Assembly and Evolution of Amorphous Precursors in Zeolite L Crystallization

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. <i>Ex situ</i> SEM images reveal the progressive formation of crystal nuclei, which deviates from the classical LaMer process that posits a nearly <i>instantaneous</i> 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 Facile Strategy To Design Zeolite L Crystals with Tunable Morphology and Surface Architecture

Tailoring the anisotropic growth rates of materials to achieve desired structural outcomes is a pervasive challenge in synthetic crystallization. Here we discuss a method to selectively control the growth of zeolite crystals, which are used extensively in a wide range of industrial applications. This facile method cooperatively tunes crystal properties, such as morphology and surface architecture, through the use of inexpensive, commercially available chemicals with specificity for binding to crystallographic surfaces and mediating anisotropic growth. We examined over 30 molecules as potential zeolite growth modifiers (ZGMs) of zeolite L (LTL type) crystallization. ZGM efficacy was quantified through a combination of macroscopic (bulk) and microscopic (surface) investigations that identified modifiers capable of dramatically altering the cylindrical morphology of LTL crystals. We demonstrate an ability to tailor properties critical to zeolite performance, such as external porous surface area, crystal shape, and pore length, which can enhance sorbate accessibility to LTL pores, tune the supramolecular organization of guest–host composites, and minimize the diffusion path length, respectively. We report that a synergistic combination of ZGMs and the judicious adjustment of synthesis parameters produce LTL crystals with unique surface features, and a range of length-to-diameter aspect ratios spanning 3 orders of magnitude. A systematic examination of different ZGM structures and molecular compositions (i.e., hydrophobicity and binding moieties) reveal interesting physicochemical properties governing their efficacy and specificity. Results of this study suggest this versatile strategy may prove applicable for a host of framework types to produce unrivaled materials that have eluded more conventional techniques

sj-docx-2-pie-10.1177_09544089221139102 - Supplemental material for Experimental and theoretical analyses of material removal in poppet valve magnetorheological finishing

Supplemental material, sj-docx-2-pie-10.1177_09544089221139102 for Experimental and theoretical analyses of material removal in poppet valve magnetorheological finishing by Manjesh Kumar, Chandan Kumar, Amit Kumar, Debashish Gogoi and Manas Das in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering</p

sj-docx-1-pie-10.1177_09544089221139102 - Supplemental material for Experimental and theoretical analyses of material removal in poppet valve magnetorheological finishing

Supplemental material, sj-docx-1-pie-10.1177_09544089221139102 for Experimental and theoretical analyses of material removal in poppet valve magnetorheological finishing by Manjesh Kumar, Chandan Kumar, Amit Kumar, Debashish Gogoi and Manas Das in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering</p

SSZ-13 Crystallization by Particle Attachment and Deterministic Pathways to Crystal Size Control

Many synthetic and natural crystalline materials are either known or postulated to grow via nonclassical pathways involving the initial self-assembly of precursors that serve as putative growth units for crystallization. Elucidating the pathway(s) by which precursors attach to crystal surfaces and structurally rearrange (postattachment) to incorporate into the underlying crystalline lattice is an active and expanding area of research comprising many unanswered fundamental questions. Here, we examine the crystallization of SSZ-13, which is an aluminosilicate zeolite that possesses exceptional physicochemical properties for applications in separations and catalysis (e.g., methanol upgrading to chemicals and the environmental remediation of NO_<i>x</i>). We show that SSZ-13 grows by two concerted mechanisms: nonclassical growth involving the attachment of amorphous aluminosilicate particles to crystal surfaces and classical layer-by-layer growth via the incorporation of molecules to advancing steps on the crystal surface. A facile, commercially viable method of tailoring SSZ-13 crystal size and morphology is introduced wherein growth modifiers are used to mediate precursor aggregation and attachment to crystal surfaces. We demonstrate that small quantities of polymers can be used to tune crystal size over 3 orders of magnitude (0.1–20 μm), alter crystal shape, and introduce mesoporosity. Given the ubiquitous presence of amorphous precursors in a wide variety of microporous crystals, insight of the SSZ-13 growth mechanism may prove to be broadly applicable to other materials. Moreover, the ability to selectively tailor the physical properties of SSZ-13 crystals through molecular design offers new routes to optimize their performance in a wide range of commercial applications