Concentration-dependent structure of mixed NH4Cl and (NH4)2SO4 aqueous solutions from the X-ray diffraction, Raman spectroscopy and molecular dynamics simulations.

Abstract Influences of concentration on micro structures of mixed NH 4 Cl and (NH 4) 2 SO 4 aqueous solutions are investigated by Raman spectroscopy, X-ray diffraction spectroscopy and molecular dynamics simulations. We deduce the reduced pair distribution function G(r) from X-ray diffraction diagrams, obtain the radial distribution function (RDF) from the molecular dynamics simulations and get the excess Raman spectroscopy from Raman spectroscopy. The results above illustrate that the formation of interaction between NH 4 + and SO 4 2− causes a characteristic peak in the X-ray diffraction spectroscopy, which can be used to prove the existence of both NH 4 + and SO 4 2− in solutions. Besides, as the mixed concentrations change, two structural turning points appear. One turning point is mixed concentrations of 23% NH 4 Cl and 10% (NH 4) 2 SO 4 , while the other one is mixed concentrations of 11% NH 4 Cl and 30% (NH 4) 2 SO 4. At these points, the old network structure and original ion contact pairs are damaged, while the new ion pairs are generated, due to the addition of mixed NH 4 Cl and (NH 4) 2 SO 4 in aqueous solutions. Furthermore, these conclusions of experimental and simulated test are completely consistent and mutually supportive. Highlights • We make a direct comparison of reduced pair distribution function and radial distribution functions. • The X-ray diffraction spectroscopy can be used to determine the existence of both NH 4 + and SO 4 2− in solutions. • NH 4 + ion in solutions behaves in a way very similar to water. • The hydrogen bond structure and original ion interactions are damaged, while new ion distances are formed. [ABSTRACT FROM AUTHOR]