Highly Ordered Mesoporous Hydroxide Thin Films through Self-Assembly of Size-Tailored Nanobuilding Blocks: A Theoretical-Experimental Approach

Mesoporous crystalline (hydr)­oxides of low-valence metal ions (M­(II) and M­(III)) are highly demanded in the context of various applications. In this study, we demonstrate key factors to the successful formation of ordered mesoporous films through the assembly of nanobuilding block (ANBB) approach using a colloidal solution of crystalline M­(OH)₂ (M = Mn, Fe, Co, Ni, and Cu). The colloidal system of α-Ni­(OH)₂ is presented in depth as a typical example. Crystal growth and aggregation kinetics of the NBB were tuned by synthetic parameters. Nanometer-sized NBBs of tailored size between oligomer scale to over 20 nm were obtained. The films prepared from α-Ni­(OH)₂ NBBs with a diameter of ≤7.5 nm showed ordered mesostructures through evaporation-induced self-assembly in the presence of supramolecular templates. Coarse-grained simulations suggest that there is a threshold diameter of NBB toward the formation of well-ordered mesostructures. It was found that, as well as limiting the diameter of NBB, inhibition of an aggregation of NBBs by using coordinative additives or diluting the NBB colloidal solution was essential to control the assembly of NBBs and templates into the ordered mesostructures. The results obtained here open up the synthesis of ordered mesoporous materials with a crystalline wall of variety of chemical compositions containing low-valence metal elements.