Direct Dual‐Template Synthesis of MWW Zeolite Monolayers

A two‐dimensional zeolite with the topology of MWW sheets has been obtained by direct synthesis with a combination of two organic structure‐directing agents. The resultant material consists of approximately 70 % single and double layers and displays a well‐structured external surface area of about 300 m² g^?1. The delaminated zeolite prepared by means of this single‐step synthetic route has a high delamination degree, and the structural integrity of the MWW layers is well preserved. The new zeolite material displayed excellent activity, selectivity, and stability when used as a catalyst for the alkylation of benzene with propylene and found to be superior to the catalysts that are currently used for producing cumene.     

Ultrathin Two‐Dimensional Organic–Inorganic Hybrid Perovskite Nanosheets with Bright,Tunable Photoluminescence and High Stability

Two‐dimensional (2D) organic–inorganic hybrid perovskite nanosheets (NSs) are attracting increasing research interest due to their unique properties and promising applications. Here, for the first time, we report the facile synthesis of single‐ and few‐layer free‐standing phenylethylammonium lead halide perovskite NSs, that is, (PEA)₂PbX₄ (PEA=C₈H₉NH₃, X=Cl, Br, I). Importantly, their lateral size can be tuned by changing solvents. Moreover, these ultrathin 2D perovskite NSs exhibit highly efficient and tunable photoluminescence, as well as superior stability. Our study provides a simple and general method for the controlled synthesis of 2D perovskite NSs, which may offer a new avenue for their fundamental studies and optoelectronic applications.     

Synthesis of Silicate Zeolite Analogues Using Organic Sulfonium Compounds as Structure‐Directing Agents

A microporous crystalline silica zeolite of the MEL structure type and three other zeolite analogues composed of germanosilicate frameworks were synthesized using tributylsulfonium, triphenylsulfonium, or tri(para‐tolyl)sulfonium as the structure‐directing agent. The germanosilicates thus obtained had ISV, ITT, or a new zeolite structure depending on the synthesis conditions. The structure of the new germanosilicate was solved using X‐ray powder diffraction data with the aid of a charge‐flipping method. The solution indicated a crystal structure belonging to the P63/mmc space group with cell parameters of a=16.2003 Å and c=21.8579 Å. After calcination, the new germanosilicate material exhibited two types of accessible micropores with diameters of 0.61 and 0.78 nm.     

Critical Factors in the Seed‐Assisted Synthesis of Zeolite Beta and “Green Beta” from OSDA‐Free Na+–Aluminosilicate Gels

Organic structure‐directing agent (OSDA)‐free synthesis of zeolite beta is a subject of both scientific and industrial interest. Herein, we report a comprehensive investigation into the effects of various parameters on the seed‐assisted crystallization of zeolite beta in the absence of OSDA. The crystallization behavior of “OSDA‐free beta” is strongly governed by the chemical composition of the starting Na⁺‐aluminosilicate gel as well as by the Si/Al ratios of the calcined beta seed crystals, which are prepared using tetraethylammonium hydroxide (TEAOH). Furthermore, OSDA‐free beta seed crystals can be used to form zeolite beta, termed “green beta”. XRD, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and ²⁷Al magic angle spinning NMR analyses showed that the OSDA‐free beta and green beta were of high purity and crystallinity. The nitrogen adsorption–desorption of OSDA‐free beta and green beta revealed higher surface areas and larger volumes in the micropore region than those of the beta seeds synthesized with OSDA after calcination. These results provide a robust and reliable process for the environmentally friendly production of high‐quality zeolite beta in a completely OSDA‐free Na⁺‐aluminosilicate system.     

Acid Exfoliation of Imine‐linked Covalent Organic Frameworks Enables Solution Processing into Crystalline Thin Films

Covalent organic frameworks (COFs) are highly modular porous crystalline polymers that are of interest for applications such as charge‐storage devices, nanofiltration membranes, and optoelectronic devices. COFs are typically synthesized as microcrystalline powders, which limits their performance in these applications, and their limited solubility precludes large‐scale processing into more useful morphologies and devices. We report a general, scalable method to exfoliate two‐dimensional imine‐linked COF powders by temporarily protonating their linkages. The resulting suspensions were cast into continuous crystalline COF films up to 10 cm in diameter, with thicknesses ranging from 50 nm to 20 μm depending on the suspension composition, concentration, and casting protocol. Furthermore, we demonstrate that the film fabrication process proceeds through a partial depolymerization/repolymerization mechanism, providing mechanically robust films that can be easily separated from their substrates.     

Synthesis of a Specified,Silica Molecular Sieve by Using Computationally Predicted Organic Structure‐Directing Agents

Crystalline molecular sieves are used in numerous applications, where the properties exploited for each technology are the direct consequence of structural features. New materials are typically discovered by trial and error, and in many cases, organic structure‐directing agents (OSDAs) are used to direct their formation. Here, we report the first successful synthesis of a specified molecular sieve through the use of an OSDA that was predicted from a recently developed computational method that constructs chemically synthesizable OSDAs. Pentamethylimidazolium is computationally predicted to have the largest stabilization energy in the STW framework, and is experimentally shown to strongly direct the synthesis of pure‐silica STW. Other OSDAs with lower stabilization energies did not form STW. The general method demonstrated here to create STW may lead to new, simpler OSDAs for existing frameworks and provide a way to predict OSDAs for desired, theoretical frameworks.     

