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Clay Mineral Catalysis of Isomerization, Dimerization, Oligomerization, and Polymerization Reactions
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
The polymerization of interlayer methyl methacrylate in montmorillonite, like that of styrene, has attracted much attention. The reaction is commonly initiated by free radicals formed by heat treatment, γ-ray irradiation, or decomposition of intercalated chemical and photochemical initiators (Blumstein 1965b; Dekking 1967; Malhotra et al. 1972; Lee and Jang 1996; Zhu et al. 2002; Liu et al. 2003a; Qu et al. 2005; Wang et al. 2005; Nese et al. 2006). Interestingly, Eastman et al. (1999) failed to detect the formation of interlayer poly(methyl methacrylate) with Cu2+-hectorite or the formation of free radicals. They suggested that polymerization was effected through an unusual cationic mechanism involving the formation of a positively charged species, stabilized by interaction with the clay surface. On the other hand, methyl methacrylate can penetrate the interlayer space of VO2+- and Fe3+-exchanged hectorite to yield the corresponding quasi-two dimensional polymer (Porter et al. 2002).
Architectural Aspects of Covalent Organic Frameworks for Energy Applications
Published in Tuan Anh Nguyen, Ram K. Gupta, Covalent Organic Frameworks, 2023
High-order structures are hardly ever controlled in artificial polymers, even though primary-order properties such as composition, links, and end groups can be conceivably synthetic polymers and chain length can be set in biological polymerization [5]. Polymers are conceivably made via either chain development or step development polymerization, depending on the method and the nature of the connections and monomer arrangement [6]. Chain-growth polymerization is useful for vinyl or heterocyclic subunits even though it is centered on the linking of C–C linkages to form the polymer framework or the ring expansion of heterocycles to form heterochains [7]. Step-growth polymerization, on the other hand, is designed for non-vinyl monomers with corresponding functional elements that can respond to form a covalent link [8]. By expanding covalent bonds along with non-covalent interactions in polymerization schemes, COFs implementing this area have evolved in the last decade [9]. The basic concept is to limit chain evolution to a two-dimensional plane in which the polymer framework is coordinated and organized [10]. The geometry-oriented topology map is necessary for directing individual monomers toward particular sites on the two-dimensional plane, and monomers possessing suitable designs and many reactive groups are required for assuring 2D polymer development [11]. As a result, the 2D polymers that arise produce expanded polygons having particular entities there at the joints and edges [12]. Systematic two-dimensional polymers can direct non-covalent interactions between planes utilizing polygon topology to produce layered as well as prolonged two-dimensional polymer structures having a distinct large structure called covalent organic frameworks (COFs) [13–16]. Similarly, 3D COFs with extended architectures will be achievable assuming the development of the polymer chain is accurately regulated in three-dimensional manner.
Quantum Mechanics of Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
Figure 4.5 illustrates a transformation from metallic to semiconductor bonds. Graphane is a two-dimensional polymer that consists of carbon and hydrogen. The formula of the molecule is (CH)n and n is large. Graphane usually alternates the hydrogen atoms in A and B sublattices sides, we receive a diamond-like structure. The graphane lattice constant, a = 0.244 nm (graphene a = 0.242 nm). The crystalline structure of graphene may be easily transformed into that of graphene by the process of annealing in the atmosphere of Ar at 450°C for 24 hours. Another version of graphene was suggested in 201011. Fluorographene is a derivative of graphene which is a fluorocarbon in chemical terms. It is a two-dimensional carbon structure that consists of sp3 hybridized carbons where every carbon atom is bound with one fluorine atom. The chemical formula, (CF)n, is close to that of Teflon (chemical formula (CF2)n) which has carbon chains: each carbon is connected with two fluorines. In contrast, graphene is unsaturated (sp2 hybridized). Fluographene has a hexagonal lattice with one fluorine at each carbon atom and lattice constant of 0.248 nm. Fluographene’s mechanical properties are similar to those of graphene. The bandgap of 3 eV modes fluorographene makes it a good isolator. Fluorine (F) is a chemical element which is the lightest halogen with the atomic number 9. Fluorine is the most electronegative element and is extremely reactive forming bonds almost with all other elements with the exception of noble gases. Fluorographene can be produced from graphite monofluoride (CF)n that has layers of weakly band stacks of fluorographene. Its most stable formation consists of an infinite array of trans-linked cyclohexane chains that have covalent C – F bonds in an AB-stacking sequence.
Bio-interactive nanoarchitectonics with two-dimensional materials and environments
Published in Science and Technology of Advanced Materials, 2022
Xuechen Shen, Jingwen Song, Cansu Sevencan, David Tai Leong, Katsuhiko Ariga
Among various examples in materials nanoarchitectonics, approaches specific to two-dimensional materials and two-dimensional environments (interfacial environments) exhibit exciting possibilities [110–112]. One of the motivations for active research on two-dimensional nanoarchitectonics is rapid advancements in two-dimensional materials. Various two-dimensional materials including graphene families [113,114], two-dimensional semiconductors [115,116], various nanosheets [117,118], two-dimensional organic polymers [119,120], two-dimensional coordination polymers [121,122], and organic thin films [123–125] have been widely researched. They are promising components for materials nanoarchitectonics. In recent reports, various functions are demonstrated by materials constructed from two-dimensional materials as structural components. For example, Tajima et al. reported long lifetimes of charge-separate states in mixed-dimensional (zero-dimensional/two-dimensional) van der Waals heterojunctions of anthracene physically adsorbed on few-layer MoS2 nanosheets [126]. The observed properties would be useful for efficient photocatalysts, photovoltaics, and optoelectronics applications. Vinu and co-workers successfully synthesized hybrids of two-dimensional mesoporous fullerene and carbon materials for energy-related applications such as Li-ion batteries and supercapacitors [127]. For environment-oriented applications, photodegradation of picric acid by two-dimensional materials made from germananes terminated with hydrogen and methyl groups was demonstrated by Sturala, Sofer, and co-workers [128]. Surface plasmon resonance sensors were nanoarchitected from two-dimensional MoS2 nanosheets modified with the supramolecule calix[4]arene as demonstrated by Hu, Chen, and co-workers [129]. This sensor system was utilized for detection of bovine serum albumin antibodies. As summarized in a recent review article by Choi and co-workers, two-dimensional materials can be used in various imaging technologies including magnetic resonance imaging, computed tomography and positron emission tomography as well as conventional optical imaging [130]. These imaging methods are expected to be utilized in image-guided and precision therapy. Free-standing conductive two-dimensional polymer nanosheets were recently reported by Fujie and co-workers [131]. The nanoarchitected polymer nanosheets can make good contact with unevenly structured surfaces, such as the veins of plant leaves. Integration of a Bluetooth system into the polymer nanosheets enables wireless biopotential measurement in plants. As Li and co-workers summarized in a recent review article, stimuli-responsive drug delivery systems can be nanoarchitected from various two-dimensional nanosheets [132]. As Oaki and Igarashi recently demonstrated, application of materials informatics for predicting exfoliation processes to prepare two-dimensional materials has also been proposed [133].