Synergistic effect of hydrogen bonding and π-π interaction for enhanced adsorption of rhodamine B from water using corn straw biochar

Dyes adsorption to biochar via hydrogen bonding, and π-π interaction alone have attracted much research attention, however, their synergism in adsorption mechanisms remains largely unnoticed. The synergistic effects of the hydrogen bonding and π-π interaction might improve the adsorption capacity and need more understanding to prepare high-capacity biochar. In this work, we evaluated the adsorption of various dyes on biochar prepared via the activation of potassium bicarbonate and urea (named BC-KN) to explore their synergistic effects. Batch experiments indicated the BC-KN showed a high adsorption capacity to rhodamine B at 4839.0 mg/g, azure B at 4477.7 mg/g, and methylene blue at 2223.0 mg/g, respectively. The mechanism of such significant adsorption was investigated by their comparative experiments, characterizations, and computational analyses. The computational analyses suggested that the synergism of the hydrogen bonding and π-π interaction improves the adsorption energies of BC-KN/RhB system from −10.35 kcal/mol to −20.49 kcal/mol. It can be concluded that the hydrogen bonding and π-π interaction can synergize to significantly improve the adsorption by increasing the π-electron density and shortening the distance of aromatic rings, thus dyes with H-donor show significantly better adsorption capacities. The insight of hydrogen bonding being the governing factor in the synergistic system will help produce high-capacity biochar in removing aromatic dyes and suggest a sustainable technology for the efficient decolorization of dye effluent to minimize its damage to the health and environment.