Highly Efficient,Conjugated‐Polymer‐Based Nano‐Photosensitizers for Selectively Targeted Two‐Photon Photodynamic Therapy and Imaging of Cancer Cells

Two‐photon photodynamic therapy (2P‐PDT) is a promising noninvasive treatment of cancers and other diseases with three‐dimensional selectivity and deep penetration. However, clinical applications of 2P‐PDT are limited by small two‐photon absorption (TPA) cross sections of traditional photosensitizers. The development of folate receptor targeted nano‐photosensitizers based on conjugated polymers is described. In these nano‐photosensitizers, poly{9,9‐bis[6′′‐(bromohexyl)fluorene‐2,7‐ylenevinylene]‐co‐alt‐1,4‐(2,5‐dicyanophenylene)}, which is a conjugated polymer with a large TPA cross section, acts as a two‐photon light‐harvesting material to significantly enhance the two‐photon properties of the doped photosensitizer tetraphenylporphyrin (TPP) through energy transfer. These nanoparticles displayed up to 1020‐fold enhancement in two‐photon excitation emission and about 870‐fold enhancement in the two‐photon‐induced singlet oxygen generation capability of TPP. Surface‐functionalized folic acid groups make these nanoparticles highly selective in targeting and killing KB cancer cells over NIH/3T3 normal cells. The 2P‐PDT activity of these nanoparticles was significantly improved, potentially up to about 1000 times, as implied by the enhancement factors of two‐photon excitation emission and singlet oxygen generation. These nanoparticles could act as novel two‐photon nano‐photosensitizers with combined advantages of low dark cytotoxicity, targeted 2P‐PDT with high selectivity, and simultaneous two‐photon fluorescence imaging capability; these are all required for ideal two‐photon photosensitizers.     

ZSM‐5 Zeolite Nanosheets with Improved Catalytic Activity Synthesized Using a New Class of Structure‐Directing Agents

A new series of multiquaternary ammonium structure‐directing agents, based on 1,4‐diazabicyclo[2.2.2]octane, was prepared. ZSM‐5 zeolites with nanosheet morphology (10 nm crystal thickness) were synthesized under hydrothermal conditions using multiquaternary ammonium surfactants as the zeolite structure‐generating agents. Both wide‐angle and small‐angle diffraction patterns were obtained using only a suitable structure‐directing agent under a specific zeolite synthesis composition. A mechanism of zeolite formation is proposed based on the results obtained from various physicochemical characterizations. ZSM‐5 materials were investigated in catalytic reactions requiring medium to strong acidity, which are important for the synthesis of a wide range of industrially important fine and specialty chemicals. The catalytic activity of ZSM‐5 materials was compared with that of the conventional ZSM‐5 and amorphous mesoporous aluminosilicate Al‐MCM‐41. The synthesis strategy of the present investigation using the new series of structure‐directing agents could be extended for the synthesis of other related zeolites or other porous materials in the future. Zeolite with a structural feature as small as the size of a unit cell (5–10 nm) with hierarchically ordered porous structure would be very promising for catalysis.     

Olefin‐Directed Palladium‐Catalyzed Regio‐ and Stereoselective Hydroboration of Allenes

An olefin‐directed palladium‐catalyzed regio‐ and stereoselective hydroboration of allenes has been developed to afford fully substituted alkenylboron compounds. The reaction showed a broad substrate scope: a number of functionalized allenes, including 2,3‐dienoate, 3,4‐dienoate, 3,4‐dienol, 1,2‐allenylphosphonate, and alkyl‐substituted allenes, could be used in this olefin‐directed allene hydroboration. The olefin unit was proven to be an indispensable element for this transformation.     

Towards the Rational Design of Efficient Organic Structure‐Directing Agents for Zeolite Synthesis

Zeolites are crystalline microporous materials with application in diverse fields, especially in catalysis. The ability to prepare zeolites with targeted physicochemical properties for a specific catalytic application is a matter of great interest, because it allows the efficiency of the entire chemical process to be increased (higher product yields, lower undesired by‐products, less energy consumption, and cost savings, etc). Nevertheless, directing the zeolite crystallization towards the material with the desired framework topology, crystal size, or chemical composition is not an easy task, since several variables influence the nucleation and crystallization processes. The combination of accumulated knowledge, rationalization, and innovation has allowed the synthesis of unique zeolitic structures in the last few years. This is especially true in terms of the design of organic and inorganic structure‐directing agents (SDAs). In this Minireview we will present the rationale we have followed in our studies to synthesize new zeolite structures, while putting this in perspective with the advances made by other researchers of the zeolite community.     

