Zero-valent Ni/NiO core-shell nanosheets supported on graphene for highly efficient dye adsorption: Isotherm, kinetic and thermodynamic study

In this study, a novel zero-valent nickel/nickel oxide@graphene nanosheets (ZVNi-NiO@Gr) composite was successfully fabricated by a single-step method and used as nanoadsorbents for removal of crystal violet dye (CV) from its contaminated aqueous. Morphological characterization of nZVNi-NiO shows unique morphology with two-dimensional core-shell nanosheets supported on graphene layers. The one-step simultaneous preparation of nZNi-NiO nanosheets on the graphene notably limits the effect of nZNi-NiO agglomeration and enhanced the adsorption sites on the surface. The adsorption performance of ZVNi-NiO@Gr was investigated in terms of pH, temperature, initial concentration of CV dye, and contact period. The results showed that the maximum adsorption capacity climbed from 1028 to 1230 mg/g with increasing temperature from 30 to 45 °C, and CV dye adsorption was preferable in alkaline media at pH 10. The isothermal and kinetic analysis showed that the nonlinear form of the Freundlich isotherm model and pseudo-second-order kinetic model is more fitting for adsorption data. The results of the thermodynamic study indicated that the adsorption of CV dye was spontaneous, endothermic and physical. The unique structure of ZVNi-NiO@Gr and the synergistic effect made it promising adsorbent for removing cationic dyes from aqueous media, and it can be used practically to treat wastewater of textile industries.