Alkylammonium Halides Research Articles

Facile Synthesis of Colloidal Lead Halide Perovskite Nanoplatelets via Ligand-Assisted Reprecipitation.

In this work, we demonstrate a facile method for colloidal lead halide perovskite nanoplatelet synthesis (Chemical formula: L2[ABX3]n-1BX4, L: butylammonium and octylammonium, A: methylammonium or formamidinium, B: lead, X: bromide and iodide, n: number of [BX6]4- octahedral layers in the direction of nanoplatelet thickness) via ligand-assisted reprecipitation. Individual perovskite precursor solutions are prepared by dissolving each nanoplatelet constituent salt in N,N-dimethylformamide (DMF), which is a polar organic solvent, and then mixing in specific ratios for targeted nanoplatelet thickness and composition. Once the mixed precursor solution is dropped into nonpolar toluene, the abrupt change in the solubility induces the instantaneous crystallization of nanoplatelets with surface-bound alkylammonium halide ligands providing colloidal stability. Photoluminescence and absorption spectra reveal emissive and strongly quantum-confined features. X-ray diffraction and transmission electron microscopy confirm the two-dimensional structure of the nanoplatelets. Furthermore, we demonstrate that the band gap of perovskite nanoplatelets can be continuously tuned in the visible range by varying the stoichiometry of the halide ion(s). Lastly, we demonstrate the flexibility of the ligand-assisted reprecipitation method by introducing multiple species as surface-capping ligands. This methodology represents a simple procedure for preparing dispersions of emissive 2D colloidal semiconductors.

Room temperature CO2 fixation via cyclic carbonate synthesis over vanadium-MOF catalysts

Vanadium containing 3D MOF, MIL-47 displayed excellent synergistic catalysis with alkyl ammonium halides (TBAX) in the room temperature fixation of CO2. Theoretical intrinsic-reaction-coordinate calculations were performed at the level of M06/LACVP**++ implemented in Jaguar v8.5 software to ascertain the mechanistic pathways of catalysis. A homogeneous complex of vanadium, vanadium acetyl acetonato [VO(acac)2], was used as a model system to investigate the mechanism behind the synergistic activity of the MIL-47/TBAX, which indeed shows that the activation energy of the CO2 fixation is considerably lowered by about 30–35 kcal compared to the uncatalyzed reactions.

Near‐Unity Photoluminescence Quantum Efficiency for All CsPbX3 (X=Cl, Br, and I) Perovskite Nanocrystals: A Generic Synthesis Approach

AbstractIn a generic synthesis approach, all three CsPbX3 (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non‐halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.

Near‐Unity Photoluminescence Quantum Efficiency for All CsPbX3 (X=Cl, Br, and I) Perovskite Nanocrystals: A Generic Synthesis Approach

In a generic synthesis approach, all three CsPbX3 (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non-halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.

Intrinsic Instability of Inorganic–Organic Hybrid Halide Perovskite Materials

Hybrid lead halide perovskite materials are used in solar cells and show efficiencies greater than 23%. Furthermore, they are applied in light-emitting diodes, X-ray detectors, thin-film transistors, thermoelectrics, and memory devices. Lead trihalide hybrid materials contain methylammonium (MA) or formamidinium (FA) (or a mixture), or long alkylammonium halides, as alternative organic cations. However, the intrinsic stability of hybrid lead halide perovskites is not very high, and they are chemically unstable when exposed to moisture, light, or heat because of their organic contents and low formation energies. Therefore, although improvements in the chemical stability are crucial, changing the material composition is challenging because it is directly related to the desired application requirements. Fortunately, hybrid lead halide perovskites have a very high tolerance toward changes in physical properties arising from doping or addition of different cations and anions, in many cases showing improved properties. Here, the intrinsic instability of hybrid lead halide perovskites is reviewed in relation to the crystal phase and chemical stability. It is suggested that FA should be used for lead halide perovskites for chemical stability instead of MA. Furthermore, additives that stabilize the crystal phase with α-FAPbI3 should eschew MA.

Annealing CsPbX3 (X = Cl and Br) Perovskite Nanocrystals at High Reaction Temperatures: Phase Change and Its Prevention.

