Layered Precursors Research Articles

Cryogenic Exfoliation of Non-layered Magnesium into Two-Dimensional Crystals.

Physical exfoliation of layered precursors is one of the most prevailing techniques to prepare two-dimensional (2D) crystals, which, however, is considered to be intrinsically inapplicable to non-layered bulks. Now, plane cleavage differentiation is identified in metallic magnesium at cryogenic temperature (CT), and a cryogenic exfoliation strategy of non-layered magnesium into 2D crystals is developed. The cleavage anisotropy of the Mg lattice in response to the external mechanical stress originates from the CT-induced specific inactivation of basal slip, which results in the basal cleavage perpendicular to c axis. The exfoliated novel 2D Mg crystals exhibit remarkable localized surface plasmon resonances, holding great promise for the applications in harvesting and converting solar energy. Beyond creating a new member for the burgeoning 2D family, this study may provide a useful tool for the physical exfoliations of various non-layered materials.

(Invited) MXenes: From Fundamental Science to Emerging Applications

Two-dimensional (2D) nanomaterials have been attractive candidates for a plethora of applications since the successful isolation and demonstration of intriguing electronic properties of graphene in 2004 by the Manchester group. The ‘beyond graphene’ march led to the discovery of new types of 2D materials, expanding the flatland research. MXenes, a relatively new and large family of 2D transition metal carbides, nitrides, and carbonitrides, which were discovered at Drexel in 2011 and have become popular due to their diverse chemistries and unique physicochemical properties. These materials are produced by top-down wet chemical or electrochemical extraction of interleaved ‘A’ atomic layers from the layered ternary carbide precursors (MAX phases). The resulting MXenes with surface terminations (-O, -F, -OH) impart negative surface charges, key for stable MXene dispersions in water and organic solvents which enable solution processing. More than 30 different MXenes have been experimentally synthesized, with dozens of new MXenes and their properties predicted computationally. The compositional versatility, metallic conductivity, control of surface chemistry, ordered structures versus solid solutions, etc. make MXenes diverse and suitable for a wide spectrum of applications including but not limited to energy storage, photo- and electro-catalysis, water desalination, optoelectronics, electromagnetic interference shielding, antennas, and smart textiles. The available 2D gallery spaces, redox chemistry at the transition metal oxide-like surface with metallic conductivity, enable MXenes as potential candidate materials for high rate capacitive energy storage applications. The ability of MXenes to spontaneously intercalate a variety of cations while promoting fast charge transfer rates, endorses them for hybrid metal-ion capacitors and battery applications. The electrocatalytic property of MXenes can be tuned based on type of transition metal, amount of defects and surface functionality. Furthermore, combination of slit-like pores with electronic conductivity, qualifies MXenes as capacitive deionization (CDI) electrodes for efficient and reversible removal of ionic species/organic molecules from brackish water. Unlike most of the 2D materials produced by bottom-up routes in small quantities, pilot scale synthesis of MXenes is a promising aspect for immediate future commercialization.

Rediscovery of the Importance of Inorganic Synthesis Parameters in the Search for New Zeolites.

Zeolites and related crystalline microporous materials with cavities and channels of molecular dimensions are of major importance for applications ranging from ion-exchange to adsorption and to catalysis. Because their unique shape-selective properties are closely related to the size, shape, and dimensionality of the intracrystalline channels and cavities, much interest has been devoted to the discovery of novel zeolitic materials over the last several decades. As a result, a dramatic expansion in the structural domain of crystalline microporous materials, as well as in their compositional range, has been achieved. This is largely due to the development of innovative synthetic strategies, for example, organic structure-directing agent (OSDA) design, introduction of heteroatoms like Ge in OSDA-mediated zeolite synthesis, topotactic transformation of two-dimensional layered zeolite precursors, assembly-disassembly-organization-reassembly method, etc. However, although many of these methodologies are quite successful in finding unprecedented zeolite structures, the resulting materials tend to be (hydro)thermally unstable and are often commercially impractical from a manufacturing perspective because of the high cost of the OSDA and/or heteroatom employed. Therefore, we focused on inorganic synthesis parameters as the key phase selectivity factor that has received relatively little attention in the search for new industrially relevant zeolites. This Account describes our recent efforts to find previously undiscovered aluminosilicate zeolites by boosting the roles of inorganic structure-directing agents (ISDAs) in the presence of OSDAs. They include the multiple inorganic cation and excess fluoride approaches, which aim to promote a synergistic cooperation between ISDAs and/or OSDAs and thus to hold a rational design concept, although the latter is not friendly to the practical zeolite manufacturing process due to the toxicity of fluoride. Using these two approaches, we were able to synthesize not only the second generation (PST-29) and four higher generations (PST-20 (RHO-G5), PST-25 (RHO-G6), PST-26 (RHO-G7), and PST-28 (RHO-G8)) of the RHO family of embedded isoreticular zeolites but also three other novel zeolite structures (EU-12, PST-21, and PST-22). We also explored the synthesis of a number of heteroatom-containing aluminophosphate (AlPO4) molecular sieves with different framework structures and unusually high framework charge density through the cooperative structure direction of alkali metal and small OSDA cations or under wholly inorganic conditions. Although we need to clarify the nature and extent of interactions between the inorganic cations and framework components in synthesis mixtures, we believe that our synthetic concepts, shedding new light on the importance of inorganic synthesis parameters, will open a door for achieving many other novel zeolite structures and compositions.

