Homogeneous Nanogels from Colloidal WO3– x Nanosheets: Controlling Gelation Kinetics through Ligand–Solvent Interactions

Abstract

Translating the solution-phase properties of colloidal nanocrystals into bulk porous monoliths requires gelation strategies that preserve the surface chemistry and electronic structure of the building blocks, a particular challenge for substoichiometric oxides whose function is tied to their oxygen vacancy population. Here, we report the homogeneous gelation of oleylamine-capped, WO3–x nanosheets through a nonredox-active, controlled destabilization route in which interparticle interactions are modulated by tuning the solvation of the ligand shell rather than by oxidative ligand removal. Two orthogonal levers, binary solvent composition and alkylamine chain length, tune the gelation time scale across orders of magnitude, from approximately 1 h to 10 days, while preserving a homogeneous, space-spanning network. Time-resolved synchrotron small-angle X-ray scattering (SAXS) resolves a hierarchical assembly pathway in which one-dimensional (1D) end-to-end attachment of the nanosheets drives network formation, followed by lamellar superstructure development upon solvent removal. Subsequent supercritical CO2 drying yields lightweight, mesoporous WO3–x monoliths that retain the oxygen-deficient character and broadband visible-to-near-infrared absorption of the constituent nanosheets, offering a versatile framework for assembling redox-sensitive oxide nanocrystals into functional porous architectures.