell microspheres, undoped and doped with gadolinium ions respectively, obtained by a chemical synthesis based on the Stöber method for the silica core and electrostatic attraction for developing the alumina shell were studied. As a result, a new alumino-silicate layer formation was proved at the interface between silica core, where aluminum diffuses, on small scale, in the silica network, and alumina shell, where silicon ions migrate, on a larger scale, in the alumina network, leading to a stable core-shell structure. Moreover, this process is accompanied by significant local structural changes in the transition zone, particularly at the aluminum neighborhood, which is quite well understood now, with the power of solid-state NMR spectroscopy.

Safe disposal of hazardous waste incineration fly ash: Stabilization/solidification of heavy metals and removal of soluble salts.

Hazardous waste incineration fly ash (HFA) is considered a hazardous waste owing to the high associated concentrations of heavy metals and soluble salts. Hence, cost effective methods are urgently needed to properly dispose HFA. In this study, geopolymers were prepared by alkali-activation technology to stabilize and solidify heavy metals in HFA. In addition, the effects of three different aluminosilicates (metakaolin, fly ash, and glass powder) on the heavy metal immobilization efficiency were investigated. Because the soluble salt content of HFA is too high for their direct placement in flexible landfill sites and water washing can lead to heavy metal leaching, water-washing experiments were conducted after alkali-activation treatment to remove soluble salts. The results suggest that the concentrations of heavy metals leached from geopolymers can satisfy the Chinese Standard limits (GB18598-2019) when the addition of aluminosilicates exceeds 20 wt%. More than 77% of Cl- and >64% of SO42- in geopolymers could be removed via water-washing treatment. The Zn leaching concentration was maintained below approximately 0.52 ppm. After alkali-activation treatment, the water-washing process could efficiently remove soluble salts while inhibiting heavy metal leaching. Sodium-aluminosilicate-hydrate (N-A-S-H) gel, a product of the geopolymerization process in this study, was demonstrated to act as a protective shell that inhibited heavy metal leaching. Hence, HFA-based geopolymers are considered suitable for disposal in flexible landfills.

Influence of drinking water quality on the formation of corrosion scales in lead-bearing drinking water distribution systems.

Lead in drinking water occurs in drinking water distribution systems (DWDS) where lead pipes are used as service lines. Using data gathered from 4 different Canadian cities, we link drinking water quality to composition of corrosion scales obtained on exhumed lead pipes servicing those municipalities. The data presented encompasses a 10-year span and a detailed layer profile analysis of the solids present in lead bearing service lines; where different layers within the corrosion scale formed inside lead pipes are identified and thoroughly characterized. The results obtained clearly show that the corrosion layers in direct contact with drinking water are rich in lead oxides phases and aluminosilicates. In contrast, lead carbonates are the main phases present on corrosion scales in direct contact with the metallic lead pipe. This heterogeneity on phase distribution is correlated to the radial distance from the corrosion scales to the water/solid interphase and water quality servicing those municipalities. Statistical analysis suggests that dissolved Al, Mn, Cu, Ni, and As accumulate on the corrosion scales with preferential accumulation of specific elements heavily dependent on distinct municipality water quality.

The Origin of Selective Adsorption of CO2 on Merlinoite Zeolites.

The CO2 adsorption behavior at 25-75 °C and 0-1.0 bar of various alkali cation-exchanged forms of merlinoite (framework type MER) zeolites with Si/Al=2.3 and 3.8 is described. The adsorption isotherms at 25 °C on the Na+ , K+ , Rb+ , and Cs+ forms of MER zeolite with Si/Al=2.3 are characterized by a clear step, the CO2 pressure of which differs notably according to the type of their extraframework cations. Structural analysis shows that CO2 adsorption on the former three zeolites includes the relocation of gating cations with high site occupancy and the remarkable concomitant structural breathing. We define this unusual adsorption phenomenon as a cooperative cation gating-breathing mechanism. The overall results suggest that the actual mechanism of selective CO2 adsorption on intermediate-silica small-pore zeolites can change from cation gating to cooperative cation gating-breathing to breathing, depending on a combination of their topological and compositional flexibilities.

