Application of Layered Double Hydroxides as Host in Controlled Release Formulation of Latex Stimulant and Metal Catalyst in Formation of Carbon Nanotube

Layered double hydroxides (LDH) have attracted a lot of attention in research area due to its unique properties. LDHs has proven to be useful in various fields of applications and due to that, LDHs have been chosen to be used in this study as precursor in two applications which are; as host in a latex stimulant controlled release formulation and metal catalyst in the formation of carbon nanotubes. Manipulation of LDHs could lead to the formation of various useful materials and this is contributed by the interesting property of LDHs which are ion exchange and high metal dispersion. From the study, the syntheses of latex stimulant nanocomposites, controlled release of latex stimulant in various aqueous solutions and formation of carbon nanotubes were proven to be successful. It is hoped that in the future the knowledge of LDHs could lead to application of many beneficial materials in various fields. In this study, Zinc-Aluminium-nitrate-LDH (ZAL) synthesised at different Zn/Al molar ratios, R=2-4 and pH = 7.50-10.00 were successfully synthesised via co-precipitation method under N2 atmosphere. Latex stimulant agent of 2,4-D and 2-CEPA have been successfully inserted into the lamella of layered double hydroxides via co-precipitation. Various parameters namely Zn to Al molar ratios of the mother liquor which are 2, 3 and 4; concentrations of anion, 2,4-D and 2-CEPA which are 0.08 M- 0.32 M; and pH which are 7.50 - 10.00 have been tested during the synthesis of Zn-Al-2,4-D (ZANDI) and Zn-Al-2-CEPA (ZANE) nanocomposites. X-ray diffraction patterns showed expansion of the precursor‟s basal spacing in order to accommodate the 2,4-D and 2-CEPA anions which are larger in size than nitrate. FTIR spectrum of both prepared ZANDI and ZANE nanocomposites resembled a mixture of each parent material, ZALs and guest anions of 2,4-D and 2-CEPA, indicating the presence of both in the resulting materials. Taken together the X-ray diffraction and FTIR analyses, successful formation of ZANDI and ZANE were further confirmed. Further physico-chemical characterisations of the resulting materials including thermal analysis, elemental analysis, surface area and porosity and surface morphology, were also carried out. The controlled release study of 2,4-D and 2-CEPA were done in aqueous media of sodium chloride, sodium carbonate and sodium phosphate at 0.05 M. Release of 2,4-D and 2-CEPA were also done in water as control. It was found that 2,4-D and 2-CEPA were rapidly released in sodium carbonate and sodium phosphate, respectively. However, the release percentage of 2,4-D was found to be the highest in carbonate at 99 % and for 2-CEPA in sodium phosphate at 98 % . The kinetic model of pseudo-second order fits well with all of the release profile with r2 > 0.9. CNT from the calcined CoNiAl-LDH was produced with high yield when compared to calcined FeCoNiAl-LDH and FeNiAl-LDH. However, CNTs from calcined FeCoNiAl-LDH was found in abundance after the purification took place. CNTs synthesised by using the metal foils afforded much smaller diameter and better surface properties which could be due to the well dispersed highly pure metal

Preparation of zinc layered hydroxides-cinnamaldehyde nanocomposites and its physico-chemical study

Cinnamaldehyde (CINN) is an organic guest anion, the main constituent of cinnamon oil was intercalated into zinc layered hydroxides (ZLHs) by ion exchange method. CINN has been reported can killed mosquito larvae. The powder X-Ray diffraction (PXRD) indicates a successful intercalation of CINN into the interlayer galleries of ZLHs matrix when 1.0 g of ZnO with 0.08M of CINN was used forming zinc layered hydroxides-cinnamaldehyde (ZCINN) exhibiting basal spacing expansion, 21.2Å. Fourier transform infrared (FTIR) results supported and confirmed the intercalation of CINN as both ZnO and CINN functional groups appeared in ZCINN spectrum. The thermal stability property of the ZCINN was enhanced as compared to the anion, CINN. Field emission scanning electron microscopy (FESEM) image of ZnO showed a nonuniform granular-like structure transforming into flaky structure with various sizes after intercalation of CINN took place. These results indicate that it is possible to design and develop the nanocomposites containing larvicide for further investigations

