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

摘要

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.