Layered double hydroxide based bionanocomposites

Layered double hydroxide based bionanocomposites

Applied Clay Science 177 (2019) 19–36 Contents lists available at ScienceDirect Applied Clay Science journal homepage: ...

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Applied Clay Science 177 (2019) 19–36

Contents lists available at ScienceDirect

Applied Clay Science journal homepage:

Review article

Layered double hydroxide based bionanocomposites a,⁎


Aniruddha Chatterjee , Preetam Bharadiya , Dharmesh Hansora a b



Department of Plastic and Polymer Engineering, Maharashtra Institute of Technology, Aurangabad, 431010, MH, India University Institute of Chemical Technology, Kavayitri Bahinabai Chaudhari North Maharashtra University, Jalgaon 425001, MH, India



Keywords: Biopolymers Layered double hydroxides Bionanocomposites

Layered double hydroxides (LDH), also identified as anionic clays, have attracted much consideration due to their excellent ion exchange capacities, shape memory effect and ability to intercalate anions. LDH have been used in the different fields of applications such as biomedical, sensors and detectors, energy storage, novel and advanced functional materials etc. On other hand, biopolymers are environment friendly, fully degradable and sustainable materials, so they can be easily composed without harming nature. Degradation of biopolymers involves loss of structural, mechanical and chemical properties of the polymer and converting into biodegradable compounds which are helpful to the environment. Thus, bionanocomposites made from LDH and different biopolymers would have synergistic effect on their properties, which are necessary for actual applications. This review article deals with the preparation, properties and applications of bionanocomposites made from LDH and biopolymers such as heparin, deoxyribose nucleic acid, vitamin C and E, cellulose, chitosan, polylactic acid, different anionic biopolymers and starch.

1. Introduction

[Me2 +(1

Clay is natural, ancient, abundant soil on the earth with particle size < 4 μm. Clay usually contains organic matters and phyllosilicate minerals that does or doesn't impart plasticity. Wet clay can be harden when dried or fired due to removal of the water molecules (Stephen and Martin, 1995). Due to high water retention capacity, low toxicity, good intercalation ability, higher internal surface area and large porosity, clays are used in medical sector such as antifungal, antimicrobial and anti-inflammatory agents, drug delivery, in cosmetic (Choy et al., 2007), in building materials, etc. Depending on their charges, clays can be classified as (i) cationic clays, which has negative charge outer layers with cations in the interlayers (Bejoy, 2001) e.g., layered silicate, mica, smectite clay such as montmorillonites (McCarthy et al., 2011) and (ii) anionic clays, which are opposite of the cationic clays containing positive charge outer layer with anions in the interlayer e.g., hydrotalcites (Bejoy, 2001), layered or lamellar double hydroxides (LDH) (Werner et al., 2013; Roy, 1998). LDH can be defined as natural or synthetic layered inorganic materials (Huang et al., 2010; Guan et al., 2014) consisting outer layer of positively charge metal hydroxide and interlayer of negative anions to counter balance both the charges. The structure of LDH is shown in Fig. 1. The chemical formula for LDH is given as

In which, Me2+ can be divalent metal such as Ca, Co, Cu, Fe, Mg, Mn, Ni, Zn and Me3+ can be trivalent metal such as Al, Cr, Fe or Ga (Werner et al., 2013). While the interlayer anion An– can be an organic or inorganic in nature (Crepaldi et al., 2000; Ziegler et al., 2013) such as OH−, CO32−, NO3− and x is defined as [Me3+]/{[Me3+] + [Me2+]} (Geng et al., 2010; Shadpour et al., 2014; Bi et al., 2014), having its values between 0.2 and 0.33 (Bejoy, 2001). LDH on exfoliation in different solvents converts into nanosheet form. The synthesis of Co–Fe based LDH nanosheet after its exfoliation are shown in Fig. 2. Due to their anion exchange property (Shu et al., 2014), capacity to intercalate anions and shape memory effect, LDH have been found in applications of different fields such as antireflection coatings (Werner et al., 2013), drug delivery (Gwak et al., 2016; Werner et al., 2013), biosensors, ion-exchanger, flame retardant (Huang et al., 2010), catalysts (Werner et al., 2013; Huang et al., 2010; Shu et al., 2014; Tang et al., 2014) precursors (Shadpour et al., 2014), water treatment, nuclear waste management, electrical, optical functional materials (Huang et al., 2010; Shu et al., 2014), electrochemistry (Tang et al., 2014) and ceramic supercapacitors and photocatalysis (Jeyalakshmi et al., 2013) etc. Biopolymers are degradable, environment friendly and sustainable. They can be easily composted without harming nature. Degradation of biopolymers involves loss of structural, mechanical and chemical

Corresponding author. E-mail address: [email protected] (A. Chatterjee). Received 6 March 2019; Accepted 19 April 2019 Available online 11 May 2019 0169-1317/ © 2019 Elsevier B.V. All rights reserved.

x) ·Me


n x (OH)2 ]A x/n·mH2 O

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aqueous solution of Magnesium Nitrate Mg(NO3)2 and Aluminium nitrate Al(NO3)3 (Mg/Al = 2) simultaneously, with an aqueous NaOH solution to a reactor containing an aqueous suspension of ADP of mass ratio in the range of 2 to 40. Mass ratios of 10 or lower value showed highest degradation rate as compared to free cells. This biohybrids maintained the biodegradative activity of (herbicide) atrazine even after four cycles of reutilization and storage at 4 °C for three weeks (Halma et al., 2015). Other common method viz.; ion exchange method was developed by (Bish, 1980). This method depends upon the electrostatic interaction between the positively charge host sheet and exchanging of these anions (Jing et al., 2006). LDH can be intercalated with different organic and inorganic anions. The ion exchange is favoured when initial anions are in excess quantity, pH is either less or > 4, appropriate temperature and the affinity for incoming anion, (Miyata, 1983). Israeli et al. (2000) described the affinity of different monovalent anions OH– > F– > Cl– > Br– > NO3– > I−. (Yamaoka et al., 1989) described for divalent anion as HPO42– > HAsO42– > CrO42– > SO42– > MoO42−. The different organic anions intercalated includes biomolecules (Choy et al., 1999), amino acids (Fudala et al., 1999), etc. The Reconstruction method involves the reconversion of the calcined LDH i.e. Layered double oxides to LDH by addition of water and different ions in presence of inert atmosphere. Different organic anions such as amino acids, peptides (Nakayama et al., 2004), can be incorporated in the layered structure. This structural change is also known as memory effect. This effect reduces on increasing temperature as it causes the formation of stable spinels (Jing et al., 2006). (Boehm et al., 1977) proposed the salt-oxide method which involves slow addition of trivalent metal salt on aqueous suspension of divalent metal oxide leading to the formation of LDH without maintaining constant pH (Roy, 1998), e.g. Mg–Al based LDH prepared using magnesium oxide (Zhang et al., 2004) or magnesium hydroxide (Li et al., 2002) and sodium aluminate. Hydrothermal method is another method which is introduced at the initial stage or post treatment. Two or more metal oxide are dispersed in aqueous solution mixed with targeted anions can be hydrothermally treated up to a certain temperature to give LDH. For example Mg–Al based LDH can be prepared by taking MgO and Al2O3 in autoclave with deionised (DI) water and temperature maintained up to 110 °C for 5–10 days (Fudala et al., 1999). Wang et al. (2013) synthesized ultrafine LDH nanoplates using hydrothermal reactor with continuous-flow by separate nucleation and aging steps (SNAS) method, developed by Zhao et al. (2002) and in-line dispersion with precipitation method, developed by Abello and Perez-Ramirez (2006). LDH nanosheets can be prepared by delamination method. This method involves dispersion of LDH in polar solvent resulting in the solvation of the hydrophobic tails of the intercalated anions and then drying of the solvent from LDH under vacuum at different temperature to give the nanosheets. There are two approach of preparation of LDH nanosheets viz.; top-down and bottom–up. Top-down approach involves delamination of LDH in different solvent such as higher alcohols like butanol (Adachi-Pagano et al., 2000), acrylates (O'Leary et al., 2002), pentanol, hexanol, carbon tetrachloride, toluene (Jobbaagy and Regazzoni, 2004), formamide (Hibino and Jones, 2001), water (Gardner et al., 2001; Hibino and Kobayashi, 2005) and N,N-dimethyl formamide-ethanol mixture (Gordijo et al., 2007). Bottom-up approach involves oil phase medium of co precipitation system taking dodecyl sulphate as surfactant and 1-butanol as co surfactant (Hu, 2005; Hu et al., 2006; Wang, 2012).

