Microscopic Study On The Effect Of Hydrat Ion Shell Structure On The Properties Of Ionic Clusters In Solution

For the Earth,water accounts for about 71%of the Earth's area,most of which is seawater.So,the most of species in nature are presented in salt solution,and the most of reactions are carried out in salt solution.Therefore,it is of great significance to study the effects of salt solutions on the presence and various reactions of various species,especially for metastable substances.However,due to the variability of the aqueous structure and the complexity of the hydrogen bond network,it is difficult to directly explore the relationship between water and these species or reactions by experimental methods.In this paper,molecular dynamics simulation,electronic continuum correction,potentials of mean force simulation,and quantum chemical calculations and spectral calculations are used to study the nature of the effects of hydration on ion cluster characteristics and ion association in aqueous solutions at the molecule level.In this paper,molecular dynamics simulations were used to study the effect of hydrated shells on the properties of ion clusters.Our results showed that the hydration shell of[CaCl_x]^2-x?x=4⁶?species can increase its stability.In aqueous solution,we can observe that the third hydration shell of the[CaCl_x]^2-x?x=4⁶?species shrinks,whereas the[CuCl]⁺or[CaCl₂]⁰ species does not.The shrinking third hydration shell of Ca²⁺together with the second hydration shell forms a dense inner hydration shell structure around the[CaCl_x]^2-x?x=4⁶?cluster,promoting the presence of[CaCl_x]^2-x?x=4⁶?species in aqueous solution.Their inner hydration shell forms a unique hydrogen bond network around the ion clusters,acting as a"hydration cage"structure that confines multiple Cl^–ions around Ca²⁺and promotes the appearance of[CaCl_x]^2-x?x=4⁶?species in aqueous solutions.Our results show that the structural characteristic s of some ion clusters combined with their unique hydration properties have a huge impact on the distribution of ionic species,ion cluster characteristics,and the ion association in the aqueous phase.In order to further study the effect of the hydration shell structure around the clusters on the presence of high-coordination chlorinated species,we compared the properties of high-coordination chlorinated species in the three systems[CuCl_x]^2-x?x=4⁶?,[ZnCl_x]^2-x?x=4⁶?and[CaCl_x]^2-x?x=4⁶?using the same calculation method.The results show that the[CaCl_x]^2-x?x=4⁶?,[CuCl₄]^2-and[ZnCl₄]^2-cluster structures can be existed in dilute solutions.For the[CuCl₄]^2-,[ZnCl₄]^2-species,there is no shrinkage of the third hydration shell and the expansion of the second hydration shell as in the[CaCl_x]^2-x?x=4⁶?species.The results here show that the hydration shells of highly coordinated chlorinated species have similar characteristics.That is,the water molecules in the second hydration shell have a longer residence time,and the density distribution of the inner hydration shell is not uniform with respect to the free metal ions,and the arrangement of water molecules in the second shell are confusing.The inner hydration shell of these highly coordinated chlorinated species has an entropy increasing effect.This entropy enhancing effect may be responsible for the stability of the hydrated shell around these highly complex chlorinated species,and also contributes to the presence of highly coordinated chlorinated species.Arsenic contamination in aqueous solutions has always been a problem that humans need to solve,and the stronger toxicity and prevalence of arsenite makes us interested in the removal of it in aqueous solution.In this paper,density functional theory calculation is used to study the removal of arsenite by iron s pecies in aqueous solution.Studies have shown that[Fe]³⁺_aqq associates with arsenite in outer spherical configuration in the aqueous solution.The iron specis has the greater hydration energy,thus that species exhibits the weaker association with arsenite species.It indicates that the weaker the hydration ability of the adsorbent material is,the more favorable it is for the removal of arsenite.The studies on the effect of acid-base conditions on the the adsortpion of arsenite have shown that the association between[Fe]_aq³⁺and arsenite may be gradually weakened as the PH value of the solution increases,but as more OH^-were considered in the associated structures,the association between ion species and arsenite species will begin to strengthen.The association between iron gel and arsenite also has the similar trend.The association calculations in the aqueous solution show that the[Fe₂O?OH?₃?H₂O?₇]⁺iron gel is more likely to associate with arsenite in an SSIP configuration.Our result show that the adsorption of arsenite by iron gel in an aqueous phase can be occurred via the shared hydration shell,and also further indicates that the hydration of the ion clusters has a great influence on the association of the clusters.