Deciphering the Atomic Patterns Leading to MnO2 Polymorphism

Summary A fundamental understanding of phase transition mechanisms for polymorphic materials is the prerequisite for developing rational synthesis strategies toward phase homogeneity. Here, we target polymorphic MnO2 as the prototype system and reveal the atomic mechanisms governing the phase selection among various MnO2 tunnel structures that are hydrothermally synthesized from a layered MnO2 precursor. A topotactic layer-to-tunnel (L-T) transition mechanism featuring solid-state Mn migration and structure rearrangement is discovered. The transition exhibits multi-step kinetics with the formation of intermediate large tunnels, which introduces structural complexity into the end product with significant phase and compositional heterogeneity within single MnO2 particles. Localized valence analysis further reveals the significant effect of Jahn-Teller Mn3+ ordering on the L-T transition kinetics. We expect these findings to assist the understanding of polymorphism evolution and be further applied to rationalize material synthesis strategies toward phase homogeneity and to establish an accurate synthesis-structure relationship.

Molecule Self-Assembly Synthesis of Porous Few-Layer Carbon Nitride for Highly Efficient Photoredox Catalysis.

Polymeric carbon nitride (C3N4) has emerged as the most promising candidate for metal-free photocatalysts but is plagued by low activity due to the poor quantum efficiency and low specific surface area. Exfoliation of bulk crystals into ultrathin nanosheets has proven to be an effective and widely used strategy for enabling high photocatalytic performances; however, this process is complicated, time-consuming, and costly. Here, we report a simple bottom-up method to synthesize porous few-layer C3N4, which involves molecule self-assembly into layered precursors, alcohol molecules intercalation, and subsequent thermal-induced exfoliation and polycondensation. The as-prepared few-layer C3N4 expose more active sites and greatly enhance the separation of charge carriers, thus exhibiting a 26-fold higher hydrogen evolution activity than bulk counterpart. Furthermore, we find that both the high activity and selectivity for the oxidative coupling of amines to imines can be obtained under visible light that surpass those of other metal-free photocatalysts so far.

Layered Double Hydroxides Precursor as Chloride Inhibitor: Synthesis, Characterization, Assessment of Chloride Adsorption Performance.

In this study, the chloride adsorption behaviors of CaAl-Cl LDH precursors with various Ca:Al ratios were investigated. The optimal chloride ion removal rate was 87.06% due to the formation of hydrocalumite. The chloride adsorption products of CaAl-Cl LDH precursors were further characterized by X-ray diffraction analysis and atomic structure analysis, the adsorption mechanism was considered to be co-precipitate process. The chloride adsorption behaviors of cementitious materials blended with CaAl-Cl LDH precursors were further investigated. Leaching test according to Test Code for Hydraulic Concrete (SL352-2006) was performed to testify the stability of chloride ions in the mortar. The results show that more than 98.3% chloride ions were immobilized in cement mortar blended with CaAl-Cl LDH precursor and cannot be easily released again. The inhibition performance of steel in the electrolytes with/without CaAl LDH precursor was investigated by using electrochemical measurements. The results indicate that CaAl LDH precursor can effectively protect the passive film on steel surface by chloride adsorption. Considering the high anion exchange capacities of the LDHs, synthesized chloride adsorbent precursor can be applied as new inhibitors blended in cementitious materials to prevent the chloride-induced deterioration. Moreover, the application of chloride adsorption on CaAl-Cl LDH could also be of interest for the application of seawater blended concrete.

