Seed-Induced Synthesis of Disc-Cluster Zeolite L Mesocrystals with Ultrashort c-Axis: Morphology Control, Decoupled Mechanism, and Enhanced Adsorption

Abstract: Zeolites with short microporous channels offer advantages in the diffusion of guest molecules, leading to significant improvements in their adsorption and catalytic performance, as well as a reduction in coke formation during catalytic reactions. However, preparing zeolite L (LTL) with an ultrashort length (20–50 nm) along the c-axis has proven challenging due to its preferential growth behavior along the one-dimensional microporous channel direction. Additionally, the conventional synthesis method of zeolite L struggles to achieve both low aspect ratio and short length along the c-axis due to the coupling of nucleation and growth stages during crystallization. In this study, we present an innovative approach by utilizing seeds of nanorod-cluster zeolite L, pre-prepared under high alkalinity conditions, to synthesize a novel morphology of zeolite L mesocrystals. The resulting zeolite L product exhibits a unique cluster structure composed of a series of disc nanocrystals with an ultrashort c-axis length (approximately 29 nm), and the entire crystallization process is completed within just 4 h in a low alkaline system without the need for additional additives. This intentionally designed seed-induced synthesis method effectively decouples the nucleation and growth stages of zeolite L, enabling precise control of each stage to achieve the desired morphology. By analyzing the time-resolved evolution of mesoscopic nuclei and microscopic building units in the synthetic system, we find that the ring-cage structures dissolved from seeds exist as four-membered rings and eight-membered rings. These structures accelerate gel ordering and shorten the induction period. Meanwhile, the reserved part of the seeds provides densely-distributed nuclei for growth, resulting in the formation of the novel disc-cluster structures. Furthermore, by controlling growth conditions, we confirm the assembly of worm-like precursor particles during the growth period, allowing for precise regulation of the length along the c-axis of each disc within the range of 18 to 55 nm. Moreover, we extensively demonstrate the significantly enhanced adsorption and diffusion properties of zeolite L with an ultrashort c-axis for a range of model molecules, spanning sizes from 0.43 to 4.5 nm, in both gaseous and liquid phase systems. Our typical sample exhibits advantages in the diffusion rate of small molecules and the adsorption capacity of large molecules in the gaseous phase. It holds great potential for practical applications in the adsorption and separation of aromatic hydrocarbons, as well as the adsorption of dyes and proteins.