Structure-directing Agent Research Articles

Ionic-Liquid-Assisted Synthesis of Mixed-Phase Manganese Oxide Nanorods for a High-Performance Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries (ZIBs) provide a safer and cost-effective energy storage solution by utilizing nonflammable water-based electrolytes. Although many research efforts are focused on optimizing zinc anode materials, developing suitable cathode materials is still challenging. In this study, one-dimensional, mixed-phase MnO2 nanorods are synthesized using ionic liquid (IL). Here, the IL acts as a structure-directing agent that modifies MnO2 morphology and introduces mixed phases, as confirmed by morphological, structural, and X-ray photoelectron spectroscopy (XPS) studies. The MnO2 nanorods developed by this method are utilized as a cathode material for ZIB application in the coin-cell configuration. As expected, Zn//MnO2 nanorods show a significant increase in their capacity to 347 Wh kg-1 at 100 mA g-1, which is better than bare MnO2 nanowires (207.1 Wh kg-1) synthesized by the chemical precipitation method. The battery is highly rechargeable and maintains good retention of 86% of the initial capacity and 99% Coulombic efficiency after 800 cycles at 1000 mA g-1. The ex situ XPS, X-ray diffraction, and in-depth electrochemical analysis confirm that MnO6 octahedra experience insertion/extraction of Zn2+ with high reversibility. This study suggests the potential use of MnO2 nanorods to develop high-performance and durable battery electrode materials suitable for large-scale applications.

Highly efficient MgF2 supported Co catalyst for cyclization reaction of o-nitroaniline and benzyl-alcohol

A highly dispersed Co-based catalyst (termed as Co@MgF2-f-h) with strong metal-support interaction has been synthesized by using ammonium-fluoride (NH4F) hexamethylenetetramine (hmta) assisted hydrothermal method. The Co@MgF2-f-h catalyst exhibited excellent performance for cyclization reaction of o-nitroaniline and benzyl-alcohol. Extensive techniques including as XRD, FESEM, TEM, HADDF-STEM-EDS and H2-TPR were conducted to reveal the reason for the enhanced performance of Co@MgF2-f-h for cyclization reaction of o-nitroaniline and benzyl-alcohol in comparison with those of reference catalysts (Co@MgF2-f and Co@MgO-h, respectively) without using ammonium-fluoride and hexamethylenetetramine structure-directing agents. This study may endow a feasible guidance for the preparation of MgF2 supported Co catalysts with excellent performance for other catalytic reactions.

Room temperature fabrication of cobalt mullite for the snappy adsorption of cationic and anionic dyes

Cobalt mullite adsorbent for the robust adsorption performance toward Victoria Blue (VB) and Metanil Yellow (MY) is fabricated by the sol-gel method at room temperature using dipropylamine as a structure-directing agent. The synthesized adsorbent is characterized by XRD, FT-IR, and HRTEM. From these analyses, it is found that dipropylamine binds with the alumina and cobalt oxide, which makes it into tetrahedral to octahedral form. This interaction causes the formation of cobalt mullite. It is observed that trigonal alumina and orthorhombic cobalt mullite are interlinked to form a hybrid network. The special feature of adopting this adsorbent for the adsorption of VB and MY is that it has a large amount of Brønsted acid site because of the octahedral coordination of Al and Co. The large availability of acid sites in the framework and hybridization of two different network systems favors robust adsorption. The rate of adsorption (K2 = 0.00402g/mg.min for VB and K2 = 0.004g/mg.min for MY) and adsorption capacity (Qe = 102.041mg/g for VB and Qe = 19.0406mg/g for MY) are greater for VB than MY. This may be due to the more steric factor involved in MY than VB. Thermodynamic parameter indicated that the adsorption of VB and MY is spontaneous, endothermic, and increased randomness in the adsorbent-adsorbate interface. The results from the enthalpy value (ΔH° = 65.43kJ/mol for VB and ΔH° = 44.729kJ/mol for MY) revealed that the chemisorption is involved in the adsorption process.

