Fig. 1. (a–d) TEM images (inset: NPs size distribution histogram and average size) of the CoFe₂O₄–rHGO composites with 5, 10, 16 and 30 wt% CoFe₂O₄, respectively; (e–h) TEM images (inset: NPs size distribution histogram and average size) of the CoFe₂O₄–rIGO composites with 5, 10, 16 and 30 wt% CoFe₂O₄, respectively; (i) TEM image (inset: NPs size distribution histogram and average size) of the pure CoFe₂O₄ NPs.