Interface engineered efficient visible light photocatalytic activity of MWCNTs/Co doped ZnO nanocomposites: Morphological, optical, electrical and magnetic properties

Abstract

Active photocatalysts composed of multi-walled carbon nanotubes (MWCNTs)/cobalt-doped zinc oxide nanocomposites were synthesized by a modified sol-gel method. Structural and morphological characterization revealed the formation of ZnO hexagonal wurtzite with cabbage-like structure. TEM and SEM images demonstrate the good surface-surface contact between the MWCNTs and ZnO particles with homogenous distribution of MWCNTs in the powders. The experimental Kubelka–Munk calculations showed that the incorporation of Co markedly reduces the band gap of ZnO, suggesting a promising photocatalytic activity under visible light. Co doping induced a reduction in the dielectric constant values assigned to the substitution of polarized Zn2+ ions by the less polarized Co2+ ions, while MWCNTs interestingly induced increments in the dielectric constant values. VSM measurements revealed that Co doping induces a clear transformation from the diamagnetic behavior of pure ZnO to ferromagnetic characteristic through Co2+-Vo-Co2+ exchange interactions. 5 wt% MWCNTs/5 wt% Co doped ZnO (5CN/5CoZ) nanocomposite showed the highest sunlight-irradiated photocatalytic activity for degradation of Congo red with degradation efficiency of 96%. The high photocatalytic activity of 5CN/5CoZ nanocomposite was assigned to its visible-light band gap, the presence of electron-hole traps and formation of MWCNTs-ZnO interface. It was found that the degradation of Congo red followed the pseudo-first-order kinetics. The 5CN/5CoZ nanocomposite exhibited the best catalytic efficiency and recyclability with 96%, 92%, and 89% degradation activities for three successive experiments.