Nanographene composite ion exchanger properties and applications

Nanographene composite ion exchanger properties and applications

Nanographene composite ion exchanger properties and applications 21 Vasi Uddin Siddiqui*, Afzal Ansari*, Imran Khan*,†, Weqar Ahmad Siddiqui*, Md Kh...

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Nanographene composite ion exchanger properties and applications

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Vasi Uddin Siddiqui*, Afzal Ansari*, Imran Khan*,†, Weqar Ahmad Siddiqui*, Md Khursheed Akram‡, Anish Khan§,¶, Abdullah Mohamed Asiri¶,k *Department of Applied Sciences and Humanities, Faculty of Engineering and Technology, Jamia Millia Islamia, New Delhi, India, †Applied Sciences and Humanities Section, University Polytechnic, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh, India, ‡Applied Sciences and Humanities Section, University Polytechnic, Faculty of Engineering and Technology, Jamia Millia Islamia, New Delhi, India, § Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia, ¶Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia, kChemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia

Chapter Outline 21.1 Introduction 629 21.2 Synthesis of a nanographene composite ion exchanger 633 21.3 Properties of a nanographene ion exchanger 641 21.4 Applications of nanographene composite ion exchangers 642 21.5 Conclusion 645 References 646

21.1

Introduction

An ion exchanger defines a wider application to some extent, in the form of different types of it. These may be ion exchanger resins (functionalized porous or gel polymer), zeolites, etc. The 21st century has brought scientific attention toward rapid industrialization, advanced agriculture, and a growing world population, which have resulted in the contamination of water, air, soil, and the aquatic ecosystem. With the need to alleviate health and environmental issues, nanotechnology has triggered interest toward its potential with diversified applications in water treatment, energy application sensing, etc. With drastic changes in material properties at the nanoscale, nanomaterials are a promising candidate. As the two-dimensional atomic thickness “magical material” comes, the solution lies with nanotechnology in this carbon form, that is graphene. Its exceptional properties take it in the environment field, it is with Nanocarbon and its Composites. https://doi.org/10.1016/B978-0-08-102509-3.00021-3 © 2019 Elsevier Ltd. All rights reserved.

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composite in photocatalytic material. It makes the next generation of water treatment membranes and electrode materials for contaminant monitoring or removal [1]. Prior to further discussion, we first discuss the basics of an ion exchanger and its reaction process with some definition. Chen et al. specified the nanographene term with the size of 1–100 nm graphene sheets and 1–5 nm PAHs as “nanographene molecules” with defined chemical structures [2]. Nanographene (NGs), nanographene platelets (NGPs), poly acrylic hydrocarbon (PAH), nanoscale graphene, and graphene quantum dots (GQDs) are referred to as nanographene. Nanographene is graphene at the nanoscale. Three different classes of NGs can be defined according to their edge structures: armchair-edged nanographenes (A-NGs), cove-edged nanographenes (C-NGs), and zigzag-edged nanographenes (Z-NGs), as shown in Fig. 21.1 [3]. Ion exchange material has a diverse range with its diverse application. Without exaggeration, separation technology is the most extensive application of ion exchange material. It possesses different appearances such as natural or artificial, inorganic and polymeric. It might be wood, paper, sand, clay glauconites, zeolite, functional resin or living organisms. Isotopic separation in the nuclear industry was probably the first extensive application in the development of ion exchangers. However, water treatment technology comes first in today’s market in which ultrapure water production

Fig. 21.1 Edge structures of graphene [3].