Fig. 1. Schematic representation of the LDH. (Reprinted with permission from Bi et al. (2014) [email protected] open access).

properties of the polymer and converting into simple compound which are helpful to the environment. Biopolymers obtained from natural resources are starch, lignin, deoxyribose nucleic acid (DNA) and cellulose, etc., while manmade polymers prepared from natural resources are chitosan, polylactic acid (PLA), carboxy methyl cellulose (CMC), polyhydroxyl alkanoates (PHA), polyhydroxyl butyrate (PHB), etc. and synthetic green polymers can be prepared from petroleum resources, e.g., polycaprolactone (PCL). Due to its biocompatibility and biodegradability, biopolymers find applications in medicine sector, sensors, drug delivery, gene therapy, as catalyst, packaging, etc. Keeping in mind the low toxicity, ability to intercalate ions, higher internal surface area, inert nature and flame retardency of LDH along with biodegradability, non-toxicity, good strength and biocompatibility of biopolymers; LDH based bionanocomposites can give synergestic properties for desired applications. This review paper covers the preparation methods, characteristic properties and application of LDH based bionanocomposites made from biopolymers such as Heparin, DNA, Vitamin C and E, cellulose, chitosan, PLA, anionic biopolymer and Starch. The different work done on LDH based bionanocomposites are shown in Table 1 respectively. 2. Preparation methods 2.1. Synthesis methods for preparation of LDH LDH can be prepared by different synthesis routes given below. 2.1.1. Common methods for preparation of LDH Common methods for the preparation of LDH includes co-precipitation, ion-exchange, reconstruction, salt-oxide, hydrothermal and delamination methods. The co-precipitation method is mostly used method for the LDH preparation. It was developed by Miyat et al., 1970. The preparation of LDH is mainly occurred by super saturation of two or more metal ions involving physical (e.g. evaporation) or chemical (e.g. variation of pH) routes. Three different types of co-precipitation phenomenon exists viz.; (a) co-precipitation by titration or sequential precipitation which involves titration of two or more metal cations in basic environment such as NaOH, NaHCO3, etc., resulting in sequential precipitation and co-precipitation of the two metals. (b) Co-precipitation by low super saturation which involves maintaining constant pH, constant temperature and constant stirring of two or more metals cationic solution throughout the reaction. (c) Co-precipitation by high super saturation method which involves rapid addition of the two or more metal cation solutions to the desired base solution under constant stirring (Cavani et al., 1991; Jing et al., 2006). A direct co-precipitation method was used to immobilize Pseudomonas sp. strain ADP (ADP) in the Mg2Al-LDH matrix for the degradation of (herbicide) atrazine. The preparation of [email protected] biohybrids were obtained at constant pH (8.0 ± 0.2) by adding an

2.1.2. Other methods The LDH can be also prepared by different other methods such as sol-gel, electro synthesis (Beleke et al., 2013), template, urea hydrolysis (Jing et al., 2006). Chubar et al. (2013) developed alkoxide free sol-gel method for synthesis of Mg–Al based LDH. It involves formation of hydrogel by using freshly synthesized Mg(HCO3)2 as a soft neutraliser 20

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Fig. 2. Topochemical synthesis and exfoliation of Co–Fe LDH nanosheets. (Reproduced with permission from Ma et al. (2007) [email protected] American Chemical Society). Table 1 Different types of LDH based bionanocomposites. Biopolymer

LDH/Biopolymer bionanocomposites (References)

Heparin DNA Vitamin Cellulose Chitosan Polylactic acid Anionic biopolymer

Shu et al., 2014; Shu et al., 2012; Lia et al., 2018; Pavlovic et al., 2016 Choy et al., 1999; Balcomb et al., 2015; Liu et al., 2013; Masarudin et al., 2009; Li et al., 2014b Choy and Son, 2004; Gao et al., 2014; Gao et al., 2013 Yadollahi et al., 2014; Barkhordari et al., 2014; Wu et al., 2011; Barik et al., 2017 Ribeiro et al., 2014; Rezvani and Shahbaei, 2015; Elanchezhiyan and Meenakshi, 2017; Shi et al., 2008; Li et al., 2018 McCarthy et al., 2011; Zhao et al., 2003; Hasook et al., 2006; Roman et al., 2013; Dagnon et al., 2009; Miao et al., 2012. Reese et al., 2015; Wang et al., 2010; Rezvani and Shahbaei, 2015; Kang et al., 2013; Sun et al., 2018; Pan et al., 2016; Ding et al., 2009; Lopeza et al., 2010; Lee and Kim, 2013; Iftekhara et al., 2018 Wilhelm et al., 2003; Zubair et al., 2018; Xiea et al., 2013; Bruna et al., 2015.


acetylated alginate were prepared by co precipitation method. Aluminium nitrate and zinc nitrate were used as a LDH precursor to form hybrid composites with alginate solution at a constant pH of 8.5–9. The d-spacing was found to increase from 1.28 to 1.85 nm with increasing guluronic acid in the alignates and also for acetylated alignates to 1.72 nm simultaneously. The NMR spectroscopy revealed the interaction of negatively charged carboxylic groups from the biopolymer with the positively charged inorganic main layer while, scanning electron microscopy confirmed the highly flexible nanofoil morphology of the hybrid composites which could function as reinforcement to the concrete applications (Reese et al., 2015). Self-assembled 3D nanostructures of different morphologies such as pompon-like, marigold-like, and coral-like were prepared for sodium alginate biopolymer-assisted Ni−Al LDH bionanocomposites using hydrothermal methods. The nanostructures could be altered by the synthesis parameters including hydrothermal aging time, concentration of metal ions, and reaction temperature. Moreover, the resulting NiObased mixed metal oxides maintained the 3D morphology of their LDH precursors to some extent even after calcinations of LDH-biopolymer nanocomposites at 500 and 700 °C, indicating the high thermal stability of nanostructures (Wang et al., 2010). LDH-lignosulfonate (LS) organoclays were successfully assembled by drop wise addition of Zinc Chloride (ZnCl2) and Aluminium Nitrate Al(NO3)3 co precipitated solution (250 mL) into lignosulfonate solution. The crystallinity was decreased for Zn2Al/LS organoclay as compared to Zn2Al organoclay due to amorphous nature of the lignosulfonate. This Zn2Al/LS organoclay (5 wt% concentration of polyester) was incorporated as a filler in three biopolyester viz.; poly (lactic acid) (PLA), poly (butylene) succinate (PBS) and poly(butylene adipate-co-terephthalate) (PBAT) by polymer extrusion process. Miscible structure was obtained for PLA and PBS while non-miscible structure for PBAT. Also, static water contact angle showed constant value for PLA and PBS but for PBAT, a decrease in value upto 10° was obtained. The complex viscosity was found to increase in LDH/LS filled PLA and PBS biocomposites as compared to decrease in Polyester and PBAT biocomposites respectively due to chain extension behaviour of the organoclay in the former and plasticizing effect in the later one. The thermal stability showed slightly higher values for PLA as compared to PBS and PBAT biocomposites respectively (Hennous et al., 2013).

in the hydrolysis of aluminium chloride. The hydrogel was aged for 24 h to give pure layered material. Ni–Al based LDH, Ni–Cr based LDH, Ni–Mn based LDH and Ni–Fe based LDH can be synthesized electrochemically with similar properties as obtained by chemical methods. Template method involves the use of template such as surfactants forming micelles, polypeptides, polysaccharides, etc. for the formation of LDH (Jing et al., 2006). Urea has weak base and it has high solubility in water and hence its hydrolysis rate can be controlled; making urea useful for precipitation of metal hydroxides (Jing et al., 2006). Hybrids of methotrexatum intercalated LDH (MTX/LDH) were synthesized by four different routes including typical co-precipitation method, reversemicroemulsion approach, ion-exchange and mechanochemical– hydrothermal method (Tian et al., 2015; Dai et al., 2015). 2.2. Preparation of different types of LDH/biopolymer based nanocomposites LDH/biopolymer based bionanocomposites contains LDH intercalated with biopolymers. Mg–Al based and Zn–Al based LDH are already used in medicine as antacid and antipepsinic agents and in many ointments and poultices for the protection of damaged skin (Costantino et al., 2013). Biopolymers are biocompatible and biodegradable. There are huge differences in the properties of biopolymers and synthetic polymers. Most biopolymers are soluble in polar solvents, water, whereas most synthetic polymers are soluble in organic solvents. Processing methods like the extrusion are widely applied for preparation of synthetic polymers composites, but they are unusable for biopolymers. Advantage of biopolymers over synthetic polymers is they are of biological origin obtained from renewable resources and they can be produced from agricultural products, food, industrial, and domestic wastes. Biopolymers are widely copious and having relatively low-cost. Biopolymer based nanocomposites can be prepared by melt processing methods, e.g., PLA. LDH/biopolymer nanocomposites can give synergistic properties for biomedical application such as drug delivery and gene therapy, etc. LDH based biopolymer nanocomposites can be prepared by same technique as that for LDH i.e. co-precipitation, ionexchange, hydrothermal, delamination and other methods. Five LDH-alignates hybrid composites of which four possessing different guluronic/mannuronic acid ratios alignates and one 21

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Fig. 3. Fabrication of the Artificial Nacre-like HEP/LDH biofilm. (Reproduced with permission from Shu et al. (2014) [email protected] American Chemical Society)

