Insights into the adsorption mechanism and dynamic behavior of tetracycline antibiotics on reduced graphene oxide (RGO) and graphene oxide (GO) materials†
The widespread use of antibiotics from both agricultural and human sources has led to their environmental dissemination which is now recognized as a potential hazard to human health and aquatic ecosystems. Along with the extensive academic and social concerns on the impact of this new kind of emerging pollutant, the knowledge on their effective removal from the environment is increasing. However, the complex interactions between antibiotics and sorbents make the experimental studies difficult at the molecular level. To provide an insight into the adsorption mechanism and dynamic behavior of antibiotics, in this work, three tetracycline molecules, namely tetracycline (TTC), oxytetracycline (OTC), and chlortetracycline (CTC), have been chosen as the representative antibiotics to present a theoretical study on their adsorption properties by reduced graphene oxide (RGO) and graphene oxide (GO). The density functional theory (DFT) method and molecular dynamics (MD) simulations were used to address a number of key issues, such as the effects of distinct adsorption sites, pH, and solvent on the adsorption capacity. A closer look at the adsorption configuration and binding energy showed that the π–π interaction was the driving force when TCs adsorbed on GO (or RGO), and hydrogen bonds played a significant role in the GO_TC systems. The computed results showed that the tetracycline adsorption affinity for the graphene-based materials followed the order CTC > TTC > OTC and TTC > CTC > OTC in the GO and RGO systems, respectively. The comparison of binding energies at different pH values and solvents proposed that low pH and less polar solvent environments were beneficial to the adsorption efficiency of TCs on GO and RGO. In addition, molecular dynamics simulations have been used to assign the dynamic behavior of the TCs, analyzing the competitive adsorption process, and the intermolecular accumulation was verified to be involved in the adsorption behavior of TCs. The CTC molecule appeared to exhibit the strongest competitiveness. Our work gives a deep insight into the interactions between the graphene-based materials and TCs, and provides a theoretical basis for the further design of adsorbents used for the removal of tetracycline antibiotics in the environment.