Masters Theses:Department of Physical Sciences

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Low Cost Pozzolana based Cement from Industrial and Agricultural Waste Materials
(Kenyatta University, 2003-09) Wachira, Jackson M.
This thesis reports the results of a study aimed at making low cost cement from some agricultural and industrial wastes. The utilization of these wastes would avail an economical and environmentally friendlier waste disposal methods and cheap cementing material. The cement made was based on the materials whose pozzolanic reaction was investigated. The materials tested for pozzolanicity included rice husks ash (RHA) from wastes of rice milling factories, spent bleaching earth (SBE) from oil processing factories and broken bricks (BB) from clay products manufacturers. Natural pozzolana (Ptuff) used for making East African Portland pozzolana cement was tested for comparative purposes. Heat content of rice husks (RH) and spent bleaching earth (SBE) was found to be adequate for activation of silica and alumina in the pozzolanic materials. Only a little kerosene was necessary for ignition. Acetylene lime sludge (ALS) from acetylene manufacturing industry and commercial hydrated lime (CHL) were used for the pozzolana-hydrated lime reaction. Pozzolanic activity of the materials with commercial hydrated lime (CHL) in different ratios was investigated on the pozzolanic materials separately. A blended calcined mix and a calcined blended raw mix of the materials was similarly tested. The results showed that the test materials were active pozzolanas. AI: 2 ratio of the pozzolanic material: CHL gave the best results. The 1: 2 ratio now using ALS was also investigated on the materials. ALS showed a superior performance than CHL with all the pozzolanic materials under test. Calcined blended raw mix exhibited a better performance than the blended calcined mix. The test materials were then singly interground in different proportions with laboratory made ordinary Portland cement (OPC) as per the Kenya Standard (KS) 02 1263 of 1993 [1] for cement tests. The resulting mixtures were then assessed using the same standard. The results showed that up to 25 percent replacement of the cement with the pozzolanic materials under test met the standard requirements. Calcined blended raw mix was interground with ALS and OPC from Bamburi Cement Factory in different percentages. The resulting products were subjected to the Kenya Standard [1]. Up to 45 percent replacement of the OPC with the material under test met the standard requirements, while higher percent replacements failed. A rough financial estimate suggested a running cost saving of up to 20 percent per tonne of PPC
Preparation and Properties of Long Afterglow CaAl2O4 Phosphors Activated by Rare Earth Metal Ions
(University of the Free State Republic of South Africa, 2011-11) Wako, Ali Halake
This work comprises of several aspects of calcium-aluminate phosphor activated with rare earth metal ions i.e. (CaAl2O4:Eu2+, Nd3+, and Dy3+). In particular the luminescent and structural properties of the long afterglow CaAl2O4:Eu2+,Nd3+,Dy3+ phosphors prepared by urea-nitrate solution-combustion method were investigated. The solution-combustion method is more efficient because phosphors with high efficiency were obtained at low temperature (500 oC) in a very short period of time (5 min). The effects of varying concentration of host matrix composition (Ca:Al), flux i.e. boric acid (H3BO3), activator (Eu2+) and co-activator (Nd3+/Dy3+) mass ratios and urea ((NH2)2CO) on the structural, luminescent, and thermoluminescent(TL) properties of the CaAl2O4:Eu2+, Nd3+, Dy3+ phosphors were studied. It was observed that Ca:Al mass ratios greatly affect the crystalline structure of the material. The results of the X-ray diffraction (XRD) analysis reveal that the formation of several crystalline phases depends on the ratios of the host material. The XRD peaks show the presence of other phases such as Ca3Al2O6 and CaAl4O7 but the predominant phase formed was that of CaAl2O4. However it was found that the crystalline structure is generally not affected by the variation of the co-dopants concentration. Photoluminescence (PL) studies