Electrolyte induced rheological modulation of graphene oxide suspensions and its applications in adsorption

• Published in: Applied surface science Vol. 435; pp. 786 - 798
• Main Authors: Ojha, Abhijeet, Thareja, Prachi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.03.2018
• Subjects: Aggregation; Nanosheets; Rheology; Suspensions; Aggregation; Nanosheets; Rheology; Suspensions
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2017.11.157

[Display omitted] •Electrolyte induced aggregation of GO leads to low viscosity liquids, fragile and solid-like gels depending on size, valence and concentration of cations.•Storage modulus (G') for GO-electrolyte gels varies as GO-FeCl3 > GO-MgCl2 > GO-KCl > GO-NaCl > GO-LiCl > GO-NH4Cl.•Porous morphology, 2 yield points and adsorption of oils by GO-electrolyte gels.•Oil adsorption capacity of GO-FeCl3 > GO-NaCl gels, concomitant with rheology.•Lyophilized GO-electrolyte gels adsorb methylene blue dye with pseudo-second-order kinetics. In this study, we report the microstructure, rheology and adsorption characteristics of aqueous suspensions of Graphene Oxide (GO) at a volume fraction (ϕGO) = 0.018, which can be transformed into gels by cation induced charge shielding and cross-linking between GO nanosheets. GO nanosheets of average thickness ∼1.5 nm and a lateral dimension of ∼750 nm are synthesized by Hummer’s process. At ϕGO = 0.018, cations of varying size and valence are systematically introduced with electrolytes NH4Cl, LiCl, NaCl, KCl, MgCl2 and FeCl3 at concentrations ranging from 10-5–10-1 M to investigate their effect on the rheology of GO suspensions. Our results suggest that depending on the electrolyte concentration, size and the valence of the cation: low viscosity suspensions, fragile gels and solid-like GO-electrolyte gels are formed. The storage modulus (G') of all GO-electrolyte gels increases with the increase in electrolyte concentration and G' follows the order GO-FeCl3 > GO-MgCl2 > GO-KCl > GO-NaCl > GO-LiCl > GO-NH4Cl. FESEM analysis shows that lyophilized GO-electrolyte gels with 10-1 M electrolytes have a porous morphology resulting from the aggregation of GO nanosheets. The GO-electrolyte gels are shown to adsorb high quantities of oils, with GO-FeCl3 gels showing a higher adsorption capacity. The GO-NaCl and GO-FeCl3 lyophilized gels are also shown to adsorb methylene blue dye and follow the pseudo-second-order kinetics of adsorption. Along with higher oil and dye adsorption efficiency, GO-electrolyte gels are easy to recollect after the adsorption, thus avoiding the potential toxicity for bio-organisms in water caused by GO nanosheets.