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is the biggest but not the only concern. Highly diluted contaminates from waste streams are the highest benefits of ion exchanger technology. The pharmaceutics and food industries used ion exchange technology in both physical and chemical perspectives. Hydrometallurgy, biochemistry, and biotechnology used ion exchange technology in ways that weren’t just conventional. Controlled drug delivery could be a major application of the ion exchanger in the medical field [4]. Ion exchange is the equivalent exchange of ions between two or more ionized species located in different phases, at least one of which is an ion exchanger. The process takes place without the formation of chemical bonds. The ion exchanger is a phase containing osmotically inactive means such that the carriers cannot migrate from the phase where it is located. Conventionally, ion exchangers are cation exchanger having a fixed negative charge with exchangeable cation. In contrast, an anion exchanger possesses a transferrable anion with an immovable cation. The framework of the cation exchanger may be regarded as a macromolecular or crystalline polyanion and that of an anion exchanger as a polychain. If both types of groups are present in the same polymer, it is called an amphoteric ion exchanger. Polymers bearing such groups are called chelating polymers or chelating resins. There is no strict difference between ion exchange resin and chelating resin because some polymers can act as chelating or nonchelating substances, depending on what the ion exchange resembles. The characteristic difference between these two phenomena is in the stoichiometric nature of the ion exchange. Every ion removed from the solution is replaced by an equivalent amount of another ion of the same sign. In sorption, on the other hand, a solute is usually taken up nonstoichiometrically without being replaced. Along with absorption and adsorption, ion exchange is a form of sorption [4]. An ion exchange reaction carried out in an ion exchanger (solid phase) and a solution phase in reversible interchange between these ions. Ion exchanger being insoluble in in the medium in which reaction is carried out. If ion exchanger F M+ carrying cation M+ as the exchange ions is placed in an aqueous solution phase containing A+ cations, an ion exchange reaction takes place, which may be represented by the following equation for cation exchange: A+ Ð F A + + M+ F M + + Solid Solution Solid Solution Where F is the insoluble fixed anion with F M+, M+ and A+ are counter cations while ions in the solution that bear the same charge as the fixed anion of the exchanger are called coions, although the contribution of the anion is not appreciably extent. Similarly, the anion exchanger reaction is written as follows: A Ð F + A + M F + M + Solid Solution Solid Solution The main fact is that the electroneutrality is always preserved in both the exchanger and solution phases, and this in turn requires that counterions are exchanged in an

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equivalent amount. Three fundamental requirements must be met to confer ion exchange properties upon a material: 1. An inert host structure that allows diffusion of hydrated ions, that is, a hydrophilic matrix. 2. The host structure must carry a fixed ionic charge, termed the fixed ion. 3. The electrical neutrality of the structure must be established by the presence of a mobile ion of opposite charge to that of the fixed ion, called a counter ion [5].

With the growth in worldwide population as well as the Industrial Revolution and urbanization, air, water, and soil have been severely affected by the pollution discharged from households and industries. Plenty of physical, chemical, and biological technologies have been developed for the removal of toxic gases such as NOx (oxides of nitrogen), SOx (oxides of sulfur), CO (carbon monoxide), NH3 (ammonia), heavy metals, and organic as well as biotoxic materials. The adsorption process leads among all technologies available because it is simple, easy, and effective for different types of pollution and does not produce secondary pollution during the process. A large surface area with pore volume and proper functionalities is the key for a good adsorbent. Among activated carbon, clays, zeolites, mesoporous oxides, polymers, and metal organic frameworks, cabanccous-based adsorbent shows great adsorption capacity and thermal stability [6]. Wang et al. summarized the recent progress of photoluminescent GQDs, including the versatile photoluminescence features, key mechanisms, and promising applications such as energy-related applications, biomedical applications for human health, and sensors for environmental applications on a single particle level [7]. Dong et al. has developed a green and facile sensing system for the detection of free residual chlorine in water based on the fluorescence quenching of GQDs [8]. Benı´tez-Martı´nez et al. also studied the GQD fluorescence nanoparticle behaviour along with some exceptional optical and electrical properties and a number of active sites provided by GQD in analytical nanoscience and technology. [9]. Zhu et al. introduced a new green and universal approach for the synthesis of GQDs with 86% high yield with the only byproducts being H2O and CO2. Different and colorful GQDs are also used in fluorescent bioimaging [10]. Liu et al. used the large surface area and strong π-π interaction on the surface of a three-dimensional (3D) graphene oxide nanostructure for the removal of methylene blue and methyl violet through strong π-π stacking and anion-cation interaction with the activation energy of 50.3 and 70.9 KJ/mol [11]. Bacon et al. studied nanometer-sized graphene, that is, GQDs, with respect to its synthesis approach as either top-down or bottom-up, with applications in energy-related fields such as photovoltaics, organic light emitting diodes, and fuel cells in life sciences such as bioimaging, biosensing, environmental monitoring gives the prospects of free chlorine sensor in water, photoluminescence phosphate sensor also [12]. As the consumption of fossil fuel increases, the growth of CO2 concentration in the atmosphere also increases. Balasubramanian et al. give advances in the development of graphene-based adsorbents for CO2 capture [13]. Gahlot et al. synthesized a nanocomposite ion exchange membrane consisting of graphene oxide and sulfonated polyethersulfone (SPES) and found that the effects on water desalination in terms of ionic flux, power efficiency, and current efficiency are 3.51 mol/m2 h, 4.3 kWh/kg, and 97.4%, respectively. This shows better performance and higher

