Confinement creates a 9 GPa ambience: emergence of cristobalite phases in a silica film

We present here the results of the x-ray fluorescence (XRF), x-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Analysis of x-rays (EDAX), x-ray Reflectivity (XRR), Secondary Ion Mass spectroscopy (SIMS) and x-ray Diffraction (XRD) studies of silica films spin-coated from a Tetraethyl Orthosilicate (TEOS) precursor on native and hydrophilized Al substrates. It is observed that the substrates are mainly porous (porosity similar to 33%) AlO(OH), there is a diffuse interlayer of highly porous (porosity similar to 90%) AlO(OH), essentially a modification of the substrate, and a top layer of silica composed of nanocrystals with in-plane dimensions of 100-300 nm and thickness of 2.5 nm with a sharply defined silica-hydrated alumina interface. The silica nanocrystals were found in the metastable high pressure cristobalite phases with the tetragonal or alpha-phase co-existing in its low (0.77 GPa) and high (9 GPa) pressure structures. This indicates a high normal stress developed from the confinement and provides a basis for the quantitative assessment of the confinement force, which comes out to be higher in value than the van der Waals force but weaker than the Hydrogen bonding force

Toxic heavy metal ion adsorption kinetics of Mg(OH)(2) nanostructures with superb efficacies

Presence of both Cd(II) and Pb(II) ions in water is highly toxic for human health. That is why WHO recommends maximum permissible values of cadmium and lead in drinking water as 0.003 mg.L-1 and 0.01 mg.L-1, respectively. Therefore, here we report for the first time the adsorption kinetics of Mg(OH)(2) for adsorptions of Pb(II) and Cd(II). To the best of our knowledge, this is the very first attempt to evaluate the Langmuir and Freundlich isotherms of Mg(OH)(2) nanostructures with different morphologies for adsorptions of Pb(II) and Cd(II). The changes in adsorption processes with temperature are also studied. The Mg(OH)(2) nanostructures reduce the concentration of Cd(II) ions from as high as 1000 mg.L-1 to as low as 0.001 mg.L-1 and that of Pb(II) ions from as high as 1000 mg.L-1 to as low as 0.009 mg.L-1 . These values are much lower than the permissible limits prescribed by WHO. To attain these very significant achievements the time dependent changes in pore size, pore size distribution and surface area are explored. Finally, the results obtained by XRD, FTIR, Raman, pore size, pore size distribution, BET surface area, FESEM, TEM, EDX and adsoption kinetics studies show that nanoplatelet Mg(OH)(2) powders exhibit the highest respective adsorption efficacies of 3700 mg.g(-1) and 3030 mg.g(-1) for Pb(II) and Cd(II). Thus, the nanoplatelet Mg(OH)(2) powders may possibly find huge usage in near future for water purification applications

Novel Growth Mechanisms of Self-assembled Mg(OH)2 Nanoplatelets

Here we report for the first time the time-dependent mechanisms of self assembly and growth of Mg(OH)2 nanoparticles. For this purpose, the nanopowders are obtained by a simple chemical precipitation route. To understand the route map of the growth process; the nanopowders are subsequently characterized by XRD, FTIR, BET, pore size distribution, FESEM and TEM analysis techniques. Based on the results obtained from aforesaid characterizations the mechanisms of self-assembly and nanoplatelets growth process as a function of reaction time are explained

Nanoflower, nanoplatelet and nanocapsule Mg(OH)(2) powders for adsorption of CO2 gas

The soft chemical synthesis of self-assembled magnesium hydroxide (Mg(OH)(2)) nanoplatelets with surface area as high as about 300 m(2) g(-1) was achieved in the present work. The nanopowders such as MHN, MHCl, MHBr were synthesized at similar to 30 A degrees C without using any catalyst or surfactant using, respectively, precursor solutions of Mg(NO3)(2), MgCl2, MgBr2 and characterized by XRD, BET surface area, BJH pore size analysis, FTIR, FE-SEM, TEM and EDX techniques. It was found that the MHN and MHCl nanopowders comprised of nanoflowers formed by self-assembly of nanoplatelets and porous nanoplatelets, while the MHBr nanopowders comprised of a random assembly of nanocapsules. The powders possessed the technologically important quality of reproducible CO2 adsorption at room temperature and its desorption at a relatively lower temperature of 75 A degrees C. Based on the experimental evidences, the mechanisms of various microstructure formations and CO2 adsorption mechanism were also proposed

In Situ-Grown Cdot-Wrapped Boehmite Nanoparticles for Cr(VI) Sensing in Wastewater and a Theoretical Probe for Chromium-Induced Carcinogen Detection

