Alkylammonium Cations Research Articles

Spontaneous multilayer formation of an amphiphilic alkylammonium cation with a long hydrocarbon chain at an air-clay dispersion interface

Langmuir film formation behavior of a trimethylammonium cation with a long hydrocarbon chain (CH3(CH2)29N+(CH3)3, C30TMA+) was investigated. To weaken the hydrophobic interactions between the hydrocarbon chains, methanol was added to the subphases. A solution of C30TMA+·I– was spread at air-water and air-clay dispersion interfaces. The surface pressure-molecular area curves of the floating C30TMA+ films showed that the surface pressure at the collapse point decreased with increasing methanol concentration in water and in the dispersion, indicating the weakening of the hydrophobic interaction. For the floating films on clay dispersions, the molecular area at the collapse point decreased with increasing methanol concentration. The decrease in the molecular area indicates multilayer formation of C30TMA+ at the air-dispersion interface at a low surface pressure, which was confirmed by the atomic force microscope images and X-ray diffraction (XRD) patterns of the deposited films. The out-of-plane and in-plane XRD results of the multilayers showed not only layer-by-layer ordering, but also lateral ordering of the closely packed C30TMA+ cations in each layer.

Cyclic versus Linear Alkylammonium Cations: Preventing Phase Transitions at Operational Temperatures in 2D Perovskites.

Two-dimensional lead halide perovskites offer numerous attractive features for optoelectronics owing to their soft, deformable lattices and high degree of chemical tunability. While alteration of the metal and halide ions gives rise to significant modification of the bandgap energy, the organic spacer cations offer in-roads to tuning phase behavior and more subtle functionalities in ways that remain to be understood. Here, we study six variations of 2D perovskites changing only the organic spacer cations and demonstrate that these components intrinsically impact material response in important ways such as altering crystallographic structure, temperature-induced phase transitions, and photoluminescence emission. Two-dimensional perovskites containing commonly utilized aliphatic linear spacers, such as butylammonium, undergo phase transitions near room temperature. These transitions and temperature changes induce spacer-dependent variations in the emission spectra. Conversely, 2D perovskites comprising cyclic aliphatic spacers, such as cyclobutylammonium, are found to lack first-order phase transitions. These cyclic molecules are more sterically hindered within the crystal lattice, leading to temperature-induced contraction or expansion along certain crystallographic planes but no other significant thermal effects; additionally, they undergo changes in their emission spectra that cannot be explained by simple thermal expansion. Given the similarities in the dielectric and chemical makeup of this set of six alkylammonium molecules, these results are unexpected and suggest a large structural and thermal phase space via spacer manipulation that could lead to improved 2D perovskite functionalization.

Direct synthesis of high silica SSZ-16 zeolite with extraordinarily superior performance in NH3-SCR reaction

The development of Cu ion-exchanged small-pore zeolites with excellent performance and high hydrothermal stability in NH3-SCR reaction is of great importance. However, many frameworks of the small-pore zeolites are Al-rich, for instance, Cu-SSZ-16 zeolite with Si/Al ratio always no more than 5, showing relatively low hydrothermal stability. In this work, inspired by theoretical calculation for the interaction between organic structural directing agents (OSDAs) and zeolite framework, high silica SSZ-16 zeolite with Si/Al ratio at 6.7 was directly synthesized using an economical diquaternary alkylammonium cation as an OSDA. After exchanged with Cu ion, the Cu-SSZ-16 catalyst shows extraordinarily superior performance in NH3-SCR reaction even after hydrothermal aging at 900 °C. The designed synthesis combined with excellent performance as well as high hydrothermal stability of the high silica SSZ-16 zeolite might provide an attractive alternative candidate for NH3-SCR catalyst on diesel vehicles and non-road mobile machinery in the future.

Dimensional Reduction of Cs2AgBiBr6 Using Alkyl Ammonium Cations CH3(CH2)nNH3+ (n = 1, 2, 3, and 6) of Varying Chain Lengths and Their Role in Structural and Optoelectronic Properties.

