Polymer layered double hydroxide hybrid nanocomposites

Polymer layered double hydroxide hybrid nanocomposites

Polymer layered double hydroxide hybrid nanocomposites 13 Shadpour Mallakpour1,2 and Elham Khadem1 1 Organic Polymer Chemistry Research Laboratory, ...

6MB Sizes 0 Downloads 63 Views

Polymer layered double hydroxide hybrid nanocomposites

13

Shadpour Mallakpour1,2 and Elham Khadem1 1 Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan, Islamic Republic of Iran, 2Research Institute for Nanotechnology and Advanced Materials, Isfahan University of Technology, Isfahan, Islamic Republic of Iran

13.1

Introduction

Polymer nanocomposites (NCs) are encouraging materials due to their multipurpose properties and huge amount of alterable composition/preparation attainable by fine tuning. Compared to nanofillers used for hybrid nanomaterials, layered double hydroxide (LDH), due to its nontoxicity, structural homogeneity, high bound water content, and high reactivity toward organic anionic species is appropriate for several specific requirements (Mallakpour et al., 2016a; Omwoma et al., 2014). The layered crystalline geometry of LDH comprises different intercalating anionic species which can interchange with much larger organic anionic molecules and make it favorable as a filler (Basu et al., 2014; Radulescu et al., 2007). On the other hand, hybrid nanostructures composited from LDH and carbonaceous nanomaterials (e.g., carbon nanotube (CNT) and graphene) have drawn a great deal of attention. It is the combination of the special properties of the parent materials, which provides unique properties to hybrid materials. The carbonaceous nanomaterials combined with LDH not only avoid the restacking and aggregation of LDH, but also develop the conductivity, catalytic activity, and thermal stability of the polymeric composites (Cao et al., 2016; Daud et al., 2016; De Marco et al., 2017). Polymer nanofiller hybrid composites developed using LDH/carbonaceous nanofiller hybrids have drawn great interest lately because of the unique properties obtained by the combination of the parent materials. Modification of LDH with carbonaceous nanomaterials and changing surface properties not only improves the compatibility between the filler and the polymer, but also creates a strong interaction and good adhesion between the components of composite (Burgos-Ma´rmol and Patti, 2017; Pavlidou and Papaspyrides, 2008; Peng et al., 2006). LDHs, due to their capacity to separate into distinct layers, and the prospect of changing their surface chemistry through ion exchange reactions with organic and inorganic anions, can have a significant role in the production of polymer NCs with high thermal stability (Choudalakis and Gotsis, 2009; Ivanov et al., 2001; Mallakpour et al., 2015).

Layered Double Hydroxide Polymer Nanocomposites. DOI: https://doi.org/10.1016/B978-0-08-101903-0.00013-6 © 2020 Elsevier Ltd. All rights reserved.

532

Layered Double Hydroxide Polymer Nanocomposites

Numerous reviews and book chapters have already been devoted to many aspects of polymer/LDH-NCs and LDH/carbonaceous nanofiller hybrids, highlighting the synthesis, characterization, properties, and use of LDH-type minerals as nanoreinforcers in polymer matrices (Basu et al., 2014; Costa et al., 2007; Leroux and Besse, 2004; Mallakpour and Khadem, 2017b; Papaspyrides and Kiliaris, 2014; Peng et al., 2006). The object of this chapter is first to update the study field of the polymer/LDH/carbonaceous nanofiller hybrid NCs by supplying as much data as needed regarding the treated LDH materials and interaction of polymer with the modified LDH/carbonaceous nanofiller hybrids and characterization, in addition to this academic point of view, the potential applications of those systems are also described.

13.2

Modification of LDHs with organic compounds

The modification of LDHs is as an inescapable method in the preparation of polymer NCs, to expand the interlayer space of LDH materials and facilitate intercalation of a large hydrophobic polymeric chain. Since the hydroxide layers of LDHs have a positive charge, organic anionic surfactants used for treatment have at least one anionic group and a long hydrophobic tail to reduce the surface energy of the treated LDHs (Costa et al., 2007; Mallakpour and Dinari, 2015a). Techniques such as coprecipitation, ion exchange, and the regeneration method not only can be used for the fabrication of LDH crystals, but also can be applied for the treatment of LDH using organic surfactants. In the LDH compound, the anion exchange capacity is highly related to the (1) electrostatic interaction among the host cationic brucite layers and the exchangeable anions and (2) quantity of free energy consisting of the changes of hydration. The order of preference for the anion exchange potential and conformation of the interlayer anions into LDH are controlled based on the electrochemical sequence shown below: 2 2 2 22 22 22 22 22 NO2 3 , Br , Cl , F 2 , OH , SO4 , CrO4 , HAsO4 , HPO4 , CO3

In the anion exchange process in the interlayer area of LDHs, factors such as increasing charge and decreasing ionic radius, pH value .4, appropriate choice of solvents, high temperature, and chemical composition and nature of the LDH, are key agents in improving the ability to exchange (Elbasuney, 2015; Saha et al., 2016). By the anionic exchange method, γ-poly(glutamic acid) (γ-PGA) is an anionic macromolecule used for the treatment of MgAl-LDH (Chiang and Wu, 2011). Changes in the basal spacing of LDH were studied at diverse temperatures by means of in situ wide-angle X-ray diffraction and in situ Fourier transform infrared (FT-IR) spectroscopy. They showed that a noteworthy reduction in the interlayer ˚ was possible by increasing the temperature spacing of LDH from 15.0 to 11.5 A   from 30 C to 130 C (Fig. 13.1). This occurrence may be related to the dehydration

Polymer layered double hydroxide hybrid nanocomposites

533

Figure 13.1 Conceptual illustration of the possible structure formation of LDH-PGA at 30 C and 130 C. Source: Adapted from Chiang, M.-F., Wu, T.-M., 2011. Intercalation of γ-PGA in Mg/Al layered double hydroxides: an in situ WAXD and FTIR investigation. Appl. Clay Sci. 51, 330334, with kind permission of Elsevier.

reaction and elimination of interlayer water molecules without destruction of the layered structure. Mallakpour et al. (2016b) used N-trimellitylimido-L-amino acids for modification of LDHs by the coprecipitation method under fast and green ultrasonic irradiation. The results of the thermogravimetric analysis (TGA) showed that the first degradation temperatures changed to lower temperatures and the thermal stability of LDH was reduced by intercalation of an organic chain into the space of the LDH. This is due to the inorganic carbonates, which have higher thermal stability than the organic dicarboxylate anions between layers. In analogous work, they prepared the modified LDHs by N,N0 -(pyromellitoyl)-bis-L-amino acids diacid as supporting agents via anion exchange reaction (Mallakpour and Dinari, 2015a). Amino acids used in this processes were L-isoleucine, L-leucine, L-phenylalanine, L-alanine, Lmethionine, and S-valine. FT-IR, X-ray diffraction (XRD), TGA, and transmission electron microscopy (TEM) were used for the characterization of the modified LDHs. For example, the XRD result showed that LDH/CO322 has a basal spacing of about 0.75 nm, which, after organic treatment via anionic exchange, XRD shifted to a lower angle position and basal spacing enlarged to maximum 2.15 nm for LDH/N,N-(pyromellitoyl)-bis-L-phenylalanine (Mallakpour et al., 2013). They showed that the best distribution was obtained for LDHs modified with N-trimellitylimido-L-amino acids compared with the N,N0 -(pyromellitoyl)-bis-L-amino acids. The TEM images of the LDH/CO322 and the LDH/N-trimellitylimido-L-leucine are displayed in Fig. 13.2. As can be observed, LDH has a smooth surface with overlapped crystal in a hexagonal form, while the modified LDH indicates dispersed hexagonal sheets with rounded corners. Li et al. (2011) mixed sulfate terminated low-molecular-weight polyethylene glycol (PEG) derivatives with MgAl-LDH and incubated it in a water-bath shaker. After surface modification of LDHs and fabrication of PEG haired LDHs, scanning electron microscopy (SEM) and TEM images (Fig. 13.3) did not show any changes in particle size, while the shape of NPs changed from hexagonal into smooth pielike disks.

Figure 13.2 TEM micrographs of the CO322/LDH (A, B) and LDH-PL (C, D). Source: Adapted from Mallakpour, S., Dinari, M., Behranvand, V., 2013. Ultrasonic-assisted synthesis and characterization of layered double hydroxides intercalated with bioactive N, N0 -(pyromellitoyl)-bis-l-α-amino acids. RSC Adv. 3, 2330323308, with kind permission of the Royal Society of Chemistry.

Figure 13.3 TEM (AC) and SEM (DF) images of sulfate PEG0.6 k/LDH (A, D), sulfate PEG2 k/LDH (B, E), and sulfate PEG5 k/LDH (C, F) composite particles after 72 h reaction. Scale bar: 100 nm; subscript represents the number average molecular weight. Source: Adapted from Li, D., Xu, X., Xu, J., Hou, W., 2011. Poly (ethylene glycol) haired layered double hydroxides as biocompatible nanovehicles: morphology and dispersity study. Colloids Surf. A: Physicochem. Eng. Aspects 384, 585591, with kind permission of Elsevier.