An Aluminosilicate Zeolite Containing Rings of Tetrahedral Atoms with All Odd Numbers from Five to Eleven.

Herein we report the synthesis, structure solution, and catalytic properties of PST-31, which has an unprecedented framework topology. This high-silica (Si/Al=16) zeolite was synthesized using a pyrazolium-based dication with a tetramethylene linker as an organic structure-directing agent (OSDA) in hydroxide media. The PST-31 structure is built from new building layers containing four-, five-, six-, and seven-membered rings, which are connected by single four-membered rings in the interlayer region to form a two-dimensional pore system. Its channels consist of [4.56 .6.9.11] and [5.6.7.9.10.11] cavities and are thus delimited by nine-, ten-, and eleven-membered rings. The OSDA cations in as-synthesized PST-31 were determined to reside without disorder in the large [42 .514 .64 .72 .94 ] cavities composed of smaller [4.56 .6.9.11] and [5.6.7.9.10.11] ones, leading to a symmetry coincidence between the OSDA and the surrounding zeolite cavity. The proton form of PST-31 was found to be selective for the cracking of n-hexane to light olefins.

Aluminosilicate-catalyzed electrochemical removal of ammonium cation from water -kinetics and selectivity.

Aluminosilicate-catalyzed electrochemical decomposition of ammonium cation (NH4+) in water was investigated using NH4+-saturated clinoptilolite and copper-nickel electrodes in the presence of different salts and acidic species. The results showed beneficial roles of chloride anion and moderately acidic media. NH4+ adsorbed by the zeolites was converted with a 98% selectivity into nitrogen. The process was found to obey zero-order kinetics in the presence of clinoptilolite and a first order process when NaCl is added. Beneficial buffering effects of the zeolite and acidic species were registered. Clinoptilolite turned out to act as both catalyst and NH4+ reservoir. These results allow envisaging effective and waste-free technology in treating NH4+-rich aqueous effluents through total electroconversion into nitrogen using low cost aluminosilicates. Clay minerals, soils, sludges and natural water turbidity are potential catalysts for this purpose.

PST-24: A Zeolite with Varying Intracrystalline Channel Dimensionality.

Herein we report the synthesis, structure solution, and catalytic properties of PST-24, a novel channel-based medium-pore zeolite. This zeolite was synthesized via the excess fluoride approach. Electron diffraction shows that its structure is built by composite cas-zigzag (cas-zz) building chains, which are connected by double 5-ring (d5r) columns. While the cas-zz building chains are ordered in the PST-24 framework, the d5r columns adopt one of two possible arrangements; the two adjacent d5r columns are either at the same height or at different heights, denoted arrangements S and D, which can be regarded as open and closed valves that connect the channels, respectively. A framework with arrangement D only has a 2D 10-ring channel system, whereas that with arrangement S only contains 3D channels. In actual PST-24 crystals, the open and closed valves are almost randomly dispersed to yield a zeolite framework where the channel dimensionality varies locally from 2D to 3D.

Mesopore Engineering for Well-Defined Mesoporosity in Al-Rich Aluminosilicate Zeolites.

Desilication has been proven an effective approach for the construction of well-defined hierarchical porosities inside zeolites with an optimal framework Al content (Si/Al=25-50). However, for the Al-rich aluminosilicate zeolites, desilication is constrained by the excess and extensive shielding effects from high Al-contents. The developments in the desilication of siliceous zeolites convey a simplified principle of controlled dissolution of the microporous matrix for the construction of hierarchical porosities, which benefits the innovation of synthetic approaches for Al-rich zeolites. The perturbations to the environments of framework Al species may alleviate the excess shielding effects. This review highlights two corresponding protocols of sequential "fluorination-desilication" and "steaming-desilication" for the construction of hierarchical porosities inside Al-rich ZSM-5 zeolites. The success of these two protocols revitalizes the prevailing understanding of the interplay between dealumination and desilication, and implies the necessity of investigating the overlooked roles of extra-framework Al species. Despite the long history and significant achievements in the last decade, fundamental understandings at the molecule level are still limited for the desilication-based top-down approaches. In particular, the investigations on Al-rich zeolites just find their growing. The bridging of dealumination and desilication is essential for other industrially relevant Al-rich zeolites (e.g., faujasite zeolites). The complexities in the inherent characters (topology, spatial distribution, proximity, etc.) and apparent parameters (morphology, crystal/particle size, etc.) demand constructive synthetic toolboxes and further fundamental understanding.