In modern society, massive industrialization escalates environmental degradation by liberating various contaminants into the environment. Hexavalent chromium is a heavy metal that is being discharged from tannery and other industries, resulting in various carcinogenic diseases. This study reports a carbon dot (cdot)-based fluorometric probe for detecting hexavalent chromium in water. This is the very first time that cdots are tailored over the boehmite nanoparticle's surface using an in situ approach. Validation of formation of the nanocomposite has been discussed in detail employing the Rietveld refinement-based X-ray crystallography method. Vibrational spectroscopy and electron microscopy of the sample authenticate the nucleation process and the growth mechanism. The Stern-Volmer approach and time-resolved fluorescence measurements justify the sensitivity of the sensor (similar to 58 nM), and selectivity is analyzed by exposing the material to different ionic environments. Density functional theory (DFT) is applied herein to analyze the origin of fluorescence and the sensing mechanism of the probe, which shows that photoinduced electron transfer is responsible for the turn-off-based sensing of Cr(VI). The molecular docking simulation is carried out to ensure the binding of cdots to the binding pocket of the glutathione enzyme, which is responsible for treating reactive oxygen species-mediated DNA damage due to elements such as hexavalent chromium. Time-dependent density functional calculations show that the fluorometric probe is capable of detecting Cr(VI) in living cells making it an early stage chromium-mediated carcinogen detector

Intelligently designed fly-ash based hybrid composites with very high hardness and Young's modulus

Currently, India generates annually about 112 million tones of fly ash (FA), as an industrial waste from thermal power plants. As part of the global journey to convert waste to wealth here we report the intelligent design based synthesis of FA based hybrid composites with spectacular improvement in Young's modulus and nanohardness. The novel design approach utilized alkali activation as well as simultaneous reinforcements of the porous FA matrix with a layered white china clay (WCC) and chopped E glass fiber. The developed materials were subsequently characterized by nanoindentation technique, pH measurement, alkali dissolution, FESEM, etc. techniques to evolve the structure-property correlation. The optimized design and optimal alkali activation lead to achievements of about 233% and 545% enhancements in Young's modulus and hardness, respectively. These results are rationalized in terms of chemical analysis, Si:Al ratio, presence of silicate network modifiers e.g., Na2O and CaO, microstructure, density, extent of polymerization due to alkali activation, processing condition and elastic recovery as well as the ratio of energy spent in elastic and plastic deformations during the nanoindentation processes. Finally, a schematic model is proposed to explain the experimental observations. (C) 2017 Elsevier Ltd. All rights reserved

Synthesis of Nano Calcium Hydroxide in Aqueous Medium

The present work reports a simple, inexpensive method for synthesis of calcium hydroxide Ca(OH)(2)] nanoparticles (CHNPs). The method involves chemical precipitation (CP) in aqueous medium at room temperature. Calcium nitrate dihydrate Ca(NO3)(2).2H(2)O] and sodium hydroxide were used as precursors. The CHNPs were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Rietveld analysis, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), BET surface area evaluation as well as particle size distribution analysis techniques. The results confirmed the synthesis of CHNPs as the major phase. The CHNPs exhibited an average size of about 350 nm. In addition, some calcite phase formed due to the inevitable carbonation process. A very minor amount of aragonite phase was also present. A schematically developed new qualitative model is proposed to explain the genesis and subsequent evolution of the various phases at the nanoscale. The model helps to identify the rate-controlling step. It also highlights the implication of reaction kinetics control in synthesis of predesigned nanophase assembly

Effect of Morphology and Concentration on Crossover between Antioxidant and Pro-oxidant Activity of MgO Nanostructures

The toxicity of nanomaterials can sometimes be attributed to photogenerated reactive oxygen species (ROS), but these ROS can also be scavenged by nanomaterials, yielding opportunities for crossover between the properties. The morphology of nanomaterials also influences such features due to defect-induced properties. Here we report morphology-induced crossover between pro-oxidant activity (ROS generation) and antioxidant activity (ROS scavenging) of MgO. To study this process in detail, we prepared three different nanostructures of MgO (nanoparticles, nanoplates, and nanorods) and characterized them by HRTEM. These three nanostructures effectively generate superoxide anions (O2 •-) and hydroxyl radicals (•OH) at higher concentrations (>500 μg/mL) but scavenge O2 •- at lower concentrations (40 μg/mL) with successful crossover at 200 μg/mL. Nanorods of MgO generate the highest levels of O2 •-, whereas nanoparticles scavenge O2 •- to the highest extent (60%). Photoluminescence studies reveal that such crossover is based on the suppression of F2+ and the evolution of F+, F2 +, and F2 3+ defect centers. The evolution of these defect centers reflects the antibacterial activity of MgO nanostructures which is initiated at 200 μg/mL against Gram-positive S. aureus ATCC 29737 and among different bacterial strains including Gram-positive B. subtilis ATCC 6633 and M. luteus ATCC 10240 and Gram-negative E. coli ATCC K88 and K. pneumoniae ATCC 10031. Nanoparticles exhibited the highest antibacterial (92%) and antibiofilm activity (17%) against B. subtilis ATCC 6633 in the dark. Interestingly, the nitrogen-centered free radical DPPH is scavenged (100%) by nanoplates due to its large surface area (342.2 m2/g) and the presence of the F2 + defect state. The concentration-dependent interaction with an antioxidant defense system (ascorbic acid (AA)) highlights nanoparticles as potent scavengers of O2 •- in the dark. Thus, our findings establish guidelines for the selection of MgO nanostructures for diverse therapeutic applications