Cyano-bridged coordination polymer hydrogel-derived Sn–Fe binary oxide nanohybrids with structural diversity: from 3D, 2D, to 2D/1D and enhanced lithium-storage performance

Abstract

Metal oxide nanohybrids with uniform dimensions and controlled architectures possess unique compositional and structural superiorities, and thus harbor promising potential for a series of applications in energy, catalysis, and sensing systems. Herein, we propose a facile, general, and scalable cyano-bridged coordination polymer hydrogel-derived thermal-oxidation route for the construction of main-group metal and transition-metal heterometallic oxide nanohybrids with controlled constituents and architectures. The formation of Sn–Fe binary oxide nanohybrids has been demonstrated as an example by using cyano-bridged Sn(IV)–Fe(II) bimetallic coordination polymer hydrogels (i.e., SnCl₄–K₄Fe(CN)₆ cyanogels, Sn–Fe cyanogels) as precursors. The physicochemical properties of Sn–Fe cyanogels with different Sn/Fe ratios have been systematically examined, and it is found that perfect Sn–Fe cyanogels without unbridged Sn(IV) or Fe(II) can be formed with Sn/Fe ratios from 2 : 1 to 1 : 2. More importantly, the simple adjustment of Sn/Fe ratios in the Sn–Fe cyanogel precursors can realize flexible dimensional control of the Sn–Fe binary oxide nanohybrids, and 2D/1D SnO₂–Fe₂O₃ hierarchitectures, 2D SnO₂–Fe₂O₃ nanosheets, and 3D SnO₂–Fe₂O₃ networks have been synthesized using the Sn–Fe 1 : 2, Sn–Fe 1 : 1, and Sn–Fe 2 : 1 cyanogels as precursors, respectively. To demonstrate their compositional/structural superiorities and potential applications, the lithium-storage utilization of the Sn–Fe binary oxide nanohybrids has been selected as an objective application, and the nanohybrids exhibit Sn/Fe ratio-dependent lithium-storage performance. As a representative example, the 2D/1D SnO₂–Fe₂O₃ hierarchitectures manifest markedly enhanced Li-storage performance in terms of reversible capacities and cycling stability in comparison with their constituent units, i.e., bare SnO₂ nanosheets and Fe₂O₃ nanorods. The proposed cyanogel-derived thermal-oxidation strategy could open up new opportunities for constructing heterometallic oxide nanohybrids, and the rationally designed metal oxide nanohybrids may find broad applications in energy, catalysis, and sensing fields by virtue of their structural and compositional features.