Showing papers on "Ammonium hydroxide published in 2022"

In-situ coprecipitation formed Fe/Zn-layered double hydroxide/ammonium polyphosphate hybrid material for flame retardant epoxy resin via synergistic catalytic charring

Abstract: Inspired by the in-situ coprecipitation technology, Fe/Zn-layered double hydroxides (Fe/Zn-LDH) doped ammonium polyphosphate (APP) was prepared for high fire-safety epoxy resins (EP). The investigation on the chemical composition and micromorphology of Fe/[email protected] confirmed the uniform deposition of Fe/Zn-LDH on the surface of APP. The results showed that EP containing 4 wt% Fe/[email protected] exhibited the highest LOI of 29.4% and passed the UL-94 V0 level. Additionally, compared to neat EP, the peak of heat release rate, peak of smoke production rate, and the fire growth rate decreased by 66.4%, 48.4%, and 80.7%. The greatly enhanced flame retardancy of EP was contributed to the highly synergistic charring catalysis via abundant interfacial contact sites. Moreover, the mechanical performance of Fe/[email protected]/EPs were slightly affected due to the improved interfacial interaction of Fe/[email protected] Generally, this work exploited a tactful strategy to construct LDH doped APP hybrid material, and presented the potential application in industry.

Cross-Linked Alkaline Anion Exchange Membrane from N-Spirocyclic Quaternary Ammonium and Polybenzimidazole

Abstract: Two major challenges, namely, hydroxide conductivity and alkaline stability of the polymer membrane, are yet to be resolved adequately in spite of significant research outcomes on alkaline anion exchange membrane (AAEM) in the recent past. To address these challenges, in this work, the development of ionically cross-linked AAEMs has been achieved by blending pyridine-bridged polybenzimidazole (PyPBI) and N-spirocyclic quaternary ammonium spiro ionene polymer (SP). Further, membranes were converted to porous membranes by adding different weight percentages of porogen in the membrane matrix. Membranes were converted to hydroxide-conducting AAEMs by dipping into 1 M KOH solution, and under this condition, a part of the −NH– groups of PyPBI was deprotonated to form ammonium–imidazolate complexes with SP, which resulted in ionic cross-linking in the AAEM. Hydroxide ion conductivity of 129 mS/cm at 90 °C was obtained in the case of the S70P30-OH membrane, which was a hydroxide-form membrane obtained from the blend of 70 wt % SP and 30 wt % PyPBI, and this membrane showed the highest KOH uptake among all other AAEMs prepared in this study. On the other hand, among the porous ionically cross-linked membranes studied here, the S50P50-P25-OH (blends of 50 wt % SP and 50 wt % PyPBI with 25% porogen) membrane showed the highest hydroxide ion conductivity (117 mS/cm at 90 °C). All the ionically cross-linked AAEMs displayed excellent alkaline stability and remained unaffected during alkaline stability test in 1 M KOH at 80 °C for as long as the test was carried out (960 h). Observing the exceptional stability in 1 M KOH of S50P50-OH and S50P50-P25-OH membranes, OH– conductivity analysis and alkaline stability tests of these samples were carried out even in 2 M KOH, and we found that these membranes retained ∼80% of their OH– conductivity value even after 500 h of alkaline treatment in 2 M KOH at 60 °C. Furthermore, membranes were found to be useful in alkaline water electrolysis, and the best performance was shown by the S70P30-OH membrane, which displayed a current density of 100 mA cm–2 at 2.6 V. Overall, these recently developed membranes retained hydroxide conductivity, structural and thermal stability even after harsh alkaline treatment for a longer period of time.

Ionic liquids for the inhibition of gas hydrates. A review

Abstract: The formation of gas hydrates is a major issue during the operation of oil and gas pipelines, because gas hydrates cause plugging, thereby disrupting the normal oil and gas flows. A solution is to inject gas hydrate inhibitors such as ionic liquids. Contrary to classical inhibitors, ionic liquids act both as thermodynamic inhibitors and hydrate inhibitors, and as anti-agglomerates. Imidazolium-based ionic liquids have been found efficient for the inhibition of CO2 and CH4 hydrates. For CO2 gas hydrates, N-ethyl-N-methylmorpholinium bromide showed an average depression temperature of 1.72 K at 10 wt% concentration. The induction time of 1-ethyl-3-methyl imidazolium bromide is 36.3 h for CO2 hydrates at 1 wt% concentration. For CH4 hydrates, 1-ethyl-3-methyl-imidazolium chloride showed average depression temperature of 4.80 K at 40 wt%. For mixed gas hydrates of CO2 and CH4, only quaternary ammonium salts have been studied. Tetramethyl ammonium hydroxide shifted the hydrate liquid vapour equilibrium to 1.56 K at 10 wt%, while tetrabutylammonium hydroxide showed an induction time of 0.74 h at 1 wt% concentration.