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stability than direct methanol fuel cell (DMFC) and electrodialysis [14]. Zarrin et al. fabricated a functionalized graphene oxide nafion nanocomposite (F-GO/nafion) membrane and functionalized as potential proton exchange membrane (PEM) for low humidity (30%) and high temperature (120°C) for proton exchange membrane fuel cells (PEMFCs) application [15]. Cao et al. synthesized a poly (ethylene oxide)/ graphene oxide (PEO/GO) composite membrane with a thickness of 80 μm and showed the increasing ionic conductivity from 0.086 to 0.134 S/cm at a temperature range from 25°C to 60°C with 100% relative humidity [16]. This chapter will introduce the different types of synthesis methods of nanographene composite ion exchangers as well as the properties and applications in the effective removal of contaminant species from wastewater. The properties and adsorption performance of nanocomposite ion exchangers will be reviewed, including recent efforts focused at improving the purification performance through chemical and biological means.

21.2

Synthesis of a nanographene composite ion exchanger

Until now, two distinct approaches have been used for the synthesis of exfoliation graphite to graphene: the top-down approach and building up graphene from molecular building blocks, that is, the bottom-up approach. Both approaches include the mechanical exfoliation of highly oriented pyrolyzed graphite. HOPG, a solution-based exfoliation of the graphene intercalation compound (GIC), chemical oxidation/exfoliation of graphite followed by reduction of GO and epitaxial growth on the metallic substrate by means of CVD, thermal decomposition of SiC, organic synthesis based on precursor molecule, respectively. PAHs are also typically molecular graphene composed of all sp2 carbon. Two chemical approaches are used to grow PAH into larger graphene: a controlled chemical reaction under mild conditions in solution and thermolysis starting from well-defined carbon-rich precursors. Whereas the fabrication of nanographene by cutting graphene sheets or via CVD fails to precisely control their resulting sizes and configurations, although the bottomup synthesis approach is available in modern synthetic organic chemistry. Most are typically carried out through the intramolecular oxidative cyclodehydrogenation of predesigned, nonplanar precursors that have oligophenylene or partially prefused oligoarylene structures [2, 17, 18]. Nanographene, or extended polycyclic aromatic hydrocarbon (PAH), has witnessed rapid development over the past few years. These developments can be summarized in four categories: (I) the nonconventional method, (II) a structure incorporating seven- or eight-membered rings, (III) selective heteroatom doping, and (IV) direct edge functionalization. On the other hand, a one-dimensional extension of the graphene molecules leads to the formation of graphene nanoribbons (GNRs) with high aspect ratios. GNRs are a longitudinally extended polymeric system made possible through the solution-mediated or surface-assisted cyclodehydrogenation or graphitization of the tailor-made polyphenylene precursor. In contrast to infinite graphene with a zero band gap, structurally confined nanoscale graphene segments, which are called

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nanographene or graphene quantum dots, show nonzero band gaps that are mainly governed by their size and edge configuration [19]. (I) Nonconventional Approaches for Nanographene Synthesis