Preparation and characterisation of carvacrol encapsulated in gellan gum hydrogel

Studies on plant materials as natural compound such as carvacrol (Carv) have gained much attention. Carv exhibits numerous potential as antimicrobial agent, food additives, antioxidant and etc. However, this free standing bioactive compound is unstable in the harsh environment conditions. Hence, the encapsulation technology provides protection to enhance the effectiveness in release manner. In this study, the preparation of Carv encapsulated in gellan gum hydrogel forming thin film (GG-Carv TF) was achieved by using 1.0 g of gellan gum at different concentrations of Carv (0.01-0.04 M). The FTIR spectra of GG-Carv TF revealed the combination of both functional groups from GG and Carv. The Carbon, Hydrogen and Nitrogen, CHN analysis further confirmed the encapsulation with the changes in the element percentage. Both swelling and degradation percentage increased with time and showed decreasing patterns in the range of 680.79-666.78 % and 26.83-19.15 % which can be observed as the concentration of Carv increased, respectively

Inorganic-based phytohormone delivery vector of 2-chloroethylphosphonate nanohybrid, a new stimulating compound with controlled release property to increase latex production.

New inorganic-based phytohormone delivery system, a stimulating compound to increase latex production was developed through hybridisation of 2-chloroethylphosphonic acid (ethephon) into the interlayer of Zn–Al-layered (ZAL) double hydroxide. The hybridisation product, ZADO, was synthesised using co-precipitation technique at pH 7.5, 0.08 M ethephon and initial molar ratio of Zn to Al, R = 4. The resulting material has a basal spacing of 11.5 Å and Fourier transform infrared spectra further supported the hybridisation episode of ethephon into the ZAL. The release behaviour of the active agent, ethephon from the nanohybrid was found to be of controlled manner, governed by pseudo-second order kinetics. These results indicate that it is possible to design and develop a new delivery system of a phytohormone, [ethephon (2-chloroethylphosphonate)] with controlled release property to increase latex production of rubber tree (Hevea brasiliensis)

Intercalation study of curcumin into zinc layered hydroxide

Zinc layered hydroxide (ZLH) intercalated with curcumin was successfully prepared by ion exchange method. The synthesised nanocomposite was characterised by Powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). The obtained intercalation compound, ZLH-curcumin nanocomposite (ZiCUR), showed a basal spacing of 10.0 Å when 0.01M of curcumin solution was used in the synthesis. The shifting in the stretching frequency of the curcumin anion provides strong evidence that the anion is bonded to the ZLH through electrostatic force. In FTIR, after intercalation, there is a noticeable shift of the O-H stretching vibrational bands. This is due to the formation of strong hydrogen bonds between curcumin and –OH groups in ZLH. Thus, this indicates that curcumin anions are present in the sample and were intercalated between positively charged ZLH layers, as indicated by the characteristics of PXRD pattern

Removal of methyl orange dye by manganese/aluminium- layered double hydroxide

As textile production flourishes nowadays, the amount of dyed wastewater entering the water body has also increased. Dyes could have serious negative impacts to the environment and also the human health, hence, they need to be removed from the water body. In this study, layered double hydroxide (LDH) of manganese/aluminium (MnAl) was synthesised to be used as a potential adsorbent to remove methyl orange (MO) dye due to its unique lamellar structure which provides LDH with high anion adsorption and exchange ability. MnAl was synthesized by using co-precipitation method and characterized by powder X-ray diffraction (PXRD), Fourier-Transform Infrared Spectroscopy (FTIR), Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and Carbon, Hydrogen, Nitrogen, Sulphur (CHNS) elemental analysers, and Accelerated Surface Area and Porosity Analyzer (ASAP). Adsorption studies were conducted at different contact times and dosages of MnAl to evaluate the performance of MnAl in removing MO from water. Kinetic and isotherm models were tested using pseudo-first order, pseudo-second order, Langmuir isotherm and Freundlich isotherm. MnAl LDH was found to be perfectly fitted into pseudo-second order and Langmuir isotherm