2.2.1. LDH/ Multifunctional heparin based bionanocomposites Among the Glycosaminoglycans, Heparin [HEP] has attracted much attention due to its anticoagulant activity and biocompatibility with blood (Shu et al., 2012; Li et al., 2018). Multifunctional heparin/ layered double hydroxide (HEP/LDH) films were prepared by simple vacuum-filtration method. The presence of highest negative charge density in the HEP molecules because of sulfonic and carboxylic groups resulted in its interaction with positive charged LDH nanosheets. Similarly, formation of a hydrogen bond was observed due to the interaction of hydroxyl groups present on the surface of HEP molecules and LDH nanoplatelets resulting in Nacre like structure (Fig. 3). This strong electrostatic interaction produces an organic/inorganic film of HEP/LDH. This hybrid nanobiocomposite film showed partial blocking of UV A and complete blocking of UV B and UV C. It also showed increment in modulus, hardness and fire resistance properties (Shu et al., 2014). Pavlovic et al. (2016) studied the colloidal stability of LDH nanoparticles in the presence of Heparin molecule. Mg-AL LDH was prepared by co precipitation method and nanoparticles were obtained after further hydrothermal treatment. These LDH nanoparticles (1 g) were allowed to be adsorbed by HEP molecules (100 mg). LDH nanoparticles were aggregated in the absence of HEP but became stable with HEP covering and showed increment of charge density up to two times and critical coagulation concentration up to 20 times than the bare nanoparticles. This kind of stable system can further be utilized for drug delivery and gene delivery purpose (Pavlovic et al., 2016).

transgene activity in the three human cell viz.; hepatocellular carcinoma (HepG2) lines, cervical cancer (HeLa), and embryonic kidney (HEK293). Among all three cells, HEK293 cells showed the best transfection activity for all biocomposites; with highest transfection activity (16 × 104 RLUmg−1 protein) observe for the DNA:MgFe.55 (1:30 w/w) (Balcomb et al., 2015). Choy et al. (2000) reported that LDH can protect degradation of DNA and also enhance the transfer of DNA into mammalian cells by endocytosic means by dissolving the LDH in slightly acidic media. Kwak et al. (2002) reported that pure LDH have no effect on the viability of human promyelocytic leukemia cell (HL-60 cells) at levels below 1000 Ag/mL for up to 4 days. As LDH are non cytotoxic on HL-60 cells and so it can act as a new inorganic carrier. 2.2.3. LDH/Vitamin based bionanocomposites Vitamins are the micronutrients required by living beings in small amount for carrying out proper metabolism in the body. Vitamins containing negative groups, on intercalation with positive groups of LDH give variety of bionanocomposites suitable for different bioapplications. Choy and Son (2004) studied bio nanohybrids made from Zn3Al (NO3−) LDH and vitamins such as ascorbic acid (Vitamin C) and topopherol acid succinate (Vitamin E) by anion exchange method. The increase in the basal spacing revealed the intercalation of vitamins in the LDH matrix. The similar peaks observed in the UV-Vis and IR absorption spectra confirmed the stable chemical and structural behaviour of the bionanohybrids without any deterioration of the bioactivities. These nano hybridized vitamins could be discharged in a controlled kinetics. Zhao et al. (2013) synthesized NiAl-NO3− LDH films by in situ method on anodic alumina/aluminium (AAO/Al) support. Anion-exchange method was used to intercalate glucose oxidase (GOD), L-ascorbic acid (vitamin C, VC) dodecylsulfate (SDS) and GOD/SDS respectively into the in-situ grown LDH films. LDH films showed petals like structure while the intercalated compounds showed sheet like structures with weak agglomeration due to molecular intercalation. The basal spacing of VC LDH and GOD LDH were slightly shifted to lower value which confirmed the replacement of NO3− ions by VC molecules and fewer GOD molecules respectively. SDS LDH (2.55 nm) and SDS/ GOD LDH (2.99 nm) showed major increase in basal spacing due to interlayer expansion of the LDH occurring by the presence of SDS. Gao et al. (2014) studied that Zn2–Al based LDH show better controlled release system in VC intercalated LDH in aqueous CO32– solutions. Different kinetic models suggested a combination process of diffusion-controlled and ion exchange intercalation mechanisms and a solution-dependent release mechanism in DI water, but an ion exchange process in CO32– solution. All the VC release curves showed broad similar features. Mg3Al–VC and Mg3Fe–VC based LDH bionanocomposites had high rates of initial VC release. The release processes in CO32– solutions were uniformly found to lead with more release after 420 min than the corresponding reactions in DI water (Gao et al., 2014).

2.2.2. LDH/deoxyribose nucleic acid based bionanocomposites DNA is a polynucleotide formed by large number of nucleotide monomer. DNA encodes genetic instructions used for the development and functioning of all known living organisms and many other viruses. DNA finds wide application in genetic therapy, biosensing and information storage. LDH contain positive charge outer layers while DNA contains negative charge. Ion exchanged ability of LDH can create electrostatic interaction between negative layers of DNA and positive layers of LDH. LDH can easily intercalate into these DNA to prevent its degradation and enhanced its stabilization energy (Choy et al., 2000; Chatterjee and Hansora, 2016). The intercalation of LDH into DNA can be observed easily from XRD patterns (Fig. 4) of Mg-Al/Zn based LDH and their DNA bionanocomposites. The presence of new peak in between 15 and 20o and change increment in basal spacing was observed for LDH/DNA bionanocomposites. This was due to the formation of the coordinate bond between DNA and LDH and loss of water molecules from inside or on the surface of LDH respectively (Li et al., 2014b). Luciferase activity in HEK293 cells of different LDH such as Mg–Al CO3, Mg- Fe CO3, Zn–Al CO3 and Zn–Fe CO3 and their DNA based biocomposites are shown in Fig. 5. Two controls were used viz.; HEK293 cells and second containing cells transfected with naked DNA i.e. pCMV-luc DNA (1.0 mg). All LDH:DNA biocomposites showed 22

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Fig. 4. XRD pattern of Mg-Al/Zn-LDH and Mg-Al/Zn LDH: DNA. (Reproduced with permission from Li et al. (2014b) [email protected]).

2.2.4. LDH/cellulose based bionanocomposites Cellulose is the abundant biopolymer that makes up the living cells of all vegetation. It is the renewable material at the centre of the carbon cycle. Carboxymethyl cellulose (CMC) is a modified cellulose containing carboxymethyl groups (eCH2eCOOH) bounded to some of the hydroxyl groups in the cellulose backbone. The carboxymethyl groups present in the CMC are responsible for its water solubility, anionic behaviour and chemical reactivity which make it suitable for ion exchange applications. (Yadollahi et al., 2014) intercalated CMC into Mg–Al LDH and Ni–Al LDH by co precipitation methods. FTIR spectra of Mg Al LDH/CMC revealed the shifting of asymmetric peaks of COOH groups to higher wavenumber confirming the intercalation of CMC in the LDH matrix. The increase in d spacing was observed from 0.862 nm, 0.816 nm for Mg Al LDH; Ni Al LDH to 1.73 nm; 2.23 nm for their respective CMC bionancomposites. TEM result revealed the presence of intercalated and non intercalated layers in both Mg–Al LDH/CMC and Ni–Al LDH/CMC respectively. The thermal stability was found to increased for Mg–Al LDH/CMC than Ni–Al LDH/CMC bionanocomposites. The swelling behaviour of the bionanocomposites showed increment with pH from 2 to 10 but sharp increased was observed for the pH 10 and above values. (Barkhordari et al., 2014) studied drug release of Ibu intercalated with nanocomposite beads prepared using LDH with CMC by co-precipitation method. At pH 1.2 the drug release from LDH-Ibu was 60% while for CMC/LDH-Ibu nanocomposites negligible amount (< 10%) was observed due to shrinkage of CMC in acidic medium and at pH 7.4 it was 40% and higher rate was observed respectively due to the presence of carboxyl groups on the CMC chains. This reveals the pH sensitive drug release pattern for LDH-CMC bionanocomposites. Yadollahi et al. (2014) prepared CMC-Mg-Al LDH bionanocomposites films by solution casting method with 0, 1, 2, 3, 4, 5, 6, 7 and 8 wt % LDH contents using water as solvent. Mechanical properties such as tensile strength of 25.65 MPa and tensile modulus of 1040 MPa was obtained for the CMC–LDH bionanocomposite film, which was 148% and 143% higher than those of pure CMC film for 3 wt% LDH content due to strong interaction of LDH sheet with CMC. Also, elongation of break and water vapour permeability showed decreased in 62% and 37% for CMC–LDH bionanocomposite film respectively.

