Cation Modification Research Articles

Potassium doping-induced variations in the structures and photoelectric properties of a MAPbI3 perovskite and a MAPbI3/TiO2 junction.

It has been experimentally demonstrated that mixed metallic cation modification could be an effective strategy to enhance the performance and stability of perovskite-based solar cells (PSCs). However, there is limited microscopic understanding at the atomic/molecular level of the behavior of small radius alkali metal cation doping in both perovskite materials and perovskite/TiO2 junctions. Here, we perform a first-principles density functional theory study on the doping-induced variation of the geometric and electronic structures of MAPbI3 (MA = methylammonium) and the MAPbI3/TiO2 junction. The impacts of different doping methods, and different charge states and locations of the given dopants have been investigated. At first, we theoretically confirm that the structures doped by K+ are the most thermally stable compared to the structures doped by the other charge states of K, and that K+ dopants prefer to modify the perovskite lattice interstitially and stay near the MAPbI3/TiO2 interface. Meanwhile, we find that a severe geometric deformation occurs if two doped lattices come into contact directly, indicating that the lattice may rapidly collapse from the interior if the doping concentration is too high. Additionally, we observe that K+ doped interstitially near the MAPbI3/TiO2 interface causes the intensive distortion of the surface Ti-O bonds and severe bond-length fluctuations. Consequently, this results in distorted TiO2 bands of the interfacial layer and a slight decrease of the band offset of conduction bands between two phases. This work complements experiments and provides a better microscopic understanding of the doping modification of the properties of perovskite materials and PSCs.

Razvoj i karakterizacija raznih katjonskih sorbenata na bazi lignocelulozne kore tikvice

The aim of this study is to develop miscellaneous cationic sorbents based on the lignocellulosic biomass of Lagenaria vulgaris fruit, with the property of efficient sorption of anionic pollutants from aqueous solutions. The lignocellulosic gourd shell (LGS biomass), as a potentially valuable agro-waste, was examined and used for the synthesis of sorbents. The preparation of synthesis precursor (LVAT) was performed by alkaline pretreatment of LGS biomass. Pretreatment under weak alkaline conditions with green carbonate solution was carried out for partial delignification and extraction of depolymerized hemicellulose, thereby achieving higher material porosity and activation of cellulose microfibrils. This activation involves the translation of available -OH functional groups into -ONa form (alkali-cellulose), while maintaining the initial biomass composition. Synthesis of the cationic sorbents was performed in three ways. Different N-reagents, such as tertiary amino and quaternary ammonium compounds, were used in the cation modification of LGS biomass and LVAT precursor, to determine the effects of reagent structure and hydrophobicity on the synthesis outcome, and primarily on the sorption properties of the resulting sorbents. The synthesized cationic sorbents were characterized by physico-chemical methods and tested for the removal of anionic pollutants from water, especially phosphates and nitrates. The various chemical modifications of lignocellulosic biomass provide a scientific contribution to a better understanding of the mechanism of anions sorption on the sorbent surface.

Effect of Cation Modification on the Physicochemical Properties and CO2 Solubility: Nonfluorinated Phosphonium-Based Ionic Liquids Incorporating a Dioctylsulfosuccinate Anion

In the current work, a series of phosphonium-based monocationic and dicationic ionic liquids (trihexyltetradecylphosphonium dioctylsulfosuccinate, [P6,6,6,14]DOSS; trioctyltetradecylphosphonium dio...

Enhanced formaldehyde oxidation performance over Pt/ZSM-5 through a facile nickel cation modification

Development of supported noble metal catalysts with ultralow noble metal loading, commercially available support with good stability and low cost, as well as facial synthesis route for indoor HCHO removal at room temperature is desirable. Herein, enhanced HCHO oxidation performance over Pt/ZSM-5 is achieved through a facile nickel cation modification. The introduction of a proper amount of nickel cations enhances nearby hydroxyl density around the Pt active sites and leads to great enhancement in HCHO oxidation activity. Pt-Ni/ZSM-5 exhibits a 90% HCHO conversion and a 100 h good stability at 30 °C with a low 0.1 wt% Pt amount and ultralow 0.05 wt% Ni addition, an initial 50 ppm HCHO and space velocity of 30000 mL h−1 g−1, which is among the best of the state-of-the-art Pt-based catalysts in consideration with Pt utilization efficiency. The facile ionic exchange approach employed in this study provides an important implication into the design of economic zeolite based catalysts for HCHO removal and other hydroxyls related reactions.