Synthesis of Fe3O4 Nanoparticles with Different Shapes Through a Co-Precipitation Method and Their Application

Abstract: Abstract Magnetic Fe 3 O 4 nanoparticles (NPs) were successfully synthesized via co-precipitation method using ferric chloride and ferrous sulphate as the starting materials. The shape and the size of Fe 3 O 4 NPs were controlled by using different types of additive including ammonium hydroxide and sodium hydroxide. The results revealed that by adding ammonium hydroxide, the particles attained a spherical shape with a uniform size. On the other hand, the shape of the particles turned from spherical to cubic using sodium hydroxide. The magnetic results showed that both samples attained hysteresis loop, which indicated that both samples have ferromagnetic behavior. In addition, Fe 3 O 4 NPs with cubic shape showed higher adsorptive behaviour towards Congo red compared to spherical Fe 3 O 4 NPs, which is attributed to the enhancement of their magnetic properties. The adsorption of Congo red onto cubic Fe 3 O 4 NPs was best described by Langmuir isotherm model, while spherical Fe 3 O 4 NPs followed Freundlich isotherm model.

Enhanced Corrosion Resistance of Layered Double Hydroxide Films on Mg Alloy: The Key Role of Cationic Surfactant

Abstract: In this study, dense anticorrosion magnesium–aluminum layered double hydroxide (MgAl-LDH) films were prepared for the first time by introducing a cationic surfactant tetradecyltrimethyl ammonium bromide (TTAB) in the process of in situ hydrothermal synthesis of Mg-Al LDH films on an AZ31 magnesium alloy. Results of XRD, FTIR, and SEM confirmed that TTAB forms the MgAl-LDH-TTAB, although TTAB cannot enter into LDH layers, and MgAl-LDH-TTAB powders are much smaller and more homogenous than MgAl-CO32−-LDH powders. Results of SEM, EDS, mapping, and XPS confirmed that TTAB forms the MgAl-LDH-TTAB films and endows LDH films with denser structure, which provides films with better shielding efficiency. Results of potentiodynamic polarization curves (PDP) and electrochemical impedance spectroscopy (EIS) confirmed that MgAl-LDH-TTABx g films have better corrosion resistance than an MgAl-CO32−-LDH film. The corrosion current density (icorr) of the MgAl-LDH-TTAB0.35 g film in 3.5 wt.% NaCl solution was reduced to 1.09 × 10−8 A.cm−2 and the |Z|f = 0.05 Hz value was increased to 4.48 × 105 Ω·cm2. Moreover, the increasing concentration of TTAB in MgAl-LDH-TTABx g (x = 0.025, 0.05, 0.1, 0.2 and 0.35) provided denser outer layer LDH films and thereby increased the corrosion resistance of the AZ31 Mg alloy. Additionally, the |Z|f = 0.05 Hz values of the MgAl-LDH-TTAB0.35 g film still remained at 105 Ω·cm2 after being immersed in 3.5 wt.% NaCl solution for 168 h, implying the good long-term corrosion resistance of MgAl-LDH-TTABx g films. Therefore, introducing cationic surfactant in the process of in situ hydrothermal synthesis can be seen as a novel approach to creating efficient anticorrosion LDH films for Mg alloys.

ZSM-5 Catalysts for MTO: Effect and Optimization of the Tetrapropylammonium Hydroxide Concentration on Synthesis and Performance

