Pseudomorphic Transformation of a Magnesium Citrate Precursor to Shape-Memory MgO Nanorods: A Facet-Specific Interaction with Graphene Oxide

The precise control of one-dimensional (1D) nanoscale architecture and facet-specific interfaces in alkaline earth metal oxides remains a critical challenge for developing advanced, multifunctional nanocomposites. Herein, we report the template- and surfactant-free mechanochemical synthesis of polyhedral magnesium oxide (MgO) nanorods via the pseudomorphic transformation of a magnesium citrate precursor (Mg-P), followed by systematic integration with graphene oxide (GO). Controlled thermal decomposition of the multiphase 1D coordination precursor yields phase-pure, shape-memory periclase nanorods that retain the precursor’s anisotropic <100> growth axis without undergoing structural collapse. Comprehensive structural and thermogravimetric analyses of the resulting MgO-GO nanocomposites (10, 30, and 50 wt.% GO) suggest a non-covalent, facet-specific interaction mechanism. GO nanosheets are shown to preferentially adhere to the {100} prismatic facets of the MgO nanorods, inducing anisotropic compressive strain, impeding lateral crystallite coarsening, and elevating the autocatalytic deoxygenation temperature of GO by over 145 °C. Furthermore, electrokinetic, and hydrodynamic assessments demonstrate an anomalous, composition-dependent colloidal evolution. While initial GO loadings mask the basic MgO surface to trigger massive hydrodynamic expansion, reaching an equimass 50 wt.% loading forces a profound electrokinetic inversion (+33.5 mV) and volumetric compaction, as the highly basic MgO interfaces re-establish dominance over the hydrodynamic shear plane. The data support a pseudomorphic route under the current conditions for the shape-directed synthesis of 1D metal oxides from coordination precursors and unravel the primitive interfacial dynamics governing the structural and colloidal stability of metal oxide–graphene hybrids.