Probing the interfacial charge transfer and defect-modulated photocatalysis in green-synthesized ZnO/F-MWCNTs ceramic nanocomposites

The escalating contamination of aquatic ecosystems by organic dyes necessitates the development of a high-efficiency, sustainable photocatalyst. This study combines Averrhoa bilimbi fruit extract-mediated, green-synthesized zinc oxide nanoparticles (ZnO NPs) with functionalized multi-walled carbon nanotubes (F-MWCNTs) to synthesize a ZnO/F-MWCNTs nanocomposite (Zn:CNTs NC) via sequential grinding, ultrasonication, and hydrothermal treatment. Comprehensive microscopic and spectroscopic characterization confirmed homogeneous decoration of ZnO NPs on F-MWCNTs, establishing a synergistic interface. Raman spectroscopy revealed a distinct stress-induced downshift of characteristic second-order E₂(high) - E₂(low) boundary phonon mode to 318.57 cm−1, validating intense interfacial tensile strain and active phonon confinement effects. Concurrently, a steady-state photoluminescence spectrum showed profound structural flattening and near-complete emission quenching across the scanned region, confirming that the F-MWCNTs suppress the radiative electron-hole recombination. The Zn:CNTs NC exhibited superior photocatalytic performance for the degradation of methylene blue (MB) under UV irradiation, achieving 90.81% efficiency within 90 min at a catalyst dosage of 30 mg. Optimization of environmental parameters demonstrated maximum degradation efficiency of 96.73% at pH 11, highlighting the role of hydroxide-mediated hydroxyl radical generation for alkaline textile wastewater remediation. Furthermore, electrochemical impedance spectroscopy (EIS) confirmed a drastic reduction in the interfacial charge-transfer resistance (R_ct), while the batch experiment demonstrated dual functionality that couples advanced surface adsorption with rapid photocatalytic mineralization. These findings demonstrate that Zn:CNTs NC serves as a resilient, high-performance candidate for advanced treatment of industrial textile effluents, offering insights into the defect-engineering of NC heterojunctions.