Polymer layered double hydroxide hybrid nanocomposites

13.3

535

Layered double hydroxide/Carbonaceous nanofiller hybrids

The mineral hydrotalcite was discovered in Sweden around 1842 and for the first time the stoichiometry formula of [Mg6Al2(OH)16]CO3  4H2O was assessed by Manasse in 1915. The major structural feature of LDH was determined by crystal XRD in 1960. LDH is a mineral material with positively charged layers made up of 2D highly tunable brucite-like layered crystal structure with an interlayer expanse comprising charge-compensating anions and some water particles, as required for the stabilization of the crystal structure (Evans and Slade, 2006; Rives, 2001). On the other hand, partial substitution of M(III) cations for M(II) cations, positively charged layers create in LDHs are neutralized by interlayer multivalent anions. The basal spacing of LDHs enlarges from 0.48 nm to about 0.77 nm due to presence of anions and solvation molecules. LDHs can be obtained by both synthetic and natural bases. Hydrotalcite with the chemical formula [Mg6Al2(OH)16]CO3  4H2O is the most usually recognized naturally occurring LDH (Rives et al., 2014; Theiss et al., 2016; Tonelli et al., 2013). Several methods, such as coprecipitation, anionic exchange, reconstruction, hydrothermal, and microwave treatments have been proposed for the synthesis of LDH. A number of reviews and books have already been issued that focus on the synthesis and application of LDHs (Galva˜o et al., 2016; He et al., 2006; Qu et al., 2016; Theiss et al., 2016). Despite the great properties that have been attained, these materials often have a rather low electric conductivity and poor adhesion, rare energy density, and low-rate performance. Another challenge is agglomeration and shrinkage of LDHs. These agents may limit the performance of LDHs in field charging/discharging cycles and lead to mechanical degradation of electrodes (Pacuła et al., 2016; Wang et al., 2016). To overcome this problem and increase the performance of pseudocapacitive materials, a combination of LDH and carbonaceous nanomaterials, such as carbon nanofiber (Ma et al., 2016), activated carbon (Lv et al., 2018; Ochai-Ejeh et al., 2017), CNT (Heli et al., 2016), and graphene (Kiran et al., 2017) have been proposed as an ideal method to optimize the electrochemical performance. Schematics of LDH/CNT and LDH/graphene hybrids are displayed in Fig. 13.4. Carbonaceous nanomaterials can serve as hard templates and support the LDHs, which facilitated the accommodation of large-volume changes during the charge/discharge process. Also, they provide a stable cycling performance and improve the chemical stability and conductivity. The resulting LDH/ nanocarbon hybrids can easily form an electron pathway and a network of stress transfer between carbonaceous nanomaterials and LDHs, which is a significant aspect for advanced functional materials. Thus, they enable fast redox charge transfer processes and synergistic enhancement of energy storage performance (Wang et al., 2016; Zhao et al., 2012). Additionally, compared to unmodified LDH, LDH/carbonaceous nanofiller hybrids exhibit the catalyst and adsorption tendency of anionic pollutants owning to their improvement in surface area, better stability, high interlayer spacing, higher anion

536

Layered Double Hydroxide Polymer Nanocomposites

Figure 13.4 Schematic illustration showing: (A) graphene 1 LDH: (a0 ) intercalation of graphene layers into the interlayer space of LDHs; (b0 ) in situ grown LDHs parallel to the graphene layer; (c0 ) in situ grown LDHs vertical to the graphene layer; (d0 ) graphene in situ grown on the surface of LDHs; and (B) CNT 1 LDH: (a) CNTs uniformly attached to the surface of LDH flakes; (b) intercalation of CNTs into the interlayer space of LDHs; (c) LDHs in situ grown on the surface of CNTs; (d) randomly entangled CNTs grown from LDHs; (e) aligned CNT arrays grown from LDHs; (f) CNT-array double helix grown from LDHs. Source: Adapted from Zhao, M.Q., Zhang, Q., Huang, J.Q., Wei, F., 2012. Hierarchical nanocomposites derived from nanocarbons and layered double hydroxides-properties, synthesis, and applications. Adv. Funct. Mater. 22, 675694, with kind permission of John Wiley and Sons.

exchange tendency, outstanding selectivity for diverse toxic metals, growth in chelating and binding sites, and low toxicity. According to these superior characteristics, they can act as a catalyst and promising adsorbent for wastewater treatment (Daud et al., 2016). Wang et al. (2017) prepared ultrathin NiCo-LDH on carbon cloth (CC) by one-pot coprecipitation approach. The prepared composite was used as a binderfree biosensor for glucose detection with a sensitivity of about 5.12 μA/μM/cm2.

13.4

Synthesis of LDH/Carbonaceous nanofiller hybrids

The first action to assay the required properties of LDH/carbonaceous nanofiller hybrids and in extensive applications is their synthesis and preparation. Several methods have so far been discovered to achieve a synergistic mixture of LDH/carbonaceous nanofiller hybrids (Cao et al., 2016; Daud et al., 2016; Zubair et al., 2017), as described below. 1. Coprecipitation synthesis This technique is widely applied for the synthesis of LDH/carbonaceous nanofiller hybrids. During the reaction, carbonaceous nanostructures are sonicated in distilled water

Polymer layered double hydroxide hybrid nanocomposites

537

and combined with an aqueous solution of cations salts (M21 and M31) under stirring at a controlled pH. Materials, such as glucose, hydrazine, urea, and sodium sulfide are used as reducing agents to adjust the pH and reduce the carbonaceous nanostructures (Bai et al., 2016; Qiao et al., 2015). Heli et al. (2016) used this method to synthesize CoAl-LDH/ multiwalled carbon nanotubes (MWCNTs) and exerted in the electroreduction, electrocatalytic oxidation, and determination of hydrogen peroxide. In other work, MgAl-LDH/ MWCNT was prepared and characterized by SEM/energy-dispersive spectroscopy (EDX), FT-IR, BET, XRD, and TGA (Long et al., 2016). The prepared nanohybride was used for the removal of Congo red with an adsorption capability of 595.8 mg/g. 2. Exfoliation-restacking synthesis In this method, delamination of LDH was performed in a formamide solution under ultrasonication. Then, second nanofiller (carbonaceous nanomaterials) self-assembly to LDH via electrostatic interaction leads to exfoliated LDHs. The negatively charged species or functional groups with negative charge on the surface nanofillers have a critical role for attaching to positively charged LDHs and successful preparation of the LDH/ nanofiller hybrid (Qiao et al., 2013; Wang et al., 2016). In a research work, MWCNT was modified with melamine and 4,40 -diphenylether dicarboxylic acid and then combined with ZnAl-LDH via electrostatic force (Fig. 13.5) (Qiao et al., 2013). The structure properties of ZnAl-LDH/MWCNT hybrids were characterized by XRD, TEM, FT-IR, and TGA. TGA results demonstrated that functionalized-MWCNTs/LDH nanosheet hybrids due to high char yield at 800oC can serve as a potential flame-retardant material. %

Figure 13.5 Schematic description of F-MWCNTs/exfoliated LDHs nanosheet hybrid composites synthesis. Source: Adapted from Qiao, Z., Gao, C., Sun, B., Ai, S., 2013. Synthesis and characterization of functionalized multi-walled carbon nanotubes/exfoliated layered double hydroxide nanosheets hybrids via electrostatic force. J. Inorg. Organomet. Polym. Mater. 23, 871876, with kind permission of Springer.

538

Layered Double Hydroxide Polymer Nanocomposites

3. Layer-by-layer assembly This method involves the electrostatic interaction between negatively and positively charged materials. In this process, from a polymeric solution such as PVA, poly(ethylene imine) (PEI), and polyaniline (PANI) and substrate supports are used to obtain a cationic surface and deposit negatively charged materials and positively charged LDHs (Wang et al., 2015). For example, Chen et al. prepared multilayer films of (LDH/PVA/graphene oxide/PVA)n by hydrogen-bonding-based layer-by-layer assembly (Chen et al., 2010). They were characterized by XRD, atomic force microscope (AFM), UV-Visible Spectroscopy and SEM. To´th et al. introduced layer-by-layer assembly as a suitable method for building a sandwich-like structure by stratifying delaminated LDH and MWCNT in the presence of a tenside (To´th et al., 2014). 4. One-pot hydrothermal synthesis This method also uses a urea-hydrolyzed method for the preparation of LDH/graphene (LDH/G) NCs and LDH/CNT NCs. In this technique, urea was mixed with a salt solution, and then was added to an ultrasonicated suspension of second nanofiller (G or CNT). The obtained mixture was transferred to a Teflon-lined stainless autoclave and heated at the required temperature for a long time to produce the reduced GO. The hydrothermal method is limited to some cationic LDHs. However, it produces a well-crystallized NC with the same morphology as coprecipitation (He et al., 2015; Peng et al., 2017a). Liu et al. fabricated [email protected] carbon nanotubes (SWCNTs) by a hydrothermal method (Fig. 13.6A) (Liu et al., 2018). The SEM (Fig. 13.6B and C) and TEM (Fig. 13.6D and E) images of [email protected] showed that the NiFe-LDHs are efficiently grown around the SWCNT units and lattice fringes of 0.25 nm attributed to the (012) lattice plane of NiFe-LDH. In this regard, the use of a microwave method in LDH/carbonaceous nanofiller hybrids synthesis over conventional hydrothermal process is gaining importance and is introduced as a reliable method to attain highly crystalline layered structures. Lonkar et al. prepared LDH/graphene nanohybrids by a facile and rapid microwave method (Lonkar et al., 2015). 5. In situ synthesis This method was done in two states, either by in situ growth of LDH on the second nanofiller (Chen et al., 2014) or by in situ growth of nanofiller on the LDH. During the first state, oxygen functional groups on the nanofiller surface attract divalent and trivalent cations in the solution by electrostatic attractions due to having negative charge. Thus, LDHs form on the carbonaceous nanostructures by the precipitation method. However, the second state is uncommon and few have been reported. This method involved formation of carbonaceous nanomaterials inside LDH corridors by carbonization of interlayer organic anions, and growth of carbonaceous nanostructures through chemical vapor deposition (Momodu et al., 2015). Wang et al. (2010) used ZnAl-LDH/CNT hybrids prepared by this method (Fig. 13.7) for photodegradation of methyl orange molecules under UV irradiation.

13.5

Applications of LDH/Carbonaceous nanofiller hybrids

13.5.1 Removal of pollution The inherent structural properties allow LDH/carbonaceous nanomaterial hybrids to become favorable sorbents to remove a range of anionic pollutants in aqueous

Polymer layered double hydroxide hybrid nanocomposites

539

Figure 13.6 (A) Schematic illustration of the synthesis process of [email protected] (B, C) SEM images of [email protected] in different magnifications. (D) TEM image of NiFe-LDH. (E) HRTEM image of [email protected] Source: Adapted from Liu, H., Zhou, J., Wu, C., Wang, C., Zhang, Y., Liu, D., et al., 2018. Integrated flexible electrode for oxygen evolution reaction: layered double hydroxide coupled with single-walled carbon nanotubes film. ACS Sustainable Chem. Eng. 6 (3), 29112915 with kind permission of the American Chemical Society.

solutions. The presence of carbonaceous nanomaterials with a distinctive nature, such as numerous oxygen-containing functional groups, robust chemical inertness, small particle sizes, low cost, high surface area, low toxicity, easy functionalization, and suitable biocompatibility, LDH hybrids can fabricate tailored functional composite-based LDHs (Cao et al., 2016; Zhao et al., 2012). Gong et al. (2011) prepared adsorbents based on direct assembling of the performed anisotropic LDH nanocrystals (LDH-NCs) onto the surface of carbon nanospheres (labeled as [email protected]) for removal of Cu21. In an initial Cu21 concentration of 10.0 mg/L, the maximum adsorption capacity of the nanoassembly toward Cu21 was calculated

Figure 13.7 Schematic illustration of the synthesis pathway for in situ growth of ZnAl-LDH on to the modified CNTs in the presence of Lcysteine. Source: Adapted from Wang, H., Xiang, X., Li, F., 2010. Hybrid ZnAl-LDH/CNTs nanocomposites: noncovalent assembly and enhanced photodegradation performance. AIChE J. 56, 768778, with kind permission of John Wiley and Sons.

