The use of growth modifiers in natural, biological, and synthetic crystallization is a ubiquitous strategy for controlling growth and achieving desired physicochemical properties. For crystals that grow classically (i.e., monomer-by-monomer addition), theories of crystallization are well established and the field of growth modification is rather mature, although many questions remain regarding the molecular driving forces of modifier–crystal interactions. A new frontier in crystallization is the application of classical methods to tailor materials that grow nonclassically (i.e., growth by the addition of species more complex than monomers). A recent surge of interest and activity in this field has been driven by mounting evidence of both inorganic and organic materials that grow via nonclassical pathways. In these systems, the challenge of elucidating the mechanism(s) of crystallization is underscored by a diversity of growth units that far outnumber those available for classical routes. In this Perspective, we discuss growth modification in nonclassical crystallization, including examples in the literature, the challenges associated with elucidating the modes of modifier action, and to what degree classical theories can be applied to these complex problems as a means of establishing versatile blueprints for crystal engineering.

The formation of amorphous bulk phases in zeolite synthesis is a common phenomenon, yet there are many questions pertaining to the physicochemical properties of these precursors and their putative role(s) in the growth of microporous materials. Here, we study the formation of zeolite L, which is a large-pore framework (LTL type) with properties that are well-suited for catalysis, separations, photonics, and drug delivery, among other applications. We investigate the structural and morphological evolution of aluminosilicate precursors during zeolite L crystallization using a variety of colloidal and microscopy techniques. Dynamic light scattering measurements of growth solutions and scanning electron microscopy (SEM) images of extracted solids collectively reveal that zeolite L precursors assemble through a series of steps, leading to branched worm-like particles (WLPs). Transmission electron microscopy and electron dispersion spectroscopy show that WLPs have a heterogeneous composition that predominantly consists of silica-rich domains. We demonstrate that static light scattering can be used to identify the approximate induction time and is a reliable method to quantitatively track the extent of crystallization. During the induction period, the average size of zeolite L precursors monotonically increases by the accretion of soluble species. Precursor growth continues until the onset of zeolite L nucleation when WLPs reach a maximum size. During zeolite L growth, the number density of precursors decreases in favor of a growing population of crystallites. Ex situ SEM images reveal the progressive formation of crystal nuclei, which deviates from the classical LaMer process that posits a nearly instantaneous generation (or burst) of nuclei. These findings provide evidence of zeolite L growth via a nonclassical pathway involving crystallization by particle attachment (CPA). Given the ubiquitous presence of WLP-like precursors in syntheses of numerous zeolites, CPA processes may prove to be broadly representative of growth mechanisms for other zeolite framework types and related materials.

A combination of bulk crystallization studies and molecular modelling are used to elucidate the role of dual inorganic/organic SDAs in ZSM-5 synthesis. Our findings reveal unexpected synergistic effects on crystallization times and physicochemical properties.

Here we summarize our recent findings in the area of zeolite synthesis, focusing on pathways to control crystallization in the absence of organics, tailoring crystal habit with growth modifiers, and pioneering techniques in zeolite surface science to elucidate the mechanisms of growth.

Developing new zeolite catalysts for (petro)chemical applications is nontrivial owing to challenges that include the identification of commercially-viable syntheses. The vast majority of syntheses require the use of an organic structure-directing agent (OSDA), which has economic and environmental shortcomings. In the search for alternative zeolites to common industrial catalysts, such as ZSM-5 (MFI), a promising candidate is ZSM-11 (MEL), a close structural analogue of MFI. ZSM-11 is comprised of 3-dimensional straight channels that have less diffusion limitations than MFI. Side-by-side comparisons of ZSM-11 and ZSM-5 catalysts reveal the former exhibits significantly longer time-on-stream lifetime in many reactions; however, there are several difficulties associated with the preparation of ZSM-11, which include the ability to identify inexpensive OSDAs that produce small crystals in high yield. Here, we examine ZSM-11 synthesis using 1,8-diaminooctane (DAO), which produces ZSM-11 crystals with sizes of ca. 300 nm. We demonstrate that the use of MEL seeds allows for an order of magnitude reduction in the quantity of DAO without sacrificing crystal purity or yield (>80 %). Catalytic tests using methanol to hydrocarbons as a representative reaction show that H-ZSM-11 lifetime and selectivity are similar for samples prepared with and without seeds. Collectively our findings highlight an efficient method to produce ZSM-11 as a potential alternative to ZSM-5 for catalytic applications.

In the present work, FeCrB(CSi) cored wires (C17, C21 and C25) were designed and deposited as coatings by wire arc spraying. The microstructure, microhardness, wear and high temperature corrosion behaviour of the new coatings were investigated in comparison with a commercial Fe-Cr-Al coating. The FeCrB(CSi) coatings presented lamellar microstructures with some pores and microcracks and a few oxide inclusions. The microhardness of the coatings is much harder than those of the substrate and the commercial Fe-Cr-Al coating. The wear resistance of the coatings is much better than that of the uncoated substrate. Thermogravimetric analysis was used to evaluate the high temperature oxidation behaviour of the coatings at a temperature of 650uC under cyclic oxidation conditions. The results show that the high temperature oxidation resistance of the C17 coating was not as good as the Fe-Cr-Al coating, while the C21 and C25 coatings exhibited better oxidation resistance than the FeCrAl coating.

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Photocatalyzed CO 2 reduction (CO 2 RR) transfers CO 2 into valuable products using renewable energy, attracting widespread attention. Composite catalysts fabricated with TiO 2 and red phosphorus (RP) might exhibit competitive advantages, but effective interphase binding is difficult to forge. The composites therefore require complex and energy-consuming syntheses, severely hindering their application in CO 2 RR. In this work, TiO 2 /RP composites with hyperefficient interphase contact, which outperform various elaborately designed catalysts, are directly prepared from commercially available materials via a green and facile hydrothermal approach. The low heating temperature and sole solvent of water diminish the energy input for synthesis and imply a potential opportunity to propel CO 2 RR with industrial waste heat and cooling water. Experimental and computational analyses reveal that hydrothermal synthesis reduces the interfering oxidized species on the exterior surface of RP, facilitating the relatively less favored interphase contact between TiO 2 and nonoxidized RP. Photoelectron transfer and catalytic performance of the composites are hence drastically enhanced. Further improvement of activity is feasible by slightly elevating the heating temperature, time, or solution acidity. Attributing to the universal applicability of this green approach, different metal oxide/RP composites (e.g., WO 3 /RP) are similarly prepared, consistently boosting the reaction rate multiple times.