Bare and functionalized nanodiamonds in aqueous media: A theoretical study

Nanodiamond particles, basically those produced by detonation method, are acquiring progressive attraction in different fields such as material, biomedical, and environmental engineering. Aqueous environments are usually dealt with at different stages of preparation, preservation, and application of these particles. The aim of this article is to perform a systematic first-principles density functional theory analysis on the interaction of C35 ultrasmall octahedral nanodiamond and its full homogeneous carboxylated and aminated forms, with water derived specie, namely, neutral, protonated, and deprotonated water and (H2O)20 water cluster. The effect of solvent media on the interactions has been considered through conductor like screening model. Through the calculations, C35 showed a hydrophobic nature, and C35(COOH)36 and C35(NH2)36 demonstrated hydrophilic characteristics. The interactions of all the water derived specie with the non-functionalized C35 were more intense compared with the functionalized C35(COOH)36 and C35(NH2)36 nanodiamonds, either in the gas phase or water media. Interestingly, in water media, the interaction energies of H3O+ and OH− with C35(NH2)36 were almost zero; only the interaction of H3O+ with C35(COOH)36 was zero, testifying to its Bronsted-Lowry acidic nature. To understand the nature of the interactions the electron density differences were utilized.