Polymer layered double hydroxide hybrid nanocomposites

541

to be only B19.93 mg/g. As seen in Fig. 13.8, LDH nanosheets were arbitrarily deposited onto the CNs’ surface. Also, the suspension of LDH hybrid in a CH3OH/ H2O solvent was stable for more than 2 months without undergoing aggregation (Fig. 13.8C). In other work, the maximum uptake capacity of Cd(II) on carbon quantum dots (CQDs)/ZnAl-LDH was estimated at about 12.60 mg/g at 20 min, owing to the accessible exterior sites on the CQD/ZnAl-LDH (Rahmanian et al., 2018). Also, the experimental data confirmed that the adsorption isotherms and adsorption kinetics of Cd(II) on adsorbent were well-fitted by the Freundlich isotherm model and pseudo-second-order kinetic model, respectively. The amount of CQD materials can have an effective role in enhancing the adsorption capacity of anions (Koilraj et al., 2017). The results of adsorption efficiency of Sr21 and SeO422 on MgAl-NO3-LDH/CQD hybrids showed that the process of adsorption occurs via coordination with the 2 COO2 group of CQD, whereas that of SeO422 is accomplished through ion exchange with NO32 in the interlayer galleries of LDH. Based on TEM images, the diameters of CQD and LDH platelets were estimated at about 35 nm and 100 nm, respectively. Also,

Figure 13.8 TEM images of (A) LDH-NCs, (B) CNs, and (D) the assembly of [email protected] composites. (C) A translucent and stable suspension of LDH-NCs in methanol/ water solvent. Source: Adapted from Gong, J., Liu, T., Wang, X., Hu, X., Zhang, L., 2011. Efficient removal of heavy metal ions from aqueous systems with the assembly of anisotropic layered double hydroxide [email protected] carbon nanosphere. Environ. Sci. Technol. 45, 61816187, with kind permission of the American Chemical Society.

542

Layered Double Hydroxide Polymer Nanocomposites

TEM image showed that the CQD was well dispersed on the layered LDH nanosheets (Fig. 13.9A,c). The elemental mapping of the prepared hybrid is displayed in Fig. 13.9B. The MgAl-LDH/CQD hybrid was also used to remove anionic organic dye (Zhang et al., 2014b). The maximum uptake capability of methyl blue (MB) was only 185 mg/g. The adsorption performance of the obtained hybrid fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model. The main reasons for the adsorption of MB on the surface of the LDH/CQD hybrid are attributed to the cooperative contribution of H-bonding between MB and CQD as well as electrostatic interaction between MB and LDH. Wang et al. (2018) synthesized hydrangea-like carbon sphere (CS)@NiAl LDH by a one-step hydrothermal synthesis strategy (Fig. 13.10). They reported that the maximum sorption capacity of U (VI) on [email protected] (0.6 mmol/g) was twice as high as that of U(VI) on NiAl LDH (0.3 mmol/g) and approximately 1.5 times higher than that of U(VI) on CS (0.4 mmol/g) at pH 5 5.0 and T 5 298K.

Figure 13.9 (A) TEM images of (a) CQD, (b) MgAl-NO3-LDH, and (c) MgAl-NO3-LDH/ CQD (20%). (B) TEM EDX elemental mapping on MgAl-NO3-LDH/CQD (20%). Source: Adapted from Koilraj, P., Kamura, Y., Sasaki, K., 2017. Carbon-dot-decorated layered double hydroxide nanocomposites as a multifunctional environmental material for Co-immobilization of SeO42 and Sr21 from aqueous solutions. ACS Sustainable Chem. Eng. 5, 90539064, with kind permission of the American Chemical Society.

Polymer layered double hydroxide hybrid nanocomposites

543

Figure 13.10 The synthetic procedure of hydrangea-like [email protected] nanocomposites using CS and NiAl LDH as monomer molecules by a two-step hydrothermal synthetic strategy. Source: Adapted from Wang, X., Yu, S., Wu, Y., Pang, H., Yu, S., Chen, Z., et al., 2018. The synergistic elimination of uranium (VI) species from aqueous solution using bifunctional nanocomposite of carbon sphere and layered double hydroxide. Chem. Eng. J. 342, 321330, with kind permission of Elsevier.

Chen et al. (2017) reported a facile route for synthesis of Ca/[email protected] hybrids, which displayed high adsorption capacity (382.9 mg/g at 289.15K) of U (VI) from aqueous solution. Furthermore, Ca/[email protected] showed an endothermic and spontaneous process during adsorption. In other work, Yu and his coworkers investigated the effect of graphene oxide/NiAl LDH on removal of U (VI) ions (Yu et al., 2017). Based on Langmuir isotherms, the maximum adsorption ability of [email protected] (160 mg/g) was much higher than those of GO (92 mg/g) and LDH (69 mg/g). Also, thermodynamic studies showed a spontaneous and endothermic chemical process.

13.5.2 Supercapacitor Compared with other batteries, supercapacitor electrode materials have attracted great attention as energy-storage devices and power sources due to high power capability, fast energy delivery, and long durability. Carbonaceous nanomaterials have significant properties, such as good conductivity, low cost, high stability, abundant resources, and lightweight design. In spite of their excellent rate capability and long cycle life, carbonaceous nanomaterials have a small specific capacitance (theoretical capacitance is 280 F/g). LDHs show high electrochemical activity, and good pseudocapacitive performance. Also, their theoretical capacitance is greater than that for carbonaceous nanomaterials. However, the limited velocity of ion diffusion and electron transfer of LDHs lead to low conductivity and poor cycle life. Therefore, the combination of LDHs with carbonaceous nanomaterials may be a good method to take the advantage of pseudocapacitance and double layer capacitance (Huang et al., 2017; Malak-Polaczyk et al., 2010). Li and his colleagues synthesized NiAl LDHs/CNT hybrids by a solution method with a specific capacitance of 1500 F/g at 1 A/g, and 70.3% retention at 10 A/g in 2 M KOH solution (Li et al., 2015). To prepare NiAl LDHs/CNTs, at first, the CNTs are precoated by γ-Al2O3 by annealing treatment of AlOOH/CNT in

544

Layered Double Hydroxide Polymer Nanocomposites

Figure 13.11 SEM images of (A) acid-treated CNTs, (B) Al2O3/CNTs, (C) NiAl LDHs/ CNTs, and (D) TEM image of NiAl LDHs/CNTs. Source: Adapted from Li, M., Liu, F., Cheng, J., Ying, J., Zhang, X., 2015. Enhanced performance of nickelaluminum layered double hydroxide nanosheets/carbon nanotubes composite for supercapacitor and asymmetric capacitor. J. Alloys Compd. 635, 225232, with kind permission of Elsevier.

a tube furnace at 700 C. Then, Ni(NO3)2U6H2O and NH4NO3 solutions were added into the AlOOH/CNT solution. Finally, the mixture was heated and refluxed at 100 C in a microwave reactor and NiAl LDH/CNT hybrids separated by filtration. The NiAl LDH/CNT hybrids can act as a positive electrode to produce an asymmetric capacitor with specific capacitance of 115 F/g and a high energy density of 52 Wh/kg at 1 A/g. Fig. 13.11A and B shows elongated CNTs (diameter of 20 nm) and Al2O3 deposited on the CNT surface, respectively. Also, SEM and TEM of NiAl LDHs/CNTs (Fig. 13.11C and D) clearly confirmed that LDHs are closely coated on the CNT surfaces. Fluorinated graphene (FGN) is introduced as a promising potential material, which has broadly served in redox for fuel cells, catalyst in hydrogen storage, and energy storage devices. This may be due to the semi-ionic CF bonds in FGHs which enhanced the electrical conductivity, facilitated the ion transportation, and provided reactive sites for Faradic reaction. Peng et al. fabricated CoAl-LDH/fluorinated graphene hybrids by a two-step hydrothermal method (Peng et al., 2017b). The resulting hybrids exhibited the maximum specific capacitance (1222 F/g at 1 A/g), the best rate capability, and the most stable capacitance retention at the optimal fluorination time. The FE-SEM and TEM images in Fig. 13.12B displayed that the thin sheets of CoAl-LDH were disorderly deposited on the corrugated and scrolled FGN sheets, and many pores created in the hybrid. In other work, pseudocapacitive performance of the NiCo-LDH decorated with nitrogen-doped graphene was investigated (Mahmood et al., 2015). The results

Polymer layered double hydroxide hybrid nanocomposites

545

Figure 13.12 (A) Schematic presentation of the preparation technique for the LFG composites. (B) Typical FE-SEM images of pLH (a) and LFG-12 (b), and TEM images of LFG-12 (c) and (d). Source: Adapted from Peng W., Li H. and Song S., Synthesis of fluorinated graphene/CoAllayered double hydroxide composites as electrode materials for supercapacitors, ACS Appl. Mater. Interfaces 9, 2017b, 52045212, with kind permission of the American Chemical Society.

showed excellent capacitance of 2925 F/g at 1 A/g, as well as long cyclic stability of 10,000 cycles with good capacity retention of 90% at 16 A/g. Also, the hybrid displays excellent energy and power densities of 52 Wh/kg and 3191 W/kg, respectively, at a discharge rate of 16 A/g. In other work, CoNi LDH nanoflakes were grown on carbon nitride-coated Ndoped graphene hollow spheres by a facile chemical bath deposition method. Ndoped graphene, due to the large surface area and hollow structure, can increase the loading of electroactive materials and accelerate electron and ion transport (Hao et al., 2017). The composite showed a specific capacitance of 1815 F/g at 1 A/g and

546

Layered Double Hydroxide Polymer Nanocomposites

excellent cycling stability of 82.1% after 4000 cycles. Wei et al. fabricated NiAl LDH/carbon composites via a facile in situ waterethanol system with capacitance of 1064 F/g at a current of 2.5 A/g (Wei et al., 2012). In this work, colloidal carbonaceous spheres (CCSs) were prepared under aromatization and carbonization of glucose at 180oC in an autoclave pressure vessel. They showed that the concentra% tion of both glucose and ethanol had an important effect on the morphology and capacitive performance of LDHs/carbonaceous nanofiller hybrids. Based on the SEM and TEM images, an increase in the amount of ethanol to 80% led to larger LDH nanosheets of 20100 nm in length (Fig. 13.13). Also, LDH nanosheets roughened the surface of CCS and provided a higher specific area to use in catalysts, adsorbents, and electrode materials.

