Browsing by Author "Ouma, Linda Immaculate"

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Assessment of Natural Radionuclides in the Top Soil Sample of Ahero Fields, Kenya
(International Journal of Modern Developments in Engineering and Science, 2023-05-22) Mukanda, Kere Wanyama; Waswa, Michael Nakitare; Ouma, Linda Immaculate
A total of 17 soil samples of Ahero fields were collected at a depth of 15 – 20 cm; five samples each of mass 170g were collected from field 1, 2, 3 and two samples from field 4. The field 1 was where rice seedlings were already transplanted, field 2 was one in which transplanting was being done, field 3 was one in which rice had been harvested and the field had just been ploughed while field 4 was a field in which farming had not been done for two years. The activity concentrations were measured, identified and detected using NaI(Ti) detector that were used in calculation of Radium Equivalent, External Hazard Indices and Internal Hazard Indices. The average radium equivalent were 185.82 ± 7.04 Bq/kg, 119.19 ± 5.95 Bq/kg, 168.78 ± 8.44 Bq/kg and 208.81 ± 10.44 Bq/kg for fields 1, 2, 3 and 4 respectively. The average internal hazard index was 0.50 ± 0.02 mSv/y, 0.32± 0.01 mSv/y, 0.45 ± 0.03 mSv/y and 0.57± 0.03 mSv/y for fields 1, 2, 3 and 4 respectively. On the other hand, the average external hazard indices for the fields were 0.59 ± 0.02 mSv/y, 0.37± 0.01 mSv/y, 0.54± 0.02 mSv/y and 0.65± 0.03 mSv/y for fields 1, 2, 3 and 4 respectively. Generally, the results from the study indicate that the radiological health risk associated with the top soils of the studyarea is insignificant.
Consistency And Stability Analysis of a Mathematical Model of Chlorine Concentration in Contact Tanks Using Numerical Solution of A 1- Dimensional Convection- Diffusion Equation
(IRE Journals, 2022-01-22) Owuor, Lucas Otieno; Kwach, Boniface O.; Tireito, Frankline; Ouma, Linda Immaculate
In this paper we consider the consistency and stability analysis of the modified convection diffusion equation: ut ut +mux − nLuxx = 0, which describes the mass transfer of chlorine in contact tank water disinfectant. We employ the concept of Dufort-Frankel based on Richardson’s scheme to discretize the modified equation. This resulted to a numerical scheme algorithm. The consistency was analyzed by Taylor’s expansion of the discretized scheme, which was found to be consistent with the original modified equation. In addition, stability was analyzed by using matrix method. The numerical computation results showed that the scheme was conditionally stable. This has been concluded by numerical computations to illustrate the consistence and stability of the scheme.
Effects of reaction parameters on the growth and optical properties of PbSe nanocrystals
(Journal of Nano Research, 2015-07-15) Ouma, Linda Immaculate; Mushonga, Paul; Onani, Martin O.
Colloidal syntheses of PbSe nanocrystals (NCs) have been widely investigated and the properties of nanocrystals have been shown to vary with reaction conditions, time, concentration and chemistry of reagents as well as the surfactants used. In this work the effects of reaction temperature, solvents, ligand purity, lead and selenium sources on the optical and structural properties of PbSe nanocrystals were investigated. PbSe NCs synthesized at 90 °C were observed to be spherical and had a narrower size distribution as compared to those synthesized at higher temperatures. 1-octadecene, trioctylphosphine and oleylamine were investigated as solvents for NC synthesis with the non-coordinating solvent octadecene showing the fastest growth rate with medium sized NCs. The coordinating solvents trioctylphosphine and oleylamine produced larger and smaller NCs respectively; this could be attributed to solvent interference during NC nucleation and growth phases. Oleate ligands were used during these syntheses and the ligand purity was not observed to have a significant effect on the NC optical and structural properties. The selenium precursor used affected the NC size and their optical properties while the lead source influenced both the NC shape and size. Lead acetate produced cubic NCs which were larger than the spherical NCs obtained when lead oxide was used.
Iron oxide nanoparticles stabilized by lignocellulosic waste as green adsorbent for Cr(VI) removal from wastewater
(European Physical Journal of Applied Physics, 2017-07-06) Ouma, Linda Immaculate; Naidoo, Eliazer B.; Ofomaja, Augustine E.
