Zeolitic Water Molecules Research Articles

Crystal structure of calcium L-5-methyltetrahydrofolate trihydrate type I, C20H23N7O6Ca(H2O)3

The crystal structure of L-5-methyltetrahydrofolate calcium trihydrate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Calcium levomefolate trihydrate crystallizes in space group P212121 (#19) with a = 7.1706(6), b = 6.5371(5), c = 53.8357(41) Å, V = 2523.58(26) Å3, and Z = 4. The structure is characterized by alternating hydrophobic and hydrophilic layers along the c-axis. The Ca cations are 7-coordinate, and share edges to form chains along the b-axis. Each of the water molecules acts as a donor in two hydrogen bonds. The coordinated water molecule makes two strong intermolecular O–H⋯O hydrogen bonds to carboxyl and carbonyl groups. The two zeolitic water molecules form weaker hydrogen bonds, to carbonyl O atoms, ring N atoms, and aromatic C atoms. Several N–H⋯O/N hydrogen bonds, as well as C–H⋯O hydrogen bonds, also contribute to the lattice energy.

Mn–Co Prussian blue analogue cubic frames for efficient aqueous Zn ion batteries

Mn based Prussian blue analogs (PBAs) have emerged as highly promising cathode materials for aqueous zinc-ion batteries (AZIBs), owing to their high specific capacity and operating potential. However, the cycling stabilities of these materials remain unsatisfactory because their structural deformation induces ion intercalation. In this study, a PVP assisted Mn–Co-PBA was synthesized using a simple hydrothermal method. Mn–Co-PBA displays unique cubic frame-like structures with a high specific surface area and fewer zeolitic water molecules in the host lattice. The Mn–Co-PBA||Zn cell displayed an excellent specific capacity of 138 mAh g−1 at 0.1 A g−1, good rate capability (95 mAh g−1 at 1 A g−1), and good cycling stability (capacity retention of 92.8% after 1000 cycles) because of its unique cubic frame structure. This structure can provide a greater number of Zn diffusion pathways and alleviate the structural strain during Zn2+ ion insertion/extraction processes. An ex-situ XRD analysis revealed that the de/intercalation of Zn2+ ions in the Mn–Co-PBA electrodes was highly reversible. These results show that Mn–Co-PBA holds great promise for advancement in the field of AZIBs and contributes to the realization of effective and sustainable battery technologies.

Study of the adsorption mechanisms of NH3, H2S and SO2 on sepiolite using molecular dynamics simulations

AbstractThe adsorption mechanisms of hazardous gas molecules such as NH3, H2S and SO2 on sepiolite have not yet been elucidated. Therefore, molecular dynamics (MD) simulations were employed to investigate the adsorption behaviour of sepiolite towards NH3, H2S and SO2. A calculation model for sepiolite containing structural and zeolitic water molecules was constructed in this study. The adsorption sites and molecular configurations of the hazardous gases in the sepiolite channels were studied. The radial distribution function was employed to evaluate the interactions between the gas molecules and sepiolite. The results show that the order of adsorption capacity of sepiolite for the gases is as follows: SO2 > H2S > NH3. These three types of gas molecules absorbed in the channel nanopores of sepiolite exhibit different atomic configurations. The diffusion coefficients of the gas molecules in the channels decreased in the following order: NH3 > H2S > SO2. In addition, the diffusion coefficients were affected significantly by the ratio of the number of gas/water molecules. This study provides new perspectives for understanding the molecular processes responsible for the adsorption properties of sepiolite.

Influences of micropores and water molecules in the palygorskite structure on the color and stability of Maya blue pigment

Maya blue is an ancient hybrid pigment composed of indigo and microporous palygorskite, with a fantastic hue and outstanding stability. Its color-causing and stabilization mechanism are unsolved problems. In this work, different palygorskite materials were obtained by heating at 180, 300 and 570 °C, with raw palygorskite as a reference. Maya blue-like pigments were prepared from these palygorskite materials and solid indigo. The microporous structure of palygorskite and the status of inside water molecules were investigated by thermal analysis, X-ray diffraction, Fourier transform infrared and microporous analysis. The color properties, chemical resistance and photostability of pigments were characterized by reflectance spectra, CIE color parameters and color differences after the attack of concentrated nitric acid, dimethyl sulfoxide, and visible light exposure equaling to about 100 years. It was confirmed that the greenish-blue and stable hybrid pigment could only be prepared when indigo molecules were inserted into the micropores of palygorskite. Zeolitic water molecules inside the micropores should be removed because they hindered the insertion of indigo molecules. The key to immobilizing indigo molecules inside micropores was hydrogen bonds between indigo and coordinated water (CO … …H–OH). This study emphasized the important role of micropores and hydrogen bonds in the synthesis of organic-inorganic hybrid pigments.