Annealing perovskite nanocrystals at high reaction temperature changes their crystal phase, shape, and optical properties. Carrying out reactions between 180 and 250 °C, the impact of thermal annealing for CsPbCl3 and CsPbBr3 nanocrystals in a reaction flask was investigated here. At higher temperature, a phase change wasobservedinstantly,whichcould not be trapped even with ice-bath cooling.Interestingly, using a calculated amount of preformed alkylammonium halides as dual passivating agents, the nanocrystals of both CsPbCl3 and CsPbBr3 could even be stabilized for hours of annealing at 250 °C. CsPbCl3, which was reported to be a poor emissive nanocrystal in comparison to CsPbBr3, could sustain even more than 5 h of annealing at 250 °C and recorded ∼51% absolutely quantum yield. Details of the interface chemistry and the role of the used dual passivating agent for providing thermal stability are studied and reported in this Letter.

Nanostructured Mechanochemically Prepared Hybrid Perovskites Based on PbI2and Alkylammonium Halides for Optoelectronic Applications

The preparation of hybrid perovskites (HPs) with small and large organic cations with a solventless mechanochemical treatment of the mixture of lead iodide and alkylammonium halides is presented. X-ray diffraction and electron microscopy show that the use of the mechanochemical approach for synthesis of HPs with small cations (CH3NH3PbI2X, X = I, Br, Cl) leads to the formation of crystalline nanoparticles with uniform shapes and sizes that do not exceed 70 nm. At the same time, the mechanochemical synthesis of HPs with large organic cations, (C6H13NH3)2PbI2X2, induces the nanostructuration with the formation of 2D structures regardless of the stoichiometry of the initial reaction mixture. We show that our mechanochemically prepared HPs exhibit a photoluminescence whose colors depend on the size of the organic cations and the type of halide ions that could be used for different optoelectronic applications, for improving color rendering index of garnet-based white-light-emitting diodes in particular.

Cycloaddition of CO2 and propylene oxide by using M(HBTC)(4,4′-bipy)·3DMF (M = Ni, Co, Zn) metal-organic frameworks

Three pillar-layered metal-organic frameworks (MOFs) based on M(HBTC)(4,4′-bipy)·3DMF (M = Ni, Co, and Zn; HBTC = 1,3,5-benzenetricarboxylic acid, 4,4′-bipy = 4,4′-bipyridine) were synthesized using a solvothermal method. Zn(HBTC)(4,4′-bipy)·3DMF was synthesized for the first time using both a solvothermal and microwave method, and subsequently characterized by various physicochemical methods. The structure of M(HBTC)(4,4′-bipy)·3DMF consisted of honeycomb grid layers of M2+ ions and BTC units, which were further linked by the 4,4′-bipy pillars to form a three-dimensional highly porous framework. All the MOFs displayed excellent synergistic catalytic properties with alkyl ammonium halides (TBAX) in the solventless fixation of CO2 with epoxides to produce cyclic carbonates. The catalytic activities of these MOFs followed the trend Zn > Co > Ni, which was explained by the acid-base bifunctional properties. The microwave-synthesized Zn(HBTC)(4,4′-bipy)·3DMF material exhibited physical, chemical, and catalytic properties that were similar to those of the catalyst obtained using a conventional solvothermal synthesis. The scope of various parameters, including recyclability, was studied, and a plausible reaction mechanism was suggested.

The capability of tetra alkyl ammonium bromides for aqueous biphasic systems formation with both polymers and electrolytes in aqueous solutions

