Factors influencing natural organic matter sorption onto commercial graphene oxides

Nanosized graphene materials are being considered as a class of new, high surface area sorbents suitable for water treatment applications. This study explored commercially available graphene powders of differing sizes, surface areas, and surface compositions for their ability to sorb dissolved natural organic matter (NOM) from water under varying solution conditions within batch reactors. The sorption kinetics of NOM on graphene powders were rapid and reached equilibrium within hours. Sorption isotherms for all graphenes and all NOM types were all best described with the Freundlich model. Sorption affinity improved with increasing graphene specific surface area, more graphene carbon content, greater NOM aromatic content, and lower solution pH. Graphene sorption behavior is compared to carbon nanotubes and granular activated carbon, and high surface area graphene may possess superior sorption rates and capacities, whereas low surface area graphene may be entirely ineffective. The high surface area graphene examined here also showed selectivity for the aromatic and high molecular weight NOM fractions within measurements of specific UV absorbance and size exclusion chromatography. The results suggest that aromatic interactions significantly participate in NOM binding, but that electrostatic interactions may also influence sorption capacity depending on solution pH and graphene surface charge.