Rajib Lochan Goswamee

Adsorption of Cr(VI) in layered double hydroxides

Abstract Adsorption of Cr(VI) by various uncalcined and calcined layered double hydroxides (LDH) of Mg–Al, Ni–Al and Zn–Cr types was investigated. Adsorption of Cr 2 O 7 2− through ion exchange in uncalcined LDH is slower in rate and smaller in amount than in calcined one where the adsorption occurs via rehydration. The nature and content of bi- and trivalent metal ions in LDH influence the adsorption. Calcined Mg–Al LDH with higher Al 3+ content in the precursor structure shows higher adsorption capacity. Adsorption is higher in the Mg–Al LDH than in Ni–Al and Zn–Cr LDH. A two-step first-order rate kinetics was observed for the adsorption process which follows the Freundlich-type adsorption isotherm. The explanation of adsorption phenomenon has been supported by X-ray diffraction patterns. The pH of initial Cr 2 O 7 2− solution has no affect on adsorption by calcined LDH. Release of Cr 2 O 7 2− from the adsorbed product depends upon the type of anion in the aqueous phase and CO 3 2− being the most effective ion. Calcination of the Cr 2 O 7 2− adsorbed product up to 1250°C has not resulted in the formation of Cr-immobilized phases.

Characterization, beneficiation and utilization of a kaolinite clay from Assam, India

Abstract Kaolin available in Deopani, Assam of northeastern region of India was characterized by FTIR, XRD, DTA and by wet chemical analysis methods. The major impurities in the clay are quartz and siderite. Wet sieving of the clay by −53-μm sieve removes almost all the quartz and a major amount of Fe bearing impurities. The iron content of the clay may be reduced further by treating with wet high intensity magnetic separator (WHIMS) or leaching with organic acids. The effectiveness of various leachants follows the order: Oxalic>Oxalic+EDTA>Malonic>Citric acid. Almost all the nonstructural iron may be removed at room temperature by using 0.4 M oxalic acid solution. The leached clay may find use as a ceramic raw material and filler material for paper and other materials.

Hybrid nanocomposites of layered double hydroxides: an update of their biological applications and future prospects

Recently, there has been a rapid growth in the research related to the synthesis of new materials with hierarchical structures and tailored properties. Different 2D materials like graphene, clay, and layered double hydroxides (LDHs) possessing organized nanosheets act as building blocks for such hierarchial structures. On combining with a range of foreign materials such as organic molecules, gels, polymers, inorganic, and metal nanoparticles, they develop a remarkable potential for application as a large number of advanced materials with tailored properties. Because of the cheaper cost, easier methods of preparation, biocompatibility, and high compositional variability of LDH, it is worthwhile to focus on LDH nanosheet-based hybrid materials. In the future, undoubtedly, this new generation of hybrid materials, mainly born from a world-wide research effort of various workers in the last decade, will open a large number of promising applications in many areas such as electronics, catalysis, energy, and environment more particularly in agriculture and medicine. In this review, it is tried to set in one place in a systematic way the different information available in various peer-reviewed journals in the field of medicine and agriculture. Their reported advantages, especially with reference to the targeted controlled-release behavior of different bioactive molecules, the structure of the component bioactive molecules, and the points for their future demands and scopes of improvements in these fields are discussed.

Biocompatible nanocomposite of carboxymethyl cellulose and functionalized carbon–norfloxacin intercalated layered double hydroxides

In recent years, the development of systems with progressive drug release properties, which is an effective technique for the use of drugs, has aroused great interest in the field of controlled release formulations. In this work, hybrid materials containing citric acid cross-linked carboxymethyl cellulose (CMC) and norfloxacin (NOR) intercalated layered double hydroxide (LDH) deposited over the surface of functionalized carbon (AC) were prepared. The synthesized CMC@AC-LDHNOR nanohybrids were characterized using different techniques and in vitro NOR release behaviors were investigated in phosphate buffer saline, pH 7.4 at 37 °C. On the basis of the release profiles, it was found that NOR release was delayed when it was intercalated in AC-LDH which in presence of modified CMC decreases further. The nanohybrids indicated enhancement of antibacterial activity against gram-negative and gram-positive bacteria. The MTT assay showed their non-toxic behavior against ovarian normal epithelial and cancer cells, suggesting their potential use as drug carriers.

Novel synthesis of active metal oxide surface from a self-organising system of inorganic solids

Abstract Self-organising aqueous suspension of layers of cationic montmorillonite and anionic mixed metal layered hydroxides (MMLH) after thermal treatment at about 500°C gives active and well-dispersed layers of metal oxides over montmorillonite matrix exhibiting enhanced reactivity with gaseous reactants. Increased absorption of H 2 S by ZnO supported on montmorillonite matrix is given as an example.

Adsorption studies of fluoride by activated carbon prepared from Mucuna prurines plant

Activated carbon synthesized from the plant Mucuna prurines have been successfully used to remove fluoride from aqueous solution by adsorption method. Batch method adsorption has been studied and the adsorption was found to be very significant. Almost 96% of fluoride could be removed by adsorption. Adsorption studies of fluoride signify the fact that among the different adsorption model, Langmuir adsorption model seems to be more favorable in the present case. Different parameters like effect ofadsorbent dosage, contact time, pH and initial concentration are studied to understand the adsorption mechanism.

A comparative study of thermal decomposition behaviour of Zn-Cr, Zn-Cr-Al and Zn-Al type layered double hydroxides

Hydrolysis of ZnO in acidic pH provides a facile route for synthesis of layered double hydroxides (LDH) bearing Zn2+ with Cr3+ and Al3+ without having carbonate ion in the inter-layer position. The thermal decomposition of the prepared LDH show that with the increase of Cr3+ content in the system there is an increase in the thermal stability of the compounds. In case of Zn-Cr LDH there is a non-mass loss transition around 420°C. Segregation of parent LDH structure to a bivalent oxide and a spinel takes place in both Zn-Cr and Zn-Al LDH only at temperatures above 550°C.

Synthesis of nanohybrid alcogels of SiO2 and Ni–Cr/Mg–Cr–LDH: study of their rheological and dip coating properties

Silica supported Ni–Cr and Mg–Cr–LDH nanohybrid alcogels were synthesized by a ‘soft chemical’ non-aqueous sol–gel route using a mixture of metal acetylacetonate and tetraethylorthosilicate (TEOS) precursors. Faster hydrolysis of the alkoxide than the metal acetylacetonates precursors gives an inner SiO2 core around which crystalline LDH sheets are dispersed to give one gel network in an organic medium. These were characterized by XRD, FT-IR, TGA-DTA, particle-size distribution, zeta-potential, SEM, TEM, EDXA, BET surface area and Rheological analysis. The steady shear and dynamic oscillatory measurements showed that the apparent viscosity decreased with shear strain and the complex viscosity decreased with angular frequency indicating the shear thinning behaviour of these nanohybrids. At the linear viscoelastic region (LVE) the storage modulus (G′) was greater than the loss modulus (G′′) indicating the presence of elastic or gel like behaviour. With the rise of the amount of SiO2 in the nanohybrids the surface area and the negative zeta potentials were found to increase. This helped the dispersibility of the alcogels as well as the formation of thin films over solid surfaces by dip-coating. These findings are expected to be useful in designing crack free catalytic barriers for inorganic membrane applications having transition metal mixed oxide/hydroxide nano-sheets as the active catalyst.