Carbon–SiO₂ Hybrid Nanoparticles with Enhanced Radical Stabilization and Biocide Activity

Nanocarbon and nanosilica are widely-used nanomaterials of significant industrial interest. Herein, a library of {carbon–SiO₂} hybrid nanoparticles, with controlled nanocarbon content and sp³/sp² profile, was engineered by a flame spray pyrolysis (FSP) process in one step. Their structure–function relationship was evaluated by studying their radical-generation and radical-stabilization activities, using electron paramagnetic resonance spectroscopy in tandem with their biocide activity toward marine bacteria Aliivibrio fischeri. The surface properties of the C–SiO₂ hybrids were studied by Raman spectroscopy and surface-charge analysis by zeta potential measurements. Raman spectroscopy indicates that the FSP process, as designed and used herein, allows the progressive incorporation of nanocarbon moieties into the SiO₂ nanostructure, which may lead to distortion of the siloxane matrix. Concurrently, the C–SiO₂ hybrids’ surface charge profile reveals a trend correlated with the acute biocide activity toward Aliiv. fischeri. Interestingly, we find no correlation between the stable radical population and the nanohybrids’ biocide activity. Within this context, we discuss the role of surface charge, radical properties, and SiO₂ lattice distortions by the nanocarbon, all of them parametrized via FSP process protocols. Thus, the present study’s findings provide critical insight into the structure–biocide activity relationship of carbon–SiO₂ hybrid nanoparticles. Technology-wise, the present work exemplifies a scalable FSP process for the industrial production of applied nanomaterials, such as C–SiO₂ nanostructures.