Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure-directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we show how zeolites with a continuously tuneable surface area and micropore volume over a wide range can be prepared. This means that a particular surface area or micropore volume can be precisely tuned. The range of porosity we can target covers the whole range of useful zeolite porosity: from small pores consisting of 8-rings all the way to extra-large pores consisting of 14-rings.

Microstructural analysis of the early stage crystal growth of zeolite A in hydrothermal synthetic conditions revealed a revised crystal growth route from surface to core in the presence of the biopolymer chitosan. The mechanism of this extraordinary crystal growth route is discussed. In the first stage, the precursor and biopolymer aggregated into amorphous spherical particles. Crystallization occurred on the surface of these spheres, forming the typical cubic morphology associated with zeolite A with a very thin crystalline cubic shell and an amorphous core. With a surface-to-core extension of crystallization, sodalite nanoplates were crystallized within the amorphous cores of these zeolite A cubes, most likely due to an increase of pressure. These sodalite nanoplates increased in size, breaking the cubic shells of zeolite A in the process, leading to the phase transformation from zeolite A to sodalite via an Ostwald ripening process. Characterization of specimens was performed using scanning electron microscopy and transmission electron microscopy, supported by other techniques including X-ray diffraction, solid-state NMR, and N(2) adsorption/desorption.

This contribution reports new methodology we have developed for the disassembly of 3-D UTL framework into 2-D lamellae followed by structure modification including pillaring. This may be widely applicable, particularly to other zeolites that have D4R units present, and so should have great impact also on other porous solids. Specifically, controlled hydrolysis of D4R units in the interlayer space provides individual ultrathin layers with UTL structure by a chemically selective method. Further manipulation of the layers gives a completely novel approach (3D to 2D to pillared) offering hitherto unprecedented opportunities for the preparation of modified zeolites with diverse chemical and structural properties.

Crystal growth of cubic BaTiO 3 in the presence of polyethylene is investigated step by step using powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Titanium precursor Ti(OC 4 H 9 ) 4 aggregates with PEG to form spherical colloidal particles at the very beginning. Multiple nucleation of BaTiO 3 takes place on the surface of these colloidal particles. The nanocrystallites then selfadjust their orientations likely under dipole−dipole interaction and/or intercrystallite interactions enhanced by surface adsorbed polymers, followed by an orientated connection and crystal extension via an Ostwald ripening process. The final BaTiO 3 crystals have a novel dodecahedral morphology. The formation mechanism is proposed to be attributed to the selective adsorption of PEG molecules on the {110} crystal planes, significantly reducing the crystal growth rate on these surfaces. A kinetic model is proposed based on the calculated crystallite sizes using the Scherrer equation. The physical meaning of the model and a significant fake reduction of the crystallite size is discussed. ■ INTRODUCTIONNucleation and early stage crystal growth are of crucial importance in relation to crystal engineering and synthesis of new materials. According to the classical theory of crystal growth, nucleation in a hydrothermal system is normally associated with a supersaturation phenomenon and is initiated by the aggregation of sub-nanosized chemical species, for example, ions and molecules (monomers). After a nucleus reaches a critical size, the growth typically takes place by further attachment of monomers to its surface, and the final morphology of a free crystal in a synthetic solution is dominated by the slow-growing faces because the fast-growing faces may grow out and not be represented in the final crystal habit. 1 In contrast, the achievement in the growth of various nanostructured materials in the past decade has suggested several nonclassical pathways where crystals may develop from an initial mesoscale solid species. 2−7 For example, a faceted nanocrystal could evolve from an amorphous colloidal particle by nucleation beginning at its core and extending to its edge or vice versa. During the incubation period, one single crystal is developed from each colloidal particle (Scheme 1a). 8 Surface crystallization of a disordered aggregate may lead to a reversed crystal growth route (Scheme 1b). 9−11 The formation of crystalline shells with a faceted polyhedral morphology indicates that Curie and Wulff's theory 12,13 is more general than the Bravais−Friedel−Donnay−Harker (BFDH) law. 14−16 The latter produces a kinetic measure of the crystal growth rates along different crystallographic orientations. The former gives a thermodynamic view in order to predict that the equilibrium shape of a free crystal is the shape that minimizes its surface free energy. These assumptions can explain the formation of polyhedral habits in both the classic crystal growth route and the reversed crystal growth route.When mult...

Extracellular electron transfer (EET) in microorganisms is prevalent in nature and has been utilized in functional bioelectrochemical systems. EET of Geobacter sulf urreducens has been extensively studied and has been revealed to be facilitated through c-type cytochromes, which mediate charge between the electrode and G. sulfurreducens in anodic mode. However, the EET pathway of cathodic conversion of fumarate to succinate is still under debate. Here, we apply a variety of analytical methods, including electrochemistry, UV−vis absorption and resonance Raman spectroscopy, quartz crystal microbalance with dissipation, and electron microscopy, to understand the involvement of cytochromes and other possible electron-mediating species in the switching between anodic and cathodic reaction modes. By switching the applied bias for a G. sulfurreducens biofilm coupled to investigating the quantity and function of cytochromes, as well as the emergence of Fecontaining particles on the cell membrane, we provide evidence of a diminished role of cytochromes in cathodic EET. This work sheds light on the mechanisms of G. sulfurreducens biofilm growth and suggests the possible existence of a nonheme, iron-involving EET process in cathodic mode.