Abstract: Light olefin production from methanol using various zeolite catalysts has industrial and economic importance considering the growth of the petrochemical market. Zeolites are generally synthesized using various organic templates as structure-directing agents (SDAs). In this study, synthesis of a series of ZSM-5 zeolites was performed systematically using the microwave-assisted crystallization method, and these samples were analyzed in detail to understand the effect of the SDA concentration. Powder diffraction, N2 adsorption, scanning electron microscopy, ammonia adsorption desorption, and 27Al and 29Si NMR spectroscopies were used for the characterization. The organic SDA tetrapropyl ammonium hydroxide (TPAOH/SiO2 mole ratio = 0.0500) is found to have an optimum concentration against the silica precursor for achieving the highest crystallinity, suitable morphology, ideal pore size, effective pore volume, and tuned microporous/mesoporous area. For samples with a template concentration ratio of 0.050 or higher, 29Si and 27Al NMR data revealed the presence of an intact ZSM-5 structure. Using a fixed bed reactor at 500 °C and atmospheric pressure, the catalytic performance of the selected catalysts from the series is investigated for the methanol-to-olefin conversion reaction. The sample with the highest crystallinity showed the best conversion, selectivity toward light olefins, and time on stream stability. It is also worth noting that the highest crystallinity, micropore area, and micropore volume are reached for the optimum value rather than the highest template concentration. This allows for a reduction in the template concentration and a move closer to a synthesis pathway benign to environment and economics.

Influence of framework Al distribution in HZSM-5 channels on catalytic performance in the methanol to propylene reaction

Abstract: Nanosized and microsized ZSM-5 samples were prepared using a two-stage crystallization method in the presence of glucose and additional post-treated by acid leaching, tetrapropylammonium hydroxide, or ammonium fluorosilicate. The characterization results show that for synthesizing ZSM-5 zeolites, glucose inhibits the position of Al atoms in the channel intersections, thus forming additional single Al atoms and making more Al pairs at the straight and sinusoidal channels rather than channel intersections. The catalytic performance in the methanol conversion reaction shows that nanosized ZSM-5 catalysts are enriched in Al pairs in the channel intersections and exhibit higher ethylene and aromatics selectivity via the aromatic-based cycle, whereas microsized ZSM-5 catalysts have multiple single Al sites and low Al pairs in the channel intersections and exhibit higher propylene selectivity but lower aromatics selectivity via olefinic-based cycle. It provides a facile method to prepare the ZSM-5 zeolite with improved catalytic performance in the MTP reaction.

Influence of framework Al distribution in HZSM-5 channels on catalytic performance in the methanol to propylene reaction

Abstract: Nanosized and microsized ZSM-5 samples were prepared using a two-stage crystallization method in the presence of glucose and additional post-treated by acid leaching, tetrapropylammonium hydroxide, or ammonium fluorosilicate. The characterization results show that for synthesizing ZSM-5 zeolites, glucose inhibits the position of Al atoms in the channel intersections, thus forming additional single Al atoms and making more Al pairs at the straight and sinusoidal channels rather than channel intersections. The catalytic performance in the methanol conversion reaction shows that nanosized ZSM-5 catalysts are enriched in Al pairs in the channel intersections and exhibit higher ethylene and aromatics selectivity via the aromatic-based cycle, whereas microsized ZSM-5 catalysts have multiple single Al sites and low Al pairs in the channel intersections and exhibit higher propylene selectivity but lower aromatics selectivity via olefinic-based cycle. It provides a facile method to prepare the ZSM-5 zeolite with improved catalytic performance in the MTP reaction.

Hydroxide Chemoselectivity Changes with Water Microsolvation.

Abstract: Solvent molecules are known to affect chemical reactions, especially if they interact with one or more of the reactants or catalysts. In ion microsolvation, i.e., solvent molecules in the first solvation sphere, strong electronic interactions are created, leading to significant changes in charge distribution and consequently on their nucleophilicity/electrophilicity and acidity/basicity. Despite a long history of research in the field, fundamental issues regarding the effects of ion microsolvation are still open, especially in the condensed phase. Using reactions between hydroxide and relatively stable quaternary ammonium salts as an example, we show that water microsolvation can change hydroxide's chemoselectivity by differently affecting its basicity and nucleophilicity. In this example, the hydroxide reactivity as a nucleophile is less affected by water microsolvation than its reactivity as a base. These disparities are discussed by calculating and comparing oxidation potentials and polarizabilities of the different water-hydroxide clusters.

Synergistic flame retardant effect of aluminum hydroxide and ammonium polyphosphate on epoxy resin

Abstract: Epoxy resin is an attractive traditional thermoset that is widely used in a variety of applications. And its flammable problem has drawn an increasing number of researchers to solve it. As flame retardants, ammonium polyphosphate (APP) and aluminum hydroxide (ATH) were mixed in the epoxy matrix to create composites with an interesting synergistic flame retardant effect, and its mechanism were thoroughly investigated. When 10 wt% APP and ATH were added at a mass ratio of 3/1, the peak of heat release rate and total heat release were reduced by 48% and 38%, with a LOI of 28.9% and a UL-94 of V-0 rating. During the combustion process, polyphosphoric acid formed by the decomposition of APP could catalyze matrix decomposition to form a charring barrier and react with alumina formed by the decomposition of ATH to produce extremely stable aluminum metaphosphate, which covered the surface of burning matrix and hampered further combustion.

