Competitive Adsorption of PbII , NiII , and SrII Ions on Graphene Oxides: A Combined Experimental and Theoretical Study.

The individual and competitive adsorption of PbII , NiII , and SrII on graphene oxides (GOs) was investigated by experimental and density functional theory (DFT) studies. Experimental results indicate that 1) in all the single, binary, and ternary metal-ion adsorption systems, the sequence of maximum adsorption capacities is PbII >NiII >SrII on GOs; 2) the desorption hysteresis of metal ions from GOs shows the adsorption affinity in the same sequence: PbII >NiII >SrII . For the first time, DFT calculations indicate that 1) PbII and NiII prefer to interact with the COH group, whereas SrII interacts with COH and COC comparably, and 2) PbII can easily abstract the OH group from the GOs to form the much more stable Pb(OH)-GO complex. These findings are very important and useful for understanding the mechanisms of heavy-metal-ion adsorption on GOs and assessing the adsorption of coexisting heavy-metal ions on GOs.