Borazine-CF3- Adducts for Rapid, Room Temperature, and Broad Scope Trifluoromethylation.

A fluoroform-derived borazine CF3- transfer reagent is used to effect rapid nucleophilic reactions in the absence of additives, within minutes at 25 °C. Inorganic electrophiles spanning seven groups of the periodic table can be trifluoromethylated in high yield, including transition metals used for catalytic trifluoromethylation. Organic electrophiles included (hetero)arenes, enabling C-H and C-X trifluoromethylation reactions. Mechanistic analysis supports a dissociative mechanism for CF3- transfer, and cation modification afforded a reagent with enhanced stability.

Borazine‐CF3− Adducts for Rapid, Room Temperature, and Broad Scope Trifluoromethylation

AbstractA fluoroform‐derived borazine CF3− transfer reagent is used to effect rapid nucleophilic reactions in the absence of additives, within minutes at 25 °C. Inorganic electrophiles spanning seven groups of the periodic table can be trifluoromethylated in high yield, including transition metals used for catalytic trifluoromethylation. Organic electrophiles included (hetero)arenes, enabling C−H and C−X trifluoromethylation reactions. Mechanistic analysis supports a dissociative mechanism for CF3− transfer, and cation modification afforded a reagent with enhanced stability.

Nanocellulose size regulates microalgal flocculation and lipid metabolism.

Harvesting of microalgae is a cost-consuming step for biodiesel production. Cellulose has recently been studied as a biocompatible and inexpensive flocculant for harvesting microalgae via surface modifications such as cation-modifications. In this study, we demonstrated that cellulose nanofibrils (CNF) played a role as a microalgal flocculant via its network geometry without cation modification. Sulfur acid-treated tunicate CNF flocculated microalgae, but cellulose nanocrystals (CNC) did not. In addition, desulfurization did not significantly influence the flocculation efficiency of CNF. This mechanism is likely related to encapsulation of microalgae by nanofibrous structure formation, which is derived from nanofibrils entanglement and intra-hydrogen bonding. Moreover, flocculated microalgae were subject to mechanical stress resulting in changes in metabolism induced by calcium ion influx, leading to upregulated lipid synthesis. CNF do not require surface modifications such as cation modified CNC and flocculation is derived from network geometry related to nanocellulose size; accordingly, CNF is one of the least expensive cellulose-based flocculants ever identified. If this flocculant is applied to the biodiesel process, it could decrease the cost of harvest, which is one of the most expensive steps, while increasing lipid production.

Effect of Sintering Temperature on the Micro Strain and Magnetic Properties of Ni-Zn Nanoferrites

In this study, nanocrystalline ferrite powders with the composition <TEX>$Ni_{0.5}Zn_{0.5}Fe_2O_4$</TEX> were prepared by the autocombustion method. The obtained powders were sintered at <TEX>$800^{\circ}C$</TEX>, <TEX>$900^{\circ}C$</TEX> and <TEX>$1,000^{\circ}C$</TEX> for 4 h in air atmosphere. The as-prepared and the sintered powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and magnetization studies. An increase in the crystallite size and a slight decrease in the lattice constant with sintering temperature were observed, whereas microstrain was observed to be negative for all the samples. Two significant absorption bands in the wave number range of the <TEX>$400cm^{-1}$</TEX> to <TEX>$600cm^{-1}$</TEX> have been observed in the FT-IR spectra for all samples which is the distinctive feature of the spinel ferrites. The force constants were found to vary with sintering temperature, suggesting a cation redistribution and modification in the unit cell of the spinel. The M-H loops indicate smaller coercivity, which is the typical nature of the soft ferrites. The observed variation in the saturation magnetization and coercivity with sintering temperature has been attributed to the role of surface, inhomogeneous cation distribution, and increase in the crystallite size.