Tuning the dimensionality in halide perovskites provides an opportunity to obtain the properties desired for optoelectronic devices. In this work, we demonstrate the dimensional reduction of 3D halide double-perovskite Cs2AgBiBr6 by systematically introducing alkylammonium organic spacer CH3(CH2)nNH3+ (n = 1, 2, 3, and 6) of varying chain lengths. The single crystals of these materials were grown, and their structures were studied at 23 and -93 °C. The ethylammonium cation led to a formation of a 0D material, whereas all the other three higher alkyl ammonium spacers resulted in two-dimensional materials. The parent material possessed symmetric octahedra, whereas the modified samples led to both inter- and intra-octahedral distortion, thereby reducing the symmetry of constituent octahedra. The reduction in dimensionality led to a blue shift in the optical absorption spectrum. All these low-dimensional materials show excellent stability, and they are employed as absorbers for solar photovoltaics.

Structural Insights into Layered Tetrahalocuprates(II) Based on Small Unsaturated and Cyclic Primary Ammonium Cations.

Layered hybrid halometallates represent a promising class of multifunctional materials, yet with many open challenges regarding the interaction between building blocks. In this work, we present a synthetic and analytical methodology for the efficient synthesis and structural analysis of a series of novel tetrahalocuprate(II) hybrids based on small alkylammonium cations. Observed robustness in geometrical motifs provided a platform for crystal structure determination, even from the complex laboratory powder diffraction data. The slight differences in inorganic layer geometry and severe differences in organic bilayer packing are quantified using well-established descriptors for these materials, and dependences of geometric parameters on anion and cation choice are accounted for. Temperature dependence of structural parameters for one of the tetrachlorocuprate hybrids that was chosen as a model unveils a possible geometrical origin of thermochromism in these materials.

Linking Molecular Structure and Lubrication Mechanisms in Tetraalkylammonium Orthoborate Ionic Liquids

While ionic liquids (ILs) have gained wide interest as potential alternative lubricants able to meet the requirements of next-generation tribological systems owing to their unique physico-chemical properties and promising lubricating behavior, our understanding of the mechanisms by which ILs reduce friction and/or wear is still elusive. Here, we combine macroscale tribological experiments with surface-analytical measurements to shed light on the lubrication mechanisms of a class of halogen-free ILs, namely tetraalkylammonium orthoborate ILs, at steel/steel sliding contacts. The tribological results indicate an improvement of the friction-reducing properties of these ILs as the length of the alkyl chains attached to ammonium cations increases. X-ray photoelectron spectroscopy analyses provide further evidence for the dependence of the lubrication mechanism of tetraalkylammonium orthoborate ILs on the IL structure. In the case of tetraalkylammonium orthoborate ILs with asymmetric ammonium cations containing a long alkyl chain, no sacrificial tribofilms were formed on steel surfaces, thus suggesting that the friction-reducing ability of these ILs originates from their propensity to undergo a pressure-induced morphological change at the sliding interface that leads to the generation of a lubricious, solid-like layered structure. Conversely, the higher friction response observed in tribological tests performed with tetraalkylammonium orthoborate ILs containing more symmetric ammonium cations and short alkyl chains is proposed to be due to the inability of this IL to create a transient interfacial layer owing to the reduced van der Waals interactions between the cationic alkyl chains. The resulting hard/hard contact between the sliding surfaces is proposed to lead to the cleavage of boron-oxygen bonds in the presence of water to form species that then adsorb onto the steel surface, including trivalent borate esters and oxalic acid from the decomposition of orthoborate anions, as well as tertiary amines from the degradation of alkylammonium cations induced by hydroxides released during the orthoborate decomposition reaction. The results of this work not only establish links between the molecular structure of a class of halogen-free ILs, their lubricating performance, and lubrication mechanism, but also provide evidence for the existence of multiple mechanisms underpinning the promising lubricating properties of ILs in general.

