Induced morphology control of Ln–asparagine coordination polymers from the macro to nanoscopic regime in polar solvent–water mixtures

Abstract

A bottom-up approach is presented here for morphology control of Ln–asparagine (Asn) coordination polymers (CPs) from the macro to nanoscopic regime by tuning solvent polarity based on the π* solvent polarity scale in polar solvent–water mixed solutions. By a simple hydrothermal treatment, large macroporous spheres with sizes up to millimeters were obtained in ethanol (π*: 0.54)–water mixtures, and their formation mechanism was proved to be particle aggregation together with a hollowing process based on Ostwald ripening. Other solvents with increasing polarity were also used, and submicrometer spheres as well as fine nanoparticles were prepared in acetone (π*: 0.71) and DMF (π*: 0.88), respectively. When dioxane (π*: 0.55) was used here, whose π* value is similar to ethanol, large macroporous spheres were also prepared. Furthermore, with Ce– and La–Asn CPs large spheres as precursors, after calcination, ceria and lanthana large spheres with hierarchical structures were fabricated, respectively. Considering that many growth media of CPs are single solvent systems, designing certain solvents mixtures and tuning their polarity would bring us new opportunities to achieve morphology and composition control of CPs materials.