Case study of freezing-induced loading of silver nanoparticles into vaterite microcrystals

Hybrid materials composed of porous vaterite CaCO3 microcrystals loaded with functional inorganic nanoparticles are actively studied with respect to various practical applications. Recently, freezing-induced loading method was demonstrated as a versatile and effective approach for preparation of vaterite-based functional hybrid microparticles. However, despite of its high efficiency, the effect of nanoparticle concentration on the freezing-induced loading process and the structural properties of the resulted hybrids were not studied previously. Herein, for the first time, we have evaluated the feasibility of the conventional adsorption models to describe the freezing-induced loading of citrate-capped silver nanoparticles (AgNPs). The fitting of the dependence of the loading capacity of vaterite crystals on the residual concentration of AgNPs to two- or three-parameter models revealed that the best fit was obtained with the Freundlich model (R2 = 0.969), suggesting non-uniform deposition of AgNPs and interparticle agglomeration (Freundlich n > 1). This was confirmed with electron microscopy and elemental analysis demonstrating the formation and growth of AgNP aggregates on the CaCO3 surface with increasing initial nanoparticle concentration. Overall, the reported findings are valuable for a better understanding of the freezing-induced loading process and for further optimization of the preparation of vaterite-based functional hybrid microparticles. [Display omitted] •Ag/CaCO3 composites were prepared by freezing-induced loading of citrate-capped AgNPs.•Conventional adsorption models can be used to describe the deposition of AgNPs.•The increase in AgNPs concentration led to deviation from Langmuir-type deposition.•The freezing-induced loading of AgNPs can be well described with the Freundlich model.•The change in AgNPs concentration allows to control Ag/CaCO3 surface morphology.