Effect of urea additive on CuSO4·5H2O crystal habit: An experimental and theoretical study
The effect of urea on the habit of copper (II) sulfate pentahydrate crystal and its mechanism have been studied. The drastic retardation of (0 1 -1) face was induced by additive, modifying crystal from a parallelogram to an oblique hexagonal prism. Two opposite effects caused by urea clearly revealed the synergistic impact of thermodynamic and kinetic factor. Density functional theory calculations have been performed to obtain the geometries and the adsorption energies of water and urea molecule on (0 1 -1), (1 -1 -1), (1 -1 0) and (1 1 0) faces respectively. It could be inferred from the calculated geometries that the formation of H2O-Cu bond was hampered by the binding of urea to Cu atoms, and the significant distinction (0.85 eV) of the adsorption energies suggests the preferential interaction on (0 1 -1) face. This work explains the mechanism rationally, and is helpful for evaluating habit modifiers under the guidance of theoretical calculations.