Synergistic effect of Cu(II) in the one-pot synthesis of reduced graphene oxide (rGO/CuxO) nanohybrids as adsorbents for cationic and anionic dyes

Abstract

The present work considered the effects of Cu(II) loadings on the shape and size of CuxO nanoparticles, (where, x = 1, 2), blended with reduced graphene oxide through the one-pot hydrothermal procedure to get rGO/CuxO nanohybrids. These nanohybrids are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infra-red (FT-IR), and thermogravimetric analysis (TGA) techniques. The formation of spherical and monoclinic Cu2O are well detected at lower Cu(II) loadings and higher NaOH concentrations, while at the highest Cu(II) loading and lower NaOH concentrations the CuO nanorods clearly observed. The nanohybrids have been utilized as adsorbents for the removal of Methyl blue (MB) and Crystal violet (CV) as models of anionic and cationic dyes, respectively. The maximum removal of MB within 20 min occurs at optimized pH = 6, while for CV the alkaline medium is desired. The adsorption data well fitted using the pseudo-second-order kinetics, whilst the adsorption isotherms best represented by the Langmuir isotherm model. The adsorption capacity with qmax = 1200 mg g−1 of MB for the nanohybrid with lowest Cu(II) loadings, rGO/Cu2O, was higher than that of CV (qmax = 238.6 mg g−1), signifying the higher perspective for anionic dye removal. Therefore, this sturdy affinity of MB comparing with CV on rGO/Cu2O is mainly due to the high degree of the aromaticity of MB and the π-π interactions with rGO nanosheets. Furthermore, the calculation of thermodynamic parameters verified the feasibility of adsorption process. Moreover, the adsorbents recovered effectively by promising recovery method and reused.