Dou et al. synthesized m-dimethoxy HBC 3 and the bisspirocyclic dienone 4 unexpectedly during a scholl reaction with 20% yield. The reaction mechanism is shown in Fig. 21.2 [20]. Arslan et al. fabricated an extended or partially fused hexabezocoronene derivative that is based on the benzannulation and cyclodehydrogenation (scholl oxidation) of simple diaryl alkyne. The partially fused derivatives are a new class of contorted aromatic systems with high solubility, enhanced visible adsorption, and reversible redox processes by using benzannulation. They also prepared a polymer poly (phenylene ethynylene). Figs. 21.3 and 21.4 represent both Schemes [21, 22]. A bowl-shaped PAH that more easily accepts electrons than their contorted hexabenzocoronene precursor and associated strongly with C70 synthesis by Whalley et al. with palladium catalyzed chemistry [23]. Hein et al. prepared an aromatic system by benzannulating silyl-protected arylacetylenes [24]. Zhang et al. synthesized threefold symmetrical and highly substituted nanographene or PAH (hexacatahexabenzocoronenes) (c-HBCs) from simple chemicals using the FeCl3 mediated process [25]. Chiu et al. gave a general method for the synthesis of contorted dibenzotetrathienocoronene (c-DBTTC), a tetrathiophene-fused version of contorted hexabenzocoronenes (c-HBC). C-DBTTC displays the flexibility to adopt either the up-down or the butterfly conformation when grown as cocrystals with the size of an electron acceptor such as C60 [26]. Chen et al. reported sulfur containing PAH and hexathienocoronenes (HTCs) 1 that allowed various substituents to be introduced easily. As compared to c-DBTTCs, the tetra-substituted HTCs leave the two α-positions of the annelated thiophene on the anthradithiophene backbone open, allowing further functionalization and polymerization. Fig. 21.5 shows the synthesis Scheme [28].

Fig. 21.2 Reaction mechanism of compound 3 and 4 [20].

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Fig. 21.3 A series of dialkyne compounds 1a–d provides partially fused HBC derivatives 4a–d and fully fused products 5a and 5d using a two-step benzannulation and cyclodehydrogenation protocol [21].

Moreover, Chen et al. gives a formation scheme to Gemini-type amphiphilic hexathienocoronene (HTCGemini), as shown in Fig. 21.6, which owes its amphiphilicity to two hydrophobic dodecyl chains on one side of the HTC core and two hydrophilic triethylene glycol (TEG) chains on the other side. HTCGemini easily forms a stable radical cation, both in solution and in the bulk, upon oxidative doping with nitrosonium tetrafluoroborate (NOBF4) [27]. In Fig. 21.7, the reaction scheme from Pena et al. for the aspect for the use of the palladium catalyst in the cyclotrimerization of arynes and synthesized triphenylenes with [Pd(PPh3)4] catalyst with reagent CsF, Bu4NF, BuLi [29]. In his further extended work, Pena et al. synthesized hexabenzotriphenylene and other strained polycyclic aromatic hydrocarbons by palladium-catalyzed cyclotrimerization of arynes [30]. Polycyclic aromatic hydrocarbon (PAH)/nanographene constitutes a broad family of organic compounds that have been extensively studied in the fields of material science, environmental chemistry, and medicinal chemistry. Romero et al. synthesized ortho-(trimethylsilyl) triphenylenyl triflates. It also a palladium catalyzed [2 + 2 + 2] cycloaddition of benzene [31]. Alonso et al. synthesized a clover-shaped cata-condensed nanographene with 16 fused benzene rings with a palladium catalyst, as shown in Fig. 21.8 [32]. Another clover-shaped nanographene threefold symmetric C78H36 molecule with 22 fused benzene rings is reported by Schuler et al. by using palladium-catalyzed cyclotrimerization of an aryne and a [2 + 2 + 2] cycloaddition synthesis scheme [33].

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Nanocarbon and its Composites

Fig. 21.4 Scheme of benzannulation of each alkyne of a substituted poly (phenyleneethynylene) 1 provides polyphenylene 3 [22]. (II) Structure Incorporating Seven- or Eight-Membered Rings

As two-dimensionally confined structure of graphene, nanographene in principle consists of only six-membered rings. However, microscopy studies have revealed that graphene contains rings of other sizes, including five-, seven-, and eight-membered rings as defects, particularly at the grain boundaries of the graphene sheet shown by CVD. Therefore, extended PAHs containing non six-membered rings can indeed be considered graphene molecules, which allows model studies of defective graphene and may also find application in optoelectronics [19]. Li et al. developed graphene by a CVD growth process on copper foil (25 μm thick) at a temperature up to 100°C using a mixture of methane and hydrogen [34]. Kim et al. synthesized polycrystalline graphene by the Li et al. method and prepared a TEM sample via the direct transfer method. Atomic resolution TEM imaging, electron diffraction, and Raman spectroscopy analysis confirmed the mostly graphene single layer. By using a complementary TEM technique, it was found that a high-angle graphene boundary (GB) consists of an

Fig. 21.5 Synthesis scheme of HTC 1 and fully cyclodehydrogenated HTC 2 based on anthradithiophene-5,11-dione 3 [27].

