Sketching Precursor Evolution to Delineate Growth Pathways for Anatase (TiO2) Crystal Design

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2024-06, Vol.20 (25), p.e2309100-n/a
• Main Authors: Jain, Anusha, Kumar, Manjesh
• Format: Article
• Language: English
• Subjects: Anatase; crystal growth; Crystallites; Crystallization; Crystals; Design engineering; Electron microscopy; Evolution; Field emission microscopy; Functional materials; Microscopy; Nanosheets; nonclassical pathway; photocatalysis; Precursors; titania; Titanium dioxide
• ISSN: 1613-6810; 1613-6829; 1613-6829
• DOI: 10.1002/smll.202309100

Engineering advanced functional materials such as Anatase crystals through the molecular tuning of crystal facets is the current enigma of interest pertinent to solving the structure‐property‐performance triad. Developing optimal shapes and sizes of crystallite necessitates exploring the nanoscopic growth mechanism via precursor tracking. Here, the tapestry of particles varying in dimensionality (0D–3D), sizes (8–3000 nm), and morphology (aggregated to highly faceted crystals) is generated. To decipher and subsequently modulate the crystallization pathways, high‐resolution microscopy (high‐resolution transmission electron microscopy(HRTEM) and field emission scanning electron microscopy(FESEM)) is used to sketch time‐stamped particle evolution. Interestingly, the studies provide evidence for 4‐distinct mechanisms where nanoparticles/nanosheets play direct and/or indirect roles in crystallization through multi‐stage aggregation (primary, secondary, and tertiary) beginning with similar growth solutions. The four distinct pathways elucidate bulk particle formation via non‐classical routes of crystallization including nanosheet alignment and aggregation, nanocrystallite formation and fusion, nanobeads formation and attachment, and direct nanosheet incorporation in bulk crystals. Notably, the direct evidence of flexible‐partially‐ordered nanosheets being subsumed along the contours of bulk crystals is captured. These novel syntheses generated uniquely faceted particles with high‐indexed surface planes such as (004), (200), and (105), amenable to photocatalytic applications. Spatiotemporal evolution from precursors to bulk crystal shows the complex mechanism of Anatase crystallization. Intermediate stages show the presence of isolated nanosheets, aggregate sheets, faceted crystallites, and nanorods. The bulk crystals exhibit varied shapes and sizes depending on growth conditions. The study captures critical steps during the multistage aggregation and final transformation to crystal establishing the role of precursors.