Olefin‐Directed Palladium‐Catalyzed Regio‐ and Stereoselective Oxidative Arylation of Allenes

An olefin‐directed palladium‐catalyzed oxidative regio‐ and stereoselective arylation of allenes to afford 1,3,6‐trienes has been established. A number of functionalized allenes, including 2,3‐ and 3,4‐dienoates and 3,4‐dienol derivatives, have been investigated and found to undergo the olefin‐directed allene arylation. The olefin moiety has been proven to be a crucial element for the arylating transformation.     

Picomolar Detection of Melamine Using Molecularly Imprinted Polymer‐Based Electrochemical Sensors Prepared by UV‐Graft Photopolymerization

Molecularly imprinted polymer (MIP) films of melamine were prepared by photopolymerization of vinylic monomers on diazonium‐modified gold electrodes. The gold‐grafted MIPs are specific and selective for melamine in either organic or aqueous media. The interferent molecules cyromazine and cyanuric acid were not recognized by the MIPs. The limit of detection was as low as 1.75×10^?12 mol L^?1 at S/N=3. Efficiency of melamine rebinding is related to the solubility parameter of the organic solvent or pH and ionic strength of the aqueous medium. It is concluded that diazonium salts permit to design robust electrochemical MIP sensors.     

Solar‐Light‐Driven Pure Water Splitting with Ultrathin BiOCl Nanosheets

A suitable photocatalyst for overall water splitting has been produced by overcoming the disadvantage of the band structure in bulk BiOCl by reducing the thickness to the quantum scale. The ultrathin BiOCl nanosheets with surface/subsurface defects realized the solar‐driven pure water splitting in the absence of any co‐catalysts or sacrificial agent. These surface defects cannot only shift both the valence band and conduction band upwards for band‐gap narrowing but also promote charge‐carrier separation. The amount of defects in the outer layer surface of BiOCl results in an enhancement of carrier density and faster charge transport. First‐principles calculations provide clear evidence that the formation of surface oxygen vacancies is easier for the ultrathin BiOCl nanosheets than for its thicker counterpart. These defects can serve as active sites to effectively adsorb and dissociate H₂O molecules, resulting in a significantly improved water‐splitting performance.     

A Multiple Structure‐Design Strategy towards Ultrathin Niobate Perovskite Nanosheets with Thickness‐Dependent Photocatalytic Hydrogen‐Evolution Performance

Hydrogen production by catalytic water splitting using sunlight holds great promise for clean and sustainable energy source. Despite the efforts made in the past decades, challenges still exist in pursuing solid catalysts with light‐harvesting capacity, large surface areas and efficient utilities of the photogenerated carrier, at the same time. Here, a multiple structure design strategy leading to highly enhanced photocatalytic performance on hydrogen production from water splitting in Dion–Jacobson perovskites KCa₂Na_{n ‐3}Nb_n O_{3n +1} is described. Specifically, chemical doping (N/Nb⁴⁺) of the parent oxides via ammoniation improved the ability of sunlight harvesting efficiently; subsequent liquid exfoliation of the doped perovskites yielded ultrathin [Ca₂Na_{n ‐3}Nb_n O_{3n +1}]⁻ nanosheets with greatly increased surface areas. Significantly, the maximum hydrogen evolution appears in the n =4 nanosheets, which suggests the most favorable thickness for charge separation in such perovskite‐type catalysts. The optimized black N/Nb⁴⁺‐[Ca₂NaNb₄O₁₃]⁻ nanosheets show greatly enhanced photocatalytic performance, as high as 973 μmol h⁻¹ with Pt loading, on hydrogen evolution from water splitting. As a proof‐of‐concept, this work highlights the feasibility of combining various chemical strategies towards better catalysts and precise thickness control of two‐dimensional materials.     

Targeting Bone Metastases with a Bispecific Anticancer and Antiangiogenic Polymer–Alendronate–Taxane Conjugate

A polymer therapeutic designed for combination anticancer and antiangiogenic therapy inhibited the proliferation of prostate carcinoma cells and the proliferation, migration, and tube‐formation of endothelial cells. The nanoconjugate was formed from an N‐(2‐hydroxypropyl)methacrylamide (HPMA) copolymer, the bisphosphonate alendronate (for bone targeting), and the chemotherapy agent paclitaxel (PTX), which is cleaved by cathepsin B (see scheme).

     

General Synthesis of Two‐Dimensional Patterned Conducting Polymer‐Nanobowl Sheet via Chemical Polymerization

Summary: A general method for the generation of two‐dimensional (2D) ordered, large‐area, and liftable conducting polymer‐nanobowl sheet has been demonstrated via chemical polymerization for the first time. The sheet is made using the monolayer self‐assembled from polystyrene (PS) spheres at the aqueous/air interface as template, followed by depositing conducting polymer on the part of PS monolayer submerging in the aqueous phase via chemical polymerization, and core extraction. During the process of polymerization, no substrate is required, which caused the as‐prepared patterned conducting polymer sheet can be easily lifted‐off and deposited, in full size, on any flat substrate. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectrum were used to characterize the products.

Morphology of the polyaniline‐CSA nanobowl sheet.