Stabilization of the Alkylammonium Cations in Halide Perovskite Thin Films by Water-Mediated Proton Transfer.

The development of alkylammonium lead trihalide perovskite (ALHP) photovoltaics has grown rapidly over the past decade. However, there are remaining critical challenges, such as proton defects, which can lead to the material instability of ALHPs. Although specific strategies, including the use of halide additives, have significantly reduced the defects, a fundamental understanding of the defect passivation mechanism remains elusive. Herein, an approach and mechanism for minimizing proton defects in ALHP crystals by adding ionized halides to the perovskite precursor solution are reported. This work clarifies that the ionized halides induced proton transfer from H2 O to the alkylammonium cation in the precursor solution, stabilizing the ALHP crystals. The fundamental characteristics of ALHP and its precursors are examined by X-ray diffraction, transmittance electron microscopy, in situ extended X-ray absorption fine structure, Fouriertransform NMR spectroscopy, and Fouriertransform infrared spectroscopy. The findings from this work will guide the development of highly stable ALHP crystals, enabling efficient and stable optoelectronic ALHP devices.

Properties of iron-functionalized organoclays. Consequences for pertechnetate sequestration

Nuclear waste repository designs require backfill materials capable of immobilizing contaminants, including high mobility pertechnetate (TcO4−). Bentonite backfill can be functionalized with organic or inorganic species to optimize the clay's retention capacity for TcO4−. The current work examines the physicochemical properties of organoclays that were functionalized with alkylammonium cations of different sizes and iron. The organoclays were characterized, and the physicochemical characteristics were correlated with the extent of TcO4− removal. The results show that the clay zeta potential and carbon content are valuable indicators for predicting the organoclay's ability to sequester TcO4− from aqueous solution. Furthermore, the Fe functionalization improves TcO4− removal.

Controlling the Photofunctionality of a Polyanionic Heteroleptic Copper(I) Photosensitizer for CO2 Reduction Using Its Ion-pair Formation with Polycationic Ammonium in Aqueous Media.

A water-soluble trianionic heteroleptic copper(I) photosensitizer having four sulfonate groups (CuPS3- ) was found to afford the 1 : 2 ion-pair adduct with dicationic alkylammonium (hexamethonium) cations (HM2+ ) in aqueous media, leading to exhibit excellent photophysical and photocatalytic performances owing to the substantial suppression of water-derived non-radiative decay of the photoexcited state.

Controlling the Photofunctionality of a Polyanionic Heteroleptic Copper(I) Photosensitizer for CO2 Reduction Using Its Ion‐pair Formation with Polycationic Ammonium in Aqueous Media

AbstractA water‐soluble trianionic heteroleptic copper(I) photosensitizer having four sulfonate groups (CuPS3−) was found to afford the 1 : 2 ion‐pair adduct with dicationic alkylammonium (hexamethonium) cations (HM2+) in aqueous media, leading to exhibit excellent photophysical and photocatalytic performances owing to the substantial suppression of water‐derived non‐radiative decay of the photoexcited state.

Synthesis and characterization of heterometallic rings templated through alkylammonium or imidazolium cations.

We report the synthesis and structural characterization of a series of heterometallic rings templated via alkylammonium or imidazolium cations. The template and preference of each metal's coordination geometry can control the structure of heterometallic compounds, leading to octa-, nona-, deca-, dodeca-, and tetradeca-metallic rings. The compounds were characterized by single-crystal X-ray diffraction, elemental analysis, magnetometry, and EPR measurements. Magnetic measurements show that the exchange coupling between metal centres is antiferromagnetic. EPR spectroscopy shows that the spectra of {Cr7Zn} and {Cr9Zn} have S = 3/2 ground states, while the spectra of {Cr12Zn2} and {Cr8Zn} are consistent with S = 1 and 2 excited states. The EPR spectra of {(ImidH)-Cr6Zn2}, {(1-MeImH)-Cr8Zn2}, and {(1,2-diMeImH)-Cr8Zn2} include a combination of linkage isomers. The results on these related compounds allow us to examine the transferability of magnetic parameters between compounds.

