Photodynamic therapy, facile synthesis, and effect of sintering temperature on the structure, morphology, optical properties, and anticancer activity of Co3O4 nanocrystalline materials in the HepG2 cell line

•Co3O4 NCMs were synthesized using a sol-gel protocol and then calcined at various temperatures.•Anticancer activity of Co3O4 nanocrystalline materials (NCMs), annealed at various temperatures in the HepG2.•Increased annealing temperature of Co3O4 NCMs resulted in decreased cytotoxicity, due to an increase in NCM diameter.•The optimized form (30 μg ml−1) of Co3O4, annealed at 700 °C, caused the highest loss in liver carcinoma cell viability.•Our experimental findings were verified by developing a mathematical model for annealed Co3O4 NCMs at various temperatures.