Abstract: The molecular behavior of aromatic compounds on the biochar surface， especially the mechanism of weak interaction， is not yet clear. In order to reveal the mechanism of weak interaction between biochar and phenol， adsorption isotherm and adsorption kinetics experiments， as well as FT-IR characterization were used to analyze the binding energy， reduced density gradient (RDG) and electron density topological relationship between biochar and phenol of different adsorption configurations with density functional theory (DFT). Results showed that the adsorption isotherm reaches the equilibrium after 72h， pH significantly affects the saturated adsorption capacity， and the adsorption capacity is the largest at pH=6. The functional groups on the biochar surface are the adsorption centers. The adsorption enthalpy (ΔH) is always in the range of hydrogen bond energy. The weak interaction of the four adsorption configurations (A/B/C/D) is dominated by van der Waals forces and weak hydrogen bonds. The B configuration has the lowest binding energy and the most stable. The C configuration has the strongest weak interaction， and the D configuration is the weakest.

Key words: biochar; phenol; density functional theory (DFT); hydrogen bond; van der Waals force