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Catalytic Application of Magnetic Nanocomposites
Published in Sam Zhang, Dongliang Zhao, Advances in Magnetic Materials, 2017
Kawamura and Sato reported that the crown ethers were supported on the silica-coated magnetic core–shell nanostructure by forming covalent bonds as shown in Figure 10.16a. The supported crown ether was used as a phase-transfer catalyst in the nucleophilic substitution reaction between benzyl bromide and potassium acetate. The supported catalyst exhibited significantly improved activity in comparison with the corresponding parent homogeneous catalyst. It was reusable at least 8 times with a conversion of greater than 99% and a TOF of >4.1 h−1 for each cycle [180]. Amine is commonly used as an organic base. Diaminosilane-functionalized MNPs (CoFe2O4) (Figure 10.16b) were prepared and used as efficient heterogeneous base catalysts for the Knoevenagel condensation of benzaldehyde with malononitrile to produce 2-benzylidenemalononitrile [182]. The reaction rates over the MNPs-supported amine catalyst are comparable to the large pore mesoporous silicas-supported diamine and higher than the small pore MCM-48 silica with ∼22 Å diameter pores-supported amines [182]. MNPs (CoFe2O4) were also used to support perfluorosulfonic acid groups by reacting triethoxysilylperfluorosulfonyl fluoride with MNPs, CoFe2O4@SiO2, followed by acidifying with nitric acid [183]. The supported acids were reported to be active for the deprotection reaction of benzaldehyde dimethylacetal with water to produce benzaldehyde (Ph − CH(OMe)2 + H2O → Ph − CHO + 2 MeOH). The catalyst exhibited a high TOF of 54 min−1, which is one-half of homogeneous catalyst triflic acid [183].
Qualitative Chemical Analysis
Published in Steven L. Hoenig, Basic Chemical Concepts and Tables, 2019
Add approximately 1 mL of 5% HCl in small portions to the test tube containing your organic compound. Shake the test tube vigorously after the addition of each portion of the aqueous solution. Solubility will be indicated by the formation of a homogeneous solution, a color change, or the evolution of gas or heat. If your compound is HCl-soluble, then it is an organic base. Amines are the most common organic base. If insoluble in all solutions, then your unknown is a large (>5–6 carbon atoms) neutral compound that has none of the acidic or basic organic functional groups mentioned above.
Preparation and characterization of graphene oxide/O-carboxymethyl chitosan (GO/CMC) composite and its unsymmetrical dimethylhydrazine (UDMH) adsorption performance from wastewater
Published in Environmental Technology, 2023
Jun Su, Ying Jia, Ruomeng Hou, Yuanzheng Huang, Keke Shen, Zhaowen Hao
Electrostatic attraction, hydrogen bonding, and surface complexation could be the main interactions in the adsorption mechanism of GO/CMC for the removal of UDMH. The porous nature of GO/CMC composites induced the adsorption of UDMH molecules by diffusion mechanism. In addition, the GO/CMC surface contained a large number of carboxyl groups, and the UDMH molecules contained amino groups. The CS fibres became water-soluble at a high degree of carboxymethylation [49]. Therefore, UDMH molecules could easily form complexes with GO/CMC. The solution pH also affected the surface properties of GO/CMC composites. UDMH is a weak organic base; it reacted with water to form conjugate acids and bases [40]. Under alkaline conditions, the GO/CMC surface was negatively charged and interacted electrostatically with the positively charged UDMH molecules through electrostatic interactions. Also, hydrogen bonding between -OH and -NH2 groups in the composite (hydrogen bond donor) and -NH2 groups (hydrogen bond acceptors) in the UDMH had some influence on the adsorption process. Although hydrogen bonding is very weak compared with other forms of interactions, it is expected that a large number of such possible interactions might contribute to the total adsorption process [50].
Magnetic polydomain liquid crystal elastomers – synthesis and characterisation
Published in Liquid Crystals, 2021
Luka Cmok, Mojca Vilfan, Sašo Gyergyek, Martin Čopič
To achieve chemical bonding of nanoparticles to the LCE matrix, a surfactant with free acrylic groups at the molecule end was needed. We used a free hydroxyl group in the tail of ricinoleic acid, which was already bound to the nanoparticle surface, to attach methacrylic anhydride (Sigma Aldrich) by acetylation and accommodate the required acrylic group (see Figure 2(a)). Although acetylation is normally mediated by an organic base, we avoided using such bases as they would induce flocculation (our previous experiments show that the formed salt of organic base and methacrylic acid strongly flocculate particles). Instead, we added methacrylic anhydride to the dispersion of nanoparticles in an organic solvent (toluene), and kept the mixture overnight at room temperature. The acetylation process still occurred, but unmediated reactions yielded lower occupancy levels of acrylic groups on the nanoparticles. After the reaction, the functionalised nanoparticles were washed in ethanol to remove unreacted precursors and stored in toluene as a stable colloid.
Thermoelectric materials and applications for energy harvesting power generation
Published in Science and Technology of Advanced Materials, 2018
Ioannis Petsagkourakis, Klas Tybrandt, Xavier Crispin, Isao Ohkubo, Norifusa Satoh, Takao Mori
The relationship between charge carrier mobility, thin film crystallinity, electrical and thermoelectric properties of conducting polymers was further elucidated by the works of Petsagkourakis et al. [22,46] on PEDOT:Tos thin films. High boiling point solvent additives (DMSO) and an organic base, pyridine, were used as means to enhance the degree of crystallinity of the PEDOT:Tos thin films (Figure 7(a)). Solvent treatment left the oxidation level of the polymers unaffected, as proven by X-ray photoelectron spectroscopy (XPS) (Figure 7(b)). Hence for the same oxidation level, the conductivity of the samples is directly related to the mobility. A relationship between Seebeck coefficient and charge carrier mobility was extracted for those films, S ~ μ0.2 (Figure 7(c)). This behavior was attributed to the enhanced degree of crystallinity, which resulted in delocalization of the charge carriers and extended the band edge at the Fermi level. Additionally, a transition between the semiconducting to the semimetallic behavior was observed as the degree of crystallinity and charge carrier mobility increased (Figure 7(d)).