Interfacial synergy between biogenic silica and reduced graphene oxide: Experimental and theoretical insights into cationic pollutants adsorption

Abstract

Understanding how carbon-silica interfaces govern molecular adsorption remains a key challenge in the design of sustainable hybrid nanomaterials. In this work, a biogenic silica (RHA)/reduced graphene oxide (rGO) hybrid material was synthesized through an aqueous reduction route that promotes direct Si-O-C coupling between rice husk ash and graphene layers. The material interface in the nanocomposite exhibits a complex balance of polarity, defect density, and π-conjugation, providing an interesting model system for studying electronic and chemical cooperation in Safranin O adsorption. Spectroscopic analyses reveal that the hybridization process induces the formation of Si-O-C bridges and increases the sp² defect population, thereby creating highly heterogeneous active sites. Upon Safranin O adsorption, FTIR signatures exhibit vibrational shifts consistent with π–π stacking, cation–π interactions, and hydrogen bonding, which are stabilized by interfacial polarization. Surface charge and morphological analyses confirm the coexistence of electrostatic and structural effects. At the same time, DFT calculations reveal strong binding energies ( ~ 1.9 eV) and charge redistribution from rGO to the aromatic ring of the dye. Drawing on experimental and theoretical insights, this study elucidates how chemical bonding and electronic coupling at the silica-carbon interface govern the adsorption mechanism at the molecular scale. The RHA–rGO hybrid thus serves as a versatile model for understanding cooperative interactions in complex hybrid surfaces, beyond immediate adsorption metrics.