Photo-catalytic degradation of brilliant green dye using recyclable ZnO/MWCNT@TiO₂ nano-composite

This study presents a sustainable photocatalytic approach using a ZnO/MWCNT@TiO2 nanocomposite to degrade Brilliant Green (BG) dye in water under visible light. The composite was synthesized via co-precipitation and wet impregnation, with varying ZnO/MWCNT ratios (2.5-10%) and fixed TiO2 (90%), labeled ZMT-1 to ZMT-5. The optical and structural features of the nano-engineered composite were verified using X-ray diffraction (XRD), scanning electron microscopy (SEM), SEM-energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), UV-diffuse reflectance spectroscopy (DRS), and Fourier-transform infrared (FTIR). The nanocomposite’s high crystallinity, morphology, particle size (25 nm), and elemental composition were confirmed through XRD and SEM-EDX analysis. The surface area of the prepared catalyst, as determined by the BET analysis, was found to be very high (133.4624 m2/g). Different operational parameters were tried to examine their photodegradation efficacy. The optimal composite (ZMT-3: 0.025:0.075:0.9 ratio) exhibited a 3.4 eV bandgap and achieved 94% BG mineralization in 120 min. BG’s degradation was also investigated in basic, acidic, and neutral environments. Degradation efficiency was tested under varying pH, showing enhanced performance at pH 9 compared to acidic conditions. Radical scavenging experiments identified hydroxyl radicals as the primary active species. The nanocomposite maintained stable catalytic activity over six cycles, demonstrating reusability. A degradation pathway for BG was proposed based on intermediate analysis. The study highlights the composite’s efficiency, stability, and potential for scalable water treatment, leveraging visible-light-driven photocatalysis to address organic pollutants sustainably.