Insights into the adsorption mechanism of tetracycline on hierarchically porous carbon and the effect of nanoporous geometry

Hierarchically porous carbons (HPCs) have been shown to be effective adsorbents for removing emerging pollutants such as antibiotics from water. To clarify the mechanisms of the transport and adsorption of antibiotics in multiscale pores of HPCs, molecular dynamics (MD) simulations are used to explore the adsorption of tetracycline (TC) on carbon adsorbents with various nanoporous geometries in this study. The layered cylindrical distribution patterns of the water molecules in nanopores are observed due to the strong interaction from the carbon surface, especially in the pores less than 3 nm in diameter. Relatively large pores (5 nm in diameter) of porous carbon are beneficial for the transport and adsorption of TCs in an aqueous solution. In the nanopores of HPCs, TC molecules tend to be trapped by the micropores located in the inner walls of mesopores, and then preferentially distribute near the edge of the pores. A faster adsorption rate and higher adsorption capacity of HPC are achieved compared with those of mesoporous carbon, which is in accordance with the experimental results. The micro/mesoporous geometry of HPC encourages the TC molecules to interact with the carbon surface and results in superior adsorption performance.