Can Nitrilotriacetic Acid (NTA) Act as a Habit Modifier for Rock Salt Crystals? An Answer from Computational and Experimental Studies

• Published in: Crystal growth & design 2011-05, Vol.11 (5), p.1675-1682
• Main Authors: Khan, Md Abdul Shafeeuulla, Singh, Ajeet, Haldar, Soumya, Ganguly, Bishwajit
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg1016017

It has been reported that nitrilotriacetic acid (NTA) has no effect on the growth habit of sodium chloride. We report here that NTA acts as a habit modifier for rock salt. The concentration of NTA required to influence the habit of salt crystals from cubic to octahedron is much less compared to the concentrations of other organic additives used for this purpose. The influence of NTA under different pH conditions toward the morphology of sodium chloride crystals has been investigated by experimental and computational methods. Prior to any analysis, a conformational search of NTA and its three dissociated forms was performed with molecular mechanics MM2* and DFT (B3LYP/6-31+G*) methods in aqueous phase. The low energy conformers were used to derive quantum chemically molecular electrostatic potential (MESP) to examine the possible sites of interaction for NTA and its dissociated forms with the important planes of NaCl. Three dimensional (3D)-slab model calculations performed to mimic the surfaces of sodium chloride with density functional theory (DFT) methods using a conductor-like screening model in aqueous phase (COSMO) for the interactions of NTA showed that there is no preference for the {111} plane of NaCl; however, the corresponding dissociated forms have pronounced preference for the {111} plane of sodium chloride. The composition analysis showed that the contributing forms of NTA toward habit modification of NaCl would be mono-deprotonated NTA (NTA−1), di-deprotonated NTA (NTA−2), and tri-deprotonated NTA (NTA−3) under different pH conditions.