13.5.3 Catalyst The tendency to aggregate and poor mechanical properties of LDH usually limit their catalytic activity. Several studies have shown that a combination of carbonaceous nanomaterials and LDHs can be an ideal approach for promoting the exceptional catalytic activity. In prepared hybrids, the high surface area of carbonaceous nanomaterials allows adequate exposure of LDH active sites, which would result in superior catalytic performance. On the other hand, the existence of carbonaceous nanomaterials and heteroatom-doped carbonaceous nanomaterials with high electrical conductivity increases the carrier mobility strongly and amends the electron hole separation efficiency of LDHs. As for photocatalysts, enhancing electronhole separation efficiency caused prolonging of the life-time of photogenerated charge carriers, which is of serious significance in improving the photocatalytic efficiency. Consequently, LDH/nanocarbon hybrids as catalyst can greatly improve the heat and mass transfers during a reaction and can easily expose more active sites to the reactant, which is helpful for the high rate conversion of the reactants (Daud et al., 2016; Zhao et al., 2012). Zhang et al. used a one-step facile technique for the preparation of carbon dots and dodecyl benzene sulfonate (DBS)-LDHs NC (Zhang et al., 2014a). A TEM micrograph of carbon dot-DBS-LDH-NCs showed that carbon dots were well distributed on the DBS-LDHs surface (Fig. 13.14A). The resulting hybrid can serve as an effective heterogeneous Fenton-like catalyst for the decomposition of acidified H2O2 to produce abundant hydroxyl radicals (Fig. 13.14B), accompanied with a noteworthy improvement in the chemiluminescence signals. Tang and coworkers prepared a CQD/NiFe-LDH nanoplate hybrid by a plain coprecipitationsolvothermal route to the oxygen evolution reaction (Tang et al., 2014). The resulting CQD/NiFe-LDH hybrid reveals inexpensive, earth abundant, and easily constructed catalyst with an over potential of B235 mV in 1 M KOH at a current density of 10 mA/cm2, which was comparable to those of the most active perovskite-based catalyst. Shan et al. found that the combination of LDH/CNT hybrid shows a positive effect on catalytic performance and uses as a basic support for selective oxidation of benzyl alcohol to benzaldehyde (Shan et al., 2015). The LDH-CNT with amphiphilicity as solid emulsifiers exhibited good capability for

Figure 13.13 SEM and TEM images of (A, B) C sphere, (C, D) NAC (U)  0, (EG) NAC (U) 50 and TEM images of (G) NAC-50, (H) NAC80. [NAC (U)  x, where x corresponds to the content of ethanol and U correspond to the addition of urea.] Source: Adapted from Wei, J., Wang, J., Song, Y., Li, Z., Gao, Z., Mann, T., et al., 2012. Synthesis of self-assembled layered double hydroxides/ carbon composites by in situ solvothermal method and their application in capacitors. J. Solid State Chem. 196, 175181, with kind permission of Elsevier.

548

Layered Double Hydroxide Polymer Nanocomposites

Figure 13.14 (A) TEM image of carbon dot-DBS-LDH nanocomposites. (B) Possible mechanism for carbon dot-DBS-LDH nanocatalyst for the decomposition of acidified H2O2 to produce abundant  OH radicals. Source: Adapted from Zhang, M., Yao, Q., Guan, W., Lu, C., Lin, J.-M., 2014a. Layered double hydroxide-supported carbon dots as an efficient heterogeneous Fenton-like catalyst for generation of hydroxyl radicals. J. Phys. Chem. C 118, 1044110447, with kind permission of the American Chemical Society.

assembling and stabilizing at the wateroil interface. Ahmed et al. investigated the catalyst performance of graphene-oxide-supported CuAl and CoAl-LDH for carboncarbon coupling (classic Ullmann homocoupling reaction) (Ahmed et al., 2017). Based on the obtained results, CuAl- and CoAl-LDHs exhibited excellent yields of 91% and 98%, respectively, at very short reaction times of 25 min. Also, the catalytic activity of the LDH/GO hybrid was up to twice as high as for the LDH, after five reuse cycles (Fig. 13.15). This phenomenon can be attributed to the presence of GO, which provided a lightweight, charge complementary, and twodimensional material which interacts effectively with the 2D LDHs.

13.6

Polymer/LDH/Carbonaceous nanofiller hybrid nanocomposites

In recent years, LDHs combined with carbonaceous nanomaterials have provided a new insight in research to explore the outstanding potential applications of LDHs. As presented above, LDHs are stimulating materials with marvelous characteristics. However, intrinsic limitations restrict their applications. For instance, the low electrical conductivity of LDHs has severely hampered their electrochemical performance, although they show high chemical reactivity. Moreover, nanostructures such as carbonaceous nanomaterials and LDH nanolayers come have difficulty from aggregation during their application process in polymeric nanocomposites. After combination, this problem can be effectively hindered. It should be mentioned that most of the properties of carbonaceous nanomaterials and LDHs are complementary. Therefore, combining them into polymeric NCs is an effective way to integrate their distinguishing properties; for example, carbonaceous nanomaterials like

Polymer layered double hydroxide hybrid nanocomposites

549

Figure 13.15 The catalytic properties of the investigated catalysts. Reaction conditions: iodobenzene (1) (2.00 mmol), catalyst (0.25 g), DMSO (4 mL); reaction temperature, 110oC. % Source: Adapted from Ahmed, N.S., Menzel, R., Wang, Y., Garcia-Gallastegui, A., Bawaked, S.M., Obaid, A.Y., et al., 2017. Graphene-oxide-supported CuAl and CoAl layered double hydroxides as enhanced catalysts for carbon-carbon coupling via Ullmann reaction. J. Solid State Chem. 246, 130137, with kind permission of Elsevier.

graphene or MWCNTs can introduce good electrical conductivity and high mechanical strength, while LDHs can contribute good chemical reactivity (De Marco et al., 2017; Zhang et al., 2017a). Preparation of polymer/LDH/other nanofiller hybrid nanocomposites is the first stage in surveying their extensive usages. Up to now, three basic procedures have been reported for the synthesis and preparation of a synergistic combination of nanofiller and polymer. Melt intercalation is introduced as one of the most widespread methods in the preparation of NCs. In this process, polymer melt is combined with nanofiller hybrids by processes such as injection molding and extrusion. The compatibility of materials and mechanical parameters has a good influence on the gradual loosening and exfoliating of LDH layers. However, complete dispersion of nanofiller hybrids would be difficult to obtain using this method. On the other hand, polymerization of a monomer in the gallery between the nanofillers leads to separation and dispersion of the nanofillers. The third method is solution-induced intercalation. During this process, nanofiller hybrids are immersed and expanded into a polymer solution. Limitations of this method include expensive solvents and their being environmentally dangerous in many reactions (Kuthati et al., 2015; Mallakpour and Khadem, 2018; Zu¨mreoglu-Karan and Ay, 2012).

550

Layered Double Hydroxide Polymer Nanocomposites

13.6.1 Polymer/LDH/CNT hybrid nanocomposites As pointed out previously, the presence of filler in polymer matrix can provide promising properties, characteristics, and performance in polymeric NCs. Various approaches have been designed for the fabrication of polymeric nanocomposites, such as in situ polymerization, solgel, solution casting, etc., which are described in detail in other chapters in this book. In the following, we illustrate some of these composites and their applications. Mallakpour and Dinari (2015b) prepared poly(amide-imide)/LDH-MWCNT NCs under ultrasonic irradiation. At first, LDH-MWCNTs were prepared by in situ growth of LDH on the acid-functionalized MWCNTs in an alkali condition under ultrasonication. Then, the obtained LDH-MWCNTs with various percentages were dispersed into PAI to improve their thermal stability. According to the results, T5 and T10 (temperature at which there is 5% and 10% mass loss) from 418oC and 451oC for pure PAI reached 508oC and 532oC for PAI/LDH-CNT NC 8% wt.%, % % % role in removal of dyes and hearespectively. These composites showed a favorable vy metal ions from wastewater. This can be related to the large specific surface area and electrostatic interaction of surface charges between adsorbents and pollutants. In their research work, Mallakpour and Behranvand (2017a) prepared recycled poly(ethylene terephthalate) (R-PET)/MWCNT/MgAl LDH-NCs under ultrasonic irradiations, then they used R-PET NCs with 4 wt.% MWNT/LDH for Cd(II) adsorption. The maximum adsorption capacity was estimated to be about 38.91 mg/g. As can be seen in Fig. 13.16, crystalline hexagonal platelets with a size of 50 nm were loaded on the MWCNTs and there was no isolation of LDH. Liu et al. (2014b) mixed a desired amount of organo-modified CoAl-LDHs, MWCNTs, and ε-caprolactam and then they were added to 6-aminocaproic acid for the preparation of nylon-6 (PA6)/LDH-CNT NCs. Techniques such as XRD, TEM, and SEM were used for their characterization. Based on mechanical tests, insertion of 1 wt.% LDHs and 0.5 wt.% CNTs into PA6 increased the tensile modulus, yield strength, as well as the hardness of the ternary composite by about 230%, 128%, and 110%, respectively, in comparison with the neat PA6. The SEM images of the fractured surfaces of PA6/2 wt.% CNT and PA6/2 wt.% CNT/1 wt.% LDH samples are shown in Fig. 13.17A and B. Based on these images, the CNTs appeared as bright spots in PA6/2 wt.% CNTs, while some areas were without CNTs and other areas with CNT aggregations were observed for PA6/2 wt.% CNT/1 wt.% LDH hybrid composite, as indicated by white arrows. In TEM micrographs (Fig. 13.17C and D), it can be seen that the binary PA6 NCs with homogeneous dispersion of 2 wt.% CNTs or 1 wt.% LDHs have successfully been prepared. For the ternary PA6/CNT/LDH-NCs, the LDH aggregations are surrounded by nanotubes and the CNTs are not beholden to the open areas that have little or no LDH sheets; this indicates that a great affinity is created between the two kinds of nanofiller. A simple method to prepare MWCNT/LDH is noncovalent assembly. In this reaction, sodium dodecyl sulfate was used as a linker between one carbonaceous nanomaterial (MWCNT and carbon nanofiber [CNF]) and ZnAl LDH, henceforth designated as SFCNT-LDH and SFCNF-LDH (Roy et al., 2016). The synthesized

