Cationic Mechanism Research Articles

Insight into the Partitioning and Clustering Mechanism of Rare-Earth Cations in Alkali Aluminoborosilicate Glasses

Rare-earth (RE) containing alkali aluminoborosilicate glasses find increasingly broad technological applications, with their further development only impeded by yet-poor understanding of coordination environment and structural role of RE ions in glasses. In this work we combine free induction decay (FID)-detected electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM), and MAS NMR spectroscopies, to examine the coordination environment and the clustering tendencies of RE3+ in a series of peralkaline aluminoborosilicate glasses co-doped with Nd2O3 (0.001-0.1 mol%) and 5 mol% La2O3. Quantitative EPR spectral analysis reveals three different Nd3+ forms coexisting in the glasses: isolated Nd3+ centers, dipole-coupled Nd clusters (Nd-O-X-O-Nd, where X = Si/B/Al), and spin-exchange-coupled Nd clusters, (Nd-O-Nd) and (Nd-O-La-O-Nd). Extensive RE clustering is observed at high RE2O3 concentrations, with more than 90% REs converting to dipole- and exchange-coupled Nd clusters already at [RE2O3] = 0.01 mol%. ESEEM analysis of the EPR-detectable Nd centers indicates a Na/Si-rich environment (four Na+ per Nd3+) for the isolated Nd3+ centers and the Na/Si/B-rich environment (2-3 Na+ and 1-2 boron per each Nd3+) for the dipole-coupled Nd clusters, while the EPR-undetectable exchanged-coupled RE clusters are predicted to exist in a Na/B-rich environment. The RE clustering induces nano-scale glass phase separation, while the Na/B-rich environment of the RE clusters implies a depletion of the same elements from the remaining host glass. Based on our results, we develop a mechanistic model that explains the high tendency of RE3+ to form clusters in alkali aluminoborosilicate glasses.

Swelling deformation of compacted bentonite considering the effects of Na cations and OH anions

Compacted bentonite has become a viable candidate as suitable artificial barrier material for restricting the movement of high-level radionuclides released from the canister in the deep geological repository. However, this material itself is fragile mainly because it is sensitive to the complex chemical environment especially alkaline components. Based on the interaction mechanism of cations and anions, this paper is mainly focused on the analysis of swelling deformation characteristics of compacted bentonite. Laboratory test results are shown that the elevated Na cations concentration can inhibit both the primary and secondary expansion process in compacted bentonite. The elevated OH anions concentration can inhibit the primary expansion process of compacted bentonite and will promote the secondary expansion process. The effects of NaOH solution with different concentrations on the swelling strain present the interaction of Na cations and OH anions. The swelling deformation of compacted bentonite is not only affected by the concentration of solution but also may be related to ionic compositions.

Li salt initiated in-situ polymerized solid polymer electrolyte: new insights via in-situ electrochemical impedance spectroscopy

Favorable interface is essential for the implementation of high energy density and high safety solid-state lithium metal battery (SSLMB). The in-situ transformation of electrolyte from liquid to solid-state is of great significance for the compatibility of interface. Herein, an in-situ polymerized glycerin triglycidyl ether (PGTE) solid polymer electrolyte (SPE) featuring excellent ion transfer capability, superior interfacial compatibility and cross-linked structure is developed by the initiation of optimal LiDFOB following cationic catalytic mechanism. Ionic conductivity of 4.16 × 10-4 S cm−1 is achieved at 60 °C due to the superiority of oxyethylene repeating units (C–C-O/C-O-C), and a discharge capacity of 135.2 mAhg−1 is obtained after 200 cycles at 0.2C for LiFePO4(LFP)/PGTE/Li battery. More importantly, as a Li salt initiated SPE, the in-situ polymerization process of PGTE is firstly investigated via ex-situ FT-IR, the ring opening catalytic activity of Lewis acid on epoxide is evaluated and the order of LiDFOB＞LiPF6＞AlCl3 is revealed. Furthermore, the effect of in-situ prepared SPE on electrode/electrolyte interface is innovatively explored using in-situ electrochemical impedance spectroscopy (EIS). The stable interfacial passivation layer is generated at platform voltage and the maximum value of average diffusion coefficient is also obtained at the plateau.