has attracted much attention due to its biomedical application. Ribeiro et al. (2014) studied the drug delivery of 5-amino salicylic acid (5ASA), a non-steroid-anti-inflammatory drug (NSAID) intercalated with LDH using the co-precipitation method and finally incorporated in a chitosan matrix for the treatment of ulcerative colitis and Crohn's disease. These LDH based biocomposites were coated with the polysaccharide pectin to protect it at the acid pH of the gastric fluid. These pectin coated LDH biocomposite beads were stable to water swelling and showed a controlled drug release along the simulated gastrointestinal tract in vitro experiments. Rezvani and Shahbaei (2015) investigated the structure and drug release properties of bionanocomposites based on Chitosan and Alginate/Zn–Al based LDH with ciprofloxacin (CFX) antibiotic drug. Zn–Al based LDH were intercalated with CFX by coprecipitation method followed by coating with Alginate and Chitosan to obtain chitosan/LDH and Alginate/LDH bionanocomposites. SEM images of the Alginate Ciprofloxacin, Chitosan-Ciprofloxacin, pristine Zn/Al-NO3LDH and LDH/CFX powders and their bionanocomposites are shown in Fig. 6(a–e) These micrographs confirmed an intercalation of CFX into LDH. XRD, FTIR and TGA analysis confirmed that the interlayer nitrate anions of LDH can be replaced by CFX anions to develop drug intercalated Zn–Al LDH with good crystallinity. The drug release rate were in following order LDH-CFX/chitosan (39%) < alginate (58%) < chitosan (62%) < LDH-CFX based nanohybrids (78%) < LDH-CFX/ alginate (92%) based nanocomposites (Rezvani and Shahbaei, 2015). Li et al. (2018) used LDH nanoparticles filled chitosan bionanocomposites as effective sorbents for selenate and selenite oxoanions. The bionanocomposites beads were prepared by direct mixing of LDH nanopowder with chitosan gel (DM-X, X stands for % LDH loading) and in-situ (IS-X, X stands for % LDH loading) method by adding (MgCl2 and AlCl3·6H2O) LDH into chitosan gel. The efficacy of Selenium removal was determined by jar test in deionised water spiked with initial 1 ppm Se(VI) concentration (Fig. 7). As compared to chitosan, 57% removal of Se(VI) was obtained for DM-30 beads. The highest efficacy was observed for IS-50 with value of > 80% due to the increment of sorption characteristics of chitosan with LDH incorporation (Fig. 7A). Furthermore, the pH was found to increase after this sorption test for IS50 beads (Fig. 7B). This is due to exchange of selenate with hydroxide and carbonate anions of LDH. The maximum removal of Se(VI) was found up to 9 pH as for IS-50 beads as compared to 6 pH for chitosan respectively.

2.2.5. LDH/chitosan based bionanocomposites Chitin is a structural polysaccharide. Chitin when deacetylated to about 50% of the free amine gives chitosan. As a biopolymer, Chitosan 23

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Fig. 5. Luciferase activity in embryonic kidney (HEK293) cells using a) Mg–Al LDH, DNA: Mg–Al LDH (1:30–1:60); b) Zn–Al LDH, DNA:Zn-Al LDH (1:40–1:70), c) Zn–Fe LDH, DNA:Zn-Fe LDH (1:30–1:40); and d) Mg–Fe LDH, DNA:Mg-Fe LDH (1:25–1:55). (Reproduced with permission from Balcomb et al. (2015). [email protected] John Wiley & Sons).

2.2.6. LDH/polylactic acid (PLA) based bionanocomposites PLA is an aliphatic polyester prepared by polymerization of cyclic dimer of lactic acid i.e. lactide. PLA, a sustainable crop-sourced substitute for synthetic polymers such as polyesters and poly(ethyleneterephthalate), find their applications in blown films, bottles and sutures and biomedical area (Zhao et al., 2003). High molecular weight PLA was produced by ring opening polymerization of lactide monomer, which was derived from the fermentation of plant starch. PLA has been studied as a base matrix for many nanocomposite materials featuring montmorillonites, smectites and LDH (Ogata et al., 1997; Krikorian and Pochan, 2003; Sinha et al., 2002; Hasook et al., 2006). These composites are produced by means of melt-blending and extrusion of existing polymer with clay. Roman et al. (2013) studied drug delivery of drugs such as chloramphenicol, ketoprofen, and diclofenac intercalated in LDH and dispersed in PLA. After 24 h the drug release was found to be 100%, 80% and 60% for these LDH intercalated drugs respectively. But with PLA incorporation the drug release was slower and it was not completed even after 3 months. Approximately, 36% of ketoprofen, 24% and 70%, in the case of diclofenac and chloramphenicol were released in LDH/ PLA-drug biocomposites.

Dagnon et al. (2009) reported the improved mechanical performance during decreased cell proliferation using Zn–Al LDH organically modified with ibuprofen (Ibu) dispersed in poly(L-lactic acid) (PLLA). The calcined Zn–Al LDH were prepared by co precipitation method and then ion exchanged using Ibu. The PLLA/LDH nanocomposites were obtained using solution casting method. Cell proliferation measurements were done by taking 1 mL of the dispersion in cylindrical glass substrates and then evaporating the solvent. The samples with and without PLLA prepared using 1, 3 and 5% LDH-Ibu or Ibu are shown Fig. 8. Reduction in cell proliferation was noticed with 1, 3 and 5 wt% LDH loaded PLLA as compared to neat PLLA. LDH-Ibu incorporated in PLLA inhibited the proliferation of smooth muscle cell after exposure of 5 days. Ibu caused the decrease in cell proliferation. While incorporating Ibu into the LDH resulted in effective drug release and also mechanical performance. Miao et al. (2012) studied drug delivery system of Ibu intercalated LDH with PCL and PLA fibers. Mg–Al based LDH Ibu was prepared by coprecipitation method. Poly(oxyethylene-b-oxypropylene-b-oxyethylene) (Pluronic) was used as hydrophilicity enhancer and released modulator into these biocomposites. In vitro drug release studies showed that initial Ibu liberation from LDH-Ibu/PCL composite fibers 24

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Fig. 6. SEM images of CFX1ALG mixture (a), CFX1CHIT mixture (b), LDH (c), LDH-CFX nanohybrid (d), LDH-CFX/alginate nanocomposite (e), LDH-CFX/chitosan nanonocomposite (Reproduced with permission from Rezvani and Shahbaei (2015) [email protected] John Wiley & Sons).

was slow as compared to that from Ibu/PCL fibers. The initial Ibu release from LDH-Ibu/PLA and LDH-Ibu/PLA/Pluronic composite fibers was faster than that from the corresponding Ibu/PLA and Ibu/PLA/ Pluronic fibers (Miao et al., 2012). Chatterjee and Hansora (2016) reviewed and reported that Ibuprofen (IBU) intercalated (LDH/PCL) and LDH–IBU/PLA can be used as effective drug delivery system.

Iftekhara et al. (2018) prepared Zn–Al LDH (ZA) by urea hydrolysis process and mixed with 2% Xantham gum solution (XG-ZA) by ultrasonication and stirring for 24 h at 60 °C. This emulsion was further added with FeCl3 or ZrOCl2·8H2O solution to obtain ([email protected], where M = Fe or Zr) bionanocomposites. The surface morphology of this bionanocomposites is shown in Fig. 9. [email protected] shows larger organic cluster than more denser [email protected] bionanocomposite (Fig. 9a,d). Also, it is confirmed that ZA is encapsulated by XG. Scutes and cycloids scale like morphologies are observed for these bionanocomposites from SEM images (Fig. 9b,e). The amount of Fe loading is higher than Zr loading due to binding of Fe by replacement of OH groups of LDH (Fig. 9c,f). Mahdi et al. (2015) used coprecipitation method to prepare Mg2Al NO3 LDH nanoplatelets and Fructose-6-phosphate aldolase enzyme immobilized Mg2–Al. NO3 LDH nanoplatelets (FSA wt @ Mg2–Al. NO3 LDH) biohybrids. Six different polysaccharides [alginate, polygalacturonic acid, κ-carrageenan (kappa), ι-carrageenan (iota), curdlan and oxidized cellulose] were taken for testing their gelation, chemical and biological stability with FSAwt. Among them, ι-carrageenan beads

2.2.7. LDH/anionic biopolymer based bionanocomposites Anionic biopolymers are very much suitable for making bionanocomposites with LDH due to their anionic charges. Bionanocomposites of [Zn2Al(OH)6]Cl·nH2O LDH intercalated with naturally occurring anionic biopolymers such as polysaccharides (alginic acid, pectin, κcarrageenan, ι-carrageenan, and xanthan gum) have been prepared by co precipitation and reconstruction method. As compared to co-precipitation method, the reconstruction method resulted in a partial intercalation of the organic guest. The anion exchange capacity of the pristine LDH converted into cation exchange capacity due to the unreacted negatively charge of the polysaccharide with positively charge LDH sheets (Darder et al., 2005). 25

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Fig. 7. Comparison of sorbent materials for 48 h of exposure time. Dosages: 1 g/L chitosan, 0.42 g/L granular LDH, 0.42 g/L in-situ LDH nanopowder; all nanocomposite beads were used at a 1 g/L dosage with respect to the amount of chitosan in the bead. (B) pH dependence of Se(VI) removal on IS-50 beads. The final pH was measured after 48 h of equilibration (each point represents an average of duplicates with error bars showing the range). (Reproduced with permission from Li et al. (2018) Copyright @Industrial and Engineering Chemistry research).

exchanger), and brucite (having a neutral structure) to modify glycerolplasticized starch films. This modification was obtained by casting method and the effect were analyzed by X ray diffraction, dynamic mechanical analysis and thermogravimetry. Kaolinite showed highest storage modulus as compared to brucite, hectorite and LDH starch composites respectively, but the intercalaction of glycerol molecules was only observed in the hectorite filler as confirmed from the shift of the interplanar basal distance to higher values. The glycerol intercalation was found to increase in the oxidized starch chains than the plasticized–oxidized starch films. Zubair et al. (2018) prepared 1:1 and 2:1 starch/NiFe(S/NiFe)-LDH bionanocomposites via co-precipitation method for the removal of methyl orange (MO) from aqueous solution by adsorption method. Both S/NiFe-LDH composites (1:1) and (2:1) removed MO from water with 99 and 90% efficiency at pH 3. The adsorption capacities calculated by Langmuir isotherm for NiFe-LDH, S/NiFe –LDH (2:1) and S/NiFe-LDH (1:1) were found to be 246.91 mg/g, 358.42 mg/g, 387.59 mg/g respectively.