Targeted Synthesis of a Zeolite with Pre-established Framework Topology.

Given their great potential as new industrial catalysts and adsorbents, the search for new zeolite structures is of major importance in nanoporous materials chemistry. However, although innumerable theoretical frameworks have been proposed, none of them have been synthesized by a priori design yet. We generated a library of diazolium-based cations inspired from the organic structure-directing agents (OSDAs) recently reported to give two structurally related zeolites (PST-21 and PST-22) under highly concentrated, excess-fluoride conditions and compared the stabilization energies of each OSDA cation in ten pre-established hypothetical structures. A combination of the ability of the OSDA selected in this way with the excess-fluoride approach has allowed us to crystallize PST-30, the targeted aluminosilicate zeolite structure. We anticipate that our approach, which aims to rationally couple computational predictions of OSDAs with an experimental setup, will advance further development in the synthesis of zeolites with desired properties.

Advanced Inorganic Nanosystems for Skin Drug Delivery.

On/into/through the skin drug delivery represents an attractive alternative for the oral route, providing local and/or systemic drug delivery. Due to its complex and well-organised structure, most of the drugs show difficulties to penetrate the human skin. Therefore, enormous efforts have been invested to develop intelligent drug delivery systems overcoming the skin barrier with particular emphasis on increasing therapeutic activity and minimizing undesirable side-effects. Most of these strategies require the use of singular materials with new properties. In particular, and on the basis of their inherent properties, including biocompatibility, biodegradability and relative low-cost, inorganic nanoparticles are ideal candidates for the development of skin drug delivery systems. This review provides an updated and comprehensive overview of the state of the art in the trends towards skin drug delivery with a particular focus in the attractive alternative offered by inorganic-based nanosystems.

The accuracy of standard enthalpies and entropies for phases of petrological interest derived from density-functional calculations.

The internal energies and entropies of 21 well-known minerals were calculated using the density functional theory (DFT), viz. kyanite, sillimanite, andalusite, albite, microcline, forsterite, fayalite, diopside, jadeite, hedenbergite, pyrope, grossular, talc, pyrophyllite, phlogopite, annite, muscovite, brucite, portlandite, tremolite, and CaTiO3-perovskite. These thermodynamic quantities were then transformed into standard enthalpies of formation from the elements and standard entropies enabling a direct comparison with tabulated values. The deviations from reference enthalpy and entropy values are in the order of several kJ/mol and several J/mol/K, respectively, from which the former is more relevant. In the case of phase transitions, the DFT-computed thermodynamic data of involved phases turned out to be accurate and using them in phase diagram calculations yields reasonable results. This is shown for the Al2SiO5 polymorphs. The DFT-based phase boundaries are comparable to those derived from internally consistent thermodynamic data sets. They even suggest an improvement, because they agree with petrological observations concerning the coexistence of kyanite + quartz + corundum in high-grade metamorphic rocks, which are not reproduced correctly using internally consistent data sets. The DFT-derived thermodynamic data are also accurate enough for computing the P-T positions of reactions that are characterized by relatively large reaction enthalpies (> 100 kJ/mol), i.e., dehydration reactions. For reactions with small reaction enthalpies (a few kJ/mol), the DFT errors are too large. They, however, are still far better than enthalpy and entropy values obtained from estimation methods.

A Zeolite Family Nonjointly Built from the 1,3-Stellated Cubic Building Unit.