Influence of catalyst pelletization on propane dehydrogenation over hierarchical MFI zeolite supported with platinum-yttrium nanoparticles

Platinum-yttrium (PtY) nanoparticles supported on a siliceous form of mesoporous MFI zeolite (MZ) were recently found to exhibit excellent catalytic performance in propane dehydrogenation (PDH). Herein, potential shaping of the PtY/MZ catalyst is investigated from the laboratory-synthesized powder form into industrially preferable pellets. The MZ zeolite powder was synthesized using multi-ammonium surfactants as a structure-directing agent and then pelletized in a hydraulic press by itself or with inorganic binders (i.e., pseudoboehmite, fumed silica, or hydrotalcite). As a part of the sequential pelletization process, pressing was followed by a high-temperature treatment (923 K). Addition of 20 wt% pseudoboehmite resulted in the highest mechanical strength without a significant loss of the initial zeolite mesoporosity. The pseudoboehmite-bound pellet also showed high catalytic activity and longevity in PDH application when simultaneously impregnated with 1 wt% Pt [Pt(NH3)4(NO3)2] and 1 wt% Y [Y(NO3)2·6H2O]. Notwithstanding the observed high propane conversion, the pseudoboehmite-bound catalyst produced an unsatisfactory result of low propylene selectivity (∼60%). Image analyses of HAADF-STEM EDS and solid-state 31P NMR spectroscopic data suggest that such findings could be attributed to Al migration from pseudoboehmite onto zeolite regime during the phase transformation of pseudoboehmite in the shaping process. Alternatively, the uses of non-acidic binders, such as fumed silica and hydrotalcite binders were also demonstrated. The silica-bound catalyst yielded high propane conversion with high propylene selectivity although mechanical strengths of the pellet were compromised to a moderate level.

Highly Tunable MOF Luminophores Featuring Anthracene Directed Assembly and Fluorescence Regulation

Metal-organic frameworks (MOFs) have been recognized as a potential platform for the development of tunable luminophores owing to their highly modulable structures and components. Herein, two MOF luminophores based on Cd(II) ions, 1,3,5-tri(4-pyridinyl)benzene (TPB), and 1,4-dicarboxybenzene (H2BDC) were constructed. The directed assembly of the metal ions and organic linkers results in [Cd2(BDC)2(TPB)(H2O)]·x(solvent) (MOF-1) featuring TPB-based blue fluorescence centered at 425 nm. By introducing anthracene as the structure directing agent (SDA) for assembly regulation, [Cd2(BDC)(TPB)2(NO3)2]·x(solvent) (MOF-2) was obtained, which reveals anthracene feeding-dependent high tunable emission in the 517-650 nm range. Detailed components, photophysical properties, and structural characteristics investigations of MOF-2 indicate the TPB and NO3- interactions as the origin of its redshifted emission compared with that of MOF-1. Furthermore, the fluorescence of MOF-2 was found to be regulatable by the anthracene feeding based on the SDA-determined crystallinity of the crystalline sample. All these results provided a unique example of the structural and fluorescence regulation of MOF luminophores.

Temperature-Controlled Transformation of WO3 Nanowires into Active Facets-Exposed Hexagonal Prisms toward Efficient Visible-Light-Driven Water Oxidation.