revealed a general rise in intensity with an increase in the mass ratio of Ca:Al. The highest PL intensity was observed with 0.7% Ca. The luminescent intensities vary from each other when co-doped with various proportions of Nd3+ and Dy3+. The addition of H3BO3 favored the formation of pure monoclinic CaAl2O4 phase while the variation of the amount of ((NH2)2CO) showed mixed phases although still predominantly monoclinic. Both boric acid and urea to some extent influence the luminescence intensity of the obtained phosphor but unlike the case of CO(NH2), the emission peak for H3BO3, does not shift evidently because the energy level difference of 4f-5d does not change obviously. The broad blue emissions consisting mainly of symmetrical bands having maxima between 440–445 nm originate from the energy transitions between the ground state (4f7) and the excited state (4f65d1) of Eu2+ ions while the narrow emissions in the red region 600-630 nm arise from the f-f transitions of the remnant unreduced Eu3+ions. High concentrations of H3BO3 generally reduce both intensity and lifetime of the phosphor powders. The optimized content of H3BO3 is 5.8 mol % for the obtained phosphor with excellent properties. XRD analysis of the influence of Eu2+ and Nd3+ doping concentrations on the morphological, structural and PL properties of the CaAl2O4: Eu2+; Nd3+ phosphor, depict a dominant monoclinic phase that indicates no change in the crystalline structure of the phosphor even with high concentration of Eu2+ or Nd3+. The Energy Dispersive x-ray Spectroscopy (EDS) and Fourier Transform Infra-Red Spectroscopy (FTIR) spectra showed the expected chemical components of the phosphor. The excitation iv spectra show one broadband from 200 nm to 300 nm centered around 240 nm corresponding to the crystal field splitting of the Eu2+ d-orbital. The prepared phosphor compositions exhibit PL emission in the blue region with a maximum around 440 nm. This is a strong indication that there was dominantly one luminescence centre, Eu2+ which represents emission from transitions between 4f7 (8S7/2) ground state and the 4f6-5d1 excited state configuration. Two other, minor peaks, at 580 and 614 nm indicate the presence of remnants of Eu3+ ions as a result of incomplete reduction during sample preparation. High concentrations of Eu2+ and Nd3+ generally reduce both intensity and lifetime of the phosphor powders. The optimized content of Eu2+ is 0.36 mol % and for Nd3+ is 0.09 mol % for the obtained phosphors with good properties. The decay characteristics exhibit a significant rise in initial intensity with increasing Eu2+ doping concentration while the decay time increased with Nd3+ co-doping. Analysis of the TL glow curves is one of the most significant ways to measure the number of traps and also the activation energy of the trap levels in luminescent materials. In the present study TL properties of the CaAl2O4:Eu2+, Nd3+,Dy3+ phosphors were investigated above room temperature by use of Nucleonix 1009I TL reader. The trap depths were estimated with the aid of the peak shape method. The glow curve of CaAl2O4:Eu2+ with a first peak at 50 °C was found to correspond to several traps. The ratio of Nd3+:Dy3+ ions were observed to influence the position, concentration and type of traps formed. The observed afterglow can be ascribed to the generation of suitable traps due to the presence of the Nd3+ trap levels. Trivalent rare earth ions (Nd3+/Dy3+) are thought to play the role of hole traps in calcium aluminate phosphors (CaAl2O4:Eu2+). In these phosphors, Eu2+ ions act as luminescent centre emitting in the blue (λ max = 440 nm) region. Despite a large number of research on the phenomenon the mechanism of the persistent luminescence of CaAl2O4:Eu2+,Nd3+,Dy3+ has not been well presented. A proper understanding of the exact luminescence mechanisms and the identification of trap levels or locations in long phosphorescent materials is required for their use in areas such as detection of radiation, sensors for cracks in buildings, fracture of materials and temperature among others.
Structure and Biomass Accumulation of Natural Mangrove Forest at Gazi Bay, Kenya
(Kenyatta University, 2013-08) Githaiga, Michael N.
