A new method for preparing ZnO/CNT nanocomposites with enhanced photocatalytic degradation of malachite green under visible light

For the first time, the two-step ball milling-hydrothermal synthetic route was used to synthesize zinc oxide/multi-walled carbon nanotube nanocomposites with different amounts of carbon nanotubes (CNTs). Under the specific conditions of ball milling, there is no need for initial functionalization of CNTs and therefore ZnO nanoparticles are directly formed on these materials. X-ray diffraction (XRD), Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of intended nanocomposites. The surface morphology of as-prepared samples was investigated with field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) and the results showed that the synthesized nanocomposites are in the range of 50-60 nm. According to extracted data from nitrogen adsorption-desorption isotherms, increase in surface area of nanocomposites along with the decrease in their pore sizes, demonstrated that the porosity in nanocomposites has been increased. The elemental mapping of nanocomposite with optimal amount of CNTs showed a homogeneous distribution of constituent elements in this sample. Prepared nanocomposites were used in photocatalytic degradation of malachite green under visible light and the synergistic effects of ZnO and CNTs was investigated. All nanocomposite samples displayed better photocatalytic behavior than the pure ZnO which shows that composing of ZnO with CNTs improves the photocatalytic performance of ZnO. The nanocomposite with 5 wt% of CNTs showed the maximum degradation efficiency of 79% under visible light in 60 min compared to pure ZnO (32%).