Assessing the synergy effect of additive and matrix on single-crystal growth: Morphological revolution resulted from gel-mediated enhancement on CIT-calcite interaction

It is well known that in biomineralization, the inorganic solids crystallized in the presence of organic phases, which are generally recognized as additives and matrix, leading to the crystal morphology modification. However, the synergy effects of both soluble additive and insoluble matrix on regulating the morphology of synthetic single-crystals are less studied. Here, we examine the morphological revolution of calcite single crystals induced by the additive, citrate (CIT), or/and the matrix, agarose gel network. The agarose gel matrix is inert to the crystal morphology in the sense that the agarose gel-grown calcite crystals maintain in characteristic rhombohedra. In contrast, CIT additives are active in crystal morphology modification and crystals begin to exhibit curved rough surfaces when grown in solution with the concentration of CIT coated Au nanoparticles (CIT-Au NPs]) of more than 2.25 mg/mL. Interestingly, once agarose gel and CIT-Au NPs are simultaneously introduced, the curved morphological feature emerges at a much lower CIT-Au NPs] of around 0.2 mg/mL. Increasing the gel concentrations further reduce the CIT-Au NPs] needed to trigger calcite morphological modification, suggesting that the gel networks reduce the CIT diffusion and thereby enhance the kinetic effects of CIT on crystallization. As such, this work may have implications for understanding the mechanism of hierarchical biominerals construction and provide rational strategy to control single-crystal morphologies.