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Carbon Nanotubes: Preparation and Surface Modification for Multifunctional Applications
Published in Vineet Kumar, Praveen Guleria, Nandita Dasgupta, Shivendu Ranjan, Functionalized Nanomaterials I, 2020
Jingyao Sun, Jing Zhu, Merideth A. Cooper, Daming Wu, Zhaogang Yang
Another type of covalent modification method of CNTs is defect modification (Strategy B in Figure 6.7). Chemical transformation of defect sites is utilized in this process for CNT modification. Here, the defect sites can be the holes in the sidewall or end-tips of CNTs, oxygenated sites, and pentagonal or heptagonal irregularities in hexagonal graphene frames (e.g., the Stone–Wales defect, also known as 7-5-5-7 defect, as seen in Figure 6.8). Stone–Wales defect on the sidewall of a CNT: (-) Thirteen-layer defect-free tube model and (α) Thirteen-layer defective tube model (Reproduced with permission (Lu, Chen, and Schleyer, 2005).).
CARBON NANOTUBES: UPDATE AND NEW PATHWAYS
Published in Rainer Wolf, Gennady E. Zaikov, A. K. Haghi, Pathways to Modern Physical Chemistry, 2016
F. RAEISI, S. PORESKANDAR, SH. MAGHSOODLOU, A. K. HAGHI
Recently, an interesting mode of plastic behavior has been predicted in nanotubes.97 It is suggested that pairs of 5-7 (pentagon-heptagon) pair defects, called a Stone-Wales defect,98 in sp2 carbon systems, are created at high strains in the nanotube lattice and that these defect pairs become mobile. This leads to a step-wise diameter reduction (localized necking) of the nanotube. These defect pairs become mobile. The separation ofthe defects creates local necking of the nanotube in the region where the defects have moved. In addition to localized necking, the region also changes lattice orientation (similar in effect to a dislocation passing through a crystal). This extraordinary behavior initiates necking, but also introduces changes in helicity in the region where the defects have moved (similar to a change in lattice orientation when a dislocation passes through a crystal). This extraordinary behavior could lead to a unique nanotube application: a new type of probe, which responds to mechanical stress by changing its electronic character. High temperature fracture of individual nanotubes under tensile loading has been studied by molecular dynamics simulations.99 Elastic stretching elongates the hexagons until, at high strain, some bonds are broken. This local defect is then redistributed over the entire surface, by bond saturation and surface reconstruction. The final result of this is that instead of fracturing, the nanotube lattice unravels into a linear chain of carbon atoms. Such behavior is extremely unusual in crystals and could play a role in increasing the toughness by increasing the energy absorbed during deformation of nanotube-filled ceramic composites during high temperature loading.
Functionalization of Graphite and Graphene
Published in Titash Mondal, Anil K. Bhowmick, Graphene-Rubber Nanocomposites, 2023
Akash Ghosh, Simran Sharma, Anil K. Bhowmick, Titash Mondal
In quest of understanding the functionalization of graphene and graphitic materials, it is important to understand the structure of the graphene and graphitic material. The contribution of thermodynamics and kinetics factors toward modification of graphene is critical to understand. Ideally, functionalization of graphene can be targeted at the basal plane or at the edges of the material. However, modification at the basal plane of the graphene is tricky. Modification at the basal plane results in the formation of high energy radicals. Thermodynamically, the formation of such radicals is highly unfavorable. In terms of the kinetic purview, change in hybridization of modified carbon (post-modification) introduces geometric constraints. Hence, modification of graphene at the basal plane is challenging task, except under specific conditions. One of such specific case is the defect specific modification of the graphene. Graphene and graphitic materials demonstrate topological isolated defects in their ring, commonly referred to as the Stone–Wales defect. In an ideal situation, graphene and graphitic materials demonstrate a perfect array of hexagonal ring system. However, in the case of Stone–Wales defect, one carbon-carbon bond of the ring is flipped by 90° (participation of four hexagonal rings) and results in the formation of two heptagonal and two pentagonal rings in the system as shown in Figure 4.2a. The other common type of defect pertains to the missing atom in the ring. Vacancy of atoms in the framework leads to Jahn–Teller distortion at those sites. This results in the saturation of three dangling bonds over the vacant site, while the other bond remains further apart due to the introduction of the constraint in the geometry. This results in the formation of five- and nine-membered ring in the skeleton as shown in Figure 4.2b. Defect specific modification of graphene and its analogs is possible and will be discussed in detail in the later section of the chapter. In contrary to the basal plane modification, edge specific modifications can be an easier route for modification of the graphene and its analogs. This is so because the C=C bonds at the edges are more strained and surface modifications favor the conversion of sp2 hybridized carbon of graphene to take up a more relaxed sp3 hybridized form.