Polymer layered double hydroxide hybrid nanocomposites

551

Figure 13.16 (A) FE-SEM images of MWCNT/LDH were taken at two magnifications and (B) TEM images corresponding to (a) pure MWCNT, (b) pure LDH, and (c) MWCNT/LDH hybrids.

nanofiller hybrids were incorporated within thermoplastic polyurethane/nitrile butadiene rubber (1:1 w/w) blends (TN). High-resolution transmission electron microscopic (HRTEM) images evidenced that 0.50 wt.% of loaded SFCNT-LDH and SFCNF-LDH hybrids have uniform network without aggregation into the polymer matrix than the polymer composite with 1 wt.% filler (Fig. 13.18). Also, they illustrated that TN/SFCNT-LDH blend NCs have better mechanical performance (storage modulus and tensile strength 321% and 126%, respectively) in comparison to the TN/SFCNF-LDH blend NCs (storage modulus and tensile strength 278% and 122%, respectively). The thermal behavior of TN/SFCNF-LDH blend NC exhibited enhanced thermal stability (25 C) and crystallization temperature (36 C) compared to the neat TN blend which had values of 16 and 23 C for TN/SFCNF-LDH blend NC, respectively. The roles of LiAl-LDH/MWCNT, MgAl-LDH/MWCNT, and CoAl-LDH/ MWCNT hybrids (with various weight ratios of 6:1, 3:1, 2:1, 1:1, 1:2) as nanoreinforcement were investigated to improve the thermal and mechanical properties of silicone rubber (SR) (Pradhan and Srivastava, 2014). The results showed that the presence of 1 wt.% MgAl-LDH/MWCNT, LiAl-LDH/MWCNT, and CoAlLDH/MWCNT hybrids into SR NC significantly improved the tensile strength by

552

Layered Double Hydroxide Polymer Nanocomposites

Figure 13.17 SEM images showing an overall morphology of failure surface for (A) binary PA6/2 wt.% CNT nanocomposite and (B) ternary PA6/2 wt.% CNT/1 wt% LDH nanocomposite. TEM images of PA6 nanocomposites with (C) 2 wt.% CNT, (D) 2 wt.% CNT/1 wt.% LDH, and (E) 1 wt.% LDH. Source: Adapted from Liu, T., Peng, H., Miao, Y.-E., Tjiu, W.W., Shen, L., Wei, C., 2014b. Synergistic effect of carbon nanotubes and layered double hydroxides on the mechanical reinforcement of nylon-6 nanocomposites. Chin. J. Polym. Sci. 32, 12761285, with kind permission of Springer.

134%, 100%, and 125%, respectively, compared to the neat SR. Also, among the prepared SR NCs, MgAl-LDH/MWCNT displayed greater thermal stability and swelling behavior due to nanoscale dispersion and strong interfacial interaction as well as high surface area (Fig. 13.19). Kong and coworkers (2017) synthesized organic NiFe-LDH/CNT nanofiller hybrids by coprecipitation with various weight ratios (10:1, 20:1, 40:1) and used 4% of them in the preparation of epoxy resin (ER) hybrid NCs. The results of flame-retardant and thermal properties showed that the ER/NiFe-LDH-CNTs hybrid NCs (specific ratio of 10:1) have a better performance than the pure ER. For instance, the pure EP had 12.5% residues at 700 C, whereas EP/NiFe-LDH-CNTs10 composites had 27.2% residues. In addition, compared with the pure EP, the PHRRs of EP/NiFe-LDH-CNTs-10 reduced by 53% (from 922 to 424 kW/m2). These phenomena are attributed to better uniform distribution, stronger interfacial interaction, outstanding charring performance of NiFe-LDH, and a synergistic effect between NiFe-LDH and CNTs. In a research work, the effect of flame retardancy of layered double hydroxide wrapped carbon nanotubes (LDH-w-CNTs) on polypropylene (PP) was investigated by Du and Fang (2010). The presence of LDH-w-CNTs into the polymer matrix caused a reduction in the peak heat release rate (PHRR) of PP and a better flame retardancy on PP with respect to LDH and CNTs. Based on reports, the incorporation of LDH (5 wt.%), CNTs (0.5 wt.%), LDH-w-CNTs, and LDH-w-acidifying CNT into PP provide PHRR of 538, 549, 490, and 495 kW/m2, respectively.

Figure 13.18 Fabrication of TN nanocomposites with hybrid fillers (left). HRTEM images of TN nanocomposites containing (A) 0.50, (B) 1 wt.% of SFCNT-LDH hybrid and (C) 0.50, (D) 1 wt.% of SFCNF-LDH hybrid. Source: Adapted from Roy, S., Srivastava, S.K., Mittal, V., 2016. Facile noncovalent assembly of MWCNT-LDH and CNF-LDH as reinforcing hybrid fillers in thermoplastic polyurethane/nitrile butadiene rubber blends. J. Polym. Res. 23, 36, with kind permission of Springer.

554

Layered Double Hydroxide Polymer Nanocomposites

Figure 13.19 TEM images of (A) LiAl-LDH/MWCNT, (B) MgAl-LDH/MWCNT, and (C) CoAl-LDH/MWCNT. (D) Digital images showing dispersion of MWCNT (1), LiAlLDH/MWCNT (2), CoAl-LDH/MWCNT (3), and MgAl-LDH/MWCNT (4) in THF at room temperature (photographs recorded after 1 day). Source: Adapted from Pradhan, B., Srivastava, S., 2014. Layered double hydroxide/ multiwalled carbon nanotube hybrids as reinforcing filler in silicone rubber. Compos. Part A: Appl. Sci. Manuf. 56, 290299, with kind permission of Elsevier.

13.6.2 Polymer/LDH/graphene hybrid nanocomposites Other considerable composites in this context are polymer/LDH-G NCs. Liu et al. (2014a) applied graphene nanosheets (GNSs) and MgAl-LDH as fillers and investigated their flame retardancy for epoxy resin (ER). With respect to the obtained results, 2.5 wt.% LDH and 2.5 wt.% GNS could reduce the total heat release (THR) of ER composites from 33.4 to 24.6 kJ/m2, better than 5 wt.% GNS (27.8 kJ/m2) or 5 wt.% LDH (25.7 kJ/m2) (Fig. 13.20). In other work by Wang and coworkers (2013), an NiFe LDH/G nanofiller hybrid was prepared by a one-pot in situ solvothermal method and then its effect on the flame retardancy of ER was studied. They demonstrated that the distribution of graphene was better after hybridization with LDH. By adding 2 wt.% of NiFeLDH/graphene NC into ER composite, the char residue of resin composite was enhanced, and its PHRR and THR were reduced by 58.0% and 61.0%, respectively. The enhancement in the fire-retardant properties of composite in the gas phase can be associated with the NiFe LDH/GNS hybrid, which acts as a physical barrier and retards and decreases the release of combustible gas (e.g., hydrocarbons and

Polymer layered double hydroxide hybrid nanocomposites

555

Figure 13.20 (A) THR of ER, ER/GNS, ER/LDH, and ER/GNS/LDH composites with different filler content. (B) SEM images of the surface char residues of (a) ER, (b) ER/ GNS5, (c) ER/LDH5, and (d) ER/GNS2.5/LDH2.5 after being calcined. Source: Adapted from Liu, S., Yan, H., Fang, Z., Guo, Z., Wang, H., 2014a. Effect of graphene nanosheets and layered double hydroxides on the flame retardancy and thermal degradation of epoxy resin. RSC Adv. 4, 1865218659, with kind permission of Elsevier.

aromatic compounds). However, in the condensed phase, the NiFe LDH/GNS hybrid, by forming a compact and insulating char layer on the composite surface, could protect the inner polymer matrix from further burning. Hong and coworkers (2014) fabricated NiAl-LDH and graphene hybrid (RGOLDH) by coprecipitation route and considered its role on the reducing flammability of polymethyl methacrylate (PMMA). Based on flame retardancy, the addition of 2 wt.% RGO-LDH in polymer decreased the PHRR of the pure PMMA from 918 to 688 kW/m2 in a PMMA/RGO-LDH composite. In other work, Huang et al. (2014) showed the presence of 10 wt.% of intumescent flame retardants (IFRs), 1 wt.% of graphene, and 5 wt.% of LDHs, into PMMA can reduce PHRR values by about 45% compared with neat PMMA, while the mechanical properties of PMMA/IFR/ RGO/LDH NC revealed almost no deterioration. Xu et al. (2016) studied the flame retardancy and smoke suppression characteristics of polyurethane elastomer (PUE) before and after incorporation of MgAl-LDHloaded graphene hybrid. In order to do this, MgAl-LDH-loaded graphene composite was synthesized by coprecipitation, and then heptamolybdateion (Mo7O2462) was intercalated into the interlayer space of LDH over ion exchange. Finally, RGOLDH/Mo was mixed with the PUE through blending under ultrasonication. They demonstrated that the heat release rate and maximum smoke density of PUE/RGOLDH/Mo 2 wt.% decreased to 448 kW/m2 (58.6%) and 331 compared to composites without Mo7O2462 (PUE/RGO-LDH 2 wt.%) with values of 509 kW/m2 (52%) and 380, respectively, which is evidenced to improve the catalytic carbonization and smoke suppression effect. In the TEM images in Fig. 13.21A and B it can be seen that the RGO-LDH and RGO-LDH/Mo are distributed well in the PUE without agglomeration. The combination of graphene with LDH can facilitate electron collection and transport as well as promote high current densities in supercapacitors. However,

556

Layered Double Hydroxide Polymer Nanocomposites

Figure 13.21 TEM images of PUE/RGO-LDH (A) and PUE/RGO-LDH/Mo composites (B), RGO-LDH (C) and RGO-LDH/Mo (D). Source: Adapted from Xu, W., Zhang, B., Xu, B., Li, A., 2016. The flame retardancy and smoke suppression effect of heptaheptamolybdate modified reduced graphene oxide/layered double hydroxide hybrids on polyurethane elastomer. Compos. Part A: Appl. Sci. Manuf. 91, 3040, with kind permission of Elsevier.

their aggregation can reduce the total energy density of supercapacitors. The presence of pseudocapacitive conducting polymer-coated carbon as an alternative substrate can overcome this problem. Accordingly, in 2017, a novel sandwich-like hybrid with ultrathin CoAl-LDH nanoplates was electrostatically coated on the surface polypyrrole/graphene substrate (denoted as CoAl-LDH/PG) via a hydrothermal route (Zhang et al., 2017b). The result showed that it has the ability to transport super high-energy density of 46.8 Wh/kg at 1.2 kW/kg and, after 10,000 cycles, capacitance is maintained at about 90.1% of its initial capacitance.

