Nonclassical and Classical Crystallization: The Formation of Spindle-Shaped CaCO₃ Covered with Abundant Nanoscale Rhombic Calcite Subunits

Abstract

As an essential inorganic material, calcium carbonate (CaCO 3 ) is one of the most abundant minerals in nature, whose preparation by the carbonation of calcium hydroxide [Ca(OH) 2 ] suspension involves complex physical and chemical processes due to the presence of gas−solid−liquid phases. It is challenging to accurately predict the final morphology of CaCO 3 . In this paper, a novel spindleshaped CaCO 3 covered with a mass of nanoscale rhombic calcite subunits was prepared via the carbonation method. This structure was mainly formed by the aggregation of nanoparticles in the pre-reaction stage and turned into a classical ion− ion growth process at the stage of the late reaction. During the pre-reaction period, solid Ca(OH) 2 kept the solution supersaturated and made the aggregation of nanoparticles dominate and assemble to form the nanochains of CaCO 3 . Subsequently, the aggregation of nanochains formed a dumbbell shape, which was accompanied by the recrystallization of nanoparticles inside aggregates to create an ordered single-crystal spindle structure. Finally, the concentration of Ca(OH) 2 decreased, and a layer of nanoscale rhombic calcite subunits grew on the surface of spindle CaCO 3 . This work will provide new insights into the industrial preparation of CaCO 3 with controlled morphology and contribute to understanding the biomineralization of aggregation-based growth in aqueous solutions.

Oriented Attachment Growth of 2,6-Diamino-3,5-dinitropyrazine-1-oxide Mesocrystals: Morphological Evolution, Regulation, and Mechanism

“…Oriented attachment (OA) is an important nonclassical crystal growth mechanism. − Different from the classical crystallization based on a layer-by-layer growth of a primary nucleus/crystal by atom/ion/molecule addition, OA involves face-specific attractive interactions between primary nanocrystals. − These interactions dictate the attachment of the nanocrystals on interfaces with common crystallographic orientations to fabricate various crystal morphologies including nanowires, rods, chains, and multipods. − To date, OA has been described as a mechanism for crystal growth in many materials including metals, metal alloys, metal oxides, metal–organic frameworks (MOFs), organic compounds, semiconductors, and carbonates . Although the OA growth mechanism has often been focused on inorganic materials, the crystallization mechanisms of some organic pharmaceutical materials were based on the OA.…”

Spraying-induced in situ growth of CaCO3 for the modification of membranes for oil/water separation

“…CaCO 3 , an abundant bio-and geomineral on earth, is widely used as a modifier to improve certain properties due to its availability and low cost. 17 CaCO 3 -modified membranes have been developed for oil-water separation. [18][19][20][21][22][23] Unfortunately, although these pioneering works have shown good separation performance, the shortcomings of incomplete utilization of raw materials, cumbersome synthesis processes, and difficulty in large-scale production still need to be further addressed.…”