A Molecular Dynamics Simulation Study of Fe-Containing Palygorskite

AbstractFe is a common substituent in palygorskites (Plg), but its effect on the microscopic properties is unclear. In the current study, molecular dynamics (MD) simulations were carried out to investigate the effect of Fe on the properties of the nano-pores in Plg. The structures and dynamics of water and Na+ ions in the pores were computed by analyzing the MD trajectories. The results revealed that for both Fe-containing and ordinary Plg, zeolitic water molecules can diffuse into the pores with very low mobility whereas Mg-coordinated water fails to escape. Na+ ions show no obvious diffusivity because they are fixed above the Si–Osix-membered rings. Detailed comparison indicates that Fe-substitution has no significant influence on the pore properties of Plg.

Preparation of effective carvacrol/attapulgite hybrid antibacterial materials by mechanical milling

A green antibacterial material was successfully prepared using natural attapulgite and carvacrol by a facile mechanical milling. The stable hybrid nanocomposites were formed after the zeolitic water molecules of attapulgite was substituted by the carvacrol molecules under the effect of mechanical force. It was found that the 30 wt% of carvacrol added amount and the 30 min of grinding time were the appropriate parameters for preparation a stable hybrid. Furthermore, the fast release behavior of carvacrol molecules provided good antibacterial property for the obtained antibacterial material, and the minimum inhibitory concentration values against both Staphylococci aureus and Escherichia coli were 2.0 mg/mL. Therefore, it is expected to develop a facile and promising strategy for preparation green antibacterial material to replace the synthetic antibiotic used in animal feeding.

Evaluation of methylene blue removal by plasma activated palygorskites

Clay minerals with fibrous morphology, such as palygorskite, have been applied as adsorbents to remove pollutants from the environment and reduce toxic compounds, such as dye, in aquatic media. Although natural palygorskite has good dye removal performance, chemical modification can improve its adsorption sites and desired properties. In this study, palygorskite was activated in H2/N2 plasma flow for 2, 4, and 6h to produce new adsorbents for the removal of methylene blue (MB). The solids were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, scanning electron microscopy (SEM) coupled to dispersive energy X-ray spectrometry and nitrogen adsorption/desorption measurements. The plasma technique induced structural defects in the palygorskite by the removal of coordinated and zeolitic water molecules, which altered the palygorskite’s specific surface area and pore volume. The adsorption capacity of the activated plasma samples for the removal of MB increased from 35.66 in the natural palygorskite to 54.17mgg−1 in the activated samples.

Organically modified sepiolite: Thermal treatment and chemical and morphological properties

The modification of sepiolite is one of the aspects well established in literature aiming to broaden the range of applications of this material. Additionally, in some requests, e.g. in polymer processing to produce sepiolite-based nanocomposites, higher temperatures are a necessity. Despite that, understanding the influence of the modifier as well as its modifications and thermal stability are not broadly contemplated. So, in this work Sepiolite (Sep) was treated with tetradecyltrimethylammonium bromide (TTAB) and hexadecyltrimethylammonium bromide (CTAB), as well as a thermal treatment was performed in the modified samples. The influence on structural, thermal properties and morphology in the treated Sep with TTAB and CTAB were investigated by using N2 adsorption/desorption isotherms, zeta potential, thermogravimetric analyses (TGA), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), 29Si solid-state nuclear magnetic resonance (29Si ss-NMR), and scanning electron microscopy (SEM). It was possible to observe a decrease of the SBET and V values for the modified samples with CTAB and TTAB, in contrast to an increase of the zeta potential. The thermal analyzes results showed that the oxidative atmosphere did not accelerate the degradation reactions of the raw and modified Sep. X-ray diffractograms showed that there was no change in the crystalline structure of the Sep after the modification. On the other hand, the thermal treatment performed on the Sep samples lead to changes in its structure, due to the release of zeolitic and coordination water molecules. Although SepTTAB exhibited a slightly higher thermal stability, as well as a lower specific surface area, no significant differences were observed between SepCTAB and SepTTAB.