Effect of Cation Structure Modification of Ionic Liquids for Lithium-Ion Batteries

Ionic liquid (ILs) have received much attention next to traditional carbonates based electrolytes, due to their high oxidation potential (above 5V vs Li/Li+ for typical pyrrolidinium based ILs) [1-2], excellent thermal stability[3], negligible vapor pressure and non-flammable nature[3]. Nevertheless, the high price of ILs represents a major drawback for the commercialization of these electrolyte materials. Furthermore, for the use of graphite anodes cells, severe reductive decomposition of ILs can be triggered by an intercalation of cation of the ILs into graphite layer[4], which results in graphite exfoliation. As a result, less reversible capacity can be achieved during the charge/discharge process. In recent years, many approaches have been pursued to optimize (1-butyl-1-methylprrolidinium bis(trifluoromethane-sulfonyl)imide (Pyr14TFSI)) based electrolyte to obtain a suitable electrolyte formulation for application in lithium-ion batteries[4-5]. More attention has been paid to accommodate the incompatibility with carbon anodes, such as mixture use of ILs and organic solvents[1] , addition of certain amount of SEI additives (e.g. VC[6-7], ClEC[7-8], FEC and ES[6-7]) and substitution of conductive salts[4-5]. The basic strategy is to form an ideal surface layer on graphite[4], which can offer sufficient ability to prevent the intercalation of the cation of ILs and avoid a continuous electrolyte decomposition of electrolyte. In order to enrich the knowledge of the ionic liquid performance in lithium ion batteries, the concept of this work is set on IL with organic functional group modifications. The structure medication is considered to be an easy way for synthesis approaching and favorable for fast change of physical and chemical properties. In this work, we synthesized a series of ester group modified ILs from Pyr14TFSI, based on our computational screening results. The synthesized ILs methyl-methylcarboxymethyl prrolidinium bis(trifluoromethane-sulfonyl)imide (MMMPyrTFSI)) and methyl-propylcarboxymethyl prrolidinium bis(trifluoromethane-sulfonyl)imide (MPMPyrTFSI)) show high oxidation stability (ca 5.4 V vs Li/Li+). TGA measurements show that modified ILs are thermally stable above 300oC. Moreover, electrolytes based either on MMMPyrTFSI or MPMPyrTFSI show excellent electrochemical performance in Li/LiFePO4cells, display a stable reversible capacity of 150 mAh/g at 1C and 110 mAh/g at higher rate of 5C. For the graphite anode, MPMPyrTFSI based electrolyte shows stable capacity of 330 mAh/g at 0.1C with an efficiency of 99% during the 100 cycles. These interesting results illustrate cation modification of ILs as an effective way for improved performance of ILs in lithium-ion batteries.

Solvent-free selective hydrogenation of o-chloronitrobenzene to o-chloroaniline over alumina supported Pt nanoparticles

A supported Pt/Al2O3 catalyst was prepared by immobilizing preformed colloidal Pt nanoparticles on Al2O3. The particle size and size distribution of Pt particles on Al2O3 remained the same as the colloidal nanoparticles. Selective hydrogenation of o-chloronitrobenzene to o-chloroaniline was performed on the as-prepared Pt/Al2O3 nanocatalyst without using any solvent and 88.5% selectivity to o-chloroaniline at 98.2% conversion of o-chloronitrobenzene was achieved. Further catalytic experiments with metal cation modification showed that some metal cations could improve the activity in various degrees while maintaining the high selectivity. Especially, 99.8% selectivity to o-chloroaniline at ~100% conversion was attained with Sn4+.

Изучение влияния катионного и анионного модифицирования на активность CuZnAlO-катализатора в реакции окислительного обессеривания дибензотиофена в модельном дизельном топливе

Изучение влияния катионного и анионного модифицирования на активность CuZnAlO-катализатора в реакции окислительного обессеривания дибензотиофена в модельном дизельном топливе

ChemInform Abstract: Effect of Ion Doping on the Electrochemical Performances of LiFePO4—Li3V2 (PO4)3 Composite Cathode Materials

AbstractReview: 81 refs.

Comprehensive Investigation on the Thermal Stability of 66 Ionic Liquids by Thermogravimetric Analysis

The thermal stabilities of 66 ionic liquids (ILs) were investigated using the thermogravimetric analysis (TGA) method. Isothermal TGA studies on the ILs showed that ILs exhibit decomposition at temperatures lower than the onset decomposition temperature (Tonset), which is determined from ramped temperature TGA experiments. Thermal decomposition kinetics of ILs was analyzed using pseudo-zero-order rate expression and their activation energy was obtained. Parameter T0.01/10h, the temperature at which 1% mass loss occurs in 10 h, was used to evaluate the long-term thermal stability of ILs. The thermal stability of the ILs was classified to five levels according to Tonset. The ILs thermal stability is dependent on the structure of ILs, i.e., cation modification, cation and anion type. The correlations between the stability and the hydrophilicity of ILs were discussed. Finally, the thermal stabilities of acetate-based ILs, amino acid ILs, and dicyanamide ILs were analyzed.

