The present contribution is about the synthesis of a composite photo-catalyst with remarkable activity and a narrow gap band to explore the possibility of using it for the removal of antibiotics in water. The synthesis of spinel ZnCr 2 O 4 (ZCO) nanoparticles in pure phase by the combination of sol-gel methodology at 700 °C was achieved. The identification and characterization were done using characterization studies such as X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and UV–Visible spectroscopy techniques. The illustration of spinel structure was done with the help of lattice constants using XRD data. The optical and dielectric properties of ZCO were measured using the UV–Visible data. The photo-electrochemical property revealed the flat band potential value of 0.3 V SCE which ascribes the n-type semiconductor. The photocatalytic activity of ZCO nanoparticles under visible light source in degrading the three pharmaceutical products such as Cefaclor (CFR), Cefuroxime (CFRM) and Cefixime (CFX) of 66.9%, 55.2% and 80.1% was also successfully studied. • Pure ZnCr 2 O 4 nanoparticles were successfully synthesized and used as catalysts. • The structure of the samples was analyzed by Rietveld refinement. • An optical gap band of 1.66 eV was determined for ZnCr 2 O 4 . • ZnCr 2 O 4 is an n-type semiconductor with a flat band potential of 0.3 V SCE . • A significant degradation of antibiotics was demonstrated by using this catalyst.