Magnetite nanoparticles and magnetite-pine cone nanocomposite were prepared and applied in the adsorption of hexavalent chromium from water. Pine cone powder stabilized the nanoparticles and acted as a support while simultaneously introducing functional groups which improved metal adsorption. The nanocomposite retained the nanoparticles magnetic properties while improving chromium adsorption efficiency. Adsorption of hexavalent chromium on both materials was pH and concentration dependent with the most efficient adsorption occurring at pH 2 and 75 mg/L. On both materials, chromium adsorption was spontaneous with Gibbs free energy values of −19.2 kJ mol−1 to −23.7 kJ mol−1 and −18.0 kJ mol−1 to −24.2 kJ mol−1 for nanoparticles and nanocomposite respectively between 298 K and 319 K. The changes in enthalpy and entropy were determined to be 44.4 kJ mol−1, 212.7 J K−1 mol−1 and 78.3 kJ mol−1, 323.3 J K−1 mol−1 for the prepared nanoparticles and nanocomposite respectively.
Microwave assisted synthesis of oleic acid modifed magnetite nanoparticles for benzene adsorption
(Environmental Nanotechnology, Monitoring & Management, 2021-01-30) Masuku, Makhosazana; Ouma, Linda Immaculate; Pholosi, Agnes
Benzene is a carcinogenic, mutagenic and highly toxic nonpolar organic compound, its presence in water occurs as a result of leakage of underground pipes and improper effluent disposal. Adsorption techniques have proven to be efficient for benzene removal from water providing a low maintenance method with high removal efficiencies. Nanoparticles provide high surface areas for adsorption and magnetite particles are specifically advantageous owing to their magnetic characteristics. Magnetite surfaces require modification with hydrophobic compounds for the adsorption of nonpolar pollutants. Herein, magnetite nanoparticles (MNP) were modified with oleic acid to form a magnetite-oleic acid composite (MNP-OA) via microwave synthesis for the adsorption of benzene from simulated wastewater. Infrared analysis confirmed the interaction between magnetite and oleic acid and particle diameters were determined by XRD analysis as 19.7 nm and 17.1 nm for MNP and MNP-OA respectively. Magnetic measurements indicated that both materials were superparamagnetic with a decrease in saturation magnetization after modification due to the non-magnetic layer on the surface. Oleic acid modification improved the benzene uptake of magnetite nanoparticles by approximately 30 % while kinetic studies suggested that a concentration driving force controlled the adsorption process. The adsorbent was regenerated and was efficient for five adsorption-desorption cycles.
Monitoring of Annual Effective Dose (Aed) in Surface Soils of Ahero Rice Fields, Kenya
(Journal of Engineering and Technology for Industrial Applications, 2023-12-30) Wanyama, Mukanda Kere; Waswa, Michael Nakitare; Ouma, Linda Immaculate
The annual effective doses (AED) both AED (in) and AED (out) in the surface soils of Ahero rice fields, Kenya were investigated. The associated health risk of the soils from the four fields Field 1, Field 2, Field 3 and Field 4 was measured using gamma ray spectrometric technique employing Sodium Iodide Thallium doped detector. Five surface soil samples were collected at a depth of 15 – 20 cm from the Field 1, Field 2, Field 3 and two samples from Field 4. The average AED (in) of 0.30 ± 0.01 mSv/y and an average AED (out) of 0.20 ± 0.01 mSv/y for field 1, an average AED (in) of 0.19 ± 0.01 mSv/y, an average AED (out) of 0.20 ± 0.01 mSv/y for field 2, an average AED (in) of 0.28 ± 0.01 mSv/y and an average AED (out) of 0.18 ± 0.01 mSv/y for field 3 and an average AED (in) of 0.34 ± 0.01 mSv/y and an average AED (out) of 0.23 ± 0.01 mSv/y for field 4. All the AED values both in and out from the four fields were below the recommended level of 1mSv/y. The values indicate that there is no health hazard associated with the surface soils of the study area to the farmers and the general population.