Effect of cation exchange on dimethyl methylphosphonate permeation kinetics in a pentablock hydrocarbon ionomer and a perfluorocarbon ionomer

The present work is concerned with the effect of cation exchange, with calcium, aluminum and cupric cations, on the permeation kinetics of dimethyl methylphosphonate (DMMP) in a pentablock ionomer (Nexar™) and a perfluoroionomer (Nafion™). The diffusion constant was determined by matching a Fickian solution to early time data, with a zero-time shift, initially attributed to the effect of immobilization. The diffusion time-lag relation was applied in an expanded form to include contributions of immobilization and relaxation. The primary effect of cation exchange was a marked reduction in diffusion constant and introduction of significant relaxation. The effects were explored in a two step procedure in which the sample was first exposed to DMMP vapor at activity 0.6 and then at activity 0.8. In cation modified Nexar at the lower activity the delay in onset of permeation was due solely to immobilization. The delay was absent at the higher activity, indicating that extent of immobilization was unchanged with increased concentration, but approach to steady state was still relaxation controlled. In cation modified Nafion delay in onset of permeation was dominated by relaxation, but kinetics at the higher activity was essentially Fickian. The strong relaxation effects appear to be a consequence of cation modification, which results in a network of ionic crosslinks formed by multivalent cation–sulfonate interactions. The combined analytical and experimental procedure developed in this study provided a systematic set of values for the effect of cation exchange and ionomer characteristics on parameters controlling DMMP permeation kinetics.

Thermodynamic Studies of Ionic Hydration and Interactions for Amino Acid Ionic Liquids in Aqueous Solutions at 298.15 K

Amino acid ionic liquids are a special class of ionic liquids due to their unique acid-base behavior, biological significance, and applications in different fields such as templates in synthetic chemistry, stabilizers for biological macromolecules, etc. The physicochemical properties of these ionic liquids can easily be altered by making the different combinations of amino acids as anion along with possible cation modification which makes amino acid ionic liquids more suitable to understand the different kinds of molecular and ionic interactions with sufficient depth so that they can provide fruitful information for a molecular level understanding of more complicated biological processes. In this context, volumetric and osmotic coefficient measurements for aqueous solutions containing 1-ethyl-3-methylimidazolium ([Emim]) based amino acid ionic liquids of glycine, alanine, valine, leucine, and isoleucine are reported at 298.15 K. From experimental osmotic coefficient data, mean molal activity coefficients of ionic liquids were estimated and analyzed using the Debye-Hückel and Pitzer models. The hydration numbers of ionic liquids in aqueous solutions were obtained using activity data. Pitzer ion interaction parameters are estimated and compared with other electrolytes reported in the literature. The nonelectrolyte contribution to the aqueous solutions containing ionic liquids was studied by calculating the osmotic second virial coefficient through an application of the McMillan-Mayer theory of solution. It has been found that the second osmotic virial coefficient which includes volume effects correlates linearly with the Pitzer ion interaction parameter estimated independently from osmotic data as well as the hydrophobicity of ionic liquids. The enthalpy-entropy compensation effect, explained using the Starikov-Nordén model of enthalpy-entropy compensation, and partial molar entropy analysis for aqueous [Emim][Gly] solutions are made by using experimental Gibb's free energy data and literature enthalpy data. This study highlights that the hydrophobic interaction persists even in the limit of infinite dilution where the hydration effects are usually dominant, implying importance of hydrophobic hydration. Analysis of the results further shows that the hydration of amino acid ionic liquids occurs through the cooperative H-bond formation with the kosmotropic effect in contrast to the usual inorganic salts or hydrophobic salts like tetraalkylammonium halides.

Chemical modification for improving activity and stability of lipase B from Candida antarctica with imidazolium-functional ionic liquids

Various imidazolium-functional ionic liquids (ILs) composed of different cations and anions were grafted onto Candida antarctica lipase B (CALB) through lysine coupling, and 4-6 of the 9 primary amino groups of the lysine residues were modified. The catalytic activity and stability were investigated in a p-nitrophenyl palmitate hydrolysis reaction. After modification, CALB was activated and achieved a high catalytic efficiency in the aqueous phase (e.g., [HOOCMMIm][Cl] modification showed a 1.5-fold increase in the catalytic efficiency). The thermostability and organic solvent tolerance were significantly increased with the ILs modification (e.g., [HOOCBMIm][Cl] owned kosmotropic cation and chaotropic anion modification showed a 7-fold thermostability increase at 70 °C, 1-fold increase in 50% aqueous dimethylformamide and 5-fold increase in 50% aqueous methanol). Conformation changes were confirmed by fluorescence spectroscopy, circular dichroism spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy.

