Effect of molecular structure on the adsorption behavior of sulfanilamide antibiotics on crumpled graphene balls

Since the 1930s, sulfonamide(SA)-based antibiotics have served as important pharmaceuticals, but their widespread detection in water systems threatens aquatic organisms and human health. Adsorption via graphene, its modified form (graphene oxide, GO), and related nanocomposites is a promising method to remove SAs, owing to the strong and selective surface affinity of graphene/GO with aromatic compounds. However, a deeper understanding of the mechanisms of interaction between the chemical structure of SAs and the GO surface is required to predict the performance of GO-based nanostructured materials to adsorb the individual chemicals making up this large class of pharmaceuticals. In this research, we studied the adsorptive performance of 3D crumpled graphene balls (CGBs) to remove 10 SAs and 13 structural analogs from water. The maximum adsorption capacity q_m of SAs on CGB increased with the number of (1) aromatic rings; (2) electron-donating functional groups; (3) hydrogen bonding acceptor sites. Furthermore, the CGB surface displayed a preference for homocyclic relative to heterocyclic aromatic structures. A leading mechanism, π-π electron-donor-acceptor interaction, combined with hydrogen bonding, explains these trends. We developed a multiple linear regression model capable of predicting the q_m as a function of SA chemical structure and properties and the oxidation level of CGB. The model predicted the adsorptive behaviors of SAs well with the exception of a chlorinated/fluorinated SA. The insights afforded by these experiments and modeling will aid in tailoring graphene-based adsorbents to remove micropollutants from water and reduce the growing public health threats associated with antibiotic resistance and endocrine-disrupting chemicals.