Preparation, properties, applications and outlook of graphene-based materials in biomedical field: a comprehensive review
Published in Journal of Biomaterials Science, Polymer Edition, 2023
Luyang Yao, Anqi Chen, Li Li, Yu Liu
Derivatives of graphene include graphene oxide (GO) and reduced graphene oxide (rGO), in addition, halogenated graphene, hydrogenated graphene and graphdiyne [37], which have different chemical and mechanical properties compared to graphene [38]. GO is obtained from graphite by using strong oxidants such as concentrated sulfuric acid, potassium permanganate. To prepare GO, Brodie, Hummers, and Staudenmaier methods are utilized, a common feature of all three methods is the ultimate oxidation of graphite to different degrees, and Hummers method is usually used which is safer and more environmentally friendly [39], and introduces functional groups–carboxyl, carbonyl groups to the edge and epoxide, hydroxyl groups to the surface (Lerf–Klinowski model) [24]. In fact, there are defects in the carbon skeleton structure, like pentagons, heptagons and their combinations, such as Stone-Wales defect [40], induce long-range deformations, which modify the electron trajectories [41]. rGO is obtained from GO which occurs in reduction reaction using chemical or physical treatments and results in partially deoxygenate compared to GO. Chemical reductants generally use hydrazine, sodium borohydride, glucose, ascorbic acid, pyrogallol, KOH, HI, and amino acid [42], and also apply some green chemical synthesis methods of natural extracts [43], like Mangifera indica L. along with Solanum tuberosum L. [14], and Euphorbia heterophylla L. [44].
A DFT Based Approach for NO2 Sensing Using Vander Wall Hetero Monolayer
Published in IETE Journal of Research, 2023
Suman Sarkar, Papiya Debnath, Debashis De, Manash Chanda
When π bonded Boron and Nitrogen atoms in h-ZBNNR are rotated with an angle 90o then a crystallographic defect is formed, known as Stone–Wales defect. As a result, the four neighboring hexagon breaks into two pentagons as well as two heptagons facing each other. Due to the breaking of the B-N bond, one B-B and one N-N bond are created on each side as shown in Figure 2(e) having bond lengths of 1.69 and 1.36 Å, respectively also B-N bonds near to distorted region change to 1.44 and 1.46 Å. After NO2 absorption to the distorted side N-B bonds are formed with B of h-ZBNNR and N of NOAl-doped2 is found to be 1.8 Å and makes an angle of 104.08o and its electrochemical properties are also studied. The adsorption energy is found −0.87 eV and due to the adsorption of NO2 on h-ZBNNR, NO2 transfers −0.141e to h-ZBNNR (S.W). The EDD diagram of the corresponding system is also shown in Figure 3(d,g).
Density functional theory study on the adsorption of CO on X= (Mn and Tc)-doped graphene sheets in the presence and absence of static electric fields
Published in Molecular Physics, 2021
Mahdi Rezaei-Sameti, Mahdi Rakhshi
Dai et al. [18] indicated that B-doped graphene was a good candidate for adsorbing NO and NO2 molecule graphene, while the S-doped was suitable for only NO2. They found that the B- and S-doped graphene could be a good sensor for detecting NO and NO2. Ao et al. [19] demonstrated that Al-doped enhancement sensitivity of graphene to determine CO gas, and with adsorbing CO gas, the electrical conductivity of CO/graphene complex increase. Other theoretical and experimental studies showed that the existence of defects, such as vacancy [20], pentagonal-octagon defect [21], Stone–Wales defect [22] and inverse Stone–Wales defect [23], in G and carbon nanotubes altered the structural, electrical, and magnetic properties of system [24–26]. The calculated results of Zhou et al. [27] indicated that the vacancy-defected graphene was more sensitive to chemisorb H2CO molecule compared with the pristine one.