A unique transformation of WO3 nanowires (NW-WO3) into hexagonal prisms (HP-WO3) was demonstrated by tuning the temperature of the (N2H4)WO3 precursor suspension prepared from tungstic acid and hydrazine as a structure-directing agent. The precursor preparation at 20 °C followed by calcination at 550 °C produced NW-WO3 nanocrystals (ca. <100 nm width, 3-5 μm length) with anisotropic growth of monoclinic WO3 crystals to (002) and (200) planes and a polycrystalline character with randomly oriented crystallites in the lateral face of nanowires. The precursor preparation at 45 °C followed by calcination at 550 °C produced HP-WO3 nanocrystals (ca. 500-1000 nm diameter) with preferentially exposed (002) and (020) facets on the top-flat and side-rectangle surfaces, respectively, of hexagonal prismatic WO3 nanocrystals with a single-crystalline character. The HP-WO3 electrode exhibited the superior photoelectrochemical (PEC) performance for visible-light-driven water oxidation to that for the NW-WO3 electrode; the incident photon-to-current conversion efficiency (IPCE) of 47% at 420 nm and 1.23 V vs RHE for HP-WO3 was 3.1-fold higher than 15% for the NW-WO3 electrode. PEC impedance data revealed that the bulk electron transport through the NW-WO3 layer with the unidirectional nanowire structure is more efficient than that through the HP-WO3 layer with the hexagonal prismatic structure. However, the water oxidation reaction at the surface for the HP-WO3 electrode is more efficient than the NW-WO3 electrode, contributing significantly to the superior PEC water oxidation performance observed for the HP-WO3 electrode. The efficient water oxidation reaction at the surface for the HP-WO3 electrode was explained by the high surface fraction of the active (002) facet with fewer grain boundaries and defects on the surface of HP-WO3 to suppress the electron-hole recombination at the surface.

Molar-Ratio-Dependent Coordination Assembly of Organoiridium(III)-Octatungstate Complexes in Aqueous Solution

We scrutinized the speciation of Cp*Ir-containing tungsten oxide clusters (Cp* is pentamethylcyclopentadienyl anion) in aqueous mixtures of [(Cp*IrCl)2(μ-Cl)2] and Na2WO4 in varying molar ratios. 1H nuclear magnetic resonance (NMR) spectroscopy revealed the formation of three distinct Cp*Ir-polyoxotungstate species in the reaction solution, and they were isolated as Na4[(Cp*Ir)2(μ-OH)3]2[(Cp*Ir)2H2W8O30] (1), [(Cp*Ir)2(μ-OH)3]2[(Cp*Ir)2{Cp*Ir(OH2)}2H2W8O30] (2), and [(Cp*Ir)2{Cp*Ir(OH2)}2{Cp*Ir(OH2)2}2H2W8O30](NO3)2 (3) from the mixtures in which iridium concentration is less than, equal to, and more than the tungsten concentration, respectively. These results show the octatungstate [H2W8O30]10- anion is the major polyoxotungstate species in the presence of {Cp*Ir}2+ cations, and it has high nucleophilicity enough to bind up to six {Cp*Ir}2+ cations on its surfaces producing a cationic Cp*Ir-octatungstate complex. The octatungstate anion was also generated from the reaction of [(Cp*IrCl)2(μ-Cl)2] and methylammonium paratungstate-B, (CH3NH3)10[H2W12O42], and was isolated as a methylamine-coordinated complex (CH3NH3)2[(Cp*Ir)2{Cp*Ir(NH2CH3)}2H2W8O30] (4), indicating {Cp*Ir}2+ cations function as a structure-directing agent that converts tungsten species into octatungstate anions in aqueous solution. In addition, the coordination environment of {Cp*Ir}2+ can be further modified by coordination with pyridine forming [{Cp*Ir(NC5H5)}2(μ-OH)2][(Cp*Ir)2{Cp*Ir(NC5H5)}2H2W8O30] (5).

Facile Fabrication of Monodispersed Carbon Sphere: A Pathway Toward Energy-Efficient Direct Air Capture (DAC) Using Amino Acids.

