Solar light-responsive g-C₃N₄ and Ni₁₋ₓMnₓCo₂₋ᵧFeᵧO₄ composites for rapid dye degradation and phytotoxicity evaluation

Abstract

A series of Ni_1-xMn_xCo_2-yFe_yO₄/g-C₃N₄ composites were prepared by co-precipitation and ultra-sonication approaches and the effect of Mn and Fe substitution and g-C₃N₄ addition was explored based on structural, dielectric, ferroelectric, optical and photocatalytic properties. The X-ray diffraction analysis confirmed the formation of a cubic structure with a particle size range of 28–35 nm of cobaltites (spinel structure). The grain size enhancement through Mn and Fe substitution was observed and the dielectric constant decreased as the frequency increased. The tangent loss was used to measure the energy loss in dielectric relaxation. The P-E loop shows enhanced coercivity (12.25 kV/cm), saturation polarization (7.72 ×10⁻³ Ps (μC/cm²) and remnant polarization (7.6 ×10⁻³ μC/cm²) for highly substituted nanocomposite. The PL analysis revealed the low recombination rate of h⁺-e^- and bandgap declined from 1.62 to 1.16 eV for the highly substituted NiCo₂O₄/g-C₃N₄ nanocomposite. Crystal violet dye was degraded under solar light exposure and Ni_1-xMn_xCo_2-yFe_yO₄/g-C₃N₄ exhibited a higher photocatalytic performance versus NiCo₂O₄/g-C₃N₄. The recyclability and reusability of the nanocomposite were assessed and the Ni_1-xMn_xCo_2-yFe_yO₄/g-C₃N₄ showed promising stability. The Zea mays germination (%), root length (cm) and shoot length (cm) were compared, and the treated dye revealed significantly lower phytotoxicity versus the untreated dye solution. Results revealed that the Ni_1-xMn_xCo_2-yFe_yO₄/g-C₃N₄ composites have the potential for photocatalytic applications under solar light irradiation, which will make the process more economical versus other photocatalytic processes.