Evaluating Biochar-Water Sorption Coefficients of Pharmaceutically Active Compounds by Using a Linear Free Energy Relationship

Abstract

A linear free energy relationship (LFER) approach was used to predict the sorption coefficients of pharmaceutically active compounds (PhACs) to commercial biochar from aqueous solution, and to investigate the contributions of different intermolecular interactions in the overall sorption process. 14 PhACs with diverse functional groups (carboxyl, hydroxyl and nitrogenous heterocyclic) were selected as sorbates. All isotherm data of PhACs sorption to commercial rice straws biochar (carbonization temperature: 400-500℃, 200 mesh) could be well fitted by the Freundlich equation. The established LFER model could predict the value of sorption coefficient lgKd,activity at arbitrary levels of chemical saturation. The values of multiple correlation coefficient (R2=0.93), standard error (SE=0.23), F-statistic (268), leave-one-out cross validation (QLOO2=0.90), external cross validation correlation coefficient (QEXT2=0.92) indicated that the model was stable and of high predictive ability. The calculated results of the LFER model showed that, at lower sorbate concentration, sorption was dominated by the positive effect of cavity and the negative effect of sorbate capability of electron donation.