Direct removal of carbon dioxide (CO2 ) from the atmosphere, known as direct air capture (DAC) is attracting worldwide attention as a negative emission technology to control atmospheric CO2 concentrations. However, the energy-intensive nature of CO2 absorption-desorption processes has restricted deployment of DAC operations. Catalytic solvent regeneration is an effective solution to tackle this issue by accelerating CO2 desorption at lower regeneration temperatures. This work reports a one-step synthesis methodology to prepare monodispersed carbon nanospheres (MCSs) using trisodium citrate as a structure-directing agent with acidic sites. The assembly of citrate groups on the surface of MCSs enables consistent spherical growth morphology, reduces agglomeration and enhances water dispersibility. The functionalization-assisted synthesis produces uniform, hydrophilic nanospheres of 100-600nm range. This work also demonstrates that the prepared MCSs can be further functionalized with strong Brønsted acid sites, providing high proton donation ability. Furthermore, the materials can be effectively used in a wide range of amino acid solutions to substantially accelerate CO2 desorption (25.6% for potassium glycinate and 41.1% for potassium lysinate) in the DAC process. Considering the facile synthesis of acidic MCSs and their superior catalytic efficiency, these findings are expected to pave a new path for energy-efficient DAC.

Fast cathodic electrodeposition of ZnTCPP-functionalized metal-organic framework films forpreparation of a fluorescent aptamer sensor for microcystindetermination.

Aone-step electrodeposition-assisted self-assembly technique has been developedfor preparation of ZnTCPP@MOF films with three-dimensional mesoporous structure in a three-electrode system. The internal structure of the ZnTCPP@MOF films was tuned by adjusting the electrochemical deposition voltage, deposition time, and the concentration of ZnTCPP at room temperature. The ZnTCPP@MOF films under different deposition conditions were characterized by scanning electron microscopy, Fourier transformation infraredspectroscopy, and X-ray photoelectron spectroscopy. The prepared ZnTCPP@MOF films exhibited excellent fluorescence properties, in which ZnTCPP molecules were encapsulated inside the MOF as fluorescent signal probes and structure-directing agents, which affected the electrochemical response of the ZnTCPP@MOF films. The sensing platform based on ZnTCPP@MOF film wasused to detect microcystin with a wide determination range (1.0 × 10-12mol/L ~ 1.0 × 10-5mol/L), low determination limit (3.8 × 10-13mol/L), and high sensitivity. More importantly, the strategy is simple, low-cost, green, and environmentally friendly, and it provides a new strategy for the direct use of MOFs films as signaling components.

Phosphotungstic acid immobilized over SnO2 mesoporous material as a heterogeneous catalyst for fructose to 5-hydroxymethylfurfural conversion

5-Hydroxymethylfurfural (HMF) is regarded as an essential platform chemical due to its flexible nature that could be converted into a variety of value-added compounds including production of liquid fuels and fine chemicals. We have developed a phosphotungstic acid (PTA) immobilized over SnO2 mesoporous material by hydrothermally employing Pluronic P123 as a structure directing agent (SDA) to obtain a heterogeneous catalyst for fructose to HMF conversion, and the catalyst is designated as MSnPTA. The powder X-ray diffraction patterns in low angle region, type IV isotherm and fringes of the catalyst confirmed the mesoporosity of the material. The catalyst is comprised of BET surface area of 85.86 m2/g and average pore diameter of 7.9 nm. Spherical shape through worm like structure formed small particles facilitated the large surface area of the MSnPTA catalyst that prefer to occur the catalytic reaction. The uniform elemental distribution of PTA over SnO2 ascribed more active sites, resulting in high acidity of the catalyst as measured by TPD of ammonia, which increased the conversion of fructose to high yield of HMF in a short reaction time. The yield of the HMF increased as increasing the amount of catalyst and temperature as expected.