Electrochemical properties of carbonized bentonite

Organomodified bentonites were obtained by modification of bentonite clay from local mine Bogovina, with four different alkylammonium ions in the amounts that correspond to cation exchange capacity. Carbonized bentonites, obtained by pyrolyzing the organomodified bentonites in the flow of nitrogen, were characterized using XRD, low-temperature N2 physisorption and Raman spectroscopy. Structural and textural properties of carbonized bentonites depended on the arrangement of alkylammonium cations in the paternal organomodified bentonite, while the Raman spectroscopy confirmed the presence of amorphous carbon. The obtained carbonized bentonites were used for modification of the carbon paste electrode. The modified electrodes were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The electrosorption of chloride and sulfate anions on carbonized bentonites was studied by chronocoulometry. The results were interpreted in the terms of surface groups and textural properties of the carbonized bentonites.

Addressing the Role of 2D Domains in High‐Dimensionality Ruddlesden–Popper Perovskite for Solar Cells

High‐dimensionality Ruddlesden–Popper (RP) perovskites, with general formula R2An−1BnX3n+1 and high n values (n ≥ 5), are regarded as viable materials for photovoltaics because they feature higher stability if compared to the 3D perovskite, i.e., ABX3, still maintaining good charge absorption and transport properties. When integrated into the actual solar cells, however, scattered, sometimes contradictory results are reported among different deposition procedures and different cations, especially for higher n resulting in not uniform morphology and mixed composition. Herein, high‐dimensionality RP perovskites with n = 1, 4, 10, 20, and 40 values are systematically investigated considering the interplay between the formation of 2D domains, their distribution along the active layer, the active layer thickness, and the solar cells’ performance. Given the complexity of the investigated system, combined advanced structural/morphological analyses are performed to explain solar cells’ performance, finding that the 2D phase segregates at the interface with the top electrode, acting as a barrier for charge extraction, overall decreasing the short‐circuit current (Jsc). Reducing the relative amount of bulky alkylammonium cation with respect to the methylammonium, the 2D perovskite overlayer is intentionally decreased leading to a recovery of the Jsc values, corroborating the hypothesis.

Design Principles for Flow Batteries: Cation Dependent Membrane Resistance and Active Species Solubility

Aqueous redox flow batteries are generally adapted from polymer electrolyte membrane fuel cells that use proton exchange membranes to balance the charge of the cell. Such membranes are well understood and exhibit excellent performance in acidic electrolytes via transport of protons. For neutral pH flow batteries however, the primary cation in solution is not H+, but the cation of the active material or supporting electrolyte salt.The nature of the cation in solution, e.g., hydrated ionic radius and charge density, significantly affects the transport resistance through the membrane and thus the area specific resistance of the cell, a critical parameter that needs to be minimized for high power applications such as flow batteries. Additionally, different cations result in vastly different solubilities of active materials based on redox active anions such as ferrocyanides; the ammonium salt for example is ca. three times more soluble than the sodium salt (1.6 M vs. 0.5 M).[1] It is therefore critical to not only maximize the concentration of an electrolyte and thus its capacity, but to also choose cations that enable efficient transport across the membrane for efficient flow battery development.Here, we study the cation dependent resistance of NafionTM 212 cation exchange membranes for 12 different alkali and alkylammonium cations and determine the solubilities of 13 ferrocyanides as well as 35 metal-organic chelates based on aminopolycarboxylate ligands. The latter are a particularly promising family of compounds for application in negative electrolytes in near neutral pH aqueous flow batteries with demonstrated discharge voltages as high as 2.1 V and excellent power performance.[2] We further discuss cation-compatibility for mixed cation electrolytes as well as membrane pretreatments that affect the cells area specific resistance and active species crossover.[3]

Effect of Iodide-Based Organic Salts and Ionic Liquid Additives in Dye-Sensitized Solar Cell Performance.

