(810g) High Capacity Adsorption of Dyes By "Super Sand"

Recent reports have shown that graphene oxide (GO), synthesised from the oxidation of graphite, has a great capacity for adsorption of model pollutants (usually dyes) from water on account of a multitude of oxygen functionalities on its surface. These same oxygen functionalities render GO soluble in water, making its removal from a solution a challenge and thus hindering its usability as a water purification tool. RGO, derived from chemical or thermal reduction of GO, has also been investigated as a potential water purification material, its surface usually retains a number of oxygen functional groups whilst being insoluble and therefore easily filtered out of water, however, typically the adsorption capacities of RGO materials have not been particularly promising.

Herein we explore GO and RGO adsorption using three dyes of different charge and size and a NaBH₄-reduced RGO which has equivalent adsorption capacity to GO (~600mg/g for methylene blue) in batch experiments. Further, we explore a facile chemically derived modification with copper which has an enhanced capacity for adsorption of basic dyes with capacities up to 600mg/g for anionic Acid Blue 9 dye, and the use of RGO as a coating over sand (RGO-sand) (following from [1]) whereby a three order-of-magnitude improvement over GO-coated sand is observed for cationic methylene blue dye in a fixed-bed-column. The superior adsorption capacity of RGO-sand is explained in terms of a water-induced swelling of the RGO coating which is not observed for the GO-coating. Batch kinetics and isotherms are presented with adsorption mechanisms confirmed by correlation between the different adsorption character of each dye and a pH-study. This work makes strides towards determining the feasibility of using GO/RGO for water purification purposes.

[1]        Engineered Graphite Oxide Materials for Application in Water Purification, Wei Gao, Mainak Majumder, Lawrence B. Alemany, Tharangattu N. Narayanan, Miguel A. Ibarra, Bhabendra K. Pradhan, and Pulickel M. Ajayan, ACS Applied Materials & Interfaces 2011 3 (6), 1821-1826