Deposition and Release of Graphene Oxide Nanomaterials Using a Quartz Crystal Microbalance

Interactions of graphene oxide (GO) with silica surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Both GO deposition and release were monitored on silica- and poly-l-lysine (PLL) coated surfaces as a function of GO concentration and in NaCl, CaCl₂, and MgCl₂ as a function of ionic strength (IS). Under favorable conditions (PLL-coated positive surface), GO deposition rates increased with GO concentration, as expected from colloidal theory. Increased NaCl concentration resulted in a greater deposition attachment efficiency of GO on the silica surface, indicating that deposition of GO follows Derjaguin–Landau–Verwey–Overbeek (DLVO) theory; GO deposition rates decreased at high IS, however, due to large aggregate formation. GO critical deposition concentration (CDC) on the silica surface is determined to be 40 mM NaCl which is higher than the reported CDC values of fullerenes and lower than carbon nanotubes. A similar trend is observed for MgCl₂ which has a CDC value of 1.2 mM MgCl₂. Only a minimal amount of GO (frequency shift <2 Hz) was deposited on the silica surface in CaCl₂ due to the bridging ability of Ca²⁺ ions with GO functional groups. Significant GO release from silica surface was observed after adding deionized water, indicating that GO deposition is reversible. The release rates of GO were at least 10-fold higher than the deposition rates under similar conditions indicating potential high release and mobility of GO in the environment. Under favorable conditions, a significant amount of GO was released which indicates potential multilayer GO deposition. However, a negligible amount of deposited GO was released in CaCl₂ under favorable conditions due to the binding of GO layers with Ca²⁺ ions. Release of GO was significantly dependent on salt type with an overall trend of NaCl > MgCl₂ > CaCl<sub>2