From Gels To Aerogels: Creating Multifunctionality Via Solvent Removal

Gels containing water or other solvents abound in applications with considerable efforts being made to fabricate new ones with enhanced functionalities. An area that remains less explored is the creation of aerogels by replacing the liquid matrix of gels with air. Can we preserve the structure of these systems on liquid removal and can we create materials that are just as versatile by doing so? We attempt to answer these questions by presenting a facile and sustainable solid templating approach to fabricate highly porous, flexible and superhydrophobic aerogels of composite nanofibers of cellulose acetate and silica which are produced through sol gel electrospinning. Scanning Electron Microscopy helps us to understand the architecture of these aerogels which consists of large secondary pores in the size range of 30-50 mm interconnected by a network of entangled nanofibers with 2-5 mm primary pores. In contrast to many other highly porous substances, these aerogels have very low densities (5-8 mg/cm3) in combination with flexible structure. Thermal crosslinking of the aerogels further stabilizes their structure and flexibility without compromising on porosity. Thermally crosslinked aerogels display superhydrophobicity while maintaining high absorption affinity for oils. In-situ Fourier Transform Infrared spectrometry and X-ray Photoelectron Spectroscopy are used to understand the structural features of the resultant aerogels while thermal studies demonstrate enhanced thermal stability and flame retardancy. Ease of processing, thermal stability, high porosity, superhydrophobicity and superoleophilic nature of these aerogels make them just as promising, if not more, than their liquid-based analogs

Morphometric forms, biovolume and cellular carbon content of dinoflagellates from polluted waters on the Karachi coast, Pakistan

19-25Present   study reports new information on the biovolume and carbon biomass estimates for dinoflagellates from Manora Channel, Karachi coast, Pakistan. Biovolume per cell was calculated using the geometric shape of dinoflagellates at species level. Both thecate and athecate species were examined under light and scanning electron microscope.  A total of 45 species were measured and their cell size was ranged between 20-450<span style="font-size:9.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-bidi-font-family:="" "times="" roman";mso-ansi-language:en-us;mso-fareast-language:en-us;="" mso-bidi-language:ar-sa"="" lang="EN-US">µm.  Geometric forms of the species were seven classed into as ellipsoidal, spherical, double cone shape, prolate sphere, cone and half sphere, “cone+3 cylinder” shape, “ellipsoidal + 2 cone+ cylinder” shape, “cylinder+ cone” shaped. Total biovolume ranged from 3.743 <span style="font-size:9.0pt;font-family:Arial;mso-fareast-font-family: " times="" new="" roman";mso-bidi-font-family:arial;mso-ansi-language:en-us;="" mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">×103 to 2.2 <span style="font-size:9.0pt;font-family:Arial; mso-fareast-font-family:" times="" new="" roman";mso-bidi-font-family:arial;="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">×105 µm3 cell-1 and estimated cellular carbon content per cell ranged from 397 × 102 to 26.5 x 104 pg C cell-1.  Carbon and biovolume relationship was significant for thecate species which can thus be used for carbon flux studies.  </span

Occurrence of HAB / toxic Dinoflagellates species from the coast of Karachi, Pakistan (Northern Arabian Sea)

73-88Morphological identification of dinoflagellate species were investigated from the coastal waters of Manora Island and Mubarak village Karachi, Pakistan throughout the two years of  study period from (Apr 2008 – Mar 2010). A total number of seventy two dinoflagellate species were identified among them, 42 toxic and 30 HAB species were morphologically differentiated. Dominant species included Alexandrium catenella, Dinophysis caudata, Gymnodinium spp., Prorocentrum micans, Noctiluca scintillans, Prorocentrum gracile, Tripos furca and Gonyaulax spp. these species were previously reported. The sampling area of Mubarak village site was discovered for the first time for dinoflagellates community analysis. This site shows interesting results as some species were observed in high abundance. The high cell concentration of these toxic/ HAB species suggests that our findings add substantially to the HAB dynamics in area and on this basis predicts future event

Occurrence of HAB / toxic Dinoflagellates species from the coast of Karachi, Pakistan (Northern Arabian Sea)

73-88Morphological identification of dinoflagellate species were investigated from the coastal waters of Manora Island and Mubarak village Karachi, Pakistan throughout the two years of  study period from (Apr 2008 – Mar 2010). A total number of seventy two dinoflagellate species were identified among them, 42 toxic and 30 HAB species were morphologically differentiated. Dominant species included Alexandrium catenella, Dinophysis caudata, Gymnodinium spp., Prorocentrum micans, Noctiluca scintillans, Prorocentrum gracile, Tripos furca and Gonyaulax spp. these species were previously reported. The sampling area of Mubarak village site was discovered for the first time for dinoflagellates community analysis. This site shows interesting results as some species were observed in high abundance. The high cell concentration of these toxic/ HAB species suggests that our findings add substantially to the HAB dynamics in area and on this basis predicts future event

