Recent Advances in Nonclassical Crystallization: Fundamentals, Applications, and Challenges

Ubiquitous crystals play an important role in our daily lives. Recent studies on the properties and formation of crystals have proven the attachment of particles ranging from ion pairs to well-crystallized nanocrystals for crystallization. Compared with the monomer-by-monomer (i.e., atoms, ions, or molecules) addition described in long-standing classical theories, so-called nonclassical crystallization pathways are more complex due to the influence of nonspecific interactions influenced by the variation in system free energy and reaction kinetics. In view of the fact that detailed insights into nonclassical crystallization pathways have broadened the scope of research across various disciplines such as geological events, biomineralization mechanisms, environmental remediation, and the development of functional materials, this paper reviews the current state of the art in nonclassical nucleation (the prenucleation clusters pathway, aggregation pathway, etc.) and growth pathways (oriented attachment and random attachment) based on several highlights. In addition, the observed specific phenomena on crystallization in the last 10 years as well as recent advancements and achievements on the synthesis of mesocrystals are also elucidated. With implications and perspectives of nonclassical crystallization research proposed in this paper, this review aims to summarize research advancements regarding crystallizing systems. Emphasis will be placed on novel insights into nonclassical crystallization of materials, which are expected to provide completely new perspectives on the underlying crystallization mechanisms.