Asymmetric Hybridization Orbitals at the Charged Interface Initiates New Surface Reactions: A Quantum Mechanics Exploration

Abstract

Although the first report of Hofmeister effects is more than 130 years old, the origins of the Hofmeister series remain debated. In this study, quantum mechanics (QM) analyses, dispersion-corrected p-DFT calculations, and dynamic light scattering (DLS) determinations are combined with the aim to unravel such a scientific basis. QM analyses show that asymmetric hybridization occurs for the outer-shell nsnp z orbitals at charged interfaces, and the asymmetric sp z hybridization further initiates two unique processes for the interfacial ions: unusual polarization with a greatly enlarged polarizability and a new type covalent bonding of surface reactions with the asymmetric sp z hybridization. The asymmetric hybridization theory is then applied and verified by surface reactions of K+ and Na+ with the charged montmorillonite surface. As predicted by QM analyses, p-DFT calculations show that, under no or low electric fields, the covalent bonding does not exist for both Na+ and K+, while under strong electric fields, covalent bonding is produced for K+ with surface-O atoms but remains absent for Na+. Also, as predicted by QM analyses, the DLS results confirm that the interfacial Na+ reactions are governed by two forces, as Coulomb interaction and unusual polarization, while in addition to these two forces (unusual polarization of K+ is 2.067 times as that of Na+), covalent bonding emerges for the interfacial K+ and plays a dominant role. This study provides new scientific bases of Hofmeister effects at the subatomic level, which is of critical importance in both physical and biological systems.

Insight into Hofmeister effects on aggregation of 2:1 and 1:1 type clay minerals

“…However, according to theory of asymmetric hybridisation of outer shell orbitals of atom/cation in the external electric field arising from clay surface charges (Q. Li et al, 2019), the O atoms as well as the adsorbed cations at surface could be non‐classically polarised. It has been shown that cations like Na + and Mg 2+ with 2s2p outer orbitals have the weakest polarisation effects, and the interactions between these cations with surface O on clay were mainly composed of electrostatic interaction and non‐classical polarisation effects (Q. Li et al, 2019). On the other hand, the polarisation of K + , Ca 2+ with 3s3p (or other cations with outer shell number of n > 3) orbitals was significantly higher than that of n = 2 (e.g., Na + and Mg 2+ ), which provided the basis for the ‘polarisation‐induced covalent bonds’ between K + , Ca 2+ , Cs + and surface O on clay (Q. Li et al, 2019).…”

“…It has been shown that cations like Na + and Mg 2+ with 2s2p outer orbitals have the weakest polarisation effects, and the interactions between these cations with surface O on clay were mainly composed of electrostatic interaction and non‐classical polarisation effects (Q. Li et al, 2019). On the other hand, the polarisation of K + , Ca 2+ with 3s3p (or other cations with outer shell number of n > 3) orbitals was significantly higher than that of n = 2 (e.g., Na + and Mg 2+ ), which provided the basis for the ‘polarisation‐induced covalent bonds’ between K + , Ca 2+ , Cs + and surface O on clay (Q. Li et al, 2019). That is, the interaction potential between K + , Ca 2+ , Cs + and surface O on clay was composed of the electrostatic potential, the non‐classical polarisation effect and the ‘polarisation‐induced covalent’ interaction energy.…”

“…However, the γ values of divalent heavy metal cations were higher than that of Ca 2+ (Table 7), indicating that covalent adsorption existed between heavy metal cations and surface O atoms on clay, and the covalent bonding for heavy metal was stronger than that for Ca 2+ . According to the atomic orbital asymmetric hybridisation theory (Q. Li et al, 2019, 2021), the atomic orbitals of surface O on clay were asymmetrically hybridised, which greatly increased the electron activity of the lone pair of O, which enabled the formation of the stable coordination bonds between surface O on Mt and the empty orbitals of heavy metal cations. Obviously, this kind of coordination was the ‘polarisation‐induced coordination’, which was different from the classical coordination.…”

“…Currently, the γ Na at Mt surface was known to be 1.21 (Q. Li et al, 2019). Then, the van der Waals attraction forces of Mt particles based on the experimental results in the Na + system were estimated.…”

Specific ion effects of incomplete ion-exchange by electric field-induced ion polarization

“…26,27 Further studies have conclusively shown that the aforementioned ionic interface behavior can be enhanced with increases in ionic size. 28 Thereby, the newly discovered interaction forces probably play an essential role in the incomplete ion-exchange state of cation adsorption, and dominate the possible specic ion effects. However, such important issues have scarcely been involved in the current research.…”