Femtochemistry of Guest Molecules Hosted in Colloidal Zeolites

The ultrafast deprotonation of 2‐(2′‐hydroxyphenyl)benzothiazole (HBT) hosted in nanometer‐sized FAU and MFI zeolites is reported. Samples are prepared via in‐situ incorporation of HBT in the precursor colloidal solutions resulting in the formation of nanometer‐sized zeolites under hydrothermal treatment. The diameter of the zeolite particles formed in the crystalline suspensions is determined by dynamic light scattering and high‐resolution transmission microscopy to lie in the range 40–100 nm. It is shown that the HBT loading does not influence the degree of the zeolite crystallinity but does change the size and the morphology of the individual zeolite nanoparticles. Colloidal suspensions containing the crystalline nanoparticles are well suited for optical investigations since they are sufficiently transparent and clear. The photochemical properties of the HBT guest in the zeolite‐host systems are studied with femtosecond transient transmission spectroscopy. Depending on the acid–base properties either the enol or the keto tautomer of HBT is found to be hosted in the internal voids of the zeolites; upon UV excitation, the HBT‐keto tautomer is converted to the enol form in both MFI‐ and FAU‐type hosts. The HBT photoconversion takes place via an ultrafast deprotonation within 1.5 ps as detected by femtosecond transient absorption spectroscopy.     

Hierarchical Y and USY Zeolites Designed by Post‐Synthetic Strategies

Strategic combinations of affordable and scalable post‐synthetic modifications enabled to design a broad family of hierarchical Y and USY zeolites (FAU topology) independent on the Si/Al ratio. Pristine (Y, Si/Al = 2.4), steamed (USY, Si/Al = 2.6), and steamed and dealuminated (USY, Si/Al = 15 and 30) zeolites were exposed to a variety of acid (H₄EDTA and Na₂H₂EDTA) and base (NaOH) treatments, which led to the introduction of mesopore surfaces up to 500 m² g^?1, while preserving the intrinsic zeolite properties. Pristine Y and USY zeolites (Si/Al ～ 2.5) required mild dealumination (to Si/Al > 4 in the case of Y) to facilitate subsequent efficient desilication. Alkaline treatment of Y and USY zeolites with low Si/Al ratios (～4–6) led to an abundance of Al‐rich debris, which could be removed by a subsequent mild acid wash. On the other hand, severely steamed and dealuminated, hence Si‐rich, USY zeolites (Si/Al = 15 and 30) proved extremely sensitive to the alkaline solution, displaying facile dissolution and substantial amorphization. For the latter group of ultra‐stable Y zeolites, the presence of TPA⁺ in the alkaline solution enables to protect the zeolite structures upon the introduction of mesoporosity by desilication, preserving crystallinity and micropore volume. The sorption and catalytic properties of the hierarchical Y and USY zeolites were superior compared to the conventional counterparts.     

影响Ga-Si-ZSM-5沸石分子筛形貌及晶粒大小的因素

考察了影响合成Ｇａ－Ｓｉ－ＺＳＭ－５分子筛形貌和晶粒大小的若干因素，实验结果表明，合成参数的影响非常大，在低温、加压条件下可获得更小晶粒的分子筛产物。     

Beyond Creation of Mesoporosity: The Advantages of Polymer‐Based Dual‐Function Templates for Fabricating Hierarchical Zeolites

Direct synthesis of hierarchical zeolites currently relies on the use of surfactant‐based templates to produce mesoporosity by the random stacking of 2D zeolite sheets or the agglomeration of tiny zeolite grains. The benefits of using nonsurfactant polymers as dual‐function templates in the fabrication of hierarchical zeolites are demonstrated. First, the minimal intermolecular interactions of nonsurfactant polymers impose little interference on the crystallization of zeolites, favoring the formation of 3D continuous zeolite frameworks with a long‐range order. Second, the mutual interpenetration of the polymer and the zeolite networks renders disordered but highly interconnected mesopores in zeolite crystals. These two factors allow for the synthesis of single‐crystalline, mesoporous zeolites of varied compositions and framework types. A representative example, hierarchial aluminosilicate (meso‐ZSM‐5), has been carefully characterized. It has a unique branched fibrous structure, and far outperforms bulk aluminosilicate (ZSM‐5) as a catalyst in two model reactions: conversion of methanol to aromatics and catalytic cracking of canola oil. Third, extra functional groups in the polymer template can be utilized to incorporate desired functionalities into hierarchical zeolites. Last and most importantly, polymer‐based templates permit heterogeneous nucleation and growth of mesoporous zeolites on existing surfaces, forming a continuous zeolitic layer. In a proof‐of‐concept experiment, unprecedented core–shell‐structured hierarchical zeolites are synthesized by coating mesoporous zeolites on the surfaces of bulk zeolites.     

Hierarchical FAU‐ and LTA‐Type Zeolites by Post‐Synthetic Design: A New Generation of Highly Efficient Base Catalysts

Hierarchical FAU‐ and LTA‐type catalysts are prepared by post‐synthetic modifications and evaluated in the base‐catalyzed Knoevenagel condensation of benzaldehyde with malononitrile. A novel route to attain mesoporous Al‐rich zeolites (A and X) is demonstrated, while mesoporous Y and USY zeolites are prepared using recently developed methods. Base functionality is introduced by alkali ion exchange (Cs, Na) or by high‐temperature nitridation in ammonia. A thorough characterization of the zeolites' structure, composition, porosity, morphology, and basicity demonstrates that the presence of a secondary mesopore network enhances the ion‐exchange efficiency and the structural incorporation of nitrogen. The modified USY zeolites display twice the conversion, while the hierarchical A, X, and Y are up to 10 times more active based on the enhanced accessibility. These results demonstrate that the Knoevenagel condensation takes place predominately at the external surface, highlighting secondary porosity as a key criterion in the design of basic zeolite catalysts.     