Transformation of Co-containing birnessite to todorokite: Effect of Co on the transformation and implications for Co mobility

The mobility and fate of bioessential transition metals, such as Ni and Co, are strongly controlled by their association with phyllomanganate minerals such as birnessite. These minerals however, can transform to tectomanganates such as todorokite during soil and sediment diagenesis, yet the mobility and fate of most metals during the transformation process remain largely unknown. Here this research investigates the effect of Co on, and the mobility and fate of Co during the transformation of birnessite into tunnel structure minerals. A range of Co-containing birnessite precursors with up to 16.9 % Co/(Co + Mn) molar ratios were synthesised, and subsequently transformed via a mild reflux procedure designed to mimic the diagenesis of these layered precursors into tunnel structures. The layered precursors and reflux products were characterized using a combination of mineralogical and geochemical techniques, including powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The results show that Co(III) is structurally incorporated into the layered precursors and reflux products, through the isomorphic substitution of Mn(III). The structural incorporation of Co(III) into the layered precursors leads to an overall reduction of Jahn-Teller distorted Mn(III) octahedra in these minerals, a key factor for their transformation to tunnel structures. As a consequence, the presence of such structural Co(III) disrupts the transformation of birnessite into todorokite, leading to the coexistence of 9.6 Å asbolane-like phyllomanganate and non-ideal 3 × n, or a-disordered, todorokite-like tectomanganates in the transformation products. Newly formed todorokite exhibits a wide range of 3 × n tunnel dimensions (n up to 13) and a plate-like morphology. Overall the structural incorporation of non Jahn-Teller distorted cations like Co(III) into birnessite might help explain the often observed predominance of phyllomanganates over tectomanganates in soils and sediments, and the persistence of phyllomanganates in ferromanganese deposits that can be many millions of years old. The results also indicate that Co(III) initially associated with birnessite is retained in the solid phase during transformation, and thus the mobility of Co(III) is limited. EXAFS data suggest that Co is mainly located in the octahedral layers of asbolane-like phyllomanganate and at non-edge sites in non-ideal todorokite. Overall the transformation of Co-containing birnessite into non-ideal todorokite and asbolane-like layered structures maintains the strong sequestration of Co by Mn oxides.

Nucleation and crystallization of the MWW-type lamellar zeolitic precursor

Abstract The nucleation and crystallization of the layered zeolitic precursor (P)MCM-22 with Si/Al gel ratio = 25 was studied by several characterization techniques such as X-ray Diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Infrared Spectroscopy (IR), Thermogravimetric Analysis (TGA) and Small-Angle X-ray Scattering (SAXS). The crystallization kinetics of the samples was firstly monitored by XRD identifying reflections from the sample obtained at 48 h. The ICP-OES analysis concluded that the Si/Al ratio was 23, which is very similar to the initial gel one. SEM analyses corroborated the XRD results observing the formation of smooth particles from 48 h of crystallization and, after 168 h, the formation of thin platelet-like particles. The IR results showed an increase of external silanol groups when the crystallization time increases, due to terminating silanol groups between zeolitic crystals, whereas the bands attributed to the structure directing agent- hexamethyleneimine (HMI) − increase up to 168 h. Finally, the SAXS results indicated the existence of primary nanoparticles population in the first stages of the reaction, allowing to follow their growth and transformation from spherical morphology to two-dimensional objects forming aggregates.

Synthesis, Transformation Mechanism and Photocatalytic Properties of Various Morphologies Anatase TiO2 Nanocrystals Derived From Tetratitanate Nanobelts

AbstractRod‐like, rhombic, octahedral bipyramid‐shaped, cuboid, and spindle‐like anatase TiO2 nanocrystals samples with part of {101}, {001} and {010} facets exposure were synthesized through a straightforward solvothermal treatment of layered tetratitanate nanobelt colloidal solution precursor. The shape and structural evolutionmechanism of the as‐synthesized anatase TiO2 nanocrystals from the layered tetratitanate nanobelts were investigated by using X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscope (TEM) and high‐resolution transmission electron microscope (HRTEM). The transformation from the layered tetratitanate nanobelts into the various morphologies anatase TiO2 nanocrystals may experience two stages during the solvothermal process including an in situ topotactic dehydration reaction of the layered tetratitanate nanobelts, and a dissolution‐recrystallization reaction of the nanobelts anatase TiO2 crystals along the different planes. Furthermore, the photocatalytic activity of the various morphologies anatase TiO2 nanocrystals was also investigated and discussed, and compared to the benchmark P25 TiO2 nanocrystals. The results revealed that the {010}‐faceted spindle‐like anatase TiO2 nanocrystals exhibited the most superior photocatalytic activity for the degradation of methylene blue.

