Defect-tailored Fe-NiCr₂O₄ nano-spinel for efficient solar-light responsive photocatalysis and water disinfection

Developing low-cost and efficient photocatalysts for solar-driven wastewater treatment remains a major scientific and environmental challenge. Although nickel chromite (NiCr₂O₄) possesses good structural stability, its practical application is limited by a wide band gap and rapid electron–hole recombination. In this study, iron-doped NiCr₂O₄ nanoparticles were synthesized via a simple co-precipitation method to overcome these limitations. Comprehensive characterization techniques, including XRD, FTIR, FE-SEM, EDX, UV–visible, and photoluminescence (PL) analyses, were employed to examine the structural, morphological, and optical properties of the prepared samples. XRD analysis confirmed the formation of a tetragonal spinel phase, while Fe incorporation induced lattice distortion, indicating successful substitution within the crystal lattice. Optical studies revealed a significant reduction in the band gap from 2.60 eV to 1.65 eV, enabling enhanced absorption in the visible-light region. PL spectra demonstrated suppressed electron–hole recombination, consistent with improved charge separation efficiency. Consequently, the optimized catalyst (NCF4) exhibited outstanding solar-light-driven photocatalytic performance, achieving 91 % degradation of bromothymol blue and 79 % of phenol, compared to 61 % and 56 % for pristine NiCr₂O₄, respectively. Scavenger experiments identified hydroxyl radicals as the dominant reactive species, confirming that Fe doping facilitates defect-assisted charge transfer and redox reactivity. Beyond photocatalysis, the NCF1 sample also displayed excellent visible-light-induced antibacterial activity, highlighting its multifunctional environmental potential. Furthermore, the NCF4 catalyst maintained high performance over multiple cycles, demonstrating strong stability and reusability. Overall, these findings establish Fe-doped NiCr₂O₄ as a robust, visible-light-active spinel photocatalyst with great promise for scalable wastewater purification and environmental remediation applications.