13.6.3 Polymer/LDH/Other nanofiller hybrids Zhou et al. (2016) introduced LDH/MoS2 hybrids as a reinforcing agent for improving the flame-retardant property of poly(vinyl alcohol) (PVA). Therefore, LDH layers with positive charge are assembled with the negatively exfoliated MoS2 nanosheets in aqueous solution by electrostatic attraction. Then PVA composites with various ratios of LDH/MoS2 (0.5, 1, 3 wt.%) were fabricated via solutionblending technique. These composites were characterized by XRD and TEM and

Polymer layered double hydroxide hybrid nanocomposites

557

showed that the flame-retardant efficiency of PVA increased after insertion of LDH/MoS2, so that in SEM images of PVA/LDH/MoS2 NC 3 wt.% observed a compact and dense layer, protecting the composite during combustion. In other work, LDH/MoS2 was introduced into epoxy to reduce its fire hazard (Zhou et al., 2017). Compared with epoxy/MoS2, the addition of CoFe-LDH/MoS2 and NiFeLDH/MoS2 into epoxy showed a more homogeneous dispersion and provided more excellent fire resistance to epoxy resin (EP) matrix, so that their PHRR values were further reduced from 1863 to 708 and 643 kW/m2, respectively. Also, THR values are decreased from 109 MJ/m2 (pure EP) to 72 MJ/m2 (EP/NiFe-LDH/MoS2 NC 2 wt.%), which is about a 34% reduction. In SEM images, pure EP shows a discontinuous char layer containing evident cracks and holes. However, for EP incorporated with MoS2, LDH, and specific for LDH/MoS2, the amount of holes and cracks on the surface reduces and it forms a compact and dense morphology (Fig. 13.22).

Figure 13.22 SEM images of the char residue for EP (A), EP/MoS2 (B), EP/CoFe-LDH (C), EP/CoFe-LDH-MoS2 (D), EP/NiFe-LDH (E), and EP/NiFe-LDH-MoS2. (F) Composites after cone test. Source: Adapted from Zhou, K., Gao, R., Qian, X., 2017. Self-assembly of exfoliated molybdenum disulfide (MoS2) nanosheets and layered double hydroxide (LDH): Towards reducing fire hazards of epoxy. J. Hazard. Mater. 338, 343355, with kind permission of Elsevier.

558

Layered Double Hydroxide Polymer Nanocomposites

Multifunctional [email protected] phytic acid (Ph)-hydroxypropyl-sulfobutyl-betacyclodextrin sodium (CDBS)-LDH hybrid is other composite that showed good performance in improving the flame-retardant and thermal conductivity properties of EP (Kalali et al., 2016). For example, the PHRR and total smoke production of the EP composite containing 8 wt.% of [email protected] were decreased by 55% and 34%, respectively, in comparison to those of the pristine EP. Also, thermal conductivity increased from 0.220 6 0.002 in pure EP to 0.270 6 0.005 (W/mK) in [email protected]/EP, association of the Fe3O4 NPs and their synergy in transferring and dissipation of the heat have an effective role in this behavior. In other work, modified SiO2 (m-SiO2), Co 2 Al LDH, and synthetic [email protected] 2 Al LDH spheres were individually inserted into EP to organize specimens for study of their flame-retardant performance (Jiang et al., 2014). They found that incorporation of 2 wt.% [email protected] 2 Al LDH into EP caused an increment in the char yield and a decrease in the derivative thermogravimetric peak value. Moreover, the PHRR, THR, effective heat of combustion (EHC), total smoke release (TSR), and maximum average heat rate emission (MAHRE) values for EP/ [email protected] 2 Al LDH were clearly decreased. These can be related to labyrinth effect of m-SiO2 and formation of graphitized carbon char catalyzed by Co 2 Al LDH, which played essential roles in the flame retardance improvement.

13.7

Conclusions

Since the 20th century up to now, the use of nanofillers with unique properties to improve polymer properties had been challenged. The use of LDHs, due to positive charge of the layers, relatively easy preparation, tuning of the crystal structures, and chemically active nature, has been proposed as an interesting nanofiller by modern researchers. Based on the investigations reported by various groups of researchers in this chapter, unmodified LDHs may not really yield any favorable improvement in polymer composites. Therefore, solutions such as modifying LDHs with organic compounds or combining them with other nanofillers such as carbonaceous nanomaterials (graphene, carbon dots, and CNTs) and other nanofillers have been designed to improve the performance of LDHs in polymer and decrease their aggregation. In this chapter, we intended to focus on the current state of the art in the preparation of polymer/LDH/any other nanofiller hybrid composite, and studied the influence of treated LDHs (such as LDH/MWCNTs and LDH/graphene) on thermal, mechanical, flame retardancy, adsorption capacity, capacitance properties etc. of polymers. In most of the results, composites reinforced with LDHs/carbonaceous nanofiller hybrids showed attractive performance, such as in thermal properties and conductivity, compared with pure polymer and polymer/LDH NC,. This is due to the appropriate compatibility, interaction, and dispersion between polymers and treated LDHs with carbonaceous nanomaterials. This area of work is very interesting and attractive and we are sure many scientists are working on it and that exciting results will be published soon. Currently we are also working on this fascinating subject.

Polymer layered double hydroxide hybrid nanocomposites

559

Acknowledgments The authors would like to thank the Research Affairs Division Isfahan University of Technology (IUT), Isfahan, I. R. Iran, National Elite Foundation (NEF), Tehran, I. R. Iran, Iran Nanotechnology Initiative Council (INIC), Tehran, I. R. Iran, and Center of Excellence in Sensors and Green Chemistry Research (IUT), Isfahan, I. R. Iran for financial support.

References Ahmed, N.S., Menzel, R., Wang, Y., Garcia-Gallastegui, A., Bawaked, S.M., Obaid, A.Y., et al., 2017. Graphene-oxide-supported CuAl and CoAl layered double hydroxides as enhanced catalysts for carbon-carbon coupling via Ullmann reaction. J. Solid State Chem. 246, 130137. Bai, C., Sun, S., Xu, Y., Yu, R., Li, H., 2016. Facile one-step synthesis of nanocomposite based on carbon nanotubes and Nickel-Aluminum layered double hydroxides with high cycling stability for supercapacitors. J. Colloid. Interface. Sci. 480, 5762. Basu, D., Das, A., Sto¨ckelhuber, K.W., Wagenknecht, U., Heinrich, G., 2014. Advances in layered double hydroxide (LDH)-based elastomer composites. Prog. Polym. Sci. 39, 594626. Burgos-Ma´rmol, J.J., Patti, A., 2017. Unveiling the impact of nanoparticle size dispersity on the behavior of polymer nanocomposites. Polymer 113, 92104. Cao, Y., Li, G., Li, X., 2016. Graphene/layered double hydroxide nanocomposite: properties, synthesis, and applications. Chem. Eng. J. 292, 207223. Chen, D., Wang, X., Liu, T., Wang, X., Li, J., 2010. Electrically conductive poly (vinyl alcohol) hybrid films containing graphene and layered double hydroxide fabricated via layer-by-layer self-assembly. ACS Appl. Mater. Interfaces 2, 20052011. Chen, H., Cai, F., Kang, Y., Zeng, S., Chen, M., Li, Q., 2014. Facile Assembly of NiCo Hydroxide Nanoflakes on Carbon Nanotube Network with Highly Electrochemical Capacitive Performance. ACS Appl. Mater. Interfaces 6, 1963019637. Chen, H., Chen, Z., Zhao, G., Zhang, Z., Xu, C., Liu, Y., et al., 2017. Enhanced adsorption of U (VI) and 241Am (III) from wastewater using Ca/Al layered double [email protected] carbon nanotube composites. J. Hazard. Mater. 347, 6777. Chiang, M.-F., Wu, T.-M., 2011. Intercalation of γ-PGA in Mg/Al layered double hydroxides: an in situ WAXD and FTIR investigation. Appl. Clay Sci. 51, 330334. Choudalakis, G., Gotsis, A., 2009. Permeability of polymer/clay nanocomposites: a review. Eur. Polym. J. 45, 967984. Costa, F.R., Saphiannikova, M., Wagenknecht, U., Heinrich, G., 2007. Layered double hydroxide based polymer nanocomposites, Wax Crystal Control  Nanocomposites  Stimuli-Responsive Polymers, vol. 210. Springer, pp. 101168. Daud, M., Kamal, M.S., Shehzad, F., Al-Harthi, M.A., 2016. Graphene/layered double hydroxides nanocomposites: a review of recent progress in synthesis and applications. Carbon 104, 241252. De Marco, M., Menzel, R., Bawaked, S.M., Mokhtar, M., Obaid, A.Y., Basahel, S.N., et al., 2017. Hybrid effects in graphene oxide/carbon nanotube-supported layered double hydroxides: enhancing the CO2 sorption properties. Carbon 123, 616627.