Impacts of Structure-Directing Agents on the Synthesis of Cu3Mo2O9 for Flexible Lignin-Based Supercapacitor Electrodes

Due to demands for sustainability, the interest in energy storage devices constructed from green materials has increased immensely. These devices currently have yet to be satisfactory. Issues include high production costs and toxicity, limited dependability, and subpar electrochemical performance. In this research, low-cost, plant-based electroactive Cu3Mo2O9 materials were synthesized via co-precipitation followed by an annealing method using two different structure-directing agents, i.e., the commonly used surfactant cetyltrimethylammonium bromide (CTAB) and the biomolecule deoxyribonucleic acid (DNA) as a greener alternative, and these materials were studied for the first time. Further, the Cu3Mo2O9 nanoparticles developed using CTAB and DNA were integrated into the lignin matrix and studied as flexible electrodes for supercapacitor application. Here, the morphological advantages of the nanorods and nanosheets formed by varying the synthesis methods and their effects during supercapacitor studies were studied in detail. After 1200 cycles, the Al/lig-Cu3Mo2O9@DNA supercapacitor exhibited higher capacitive performance when compared to the Al/lig-Cu3Mo2O9@CTAB supercapacitor. The Al/Lig-Cu3Mo2O9@DNA supercapacitor had an initial specific capacitance of 404.64 mF g−1 with a ~70% retention, while the Al/Lig-Cu3Mo2O9@CTAB supercapacitor had an initial specific capacitance of 309.59 mF g−1 with a ~50% retention. This study offers a new approach to creating scalable, low-cost, green composite CuMoO4-based electrodes for flexible supercapacitors.

Organic Structure-Directing Agent Free Synthesis of Mordenite with Seeds, Used as A Support for Mo Catalysts in the Transesterification of Soybean Oil

This work prepared mordenite using seeds and without organic structure-directing agents (OSDAs). The Mo/Mordenite was prepared through wet impregnation and the catalysts’ performance was checked for transesterification of soybean oil with methanol. The mordenite zeolite was prepared through hydrothermal crystallization under static conditions with a molar composition of 6Na&lt;sub&gt;2&lt;/sub&gt;O:Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;:30SiO&lt;sub&gt;2&lt;/sub&gt;:780H&lt;sub&gt;2&lt;/sub&gt;O. The catalyst samples were characterized crystallinity through X-ray diffraction, elemental composition by X-ray fluorescence spectroscopy, Surface areas by N&lt;sub&gt;2&lt;/sub&gt; adsorption-desorption, surface morphology scanning electron microscopy, functional group by infrared spectroscopy and active sites by temperature programmed desorption of ammonia. The transesterification of soybean oil was carried out using the following parameters: 5% catalyst by weight, 1:12 oil to methanol molar ratio, at 200°C for either 12 h or 24 h. X-ray diffraction patterns showed the characteristic peaks of the mordenite structure. After molybdenum oxide was added, the structure of mordenite zeolite was conserved while the specific surface area was reduced. The morphology can be described as a highly crystalline material with well-defined crystalline particles having a spherical profile characteristic of the typical morphology of sodium mordenite zeolite with a low silicon/aluminum ratio. The catalyst samples exhibited sites of a weak and medium-strength nature. The higher activity of the catalyst (Mo/Mordenite) about mordenite zeolite, could be justified by the existence of molybdenum. The wet impregnation of metal (Mo) on the surface of the MOR zeolite is an effective option to increase the acidity of the solid catalysts. Mordenite with 8.84% Mo could be a promising catalyst for the biodiesel factory.

Atom-Selective Analyses Reveal the Structure-Directing Effect of Cs Cation on the Synthesis of Zeolites.

To understand the crystallization mechanism of zeolites, it is important to clarify the detailed role of the structure-directing agent, which is essential for the crystallization of zeolite, interacting with an amorphous aluminosilicate matrix. In this study, to reveal the structure-directing effect, the evolution of the aluminosilicate precursor which causes the nucleation of zeolite is analyzed by the comprehensive approach including atom-selective methods. The results of total and atom-selective pair distribution function analyses and X-ray absorption spectroscopy indicate that a crystalline-like coordination environment gradually forms around Cs cations. This corresponds to the fact that Cs is located at the center of the d8r units in the RHO structure whose unit is unique in this zeolite, and a similar tendency is also confirmed in the ANA system. The results collectively support the conventional hypothesis that the formation of the crystalline-like structure before the apparent nucleation of the zeolite.

