Waste-derived SnO₂–polystyrene nanocomposites: structural, optical, and photocatalytic performance for dye degradation applications

The growing accumulation of non-biodegradable plastic waste and the discharge of persistent industrial dyes represent two critical environmental challenges worldwide. Developing sustainable materials that simultaneously address plastic recycling and wastewater remediation remains an important scientific goal. In this context, converting waste expanded polystyrene (EPS) into functional photocatalytic materials offers a promising circular-economy strategy. In this work, tin oxide (SnO₂) embedded polystyrene (PS) nanocomposites were successfully synthesised using waste-expanded polystyrene (EPS) as a recyclable precursor, thereby addressing plastic pollution through a sustainable materials approach. Unlike previously reported SnO₂–polymer systems that typically rely on virgin polymers or powder photocatalysts, the present work demonstrates the fabrication of reusable self-supported SnO₂–PS nanocomposite films derived from plastic waste, enabling easy catalyst recovery and improved environmental sustainability. The structural, morphological, and optical properties of the nanocomposites were systematically characterised. While pristine PS was amorphous, incorporation of SnO₂ induced crystallinity consistent with the tetragonal phase, as confirmed by prominent (110), (101), (200), and (211) diffraction peaks. AFM analysis revealed a unique vertically aligned hollow chain-like architecture, with surface roughness increasing as SnO₂ loading increased. UV–Vis absorption spectra showed a progressive redshift and band gap narrowing (from ~3.2 to ~3.0 eV), enhancing visible-light harvesting. Photoluminescence intensity decreased with higher SnO₂ content, suggesting suppressed electron–hole recombination and improved charge separation. Photocatalytic activity was evaluated against Indigo Carmine dye, chosen for its wide industrial use, recalcitrant structure, and environmental toxicity. Using a custom-designed 40 W LED photoreactor, the optimum composite achieved ~99% degradation within 30 minutes, with kinetics following a pseudo-first-order model. Preliminary recycling tests confirmed the reusability of the films over multiple cycles with minimal loss of activity. These results demonstrate not only the novelty of converting non-biodegradable EPS into functional photocatalyst films but also their practical potential for wastewater treatment. While advanced photoelectrochemical studies remain a future scope, this work establishes a green, low-cost, and scalable strategy for fabricating reusable polymer–inorganic nanocomposites for environmental remediation. This approach simultaneously addresses plastic waste valorization and dye-contaminated wastewater treatment, highlighting the potential of waste-derived nanocomposites for scalable environmental remediation technologies.