Interlayer self-assembly of 2D antimony/multigrapnene nanocomposites

Paper studies conditions for the formation of 2D allotropes of layered precursors (antimony, graphite) and self-assembled composite structures based on them. The latter assemble from colloidal solution of the inter-layers. The above conditions have been studied both experimentally and theoretically within the framework of our research. The modes for the isopropanol/antimony self-activated colloidal solutions have been set up. These processes are accompanied by the long-term nonlinear hydrodynamic effects in a colloidal solution that correlate with periodic changes of solution particle sizes. It has been proved theoretically that the charge properties of multilayers of antimony are different, whereas the processes observed during the tests indicate the presence of 2D structures within different number of layers of the solution volume, ranging in type and magnitude of the charge. Two types of composite structures have been obtained: a multilayer multigraphene/antimony structure and a polymorphic multigraphene/nanofiber.

La2O2SO4:RE/Yb new phosphors for near infrared to visible and near infrared upconversion luminescence (RE=Ho, Er, Tm)

AbstractThe 3 new upconversion (UC) phosphors of La2O2SO4:RE/Yb (RE=Ho, Er, and Tm, respectively) were derived via facile dehydration of their layered hydroxide precursors that were hydrothermally synthesized at 100°C. Rietveld XRD refinement found contracting cell dimension with decreasing RE3+ size, confirming the direct crystallization of solid solution. The Er3+ and Ho3+ activators both exhibited simultaneous green and red (dominant) emissions under 978‐nm near‐infrared (NIR) laser excitation (NIR‐Vis UC). Particularly, Tm3+ produced a Gaussian‐shaped pure NIR emission band at ~812 nm via its 3H4 → 3H6 transition (NIR‐NIR UC), which is highly desired for NIR biological application. Analysis of the excitation‐power dependent UC properties manifested a 3‐photon mechanism for the 3 phosphors, and the possible photon reactions leading to UC were illustrated.

Pillaring of layered zeolite precursors with ferrierite topology leading to unusual molecular sieves on the micro/mesoporous border.

Layered zeolite materials with FER layer topology can produce various condensed and expanded structures including zeolite frameworks, FER and CDO, their interlayer expanded forms (IEZ), and organic-intercalated and pillared derivatives. This work concerns pillaring of the surfactant-swollen derivative with a gallery height of ca. 2.5 nm between layers by treatment with tetraethylorthosilicate (TEOS) at room and elevated temperatures. The materials obtained at 100 °C and higher showed unusual properties including 2 nm pores on the micro/mesoporous border and disordered layer packing indicated by the absence of distinct low angle interlayer peaks at d-spacing >3 nm (∼3° 2θ Cu Kα radiation) in the X-ray diffraction pattern (XRD). TEOS treatment at room temperature produced a pillared molecular sieve with the expected mesoporous characteristics, namely a pore size of around 3 nm and a high intensity low angle (001) peak at 2.3° 2θ, and a d-spacing of 3.8 nm, in the XRD. The characterization aiming to elucidate the nature of the obtained unusual products included gas adsorption isotherms, aberration corrected (Cs-corrected) Scanning Transmission Electron Microscopy (STEM) studies and 29Si solid state NMR. BET surface area values decreased with the temperature of TEOS treatment from approximately 1200 m2 g-1 to ∼900 and 600 m2 g-1, at room temperature, 100 °C, and 120 °C, respectively. The 29Si solid state NMR revealed the presence of both Q3 ((SiO)3SiOX, X = H or minus charge) and Q4 ((SiO)4Si) centers giving separated signals up to the pillaring step. After pillaring at 100 °C and calcination, the nominal intensity ratios Q4 : Q3 were 2.17 and 2.61 but the signals were merged into one broad peak indicating the structural heterogeneity of Si-O coordination. The microscopy showed the presence of FER layers in the samples but the overall structure and composition were not well-defined. The observed unusual disorganization and possible partial degradation of layers during pillaring may result from the combination of high temperature, alkalinity (surfactant hydroxide) and siliceous composition of the layers. The obtained pillared products are of interest for the preparation of larger pore catalysts and sorbents or controlled drug delivery.

SSZ-70 borosilicate delamination without sonication: effect of framework topology on olefin epoxidation catalysis.

