Improved nanocomposite of montmorillonite and hydroxyapatite for defluoridation of water

A novel hydroxyapatite montmorillonite (HAP-MMT) nanocomposite system was synthesized using a simple wet chemical in situ precipitation method. Neat nano hydroxyapatite (HAP) was also synthesized for comparison. The characterization of the materials was carried out using Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) isotherms to study the functional groups, morphology, crystallinity and the surface area respectively. Batch adsorption studies and kinetic studies on fluoride adsorption were conducted for the HAP-MMT system and for neat HAP. The effect of parameters such as contact time, pH, initial concentration, temperature, and thermodynamic parameters and the effect of coexisting ions on fluoride adsorption by HAP-MMT were studied. Results of the isotherm experiments were fitted to four adsorption isotherm models namely Langmuir, Freundlich, Temkin and Dubinin Radushkevich. Fluoride adsorption over HAP-MMT fitted to the Freundlich adsorption isotherm model and showed more than two-fold improved adsorption capacity (16.7 mg g−1) compared to neat HAP. The best-fitting kinetic model for both adsorbents was found to be pseudo second order. Calculated thermodynamic parameters indicated that the fluoride adsorption by HAP-MMT is more favorable compared to that on HAP within the temperature range of 27 °C–60 °C. Improved fluoride adsorption by HAP-MMT is attributed to the exfoliated nature of HAP-MMT. Gravity filtration studies carried out using a 1.5 ppm fluoride solution, which is closer to the ground water fluoride concentrations of Chronic Kidney Disease of unknown etiology (CKDu) affected areas in Sri Lanka, resulted in a 1600 ml g−1 break through volume indicating the potential of HAP-MMT to be used in real applications

Magnesium Oxide Nanoparticles Reinforced Electrospun Alginate-Based Nanofibrous Scaffolds with Improved Physical Properties.

Mechanically robust alginate-based nanofibrous scaffolds were successfully fabricated by electrospinning method to mimic the natural extracellular matrix structure which benefits development and regeneration of tissues. Alginate-based nanofibres were electrospun from an alginate/poly(vinyl alcohol) (PVA) polyelectrolyte complex. SEM images revealed the spinnability of the complex composite nanofibrous scaffolds, showing randomly oriented, ultrafine, and virtually defects-free alginate-based/MgO nanofibrous scaffolds. Here, it is shown that an alginate/PVA complex scaffold, blended with near-spherical MgO nanoparticles (⌀ 45 nm) at a predetermined concentration (10% (w/w)), is electrospinnable to produce a complex composite nanofibrous scaffold with enhanced mechanical stability. For the comparison purpose, chemically cross-linked electrospun alginate-based scaffolds were also fabricated. Tensile test to rupture revealed the significant differences in the tensile strength and elastic modulus among the alginate scaffolds, alginate/MgO scaffolds, and cross-linked alginate scaffolds (P < 0.05). In contrast to cross-linked alginate scaffolds, alginate/MgO scaffolds yielded the highest tensile strength and elastic modulus while preserving the interfibre porosity of the scaffolds. According to the thermogravimetric analysis, MgO reinforced alginate nanofibrous scaffolds exhibited improved thermal stability. These novel alginate-based/MgO scaffolds are economical and versatile and may be further optimised for use as extracellular matrix substitutes for repair and regeneration of tissues.Peer Reviewe

Cellular Radiosensitivity: How much better do we understand it?

Purpose: Ionizing radiation exposure gives rise to a variety of lesions in DNA that result in genetic instability and potentially tumorigenesis or cell death. Radiation extends its effects on DNA by direct interaction or by radiolysis of H2O that generates free radicals or aqueous electrons capable of interacting with and causing indirect damage to DNA. While the various lesions arising in DNA after radiation exposure can contribute to the mutagenising effects of this agent, the potentially most damaging lesion is the DNA double strand break (DSB) that contributes to genome instability and/or cell death. Thus in many cases failure to recognise and/or repair this lesion determines the radiosensitivity status of the cell. DNA repair mechanisms including homologous recombination (HR) and non-homologous end-joining (NHEJ) have evolved to protect cells against DNA DSB. Mutations in proteins that constitute these repair pathways are characterised by radiosensitivity and genome instability. Defects in a number of these proteins also give rise to genetic disorders that feature not only genetic instability but also immunodeficiency, cancer predisposition, neurodegeneration and other pathologies. Conclusions: In the past fifty years our understanding of the cellular response to radiation damage has advanced enormously with insight being gained from a wide range of approaches extending from more basic early studies to the sophisticated approaches used today. In this review we discuss our current understanding of the impact of radiation on the cell and the organism gained from the array of past and present studies and attempt to provide an explanation for what it is that determines the response to radiation

Photocatalytic activity of electrospun MgO nanofibres: Synthesis, characterization and applications

