Green fabrication of CuO-Fe2O3 and CuO-Fe2O3@Chitin nanocomposites using rosemary extract: Structural, antioxidant, antibacterial, and catalytic Indigo Carmine dye degradation performance.

In this work, the green and sustainable synthesis of CuO-Fe2O3 and CuO-Fe2O3@Chitin nanocomposites is described, using the extract of Rosmarinus officinalis as a bioreductant and chitin, a natural, non-toxic stabilizing biopolymer. UV-Vis spectroscopy indicated two absorption peaks with redshift and bandgap narrowing from 2.71 to 2.61 eV upon chitin incorporation, indicating enhanced electronic coupling and visible-light absorption. TEM and SEM images indicated that chitin inhibited the aggregation, and hence, the uniformly dispersed CuO-Fe2O3 NPs were obtained within the biopolymer matrix. This was further confirmed by elemental mapping analysis, where a homogenous distribution of Cu, Fe, O, C, and N was observed. XRD analysis confirmed the existence of monoclinic CuO and rhombohedral α-Fe2O3 crystalline phases that formed crystalline p-n heterojunctions. Phytochemical analysis revealed high consumption of phenolics, flavonoids, and tannins during nanoparticle synthesis, while improved carbohydrate retention in CuO-Fe2O3@Chitin facilitated steric stabilization. CuO-Fe2O3@Chitin exhibited improved antioxidant activity, IC50 = 0.141 mg/mL, and stronger antibacterial effects (12 ± 0.01 to 18 ± 0.49 mm) due to synergistic ROS generation, surface functionalization, and moderated metal-ion release. The Central Composite Design indicated that concentration and temperature are major parameters controlling Indigo Carmine degradation, achieving 96.4% removal under optimum conditions (60 °C, pH 8, 6 mg/mL). In conclusion, it is evident that incorporation of chitin into the composite greatly enhances its dispersion, optical, and stability characteristics as well as its catalytic activity, indicating that CuO-Fe2O3@Chitin is a potential catalyst for various applications.