We report a scalable delamination procedure for a SSZ-70-framework layered-zeolite precursor, which for the first time does not involve either sonication or long-chain surfactants. Our approach instead relies on the mild heating of layered zeolite precursor B-SSZ-70(P) in an aqueous solution containing Zn(NO3)2 and tetrabutylammonium fluoride. Powder X-ray diffraction data are consistent with a loss of long-range order along the z-direction, while 29Si MAS NMR spectroscopy demonstrates preservation of the zeolite framework crystallinity during delamination. The resulting delaminated material, DZ-2, possesses 1.4-fold higher external surface area relative to the nondelaminated three-dimensional zeolite B-SSZ-70, based on N2 physisorption data at 77 K. DZ-2 was functionalized with cationic Ti heteroatoms to synthesize Ti-DZ-2 via exchange with framework B. Ti-DZ-2 contains isolated titanium centers in its crystalline framework, as shown by UV-Vis spectroscopy. The generality of the synthetic delamination approach and catalyst synthesis is demonstrated with the synthesis of delaminated material DZ-3, which is derived from layered zeolite precursor ERB-1(P) with MWW framework topology. Upon catalytic testing for the epoxidation of 1-octene with ethylbenzene hydroperoxide as oxidant, under harsh tail-end conditions that deactivate amorphous Ti-silica-based catalysts, Ti-DZ-2 exhibits the highest per-Ti-site activity, selectivity, and stability for 1-octene epoxidation of all catalysts investigated. This testing includes the prior benchmark delaminated zeolite catalyst in this area, Ti-UCB-4, which possesses similar external surface area to Ti-DZ-2 but requires sonication and long-chain surfactants for its synthesis. The synthesis of DZ-2 is the first example of an economical delamination of layered zeolite precursor SSZ-70(P) and opens up new doors to the development of delaminated zeolites as commercial catalysts.

Recent trends in the synthesis of high-silica zeolites

ABSTRACTNovel zeolites continue to be synthesized using organic structure directing agents in combination with unconventional choices of inorganic conditions. The latter include synthesis in concentrated fluoride media, synthesis in concentrated hydroxide media, synthesis in the presence of germanium, and synthesis with high concentrations of boron. Post-synthetic treatments of germanosilicates with the ADOR method have resulted in fully intact zeolites that cannot be obtained through direct synthesis. Unusual compositions of known frameworks have been obtained through topotactic condensation of layered precursors. Coupled with the appropriate choice of inorganic conditions, the use of new SDA molecules has also produced materials with known frameworks but with amazingly small crystal dimensions that are less than 10 nm. The preparations of once “exotic” materials are now being performed with commercially available or easily prepared organic structure directing agents. In some instances methods have been found to prepare high-silica zeolites from seeded preparations in the absence of an organocation. Methods to target zeolite catalysts for a particular reaction have been realized by identifying structure directing agent molecules that are a mimic of the transition state of the reaction.

ICP-2: A New Hybrid Organo-Inorganic Ferrierite Precursor with Expanded Layers Stabilized by π–π Stacking Interactions

In this work we present the synthesis, characterization, and molecular modeling of ICP-2, a new layered ferrierite precursor with expanded layers. ICP-2 is obtained in fluoride medium from aluminosilicate gels with low H2O content, using the chiral cation (1R,2S)-dimethylephedrinium (DMEP) as the organic structure-directing agent; ICP-2 can also be obtained as the Al-free form. The combination of physicochemical characterization of the material with molecular modeling indicates that ICP-2 is a layered material composed of ferrierite layers, where the organic cations play a dual structural role through the formation of supramolecular aggregates. On one hand, the organic cations stabilize the formation of the ferrierite layers with a core–shell structure, directing the formation of both the pseudo-10R channels (by supramolecular dimers aligned with the channel direction) and of the pseudocavities, with the trimethylammonium groups of DMEP fitting within. On the other hand, the aromatic rings of these organi...

