Nanostructuring niobium oxides using polymer-grafted cellulose nanocrystals and nanofibers as sacrificial scaffolds†

Abstract

The unique one-dimensional structure and surface functionality of cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) render them promising candidates for renewable nanomaterials. Here, we report the template-directed synthesis of highly polycrystalline Nb₂O₅ polymorphs using polymer brush-grafted CNCs and CNFs as sacrificial scaffolds. The scaffolds consisted of a CNC or CNF core, from which poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes were grafted using surface-initiated atom transfer radical polymerization (SI-ATRP). The nanocellulose-g-PDMAEMA nanoreactors were complexed with a water-soluble Nb₂O₅ precursor, ammonium niobate(V) oxalate hydrate (NbOxA), via electrostatic interaction before they were heated to different temperatures to fabricate one-dimensional polycrystalline niobium pentoxides (nc-Nb₂O₅ and nf-Nb₂O₅) with controllable polymorphism. Specifically, phase-pure pseudohexagonal Nb₂O₅ (TT-Nb₂O₅), orthorhombic Nb₂O₅ (T-Nb₂O₅) and monoclinic Nb₂O₅ (H-Nb₂O₅) were synthesized. Finally, we show that the polycrystalline nc-Nb₂O₅ and nf-Nb₂O₅ can function as photocatalysts for decomposing rhodamine B.