Improved rate performance of Prussian blue cathode materials for sodium ion batteries induced by ion-conductive solid-electrolyte interphase layer

Prussian blue (PB) and its analogues (PBAs) are promising cathode materials for sodium ion batteries (SIBs) because of their wide diffusion tunnels for sodium ions. However, water molecules typically contained within PB structures have been hypothesized to undermine their stability and rate performance. Here we report that zeolite water molecules in PB structures may induce the formation of Na2CO3 as one of the main components in SEI layer on the surface of PB materials. From PB samples containing zeolite water synthesized via a solvothermal method at different temperatures, a specific capacity of 113 mAh g−1 is demonstrated at 10 mA g−1, with a capacity retention of 75% at 1000 mA g−1. Cycling tests reveal a capacity loss of only 1.2% after 100 cycles at 200 mA g−1. It is suggested that Na2CO3 contained in the SEI layer not only protects the electrode materials from side reactions with the electrolyte, but also facilitates quick charge transfer at the interfaces, leading to improved electrochemical performances.

Neutron Diffraction and EXAFS Studies of K2x/3Cu[Fe(CN)6]2/3·nH2O

The crystal structure of copper hexacyanoferrate (CuHCF), K2x/3Cu[Fe(CN)6]2/3·nH2O, with nominal compositions x = 0.0 and x = 1.0 was studied by neutron powder diffraction (NPD) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The compound crystallizes in space group Fm3m, with a = 10.1036(11) A and a = 10.0588(5) A for x = 0.0 and x = 1.0, respectively. Difference Fourier maps for x = 0.0 show that the coordinated water molecules are positioned at a site 192l close to vacant N positions in the −Fe–C–N–Cu– framework, while additional zeolitic water molecules are distributed over three sites (8c, 32f, and 48g) in the −Fe–C–N–Cu– framework cavities. The refined water content for x = 0.0 is 16.8(8) per unit cell, in agreement with the ideal 16 (n = 4). For x = 1.0, the refinement suggests that 2.6 K atoms per unit cell (x = 0.98) are distributed only over the sites 8c and 32f in the cavities, and 13.9(7) water per unit cell are distributed over all the four positions. The EXAFS data for Fe...

Syntheses, Crystal Structures, and Properties of the Isotypic Pair [Cr(H2O)6]2[B12H12]3·15H2O and [In(H2O)6]2[B12H12]3·15H2O

AbstractSingle crystals of [Cr(H2O)6]2[B12H12]3·15H2O and [In(H2O)6]2[B12H12]3·15H2O were obtained by reactions of aqueous solutions of the acid (H3O)2[B12H12] with chromium(III) hydroxide and indium metal shot, respectively. The title compounds crystallize isotypically in the trigonal system with space group R$\bar{3}$c (a = 1157.62(3), c = 6730.48(9) pm for the chromium, a = 1171.71(3), c = 6740.04(9) pm for the indium compound, Z = 6). The arrangement of the quasi‐icosahedral [B12H12]2– dianions can be considered as stacking of two times nine layers with the sequence …ABCCABBCA… and the metal trications arrange in a cubic closest packed …abc… stacking sequence. The metal trications are octahedrally coordinated by six water molecules of hydration, while another fifteen H2O molecules fill up the structures as zeolitic crystal water or second‐sphere hydrating species. Between these free and the metal‐bonded water molecules, bridging hydrogen bonds are found. Furthermore, there is also evidence of hydrogen bonding between the anionic [B12H12]2– clusters and the free zeolitic water molecules according to B–Hδ–···δ+H–O interactions. Vibrational spectroscopy studies prove the presence of these hydrogen bonds and also show slight distortions of the dodecahydro‐closo‐dodecaborate anions from their ideal icosahedral symmetry (Ih). Thermal decomposition studies for the example of [Cr(H2O)6]2[B12H12]3·15H2O gave no hints for just a simple multi‐stepwise dehydration process.

Solid-state magnetic switching triggered by proton-coupled electron-transfer assisted by long-distance proton-alkali cation transport.

