ZnCo₂O₄ nanorods as a novel class of high-performance adsorbent for removal of methyl blue

Spinel ZnCo₂O₄ nanorods were synthesized by a simple template-free hydrothermal method in the presence of zinc chloride, cobalt chloride, glucose, and urea. The phase structure, morphology and chemical composition have been characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED). The results showed that the typically porous and poly-crystalline structure was successfully grown on the surface of ZnCo₂O₄ nanorods. The ZnCo₂O₄ nanorods were further applied to remove methyl blue (MB), which was used as a model of organic pollutants in aqueous solution. In particular, the maximum equilibrium adsorption capacity of MB in ZnCo₂O₄ nanorods reaches up to 2400 mg/g, which is higher than that of most adsorbents. The adsorption isotherms and kinetics followed standard Langmuir and pseudo-second-order models, respectively. MB adsorption decreased with increasing solution pH at pH > 7 implying that MB adsorption on ZnCo₂O₄ nanorods may via chemisorption between negatively charged MB molecular and positively charged adsorption sites on the surface of ZnCo₂O₄ nanorods. This study provides great promise of using ZnCo₂O₄ nanorods as adsorbent for removal of pollutant dyes.