560

Layered Double Hydroxide Polymer Nanocomposites

Du, B., Fang, Z., 2010. The preparation of layered double hydroxide wrapped carbon nanotubes and their application as a flame retardant for polypropylene. Nanotechnology 21, 315603. Elbasuney, S., 2015. Surface engineering of layered double hydroxide (LDH) nanoparticles for polymer flame retardancy. Powder Technol. 277, 6373. Evans, D.G., Slade, R.C., 2006. Structural aspects of layered double hydroxides, Layered Double Hydroxides, vol. 119. Springer, pp. 187. Galva˜o, T.L., Neves, C.S., Caetano, A.P., Maia, F., Mata, D., Malheiro, E., et al., 2016. Control of crystallite and particle size in the synthesis of layered double hydroxides: macromolecular insights and a complementary modelling tool. J. Colloid. Interface. Sci. 468, 8694. Gong, J., Liu, T., Wang, X., Hu, X., Zhang, L., 2011. Efficient removal of heavy metal ions from aqueous systems with the assembly of anisotropic layered double hydroxide [email protected] carbon nanosphere. Environ. Sci. Technol. 45, 61816187. Hao, X., Jiang, Z., Tian, X., Hao, X., Jiang, Z.-J., 2017. Facile assembly of Co-Ni layered double hydroxide nanoflakes on carbon nitride coated N-doped graphene hollow spheres with high electrochemical capacitive performance. Electrochim. Acta 253, 2130. He, J., Wei, M., Li, B., Kang, Y., Evans, D.G., Duan, X., 2006. Preparation of layered double hydroxides. Layered Double Hydroxides. Springer, pp. 89119. He, F., Hu, Z., Liu, K., Guo, H., Zhang, S., Liu, H., et al., 2015. Facile fabrication of GNS/ NiCoAl-LDH composite as an advanced electrode material for high-performance supercapacitors. J. Solid State Electrochem. 19, 607617. Heli, H., Pishahang, J., Amiri, H.B., 2016. Synthesis of hexagonal CoAl-layered double hydroxide nanoshales/carbon nanotubes composite for the non-enzymatic detection of hydrogen peroxide. J. Electroanal. Chem. 768, 134144. Hong, N., Song, L., Wang, B., Stec, A.A., Hull, T.R., Zhan, J., et al., 2014. Co-precipitation synthesis of reduced graphene oxide/NiAl-layered double hydroxide hybrid and its application in flame retarding poly (methyl methacrylate). Mater. Res. Bull. 49, 657664. Huang, G., Chen, S., Song, P., Lu, P., Wu, C., Liang, H., 2014. Combination effects of graphene and layered double hydroxides on intumescent flame-retardant poly (methyl methacrylate) nanocomposites. Appl. Clay Sci. 88, 7885. Huang, Q., Liu, K.-y, Fang, H., Zhang, S.-r, Xie, Q.-l, Cheng, C., 2017. Fabrication of cobalt aluminum-layered double hydroxide nanosheets/carbon spheres composite as novel electrode material for supercapacitors. Trans. Nonferrous Metals Soc. China 27, 18041814. Ivanov, Y., Cheshkov, V., Natova, M., 2001. Polymer Composite Materials—Interface Phenomena & Processes, vol. 90. Springer Science & Business Media, pp. 1161. Jiang, S.-D., Bai, Z.-M., Tang, G., Song, L., Stec, A.A., Hull, T.R., et al., 2014. Synthesis of mesoporous [email protected] CoAl layered double hydroxide spheres: layer-by-layer method and their effects on the flame retardancy of epoxy resins. ACS Appl. Mater. Interfaces 6, 1407614086. Kalali, E.N., Wang, X., Wang, D.-Y., 2016. Synthesis of a Fe3O4 [email protected] MgAl layered-double-hydroxide hybrid and application in the fabrication of multifunctional epoxy nanocomposites. Ind. Eng. Chem. Res. 55, 66346642. Kiran, S.K., Padmini, M., Das, H.T., Elumalai, P., 2017. Performance of asymmetric supercapacitor using CoCr-layered double hydroxide and reduced graphene-oxide. J. Solid State Electrochem. 21, 927938.

Polymer layered double hydroxide hybrid nanocomposites

561

Koilraj, P., Kamura, Y., Sasaki, K., 2017. Carbon-dot-decorated layered double hydroxide nanocomposites as a multifunctional environmental material for Co-immobilization of SeO42 and Sr21 from aqueous solutions. ACS Sustainable Chem. Eng. 5, 90539064. Kong, Q., Wu, T., Tang, Y., Xiong, L., Liu, H., Zhang, J., et al., 2017. Improving thermal and flame retardant properties of epoxy resin with organic NiFe-layered double hydroxide-carbon nanotubes hybrids. Chin. J. Chem. 35, 18751880. Kuthati, Y., Kankala, R.K., Lee, C.-H., 2015. Layered double hydroxide nanoparticles for biomedical applications: current status and recent prospects. Appl. Clay Sci. 112, 100116. Leroux, F., Besse, J.-P., 2004. Layered double hydroxide/polymer nanocomposites. Interface Sci. Technol. 1, 459495. Li, D., Xu, X., Xu, J., Hou, W., 2011. Poly (ethylene glycol) haired layered double hydroxides as biocompatible nanovehicles: morphology and dispersity study. Colloids Surf. A: Physicochem. Eng. Aspects 384, 585591. Li, M., Liu, F., Cheng, J., Ying, J., Zhang, X., 2015. Enhanced performance of nickelaluminum layered double hydroxide nanosheets/carbon nanotubes composite for supercapacitor and asymmetric capacitor. J. Alloys Compd. 635, 225232. Liu, S., Yan, H., Fang, Z., Guo, Z., Wang, H., 2014a. Effect of graphene nanosheets and layered double hydroxides on the flame retardancy and thermal degradation of epoxy resin. RSC Adv. 4, 1865218659. Liu, T., Peng, H., Miao, Y.-E., Tjiu, W.W., Shen, L., Wei, C., 2014b. Synergistic effect of carbon nanotubes and layered double hydroxides on the mechanical reinforcement of nylon-6 nanocomposites. Chin. J. Polym. Sci. 32, 12761285. Liu, H., Zhou, J., Wu, C., Wang, C., Zhang, Y., Liu, D., et al., 2018. Integrated flexible electrode for oxygen evolution reaction: layered double hydroxide coupled with singlewalled carbon nanotubes film. ACS Sustainable Chem. Eng. 6 (3), 29112915. Long, Y.-L., Yu, J.-G., Jiao, F.-P., Yang, W.-J., 2016. Preparation and characterization of MWCNTs/LDHs nanohybrids for removal of Congo red from aqueous solution. Trans. Nonferrous Metals Soc. China 26, 27012710. Lonkar, S.P., Raquez, J.-M., Dubois, P., 2015. One-pot microwave-assisted synthesis of graphene/layered double hydroxide (LDH) nanohybrids. Nano-Micro Lett. 7, 332340. Lv, X., Xiao, X., Cao, M., Bu, Y., Wang, C., Wang, M., et al., 2018. Efficient carbon dots/ NiFe-layered double hydroxide/BiVO4 photoanodes for photoelectrochemical water splitting. Appl. Surf. Sci. 439, 10651071. Ma, K., Cheng, J., Liu, F., Zhang, X., 2016. Co-Fe layered double hydroxides nanosheets vertically grown on carbon fiber cloth for electrochemical capacitors. J. Alloys Comps. 679, 277284. Mahmood, N., Tahir, M., Mahmood, A., Yang, W., Gu, X., Cao, C., et al., 2015. Role of anions on structure and pseudocapacitive performance of metal double hydroxides decorated with nitrogen-doped graphene. Sci. China Mater. 58, 114125. Malak-Polaczyk, A., Vix-Guterl, C., Frackowiak, E., 2010. Carbon/layered double hydroxide (LDH) composites for supercapacitor application. Energy Fuels 24, 33463351. Mallakpour, S., Dinari, M., 2015a. Intercalation of amino acid containing chiral dicarboxylic acid between MgAl layered double hydroxide. J. Therm. Anal. Calorim. 119, 11231130. Mallakpour, S., Dinari, M., 2015b. Hybrids of MgAl-layered double hydroxide and multiwalled carbon nanotube as a reinforcing filler in the l-phenylalanine-based polymer nanocomposites. J. Therm. Anal. Calorim. 119, 19051912.

562

Layered Double Hydroxide Polymer Nanocomposites

Mallakpour, S., Behranvand, V., 2017a. Water sanitization by the elimination of Cd21 using recycled PET/MWNT/LDH composite: morphology, thermal, kinetic, and isotherm studies. ACS Sustainable Chem. Eng. 5, 57465757. Mallakpour, S., Khadem, E., 2017b. Opportunities and challenges in the use of layered double hydroxide to produce hybrid polymer composites. In: Thakur, V.K., Thakur, M.K., Gupta, R.K. (Eds.), Hybrid Polymer Composite Materials, vol. 1. Elsevier, pp. 235261. Mallakpour, S., Khadem, E., 2018. Applications of biodegradable polymer/layered double hydroxide nanocomposites: current status and recent prospects. In: Shimpi, N.G. (Ed.), Biodegradable and Biocompatible Polymer Composites Processing, Properties and Applications. Elsevier, pp. 265296. Mallakpour, S., Dinari, M., Behranvand, V., 2013. Ultrasonic-assisted synthesis and characterization of layered double hydroxides intercalated with bioactive N, N0 -(pyromellitoyl)-bis-l-α-amino acids. RSC Adv. 3, 2330323308. Mallakpour, S., Dinari, M., Hatami, M., 2015. Novel nanocomposites of poly (vinyl alcohol) and MgAl layered double hydroxide intercalated with diacid N-tetrabromophthaloylaspartic. J. Therm. Anal. Calorim. 120, 12931302. Mallakpour, S., Dinari, M., Behranvand, V., 2016a. Structure and thermal degradation properties of nanocomposites of alanine amino acid-based poly (amideimide) reinforced with carboxymethyl-β-cyclodextrin intercalated in a layered double hydroxide. PolymerPlast. Technol. Eng. 55, 223230. Mallakpour, S., Dinari, M., Behranvand, V., 2016b. Design of one-pot green protocol for the synthesis of novel modified LDHs with diacids based on amino acids: morphology and thermal examinations. J. Iran. Chem. Soc. 13, 16351642. Momodu, D., Bello, A., Dangbegnon, J., Barzeger, F., Fabiane, M., Manyala, N., 2015. P3HT: PCBM/nickel-aluminum layered double hydroxide-graphene foam composites for supercapacitor electrodes. J. Solid State Electrochem. 19, 445452. Ochai-Ejeh, F., Madito, M., Momodu, D., Khaleed, A., Olaniyan, O., Manyala, N., 2017. High performance hybrid supercapacitor device based on cobalt manganese layered double hydroxide and activated carbon derived from cork (Quercus Suber). Electrochim. Acta 252, 4154. Omwoma, S., Chen, W., Tsunashima, R., Song, Y.-F., 2014. Recent advances on polyoxometalates intercalated layered double hydroxides: from synthetic approaches to functional material applications. Coord. Chem. Rev. 258, 5871. Pacuła, A., Uosaki, K., Socha, R.P., Biela´nska, E., Pietrzyk, P., Zimowska, M., 2016. Nitrogen-doped carbon materials derived from acetonitrile and Mg-Co-Al layered double hydroxides as electrocatalysts for oxygen reduction reaction. Electrochim. Acta 212, 4758. Papaspyrides, C.D., Kiliaris, P., 2014. Polymer Green Flame Retardants: A Comprehensive Guide to Additives and Their Applications, Elsevier, pp. 1942. Pavlidou, S., Papaspyrides, C., 2008. A review on polymerlayered silicate nanocomposites. Prog. Polym. Sci. 33, 11191198. Peng, D., Wei, C., Baojun, Q., 2006. Recent progress in polymer layered double hydroxide nanocomposites. Prog. Nat. Sci. 16, 573579. Peng, W., Li, H., Liu, Y., Song, S., 2017a. Effect of oxidation degree of graphene oxide on the electrochemical performance of CoAl-layered double hydroxide/graphene composites. Appl. Mater. Today 7, 201211. Peng, W., Li, H., Song, S., 2017b. Synthesis of fluorinated graphene/CoAl-layered double hydroxide composites as electrode materials for supercapacitors. ACS Appl. Mater. Interfaces 9, 52045212.