Fig. 8. LDH Ibu blended PLLA films' reduced SMC proliferation. The cells were cultured in glass vials (control) or PLLA, PLLA/LDH Ibu, PLLA/Ibu, LDH Ibu, or Ibu samples with Ibu concentrations of 1, 3, and 5%. (Reproduced with permission from Dagnon et al. (2009) [email protected] John Wiley & Sons).

3. Properties

showed highest enzyme retaining capacity of 87% similar thermal stability respectively, for encapsulated FSA [email protected]–Al. NO3 LDH as compared to free FSA wt. The catalytic activity yield was higher for crushed ι-carrageenan beads encapsulated FSA [email protected]–Al. NO3 LDH as compared to uncrushed beads. ι-carrageenan beads encapsulated FSA [email protected]–Al NO3 LDH showed the catalytic efficiency of 80% and slight decrease in cyclic stability after fourth cycle simultaneously, after carrying aldolisation reaction between hydroxyacetone (HA) and formaldehyde. The catalytic activity of these beads kept in KCl 1 M solution after 12 days storage was 60% as compared to 28% for the beads without KCl respectively.

3.1. Crystallinity Powdered X-ray Diffraction (PXRD) is used to determine the crystalline nature of LDH. PXRD determines any impurity present in the LDH. PXRD determine the crystal lattice pattern of the LDH. Bragg's equation (λ = 2·d·Sinθ) is used to calculate crystal plane distance, where ‘λ’ indicates the wavelength of X-ray radiation, ‘d’ indicates the crystal plane distance. Scherer's formula is used for calculation of crystallite size. It is given by Crystallite size d = k·λ/Δ2θ·cosθ, where ‘k’ indicates order of reflection, λ is wavelength (=1.542), θ indicates diffraction angle, Δ2θ is full width at half-maximum (FWHM). Fig. 10 shows the XRD spectrum of Mg–Al LDH and Carboxymethylcellulose (CMC)–LDH bio nanocomposite films containing (1, 3, 5, and 8 wt%) of LDH. The XRD diffraction peaks at 10.26°, 11°and ∼20° corresponds to the formation of LDH and bionanocomposites or disordered system in LDH, CMC and CMC-LDH bionanocomposites respectively. Also, for 8 and 5 wt% LDH content new broad peaks at 5° and 3.5° are occurring due to exfoliated/intercalated nanostructure for CMC–LDH bio nanocomposites. But below 5 wt% LDH content, absence of diffraction peak can be observed in 2ϴ = 2°−10° because of fully exfoliated CMC–LDH bionanocompsite (Yadollahi et al., 2014).

2.2.8. LDH/starch based bionanocomposites Starch is difficult to intercalate in the LDH matrix. But (Wu et al., 2011) used carboxymethyl cellulose sodium (CMC) as a stabilizer to disperse LDH stacks in the starch matrix. With 6 wt% LDH loading mechanical properties was found to increase while water resistance and thermal stability was found to decrease. Wilhelm et al. (2003) used natural layered compounds such as kaolinite (a neutral mineral clay) and hectorite (a cationic exchanger mineral clay) and synthetic layered compound such as LDH (an anionic 26

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Fig. 9. TEM, SEM images and EDX spectra of [email protected] (a–c) and [email protected] (d–f), respectively. (Reproduced with permission from Iftekhara et al. (2018). [email protected] Carbohydrate Polymers).

and pectin biopolymers the carboxylate groups appear at 1743 cm−1, 1754 cm−1, 1422 cm−1 and 1445 cm−1 wavenumbers while in their corresponding LDH nanocomposites spectra, these peaks are shifted to 1604 cm−1, 1612 cm−1, 1419 cm−1 and 1420 cm−1 wavenumbers respectively. As compared to alginate and pectin biopolymers, for ιcarrgeenan and ι-carrgeenan-biopolymer nanocomposites, the SeO bond, (3,6-anhydro-L-galactose), (C-O-S of SO4−4, secondary axial C-4), (C-O-S of 3,6-anhydro-L-galactose), (glycosidic) groups are obtained at 1237 cm−1, 930 cm−1, 849 cm−1,805 cm−1 and 902 cm−1 respectively. (Zubair et al., 2018) studied starch-Ni-Fe LDH bionanocomposites for effective removal of methyl orange from aqueous phase. Fig. 12 shows the SEM micrograph of (a) starch, (b) NiFe-LDH, (c) starch/NiFe-

3.2. Surface and morphological properties Darder et al. (2005) studied biopolymer-LDH nanocomposites based on the intercalation of [Zn2Al (OH)6]Cl.nH2O LDH and anionic biopolymers including alginate, pectin, ι-carrgeenan and xanthan gum. Fig. 11 shows the FTIR spectra of (a) [Zn2Al]Cl LDH, (b) alginate, (c) alginate-LDH, (d) pectin, (e) pectin-LDH, (f) ι-carrgeenan and (g) ιcarrgeenan-LDH. From Fig. 11 it can be observed that all samples shows strong vibration band near 3450 cm−1 corresponding to the OH group of water molecules and hydroxyl group of brucite layers. LDH shows the different peaks at 1619 cm, 1359 cm−1, 776 cm−1, 625 cm−1 and 430 cm−1 corresponding to the HOH, asymmetric C–O stretching of carbonate, M-O stretching and O-M-O groups respectively. For alginate 27

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Fig. 11. FTIR spectra of (a) [Zn2Al]Cl LDH, (b) alginate, (c) alginate-LDH, (d) pectin, (e) pectin-LDH, (f) ι-carrgeenan and (g) ι-carrgeenan-LDH. (Reproduced with permission from Darder et al. (2005) @copyright Chemistry of Materials).

Miao et al. (2012) fabricated electrospun fibers of LDH/biopolymer nanocomposites for effective drug delivery application. Fig. 13 shows low and high magnification TEM images of (a and b) 5 wt% LDH-Ibuprofen (LDH-IBU)/Polycaprolactone (PCL) composite fibers; (c and d) 5 wt% LDH-IBU/Polylactic acid (PLA) composite fibers. TEM morphologies revealed the uniform dispersion of LDH-IBU nanoparticles in PCL and PLA fibers even at 5 wt% LDH-IBU due to the minute size of LDH-IBU and good compatibility of LDH with polymer matrix because of organic surfactant behaviour of IBU. 3.3. Mechanical properties LDH is responsible for increasing the mechanical properties of biopolymers. Fig. 14 shows the tensile and elongation at break of Glycerol plasticised starch (GPS)/LDH bionanocomposites. The tensile properties of GPS matrix increased with increase in LDH-CMC contents from 3.3 MPa to 6.75 MPa for 0 wt% and 6 wt% respectively. This increase in mechanical properties was due to the good interaction between starch and CMC because of similar polysaccharide structures. But above 8 wt% LDH–CMC contents the tensile strength reduced to 4.75 MPa due to agglomeration of LDH-CMC. The elongation at break was reduced due to decrease in mobility of the matrix because of well dispersed LDHCMC contents (Xiea et al., 2013; Wu et al., 2011).

Fig. 10. XRD of CMC film, Mg–Al LDH and CMC-LDH bionanocomposites films (Reproduced with permission from Mehdi Yadollahi et al. (2014) Copyright @Carbohydrate polymers).

LDH (1:1), (d) starch/NiFe-LDH (2:1) and (e) high resolution starch/ NiFe-LDH (1:1), (f) starch/NiFe-LDH (2:1). Starch showed smooth morphology as compared ratted flowered like particles with serrated and sharp ends and rough and porous morphologies for NiFe-LDH and starch/NiFe-LDH composites respectively. Also, the high magnification images of starch/NiFe-LDH composites confirmed the reaction of starch hydroxyl groups with NiFe-LDH functional groups during precipitation which was responsible for small cracks on the surface of the composites.

3.4. Thermal properties Lignosulfonate consisting of sulfonate group attach to lignin. LS decomposes in different steps (Fig. 15(a)) with a final end-product as Na2SO4 obtain at 1100 °C. With Zn2 Al LDH incorporation in LS the final weight loss is decreased from 80% for LS as compared to 60% for Zn2 Al LDH/LS bionanocomposites (Fig. 15(b)). For LS the higher loss is due to higher hydration rate of 4.9 water molecule per formula weight 28

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Fig. 12. SEM micrographs of (a) starch, (b) NiFe-LDH, (c) Starch/NiFe-LDH (1:1), (d)Starch/NiFe-LDH (2:1) and (e) high resolution Starch/NiFe-LDH (1:1), (f) Starch/NiFe-LDH (2:1). (Reproduced with permission from Zubair et al. (2018) [email protected] Journal of molecular liquids-Elsevier).