Probing of the hydrated cation bridges in the oil/brine/silica system via atomic force microscopy and molecular dynamics simulation

Strong interaction between oil and rock in oil/brine/silica system can not only lay a theoretical foundation for improving the crude oil recovery of unconventional reservoirs, but also provide ideas for the remediation of oil-contaminated soil and the reduction of energy consumption in the process of oil pipeline transportation. Cations have a substantial impact on the interaction between oil and rock, and low salinity water flooding can enhance oil recovery by 4%~38%. However, the existence form and functional mechanism of cations between oil and rock remain to be elucidated. In this paper, the interaction between oil and rock is quantitatively characterized via atomic force microscopy (AFM). The polar components of oil have a strong interaction with rock, which is 2–10 times stronger than that between the nonpolar components of oil and the quartz glass in the same cationic environment. Cations have readily observable impacts on the interactions between the polar components of oil and rock. The interactions are strong in brine with high valence cations and a high cation concentration. Molecular dynamics simulation (MD) was used to investigate the micro conformation between oil and rock and to identify the existence form and functional mechanism of cations. The results demonstrate that cations act as bridges that connect polar components in oil to rock surfaces. Besides, we also found that cations are present as hydrated cations and the water molecules that form the hydrated cations connect oil to the rock surface via hydrogen bonds. Hydrogen bonds are essential for the strong interaction between oil and rock. Therefore, the strength of the hydrogen bonds that connect the oil to the rock surface in systems with Na+, Ca2+ and Al3+ was calculated using density functional theory (DFT), and the result is consistent with that of AFM experiments. This study identifies the key action site of the strong interaction between the oil film and rock and provides a theoretical basis for the study of peeling oil films and renovating oil-contaminated soil.

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Ring-Opening Polymerization of CO2-Based Disubstituted δ-Valerolactone toward Sustainable Functional Polyesters.

3-Ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVL) is a disubstituent δ-lactone derived from CO2 and 1,3-butadiene. In this contribution, we report the ring-opening polymerization (ROP) of EVL with β-butyrolactone (BBL) as the comonomer catalyzed by scandium triflate [Sc(OTf)3]. The obtained polyester bearing active unsaturated bonds has the weight-average molecular weight (Mw) of 4.1 kg/mol, in which the EVL content is 38 mol % in accordance with the initial ratio of 40 mol %. The copolymers are characterized in detail and the cationic ROP mechanism has been confirmed by kinetic study, chain end analysis and density functional theory (DFT) calculation. The modification of the unsaturated bonds in EVL repeating units via the thio-ene click reaction with mercapto-ended polysarcosine polysarcosine yields the amphiphilic grafting polymers. It is a CO2 fixation approach toward the functional poly(EVL-r-BBL) that is promising as a degradable polyester precursor for adhesive or surface-coating materials.

Photocurable Epoxy Acrylate Coatings Preparation by Dual Cationic and Radical Photocrosslinking

In this work, epoxy acrylate resin (EA) based on the industrial-grade bisphenol A-based epoxy resin (Ep6) and acrylic acid (AA) has been synthesized in order to develop hybrid resin comprising both epoxide group and reactive, terminal unsaturation. Obtained epoxy acrylate prepolymer was employed to formulate photocurable coating compositions containing, besides the EA binder, also cationic or radical photoinitiators. Hence, when cationic photoinitiators were applied, polyether-type polymer chains with pending acrylate groups were formed. In the case of free radical polymerization, epoxy acrylates certainly formed a polyacrylate backbone with pending epoxy groups. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Therefore, photopolymerization behavior of synthetized hybrid resin with various photoinitiators was determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) methods, and properties of cured coatings were investigated. The performance of the following type of photoinitiators was tested in the cationic photopolymerization: diaryliodonium cations or triarylsulfonium cations, and the following type of photoinitiators were used to induce free radical photopolymerization: α-hydroxyketones, acylphosphine oxides, and their mixtures. Lastly, the basic physicomechanical properties of cured coatings, such as tack-free time, hardness, adhesion, gloss, and yellowness index, were evaluated. Some structural factors and parameters of cationic and radical photoinitiators and photopolymerization mechanisms affecting the epoxy acrylate hybrid coatings performance are discussed.

Synthesis of Methanesulfonic Acid Directly from Methane: The Cation Mechanism or the Radical Mechanism?

In 2019, Diaz-Urrutia and Ott developed a high-yield method for direct conversion of methane to methanesulfonic acid and proposed a cationic chain reaction mechanism. However, Roytman and Singleton questioned this mechanism, and they favored a free-radical mechanism. In the present paper, we studied both the cationic chain and radical mechanisms and found the radical mechanism is more favorable, since it has a much lower energy barrier. However, the radical mechanism has not considered the effect of ions for the reaction taking place in oleum. Thus, we studied a simple model of a protonated radical mechanism, which further lowers the energy barrier. Although the true mechanism for the CH4 + SO3 reaction could be more complicated in electrolyte solutions, this model should be helpful for the further study of the mechanism of this reaction.

