Browsing by Author "Ombaka, O. 1"

Now showing 1 - 2 of 2

Geochemical and Mineralogical Characteristics of Geophagic Materials from Kiambu, Kenya
(Modern Scientific Press Company, Florida, USA, 2012-09) Gichumbi, J.M. 1, *; Ombaka, O. 1; Gichuki, J.G. 2
Geophagia is the deliberate consumption of soil and clay. The practice of geophagia is due to reasons of culture, medicinal, religious and mineral deficiency. Geophagy is widespread among pregnant and breast feeding women in sub-Saharan Africa and this is evidenced by the sale of geophagic materials in markets across Africa. This study is aimed at studying the geochemistry and mineralogy of geophagic samples sold in Kiambu County, Kenya. The geophagic samples were analyzed by atomic absorption spectrometry, X-ray fluorescence spectrometry, X-ray diffractometry, Fourier transform infrared spectrometry. The results obtained showed that the materials consist mainly of silica (SiO2) and alumina (Al2O3). They also contain the elevated levels of iron oxides. The mineralogical analysis showed that quartz and kaolinite were the major phases.
Synthesis, characterization and applications of transition metal-doped manganese oxide catalysts.
(2019) Muya, R. K. 1; Achola, L. 2; Njagi, E. C. 1; Ombaka, O. 1; Suib, S. L. 2
Manganese oxide octahedral molecular sieves exhibit good conductivity, tunable redox properties, high porosity and excellent thermal stability. Thus, these materials have several potential applications as cathodic materials in batteries, adsorbents, catalysts, sensors and electromagnetic materials. In this study, synthetic cryptomelane (K-OMS-2) and framework doped K-OMS-2 materials were synthesized using a facile reflux method. The synthesized materials were characterized using powder X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR) spectroscopy, Field Emission-Scanning Electron Microscopy (FE-SEM), N2 sorption, X-ray fluorescence (XRF) and Thermogravimetric analysis (TGA). The synthesized materials were highly crystalline with the structure of tetragonal cryptomelane. Characterization data suggests that dopant cations were incorporated in the structure of K-OMS-2 without the formation of segregated dopant oxides or other impurities. Morphological analyses revealed that K-OMS-2 was composed of nanofibres of ca. 500 nm. The length of the nanofibres decreased significantly on doping K-OMS2 to form irregular aggregated nanoparticles of ca. 100 nm. Doped K-OMS-2 materials had higher surface areas and porosities but lower thermal stability than K-OMS-2. The V-Cu-Co-K-OMS-2 material exhibited the highest degradation capacity for methylene blue.