C10H12O10SNa as compared to lower hydration rate of 1.7 water molecule per formula weight Zn2Al(OH)6 for Zn2Al/LDH respectively. This is because the non sulfonated polymer are not contributing to the organoclay formation and the coprecipitation process acting as selective sieves which impede the neutral polymer chain to interact with the inorganic sheets (Hennous et al., 2013). Fig. 16 shows the TGA curves of (a) pure alignate (b) NO3−–LDH and (c) alginate/LDH nanobiocomposite. For pure alginate (Fig. 16a), weight loss of 8% below 200 °C was because of the evaporation of physically adsorbed water. The weight loss of 52% from 200 °C to 586 °C was due to thermal degradation and combustion, and weight loss beyond 586 °C occurred due to the decomposition of the sodium salts. As compared to NO3−–LDH (Fig. 16b), where water evaporation (about 8%) was observed in the temperature range of 20–174 °C, for alginate/ LDH nanocomposites (Fig. 16c), the degradation (about 13%) was observed in the range of 20 °C and 195 °C. The removal of the NO3− anions and the dehydroxylation of the layers was observed in between 174 °C and 586 °C (about 40%) for NO3−–LDH as compared to the temperature range of 195–672 °C for its degradation and combustion of alginate in alginate/LDH bionanocomposites respectively (Kang et al., 2013).

4. Applications Wang (2012) reviewed and summarized the recent advances in the development and application of LDH nanosheets. LDH and their bionanocomposites can be useful as catalysts, sensors, as catalysts, in waste-water treatment, as flame retardants, as sensors, in biomedical sectors etc. (Darder et al., 2005; Mousty and Prévot, 2013). 4.1. As catalysts Ni-Amino acid-CaAl LDH bionanocomposite has been reported as a catalyst. Varga et al. (2017) prepared Ca–Al based LDH by co-precipitation methods using Ca(NO3)2·4H2O and Al (NO3)3·9H2O as a precursor. Ni-Amino acid intercalation was obtained by two methods. The first method consist of intercalation of amino acid using L-cystein, Lhistidine or L-tyrosine as precursor followed by introduction of Ni(II) ions with varying concentration (ratio of Ni (II) to amino acids from 1:2 to 1:6) to form CaAl-Ni(II)-amino acid anion- LDH bionanocomposite. The second method involves the preparation of Ni(II)- amino acid complex separately with different ratio and intercalating in the Ca–Al LDH forming Ni(II)-amino acid anion-CaAl-LDH bionanocomposites. 29

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Fig. 13. Low and high magnification TEM images of (a and b) 5 wt% LDH-IBU)/PCL nanocomposite fibers; (c and d) 5 wt% LDH-IBU/PCL nanocomposite fibers. (Reproduced with permission from Miao et al. (2012) @copyright Material Chemistry and Physics).

Fig. 15. TGA analysis for a) sodium lignosulfonate (Na–LS), b) Zn2Al/LS (Reproduced with permission from Hennous et al. (2013) copyright @Applied Clay Science).

Fig. 14. Tensile properties and Elongation at break of GPS/LDH-CMC contents. (Reproduced with permission from Wu et al. (2011) @copyright Carbohydrate Polymer).

used to hydrolyze starch in an aqueous solution. The catalytic activity of the AAM/LDH bionanocomposite was tested for the hydrolysis of starch obtained from the different adsorption isotherm points with concentration between 17 and 65 mg/g, the loading values of ca. 50 mg/g of AAM/LDH showed enhanced efficiency. Also the biocatalyst activity followed a slight sigmoid pattern with increased in the amount of enzyme immobilization (Fig. 17). This AAM/LDH biocatalyst can serve as a cheaper and environment friendly alternative to AAM pristine biocatalyst.

The CaAl-LDH, CaAl-Ni(II)-amino acid anion- LDH bionanocomposite and Ni(II)-amino acid anion-CaAl-LDH bionanocomposites were further tested for catalytic conversion of cyclohexene to epoxide group using peracetic acid as oxidant (Table 2) and to cis diol using iodosyl benzene as oxidant (Table 3) respectively. Also, the catalytic activity showed good recycling properties. Bruna et al. (2015) developed α-amylase (AAM) biocatalyst based on Mg3Al-LDH matrix using adsorption method. This biocatalyst was 30

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nanocomposite by solvothermal method and immobilized it with calcium alginate (CA) to obtained magnetic alginate microsphere of Fe3O4/MgAl-LDH (Fe3O4/LDH-AM). These bionanocomposites was used to remove Cd2+, Pb2+, and Cu2+ from aqueous solutions by adsorption phenomenon. The maximum adsorption capacity of these bionanocomposites was 64.66 mg/g, 74.06 mg/g, and 266.6 mg/g for the Cu2+, Cd2+ and Pb2+ respectively (Sun et al., 2018). 4.3. In UV protection and as flame retardant LDH, commercially promising material, are used as flame retardants. As compared to other flame retardants, LDH is reported as new material due to high smoke suppression and low toxicity. LDH platelets have a good fire-resistance and heat-shield capabilities along with mechanical properties. (Barik et al., 2017) applied Mg–Al LDH nano-particles to cotton fabric for improving the mechanical, ultraviolet protection and flame retardancy properties of the cotton which can be used for textile applications due to low cytotoxicity. Mg–Al LDH nano-particles were prepared by co-precipitation method. These Mg–Al LDH nanoparticles were mixed with remazol ultra RGB orange dye by sonication for dyeing the cotton fabric using 1% stock solution of this mixture with various percentage i.e. nano-LDH and dye (1.5 + 98.5)%, (3 + 97) %, etc. followed by exhaustion stage with NaOH. The dye of reactive remazol and Mg–Al nano-LDH (98.5 + 1.5) % showed lowest cytotoxicity as well as UV protection factor: 20.18; which is > 15 means good UV protection (Table 4). Also the tensile strength, flammability and limiting oxygen index increased from 4.06 (Kgf/10), 250s and 16.5 for cotton to 7.18 (Kgf/10), 330s and 20.18 for cotton fabric dyed with nano-LDH respectively making it suitable for wearable textile applications. Shu et al. (2014) placed cotton behind a 0.2 mm thick HEP/LDH hybrid films which retarded fire even prolonged exposure. HEP/LDH coated cotton hybrid films on exposure to a high temperature gas flame (ca. 2000 °C) showed a fire retardant behaviour. Initially the HEP adsorbed on the LDH nanosheets burn in the flame to form black carbon but LDH retarded the flame for prolong duration protecting the cotton from burning. This bionanocomposite film developed by simple vacuum-filtration technology can act as an efficient thermal and flame shielding material finding application such as transportation, construction, and insulation. Pan et al. (2016) prepared MgAl–NO3 LDH by hydrothermal method and (0.3 wt%) alignate solution in deionised water. The cotton fabric was dip coated with this prepared LDH and alignate solution alternately followed by rinsing with deionised water. Different bilayers such as 5, 10 and 20 were coated on the cotton fabric and dried at 70° C for 12 h. These coated cotton fabric showed excellent thermal and flammability resistance properties. The solid residue of these fabrics are higher than uncoated fabric in the temoperature range 400–700 °C. The peak heat release rate (PHRR) and total heat release (THR) for 20 bilayer MgAl–NO3 LDH–Alignate coated fabric were reduced by 34.6% and 25.6% to 134 W g−1 and 6.1 kJ g−1 respectively compared to uncoated cotton fabric (Pan et al., 2016).

Fig. 16. TGA curves of (a) alginate, (b) NO3−–LDH and (c) alginate/LDH nanobiocomposite. (Reproduced with permission from Kang et al., 2013 copyright @ Carbohydrate polymer).

4.2. As Adsorbent Elanchezhiyan and Meenakshi (2017) utilise chitosan/MgAl LDH (CS-LDHCs) bionanocomposite for the recovery of oil from oil-in-water emulsion. The bionanocomposites CS-LDHCs were prepared by coprecipitaion process. The separation was obtained using adsorption of oil by CS-LDHCs. Different parameters such as effect of contact time, pH, adsorbent dosage and initial oil concentration were studied w.r.t. the % oil removal. % Oil removal saturated at 90 min and showed 78% removal for CS-LDHC as compared to 30% for pure LDH (Fig. 18). The change in pH in the range 3–11 was studied using 0.1 M HCl/ NaOH solution, which showed that oil adsorption was 11% at > 9.0 pH and it increased with 3.0 pH respectively. With increase in CS-LDHs dosage concentration in the range of 100–300 mg, the adsorption was increased with optimum dosage concentration upto 250 mg respectively. This CS-LDHs can be utilized for efficient removal of oil from water. Zubair et al. (2018) applied starch (S)-NiFe-LDH bionanocomposites for efficient removal of methyl orange (MO) from aqueous phase using adsorption. S/NiFe-LDH (1:1) and S/NiFe-LDH (2:1) were synthesized by coprecipitation method and their adsorption performance was compared with pure NiFe-LDH with respect to change in pH, initial MO concentration, adsorbent dosage and contact time. S/NiFe-LDH (1:1) showed 99% removal of MO from water at pH 3 as compared to 90% for S/NiFe-LDH (2:1) respectively. From Langmuir isotherm the maximum adsorption capacities calculated were 246.91 mg/g for NiFe-LDH, 358.42 mg/g for S/NiFe- LDH (2:1) and 387.59 mg/g for S/NiFe-LDH (1:1) respectively. NaOH solution was used to regenerate starch-NiFeLDH easily with a minimum loss in adsorption capacity up to four cycles (Zubair et al., 2018). Sun et al. (2018) prepared Fe3O4/MgAl-LDH magnetic