A Metal-free ionic liquid Dual-ion battery based on the reversible interaction of 1-Butyl-1-Methylpyrrolidinium cations with 1,4,5,8-Naphthalenetetracarboxylic dianhydride

The strong self-discharge reaction is one of the key factors limiting the practical use of dual-ion batteries, which leads to low coulombic efficiency and discharge capacity loss. It is of great significance to effectively reduce the self-discharge effect through redox reactions between organic electrodes and electrolytes. Herein, a dual-ion battery study that uses 1,4,5,8-naphthalenetetracarboxylic dianhydride as the anode and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide as the electrolyte is conducted. Due to the introduction of organic materials, the storage mechanism of cations on the anode is changed, which weakens the self-discharge effect. The battery shows a low self-discharge rate of 6.12% h−1 and a high discharge capacity of 114 mAh g−1. The voltage declines by only 0.14 V after resting for 15 h due to the strong redox reaction between Pyr14+ cations and the CO groups of NTCDA. Meanwhile, a double-layer filter paper system with small porosity is used to improve the cycle performance of the battery.

Scholl Reaction of Perylene‐Based Polyphenylene Precursors under Different Conditions: Formation of Hexagon or Octagon?

AbstractA planar dibenzo‐peri‐hexacene derivative (2) was synthesized via FeCl3‐mediated Scholl reaction from a cyclopenta‐fused perylene (CP) based polyphenylene precursor (1). However, an unexpected octagon‐containing, negatively curved molecule (3) was obtained in nearly quantitative yield when 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and methanesulfonic acid (MeSO3H) were used. Similar results were observed when two smaller‐sized precursors containing one (4) or two CP units (5) were tested. X‐ray crystallographic analysis also revealed that there is no close π–π stacking between neighboring π‐conjugated skeletons. DFT calculations suggest a radical cation mechanism in the presence of FeCl3 while an arenium ion pathway for the DDQ/MeSO3H mediated Scholl reaction, which can well explain the selective formation of hexagons and octagons under different conditions. The obtained compounds showed tunable optical and electrochemical properties.

Theoretical study on isomerization of α-acids: A DFT calculation

The α-acids contained in hops are one of the ingredients of beer. The isomerization of α-acids produces iso-α-acids, the main source of bitterness in beer. In this study, the isomerization mechanism of the α-acid, cohumulone, was elucidated by using density functional theory in conjunction with the polarizable continuum model or 3D-RISM integral equation theory of liquids. The calculated reaction diagram is consistent with experimental results; the activation free energy difference between the cis and trans isomers is in good agreement with the experimental estimate. The activation energy difference results from solvation energy. Additionally, a calculation of NMR chemical shifts showed that the proton position of isocohumulone is different from that proposed previously. The effect of Mg2+ cation on the isomerization was also investigated. Both the activation and reaction free energy are stabilized by the presence of Mg2+, which is consistent with experimental results. Water solvation reduces the activation free energy.

Molecular Dynamics Simulation of Clay Hydration Inhibition of Deep Shale

In the process of the exploitation of deep oil and gas resources, shale wellbore stability control faces great challenges under complex temperature and pressure conditions. It is difficult to reflect the micro mechanism and process of the action of inorganic salt on shale hydration with the traditional experimental evaluation technology on the macro effect of restraining shale hydration. Aiming at the characteristics of clay minerals of deep shale, the molecular dynamics models of four typical cations (K+, NH4+, Cs+ and Ca2+) inhibiting the hydration of clay minerals have been established by the use of the molecular dynamics simulation method. Moreover, the micro dynamics mechanism of typical inorganic cations inhibiting the hydration of clay minerals has been systematically evaluated, as has the law of cation hydration inhibition performance in response to temperature, pressure and ion type. The research indicates that the cations can promote the contraction of interlayer spacing, compress fluid intrusion channels, reduce the intrusion ability of water molecules, increase the negative charge balance ability and reduce the interlayer electrostatic repulsion force. With the increase in temperature, the inhibition of the cations on montmorillonite hydration is weakened, while the effect of pressure is opposite. Through the molecular dynamics simulation under different temperatures and pressures, we can systematically understand the microcosmic dynamics mechanism of restraining the hydration of clay in deep shale and provide theoretical guidance for the microcosmic control of clay hydration.