SCSC Transformation and Post-Synthesis Modification of MOFs with Proton Conduction and Ratiometric Fluorescence-Sensing Properties.

The modification of metal-organic framework (MOF) materials to facilitate their practical applications is an extremely challenging and meaningful topic. In this work, two stepwise modification strategies for MOFs were conducted. First, we have demonstrated a single-crystal-to-single-crystal (SCSC) transformation from a microporous three-dimensional (3D) MOF to a two-dimensional (2D) coordination polymer (CP). The centrosymmetric [Cd(3-bpdb)(MeO-ip)]n (1) transforms into a chiral [Cd2(3-bpdb)(MeO-ip)2(CH3OH)2]n (2), which is triggered by the reaction time with methanol that acts as a structure-directing agent. The conversion relationship of 1 to 2 at different reaction times was studied in detail. Density functional theory (DFT) calculations clearly state that the irreversible formation of 2 is thermodynamically favorable. Intriguingly, 2 exhibits good proton conduction of 1.34 × 10-3 S cm-1 under 363 K and 98% relative humidity (RH) due to unique H-bond network characteristics. To the best of our knowledge, there are very few cases of 3D to 2D SCSC transformation stimulated by reaction time. The results have important implications for understanding the SCSC transformation mechanism and synthetic chemistry. On the other hand, the lanthanide3+-functionalized hybrids (Ln3+-MOF), Ln3+@1, were continuously prepared by incorporating luminescent Ln3+ ions into the structure of 1 through encapsulating post-synthesis modification (PSM). Tb3+@1 exhibits double emission in water and shows visual ratiometric fluorescence behavior for sensing glutamic acid (Glu), tryptophan (Trp), and Al3+, which is more reliable and accurate than single emission. Our work may not only provide new insights into the multiple modification of MOF materials but also promote the practical application of such materials.

Benzimidazole-based covalent organic polymer nanosheets incorporated in mesoporous organosilica nanoparticles with excitation-dependent fluorescence for sensing of Cu2+

A novel type of small-sized nanosheets (TD-Si) was prepared by chemical exfoliating stacked bulk materials of benzimidazole-based covalent organic polymer (TpDAB). Then TD-Si was used as organosiloxane precursor to incorporate into silica frameworks of mesoporous organosilica nanoparticles (TD-MONs) using CTAB as structural-directing agents. The obtained TD-MONs show a clearly hexagonal mesoporous structure with high surface area. Moreover, the optical properties of TD-MONs were measured with fluorescence and Ultraviolet–visible (UV–vis) spectroscopies. The results showed that TD-MONs possessed excitation wavelength dependent fluorescence and had better fluorescence properties due to the reduction of π-π stacking between nano-layers of TpDAB polymer. The emission peaks of TD-MONs were red-shifted as the excitation wavelength increases and TD-MONs exhibited the optimal fluorescence emission at 525 nm when excited at 400 nm. TD-MONs showed high selectivity, sensitivity and recyclability toward copper ions and could be used for the detection of Cu2+ with a low limit of detection (LOD) as low as 3.77 × 10−7 M. In addition, the coordination interaction between TD-MONs and copper ions was demonstrated by FT-IR spectra and high-resolution X-ray photoelectron spectra, and further proved that the binding sites were carbonyl oxygen atoms and imidazole nitrogen atoms in TD-MONs. Therefore, TD-MONs is expected to be a high-sensitive chemical sensor for detecting Cu2+.