Theoretical and experimental models for the synthesis of single-walled carbon nanotubes and their electrochemical properties

A major challenge in the field of selective synthesis of single-walled carbon nanotubes (SWCNTs) via chemical vapor deposition (CVD) method is lack of established theoretical model for direct selection of metal/support catalyst to grow the corresponding SWCNTs. This has limited the application of these materials, especially, in electronics. In this report, we introduced circumferential and axial distortions in the Extended Tight Binding (ETB) equations to generate our model equations which correlated the numerical magnitude of chiral index (n, m) of SWCNTs directly with mass fractions of metal/support catalyst matrix, respectively. Theoretical predictions of our model equations showed acceptable deviations with ETB model, and two Fe2O3/Al2O3 catalysts were prepared according to this model to grow corresponding SWCNTs (10, 7) and (8, 8) via CVD pyrolysis of C6H14/N2 feedstock. High-resolution transmission electron microscopy analysis revealed bundled SWCNTs while analysis of their Raman profiles showed consistency with the radial breathing modes, diameter and energy band gaps of SWCNTs (10, 7) and (8, 8). Electrochemical analysis of the samples suggested potentials as pseudocapacitor electrodes. If fully explored and optimized, this model may complement or augment the existing in-situ epitaxial growth model

Preparation of Layered Double Hydroxides with Different Divalent Metals for the Adsorption of Methyl Orange Dye from Aqueous Solutions

In this study, layered double hydroxides (LDHs) with different divalent metal cations were prepared and then utilized as adsorbent for the removal of dye from aqueous solutions. LDHs are positively charged lamellar solids consisting of divalent and trivalent metallic cations and exchangeable interlayer anions. The potential combinatorial series of M/aluminum (M=Ca, Mn and Zn) LDHs for the removal of methyl orange (MO) dye from aqueous solutions were investigated.  LDHs were synthesized via a co-precipitation method and characterized using powder X-Ray diffraction (PXRD) and Fourier-transform infrared spectrophotometer (FTIR). The LDHs were then used as adsorbent for the removal of MO dye at different LDH dosages. As the LDH dosage increased, the removal percentage of MO dye also increased. CaAl, MnAl and ZnAl LDHs were able to adsorb up to 96.6%, 97.9% and 99.8% of MO dye, respectively, after being put in contact with the LDHs for 24h. Their adsorption ability was further analyzed by using Langmuir and Freundlich isotherm models in which the adsorption mechanism was determined. Adsorption of MO by CaAl, and ZnAl LDHs was governed by the Langmuir isotherm model while the adsorption data for MnAl LDH was found to fit well with the Freundlich isotherm model

Theoretical model for prediction of metal catalyst in the chemical vapour deposition of carbon nanotubes

One of the major challenges in the fields of heterogeneous catalysis and carbon nanotubes (CNTs) synthesis via chemical vapour decomposition (CVD) method is lack of established theoretical model for direct selection of carbon precursor/metal catalyst matrix, which constitutes the most important material parameters of the whole process. In the present report, a theoretical model is proposed via kinetic theory and applied in correlating gas stoichiometry equations and the decomposition of carbon precursors with electrons of metal atoms. Theoretical predictions of this model were found to be in conformity with recent advances in the fields of heterogeneous catalysis in general and CVD synthesis of CNTs in particular. The proposed theory may compliment the current selection of carbon precursor/catalyst matrix through experimental trial and error

A brief review on recent graphene oxide-based material nanocomposites: synthesis and applications

In a past few years, more focus has been given to graphene, especially for its facile synthesis, novel hybrids materials and applications. Recently, researchers' attention has also focused on graphene oxide (GO) and reduced graphene oxide (rGO) nanocomposites, which lead to the development of various applications. Their superb and impressive characteristic makes them suitable candidates to be hybridized with polymer, metal oxide, and biomaterials. In this brief review, we will run through the accomplishments of effective approaches for synthesizing graphene oxide-based material nanocomposites together with their recently developed applications