Nitrogen modified graphene nanowalls for retrieval of trace level cerium from aqueous medium

Removal of cerium from environmental and aqueous streams is essential in waste water rejuvenation processes. Nitrogen modified graphene nano walls (N-GNWs) have shown ultra-high sorption efficiency of trivalent cerium from aqueous medium (K_d > 2 × 10⁷) and a large sorption capacity of ∼ 2500 mg/g is achieved. N-GNWs were deposited on carbon paper substrate using PECVD technique. The three-dimensional nature of N-GNWs are revealed from high resolution FESEM images. Raman spectroscopic studies have shown that GNWs are defective and possess a few layer graphene like structure. Secondary Ion Mass Spectroscopic studies of the Ce sorbed N-GNWs and optical emission spectroscopy of the residual solution confirm the sorptive retrieval of cerium. Visual Minteq based ionization model is introduced to explain high (>90 %) sorption of Ce at pH≥7 and the mechanistic aspects of sorption for standard Cerium solution is discussed. The sorption involves attachment of cerium hydroxyl ions to the active cites on the sorbent surface.