Pelagia Irene Gouma

Synthesis and Sensing Properties to NH3 of Hexagonal WO3 Metastable Nanopowders

WO3 is an important kind of wide-bandgap semiconducting metal oxides, which has a very promising property in gas-detection behavior. It has several polymorphs with triclinic, monoclinic, orthorhombic structures being the stable forms of this oxide. However, by a method known as acid precipitation, new metastable open crystalline forms with hexagonal structure have been successfully synthesized. The nanopowders were characterized by SEM, TEM, and XRD, and their sensing response to reducing gases (NH3) was measured and compared to monoclinic WO3, showing a much better sensing property of the hexagonal WO3.

Nanostructured hexagonal tungsten oxides for ammonia sensing

Among the family of wide band-gap semiconducting metal oxides, tungsten trioxide is the most promising oxide for gas sensing. A metastable open-structured hexagonal phase of WO3 was successfully synthesized using acid precipitation method. The oxide was characterized using SEM, TEM and XRD. The sensing property to reducing ammonia gas was measured. The sensitivity is much higher than that of monoclinic tungsten oxides. The oxide polymorph exhibits a p-n type transition when the temperature goes from 100 °C to 300 °C.

Biopolymer-Hydroxyapatite Scaffolds for Advanced Prosthetics

Biocompatibility in research and development of advanced prosthetics is a current problem faced by medical researchers. A major challenge in tissue engineering is to find materials and processing techniques that allow them to produce extracellular matrices (ECM) mimicking scaffolds that promote cell growth and organization into a specific architecture, inducing cell differentiation and subsequent cell function. The ideal tissue repair material thus should consist of synthetic biomaterials, such as natural polymers mimicking the mechanical and biological functionality of the ECM. Cellulose acetate membranes were used as scaffolds for microvascular cell growth. Hydroxyapatite (HA) is a natural ceramic (responsible for strength and stability in the human skeletal system) operable as a biocomposite coating to improve the biocompatibility of implant substrates. In this work, HA was prepared from low cost natural calcium source — eggshells. Its structural properties were investigated by scanning (SEM), transmission (TEM) electron microscopies and Fourier Transformed Infrared spectroscopy (FT-IR). The composition analyses of HA were measured by the total reflection X-ray fluorescence spectrometer (TXRF) and by prompt gamma activation analysis (PGAA). Hydroxyapatite added biodegradable scaffolds have been prepared by electrospinning method to enhance biological functionality.

Optimized Nanostructured TiO2 Photocatalysts

Titania is the most widely studied photocatalyst. In it’s mixed-phase configuration (anatase-rutile form) -as manifested in the commercially available P25 Degussa material- titania was previously found to exhibit the best photocatalytic properties reported for the pure system. A great deal of published research by various workers in the field have not fully explained the underlying mechanism for the observed behavior of mixed-phase titania photocatalysts. One of the prevalent hypothesis in the literature that is tested in this work involves the presence of small, active clusters of interwoven anatase and rutile crystallites or “catalytic “hot-spots””. Therefore, non-woven nanofibrous mats of titania were produced and upon calcination the mats consisted of nanostructured fibers with different anatase-rutile ratios. By assessing the photocatalytic and photoelectrochemical properties of these samples the optimized photocatalyst was determined. This consisted of TiO2 nanostructures annealed at 500˚C with an anatase /rutile content of 90/10. Since the performance of this material exceeded that of P25 complete structural characterization was employed to understand the catalytic mechanism involved. It was determined that the dominant factors controlling the photocatalytic behavior of the titania system are the relative particle size of the different phases of titania and the growth of rutile laths on anatase grains which allow for rapid electron transfer between the two phases. This explains how to optimize the response of the pure system.

Biopolymer-Hydroxyapatite Nanocomposite from Eggshell for Prospective Surgical Applications

From biological perspectives, biopolymer - hydroxyapatite nanocomposites for tissue replacement interact with the surrounding in vivo environment chemically, mechanically and morphologically. Hydroxyapatite (HA) is a natural ceramic operable as a biocomposite coating to improve the biocompatibility of implant substrates. To fulfill this requierements hydroxyapatite added biodegradable scaffold were prepared by electrospinning method to enhance biological functionality. In this work, firstly a novel synthesis of the hydroxyapatite nanocrystals prepared from eggshell are presented. Polymer based composites were prepared by electrospinning hydroxyapatite with a biocompatible polymer for the development of a structurally stable casing for prosthetic devices.