Acidity of water molecules coordinated to Co ions in CoFe Prussian blue analogues (PBA) has been used to reversibly activate the Co(III)Fe(II) ↔ Co(II)Fe(III) electron transfer. The study of the structure and the electronic structure shows that the process implies an original PCET reaction between a solid-state porous coordination polymer and hydroxide ions in solution. The PCET reaction spreads throughout the solid network thanks to a long-range H(+) and Rb(+) transport within the pore channels of PBA taking advantage of the hydrogen-bonding network of zeolitic water molecules acting as proton wires.

Phase transformation of calcium oxalate dihydrate–monohydrate: Effects of relative humidity and new spectroscopic data

New data on vibrational properties of calcium oxalates and their controversial transformation mechanism are presented. We have focused on whewellite (CaC2O4·H2O) and weddellite [CaC2O4·(2+x) H2O], the most common phases of calcium oxalate; these compounds occur in many organisms, in kidney stones and in particular kinds of films found on the surface of many works of art. Low temperature experiments carried out by Fourier transform infrared spectroscopy have highlighted both the high structural order in the crystalline state of whewellite and the disordered distribution of the zeolitic water molecules in weddellite. The synthesised nanocrystals of weddellite have been kept under different hygrometric conditions in order to study, by X-ray powder diffraction, the role of “external” water molecules on their stability. Moreover, in order to identify the different kinds of water molecules, a re-investigation, supported by quantum chemical calculations, of the observed vibrational spectra (IR and Raman) of whewellite has been conducted.

Microwave absorption and structure of zeolite water in heulandite and clinoptilolite by 1H NMR

The structure of zeolite water in single crystals of natural zeolites represented by clinoptilolite Na2K2Ca[Al6Si30O72]·22H2O and heulandite Ca3Mg[Al8Si28O72]·24H2O is studied with 1H NMR. Below 170 K the distribution of H2O over the structural positions is shown to be fixed but different for the two minerals. Above 290 K translational and orientational diffusion of zeolite water molecules is observed and the structure of water is almost identical in both heulandite and clinoptilolite. Diffusion mechanism may be associated with the interaction between librational modes of H2O and high-frequency oscillations of aluminosilicate framework. The microwave absorption is shown to be caused in certain conditions by this type of interaction.

Role of water on formation and structural features of Maya blue

The Maya blue (MB) is an artificial pigment created between 500-800 A.D. and used in murals, pottery and sculptures by Mayas and other people in Mesoamerica. MB is resistant to age, acid, weathering, biodegradation and even modern chemical solvents, but the chemical reasons behind the resistance to chemical aggressions are still under debate. Water plays a fundamental role in the interactions between indigo and clay. The dynamics of the clay's zeolitic and structural water molecules during the formation of MB, usually stabilized by moderate heating, has been monitored by means of neutron inelastic scattering. Neutron incoherent scattering in these samples is only due to the hydrogen atoms, so the signal is very sensitive to the amount of released water, providing detailed information on the dehydration process. A simultaneous analysis of the coherent elastic scattering and the incoherent scattering allows observing and quantifying how the structure of the clay is affected by dehydration. Here we show that a quite resistant pigment can be obtained at room temperature simply by dehydrating a palygorskite-indigo mixture employing only vacuum, without any thermal treatment.

Lead hexacyanoferrate(II) tetrahydrate: Crystal structure, FTIR spectroscopy and thermal decomposition studies

Pb2[Fe(CN)6]·4H2O was synthesized by mixing aqueous solutions of lead(II) nitrate and potassium ferrocyanide. Its crystal structure was solved ab initio from synchrotron powder X-ray diffraction data using the direct methods and refined by the Rietveld method. Thermal analysis (TGA and DTA), Fourier Transform Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM) studies were also used for the solid state characterization of this compound and its decomposition products. The complex crystallizes in the monoclinic crystal system, space group P21/n. The Fe2+ cation is octahedrally coordinated to six cyano groups, and the Pb2+ cation is penta-fold coordinated to three N atoms from CN ligands and two O atoms from coordinated water molecules. The most important peculiarity of the structure of this complex is the occurrence of water bridges linking two neighboring Pb2+ cations. An unusual Fe–CN–Pb(H2O)2–Pb–NC–Fe linkage alternates with a usual Pb–NC–Fe one. Zeolitic water molecules are also observed in the structure; they are located in small channels in the structure and they are hydrogen bonded to coordinated water molecules forming a cumulus. Coordinated water and zeolitic water molecules in this complex can be removed without affecting the hexacyanometallate framework. The thermal decomposition in air to produce Pb2Fe2O5 and PbO as final products has been studied by thermogravimetric and differential thermal analysis, FTIR spectroscopy and laboratory powder X-ray diffraction. The crystallite size and morphology of the complex and its thermal decomposition products were evaluated by SEM.