The use of ionic liquid and organic salts as additives for electrolyte systems in dye-sensitized solar cells have been widely described in recent years. The tunability of their physical-chemical properties according to the cation–anion selection contributes toward their high efficiencies. For this purpose, several iodide-based organic salts including imidazolium, picolinium, guanidinium and alkylammonium cations were tested using acetonitrile/valeronitrile electrolytes and their photovoltaic parameters were compared. A best efficiency of 4.48% (4.15% for the reference) was found for 1-ethyl-2,3-dimethylimidazolium iodide ([C2DMIM]I) containing electrolyte, reaffirming the effectiveness of these additives. 4-tertbutylpyridine was included into the formulation to further improve the performance while determining which iodide salts demonstrate the highest synergy with this additive. [C2DMIM]I once again proved to be the superior additive, achieving an efficiency of 6.48% (6% for the reference). Electrochemical impedance spectroscopy was employed to elucidate the effects of the various additives, demonstrating the relevance of the counter electrode resistance on device performance. Finally, several computational descriptors for the cationic structures were calculated and correlated with the photovoltaic and resistance parameters, showing that properties related to polarity, namely relative positive charge, molecular polarizability and partition coefficient are in good agreement with the counter-electrode resistance.

Determination of layer charge density in expandable phyllosilicates with alkylammonium ions: A combined experimental and theoretical assessment of the method

Layer charge deficit is a key crystal-chemical parameter for the classification and nomenclature of 2:1 phyllosilicates that also controls some of their fundamental properties such as cation exchange capacity, expandability, water content, or rheology. The clay community has thus devoted significant efforts to determine this parameter either from the smectite/vermiculite chemical composition (the structural formula method) or experimentally using the alkylammonium method, that theoretically allows the determination of the mean layer charge density and of its distribution. In the present study density functional theory (DFT) and molecular dynamics (MD) simulations are compared to experimental X-ray diffraction data for a series of synthetic saponites with layer charge ranging from medium-charge smectite to medium-charge vermiculite. Consistency of computed and measured layer-to-layer distances confirms the ability of computational approaches to accurately predict the organization of alkylammonium cations in smectite interlayers. Thermalization of DFT-optimized structure models through MD simulations allows probing possible alternative interlayer configurations such as the electrostatically-favored location of ammonium heads above/below Al-substituted tetrahedra. X-ray diffraction results showed that layer-to-layer distances intermediate between those corresponding to the stable h1, h2, etc. interlayer configurations described in the literature result from the interstratification of different stable configurations. The overall consistency of computational and experimental results confirms also the ability of the alkylammonium method to accurately determine a mean value of layer charge density consistent with smectite structural formula when using the revised equations proposed by Laird et al. (1989). The validity of the method appears however limited to smectite-group minerals [layer charge density ranging from ~0.5 to ≤1.2 per O20(OH)4] most likely owing to the coexistence of both stable “layered” and paraffin-like interlayer configurations for higher values of layer charge. In addition, this consistency challenges the ability of the method to quantitatively describe distributions of layer charge in expandable phyllosilicates even when using the complete series of alkylammonium cations.

