Facile Fabrication of NiCoAl-LMO/Graphene Nanosheets for Efficient Capacitive Deionization Defluorination.

Capacitive deionization (CDI) has attracted extensive attention as a prospective technology for different ionic species removal from aqueous solutions. Traditional studies on the adsorption and desorption of fluoride from wastewater are energy intensive and may have harmful effects on the environment. Herein, the feasibility of fluoride removal from wastewater by CDI was investigated. NiCoAl-layered metal oxide nanosheets (NiCoAl-LMO) and reduced graphene oxide (rGO) composites (NiCoAl-LMO/rGO) were synthesized and used as CDI electrode materials for fluoride ion removal. The as-obtained NiCoAl-LMO/rGO with unique structure and high conductivity is beneficial to the adsorption of fluoride ions. In addition, the introduction of Co element in the laminate enhances the pseudo-capacitive behavior of the electrode material. As expected, the CDI system with NiCoAl-LMO/rGO composites as anode and activated carbon treated by nitric acid (H-AC) as cathode exhibits an outstanding defluorination performance. The maximum adsorption capacity of NiCoAl-LMO/rGO can be reached 24.5 mg g-1 at 1.4 V applied voltage when the initial NaF concentration is 500 mg L-1. The composites also show good cycle stability over 40 cycles of consecutive CDI defluorination process. The excellent defluorination performance of NiCoAl-LMO/rGO makes it possible for its practical application in wastewater treatment.