Polymer layered double hydroxide hybrid nanocomposites

563

Pradhan, B., Srivastava, S., 2014. Layered double hydroxide/multiwalled carbon nanotube hybrids as reinforcing filler in silicone rubber. Compos. Part A: Appl. Sci. Manuf. 56, 290299. Qiao, Z., Gao, C., Sun, B., Ai, S., 2013. Synthesis and characterization of functionalized multi-walled carbon nanotubes/exfoliated layered double hydroxide nanosheets hybrids via electrostatic force. J. Inorg. Organomet. Polym. Mater. 23, 871876. Qiao, L., Guo, Y., Sun, X., Jiao, Y., Wang, X., 2015. Electrochemical immunosensor with NiAl-layered double hydroxide/graphene nanocomposites and hollow gold nanospheres double-assisted signal amplification. Bioprocess. Biosyst. Eng. 38, 14551468. Qu, J., Zhang, Q., Li, X., He, X., Song, S., 2016. Mechanochemical approaches to synthesize layered double hydroxides: a review. Appl. Clay Sci. 119, 185192. Radulescu, A., Fetters, L., Richter, D., 2007. Polymer-driven wax crystal control using partially crystalline polymeric materials, Wax Crystal Control  Nanocomposites  StimuliResponsive Polymers, vol. 210. Springer, pp. 1100. Rahmanian, O., Dinari, M., Abdolmaleki, M.K., 2018. Carbon quantum dots/layered double hydroxide hybrid for fast and efficient decontamination of Cd (II): the adsorption kinetics and isotherms. Appl. Surf. Sci. 428, 272279. Rives, V., 2001. Layered Double Hydroxides: Present and Future. Nova Publishers. Rives, V., del Arco, M., Martı´n, C., 2014. Intercalation of drugs in layered double hydroxides and their controlled release: a review. Appl. Clay Sci. 88, 239269. Roy, S., Srivastava, S.K., Mittal, V., 2016. Facile noncovalent assembly of MWCNT-LDH and CNF-LDH as reinforcing hybrid fillers in thermoplastic polyurethane/nitrile butadiene rubber blends. J. Polym. Res. 23, 36. Saha, S., Ray, S., Acharya, R., Chatterjee, T.K., Chakraborty, J., 2016. Magnesium, zinc and calcium aluminium layered double hydroxide-drug nanohybrids: a comprehensive study. Appl. Clay Sci. 135, 493509. Shan, Y., Yu, C., Yang, J., Dong, Q., Fan, X., Qiu, J., 2015. Thermodynamically stable pickering emulsion configured with carbon-nanotube-bridged nanosheet-shaped layered double hydroxide for selective oxidation of benzyl alcohol. ACS Appl. Mater. Interfaces 7, 1220312209. Tang, D., Liu, J., Wu, X., Liu, R., Han, X., Han, Y., et al., 2014. Carbon quantum dot/NiFe layered double-hydroxide composite as a highly efficient electrocatalyst for water oxidation. ACS Appl. Mater. Interfaces 6, 79187925. Theiss, F.L., Ayoko, G.A., Frost, R.L., 2016. Synthesis of layered double hydroxides containing Mg21, Zn21, Ca21 and Al31 layer cations by co-precipitation methods—a review. Appl. Surf. Sci. 383, 200213. Tonelli, D., Scavetta, E., Giorgetti, M., 2013. Layered-double-hydroxide-modified electrodes: electroanalytical applications. Anal. Bioanal. Chem. 405, 603614. ´ ., Ko´nya, Z., Sipos, P., et al., 2014. Carbon To´th, V., Sipiczki, M., Bugris, V., Kukovecz, A nanotube-layered double hydroxide nanocomposites. Chem. Pap. 68, 650655. Wang, H., Xiang, X., Li, F., 2010. Hybrid ZnAl-LDH/CNTs nanocomposites: noncovalent assembly and enhanced photodegradation performance. AIChE J. 56, 768778. Wang, X., Zhou, S., Xing, W., Yu, B., Feng, X., Song, L., et al., 2013. Self-assembly of NiFe layered double hydroxide/graphene hybrids for reducing fire hazard in epoxy composites. J. Mater. Chem. A 1, 43834390. Wang, Z., Jia, W., Jiang, M., Chen, C., Li, Y., 2015. Microwave-assisted synthesis of layerby-layer ultra-large and thin NiAl-LDH/RGO nanocomposites and their excellent performance as electrodes. Sci. China Mater. 58, 944952.

564

Layered Double Hydroxide Polymer Nanocomposites

Wang, Y., Chen, Z., Li, H., Zhang, J., Yan, X., Jiang, K., et al., 2016. The synthesis and electrochemical performance of core-shell structured Ni-Al layered double hydroxide/carbon nanotubes composites. Electrochim. Acta 222, 185193. Wang, X., Zheng, Y., Yuan, J., Shen, J., Hu, J., Wang, A.-J., et al., 2017. Three-dimensional NiCo layered double hydroxide nanosheets array on carbon cloth, facile preparation and its application in highly sensitive enzymeless glucose detection. Electrochim. Acta 224, 628635. Wang, X., Yu, S., Wu, Y., Pang, H., Yu, S., Chen, Z., et al., 2018. The synergistic elimination of uranium (VI) species from aqueous solution using bi-functional nanocomposite of carbon sphere and layered double hydroxide. Chem. Eng. J. 342, 321330. Wei, J., Wang, J., Song, Y., Li, Z., Gao, Z., Mann, T., et al., 2012. Synthesis of selfassembled layered double hydroxides/carbon composites by in situ solvothermal method and their application in capacitors. J. Solid State Chem. 196, 175181. Xu, W., Zhang, B., Xu, B., Li, A., 2016. The flame retardancy and smoke suppression effect of heptaheptamolybdate modified reduced graphene oxide/layered double hydroxide hybrids on polyurethane elastomer. Compos. Part A: Appl. Sci. Manuf 91, 3040. Yu, S., Wang, J., Song, S., Sun, K., Li, J., Wang, X., et al., 2017. One-pot synthesis of graphene oxide and Ni-Al layered double hydroxides nanocomposites for the efficient removal of U (VI) from wastewater. Sci. China Chem. 60, 415422. Zhang, M., Yao, Q., Guan, W., Lu, C., Lin, J.-M., 2014a. Layered double hydroxidesupported carbon dots as an efficient heterogeneous Fenton-like catalyst for generation of hydroxyl radicals. J. Phys. Chem. C 118, 1044110447. Zhang, M., Yao, Q., Lu, C., Li, Z., Wang, W., 2014b. Layered double hydroxidecarbon dot composite: high-performance adsorbent for removal of anionic organic dye. ACS Appl. Mater. Interfaces 6, 2022520233. Zhang, L., Chen, R., Hui, K.N., San Hui, K., Lee, H., 2017a. Hierarchical ultrathin NiAl layered double hydroxide nanosheet arrays on carbon nanotube paper as advanced hybrid electrode for high performance hybrid capacitors. Chem. Eng. J. 325, 554563. Zhang, Y., Du, D., Li, X., Sun, H., Li, L., Bai, P., et al., 2017b. Electrostatic self-assembly of sandwich-like CoAl-LDH/polypyrrole/graphene nanocomposites with enhanced capacitive performance. ACS Appl. Mater. Interfaces 9, 3169931709. Zhao, M.Q., Zhang, Q., Huang, J.Q., Wei, F., 2012. Hierarchical nanocomposites derived from nanocarbons and layered double hydroxides-properties, synthesis, and applications. Adv. Funct. Mater. 22, 675694. Zhou, K., Hu, Y., Liu, J., Gui, Z., Jiang, S., Tang, G., 2016. Facile preparation of layered double hydroxide/MoS2/poly (vinyl alcohol) composites. Mater. Chem. Phys. 178, 15. Zhou, K., Gao, R., Qian, X., 2017. Self-assembly of exfoliated molybdenum disulfide (MoS2) nanosheets and layered double hydroxide (LDH): towards reducing fire hazards of epoxy. J. Hazard. Mater. 338, 343355. Zubair, M., Daud, M., McKay, G., Shehzad, F., Al-Harthi, M.A., 2017. Recent progress in layered double hydroxides (LDH)-containing hybrids as adsorbents for water remediation. Appl. Clay Sci. 143, 279292. Zu¨mreoglu-Karan, B., Ay, A., 2012. Layered double hydroxides—multifunctional nanomaterials. Chem. Pap. 66, 110.