How boron is adsorbed by oxygen-containing groups functionalized graphene: A density functional theory study

We employed density functional theory to investigate the adsorption mechanism of B(OH)3 and B(OH)4- on different graphene models: graphene with 20 carbon rings (G20), hydroxyl-modified graphene (G20-OH), and carboxyl-modified graphene (G20-COOH). The enthalpy of adsorption for B(OH)3 and B(OH)4- was as follows: G20 (-9.24 and-3.51 eV), G20-OH (-9.38 and-3.89 eV), and G20-COOH (-10.28 and-4.83 eV). The free energy of adsorption values were: G20 (-8.82 and-3.16 eV), G20-OH (-8.85 and-3.45 eV), G20-COOH (-9.66 and-4.27 eV). B(OH)3 exhibited easier adsorption than B(OH)4- within these groups. The interaction forces between B(OH)3/B(OH)4- and oxygen-containing groups were quantified, highlighting their role in determining the differential adsorption of B(OH)3 and B(OH)4-. Hydrogen bonding, van der Waals interaction, and steric effects were the main contributing factors to the adsorption process. G20 displayed stronger van der Waals forces with B(OH)3 than with B(OH)4- , while G20-COOH exhibited significantly stronger van der Waals forces with B(OH)3. The decreased steric hindrance contributed to the increased adsorption of G20-COOH with B (OH)3. Hydrogen bonding and reduced van der Waals forces played a role in the higher adsorption of G20-COOH with B(OH)4-. These findings inform strategies for efficiently removing boron species by understanding their adsorption mechanism on graphene.