| Graphene materials are increasingly being incorporated into water treatment technologies due to their rapid and non-selective sorption abilities to small molecular weight organic contaminants. This study first examines some of the mechanistic interactions between commercial graphene oxides and endocrine disrupting compounds, pharmaceuticals, and natural organic matter in order to determine which physicochemical properties should be considered when choosing a graphene material. In addition, two more graphene based nano composites including ethylenediamine functionalized graphene (ED-G) and black carbon magnetite (BC-Mag) was synthesized in the lab and tested for their sorption performance on targeted contaminants. Graphene oxides of varied particle sizes, specific surface areas, and surface chemistries were evaluated within batch reactors. Specific surface area (SSA), surface charge, and phenolic content of graphene oxides was determined to have the greatest control on sorption extent of carbamazepine, an anticonvulsant used as a probe compound. Only graphene with SSA much larger than 100 m2g-1 could out-compete granular activated carbon or multi-walled carbon nanotubes, other carbonaceous sorbents currently used in water technologies. Pi-pi dispersion interactions appear to govern sorption of neutral compounds, and electrostatic interactions also strongly influenced cationic and anionic compounds, increasing or decreasing sorption two-fold, respectively, as graphene surface charge becomes more negative at higher pH. Sorption extents for various humic acids, fulvic acids, and organic matter by graphene showed good correlation with aromatic content, indicating a preference for the more hydrophobic fraction in organic matters. A concomitant decrease in specific UV absorbance was also observed. Size exclusion chromatography revealed a preference for sorption of the larger molecular weight fraction of organic matters. Enhanced or diminished sorption of organic compounds in the presence of organic matter depended on compound charge. ED-G with positive surface charge was observed to have preferable sorption of negative charged ibuprofen over neutral and positive charged compounds carbamazepine and atenolol, which suggested ED-G as a strong addition to widely present negative charged graphitic materials. BC-Mag has the fastest sorption kinetic among all of tested sorption materials, and its retrieval, regeneration and reuse could be easily achieved by a strong magnet and washing with alcohol. |