Table 2 The Turn over frequency (TOF)/conversion of cyclohexene after 3 h using peracetic acid as oxidant. (Reproduced with permission from Varga et al. (2017) Copyright @Top Cata.) Catalyst

TOF (1/h)/con-version (%)

Epoxide (%)


2-Chex-1-one (%)

trans Diol (%)

CaAl-LDH Ni(II)-Tyr-CaAl-LDH CaAl-Ni(II)-Cys-LDH Ni(II)-His-CaAl-LDH

nr/21 nr/18 67/30 44/40 31/47

64 63 100 100 100

4 4 0 0 0

2 5 0 0 0

30 28 0 0 0


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Table 3 The Turn over frequency (TOF)/conversion of cyclohexene after 3 h using iodosyl benzene as oxidant. (Reproduced with permission from Varga et al. (2017), Copyright @ Top Cata.) Catalyst

TOF (1/h)/conversion (%)

Epoxide (%)

2-Chex-1-ol (%)

2-Chex-1-one (%)

cis Diol (%)

Ni(II)-Tyr-CaAl-LDH CaAl-Ni(II)-Cys-LDH Ni(II)-His-CaAl-LDH

nr/19 44/20 58/53 27/41

49 0 0 0

28 0 0 0

17 0 0 0

6 100 100 100

Fig. 18. Effect of Contact time of LDH and CS-LDHs on the recovery of oil from oil-in-water emulsion using 25 mL of 4% initial oil concentration at pH 3.0 (Reproduced with permission from Elanchezhiyan and Meenakshi (2017) copyright @ International journal of Biological molecules). Table 4 UPF reading of Mg–Al LDH (98.5 + 1.5) % dye at 2% shades (Reproduced with permission from Sunita Barik et al. (2017) copyright @Cellulose). Specimen no


Fig. 17. Hydrolysis of starch for increasing amounts of LDH and biohybrids corresponding to loadings Cs = 0, 48, and 65 mg AAM/g LDH (black triangles, blue circles, and red squares, respectively). (B) Effect of α-amylase loading on the enzyme activity (black circles) and efficiency (blue squares). (Reproduced with permission from Bruna et al. (2015). Copyright @ACS Appl. Mater. Interfaces). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

98-I 98-II 98-III 98-IV


UVA av.(%)

UVB av. (%)

UVR av. (%)


315–400 nm

290–315 nm

290–400 nm

16 22.5 20 22

5 3 3.5 3.5

6 4 5 4.5

5 3.5 3.8 3.8

potentiostating this biosensor to oxidize enzymatically generated hydrogen peroxide. It showed highest response towards glucose at pH 6.5, potential of 0.6 V and temperature 333.15 K respectively. This biosensor reached 95% of the steady current in 10s with linear range of (1.6 × 10−5–2.0 × 10−3) M. The glucose sensitivity was two times greater for this biosensor than GOD/LDH/Pt biosensor. Also, 87% storage stability was obtained after 28 days as compared to 60% for GOD/ LDH/Pt biosensor. Lopeza et al. (2010) prepared Zn2–Al LDH-Alignate biocomposites by coprecipitation method and applied to entrap polyphenol oxidase (PPO) followed by cross-linking with glutaraldehyde (GA) or calcium complexation and subsequently used it for sensing of phenol derivatives in Tris–HCl buffer (pH 7.0) and organic solvents. PPO/Zn2Al–Alg/GA exhibited a very high sensitivity for catechol in water as compared to chloroform. For catechol sensing, the highest sensitivity of 73.6 AM−1 cm−2 was obtained with a detection limit of 0.5 nM in water as compared to 4.9 AM−1 cm−2 with a detection limit of 0.01 nM respectively (Lopeza et al., 2010).

4.4. As sensors LDH are widely used as electrochemical sensing when combined with chitosan and alignate biopolymers. (Ding et al., 2009) immobilized glucose oxidase (GOD) in Alignate/LDH bionanocomposite for biosensing of glucose. Coprecipitation method was adopted for preparation of LDH (Zn3Al (OH)8Cl). Biosensor was prepared by dissolving 0.4 wt% Alg solution, 2 mg mL−1 LDH solution and 4 mg mL−1 GOD simultaneously in deionised and decarbonated water. This (Alg/ LDH/GOD) solution was dried on platinum disk electrode at 4° C in refrigerator. The amperometric detection of glucose was confirmed by 32

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Xu et al. (2011) prepared cheap biosensor on glassy carbon electrode modified with a nanostructured material Ni2+/MgFe LDH, chitosan (CHT) and glucose oxidase (GOD). The LDH was prepared by co precipitation method and used for the fabrication of biosensor GOD–NLDH–CHT–GCE. 1–20 mM glucose concentration was detected by this biosensor with a detection limit of 0.12 mM (S/N = 3) and a fast response (b5 s). This biosensor retained 90% of its original activity after 30 days (Xu et al., 2011). Among the four anionic biopolymers such as alginate, pectin, κcarrageenan, ι-carrageenan, and xanthan gum intercalated [Zn2Al]; alginate−LDH and ι-carrageenan−LDH nanocomposites based sensors showed best detection for potentiometric sensing of calcium ions (Darder et al., 2005). Liu et al. (2013) reported haemoglobin (Hb) intercalated/DNA/ Ni–Al LDH bionanocomposites for enhancing the bioactivity of Hb towards H2O2 and NO2. Hb/DNA/Ni–Al LDH bionanocomposites films were prepared via delamination-reassembly procedure. This Hb/DNA/ LDH bionanocomposite film, after depositing on glassy carbon electrode was utilized as a mediator-free biosensor. This bionanocomposite showed the detection limit of 4.28 × 10−7 M (signal-to-noise ratio (S/ N) while sensitivity of 0.45 A M −1 cm−2 respectively with constant response above 339.68 M H2O2 concentration. Shi et al. (2008) reported GOD immobilized LDH/ Chitosan biosensor for detection of glucose. Chitosan (CHT) solution was prepared by dissolving CHT flakes in acetic acid (2 wt%) and diluting into 0.2 wt % by water. Zn3Al (OH)8 Cl (LDH) was prepared by co precipitation of aqueous ZnCl2 and AlCl3 at pH 8. Bioelectrode of GOD/LDH/CHT was obtained by hand mixing of 40 μL each GOD, CHT and LDH and simultaneously spraying on the platinum disk electrode at 4° in refrigerator. Fig. 19 shows the calibration curves of LDH /chitosan bionanocomposites. Three GOD can be observed from the graph viz.; a) LDH/CHT/GOD, b) LDH/GOD and c) CHT/GOD. The LDH/CHT/GOD bioelectrode showed best linear response to glucose in the concentration range of 1 × 10−6 to 3 × 10−3 M, detection limit of 0.1 μM and highest sensitivity of 62.6 mA M−1 cm−2. This sensitivity for glucose was 1.7 and 3 times higher than that based on pure LDH and pure CHT based GOD biosensors The lowest response time due to the synergestic properties of the LDH and CHT in this bionanocomposites.

