How boron is adsorbed by D-glucamine: A density functional theory study

Understanding energies and structures related to boron adsorption by D-glucamine group has an essential role in the improvement of boron removal from wastewater. In this study, we carried out a molecular scale analysis of boron adsorption by density functional theory (DFT) computations. All 30 species of boron-bonding D-glucamine were considered in an adsorption site model. Moreover, a total of 24 bis-D-glucarnine adsorption sites, including five-membered and six-membered chelate rings were calculated. The values of Delta H and Delta G in the boron adsorption reaction were obtained by the PW6B95-D3(ATM)/ma-def2-TZVP//PBE0/6-31 + G(d,p) level of theory with the SMD solvation energy. Moreover, the B-11 NMR chemical shift was also computed to compare the experimental results. Our computational results concluded that the adsorption of boron was achieved through two D-glucamine groups. The boron-adsorbed species has five-membered and/or six-membered chelate rings. The predicted B-11 NMR chemical shift of the species matched with the experimental value. We conclude that the adsorption of boron by the bis-D-glucamine site is an endothermic reaction despite adsorption, which means the driving force of the reaction is entropy. These results suggested that there is a possibility for improvement in boron adsorption from the design of the adsorption functional group.