It was found that the tetra alkyl ammonium halides can solute-out the water soluble polymers and solute out by electrolyte in aqueous solutions and form the aqueous biphasic systems (ABS). To investigate these new kinds of ABS, vapor – liquid equilibria (VLE), vapor – liquid - liquid equilibria (VLLE) and liquid – liquid equilibria (LLE) measurements were carried out for ternary systems containing tetra alkyl ammonium bromides (TAAB): tetra methyl ammonium bromide (TMAB), tetra ethyl ammonium bromide (TEAB), tetra propyl ammonium bromide (TPAB) and tetra butyl ammonium bromide (TBAB); electrolytes: NaCl, NaNO3, Na2CO3 and Na3Cit; and polymers: polypropylene glycol400 (PPG400) and polyethylene glycol400 (PEG400) at different temperatures. It was found that in these systems the soluting-out effect and then the tendency to ABS formation increases by increasing the difference between the hydrophilicity of two components. In the case of TAAB + polymer aqueous systems, the polymer is solute out by the more hydrophilic component TAAB and therefore ABS are formed for aqueous solutions containing PPG (which is more hydrophobic than PEG) and TMAB/TEMB (which are more hydrophilic than TPAB and TBAB). In these types of ABS, the soluting-out effects increase with an increase in temperature. On the other hand, in the case of TAAB + salt aqueous systems, the TAAB is solute out by salt which is the more hydrophilic than TAAB and therefore aqueous solutions containing (TBAB + NaNO3, Na2CO3 and Na3Cit), (TPAB and TEAB + Na2CO3 and Na3Cit) and (TMAB + Na2CO3) are undergoing phase separation and their soluting-out effects increase with decreasing temperature. The isopiestic measurements of the investigated systems show that the constant water activity lines of aqueous PPG + TAAB systems show the positive and the negative deviation from the semi-ideal behavior respectively in biphasic and monophasic area, but those of aqueous salt + TAAB systems show the negative deviation in both biphasic and monophasic area. However, the constant water activity lines of the systems with soluting-in effect, show the positive deviation from the semi-ideal behavior.

Metal to Halide Perovskite (HaP): An Alternative Route to HaP Coating, Directly from Pb(0) or Sn(0) Films

Halide perovskite film-based devices (e.g., solar cells and LEDs) have shown unique device performance. These films are commonly prepared from toxic solutions of metal salts (e.g., Pb2+ in DMF or DMSO). We describe a method to form halide perovskite films by simply reacting metal (Pb or Sn) films with alcoholic solutions of monovalent alkali metal or alkyl ammonium halides, which avoids the use of toxic Pb2+ solutions in the manufacturing step. We show how the morphology of the films can be controlled by variation in reaction parameters and also how mixed halide perovskite films can be prepared. A mechanism for the metal-to-perovskite conversion is suggested. We further show how electrochemically assisted conversion can allow control over the oxidation state of the metal and increase the reaction rate greatly.

Demulsification of Water-in-Heavy Crude Oil Emulsion using Amphiphilic Ammonium Salts as Demulsifiers

Abstract In this work, six ionic surface-active alkyl ammonium halides were synthesized and evaluated as demulsifiers of W/O emulsions obtained from a Mexican heavy crude oil. A centrifugation test was employed as a fast method for following the kinetics of the demulsification process with the synthesized demulsifiers. Trioctylmethylammonium bromide showed the best performance as demulsifier.

Effect of Deep Eutectic Solvent Nanostructure on Phospholipid Bilayer Phases

Phospholipids are shown by solvent penetration experiments to form lamellar phases and spontaneously spawn vesicles in a wide range of deep eutectic solvents (DESs) composed of alkylammonium halide salts and glycerol or ethylene glycol, which are shown to be nanostructured by X-ray scattering. In contrast with molecular solvents, the chain melting temperature of each phospholipid, which determines the stability of the swellable bilayer phase, depends on the structure of the cation, anion, and molecular H-bond donor that constitute the DES. Chain melting is most sensitive to the length of the alkyl chain of the cation, which is partitioned between apolar domains in the bulk, nanostructured DES and those within the lipid bilayer. This is moderated by the structures of the anion and the molecular hydrogen bond donor, which determine the extent of polar/apolar segregation in the bulk liquid.

Amine‐Free Synthesis of Cesium Lead Halide Perovskite Quantum Dots for Efficient Light‐Emitting Diodes

Cesium lead halide perovskite quantum dots (PQDs) have attracted significant interest for optoelectronic applications in view of their high brightness and narrow emission linewidth at visible wavelengths. A remaining challenge is the degradation of PQDs during purification from the synthesis solution. This is attributed to proton transfer between oleic acid and oleylamine surface capping agents that leads to facile ligand loss. Here, a new synthetic method is reported that enhances the colloidal stability of PQDs by capping them solely using oleic acid (OA). Quaternary alkylammonium halides are used as precursors, eliminating the need for oleylamine. This strategy enhances the colloidal stability of OA capped PQDs during purification, allowing us to remove excess organic content in thin films. Inverted red, green, and blue PQD light‐emitting diodes (LED) are fabricated for the first time with solution‐processed polymer‐based hole transport layers due to higher robustness of OA capped PQDs to solution processing. The blue and green LEDs exhibit threefold and tenfold improved external quantum efficiency (EQE), respectively, compared to prior related reports for amine/ammonium capped cross‐linked PQDs. The brightest blue LED based on all inorganic CsPb(Br1−xClx)3 PQDs is also reported.