4.5. As biopolymer reservoir, in gene delivery and drug delivery LDH are most suitable reservoir for different biopolymers like RNA, DNA, alginic acids, pectin, carrageenan, xanthan gum, functional biopolymer such as peptides, collagens, etc. due to good compatibility and protective shielding properties (Oh et al., 2009). Li et al. (2014a) co-delivered 5-fluorouracil (5-Fu) and Allstars Cell Death siRNA (CD-siRNA) using LDH nanoparticles as a reservoir. For CD-siRNA-5-Fu-LDH and only 5-Fu-LDH, the cell death occurring in human breast adenocarcinoma cell culture line (MCF-7 cells) was 70% and 46% respectively when treated with 1.2 μg/mL concentration of 5Fu and 40 nM of siRNA. This suppression in cancerous cell growth was due to synergy effect of CD-siRNA and 5-Fu with LDH nanoparticles. DNA is easily degraded by endonucleases. DNA shows decrease in the cellular uptake during delivery due to electrostatic repulsion occurring between the cell membrane and the therapeutic DNA. In order to inhibit the degradation of DNA and to promote the cellular uptake; DNA can be intercalated in LDH which will serve as reservoir. Lee and Kim (2013) prepared magnetic alginate-LDH biocomposites by mixing powdered forms of both calcined Mg–Al LDH (6 g) and magnetic iron oxide (2 g) in an sodium alginate hydrogel (100 mL). This biocomposite effectively removed phosphate with the sorption capacity of 5.0 ± 0.1 mgP/g under given experimental conditions (adsorbent dose = 0.05 g in 30 mL solution; initial phosphate concentration = 10 mgP/L; reaction time = 24 h). This removal was obtained due to phosphate adsorbent behaviour of calcined Mg–Al LDH while magnetic and sorption behaviour of magnetic iron oxide. The maximum phosphate sorption capacity was determined to be 39.1 mg P/g at equilibrium (24 h). Also when the solution pH increased from 4.1 to 10.2, 9% of the phosphate sorption capacity got reduced. LDH based biopolymer nanocomposites have been used as carrier for genes and drugs. Tyner et al. (2004) intercalated linear DNA into Mg/Al- LDH host to encode the green fluorescent protein (GFP) marker in various cell lines. GFP efficiently showed expression with LDH which was absent in naked DNA alone. Further, Masarudin et al. (2009) intercalated circular-structured nucleic acids i.e. plasmid DNA in Mg/AlNO−3 LDH in potentially low efficacy systems. This intercalated bionanocomposite was used to deliver the plasmid DNA and for expression of the green fluorescence protein gene in the African monkey kidney (Vero3) cell lines. This LDH serve as reservoir for protecting the plasmid DNA from degradation effects of nucleases as confirmed by Agarose gel electrophoresis. Fluorescence as early as 12 h post-transfection was observed in cells treated with this nanobiocomposites. Mg2Al LDH intercalated with 5-aminosalicylic acid (5ASA) drug were prepared by coprecipitation method and immersed in chitosan (CHT) matrix followed by protective pectin (PCT) coating against acid pH of gastric fluid. This hybrid nanobiocomposites was used for successful controlled drug delivery for colon diseases. Fig. 20 shows the in vitro 5ASA drug profile release from CHT and PCT biopolymers (a) based on PCT and CHT systems (b) in conditions that simulate the gastrointestinal tract passage (pH and time) at 37 °C. For pure [email protected] release, CHT/5ASA and CHT/LDH-5ASA the drug release was 100%, 95% and 90% respectively at pH 1.2 in the first 2 h. But only PCT containing drug showed good stability and < 10% was released. But with pH 6.8 and 7.4, the release was even higher except for PCT incorporating LDH system. With increase in pectin coating (from 0.5, 1 and 1.5%) release was slower in acidic pH suggesting protective coating on the drug in gastric acid fluid (Ribeiro et al., 2014). Nano-sized LDH has been used as delivery carrier with DNA and cantisense oligonucleotide (As-myc). The basal spacing of LDH increases from 8.7 A° to 23.9 A° and 17.1 A ° for DNA and As-myc respectively. 65% suppression of HL-60 cells growth is observed with 20 AM Asmyc–DNA LDH hybrid nanobiocomposites (Kwak et al., 2002). Ladewig et al. (2010a) studied in vitro delivery system developed from LDH for siRNA to mammalian cells. LDH mediated siRNA showed a pronounced down-regulation of protein upon transfection of human

Fig. 19. Calibration curves of LDHs/CHT/GOD (a), LDHs/GOD (b) and CHT/ GOD (c) for glucose, in 0.1 M PBS (pH 6.5) at 25 °C, Eapp = 0.60 V. Insets show the amperometric current response of the biosensor to 1 mM glucose. (Reproduced with permission from Shi et al. (2008) [email protected] Biosyst Eng). 33

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5. Conclusions This chapter deals with the synthesis of LDH based bionanocomposites along with characterisation and application in different fields. Different types of biopolymers such as heparin, DNA, Vitamin, cellulose, chitosan, polylactic acid, anionic biopolymer and starch based LDH bionanocomposites are addressed in this review. Combining the anion exchange properties of LDH with biocompatibility of biopolymers shows good advantage for its applications as catalyst, as adsorbent, in UV protection and flame retardant behaviour, as sensor, as biopolymer reservoir, in drug and gene delivery. Biopolymers such as DNA when combined with LDH are best suited for gene delivery due to their biocompatibility and biodegradability. Vitamin C and Vitamin E are the basic need of human body and when scarce or in excess in the body can cause disease to occur. LDH have shown promising agents for protecting and transporting these Vitamins by delivering to a particular part of the body due to low toxicity as compared to other drug carriers. Heaparin, Starch, Aliginate, Cellulose, chitosan and PLA based biopolymers are also capable as sensor, in UV protection, flame retardency and drug and gene delivery when combined with LDH. This type of bionanocomposites represents more future ahead. Acknowledgement Authors are thankful to Government of India, Ministry of Science & Technology, Department of Science and Technology (DSTNanomission), New Delhi [Project File No. SR/NM/NS-1106/2016, dated September 5th, 2018] for selecting the research project on interested research area, which is gratefully acknowledged. References Abello, S., Perez-Ramirez, J., 2006. Tuning nanomaterials' characteristics by a miniaturized in-line dispersion–precipitation method: application to hydrotalcite synthesis. Adv. Mater. 18, 2436–2439. Adachi-Pagano, M., Forano, C., Besse, J.P., 2000. Delamination of layered double hydroxides by use of surfactants. Chem. Commun. 91–92. Balcomb, B., Singh, M., Singh, S., 2015. Synthesis and characterization of layered double hydroxides and their potential as nonviral gene delivery vehicles. Chem. Open 4, 137–145. Barik, S., Khandual, A., Behera, L., Badamali, S.K., Luximon, A., 2017. Nano-Mg–Allayered double hydroxide application to cotton for enhancing mechanical, UV protection and flame retardancy at low cytotoxicity level. Cellulose 24 (2), 1107–1120. Barkhordari, S., Yadollahi, M., Namazi, H., 2014. pH sensitive nanocomposite hydrogel beads based on carboxymethyl cellulose/layered double hydroxide as drug delivery systems. J. Polym. Res. 21 (454), 1–9. Bejoy, N., 2001. Hydrotalcite hydrotalcite (HT) is an anionic clay found in nature. It has a variety of pharmaceutical applications. This article focuses on the versatility of this compound in the prevention and cure of peptic ulcer. Reson 6, 57–61. Beleke, A.B., Higuchi, E., Inoue, H., Mizuhata, M., 2013. Effects of the composition on the properties of nickel–aluminum layered double hydroxide/carbon (Ni–Al LDH/C) composite fabricated by liquid phase deposition (LPD). J. Power Sources. 225, 215–220. Bi, X., Zhang, H., Dou, L., 2014. Layered double hydroxide-based nanocarriers for drug delivery. Pharmaceutics 6, 298–332. Bish, D.L., 1980. Anion-exchange in takovite: applications to other hydroxide minerals. Bull. Mineral. 103, 170–175. Boehm, H.P., Steinle, J., Vieweger, C., 1977. [Zn2Cr(Oh)6]X·2H2O, new layer compounds capable of anion exchange and intracrystalline swelling. Angew. Chem. Int. Ed. Engl. 16, 265–266. Bruna, F., Pereira, M.G., Lourdes, M. de, Polizeli, T.M., Valim, J.B., 2015. Starch biocatalyst based on α-amylase-Mg/Al-layered double hydroxide nanohybrids. ACS Appl. Mater. Interfaces 7, 18832–18842. Cavani, F., Trifirb, F., Vaccari, A., 1991. Hydrotalcite-type anionic clays: preparation, properties and applications. Catal. Today 11, 173–301. Chatterjee, A., Hansora, D.P., 2016. Green Polymer nanocomposites: Preparation and properties. In: Green Polymer Composite Technology: Preparation and Properties. CRC Press (ISBN 9781498715461). Choy, J.H., Son, Y.H., 2004. Intercalation of vitamins into LDH and their controlled release properties. Bull. Kor. Chem. Soc. 25, 122–126. Choy, J.H., Kwak, S.Y., Park, J.S., Jeong, Y.J., Portier, J., 1999. Intercalative nanohybrids of nucleoside monophosphates and DNA in layered metal hydroxide. J. Am. Chem. Soc. 121, 1399–1400. Choy, J.H., Kwak, S.Y., Jeong, Y.J., Park, J.S., 2000. Inorganic layered double hydroxides as nonviral vectors. Angew. Chem. Int. Ed. 39, 4041–4045. Choy, J.H., Choi, S.J., Oh, J.M., Taeun, P., 2007. Clay minerals and layered double

Fig. 20. Profiles of in vitro 5ASA release from beads based on CHT and PCT biopolymers (a) and from beads based on [email protected] systems (b) in conditions that simulate the gastrointestinal tract passage (pH and time) at 37 °C. Reproduced with permission from Ribeiro et al. (2014).

sprouting kidney with T-antigen cells. LDH based nanoparticles (NP) are particularly well suited as potential carriers for bio-active molecules and genes applications due to their potential properties. NP of co-precipitately and hydrothermally prepared Mg2Al(OH)6NO3-LDH of varying lateral sizes can be used as gene delivery vehicles. These hybrid bionanoparticles can be used as transfection agents for mammalian cells due to strong interaction between LDH NP and DNA. Hybrid LDH particles were analyzed using a commercial proliferation assay and trypan blue exclusion. The results revealed that LDH NP had safe concentration (0.050 mg/mL) for performing any subsequent delivery experiments (Ladewig et al., 2010b). Intercalated form of natural nucleic acid biopolymers and LDH were also reported to be used in gene therapy. These biopolymer based layered nanocomposites can enter into the cell, and the slightly acidic pH of the lysosome may dissolve the LDH for releasing the DNA that is then transferred to the cell nucleus. Nanohybrid particles consisting of DNA intercalated in LDH can easily enter leukemia cell lines and release the oligonucleotides to inhibit cancerous cell growth. Thus, these bionanocomposites are capable as nonviral vectors for gene therapy of cancers and other diseases (Chatterjee and Hansora, 2016; Reddy et al., 2013). 34

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