Synthesis and Characterization of Silicoaluminophosphate CIT-16P and Its Transformation to SAPO-17

A silicoaluminophosphate molecular sieve, CIT-16P, is synthesized using butane-1,4-bis(quinuclidinium) [(C7H13N)-(CH2)4-(NC7H13)]2+ dihydroxide (DiQ-C4-(OH)2) as an organic structure-directing agent (OSDA). Upon the removal of the OSDA, either by thermal treatment in air at temperatures exceeding 490 °C or by extended ozone treatment at 150 °C, CIT-16P transforms to SAPO-17 (ERI topology). The structure solution of CIT-16P in its as-synthesized form is obtained using a Rietveld refinement of the powder X-ray diffraction pattern. The primary composite building units (CBUs) of CIT-16P are highly distorted cancrinite (can) CBUs that transform into stable can units of the ERI-type framework as a result of the OSDA removal. The distortion of can CBU is maintained without transformation by the presence of tightly bound DiQ-C4 dications in the as-synthesized form of CIT-16P. The transformed material is characterized and evaluated as a catalyst in the methanol-to-olefins (MTO) reaction. The catalytic behavior of the formed SAPO-17 (Si/T-atom = 0.022) (T = Si + Al + P) at 400 °C and WHSV of 1.3 h-1 produces elevated C3+ olefin products (i.e., propylene, butenes, and pentenes) in early stages of the reaction. However, as the reaction proceeds, the C3+ fraction decreases in favor of more ethylene.

Interzeolite transformation from H+-type FAU zeolite into pure CHA zeolite via OSDA/seeds-free and steam-assisted conversion process

Pure CHA zeolite was transformed from FAU zeolite via organic structure-directing agent (OSDA)/seeds-free steam-assisted conversion (SAC). CHA zeolite was transformed using H+-type FAU zeolite with a low Si/Al ratio (Si/Al = 2.8) and a small amount of potassium hydroxide (KOH) and H2O. The Si/Al ratio of the CHA zeolite of the final product was the same as that of FAU-type zeolite as raw material because OH− ions derived from KOH reacted with H+ ions in FAU zeolite. Then, Si constituting FAU zeolite was little dissolved in a small amount of the basic solvent during the interzeolite transformation process. In general, in the interzeolite transformation process, the Si/Al ratio of the final product is lower than that of zeolite as raw material due to the dissolution of Si in the framework in the basic solvent. However, the interzeolite transformation process in this study can reduce the dissolving Si ratio using H+-type FAU zeolite. In addition, the PHI framework with low CO2 adsorption capacity arose with CHA zeolite transformed from Na+-type FAU zeolite via OSDA-free interzeolite SAC in a previous study. However, in this study, the PHI framework did not arise in OSDA-free steam-assisted interzeolite transformation process due to the use of H+-type FAU zeolite. Furthermore, the second particle morphology of CHA zeolite transformed from H+-type FAU zeolite was spherical, which has not been seen in CHA zeolite particles synthesized in previous reports. Finally, the CO2 adsorption capacity and performance of FAU and CHA zeolites were measured. CHA zeolite showed higher CO2 adsorption capacity than H+-type FAU zeolite as the starting material and high CO2 loadings at low CO2 equilibrium pressure. This study investigated that the synthesis condition, chemical properties, and CO2 adsorption performance of CHA zeolite transformed from H+-type FAU zeolite via the OSDA/seeds-free steam-assisted interzeolite transformation process.

Ultra-responsive and selective ethanol and acetone sensor based on Ce-doped Co3O4 microspheres assembled by submicron spheres with multilayer core-shell structure