Insight into mechanism of divalent metal cations with different d-bands classification in layered double hydroxides for light-driven CO2 reduction

By varying divalent-metal cations (M = Mg2+, Ni2+, Cu2+, Zn2+) with different d-bands classification, MAl-LDHs were prepared and inspected for solar-driven CO2 conversion. The CO and CH4 yields over these LDHs followed an order of: NiAl-LDHs > CuAl-LDHs > ZnAl-LDHs > MgAl-LDHs. Coupled with multiple characterizations, the activity distinction was revealed from three crucial perspectives: (i) light harvesting, (ii) charge separation and transfer, (iii) surface reactions. The results affirmed that when d orbital was partially occupied with active electrons, both activation of CO2 and excitation of electrons were much easier to achieve. In-situ DRIFTS manifested that NiAl-LDHs and CuAl-LDHs exhibited more active reaction with CO2, which may be related to the upward shifts of the d-band center determined by Valence-band XPS. Particularly, these LDHs exhibited various catalytic stabilities, which was explained by Pearson׳s hard and soft acid–base (HSAB) principle for the first time in this field.

Undiscovered Multiple Roles of Multivalent Cations in the Pollutant Removal from Actual Water by Persulfate Activated by Carbon Materials

Enormous works have focused on the influence of natural organic matter (NOM) and anions (e.g., Cl– and HCO3–) on the pollutant removal efficiency by persulfate activation technologies. However, the impact of multivalent cations in actual water, e.g., Ca2+, on the pollutant removal has been overlooked in past research. In this work, we surprisingly found that pollutant degradation by the carbon materials activating persulfate in some actual water (e.g., groundwater) was higher than that in the buffer solution, and the bridging effect of multivalent cations in the actual water was the main reason. Through the bridging effect of multivalent cations, persulfate was bound on the surface of carbon materials to accelerate its decomposition. However, the promotion mechanism of multivalent cations on the radical and nonradical pathways of persulfate activation was different. Furthermore, the NOM aggregation was also promoted by multivalent cations, thereby inhibiting its quenching effect on the pollutant degradation. Besides that, these multivalent cations could lead to the coagulation of carbon materials, which was harmful for its catalytic performance. This work highlights the multiple roles of multivalent cations in the actual water in the persulfate activated by the carbon material process, and it was conducive to the practical application of Fenton-like technologies in actual water treatment.

Anodic Olefin Coupling Reactions: Elucidating Radical Cation Mechanisms and the Interplay between Cyclization and Second Oxidation Steps.

Anodic olefin coupling reactions generate new bonds and ring skeletons through a net two electron process that reverses the polarity of a known, electron-rich functional group. While much of the early work on the mechanism of these reactions focused on the initial oxidation and cyclization steps of the process, the second oxidation step also plays a central role in determining the success of the reaction. Evidence supporting this observation is presented, along with evidence that optimization of this second oxidation step is not enough to pull a poor cyclization to the desired product. Successful cyclization reactions require optimization of both processes.

Effects of various treatment procedures and pulse power modes on the photoelectric efficiency of Ti-PEO photocatalysts

In this study, various treatment methods were developed to achieve suitable structural phase control for the oxide layer of Ti plasma electrolytic oxidation (PEO) photocatalysts to improve their photoelectric conversion efficiency. To achieve the aforementioned purpose and to increase the doping efficiency, a three-stage PEO manufacturing procedure was developed and applied. In the first stage, the porous morphology and specific structural phases of a pretreated layer were controlled for doping preparation. In the second stage, doping elements were added into the surface and pores of the pretreated layer using the impregnation method. Finally, in the third stage, PEO was performed with different control parameters. The treatment factors in this study were the amount of manganese ion impregnation; the porosity, pore diameter, crystal structure, and carrier used in the treatment process; and the applied power mode. The effects of structural phase control, the Mn+ impregnation concentration, and the applied power modes on the carrier concentration were studied. The results indicated that the designed treatment method can effectively control the characteristics of oxide layers. By applying the impregnation method, the doping amount of Mn+ was increased more than five-fold compared with that in the single-step PEO treatment. Furthermore, to understand the treatment mechanism, the absorption spectrum, doping efficiency, Mn+ distribution, and mass transfer mechanism (of anions and cations) were investigated under direct, pulsed unipolar, and pulsed bipolar current. Finally, the functioning of the manufactured Mn: TiO2 (PEO) photocatalyst was verified with toluene under ultraviolet A, blue, and white LED light.

