Interfacial confinement-driven non-classical crystallization: activated mesocrystals for calcium-based CO 2 capture

Abstract

Crystallization control is of fundamental importance for the preparation of nanomaterials with multi-scale morphologies and tailored functionalities. This work presents an interface-confined non-classical crystallization pathway for calcite, enabled by insoluble g-C3N4 that concurrently serves as a C/N donor, a surface-directing functional matrix, and a physical nanoscale confining scaffold. The resulting nitrogen-incorporated hybrid products exhibit a particle-attachment assembly superstructure with abundant interfacial porosity. A comparative control with soluble urea, which follows a classical ion-mediated crystallization pathway under identical hydrothermal conditions, confirms the critical role of g-C3N4 in directing particle-mediated growth. X-ray absorption near-edge spectroscopy (XANES) analyses reveal that g-C3N4-directed oriented attachment is effective in promoting heteroatom incorporation and exposing active sites, owing to the intrinsic coordination structure that enables in situ nitrogen incorporation within primary particles. Moreover, the resulting olive-shaped hybrid superstructure facilitates dopant diffusion and pore formation during subsequent decarbonation. The derived CaO exhibits a non-monotonic CO2 uptake behavior, peaking at 0.701 g-CO2/g-CaO during the second cycle while sustaining a capacity retention of 70.2% over 30 cycles. Density functional theory (DFT) analysis verified that nitrogen-induced oxygen defects can induce pronounced charge redistribution at the CO2/CaO interface and strengthen the adsorbate-surface interaction. These findings demonstrate a non-classical crystallization pathway for constructing heteroatom-modified Ca-based materials, with potential for application in calcium looping for CO2 capture.