Mangroves occupy only 0.4% of forested areas globally but are among the most productive ecosystems on earth. They account for about 11% of the total input of terrestrial carbon into the oceans. The above ground carbon stock in mangroves in some parts of the World has been estimated to be as high as 8 kg C m -2 ; with a similar amount reported for below ground components. Although a lot of research has been done on estimates of mangrove biomass in Kenya, there is no information on biomass accumulation across the zones. The present study aimed at determining the forest structure and estimating above and below ground biomass accumulation in Gazi Bay mangrove forest. Forest structure was determined in the western, middle and eastern forest blocks of the Gazi Bay mangrove forest while biomass accumulation studies were done in the western forest block. In-growth cores of 80 cm long × 20 cm wide and 60 cm-depth were used to estimate below ground biomass accumulation. Data on tree height and stem diameter at breast height (DBH-130) were used to estimate above ground biomass accumulation. Shoots were tagged for monitoring leaf phenology. Periodic measurements of environmental variables across four mangrove species zones were done at the beginning, thereafter every four months for a year. Composition and distribution pattern of natural regeneration was obtained using the method of linear regeneration sampling (LRS). Among the soil environment properties investigated, salinity had a significant negative correlation with above ground biomass accumulation. Comparing the four forest zones, Sonneratia alba had the highest biomass accumulation rate of 10.5 ± 1.9 t ha-1 yr -1 . This was followed by Rhizophora mucronata (8.5 ± 0.8 t ha-1 yr -1 ), Avicennia marina (5.2 ± 1.8 t ha-1 yr -1 ), and Ceriops tagal (2.6 ± 1.5 t ha-1 yr -1 ). There were significant differences in above ground and below ground biomass accumulation across zones (F (3, 8) = 5.42, p = 0.025) and (F (3, 8) = 16.03, p = 0 001) respectively. Total biomass accumulation was significantly different across zones (F (3, 8) =15.56, p = 0.001). A root: shoot biomass accumulation ratio of 2:5 was computed for the whole forest. The finding of this study gives better estimates of mangrove carbon capture and storage which can be used in negotiations for carbon credits in the evolving carbon market.
Microplastic Abundance, Composition and Distribution in the Endorheic Lake Naivasha, Kenya
(University of Embu, 2020-10-28) Migwi, Francis Kigera
Plastic pollution has recently gained global concern due to the negative effect it presents on both the environment and human health. In the environment, plastics degrade yielding millions of micro- and nano-scale plastic particles. The microplastics have the ability to adsorb organic pollutants, heavy metals, and micro-organisms in either the aquatic or terrestrial environments. The microplastics size range and ubiquity in the environment provides an easy pathway into the food chain through ingestion, bio-accumulation and bio-magnification. This study was conducted with an aim of determining the abundance and composition of microplastic particles in Lake Naivasha surface waters and sediments. The study also entailed the evaluation of the possible physical chemical parameters that could affect the distribution of microplastic within the lake. Volume reduced and bulk sampling methods were used to collect samples of floating debris in surface waters and sediments respectively. The physical chemical parameters were measured in situ whereas the nitrogen and phosphorus nutrient levels were determined in the laboratory. Density separation using concentrated brine solution and wet peroxide oxidation methods were used for microplastics extraction. The recovered particles were analyzed using microscopy for physical characteristics (shape and color) while the microplastics chemical composition was determined using Fourier-transform infrared spectroscopy (FTIR). All the physical-chemical parameters in the sampled locations of Lake Naivasha exhibited significance differences (p<0.05) except salinity. These differences were attributed to the infestation by water hyacinth (lower dissolved oxygen and temperatures), originality of the lake (pH and total dissolved solids), and anthropogenic activities (higher turbidity, conductivity and nutrient levels). The average microplastic concentration was found to be 0.407±0.135 particles/m 2 and 177.3±87.4 particles/kg in surface waters and surface sediments respectively. The post-hoc Tukey Honest Significance Difference test exhibited significant differences (p<0.05) in the microplastics abundance in the studied locations of the lake. The highest microplastic levels were recovered in the lakes’ major inflow, River Malewa. The high variability in the microplastic densities exhibited between the sampled locations was attributed to human activities, water and wastewater intake through rivers and tributaries, and the presence of local wind patterns responsible for the general water circulation. Colored and non-colored microplastics, of shapes categories fragments, fibers and films were identified and were majorly composed of polypropylene, polyethylene, and polyester in surface waters, whereas polyethylene terephthalate, polyvinylchloride and nylon polymers were dominant in the surface sediments. The lakes’ dominating abundance of fibrous, fragmented and colored (83%) microplastics was an indication that secondary microplastics were the major source of pollutants in the lake. Moreover, correlational analysis done exhibited a strong positive existing association between microplastic quantities and turbidity, total nitrogen, and total phosphorus in Lake Naivasha surface waters. Thus, this study concludes that the microplastic pollution in Lake Naivasha is contributed by anthropogenic activities with the distribution drivers being related to the nutrients and turbidity levels of the lake. This study recommends on the improvement on microplastic waste management around rivers and lakes by local authorities and the National Environment Management Authority (NEMA), and increase in the public awareness and education.
