Commelina benghalensis-mediated CuO–ZnO nanocomposite: Effect of the p-n heterojunction on the photocatalytic activity against Congo red and carbamazepine

• Biosynthesis of CuO-ZnO nanoparticles using C. benghalensis for the first time. • 98% and 90 % degradation of pharmaceutical CBZ drug and CR dye, respectively. • XRD confirmed the formation of nanocomposite. • FTIR confirmed the phytochemicals in both extracts and CuO-ZnO. • Superoxides were the major species responsible for CR degradation. In this study, 30:70 CuO–ZnO nanocomposites (by mass %) were green-synthesised using Commelina benghalensis plant extracts, and their performance for the photocatalytic degradation of Congo Red (CR) dye and carbamazepine (CBZ) were investigated. Fourier-transform infrared (FTIR) analysis confirmed the bond characteristics and the presence of various functional groups within the CuO–ZnO nanocomposite. Structural analysis using X-ray diffraction (XRD) confirmed the presence of tenorite CuO and hexagonal zincite ZnO phases, which were further verified in the CuO–ZnO nanocomposite. The average crystallite sizes were determined to be between 13 nm and 18 nm for ZnO, CuO, and the 30:70 CuO–ZnO nanocomposite, respectively. Scanning electron microscopy (SEM) revealed a mixture of spherical and rod-like morphologies for the 30:70 CuO–ZnO nanocomposites, with a particle size distribution of 2–20 nm. In assessing the photocatalytic performance of the nanomaterials against Congo Red (CR) dye, a 90 % degradation was achieved under optimal conditions of pH 3, a catalyst dosage of 50 mg, a reaction time of 120 min, and a CR concentration of 5 ppm. Furthermore, superoxide ions (O 2 2 − ) were identified as the dominant species responsible for the degradation of CR. The heterostructure demonstrated reusability, maintaining its effectiveness for up to four cycles. For carbamazepine (CBZ), the 30:70 CuO–ZnO nanocomposites achieved a higher degradation efficiency of 98 %. The nanocomposites were more effective in removing CBZ than CR dye, highlighting their potential for diverse photocatalytic applications.