Fig. 21.6 Molecular structure of HTCGemini [27].

Fig. 21.7 Scheme for the cyclotrimerization of arynes.

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Nanocarbon and its Composites

Ph Ph OTf

Ph

Ph

Ph

Ph

CsF, [Pd(PPh3)4]

OTf

CH2Cl2/MeCN, 40 °C

Ph Ph

Fig. 21.8 Synthesis of cloverphene.

array of alternating pentagons and heptagons without other defect structures such as vacancies. The pentagon and heptagon GB is fairly stable under the electron beam providing its mechanical integrity [35]. Kurasch et al. observed the GB migration in synthesized polycrystalline graphene atom by atom in real time utilizing AC-HRTEM. These findings suggest that graphene may offer the first experimentally accessible platform for in situ atomic level investigation of a host of GB phenomena, including solute drag, Zener pinning, interaction with other lattice defects, and coupling to mechanical stresses [36]. Lahiri et al. grew graphene layers on a 10 mm diameter Ni (111) single crystal wafer and reported the realization of one-dimensional topological defects in graphene containing octagonal and pentagonal sp2 hybridized carbon rings embedded in a perfect graphene sheet. When the surrounding graphene lattice is doped, the defect acts as a quasi one-dimensional metallic wire. The octagonal containing a defect molecule extends the application of graphene as a membrane material for the selective diffusion of atoms of small molecules through an otherwise impermeable graphene membrane [37]. Bunch et al. demonstrated that a monolayer graphene membrane is impermeable to standard gases, including helium. This pressurized graphene membrane is the world’s thinnest balloon and provides a unique separation barrier between two distinct regions that is only one atom thick [38]. Luo et al. explained that the properties of curved π molecules depend on their curvature by synthesizing and characterizing two types of curved π molecules that are π isoelectronic to the planar HBC. The curvature of the π-face plays a role in determining the frontier molecular orbital energy levels and the π-π interaction embedding heptagon in HBC leads to a novel saddle-shaped molecule [39]. Cheung et al. synthesized two heptagonembedded soluble derivatives of C70H26 (1a, b) and C70H30 (2a, b), a new saddleshaped polycyclic arene, as shown in Fig. 21.9. From saddle-shaped diketones (3a, b), it was found that 1b and 3b behaved as p-type semiconductors in solutionprocessed thin film transistor while the amorphous thin film of 2b appeared as an insulator [40]. Kawasumi et al. synthesized a 26-ring C80H30 nanographene that incorporates five- and seven-membered rings and one five-membered ring by stepwise chemical

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Fig. 21.9 Molecular structures of saddle-shaped conjugated molecules 1a, b, 2a, b, and 3a–c [37].

methods. This new type of nanocarbon has a grossly wrapped structure and the largest PAH other than fullerene and its derivatives, whose structure (Fig. 21.10) has been determined by X-ray crystallography. Nonhexagonal ring defects, particularly the imposition of seven-membered ring negative curvature, not only cause graphene sheets to wrap but also are predicted to alter their electronic and optical properties. That wrapping causes dramatic improvements in the solubility properties of the material [41]. (III) Selective Heteroatom Doping

Heteroatoms can be incorporated in the graphite lattice either during synthesis or postsynthetic treatment. Wang et al. comprised the in situ and posttreatment approaches for the heteroatom doping synthesis method, including chemical vapor deposition (CVD) and the ball milling in situ method while wet chemical methods, thermal annealing of graphene oxide (GO) with heteroatom precursors, and plasma arc discharge approaches are postsynthetic methods. Significant changes in properties come when graphene is doped with group IIIa elements (B), group Va elements (Na nd P), group VIa elements (O and S), group VIIa elements (F, Cl, Br and I), and other dopants such as Si, H2O, O2, and NO [42]. Maiti et al. summarized some of the precursors used in different processes for heteroatom-doped graphene. Benzylamine, imidazole, ethylene diamine, Fe-phthalocyanine, N, N0 -dimethylformamide, polymers (P4VP, PMPY, PPP, PMV1, PMV1) and ammonia, melamine, acetonitrile, and pyridine at 500–1100°C are some of the N (nitrogen) precursors used in the vapor phase growth process for heteroatom-doped CNTs and graphene. In the postsynthetic annealing

