<p>Photocatalytic<?tk 4?> and dielectric properties of undoped, Ba/Bi doped and co-doped Co₃O₄ nanoparticles (NPs) have been studied in detail. The Rietveld refinement of XRD data validated the crystallinity and pure phase of the prepared NPs. The average crystallite size slightly decreased from 23 to 21&#xa0;nm with doping and co-doping. Fourier infrared spectroscopy analysis showed two sharp dips at 611&#xa0;cm⁻¹ and 698&#xa0;cm⁻¹ representing Co³⁺–O and Co²⁺–O vibrational bonds, respectively. A notable decrease in bandgap from 3.91&#xa0;eV for undoped to 3.75, 3.55, 3.51&#xa0;eV for Ba8 (8% Ba doped), Bi8 (8% Bi doped) and BaBi44 (4% Ba and 4% Bi co-doped) NPs samples, respectively was attributed to the formation of mid band energy levels. Photocatalytic measurements of the prepared NPs revealed an improved degradation ability for MO dye with doping. The maximum efficiency of 94% was obtained with single doped Bi8 NPs sample. The reaction kinetics analysis indicated the involvement of pseudo 2nd order kinetics for doped and co-doped samples indicating adsorbent-adsorbate chemical bonding, causing a rapid increase in overall rate constant especially 0.18&#xa0;min⁻¹ with Bi 8% doping. Dielectric measurements revealed a good and notable increase in dielectric parameters with doping and co-doping especially in the case of the BaBi44 co-doped sample due to homogeneous doping.</p> Graphical abstract <p>Graphical abstract for photocatalytic and dielectric study of Ba/Bi doped and codoped Co₃O₄ NPs.</p>