Dielectric relaxation of alkyl chains in graphite oxide and n-alkylammonium halides

The dynamic of n-alkylammonium halides and n-alkylammonium cations (n = 12, 14, 16, 18) intercalated in graphite oxide (GO) have been investigated with complex impedance spectroscopy. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, elemental analysis and thermogravimetry served to characterize the materials. The intercalated alkylammonium cations distributes as monolayers (when n = 12, 14 or 16) or bilayers (when n = 18), with their long axis parallel to GO layers, and with cations of headgroups bonded ionically to C-O- groups of GO; backbones of the confined molecules remain free. All halides and intercalation compounds suffer dielectric loss at low temperature. Arrhenius plots of the thermal dependence of the loss peaks, which are asymmetric, produce apparent activation energies that rise with increasing n. Ngai’s correlated-state model helps to correct for effects of dipole-dipole interaction, leading to virtually identical values for actual activation energy of 110 meV ± 5%; the values are also almost the same as the barrier energy for internal rotation in the alkyl macromolecule. We conclude that the relaxation of the alkylammonium cations arises not from C3 reorientation of the CH3 at its headgroup, but from small-angle wobbling around its major axis, an intrinsic motion.

Making and Breaking of Lead Halide Perovskites.

A new front-runner has emerged in the field of next-generation photovoltaics. A unique class of materials, known as organic metal halide perovskites, bridges the gap between low-cost fabrication and exceptional device performance. These compounds can be processed at low temperature (typically in the range 80-150 °C) and readily self-assemble from the solution phase into high-quality semiconductor thin films. The low energetic barrier for crystal formation has mixed consequences. On one hand, it enables inexpensive processing and both optical and electronic tunability. The caveat, however, is that many as-formed lead halide perovskite thin films lack chemical and structural stability, undergoing rapid degradation in the presence of moisture or heat. To date, improvements in perovskite solar cell efficiency have resulted primarily from better control over thin film morphology, manipulation of the stoichiometry and chemistry of lead halide and alkylammonium halide precursors, and the choice of solvent treatment. Proper characterization and tuning of processing parameters can aid in rational optimization of perovskite devices. Likewise, gaining a comprehensive understanding of the degradation mechanism and identifying components of the perovskite structure that may be particularly susceptible to attack by moisture are vital to mitigate device degradation under operating conditions. This Account provides insight into the lifecycle of organic-inorganic lead halide perovskites, including (i) the nature of the precursor solution, (ii) formation of solid-state perovskite thin films and single crystals, and (iii) transformation of perovskites into hydrated phases upon exposure to moisture. In particular, spectroscopic and structural characterization techniques shed light on the thermally driven evolution of the perovskite structure. By tuning precursor stoichiometry and chemistry, and thus the lead halide charge-transfer complexes present in solution, crystallization kinetics can be tailored to yield improved thin film homogeneity. Because degradation of the as-formed perovskite film is in many ways analogous to its initial formation, the same suite of monitoring techniques reveals the moisture-induced transformation of low band gap methylammonium lead iodide (CH3NH3PbI3) to wide band gap hydrate compounds. The rate of degradation is increased upon exposure to light. Interestingly, the hydration process is reversible under certain conditions. This facile formation and subsequent chemical lability raises the question of whether CH3NH3PbI3 and its analogues are thermodynamically stable phases, thus posing a significant challenge to the development of transformative perovskite photovoltaics. Adequately addressing issues of structural and chemical stability under real-world operating conditions is paramount if perovskite solar cells are to make an impact beyond the benchtop. Expanding our fundamental knowledge of lead halide perovskite formation and degradation pathways can facilitate fabrication of stable, high-quality perovskite thin films for the next generation of photovoltaic and light emitting devices.

