Asymmetric response of transition metal cationic orbitals to applied electric field.

Understanding the quantum mechanical mechanisms underlying atomic/ionic interfacial processes and phenomena, particularly their dependence on the electronic orbital rearrangement of atoms/ions in an external electric field, remains a significant challenge. This study investigated the asymmetric response of transition metal (TM) cationic orbitals when subjected to an applied electric field. Quantum mechanical calculations were employed to quantify the newly formed hybrid orbitals and evaluate the corresponding orbital energies of the TM cations. Analysis of the quantitative contribution of asymmetric orbital hybridization to TM-surface interactions showed a significant change in orbital energy and increased effective charges of TM cations at the charged surface. This asymmetric response, induced by a negative external electric field generated from the structural charges of clay minerals (e.g., montmorillonite), repels electrons from the outer-shell orbital. This repulsion consequently increases the electron binding energy of the inner-shell orbitals, leading to new surface reactions, polarization-enhanced induction force, and polarization-induced covalent bonding between the TM cations and the charged surface. Our theoretical predictions regarding TM-clay mineral interactions are consistent with the experimental observations of TM cation adsorption. This finding has significant implications for the adsorptive removal of TM cations from wastewaters and for enhancing the catalytic efficiency of TM-surface catalysts. The unique physical and chemical characteristics exhibited by TMs at charged particle surfaces, resulting from their asymmetric response, can play pivotal roles in environmental and chemical engineering.

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

Incomplete ion-exchange results from ion interfacial reactions portray a particular scenario of interactions between ions and charged surfaces. In this study, the constant flow method was adopted to study the incomplete ion-exchange state of mono-valent cation adsorption of X+ (X+ = Cs+, Na+ and Li+) in X+/K+ exchange at the montmorillonite particle surface. The pronounced incomplete ion-exchange state and strong specific ion effects were experimentally observed. Further research found that the disparity in the activation energies for different ion exchange systems caused by electric field-induced ion polarization was responsible for the observations. Thus, a theoretical description of the incomplete ion-exchange state by taking the ion polarization into account was established and verified. Applicable new approaches to measuring the cationic diffusion coefficient in heterogeneously charged systems and the cationic actual diffuse depth in the electric double layer were also derived from the theory.

A how-to approach for estimation of surface/Stern potentials considering ionic size and polarization.

Electrostatic potential in the electric double layer is an important parameter that significantly affects a large number of physical, chemical and biological properties and processes. In the present study, a new approach for the estimation of surface potential and Stern potential considering ionic volume and polarization was developed. Ionic strong polarization in the diffuse layer increases its effective charge and determines the Stern potential, while ionic volume in the Stern layer strongly decreases its effective charge and determines the surface potential. For example, the effective charge of K(+) is increased by 0.699 (from 1 to 1.699) resulting from polarization, while it is decreased by 1.359 (from 1.699 to 0.240) due to finite size. The determined surface potential is about 7 times as high as the Stern potential. The effects of volume and polarization on the surface/Stern potentials were quantified respectively, and the former was stronger than the latter. A new theory was verified by the experiments for aggregates stability. The present work also showed that only introduction of the strong polarization into the DLVO theory can describe the interactions of colloidal particles.

[Simultaneous Determination of Hydroquinone and Catechol Based on L-Histidine-Erythrosine Composite Film Modified Glassy Carbon Electrode].

By using cyclic voltammetry method, L-histidine and erythrosine was electrodeposited on the surface of glassy carbon electrode (GCE) to obtain the modified electrode (denoted as L-His-Erythrosine/GCE). The morphology of L-His-Erythrosine/GCE was characterized by scanning electron microscopy (SEM), and the electrochemical property characterization of L-His-Erythrosine/ GCE was investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The electrocatalytic oxidation of hydroquinone (HQ) and catechol (CC) on the modified electrode was discussed by differential pulse voltammetry (DPV) in this study. The L-His-Erythrosine/GCE had shown an excellent electrocatalytic activity for HQ and CC. The oxidation overpotentials of HQ and CC decreased significantly and the corresponding oxidation currents increased remarkably. Due to the large separation of oxidation peak potentials (108 mV), concentrations of HQ and CC can be easily determined simultaneously. Under the optimum conditions, the oxidation peak currents for both HQ and CC increased linearly with the respective concentrations in the 1.2 x 10(-6) to 1.1 x 10(-4) mol x L(-1) concentration range, with the detection limits of 0.19 and 0.16 µmol x L(-1) (S/N = 3), respectively. Furthermore, the modified electrode exhibited good reproducibility and selectivity. The modified electrode was successfully applied to the simultaneous determination of HQ and CC in actual water samples, the recoveries got by standard addition method were in ranges of 99.9% - 100.6% (HQ) and 99.2% - 100.2% (CC).

Quantitative characterization of non-classic polarization of cations on clay aggregate stability.

Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10-5 to 10-1 mol L-1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation-surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability.

[Influence of perennial flooding and drought on growth restoration of Acorus calamus in water-level-fluctuation zone of the Three Gorges Reservoir].

Acorus calamus L. is a common kind of wetland plant species in the Three Gorges Reservoir. In this study, we investigated the influence of perennial flooding on growth restoration of A. calamus in the lightless conditions and the drought stress on this plant species' growth after flooding. Our research provided the scientific basis for the selection of candidate species for vegetations restoration in water-level-fluctuation zone of the Three Gorges Reservoir. A. calamus plants were exposed to waters in the lightless conditions in September 2009 and September 2010 respectively and taken away from the waters and grew in natural conditions in the following March, April and May (named as S1, S2, S3). All plants in the control, S1 and S2 groups were challenged with drought stress in May for 20 days. During the experiment, the plant number and leaf number were recorded regularly, as well as leaf length and leaf width. The results showed that flooding restrained the germination of the plants with much less plant in flooding groups than the control, and the plant germination rate had inverse relation to the flooding time. Flooding promoted formation and elongation of the leaves in S1 and S2 groups, which showed higher leaf growth parameters, such as leaf length, leaf number, total leaf length of one plant and total leaf length of all plants than the control. However, all of these growth parameters in S3 group had significantly lower values compared to the control. The survival rate of the plants after flooding decreased significantly with longer flooding time. Besides, the leaf length and leaf width in S1 and S2 groups increased significantly but with decreased leaf number. Additionally, all growth parameters (leaf length, leaf width, leaf number, total leaf number, total leaf length of one plant, total leaf length of all plants) in S3 group decreased remarkably. Furthermore, drought decreased the values of all growth parameters and the plant number in the control, S1 and S2 groups notably. When drought stress was removed for 25 days, the leaf number in the control, S1 and S2 groups increased by 67.0% (P < 0.05), 66.7% (P < 0.05) and 36.2% (P < 0.05), respectively, and the total leaf length of one plant, total leaf length of all plants and total leaf number in S1 and S2 groups increased by 48.2%, 18.1%, 66.7%, 35.0%, 75.0% and 64.3%, respectively (P < 0.05). Therefore, A. calamus exhibited not only strong adaption and tolerance to flooding,but also robust growth restoration ability after flooding, as well as good restoration ability to the drought stress. In summary, A. calamus could be used as one kind of restoration or reconstruction species in water-level-fluctuation zone (especially not exposed to flooding in March or April) of the Three Gorges Reservoir.