Exploring the Steric Hindrance of Alkylammonium Cations in the Structural Reconfiguration of Quasi‐2D Perovskite Materials Using a High‐throughput Experimental Platform

AbstractReduced‐dimensional (2D or quasi‐2D) perovskites have recently attracted considerable interest due to their superior long‐term stability. The nature of the intercalating cations plays a key role in determining the physicochemical properties and stability of the quasi‐2D perovskites. Here, the thermal stability of a series of 2D Ruddlesden−Popper (RP) perovskites is studied using seven types of intercalating cations with increasing linear carbon‐chain length from ethylammonium (EA) to n‐dodecylammonium (DA) through a high‐throughput platform. The results show that long‐chain cations in quasi‐2D perovskite films lead to strong steric hindrance between adjacent perovskite domains, thus suppressing Ostwald ripening during the thermal‐aging process. For short‐chain cations, increased‐dimensional phase redistribution during the aging period is observed, which can benefit a concomitant regeneration of the 3D/3D‐like perovskite phases. The impact of steric hindrance on structural reconfiguration and the subsequent phase redistribution in quasi‐2D perovskites are systematically characterized by UV–vis absorption spectra, photoluminescence spectra, and X‐ray diffraction patterns. Due to the steric hindrance effect, an optimal chain length is found to maximize film stability by balancing the water/oxygen resistance and increased‐dimensional phase redistribution. This study provides new insight into the thermal stability of quasi‐2D perovskites.

Modified Polymer Surfaces: Thin Films of Silicate Composites via Polycaprolactone Melt Fusion

Polymer/layered silicate composites have gained huge attention in terms of research and industrial applications. Traditional nanocomposites contain particles regularly dispersed in a polymer matrix. In this work, a strategy for the formation of a composite thin film on the surface of a polycaprolactone (PCL) matrix was developed. In addition to the polymer, the composite layer was composed of the particles of saponite (Sap) modified with alkylammonium cations and functionalized with methylene blue. The connection between the phases of modified Sap and polymer was achieved by fusing the chains of molten polymer into the Sap film. The thickness of the film of several μm was confirmed using electron microscopy and X-ray tomography. Surfaces of precursors and composite materials were analyzed in terms of structure, composition, and surface properties. The penetration of polymer chains into the silicate, thus joining the phases, was confirmed by chemometric analysis of spectral data and changes in some properties upon PCL melting. Ultimately, this study was devoted to the spectral properties and photoactivity of methylene blue present in the ternary composite films. The results provide directions for future research aimed at the development of composite materials with photosensitizing, photodisinfection, and antimicrobial surfaces.

Tailored texture synthesized LDH catalysts in the presence of quaternary ammonium salts

Tetramethylammonium- and tetrabutylammonium-hydroxides operate as alternative bases to the traditional inorganic ones for the LDH structures synthesis with controlled texture. This is valuable for both co-precipitation and mechano-chemical routes, where these organic bases limited the production of wastewaters by more than ten times, the contamination of hydrotalcites with other metallic cations, an important decrease of the energy consumed in the synthesis and, also as a template for generating predetermined porosity. The crystallinity of the produced LDH is influenced by the nature of the alkyl ammonium cation. The catalytic behavior of the catalysts has been evaluated in the cyanoethylation, Claisen-Schmidt and self-cyclohexanone condensation.

Hydrophobic interaction of V12 bowl-type dodecavanadates with alkyl ammonium cations

The V12 dodecavanadate, [V12O32]4−, that is one of a dominant polyoxovanadate species in non-aqueous media, was investigated focusing on the interaction of alkyl chains on its counter cations. Although the presence of such a species is not reported in any biological system, the unique V12 bowl anions have exhibited a host-guest property to accommodate a biologically active anion such as a halide, a cyanide or an azide for its delivery to the system. The nonpolar interactions between alkyl chains and the surface oxygen atoms on the V12 is of significance in the host-guest property and the reactivity of the V12. In the solid state, a tetraethyl ammonium (TEA) cation approached 3 Å above the cavity of the V12 via non-covalent interaction showing the lid effect. This interaction induces a distortion of its flexible framework even in a solution state. From the solution state 51V NMR and IR spectra, the orientation of an azide in the cavity was altered between TEA and tetra-n-butyl ammonium (TBA) salts. The modification of the non-covalent interaction also affected an oxidative catalytic performance with H2O2. The rate of the formation of active species of a TEA salt of [V12O32(Br)]5− was shorter than that of a TBA salt.