Green-Synthesized Co₃O₄ Heterostructures With ZnO and CuO for Photocatalytic Degradation and Antibacterial Activity

The green synthesis of transition metal oxide-based nanocomposites using plant extracts eliminates the use of harmful chemicals. Nonbiodegradable dyes and antibiotic resistance are a global health concern. In this study, ZnO-Co₃O₄ and CuO-Co₃O₄ nanocomposites were green-synthesized using the Litsea glutinosa leaf extract as a natural reducing agent, and their photocatalytic and antibacterial properties were evaluated. ZnO-Co₃O₄ showed a narrow bandgap of 1.5 eV, favoring sunlight absorption, while CuO-Co₃O₄ exhibited a wider bandgap of 3.49 eV, absorbing primarily in the UV range. XRD revealed crystallite sizes of 12.45 nm of ZnO-Co₃O₄ and 8.93 nm of CuO-Co₃O₄, and FT-IR confirmed metal-oxygen stretching bands below 600 cm⁻¹. SEM analysis showed spherical ZnO combined with rod-shaped Co₃O₄ in the ZnO-Co₃O₄ hybrid, while CuO-Co₃O₄ formed porous, agglomerated particles. ZnO-Co₃O₄ resulted in a superior methylene blue degradation of 84.77%, with rate constant, k = 1.05 × 10⁻² min⁻¹ under optimized conditions (i.e., 7 ppm dye, 0.6 mg catalyst, pH 11, 180 min), while CuO-Co₃O₄ offered a 75.59% degradation with k = 0.78 × 10⁻² min⁻¹ under the similar conditions which differed only in dye concentration (13 ppm) under sunlight irradiation. The catalysts exhibited moderate antibacterial activity against E. coli and B. cereus, highlighting their potential photocatalytic and antimicrobial applications.