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Fig. 21.10 Molecular structure of C80H30 (4) and its deca-t-butyl derivative C120H110 (8) [41].

process, ammonia is used as the N precursor in which oxidized CNT or graphene oxide are used as the starting material. At 400–1100°C in pristine graphene as a starting material, melamine, polypyrrole, urea, and cyanamine are used as N precursors. In another technique used for N-atom doping with GO as the starting material, urea, ammonia, hydrazine, and dicyandiamide are used for the N precursor. A vapor phase growth process carrying aliphatic or aromatic small molecules or polymers as a carbon source doped Boron with Triphenyl borane, Boron powder, Diborane as B (Boron)-precursor. Boric acid as a B precursor is used in the postsynthetic annealing process. Boron or boron tribromide as the B precursor is used in solution processing with GO as the starting material. P (Phosphorous)-precursor, Triphenyl phosphine used in vapor phase growth process methane, ethane, acetylene, benzene as starting material. In the postsynthetic annealing process, triphenyl-phosphine or 1-butyl-3-ethlyimidazoliumhexafluorophos phate used as the P precursor. Dimethyl sulfide, sulfur powder, thiophene, and benzyl disulfide are also used as the S (sulfur) precursor in various processes of synthesis such as the vapor phase growth process, postsynthetic annealing, etc. [43]. (IV) Direct edge functionalization

Polycyclic aromatic hydrocarbons (PAHs) such as pyrene, triphenylenes, and HBC have attracted much attention as fragments of graphene [44]. By electrophilic substitution of graphene, Tan et al. reported the atomically precise chlorination of a nanographene series with a carbon number ranging from 42 to 222 with a molecular size of 1.2–3.4 nm in high yield [45]. According to Tan et al., sulfur annulation of hexa-peri-hexabenzocoronene (HBC) by thiolation of perchlorinated HBC gave on efficient route to modulate the optical and electrochemical properties [46]. Yamaguchi et al. used iridium catalysis for direct C-H borylation of HBC and synthesized

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hydroxy-substituted HBC by oxidation of the boryl group [44]. Ozaki et al. presented APEX (annulative π-extension) methodology, which is a two-step nanographene synthetic method occur at K-resin by Palladium catalyst it unfunctionalized PAH can be directly used for π-component assembly and π-extension without any prefunctionalization [47].

21.3

Properties of a nanographene ion exchanger

Mo et al. designed and synthesized graphene/ionic liquid composite films and investigated five different self-assembled monolayers (SAM) of 1-alkyl-3-(3triethoxysilylpropyl) imidazolium (TSM) salts having different anions [Cl, PF6, SO3, BF4, N(SO2CF3)2] for ion exchange. The results indicated that anions played a great role in determining the graphene surface properties and sensitivity to the solvent system. The effect of the solvent system on the ion exchange ratio on the graphene surface has also been investigated through the anion exchange from Cl to NðSO2 CF3 Þ2  . It was completed in 2 h while the exchange took 24 h in acetone. Meanwhile, the contact angle of ion exchange in pure water was stable at 76 degrees. In contrast, the contact angle of ion exchange in acetone was approximately 65 degrees. The results indicate that the solvent system significantly affected the ion exchanger procedure through the conversion rate and ionic equilibrium [48]. Jang et al. collected the estimated physical constant of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and nanographene platelets (NGPs) from various open literature sources and their own estimations [49] (Table 21.1). Altan et al. studyied the heat epoxy polymer and nanocomposite with 0.5 and 1 wt% of nanographene particles. In Fig. 21.11, a SEM micrograph shows the good dispersion of nanographene particles in the epoxy matrix. The tensile strength increased about 0.5% and 5.2% with the neat epoxy. Stress-strain curves for the neat epoxy and nanographene particle-reinforced epoxy composite can be seen in Fig. 21.12. The result is compatible with the literature in which it is expected that the mechanical properties of the polymer material are generally enhanced by adding nanographene particles [50]. When a graphene sheet is cut into nanofragments, two distinct edge types-zigzag and armchair-are created. Fujii et al. shows the electronic structure of the nanographene or graphene edge, depending on the distinct edge type. Fig. 21.13 shows typical examples of UHV-STM images and scanning tunneling spectroscopy (STS) spectra of hydrogenated graphene edges [51]. Because of the special shape and edge structure, different types of NGs are usually claimed to have a non-Kekule or an open shell structure, which inevitably results in one or more unpaired electrons within the molecule. Thus, Z-NG offers promising potential in electronics and spintronic devices [3]. Gahlot et al. performed the desalination application with a nanocomposite ion exchange membrane (IEM) consisting of GO (0.5, 1.0, 2.5, and 10% w/w). Fig. 21.14 shows the proposed scheme for the water desalination process [14].

