Effect of Protonation and Deprotonation on Oxygen-Containing Groups Functionalized Graphene for Boron Adsorption Removal

This study investigated the adsorption mechanisms of boron on protonated and deprotonated graphene with oxygen-containing functional groups. Six representative adsorption conformations of boron predominant species (B(OH)3 (B3) and B(OH)4− (B4)) on graphene were proposed. Protonation and deprotonation of graphene had significant effects on boron adsorption. Deprotonation of hydroxyl-modified (G20-OH) and carboxyl-modified graphene (G20-COOH) with 20 carbon rings decreased B3 and B4 adsorption. Protonation of G20-OH enhanced B3 adsorption. The adsorption interface, mainly around hydrogen atoms associated with protonated groups, exhibited a sharp gradient, due to the increased electron density from OH bond formation. B3 showed stronger electron sharing, emphasizing robust interactions. Hydrogen bonding dominated G20-OH2-B3, while G20-O-B4 exhibited more substantial hydrogen bond interactions. In summary, hydrogen bond strength was crucial in B3 adsorption, while electrostatic repulsion hindered B4 adsorption on deprotonated graphene. These findings highlight the importance of graphene protonated and deprotonated states in effectively removing various pKa contaminants.