Hybrid Carbon Silica Nanofibers through Sol–Gel Electrospinning

A controlled sol–gel synthesis incorporated with electrospinning is employed to produce polyacrylonitrile–silica (PAN–silica) fibers. Hybrid fibers are obtained with varying amounts of silica precursor (TEOS in DMF catalyzed by HCl) and PAN. Solution viscosity, conductivity, and surface tension are found to relate strongly to the electrospinnability of PAN–silica solutions. TGA and DSC analyses of the hybrids indicate strong intermolecular interactions, possibly between the −OH group of silica and −CN of PAN. Thermal stabilization of the hybrids at 280 °C followed by carbonization at 800 °C transforms fibers to carbon–silica hybrid nanofibers with smooth morphology and diameter ranging from 400 to 700 nm. FTIR analysis of the fibers confirms the presence of silica in the as-spun as well as the carbonized material, where the extent of carbonization is also estimated by confirming the presence of −CC and −CO peaks in the carbonized hybrids. The graphitic character of the carbon–silica fibers is confirmed through Raman studies, and the role of silica in the disorder of the carbon structure is discussed

Hybrid Silica–PVA Nanofibers via Sol–Gel Electrospinning

We report on the synthesis of poly­(vinyl alcohol) (PVA)–silica hybrid nanofibers via sol–gel electrospinning. Silica is synthesized through acid catalysis of a silica precursor (tetraethyl orthosilicate (TEOS) in ethanol–water), and fibers are obtained by electrospinning a mixture of the silica precursor solution and aqueous PVA. A systematic investigation on how the amount of TEOS, the silica–PVA ratio, the aging time of the silica precursor mixture, and the solution rheology influence the fiber morphology is undertaken and reveals a composition window in which defect-free hybrid nanofibers with diameters as small as 150 nm are obtained. When soaked overnight in water, the hybrid fibers remain intact, essentially maintaining their morphology, even though PVA is soluble in water. We believe that mixing of the silica precursor and PVA in solution initiates the participation of the silica precursor in cross-linking of PVA so that its −OH group becomes unavailable for hydrogen bonding with water. FTIR analysis of the hybrids confirms the disappearance of the −OH peak typically shown by PVA, while formation of a bond between PVA and silica is indicated by the Si–O–C peak in the spectra of all the hybrids. The ability to form cross-linked nanofibers of PVA using thermally stable and relatively inert silica could broaden the scope of use of these materials in various technologies

Phytochemicals of mustard (Brassica Campestris) leaves tuned the nickel-cobalt bimetallic oxide properties for enzyme-free sensing of glucose

The fabrication of enzyme-free glucose sensors is highly demanded for the biological, clinical, and food applications. In this study, we have developed a green method for tuning the surface properties of nickel-cobalt bimetallic oxide (NiCo2O4) by adding mustard (Brassica Campestris) leaves extract during hydrothermal growth. The mustard (Brassica Campestris) leaves extract is rich with a variety of phytochemicals, which can easily tune the surface properties of NiCo2O4 nanostructures, thereby paving the way toward the development of sensitive and selective non-enzymatic glucose sensors. The effect of various amounts of mustard (Brassica Campestris) leaves extract (0-20 ml) was also studied to find out the optimal conditions for growing surface-modified NiCo2O4 nanostructures. The morphology and crystalline structure of the nanomaterials were studied by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques, respectively. The presence of an increasing quantity of mustard (Brassica Campestris) extract keeps the crystalline structure and the morphology of the NiCo2O4 nanostructures unaltered but changes their dimensions. All nanostructures show the same cubic spinel structure of NiCo2O4 and a morphology of spherical urchins composed of nanorods, but the diameter of the urchins decreases from similar to 10 mu m to several nanometers, thus increasing the surface area of the nanomaterial. Furthermore, NiCo2O4 nanostructures were deposited onto glassy carbon electrodes (CGE), showing excellent catalytic properties toward the enzyme-free detection of glucose using cyclic voltammetry. Importantly, the intensity of the oxidation current peak was linear over a wide range of glucose concentrations (from 0.1 to 10 mM) and the limit of detection (LOD) was estimated around 0.001 mM. Additionally, NiCo2O4 nanostructures grown in the presence of 20 ml of mustard leaf extract demonstrated good repeatability and excellent selectivity for glucose, without interference by other components such as urea, lactic acid, uric acid, ascorbic acid, as well as potassium and sodium ions. The combined results attest that mustard leaf extract has high potential as a green approach to improve the electrochemical properties of nanostructured materials, and could be useful for a wide range of materials for future electrochemical applications