Highly efficient removal of Gd(III) using hybrid hydrosols of carbon nanotubes/graphene oxide in dialysis bags and synergistic enhancement effect

The spontaneous stacking of graphene oxide (GO) nanosheets for the adsorptive remediation of wastewater has been severely restricting their inherent adsorption ability from being brought into full play. Herein, hydrosols of carbon nanotubes/graphene oxide (CNTs/GO) sealed in dialysis bags were utilized for the highly efficient and repollution-free removal of trace Gd(III) from water for the first time. The effects of mass ratio between CNTs and GO (M-CNTs:M-GO), pH value and contact time on Gd(III) adsorption of CNTs/GO hybrid hydrosol (M-CNTs:M-GO=1:6) as well as its adsorption kinetics and thermodynamics were studied by comparison with GO hydrosol. The pH-dependent desorption and regeneration of the CNTs/GO hybrid hydrosol were also investigated. The results showed that CNTs/GO hybrid hydrosols with M-CNTs:M-GO from 1: 8 to 1: 2 exhibited the remarkable synergistic enhancement effect. The CNTs/GO hybrid hydrosol with M-CNTs:M-GO=1: 6 had the theoretical maximum Gd(III) adsorption capacity of 534.76 mg.g(-1) (pH=5.9, t=60 min, T=303 K) with a leap of 86.42% compared to GO and remained the sorption capacity of 347.83 mg.g(-1) at the fourth cycle, showing the excellent regeneration performance. Moreover, the adsorption of Gd(III) on CNTs/GO hybrid hydrosols agreed well with the pseudo-second-order model and Langmuir isotherm adsorption model. In prospect, CNTs/GO hybrid hydrosols in dialysis bags promises of extensive application in the highly efficient and re-pollution free elimination of metal ions from water.