A photoactive titanate with a stereochemically active Sn lone pair: Electronic and crystal structure of Sn2TiO4 from computational chemistry

TiO2 remains the most widely studied metal oxide for photocatalytic reactions. The standard approach to reduce the band gap of titania, for increasing the absorption of visible light, is anion modification. For example the formation of an oxynitride compound, where the nitrogen 2p states decrease the binding energy of the valence band. We demonstrate that cation modification can produce a similar effect through the formation of a ternary oxide combining Ti and an ns2 cation, Sn(II). In Sn2TiO4, the underlying Ti 3d conduction states remain largely unmodified and an electronic band gap of 2.1eV (590nm) is predicted by hybrid density functional theory. Our analysis indicates a strong potential for Sn2TiO4 in visible-light driven photocatalysis, which should prove superior to the alternative (SnO2)1−x(TiO2)x solid-solution.

Nanocomposite structure and reactivity of perovskites based on lanthanum manganites

Data on the real/defect structure of anion-excess lanthanum manganites are analyzed. It is shown that low-temperature materials, especially those synthesized with the use of organic additives, form nanocomposite structure due to stabilization of manganese and dopant cations in highly charged states (≥4+) at anion excess. It is established that domains (layers) with perovskite structure containing point defects are separated/intergrown by extended defect regions enriched with lanthanum or promoter cations. It is noted that the composition and concentration of extended defects are controlled by the conditions of synthesis, the calcination temperature, and the nature of the promoter; these defects, which are partly retained after high-temperature treatment, can affect the functional properties of materials. Features of the cation and anion modification of lanthanum manganites and the reactivity of nanocomposite structures with respect to oxidation reactions are analyzed. It is concluded that at a high content of weakly bound oxygen and a noticeable mobility of the lattice oxygen, the activity of these materials in various oxidation reactions is determined by their defect structure and specificity of the catalytic action.

Communication: Are hydrodynamic models suited for describing the reorientational dynamics of ions in ionic liquids? A case study of methylimidazolium tetra(hexafluoroisopropoxy)aluminates

We report on dielectric relaxation spectra of six homologous ionic liquids (ILs) with tetra(hexafluoroisopropoxy)aluminate ([Al(hfip)(4)](-)) as a common anion. The dominating mode on the time scale of several 100 ps mainly results from cation reorientation. Because the viscosities are low and cation modification does not substantially change the viscosity, these ILs are interesting candidates for testing hydrodynamic models of rotational dynamics. The calculated hydrodynamic volumes are extraordinarily low, and roughly agree with values calculated from literature data for ILs with the same cations, but different anions. Comparison with magnetic relaxation data shows that the peculiarities are founded in the rotational dynamics and are not special to dielectric relaxation. Collectively, the observations make a strong case against the applicability of hydrodynamic approaches to the orientational dynamics of ions.

Activity and thermal stability of lysozyme in alkylammonium formate ionic liquids—influence of cation modification

The stability and activity of hen's egg white lysozyme in the presence of four protic room temperature ionic liquids (ethylammonium formate (EAF), propylammonium formate (PAF), 2-methoxyethylammonium formate (MOEAF) and ethanolammonium formate (EtAF)) have been investigated. Near UV CD experiments have been used to determine protein structure in aqueous solutions of 25 wt%, 50 wt% and 75 wt% ionic liquid, and to assess the proteins ability to refold after heating to 90 °C. It was determined that EAF and MOEAF are similarly effective refolding additives, while PAF is more effective at promoting refolding at concentrations up to ∼62.5 wt%, but at higher PAF concentrations the protein spontaneously denatures. Both of these effects are attributed to the increased hydrophobicity of the cation. EtAF is shown to stabilise lysozyme against unfolding at high temperature, and renaturing appears to be near complete upon cooling. Studies of enzyme kinetics reveal increased protein activity in the presence of all ionic liquids examined, but the most significant increase is noted for EtAF, where rates are six times higher than those determined for lysozyme in buffered water.