Influence of Formamide on the Crystal Habit of LiF, NaCl, and KI: A DFT and Aqueous Solvent Model Study

Abstract

We have performed a density functional study to examine the effect of formamide on the morphology of different alkali halide (namely LiF, NaCl, and KI) crystals. The calculations were performed both in the gas phase and aqueous phase using a continuum model (COSMO/COSMO-RS). Solvation is observed to have a major effect on the interaction energies whereas the matching of the size of the additive with the neighboring ion spacing on the lattice planes of the different alkali halides is seen to be less important. The calculated results employing the slab models show that, in the aqueous phase, formamide interacts preferentially with the {111} surface of sodium chloride (∆E ) -23.8 kcal/mol for {111} vs -0.4 and -4.3 kcal/mol for {100} and {110}, respectively). This would favor the formation of octahedral-shaped crystals as reported experimentally (Surf. Sci. 2003, 523, 307-315). On the other hand, interaction of formamide with all the surfaces of LiF are found to be repulsive in the aqueous phase while, in the case of KI, the interactions are weak (∼-2 to -5 kcal/mol) on all surfaces, i.e., no pronounced effect of formamide on morphology is expected.

Selective Adsorption/Absorption of Formamide in NaCl Crystals Growing from Solution

“…This change was attributed to the adsorption of isolated formamide molecules on the {111} surfaces 10,33 . Through the observation of macrosteps spreading on the {111} surfaces (Figure1c) we found that formamide induces a K  F change in the character of the {111} form and, having found significant lattice coincidences, we put forward the hypothesis of a 2D epitaxy setting up between the 101 formamide lattice planes and the {111} NaCl surfaces.…”

Unveiling the role of molecular interactions in crystal morphology prediction

“…An estimation of the type of interaction with the crystallization solvent could be inferred by means of a careful analysis of the figure. This is particularly evident in the case of the solvent actually used to harvest the crystals -DMF -but could be also a useful hint for further crystallization attempts [13,[43][44][45][46][47][48][49][50]. Solvent choice, and its characteristics such as permittivity and volatility etc., are the major environmental perturbation normally performed during crystallization at atmospheric pressure and room temperature.…”

Continuous Production of Water‐Soluble Nanocrystals through Anti‐Solvent Precipitation in a Fluidic Device

“…In a typical experiment, the flow rate ratio (R) of the focusing to focused phase and total volumetric rate (Qt) were fixed at 50 and 750 μL/min, respectively, while the molar concentration of the aqueous NaCl was kept at 2 M. Under such a condition, the as‐prepared NaCl nanocrystals exhibited a cubic shape and an edge length of 20±1.2 nm, together with good uniformity (Figure B). As revealed by the X‐ray diffraction (XRD) pattern (Figure S1 in the Supporting Information), the NaCl nanocrystals were crystallized in a face‐centered cubic phase, with the characteristic peaks at 31.1°, 44.5°, 55.3°, and 73.6° corresponding to diffraction from the crystallographic planes of (200), (220), (222), and (420), respectively . The EDX mapping results further confirmed that the nanocrystal was made of Na and Cl element (Figure C).…”