Properties and Applications of Copper(I) Thiocyanate Hole‐Transport Interlayers Processed from Different Solvents

Abstract: Copper(I) thiocyanate (CuSCN) is an effective interlayer material for hole injection and transport in organic electronic devices but its solution processing has conventionally utilized undesirable di‐n‐alkyl sulfide solvents such as diethyl‐ (DES) and dipropyl‐sulfide (DPS). Herein, this paper reports on the use of N,N‐dimethylformamide (DMF) and 1‐methyl‐2‐pyrrolidinone (NMP) as alternative solvents for CuSCN interlayers and performs a detailed comparison of the resulting properties relative to films processed from DES and DPS and two other recent alternatives, dimethyl sulfoxide (DMSO) and ammonium hydroxide. The surface roughness, polymorphism, and surface chemistry of the resulting CuSCN layers are reported. The interlayer surface energy and ionization potential that are key to the overlying semiconductor microstructure and interfacial energy barrier, and hence to charge transport and injection, are also discussed. Finally, systematic device tests using well‐known organic semiconductors in light‐emitting diode, solar cell and field‐effect transistor structures demonstrate the overall suitability of DMSO and DMF as solvents for CuSCN interlayer deposition to achieve better device performance. This study broadens the applicability of CuSCN as a highly efficient hole injection/transport material for organic semiconductor devices by expanding the documented range of suitable CuSCN solvents.

Fabrication of cellulose cryogel beads via room temperature dissolution in onium hydroxides

Abstract: In recent years, there has been a growing interest in green solvents to dissolve and shape cellulose into microspheres. However, development of solvents suitable for room temperature dissolution and shaping of cellulose spheres is very limited. In this work, a novel process to fabricate cellulose microspheres is presented. First, the effect of ethanol-hydrochloric acid pulp pretreatment on cellulose solubility in aqueous tetra-n‑butyl phosphonium hydroxide and tetra-n‑butyl ammonium was investigated. While the dissolution of untreated pulp remained limited to 5 wt%, the pretreatment boosted pulp solubility to 15 wt%. Spherical beads were obtained via dropwise addition of the solution in ethanol. Cryogels beads with a BET surface area of 218.1 m²/g were collected when using 90 v% tert‑butyl alcohol as the freeze-drying medium. After gathering the spent ethanol and initial washing of the beads, 90.7% of the tetra-n‑butyl phosphonium hydroxide solution was recovered and successfully reused to prepare a subsequent batch of beads. The proposed bead preparation system further fits within the concept of topochemical design as beads could be fabricated from low to high cellulose concentrations, regardless of temperature, therefore offering great opportunities to design gels for different applications such as drug delivery systems, protein conjugation or wastewater treatment.

Fabrication and Characterization of Hydrophobic Cellulose Nanofibrils/Silica Nanocomposites with Hexadecyltrimethoxysilane

Abstract: Cellulose nanofibrils (CNFs) have attracted much attention because of their renewability and potential biocompatibility. However, CNFs are extremely hydrophilic due to the presence of a large number of hydroxyl groups, limiting their use as a water-resistant material. In this work, we controlled the adsorption behavior of silica nanoparticles on the surface of CNFs by adjusting the synthesis conditions. The silica nanoparticle size and packing efficiency on the CNF surface could be controlled by varying the ammonium hydroxide and water concentrations. In addition, hexadecyltrimethoxysilane (HDTMS) was successfully grafted onto CNF or CNF/silica nanocomposite surfaces, and the quantitative content of organic/inorganic substances in HDTMS was analyzed through XPS and TGA. The HDTMS-modified CNF/silica nanocomposites were more advantageous in terms of hydrophobicity than the HDTMS-modified CNF composites. This is because the silica nanoparticles were adsorbed on the surface of the CNFs, increasing the surface roughness and simultaneously increasing the amount of HDTMS. As a result, the HDTMS-modified CNFs showed a water contact angle (WCA) of ~80°, whereas HDTMS-modified CNF/silica nanocomposites obtained superhydrophobicity, with a WCA of up to ~159°. This study can provide a reference for the expansion of recyclable eco-friendly coating materials via the adsorption of silica nanoparticles and hydrophobic modification of CNF materials.