Infrared spectroscopy study of the sorption of selenium(IV) on natural zeolites

The sorption of selenium(IV) ions on single crystals of natural shabazite, analcime, mesolite, stilbite, and on clinoptilolite- and mordenite-containing tuffs in dependence on the concentration and pH of a solution of sodium selenite was studied by infrared spectroscopy. It was assumed that sorption on clinoptilolite and mordenite tuffs from a 0.1 M solution of sodium selenite with pH 9 occurs in the form of selenite and pyroselenite anions forming a hydrogen bond with the zeolite water molecules. It was established that water molecules in analcime, unlike stilbite, shabazite and mesolite, also form hydrogen bonds with the selenite ion in an alkaline medium. No hydrogen bonds are formed in diluted solutions or an acid medium. The partial desilylation and dealumination of zeolites in alkaline and acid media respectively, were observed.

Characterization of the structural properties and Pb(II) adsorption behavior of iron oxide coated sepiolite

This paper presents the adsorption of Pb(II) from aqueous solution by raw sepiolite (RS) and iron oxide-coated sepiolite (ICS) samples. Adsorption of Pb(II) by RS and ICS sample was investigated as a function of the initial Pb(II) concentration, solution pH, ionic strength, temperature and inorganic ligand (Cl −). Changes in the surfaces and structure of sepiolite samples were characterized by means of IR and thermal analysis (TG-DTA). The perturbation observed on the zeolitic and bound water vibrations of ICS indicates that some of iron oxide particles enter the interior channels and replace zeolitic water molecules. The exothermal peak at 834 °C for RS and at 774 °C for ICS in the thermal analysis curves is assigned to the phase transformation of sepiolite to enstatite (MgSiO 3). The Langmuir monolayer adsorption capacities of RS and ICS in 0.1 M NaNO 3 solution at 298 K were estimated as 5.36 and 75.79 mg/g, respectively. Thermodynamic parameters such as change in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were evaluated for RS and ICS to be − 15.46 kJ/mol (at 298 K), 47.78 kJ/mol and 212 J/mol K, and − 16.03 kJ/mol (at 298 K), 47.48 kJ/mol and 213 J/mol K, respectively.

Humidity‐Sensitive Magnet Composed of a Cyano‐Bridged CoII–NbIV Dimetallic Assembly

AbstractNanoporous magnetic materials composed of metal‐assembled complexes are expected to exhibit chemical sensitivity. In this work, we observed a humidity‐induced reversible change between ferromagnetism and antiferromagnetism in a new type of a cobalt octacyanoniobate based magnet in the high‐humidity region. This humidity response is caused by the adsorption and desorption of non‐coordinated water (so‐called zeolitic water) molecules in the interstitial site. Such a phenomenon is achieved by the structural flexibility of an octacyanometalate‐based magnet.

Synthesis, crystal structure, and magnetic properties of a copper(II) octacyanotungstate(V)-based magnet containing two types of organic ligands

Cu 3[W(CN) 8] 2(pyrimidine) 2(3-cyanopyridine) 2 · 4H 2O, a cyanide-bridged copper(II) octacyanotungstate(V) with two types of organic ligands (pyrimidine and 3-cyanopyridine), is prepared. In this compound, the coordination geometry of W is an 8-coordinated bicapped trigonal prism where five CN groups of [W(CN) 8] are bridged to five Cu ions, and the remaining three CN groups are free. The coordination geometries of the three types of Cu ions (Cu1, Cu2, and Cu3) are 6-coordinated pseudo-octahedron. The cyano-bridged-Cu2–W–Cu3-layer is linked by a Cu1 pillar unit, and a cavity along the a axis, which is occupied by 3-cyanopyridine molecules and zeolitic water molecules, exists. The present compound shows ferrimagnetism with a Currie temperature of 7 K, a saturation magnetization of 2.9 μ B, and a coercive field of 7 Oe at 2 K.