Front velocity dependence on vinyl ether and initiator concentration in radical‐induced cationic frontal polymerization of epoxies

AbstractFormulations containing vinyl ethers and epoxy were successfully polymerized through a radical‐induced cationic frontal polymerization mechanism, using an iodonium salt superacid generator with a peroxide thermal radical initiator and fumed silica as a filler. It was found that an increase of vinyl ether content resulted in higher front velocities for divinyl ethers in formulations with trimethylolpropane triglycidyl ether. However, increased hydroxymonovinyl ether either decreased the front velocity or suppressed frontal polymerization. The kinetic effects of the superacid generator and thermal radical initiator with varying vinyl ether content were also studied. It was observed that increasing concentrations of initiators increased the front velocity, with the system exhibiting higher sensitivity to the superacid generator concentration.

An Ion‐Pairing Approach to Stereoselective Metal‐Free Ring‐Opening Metathesis Polymerization

AbstractStereochemistry can have a profound impact on polymer and materials properties. Unfortunately, straightforward methods for realizing high levels of stereocontrolled polymerizations are often challenging to achieve. In a departure from traditional metal‐mediated ring‐opening metathesis polymerization (ROMP), we discovered a remarkably simple method for controlling alkene stereochemistry in photoredox mediated metal‐free ROMP. Ion‐pairing, initiator sterics, and solvation effects each had profound impact on the stereochemistry of polynorbornene (PNB). Simple modifications to the reaction conditions produced PNB with trans alkene content of 25 to >98 %. High cis content was obtained from relatively larger counterions, toluene as solvent, low temperatures (−78 °C), and initiators with low Charton values. Conversely, smaller counterions, dichloromethane as solvent, and enol ethers with higher Charton values enabled production of PNB with high trans content. Data from a combined experimental and computational investigation are consistent with the stereocontrolling step of the radical cationic mechanism proceeding under thermodynamic control.

An Ion‐Pairing Approach to Stereoselective Metal‐Free Ring‐Opening Metathesis Polymerization

Stereochemistry can have a profound impact on polymer and materials properties. Unfortunately, straightforward methods for realizing high levels of stereocontrolled polymerizations are often challenging to achieve. In a departure from traditional metal-mediated ring-opening metathesis polymerization (ROMP), we discovered a remarkably simple method for controlling alkene stereochemistry in photoredox mediated metal-free ROMP. Ion-pairing, initiator sterics, and solvation effects each had profound impact on the stereochemistry of polynorbornene (PNB). Simple modifications to the reaction conditions produced PNB with trans alkene content of 25 to >98 %. High cis content was obtained from relatively larger counterions, toluene as solvent, low temperatures (-78 °C), and initiators with low Charton values. Conversely, smaller counterions, dichloromethane as solvent, and enol ethers with higher Charton values enabled production of PNB with high trans content. Data from a combined experimental and computational investigation are consistent with the stereocontrolling step of the radical cationic mechanism proceeding under thermodynamic control.

Insight the roles of loosely-bound and tightly-bound extracellular polymeric substances on Cu2+, Zn2+ and Pb2+ biosorption process with Desulfovibrio vulgaris

The aim of this study is to explore the fate and mechanism of metal cations of biosorption in the Desulfovibrio vulgaris system (including bacterial cells and secreted loosely-bound extracellular polymeric substances (LB-EPS) and tightly-bound extracellular polymeric substances (TB-EPS)). The relative contribution of EPS (TB-EPS and LB-EPS) to the adsorption of three metal cations is much greater than that of bacterial cells, and the adsorption capacity of Pb2+ on EPS (TB-EPS and LB-EPS) is much greater than that of Cu2+ and Zn2+ (Pb2+ > Cu2+ > Zn2+). The order of absorption capacity was as follows: LB-EPS > TB-EPS > bacterial cells, the adsorption contribution of EPS (including TB-EPS and LB-EPS) to Cu2+, Zn2+ and Pb2+ accounted for total adsorption capacity was 82%, 83% and 86%, respectively. It was suggested that LB-EPS was the first reaction barrier of immobilization metal cations before metal cations was able to pass through EPS and react with cells. The adsorption process was dominated by complexation and electrostatic interaction. The three-dimensional excitation-emission matrix (3D-EEM) identified two main fluorescence peaks of the aromatic and tryptophan protein-like substances in EPS. According to the synchronous fluorescence spectra, the tryptophan protein-like substances were gradually quenched with increased metal cations concentrations, which the quencher mechanism is dynamic quenching. The findings of this work are significant to reveal the fate of Cu2+, Zn2+ and Pb2+ during its sorption process onto Desulfovibrio vulgaris, and provide useful information of the interaction between Desulfovibrio vulgaris and its secreted EPS with metal cations.