One-Pot Green Synthesis of Ashy Single-Crystalline NiO Nanoparticles Using Date Molasses for Enhanced Photo-Fenton-Like Degradation of Pyronin Y Under Solar Illumination

A one-pot green combustion route was developed for the synthesis of ashy single-crystalline NiO nanoparticles using date molasses as a biogenic fuel and complexing medium. The obtained DM–NiO showed phase-pure cubic NiO with an average crystallite size of about 18 nm, a mesoporous texture with a BET surface area of 68.9 m2 g−1, a pore volume of 0.59 cm3 g−1, an average pore diameter of 17.6 nm, and a mean particle size of 43.6 ± 8.13 nm. Optical characterization revealed defect-mediated light absorption with an energy gap of 3.11 eV, supporting solar-light-driven activity. In the photocatalytic degradation of pyronin Y, the catalyst exhibited strong pH dependence, reaching its best H2O2-free performance at pH 11 with a pseudo-first-order rate constant of 0.0072 min−1, nearly six times higher than that at pH 3. The introduction of H2O2 markedly intensified the process, and at 9 mM H2O2, the rate constant increased to 0.048 min−1, representing more than a sixfold enhancement over photocatalysis alone, while complete disappearance of the main visible absorption band was achieved within 38 min under solar illumination. Radical trapping experiments identified photogenerated holes and hydroxyl radicals as the dominant oxidative species. The catalyst also retained high activity over four successive cycles, with degradation efficiencies decreasing only slightly from 91.8% to 85.7%. These results demonstrate that date-molasses-assisted combustion synthesis provides a sustainable route to defect-active mesoporous NiO with highly enhanced solar photo-Fenton-like performance for dye-contaminated wastewater treatment.