EFFECTS OF TEMPERATURE, DEFECT, AND ph ON PROPERTIES OF caal2o4: Eu2+, Dy3+ PHOSPHOR FOR LIGHTING APPLICATION
(Samuel Ndung’u Waithira, 2024-08)
Electricity is the main source of energy used for lighting but still worldwide, a population of about 1.4 billion does not have any access to electricity, with 85 % of them coming from rural areas. Most of the people in the rural areas use kerosene oil as the main source of energy for lighting which produces smoke that does not only pollute the environment but has adverse health effects on the people. CaAl2O4: Eu2+ , Dy3+phosphor is a very promising source of energy in the future. It is environmentally safe and involves less cost of installation and energy production. Phosphors are solid substances that give off light, a phenomenon known as luminescence and consist of a host matrix and dopants. In this work, effects of synthesis temperature, defect, and pH on both structural and optical properties of CaAl2O4: Eu2+, Dy3+ phosphor were investigated. Europium doped and dysprosium co-doped Calcium aluminate nanomaterial (CaAl2O4: Eu2+, Dy3+) was prepared using a facile solution combustion technique. Combustion synthesis method is better compared than other conventional methods because of its benefits such as its low synthesis temperature of 500 - 600 °C and its quick processing time. Furthermore, the combustion method is an energy-saving technique that is highly exothermic, and homogenous products are formed within a short time. Similarly, combustion synthesis produces a much smaller grain size compared to alternative conventional approaches. Although the phosphorescence of CaAl2O4:Eu2 is known, information about the effect of different dopants and other synthesis conditions is scant. All the synthesized samples underwent characterization employing a range of analytical methods. The findings of X-ray diffraction (XRD) verified that every sample had the monoclinic phase and all the peaks can be matched well with the typical monoclinic CaAl2O4 peak matching with the ICDD data file (no.069-0033) for orthorhombic structure. The anticipated chemical combustion results of the finished product were provided by the Fourier-transform infrared analysis. The XRD patterns displayed that there was a notable shift to higher 2theta of the prominent peaks diffraction angles with change in synthesis parameters. This is attributed to an increase in particle sizes which led to an increase in lattice parameters. The Debye-Scherrer relation was utilized to ascertain the crystallite sizes of the samples in their prepared state. It was noted that there is variation in the crystallite sizes with synthesis conditions. Analysis of the UV-Vis spectra revealed that the absorption edges also shifted with synthesis parameters. Images captured by a scanning electron microscope revealed that every sample had pores and cracks in an uneven shape. The EDS outcome indicated that the elements of the phosphor for all samples are components of O, Al, and Ca indicating that the phase of final product was actually made of calcium aluminate. The study offers a straightforward path to synthesize CaAl2O4: Eu2+, Dy3+ phosphors with ideal pH, barium concentration, and synthesis temperature generating the sample that exhibits the highest degree of crystallinity suitable for incorporation into lighting fixtures.