The sensitive detection of ethanol and acetone is of great significance to address environmental toxicity concerns. Herein, a novel Ce-doped Co3O4 microsphere is precisely fabricated and assembled by abundant submicron spheres with multilayer core-shell configuration employing metal-organic frameworks (MOFs) as template and PVP as the structure-directing agent, and the formation mechanism of the microspheres with hierarchical structure is explored. Moreover, the gas sensing performance of Ce-doped Co3O4 sensor are investigated toward ethanol and acetone. The sensor based on CoCe0.025-350 (the molar ratio of CeCo = 0.025) microspheres exhibits remarkable responsiveness toward ethanol and acetone at relatively low operating temperatures (180 and 200 °C, respectively) and excellent long-term durability. The excellent sensing properties are firstly ascribed to the existence of abundant active sites and surface defects induced by Ce doping, and secondly originated from the hierarchical structure which benefits the absorption, diffusion of the gases on the sensor surface. Furthermore, detection limits as low as 0.1 ppm are achieved by the CoCe0.025–350 sensor. The sensing dynamics of the sensors are also investigated. The versatile strategy report herein can be employed to construct other transition metal oxides with excellent gas sensing properties.

Synthesis and Structure of RUB-58: An Almost Ordered, Highly Crystalline Member of the ZSM-48 Family of Zeolites

ZSM-48 describes a family of disordered high-silica zeolites with a one-dimensional pore system of straight 10-ring channels. Although many different synthesis procedures and various organic structure-directing agents have been tried, all ZSM-48-type materials produced to date have proven to be highly disordered. A few structural models were proposed by Schlenker et al. ( Zeolites 1985, 5, 355−358) and by Lobo and van Koningsveld ( J. Am. Chem. Soc. 2002, 124, 13222−12230) to describe the framework topology and the disorder of the real structure, but it has not been possible to refine the structure of a ZSM-48-type material using experimental diffraction data. RUB-58 was synthesized under hydrothermal conditions at 160 to 200 °C in the system SiO2/H2O/ethylenediamine/pyridine. The product consists of spherelike aggregates of small, needlelike, colorless crystals and has an X-ray powder diffraction (XPD) pattern similar to those published for ZSM-48-type materials. The pattern, however, contains a much larger number of sharp reflections indicative of a more ordered, crystalline material. The reflections could be indexed with the unit cell parameters a = 14.2095(3) Å, b = 20.0874(5) Å, c = 8.3752(2) Å in the space group Pna21, a sub-subgroup of Imma, which is the highest possible symmetry of the ordered ZSM-48 polymorph A (see the Database of Disordered Zeolite Structures). The structure analysis was performed in successive steps: (I) analysis of the average structure, which showed that the framework structure of RUB-58 can be described in terms of polymorph A and that the pyridine molecules occupy defined positions in the elliptical 10-ring channels; (II) refinement of a faulted structure using two separate, but identical polymorph A-type framework structures, with one shifted by exactly 0.5 of the unit cell along the channel direction (volume ratio: 92/8); (III) analysis of the structure of guest-free RUB-58 to examine the geometry of the channels in the empty framework (elliptical cross section nearly identical to that of the as-made material); and (IV) development of convincing disordered models to describe the real structure of RUB-58.

Pure Silica with Ordered Silanols for Propylene/Propane Adsorptive Separation Unraveled by Three-Dimensional Electron Diffraction.

Adsorptive separation of propylene (C3H6) from propane (C3H8), which could deal with energy-intensive cryogenic distillation technologies, remains challenging due to their similar physiochemical properties. Herein, we present a pure silica zeolite with ordered silanols (OSs), whose crystallographic structure was unraveled by the advanced three-dimensional electron diffraction (3D ED), displaying the highly efficient separation of propylene from propane under ambient conditions. The 3D ED technique enables us to investigate its 8-ring pore opening transformation from the round one to the elliptical one during the removal of organic structure-directing agents. Such unique elliptical 8-ring pore openings can exclude larger-size propane and only adsorb propylene. Its C3H6/C3H8 separation performance is also confirmed by column breakthrough experiments, showing a high dynamic adsorption capacity of 53.36 cm3 g-1 for C3H6 but negligible C3H8 under ambient conditions. The dynamic capacity for C3H6 is superior to that of the well-known pure silica DDR-type zeolite (31.07 cm3 g-1). The density functional theory calculation demonstrates that the adsorbed propylene is distributed in the heart-shaped cavity and has a weak interaction with the OSs.