Green‐Synthesized Co 3 O 4 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‐Co 3 O 4 and CuO‐Co 3 O 4 nanocomposites were green‐synthesized using the Litsea glutinosa leaf extract as a natural reducing agent, and their photocatalytic and antibacterial properties were evaluated. ZnO‐Co 3 O 4 showed a narrow bandgap of 1.5 eV, favoring sunlight absorption, while CuO‐Co 3 O 4 exhibited a wider bandgap of 3.49 eV, absorbing primarily in the UV range. XRD revealed crystallite sizes of 12.45 nm of ZnO‐Co 3 O 4 and 8.93 nm of CuO‐Co 3 O 4 , and FT‐IR confirmed metal‐oxygen stretching bands below 600 cm −1 . SEM analysis showed spherical ZnO combined with rod‐shaped Co 3 O 4 in the ZnO‐Co 3 O 4 hybrid, while CuO‐Co 3 O 4 formed porous, agglomerated particles. ZnO‐Co 3 O 4 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‐Co 3 O 4 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.