Synergistic radical scavenging effect of NiSe2-doped SnO2 nanocomposites: role of oxygen vacancies revealed by post-reaction characterizations

Abstract

Antioxidant imbalance plays a major role in triggering inflammation, cellular damage, and the progression of chronic diseases. Conventional antioxidants are limited by rapid degradation, poor stability, and low radical scavenging efficiency, creating the need for sustainable materials with improved antioxidant properties. Designing such materials requires a precise understanding on the fundamental radical scavenging mechanisms, particularly how electron transfer, surface defects and reactive active sites contribute to efficient radical neutralization for light-free scavenging. In this work, undoped and NiSe₂-doped SnO₂ nanocomposites (10%, 20% and 30%) were synthesised and evaluated for antibacterial and antioxidant activity using the DPPH assay (light-free scavenging). XRD, UV-vis spectroscopy, FTIR spectroscopy, HRSEM, HRTEM, FESEM, ESR, and XPS techniques were used to confirm the formation of nanocomposites and to characterise their structural and physicochemical properties. XRD peak shifts confirmed the successful incorporation of NiSe₂ into the SnO₂ lattice, while secondary peaks indicated nanocomposite formation. HRTEM results revealed the size of the material (SnO₂: 36 nm and NiSe₂: 18 nm). In the DPPH scavenging studies, we optimized concentration, pH and time kinetics. The 30% NiSe₂-doped SnO₂ NCs showed superior activity, with an IC₅₀ value of 41.2 µg mL⁻¹ (first-order kinetics), compared with other materials. Post-antioxidant ESR confirmed radical scavenging by NCs, and FTIR spectral results confirmed the structural rigidity of DPPH. Post-reaction XPS analysis revealed a notable change in the oxygen vacancy signal in the oxygen 1s spectrum, confirming that electron originating from an oxygen vacancy to scavenge the free radical's mechanism. Additionally, the 30% NiSe₂-doped SnO₂ NCs exhibited strong antibacterial activity against K. pneumoniae, P. aeruginosa, E. coli, and S. aureus, demonstrating their potential for biomedical applications.