Graphene Oxides in Water: Correlating Morphology and Surface Chemistry with Aggregation Behavior

Aqueous aggregation processes can significantly impact function, effective toxicity, environmental transport, and ultimate fate of advanced nanoscale materials, including graphene and graphene oxide (GO). In this work, we have synthesized flat graphene oxide (GO) and five physically crumpled GOs (CGO, with different degrees of thermal reduction, and thus oxygen functionality) using an aerosol method, and characterized the evolution of surface chemistry and morphology using a suite of spectroscopic (UV–vis, FTIR, XPS) and microscopic (AFM, SEM, and TEM) techniques. For each of these materials, critical coagulation concentrations (CCC) were determined for NaCl, CaCl2, and MgCl2 electrolytes. The CCCs were correlated with material ζ-potentials (R2 = 0.94–0.99), which were observed to be mathematically consistent with classic DLVO theory. We further correlated CCC values with CGO chemical properties including C/O ratios, carboxyl group concentrations, and C–C fractions. For all cases, edge-based carboxyl func...