Radiological Risk Assessment of 238u, 232th And 40k in the Top Soils of Ahero Paddy Fields of Kisumu County, Kenya
(Journal of Engineering and Technology for Industrial Applications, 2022-08-22) Mukanda, Kere Wanyama; Waswa, Michael Nakitare; Ouma, Linda Immaculate
A radiological risk assessment of 238U, 232Th and 40K in the top soils of Ahero paddy fields of Kisumu County has been measured using NaI(TI) gamma ray spectroscopy. A total of 17 samples were collected at a depth of 15 - 20 cm and measured for activity concentrations of three radionuclides which were used to calculate the absorbed dose rates and Annual effective dose rates of the samples. Samples were collected from fields at various stages of farming process i.e., four (4) weeks after transplanting (field 1), during transplanting (field 2), after harvesting and land ploughed (field 3) and a control field (field 4) where rice farming had not been done for 2 years. The average activity concentrations for the three radionuclides for field 1 were 32.63 ± 1.63 Bq/kg for 238U, 104.69 ± 5.20 Bq/kg for 232Th and 75.00 ± 3.2 6 Bq/kg for 40K. The average activity concentrations of the radionuclides from field 2 were 16.97 ± 0.84 Bq/kg, 68.03 ± 3.40 Bq/kg and 70.31 ± 3.51 Bq/kg for 238U, 232Th and 40K respectively. The average activity concentrations of the radionuclides from field 3 (post harvesting) were 28.92 ± 1.44 Bq/kg, 91.73 ± 4.58 Bq/kg and 122.60 ± 6.13 Bq/kg for 238U, 232Th and 40K respectively. The average activity concentrations of the radionuclides were 29.74 ± 1.48 Bq/kg, 121.11 ± 6.05 Bq/kg and 87.51 ± 4.37 Bq/kg for 238U, 232Th and 40K respectively. The average Absorbed Dose Rates were 81.50 ± 4.07 nGy/h for field 1, 52.59 ± 2.62 nGy/h for field 2; 74.68 ± 3.73 nGy/h for field 3 and 91.79 ± 4.59 nGy/h for field 4. The values were below the permissible limit of 1500 nGy/h, thus the radiological risk associated with the top soils of the Ahero Paddy fields of Kisumu County, Kenya is insignificant.
Sequestration of Heavy Metal Pollutants by Fe3O4-based Composites
(Springer, 2022-07-22) Ouma, Linda Immaculate; Onani, Martin
Heavy metal pollution poses a grave environmental threat. Some of the most toxic metals are highly mobile and, therefore, easily transported through ground water systems, thus, affecting large areas. Over the last decade, adsorption has been greatly focused on as a strategy for contaminated water treatment. Its versatility and relative ease of application have been a major determinant of its preference. Nanosized adsorbents have high surface areas and are size tunable and, hence, have been favored in adsorption applications. The magnetic properties of nanosized magnetite (Fe3O4) have made them particularly favorable. Magnetite composites with various materials have widely been applied in the adsorptive treatment of real and synthetic water containing heavy metal pollutants. This review outlines the application of Fe3O4 nanoparticles and Fe3O4 organic composites in the adsorption of heavy metal ions in aqueous solution. The reviewed articles indicate that the formation of Fe3O4 inorganic–organic composites improves the adsorption efficiencies of the composites and improves their applicability by providing magnetic separability. The presence of Fe3O4 nanoparticles in the composite materials also provides for improved reusability of the adsorbent. Generally, the formation of these composites tends to make adsorption a more viable alternative to conventional water treatment options for heavy metal pollutants in water.
Synthesis And Characterization Of Struvite By Aqueous Precipitation Using Wastewater And Hot Spring Water
(IOSR Journal of Applied Chemistry, 2024-07-22) Nasambu, Edith; Maingi, Francis; Ouma, Linda Immaculate
Struvite (MgNH4PO4.6H2O) is a phosphate mineral that has recently become a prudent venture for many researchers due to its nutritional value to plants in the field of agriculture. The cost of production of this mineral heavily relies on the cost of the magnesium source used. In this study, hot spring water was investigated as a potentially cheaper natural source of magnesium ions while sewage wastewater was used as a source of phosphate and ammonium ions for the struvite synthesis. The synthesized struvite composite was then characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), and Scanning electron microscope (SEM). The precipitate purity and phosphorous recovery were analysed. XRF results showed that synthesized struvite majorly consisted of magnesium oxide and phosphorous oxide. XRD analysis showed the presence of orthorhombic crystalline phases between 4-9 degrees (2𝜃) with struvite peaks at 2𝜃 values 15.8, 20.9and 46.3 which matched struvite ICDD card information. SEM revealed irregular, crystalline, and rod-like morphological structures that were consistent with those identified in the literature. The synthesized composite contained a percentage purity of 68.61% and phosphorous recovery of 76.15%. The presence of phosphorous and nitrogen in the struvite which is plant macronutrients makes the composite potential fertilizer for agricultural applications.
Synthesis, optical and morphological characterization of doped InP/ZnSe NCs
(Physica B: Condensed Matter, 2013-07-22) Mushonga, Paul; Ouma, Linda Immaculate; Madiehe, Abram M.; Meyer, Mervin; Dejene, Francis B.; Onani, Martin O.
We report on the Ag-, Fe-, and Co-doping of InP/ZnSe QDs using the growth-doping method. Doping the InP/ZnSe NCs with Ag caused a red-shift in the emission spectra with increasing dopant levels while the PL intensity decreased. Fe-doping resulted in blue-shifted emission spectra. The cobalt-doping (Co-doping) had no effect on the emission peak position. Instead, it had a quenching effect on the PL intensities. The HRTEM images showed well-defined lattice fringes for the doped InP/ZnSe NCs while the XRD analyses showed that they retained their zinc blende structure even after doping.