Asma Tufail Shah

Direct synthesis of Ti-containing SBA-16-type mesoporous material by the evaporation-induced self-assembly method and its catalytic performance for oxidative desulfurization.

A novel Ti-containing SBA-16-type mesoporous material (with various Ti loadings of 5, 10, and 15 wt%) was synthesized by an evaporation-induced self-assembly method using F127 copolymer as template. The materials were characterized by XRD, FTIR, TG-DTA, N(2) adsorption, SEM, HRTEM, and XPS. The characterization results show that the material possesses high thermal stability, thick pore walls (10.43-10.68 nm), and high surface area (642.26-691.5 m(2)/g) with a mesoporous worm-like structure, and titanium was successfully incorporated into the silica matrix with a tetrahedral environment. The material showed high activity in the oxidative desulfurization of DBT and its activity was not reduced even after three times recycling; further reuse resulted in a gradual decrease in its activity.

Influence of carbon nanotube dimensions on the percolation characteristics of carbon nanotube/polymer composites

The effect of carbon nanotube aspect ratio (AR) on the percolation characteristics of their polymer composites was investigated by melt blending the multi-wall carbon nanotubes (MWCNTs) with different AR with a thermoplastic elastomer. Previously, most studies reported the effect of aspect ratio of MWCNTs only in the context of achieving the maximum electrical conductivity at lower percolation thresholds in the polymer composites. In this study, our results indicate that aspect ratio can also influence other percolation properties such as the pre-percolation conductivity, percolation conductivity and post-percolation conductivity, shape of the percolation curve, and the width of the insulator-conductor transition. We have established that AR can be used to tailor the percolation curves from sharp to quasi-linear ones, which can help us fabricate the percolative composites with stable electrical properties. Experimental results suggested that the mathematically calculated nominal AR of the MWCNTs was an un...

Green Synthesis and Characterization of Silver Nanoparticles Using Ferocactus echidne Extract as a Reducing Agent

The green synthesis of silver nanoparticles using an aqueous extract of Ferocactus echidne(a member of the cactus family) as a reducing agent is reported. It is simple, efficient, rapid, and ecologically friendly compared to chemical-mediated methods. Ferocactus echidne is a plant of high medicinal value and rich in polyphenolic antioxidants. The extraction is simple and the product rapidly reduces silver ions without involvement of any external chemical agent. The reduction of silver nanoparticles was characterized by ultraviolet-visible spectrometry as a function of time and concentration. The results show that Ferocactus echidne reduces silver ions within 6 h depending upon the concentration. Further increases in reaction time may result in a blue shift, indicating an increase in particle size, whereas concentration had a minor effect on the particle size. The structure of synthesized nanoparticles was investigated by infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The infrared spectra indicated the association of organic materials with silver nanoparticles to serve as capping agents. Scanning electron micrographs showed that synthesized silver nanoparticles were nearly uniform and elliptical in shape with diameters of 20 to 60 nm. X-ray diffraction confirmed the formation of silver nanoparticles with an approximate 20 nm particle size calculated using the Debye-Scherer equation. Biological tests revealed that the silver nanoparticles were active against gram positive and negative bacteria( Escherichia coli and Staphylococcus aureus) and fungi (Candida albicans), indicating their broad spectrum antibiotic and antifungal abilities.

Synthesis of mesoporous zeolite Ni-MFI with high nickel contents by using the ionic complex [(C4H9)4N]2(+)[Ni(EDTA)]2- as a template.

Ni-MFI zeolites with high percentage of Ni (5-15 wt%) were prepared by using an ionic complex [(C(4)H(9))(4)N](2)(+)[Ni(EDTA)](2-) by one step synthesis. These molecular sieves were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-vis), differential scanning calorimeter (DSC) and nitrogen adsorption-desorption isotherms. The results showed that heteroatom Ni was successfully introduced into the MFI framework up to 15 wt%. Moreover, this Ni-MFI possessed regular and stable structure with high specific surface area and average pore diameter of 388-439 m(2) g(-1) and 2.566-3.828 nm, respectively, compared to MFI prepared by traditional methods. These samples also showed good thermal and hydrothermal stability.

Adsorption Optimization of Lead (II) Using Saccharum Bengalense as a Non-Conventional Low Cost Biosorbent: Isotherm and Thermodynamics Modeling

In the present study a novel biomass, derived from the pulp of Saccharum bengalense, was used as an adsorbent material for the removal of Pb (II) ions from aqueous solution. After 50 minutes contact time, almost 92% lead removal was possible at pH 6.0 under batch test conditions. The experimental data was analyzed using Langmuir, Freundlich, Timken and Dubinin-Radushkevich two parameters isotherm model, three parameters Redlich—Peterson, Sip and Toth models and four parameters Fritz Schlunder isotherm models. Langmuir, Redlich—Peterson and Fritz-Schlunder models were found to be the best fit models. Kinetic studies revealed that the sorption process was well explained with pseudo second-order kinetic model. Thermodynamic parameters including free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) have been calculated and reveal the spontaneous, endothermic and feasible nature of the adsorption process. The thermodynamic parameters of activation (ΔG #, ΔH #and ΔS #) were calculated from the pseudo-second order rate constant by using the Eyring equation. Results showed that Pb (II) adsorption onto SB is an associated mechanism and the reorientation step is entropy controlled.

