Bryophyllum pinnatum mediated eco-friendly synthesized porous microstructures of self-assembled Co-doped ZnO nanoparticles for methylene blue removal

Abstract

Cobalt-doped ZnO nanoparticles (Co-ZnO NPs) were synthesized using a phytoextract mediated technique with varying concentrations of Co (2.5, 5.0, and 7.5 at.%), employing Bryophyllum pinnatum leaf extract as the stabilizing/capping agent. XRD analysis revealed that the synthesized Co-ZnO crystallize in a wurtzite crystalline phase with P63mc space group. FE-SEM imaging depicted the self-assembly of nanoparticles, forming porous microstructures. UV–Visible spectra analysis indicated a gradual decrease in the bandgap energy of the ZnO lattice with increasing Co concentration. Additionally, by examining the photocatalytic removal of methylene blue (MB), the photocatalytic activity of the Co-ZnO NPs was assessed. Results showed that Co-ZnO NPs with 5 % Co exhibited the highest photocatalytic activity, suggesting an optimal Co dopant concentration that minimizes the recombination of photogenerated charge carriers compared to other samples. Under sunlight exposure, Co-ZnO NPs with 5 % Co demonstrated effective photocatalytic activity, achieving the degradation of 98.08 % of a 10 mg/L MB solution within 60 min using a 1.2 g/L dosage, with a rate constant of 0.0582 min−1.