Enhanced adsorptive removal of selected pharmaceutical antibiotics from aqueous solution by activated graphene

Activated graphene adsorbents (G-KOH) were synthesized by a one-step alkali-activated method, with a high specific surface area (SSA) and a large number of micropores. As a result, the SSA of the final product greatly increases to ∼512.6 m(2)/g from ∼138.20 m(2)/g. The resulting G-KOH was used firstly as an adsorbent for the removal of ciprofloxacin (CIP) in aqueous solutions. Experimental results indicated that G-KOH has excellent adsorption capacity (∼194.6 mg/g). The alkali-activation treatment introduced oxygen-containing functional groups on the surface of G-KOH, which would be beneficial to improving the adsorption affinity of G-KOH for the removal of CIP. Kinetic regression results showed that the adsorption kinetic was more accurately represented by a pseudo-second-order model. The overall adsorption process was jointly controlled by external mass transfer and intra-particle diffusion, and intra-particle diffusion played a dominant role. A Langmuir isotherm model showed a better fit with adsorption data than a Freundlich isotherm model for the adsorption of CIP on G-KOH. The remarkable adsorption capacity of CIP onto G-KOH can be attributed to the multiple adsorption interaction mechanisms (hydrogen bonding, π-π electron donor-acceptor interactions, and electrostatic interactions). Results of this work are of great significance for environmental applications of activated graphene with higher SSA as a promising adsorbent for organic pollutants from aqueous solutions.