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Table 21.1 Estimated physical constants of CNTs, CNFs, and NGPs [49] Carbon nanofibers

Property

Single-walled CNTs

Specific gravity

0.8 g/cm3

Elastic modulus Strength

1 TPa (axial direction)

Resistivity

5–50 μΩ cm

Thermal conductivity

Up to 2900 Wm/K (estimated)

Magnetic susceptibility

22  106 emu/g (radial) 0.5  106 emu/g (axial)

N/A

Thermal expansion

Negligible in the axial direction

1  106 K1 (HT; axial)

Thermal stability Specific surface area

>700°C (in air); 2800°C (in vacuum) Typically, 10–200 m2/g up to 1300 m2/g

450–650°C (in air)

21.4

50–500 GPa

1.8 (AG)–2.1 (HT) g/cm3 AG ¼ as grown; HT ¼ heat-treated (graphitic) 0.4 (AG)–0.6 (HT) TPa 2.7 (AG)–7.0 (HT) GPa 55 (HT)–1000 (AG) μΩ cm 20 (AG)–1950 (HT)Wm/K

10–60 m2/g

NGPs 1.8–2.2 g/cm3

1 TPa (in-plane) 100–400 GPa 50 μΩ cm (in-plane) 5300 Wm/K (in plane) 6–30 Wm/K (c-axis) 22 9106 emu/g (\ to plane); 0.5 9106 emu/g (jj to plane) 1  106 K1 (in-plane) 29  106 K1 (c-axis) 450–650°C (in air) Typically, 100–1000 m2/g, up to 2600 m2/g

Applications of nanographene composite ion exchangers

As graphene becomes the promising candidate for several applications in diverse fields of technology, likewise nanographene puts its hold on environment and health applications which usually done by filtration process of surrounding in terms of water, air and soil which affected most by the urbanization and industrialization. The scientific community takes concerns with NG and its composites and has used the separation technique as a tool for purification of waste. Water desalination, reverse osmosis and nanofiltration, sorption, and chlorine sensors are the progressive applications done by the NG and its composite. They give better results than traditional adsorbents/ion exchangers. All these processes are part of the ion exchanger techniques used in [8, 13, 14, 16, 52, 53].

Fig. 21.11 (A) SEM micrograph of nanographene particles, (B) SEM micrograph of the neat epoxy, (C) SEM micrograph of 0.5 wt% nanographene particles in epoxy matrix, and (D) SEM micrograph of 1 wt% nanographene particles in epoxy matrix [47].

20 1wt% graphene/epoxy

Stress (MPa)

Neat epoxy

0.5wt% graphene/epoxy

10

0 0

5

10

Strain(%) Fig. 21.12 Stress-strain curves of the samples [47].

15

20

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Nanocarbon and its Composites

Fig. 21.13 (A) Atomically resolved UHV-STM tunneling current image (5.6  5.6 nm2) of an armchair edge. A model of the honeycomb lattice is superimposed on the image to clarify the edge structures. (B) dI/dVs curve from STS measurements taken at the edge shown in (A). (C) Atomically resolved STM image of zigzag and armchair edges (9  9 nm2). (D) dI/dVs curve from STS data at a zigzag edge in (C). Images were acquired with a sample bias voltage of Vs ¼ 20 mV.

