Controlled Crystallinity of SnO₂ Nanoparticles Through Solvent Engineering and Thermal Treatment

Abstract

SnO₂ nanocrystals were engineered by sol‑gel calcination in mixed solvent systems (methanol: ethylene glycol: water) and fired at 550 °C and 750 °C. Structural analysis by X‑ray diffraction revealed phase‑pure, tetragonal rutile SnO₂ with a pronounced (110) texture. Crystalline diameters increased from 19.2 → 21.8 nm (550 °C) and 27.4 → 30.1 nm (750 °C) as water content rose. FESEM imaging revealed morphological evolution from smaller, less-agglomerated particles in organic-rich media to larger, aggregated structures in aqueous-rich systems. EDX verified stoichiometric Sn and O, while FTIR displayed strong Sn–O vibrations (622–668 cm⁻¹). DRS-UV‑Vi’s spectra showed excitonic onsets red‑shifted beyond bulk SnO₂ (344 nm), with band‑gap energies narrowing modestly as organic content declined—consistent with minimal quantum‑confinement effects at the measured sizes. Overall, solvent polarity proved decisive: organic‑rich media favoured smaller, less‑agglomerated crystals, whereas water promoted growth. Tailoring solvent composition and calcination temperature therefore enables controlled size, morphology, and high‑energy‑plane exposure, providing a straightforward route to SnO₂ nanomaterials optimized for visible‑light photocatalysis.