<p>The utilization of visible light to carry out organic transformations is useful from the viewpoint of solar energy conversion. In the present work, magnetite nanoparticles (Fe₃O₄ NPs) were synthesized and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), UV-visible diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy. The material was found to possess cubic spinel phase. The particles were found to be 20 to 45&#xa0;nm in size. The band gap of the semiconductor was determined as 2.31&#xa0;eV using Tauc’s plot. The Fe₃O₄ NPs were employed as a photocatalyst for studying the oxidation of phenol under visible light irradiation. Nearly, 69% phenol was converted to product(s) during 30&#xa0;min of irradiation. The photocatalytic process was found to follow first-order kinetics with a rate constant of 0.039&#xa0;min^− 1. The product of the visible light induced oxidation of phenol was identified as maleic acid based on the liquid chromatography-mass spectrometry (LC-MS) analysis. A probable reaction mechanism for the formation of maleic acid from phenol has been presented. The effect of key parameters such as solution pH and catalyst loading on the conversion efficiency of phenol were investigated. The Fe₃O₄ NPs were found to possess good catalytic activity for three cycles.</p> Graphical Abstract <p></p>