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

Abstract

This study investigated the adsorption mechanisms of B(OH)3 (B3) and B(OH)4- (B4) on protonated and deprotonated graphene with oxygen-containing functional groups. Protonation or deprotonation conditions were found to significantly influence boron adsorption. Deprotonation of hydroxyl-modified graphene with 20 carbon rings (G20-OH) and carboxyl-modified graphene with 20 carbon rings (G20-COOH) led to decreased adsorption capacities for both B3 and B4. Protonation of G20-OH enhanced B3 adsorption. The adsorption interface, mainly around hydrogen atoms associated with protonated groups, exhibited a sharp gradient, likely due to increased electron density from O-H bond formation. B3 showed stronger electron sharing, emphasizing robust interactions. Hydrogen bonding dominated in G20-OH2-B3, while G20-O-B4 exhibited more substantial hydrogen bond interactions. In summary, hydrogen bond strength played a crucial role in B3 adsorption, while electrostatic repulsion hindered B4 adsorption on deprotonated graphene. This highlights the importance of graphene protonated and deprotonated states in effectively removing various pKa contaminants.

Keywords: Boron, Graphene, Protonation, Deprotonation, adsorption, Density functional theory