Biological behavior of bioactive glasses and their composites

Bioactive glasses (BGs) as third generation biomaterials have the ability to form an interfacial bonding more rapidly than other bioceramics between implant and host tissues in defect treatment. Therefore, BGs have shown great applications in the field of bone tissue engineering, dental materials, skin and other tissue regeneration. This review is based on inorganic and organic BG composites being used in bone tissue engineering and summarizes current developments in improving the biological behavior of BGs and their composites. A main focus was given to highlight the role of BGs and their composites in osteogenic differentiation and angiogenesis, followed by their cytotoxicity, protein adsorption ability and antibacterial properties. BGs were found to enhance the cell proliferation and cell attachment without any toxic effects with a significant increase in metabolic activity and possess osteogenic properties. Organic and inorganic dopants have been used to improve their cytocompatibility, osteoconductivity and promote stem cell differentiation towards the osteogenic lineage. BGs have also been used as graft materials because of their significant role in angiogenesis, as they stimulate relevant cells (i.e. fibroblasts, osteoblasts and endothelial cells) to release angiogenic growth factors. They show good protein adsorption because they act as templates for the adsorption of proteins which in turn depends upon surface properties. Antibacterial effects were also observed in BGs as a result of the high aqueous pH value in body fluids due to the presence of alkaline ions. There has been significant research work performed on silica-based bioactive glasses but not much literature can be found on phosphate- and borate-based bioactive glasses, which have good solubility and degradation, respectively.

Effect of calcium hydroxide on mechanical strength and biological properties of bioactive glass.

In this manuscript for the first time calcium hydroxide (Ca(OH)2) has been used for preparation of bioactive glass (BG-2) by co-precipitation method and compared with glass prepared using calcium nitrate tetrahydrate Ca(NO3)2·4H2O (BG-1), which is a conventional source of calcium. The new source positively affected physical, biological and mechanical properties of BG-2. The glasses were characterized by Fourier transform infrared (FTIR), X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA-DSC), BET surface area analysis and Knoop hardness. The results showed that BG-2 possessed relatively larger surface properties (100m(2)g(-1) surface area) as compared to BG-1 (78m(2)g(-1)), spherical morphology and crystalline phases (wollastonite and apatite) after sintering at lower than conventional temperature. These properties contribute critical role in both mechanical and biological properties of glasses. The Knoop hardness measurements revealed that BG-2 possessed much better hardness (0.43±0.06GPa at 680°C and 2.16±0.46GPa at 980°C) than BG-1 (0.24±0.01 at 680°C and 0.57±0.07GPA at 980°C) under same conditions. Alamar blue Assay and confocal microscopy revealed that BG-2 exhibited better attachment and proliferation of MG63 cells. Based on the improved biological properties of BG-2 as a consequent of novel calcium source selection, BG-2 is proposed as a bioactive ceramic for hard tissue repair and regeneration applications.

Hydroxypropylmethyl cellulose (HPMC) crosslinked chitosan (CH) based scaffolds containing bioactive glass (BG) and zinc oxide (ZnO) for alveolar bone repair

The success of a dental implant relies on the presence of an optimal alveolar ridge. The aim of this study was to fabricate HPMC crosslinked chitosan based scaffolds for alveolar bone repair. Our results indicated that HPMC crosslinked CH/BG foams presented better morphological structure (132-90.5 μm) and mechanical responses (0.451 MPa with 100 mg BG) as confirmed by SEM analysis and fatigue testing respectively. Cytotoxicity analysis at day 2, 4 and 8 demonstrated that all composites were non-toxic and supported cellular viability. Calcein AM/propidium iodide staining, Hoechst nuclear staining and cell adhesion assay reiterated that scaffolds supported pre-osteoblast cell growth, adhesion and proliferation. Differentiation potential of pre-osteoblast cells was enhanced as confirmed by alkaline phosphate assay. Furthermore, loss of S. aureus viability as low as 35% was attributed to synergistic effects of components. Overall, our results suggest that HPMC crosslinked scaffolds are potential candidates for alveolar bone repair.

Catalytic Pyrolysis of Low Density Polyethylene Using Cetyltrimethyl Ammonium Encapsulated Monovacant Keggin Units and ZSM-5

The effect of the catalysts on the pyrolysis of commercial low density polyethylene (LDPE) has been studied in a batch reactor. The thermal catalytic cracking of the LDPE has been done using cetyltrimethyl ammonium encapsulated monovacant keggin units (C19H42N)4H3(PW11O39), labeled as CTA-POM and compared with the ZSM-5 catalyst. GC-MS results showed that catalytic cracking of LDPE beads generated oilier fraction over CTA-POM as compared to ZSM-5. Thus, the use of CTA-POM is more significant because it yields more useful fraction. It was also found that the temperature required for the thermal degradation of LDPE was lower when CTA-POM was used as a catalyst while high temperature was required for degradation over ZSM-5 catalyst. Better activity of CTA-POM was due to hydrophobic nature of CTA moiety which helps in catalyst mobility and increases its interaction with hydrocarbons.

Tailoring Imprinted Titania Nanoparticles for Purines Recognition

Molecular imprinted titania nanoparticles were developed for selective recognition of purines, for example, guanine and its final oxidation product uric acid. Titania nanoparticles were prepared by hydrolysis of titanium butoxide as precursor in the presence of pattern molecules. The morphology of synthesized nanoparticles is evaluated by SEM images. Recognition characteristics of imprinted titania nanoparticles are studied by exposing them to standard solution of guanine and uric acid, respectively. The resultant change in their concentration is determined by UV/Vis analysis that indicated imprinted titania nanoparticles possess high affinity for print molecules. In both cases, nonimprinted titania is taken as control to observe nonspecific binding interactions. Cross sensitivity studies suggested that imprinted titania is at least five times more selective for binding print molecules than competing analyte thus indicating its potential for bioassay of purines.