Optically Functional Zeolites: Evaluation of UV and VUV Stimulated Photoluminescence Properties of Ce3+‐ and Tb3+‐doped Zeolite X

The optical properties of Tb³⁺/Ce³⁺ doped zeolites are elucidated with emphasis on ultraviolet (UV) and vacuum ultraviolet (VUV) excitation and luminescence. Ce³⁺ sensitized Tb³⁺ emission with quantum yields of 85 % may be obtained at 330 nm excitation. Low absorptivity at 254 nm due to low Ce³⁺ concentrations or low Ce³⁺/Tb³⁺ ratios, which are required for the suppression of UV components, restricts their applicability as phosphors for Hg‐based discharges, e.g., in conventional fluorescent lamps. Near band edge excitation at 172 nm revealed an immediate quantum yield of 50 % enabled by a zeolite → Ce³⁺ (5d¹) → Tb³⁺ (4f⁷5d¹) energy transfer channel, which may be exploited for the down‐conversion of the Xe₂ excimer emission.     

U.H.F. low-noise GaAs m.e.s.f.e.t. amplifier for colour t.v. broadcasting translator

Low-noise amplifiers for u.h.f. colour t.v. broadcasting translator use have been successfully developed by using 1 ?m gate GaAs m.e.s.f.e.t.s. The obtained performances revealed that a GaAs m.e.s.f.e.t. has low-noise and low intermodulation distortion characteristics, even in the 500?800 MHz frequency range, compared with a Si bipolar transistor.     

Current-kink noise of n-channel enhancement e.s.f.i.-m.o.s. s.o.s. transistors

An experimental study of the low-frequency-noise properties of n-channel epitaxial silicon films on insulator m.o.s. s.o.s. transistors has been performed. The measurements show an excessive noise contribution at drain voltages corresponding to the current-kink effect for temperatures ranging from 4.2 to 300 K.     

Switching in m.i.s.m. and m.i.s.i.m. structures

Switching has been observed in metal?thin-insulator?n-p+ structures, where the thin insulator is SiO2, or polycrystalline silicon. In this letter two alternative structures are discussed in which the n-p+ junction is replaced by a Schottky barrier. In the second device proposed two thin-insulator structures back-to-back are shown to exhibit bidirectional switching.     

GaAs m.a.o.s.f.e.t. memory transistor

A new non-volatile memory device is reported. This device is a GaAs m.o.s.f.e.t. with charge storage in the gate in which is a double oxide structure of aluminium oxide and GaAs native oxide, both oxides are grown anodically. The fabrication of the device is described and the results of initial measurements on the charging and charge retention properties are presented.     

Noise behaviour of the m.o.s.f.e.t. at v.h.f. and u.h.f.

The optimum noise figures of an m.o.s.f.e.t. at u.h.f. and at pinch-off are calculated using a simplified equivalent circuit. The noise parameters are also determined experimentally. Theory and experiment are shown to be in good agreement. Noise parameters of the m.o.s.f.e.t. for the frequency range 0.1?0.8 GHz are given.     

Wide-range monolithic bipolar?j.f.e.t. c.c.o.

A new monolithic current-controlled oscillator (c.c.o.) has been realised in a j.f.e.t.-bipolar technology. Its main advantages are a highly-linear seven decade frequency range and easy temperature compensation for frequency and output voltage.     

V.H.F. and u.h.f. Gunn-effect oscillators

In this letter, the use of the Gunn device as a broadband negative resistance, somewhat analogous to a tunnel diode, is explored. v.h.f. and u.h.f. oscillators are described; the frequency is determined by an external resonant circuit and is very nearly independent of the parameters of the Gunn-effect sample.     

More active RC filters using the d.v.c.c.s./d.v.c.v.s.

Novel configurations using a differential-voltage-controlled current source, differential-voltage-controlled voltage source (d.v.c.c.s./d.v.c.v.s.) as the active building block are described. The configurations assume that the active building block is divided into two independent parts initially.     

New V-groove double-diffused m.o.s. (v.d.m.o.s.)

A new V-groove double-diffused m.o.s. (v.d.m.o s.) is proposed which combines the V-groove technology and the double-diffused m.o.s. (d.m.o.s.) technology. The fabrication processes arc qualitatively described. The gate is located on the vertical V-shaped surface, and the effective channel length is controlled by the vertical-diffusion process of the double-diffusion step. The v.d.m.o.s. is expected to have a faster speed and higher production yield than the ordinary d.m.o.s.     

V.P.E. GaAs m.e.s.f.e.t. structure using oxygen injection during buffer layer growth

GaAs m.e.s.f.e.t. structures with high-resistivity buffer layers were prepared by introducing oxygen into the deposition system during growth. The electrical properties of the buffer layers are independent of the oxygen content of the gas phase over a large range of partial pressures. The characteristics of devices prepared with such layers are excellent.