One dimensional MgO nanofibres with high photocatalytic activity were fabricated using the electrospinning method via a polyvinyl alcohol (PVA)/magnesium precursor based system and the dye degradation efficacy of MgO nanofibres was compared with MgO nanospheres. Optimum electrospinning parameters including suitable magnesium precursors were investigated and the formation of MgO nanofibres were confirmed with scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) mapping. Furthermore, the crystalline lattice structure and surface roughness of fabricated nanofibres were evaluated using transmission electron microscopic-electron diffraction mode (TEM-SAED) and atomic force microscopy (AFM), respectively. Fabricated MgO nanofibres exhibited excellent photocatalytic degradation activity against widely used model reactive dye, Reactive Yellow (RY). In contrast to MgO nanospheres, electrospun MgO nanofibres completely degraded the reactive dye under UV irradiation. These photocatalytic MgO nanofibres show a great potential to be used in efficient treatment of industrial dye effluents

Nano-MgO reinforced chitosan nanocomposites for high performance packaging applications with improved mechanical, thermal and barrier properties

Chitosan nanocomposite thin films were fabricated by incorporating MgO nanoparticles to significantly improve its physical properties for potential packaging applications. A novel in-situ method was developed to synthesise spherical shaped MgO nanoparticles by heat-treating magnesium carbonate/poly(methyl methacrylate) (PMMA) composite precursor. Optimum mechanical properties of chitosan composites were yielded at 5 (w/w%) of MgO concentration, where tensile stress and elastic modulus significantly improved by 86% and 38%, respectively, compared to those of pure chitosan films. These improvements are due to the interaction of hydroxyl and amine groups of chitosan with MgO as confirmed by FTIR spectroscopy. Fracture surface morphology indicated the interplay between MgO dispersion and aggregation on the mechanical properties at different MgO concentrations. Furthermore, the chitosan/MgO nanocomposites displayed remarkable thermal stability, flame retardant properties (satisfied V0 rating according to the UL-94 standards), UV shielding and moisture barrier properties, which could certainly add value to the packaging material

Oxidation protection of carbon fiber by sol-gel derived boron doped yttria stabilized zirconia coatings

The sol-gel approach was utilized to prepare boron doped yttria stabilized zirconia coated carbon fiber and their thermal characteristics were evaluated against yttria stabilized zirconia coated carbon fiber and uncoated fiber. Coated carbon fiber was characterized by TGA, SEM and FT-IR while calcined sols were analyzed by XRD to study the phase composition. Carbon fiber was coated multiple times and the coating thickness was observed to increase with the number of dipping cycles. Nanoparticles obtained by calcining the boron doped yttria stabilized zirconia system, exhibited the cubic phase while pure zirconia nanoparticles represented monoclinic and tetragonal phases. The sol system with Zr: B: Y molar ratio set as 1: 1: 0.14 was observed to provide superior oxidation protection of carbon fiber compared to the conventional yttria stabilized zirconia sol system. The new coating system showed promise concerning oxidation retardation of carbon fiber and its composites at high temperatures

Carbon quantum dots-decorated nano-zirconia: A highly efficient photocatalyst

A unique and efficient composite material was synthesized by incorporating carbon quantum dots on to the surface of zirconia (ZrO2) nanoparticles. ZrO2 nanoparticles with an average diameter of 40 nm were synthesized by a sol-gel process with zirconium oxychloride as the precursor. Carbon quantum dots (CQDs) were synthesized via a facile method by calcining a solution of ammonium citrate. Synthesized CQDs suspended in absolute ethanol emitted a green glow under UV irradiation. A convenient one-step process involving mixing in absolute ethanol under sonication was adopted for the formation of CQD-decorated ZrO2 nanoparticles (CQDZ). The dried final composite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Fourier transform infrared (FT-IR) spectroscopy. The photocatalytic performance of CQDZ was evaluated by quantifying the removal efficiency of methylene blue dye. CQDZ managed to remove methylene blue by 66.5%, 76.5%, 84.3% and 95.0% under UV-irradiation of 10, 20, 40 and 60 min respectively. Under the same experimental conditions, pure ZrO2 nanoparticles managed to remove only 34% of the dye under 60 min of UV irradiation. The produced composite showed promise as a formidable contender to be used in industrial dye removal from waste water

Combined Zr and Y phosphate coatings reinforced with chemically anchored B<inf>2</inf>O<inf>3</inf> for the oxidation inhibition of carbon fiber

The use of carbon fiber-based composites in high-temperature environments has been hindered due to the inferior oxidation resistance of standard carbon fiber. Protective coatings comprised of refractory ceramics have served in enhancing the thermal endurance of carbon fiber significantly. Although zirconium and yttrium-based materials have been highly studied on their refractory characteristics, phosphate-based thermal barrier systems are scarce. Herein, we report the oxidation retardation capability of a B2O3-chemically anchored, Zr3(PO4)4/YPO4 coating system on carbon fiber. In-situ, sol-gel-developed coatings with varying thicknesses and constructs were investigated for morphology, crystallography, composition, mechanical properties and thermal integrity. A uniquely consolidated B2O3@Zr3(PO4)4/YPO4 molecular arrangement was indicated in coatings by infra-red and X-ray spectroscopy. Ultimately, superior oxidation protection with an enhancement of ~180 °C over uncoated fiber was exhibited by the integrated nanocoatings, indicating its potential suitability for thermal shielding of carbon-based composites at temperatures in the range of 900–1000 °C. The exhibited improvement in thermal performance was attributed to the fortification provided by the coordinated B2O3 network on the fundamental Zr3(PO4)4/YPO4 system