Growth of gold nanostructures on a Si wafer by concerted mechanisms of photoreduction and galvanic displacement

The development of a facile growth method of gold nanocrystals with a controlled shape is of crucial importance to expand the potential applications of gold nanoarchitectures which have various unique and useful physicochemical properties. Here, we report the site-preferential formation of gold nanostructures with various shapes on Si substrates. When a Si wafer covered with cetyltrimethylammonium bromide (CTAB, an organic salt) is immersed in Au(OH)4− aqueous solution and immediately photoirradiated, dendritic gold nanostructures grow on the surface of the Si wafer. Interestingly, the gold nanodendrites preferentially grow on scratched portions drawn by using a pen-type diamond glass cutter on the Si wafer. The shape of gold nanocrystals depends on the structure of both quaternary alkylammonium cations and halide anions, which are components of the organic salt film, and gold nanostructures with various shapes are successfully obtained at the scratched portions. It is revealed that concerted mechanisms of photoreduction of Au3+ ions and a new type of galvanic displacement reaction between Si and Au(OH)4− cause the site-preferential growth of gold nanoarchitectures.

암모니움 디티오카바메이트계 이온성 액체의 합성 및 내마모성능 (I)

The friction-reducing properties of lubricants containing ionic liquids based on ammonium dithiocarbamate are studied. The ionic liquids are produced through the following two steps: the synthesis of sodium alkyl dithiocarbamates via the substitution reaction of dialkylamine and carbon disulfide and their subsequent conversion into ammonium dithiocarbamate-based ionic liquids through an ion-exchange reaction with a quaternary alkyl ammonium halide salt. The structures of the ionic liquids are characterized by NMR spectroscopy and Fourier transform infrared spectroscopy. The isolated yields of the ionic liquids, which are viscous and pale yellow, are approximately 92%. The Brookfield viscosities and pour points of the ionic liquids are determined. Further, their wear resistances are measured through the four-ball wear test and the Schwingung Reibung Ver-schleiss (oscillation, friction, wear) test. The wear scar diameter of the lubricants containing 1 wt of the quaternary alkyl ammonium dithiocarbamate-based ionic liquids (0.475-0.631 mm) is significantly lower than that of the base oil (0.825 mm), proving that the ammonium dithiocarbamate-based ionic liquids have good friction-reducing characteristics. However, these friction-reducing characteristics fade significantly after long-term storage, owing to the degradation of the ionic liquids.

Ionic Liquids Synthesis – Methodologies

Ionic Liquids (IL) are salts with at least one organic cation. The term “Ionic Liquid” has been restricted to salts with melting point below 100 ° C [1]. In the recent years, (ILs) have gained popularity in science and technology. The large number of possible cation/ anion combinations allows a great variety of tunable interactions; also their unique properties and characteristics make it a promising and an attractive to work with in several fields. However, how ILs are produced? This editorial pretends to make a brief commentary of some of the main methodologies of ILs synthesis. ILs are frequently produced from ammonium, phosphonium or sulphonates ions [2]. There are two main methods of preparing ILs: metathesis and acid base neutralization (Scheme 1). We could also consider another method, for imidazolium cations that was developed by Earl and Seddon: the reaction of imidazole carbenes as strong bases [3]. There are several alkylammonium halides commercially available

The exhibition of isomorphism in alkylammonium halides withrac-1,1′-bi-2-naphthol

The exhibition of isomorphism in alkylammonium halides with<i>rac</i>-1,1′-bi-2-naphthol

Temperature‐dependent Raman spectroscopy of anilinium chloride near phase transition

AbstractThe existence of various solid phases of organic ammonium halides, due to the presence of hydrogen bonding, has long been established but is limited to alkyl ammonium halides. On the other hand, the presence of such phase transitions was eluded in case of anilinium chloride. In the present work, we have undertaken a systematic temperature dependent Raman spectroscopic study on anilinium chloride, in the range 300–100–350 K. Spectral variation in the low frequency (100–400 cm−1) and high frequency (2500–3700 cm−1) regions around 350 and 260 K shows the signature of the phase transitions in this compound. These phase transitions were reversible in nature. The latter transition is in agreement with DSC measurements.magnified image