From a technological point of view, the synthesis of new high-silica zeolites is of prime importance owing to their high potential as industrial catalysts and catalyst supports. Two such materials have been synthesized which are made up of the 1,3-stellated cubic unit (hexahedral ([42 54 ]) bre unit) as a secondary building unit, with the aid of existing imidazolium-based structure-directing agents under "excess fluoride" conditions. One of them, denoted PST-21, is the first aluminosilicate zeolite consisting of 9-ring apertures solely; it displays exceptional activity towards steering the skeletal isomerization of 1-butene to isobutene and bridges the gap between small- and medium-pore structures. A series of hypothetical structures are also described that are nonjointly built from the bre unit; all of these structures are chemically feasible and will thus be helpful in designing the synthesis of novel zeolites containing 9-ring and/or 10-ring channels.

Acid-Mediated Synthesis of Ordered Mesoporous Aluminosilicates: The Challenge and the Promise.

A new intrinsic hydrolysis method was employed, for the first-time, to synthesize well-ordered H-AlSBA-15 with trivalent aluminium exclusively in the tetrahedral framework structure of SBA-15. Unlike other methods, which involve incorporation of aluminium ions in both the framework (Brønsted) and non-framework (Lewis) sites of the silicate matrix, the intrinsic hydrolysis method isomorphously substitutes aluminium ions in the tetrahedral network even at high aluminium content. This unique approach relies mainly on the hydrolysis rates of the inorganic (silicon and aluminium) precursors used for the preparation in such a way that the condensation occurs simultaneously so as to overcome the usually encountered difficulties in stabilizing aluminium ions in the silicate matrix. In this way, we could successfully synthesize high quality Brønsted acidic H-AlSBA-15, hitherto not reported. The synthesized materials were systematically characterized by various analytical, spectroscopic, and imaging techniques, including XRD, Brunauer-Emmett-Teller (BET) surface area measurements, TEM, SEM, 29 Si and 27 Al magic angle spinning NMR spectroscopy, X-ray fluorescence (XRF), and NH3 temperature-programmed desorption (TPD). The characterization results reveal the presence of a highly porous structure (with narrow pores) and tetrahedrally coordinated trivalent aluminium in the silicate matrix with more medium to strong Brønsted acid sites. The resulting high quality catalysts exhibit excellent activity for tert-butylation of phenol with high selectivity towards para-tert-butyl phenol and 2,4-di-tert-butyl phenol.

Isopropanol Dehydration on Amorphous Silica-Alumina: Synergy of Brønsted and Lewis Acidities at Pseudo-Bridging Silanols.

The mechanism of isopropanol dehydration on amorphous silica-alumina (ASA) was unraveled by a combination of experimental kinetic measurements and periodic density functional theory (DFT) calculations. We show that pseudo-bridging silanols (PBS-Al) are the most likely active sites owing to the synergy between the Brønsted and Lewis acidic properties of these sites, which facilitates the activation of alcohol hydroxy groups as leaving groups. Isopropanol dehydration was used to specifically investigate these PBS-Al sites, whose density was estimated to be about 10-1  site nm-2 on the silica-doped alumina surface under investigation, by combining information from experiments and theoretical calculations.

29Si{27Al} TRAPDOR MAS NMR to distinguish Qn(mAl) sites in aluminosilicates. Test case: Faujasite-type zeolites.

29Si{27Al} TRAPDOR MAS NMR was applied to two faujasite-type zeolites with Si/Al ratios of 1.3 (Na-X) and 2.7 (Na-Y). The aim of this test study is to show that different Q4(mAl) sites (m =4, 3, 2, 1) can be distinguished by differently strong TRAPDOR effects (ΔS/S0). Indeed, it was found that the TRAPDOR effect depends on the number m of AlO4 units connected to the Q4 silicon tetrahedrons. For Na-X, the measured ΔS/S0 values are 1 : 0.81 : 0.56 for Q4(4Al), Q4(3Al) and Q4(2Al), respectively (normalized to Q4(4Al)). The corresponding ΔS/S0 values are the same for Na-Y within the error bars, although the silicon sites are different: Q4(3Al), Q4(2Al) and Q4(1Al) and now normalized to Q4(3Al) as no Q4(4Al) is present. Nevertheless, the proposed method opens up the possibility to distinguish overlapping 29Si NMR signals of the Qn(mAl) sites in amorphous materials as the main goal of these investigations.