Torsional Ordering as a Prerequisite for Zeolite Crystallization Revealed by X-ray Emission Spectroscopy

Understanding how ordered crystals emerge from disordered precursors is a grand challenge in materials science. Resolving this question is critical for tailoring the properties of network materials, particularly zeolitic silicates, which are indispensable in energy and environmental catalysis. This challenge has been particularly acute as the key three-dimensional (3D) ordering of the silicate network has remained experimentally inaccessible. However, detailed knowledge of crystallization would enable tailoring of key properties for improved applications. Here, we provide direct observation of this process using O 1s X-ray emission spectroscopy (XES) as a spectroscopic ruler for the 3D network geometry. Supported by ab initio simulations, our results reveal the systematic evolution of the O-Si-O-Si torsion angles during the crystallization of an MWW-type zeolite. We discovered that the progressive ordering of these angles into a staggered conformation is a decisive early-stage event that precedes the formation of the crystalline framework. This work establishes O 1s XES as a powerful tool for probing local network topology, enabling quantitative access to key geometric parameters of 3D silicate networks, including bond distances, bond angles, and torsion angles. This reveals a fundamental principle: topological ordering is a distinct, precursorial event that occurs prior to the emergence of long-range crystalline order. This "topology-first" insight fundamentally advances the rational design of zeolites and other complex network materials with atomic-level precision.