Enhanced adsorption of Pb(II) onto modified hydrochar: Modeling and mechanism analysis.

A highly efficient modified hydrochar material by H2O2 and ultrasonic synergistic treatment was prepared for Pb2+ removal in aqueous solution. The removal mechanism was investigated by a number of techniques and was provided by quantitative calculation. The maximum adsorption capacity of Pb2+ by the modified hydrochar was calculated to be 92.80 mg g-1 at pH 5.0 and 298 K, which was more than 42 times higher than pristine hydrochar (2.20 mg g-1) and much higher than the other reported modified hydrochar materials. The characterization results showed that H2O2 treatment changed elemental composition, surface charge and increased oxygen-containing functional groups of the hydrochar. The mechanism study indicated that complexation with free carboxyl and hydroxyl and cation-π interaction were main mechanisms responsible for Pb2+ sorption and their corresponding contribution percentage of different mechanisms to the Pb2+ sorption was accounting for 62.12%, 27.14% and 10.74%, respectively.