Preparation, characterization, and post-synthetic modification of layered MCM-22 zeolite precursor

Hydrothermal synthesis of MCM-22(P) was carried out with two different silica sources, colloidal silica (28%) and silicic acid with different gel composition. The synthesis was carried out in stirring and static conditions with different crystallization time. MCM-22(P) modified with swelling-sonication method resulted in swollen MCM-22, while alkali treatment yielded desilicated MCM-22. The materials were characterized by X-ray diffraction, low-angle XRD, FE-SEM-EDX, FT-IR, TGA, $$\hbox {N}_{2}$$ adsorption and $$\hbox {NH}_{3}$$ -TPD analysis. The results revealed that MCM-22 has a layered sphere, doughnut like morphology and after modification, swollen and broken sphere was observed. Physicochemical analysis revealed that the materials’ mesoporosity increased and acidity also changed. Energy dispersive X-ray analysis revealed the high amount of desilication in alkali-treated MCM-22(P). SYNOPSIS Hydrothermal synthesis of layered MCM-22 using two different silica sources under stirring and static condition is reported. Layered zeolite MCM-22 synthesized from colloidal silica under stirring conditions was modified with swelling-sonication and alkali-treatment methods respectively. Crystal structure of MCM-22 remain unchanged while morphology was different when synthesized using different silica sources.

Frontispiece: Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a Layered Double Hydroxide Precursor and Their Application in Oxidation Catalysis

Frontispiece: Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a Layered Double Hydroxide Precursor and Their Application in Oxidation Catalysis

Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a Layered Double Hydroxide Precursor and Their Application in Oxidation Catalysis.

Monocrystalline, yet porous mosaic platelets of cobalt ferrite, CoFe2 O4 , can be synthesized from a layered double hydroxide (LDH) precursor by thermal decomposition. Using an equimolar mixture of Fe2+ , Co2+ , and Fe3+ during co-precipitation, a mixture of LDH, (FeII CoII )2/3 FeIII1/3 (OH)2 (CO3 )1/6 ⋅m H2 O, and the target spinel CoFe2 O4 can be obtained in the precursor. During calcination, the remaining FeII fraction of the LDH is oxidized to FeIII leading to an overall Co2+ :Fe3+ ratio of 1:2 as required for spinel crystallization. This pre-adjustment of the spinel composition in the LDH precursor suggests a topotactic crystallization of cobalt ferrite and yields phase pure spinel in unusual anisotropic platelet morphology. The preferred topotactic relationship in most particles is [111]Spinel ∥[001]LDH . Due to the anion decomposition, holes are formed throughout the quasi monocrystalline platelets. This synthesis approach can be used for different ferrites and the unique microstructure leads to unusual chemical properties as shown by the application of the ex-LDH cobalt ferrite as catalyst in the selective oxidation of 2-propanol. Compared to commercial cobalt ferrite, which mainly catalyzes the oxidative dehydrogenation to acetone, the main reaction over the novel ex-LDH cobalt is dehydration to propene. Moreover, the oxygen evolution reaction (OER) activity of the ex-LDH catalyst was markedly higher compared to the commercial material.

Charge Density Wave Transition in (PbSe)1+δ(VSe2)n Compounds with n = 1, 2, and 3

A series of (PbSe)1+δ(VSe2)n heterostructures with extensive turbostratic disorder were synthesized with n = 1–3 through low temperature annealing of appropriately designed layered precursors. The crystal structures consist of alternating layers of CdI2 type structured VSe2 and distorted NaCl type structured PbSe. The n = 1 compound has a positive Hall coefficient and a charge density wave like transition at 100 K, during which the resistivity increases by a factor of 3.5 and the Hall coefficient increases by a factor of 8. The n = 2 and 3 compounds have negative Hall coefficients and significantly smaller changes in the slope of the resistivity and Hall coefficient as a function of temperature at similar temperatures. The distinctly different transport properties of the compound containing a monolayer of VSe2 compared to compounds with thicker VSe2 layers highlights the complexity of the electronic structure of these stacked systems. The differences cannot be simply explained by charge transfer between V...

Fast synthesis of hierarchical Beta zeolites with uniform nanocrystals from layered silicate precursor

Hierarchical Beta zeolite composed of uniform nanocrystals with high pore volume and external surface area was fast synthesized within 4 h at a high yield using layered silicate precursor (H-kanemite) as silica source. The transformation process of layered silicate precursor into Beta zeolite is investigated carefully by XRD, FT-IR, NMR spectroscopies, SEM, and TEM techniques. TEM and SEM images indicated the obtained Beta zeolite is consisted of self-sustaining macrosized zeolitic aggregates assembled from uniform nanosized crystals, and it possesses relatively narrow distributed intercrystal mesopores. The hierarchically structured Beta zeolite, with an enhanced accessibility for bulky molecule to acid sites in the framework, shows better catalytic behaviors in the industrially-relevant Friedel-Crafts acylation reaction in comparison to commercially available or traditional Beta zeolite.