Liang et al. synthesized graphene oxide through the thermal exfoliation method and used this graphene oxide membrane for the removal of Ca+2 and Mg+2 ions from water with an excellent efficiency, that is, a 1 mg GO membrane can absorb as much as 0.05 mg Ca+2 ions or a 1 g GO membrane can remove 50 mg Ca+2 ions [54]. Tju et al. studied the Fe3O4/CuO/ZnO composite with various concentrations of NGPs as the adsorbent to degrade the organic dye methylene blue. The results were best with 15 wt% concentration of NGP in a dark alkaline condition, that is, 29 mg/g than 18 mg/g without NGP [55]. Sadegh et al. reviewed nanomaterials as effective adsorbents and their applications in wastewater; they found graphene-based adsorbents to be the best with some limitations [56]. Rashvand et al. synthesized a novel graphenebased magnetic nanocomposite sorbent via a one-step coprecipitation method for the extraction and quantification of targeted pharmaceutical and personal care products (PPCPs), that is, ethyl paraben (Et-P), propyl paraben (Pro-P), butyl paraben (ButP), benzophenone 3 (BZ-3), 4-methylbenzilidine camphor (4-MBC), diclofenac (Dic), and ibuprofen (Ibu), in complex environmental water samples [57]. Xu et al. presented the broader perspective of graphene-based materials for radionuclide from water and wastewater along with heavy metals and came to the conclusion that arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), lead (Pb), and

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Fig. 21.14 Schematic representation for graphite to composite membrane preparation [14].

uranium (U) have been studied much more than cobalt (Co), nickel (Ni), antimony (Sb), zinc (Zn), radionuclides, light metalsm and nonmetals ions. Due to a large surface area, an abundant functionalized group, and extremely hydrophilic properties, graphene or graphene oxide as the adsorbent has more advantages [58]. Shabrany et al. also studyied the ZnO/CuO/NGP catalytical activity for the degradation of methylene blue from aqueous solutions. ZnO/CuO with a 10 wt% NGP composite exhibited the highest catalytic activity; it was also found that holes are the main charged carriers on the degradation of MB under visible light and ultrasound irradiation [59]. Firdhouse et al. prepared a low-cost adsorbent using the aqueous extract of Amaranthus polygonoides for the reduction of GO. The synthesized graphene was embedded with silver nanoparticles and Moringa oleifera pulverized seed powder, which possessed better adsorbent properties than conventional activated charcoal in wastewater treatment. This modified graphene was used as an adsorbent for simulated textile, tannery, and paper mill effluents [60]. Li et al. evaluated bird’s nest-like, nanographene-shell encapsulated [email protected] nanoparticles for the Li-ion anode; this revealed a specific capacity of 2634 mAh/g at a current density of 0.2 A/g and an excellent rate and cyclic performance [61].

21.5

Conclusion

Carbon-based graphene nanocomposites are currently controlling the groundbreaking applications in wastewater purification in research fields, all described with an adsorbent, permeable membrane and antimicrobial activity. As we can find, to simplify opened new pathways of purification of wastewater from graphene nanocomposite

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with combination of various properties as nanofillers. This chapter has highlighted the different types of fabrication processes and the applications of different types of graphene nanocomposites as ion exchangers in microextraction techniques. It is evident from the recent research that four different types of novel preparation methods of graphene nanocomposites via different precursors which is act as a catalyst. Certain modified methods have also been shown for nanocomposite fabrication that are effective for the sorption of different heavy metals from the water. Newly designed and synthesized nanocomposite films play a significance role in determining graphene surface properties and solvent systems through ion exchange. The estimated properties of different types of NG, NGPs, GQT, CNF, and CNT are specific gravity, elastic modulus, strength resistivity, thermal conductivity, magnetic susceptibility, thermal expansion, thermal stability, and specific surface area, respectively. The applications of graphene nanocomposites or nanoparticle sheets have been extensively used in water purification. Recently, graphene nanocomposites have shows very capable application in water purification, that is, water desalination, sorption, catalytic activity, reverse osmosis, nanofiltration, chlorine sensors, and remediation of radionuclide and heavy metal agents in complete water purification systems.

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