Harnessing the nutraceutical properties, Microbial composition of scarabaeoid beetle Larvae and antibacterial compounds of its Endozoic fungus (aspergillus welwitschia)
(Sylviah Syombua Mwanza, 2024-08) MWANZA, SYLVIAH SYOMBUA
The systematic development of antibiotic resistance poses huge worldwide health challenges, specifically in low- and middle- income countries (LMICs) increasing the treatment costs. There is heightened need to broaden the search for new antibiotic sources such as exploration of insects beyond soil microorganisms. Insects harbor symbiotic microbes in their guts which can be utilized in developing effective antimicrobial agents. However, entomophagy is the main activity associated with edible insects leaving a paucity of knowledge on their therapeutic benefits. Further, very few researches have been done to understand the microbial composition of comestible insects. This research focused on exploring novel functional properties and characterizing the associated microbiota from the gut of two scarabaeoid larvae collected from Embu, Murang’a and Nairobi counties. Further, the culturable fungal organisms were investigated for their antibacterial potency. The larvae were dissected to obtain the gut portions then pooled and divided into two proportions. One part was used for culturing the fungal isolates and the other was used to obtain DNA for metagenomics analysis. The degutted body remains were used for nutritional profiling. Bioassay-guided isolation was carried out to obtain the bio-active compounds whose structures were elucidated using spectroscopic techniques. The most bioactive fungus was identified using Sanger sequencing targeting the Internal Transcribed Spacer (ITS) gene. The larvae were identified using morphological features and molecular tools as Cetonia aurata and Oryctes rhinoceros. They were also found to be excellent sources of both macro [44% for O. rhinoceros and 63% for C. aurata] and micronutrients calcium (20.42–22.65 mg/g) and zinc minerals (0.28–0.3 mg/g). The dominant bacterial communities in their gut were Firmicutes (42.10%) and Bacteroidota (32.50%) for C. aurata, while O. rhinoceros was dominated by Proteobacteria (35.00%), Actinobacteriota (11.40%), and Desulfobacterota (7.40%). The fungal community was represented by the class Lecanoromycetes (92.60%) in O. rhinoceros, whereas Saccharomycetes (92.60%) prevailed in C. aurata. This work uncovered possible microbiota functions to include the generation of biosynthetic intermediates necessary for anabolic and catabolic activities, adaptive metabolism and energy production. The screening antibacterial results revealed that the most active mixed fungal extract originated from dung beetle larvae in Murang'a. Sub-culturing yielded to the 15 axenic strains. Antibacterial assays identified the most active strain to be Aspergillus welwitschia, with ethyl acetate fraction displaying the highest activity against the tested bacterial strains. Rubasperone B and rubrofusarin B were successfully isolated from this fraction and linked to the observed antibacterial activity. These findings indicate that the Scarabaeoid beetle larvae are endowed with macronutrients and entomochemicals that could find application in fortifying food and feed substances. Additionally, the predicted functions of the gut microbiota provide a theoretical framework for biotechnological uses in waste management and bio-functional foods. In pharmacology, the characterized compounds are significant in the development of new medications to help combat the impacts of Multi-Drug Resistant (MDR) bacteria and contribute to the accomplishment of the UN Sustainable Development Goals (SDGs) chiefly SDG 3 on well-being and good health.
Synthesis of Luminescent sral2o4:Eu2+,Dy3+ Nanomaterials for Emergency Displays
(Victor Saidi Kadenge, 2024-08)
SrAl2O4:Eu2+,Dy3+ are phosphors with unique tuneable properties. This work comprises of several aspects of strontium-aluminate phosphor doped with rare earth metal ions (SrAl2O4:Eu2+,Dy3+). In particular the optical and structural properties of the long afterglow SrAl2O4:Eu2+,Dy3+ phosphors prepared by urea-nitrate solution-combustion method were investigated. The solution-combustion method is more efficient because phosphors with high efficiency were obtained at low temperature in a very short period of time (5 min). The effects of varying concentration of host matrix composition (Sr:Al), co-dopant and growth temperature on the structural and optical properties of the SrAl2O4:Eu2+,Dy3+ phosphors were studied. Temperature is a critical variable in thermodynamics that has a substantial impact on the shape, size, and surface properties of the produced nanoparticles. A study was carried out to investigate the influence of this factor on the optical and structural characteristics of SrAl2O4:Eu2+, Dy3+. The results of the X-ray diffraction (XRD) analysis reveal that the 2mol % favored the formation of monoclinic phase. The X-ray diffraction patterns for all the SrAl2O4:Eu2+,Dy3+ NPs exhibited a highly crystalline and monoclinic structure of SrAl2O4:Eu2+,Dy3+ with no impurity phases. The values of the crystallite sizes range from 35 to 42 nm and 32.23 to 29.7 nm for the NPs prepared at different furnace temperatures and varied concentrations respectively. A similar trend was observed also for other growth on varying concentration of host matrix composition (Sr:Al). The research on the impact of Dy3+ concentration revealed that the average lattice constants 'a' were determined to be a = 0.84470 nm, indicating a decreasing tendency with higher degrees of Dy3+ doping and Al/Sr ratios. The results closely match the bulk SrAl2O4:Eu2+, Dy3+ lattice constants provided in the standard JCPDS data file No.34-0379. The ultraviolet and visible analysis (UV-Vis) displayed well-resolved absorption maxima which were red shifted upon increase in growth temperature and varying concentration of host matrix composition (Sr:Al) concentration. There was an inverse relation between the bandgap and the reaction parameters under study (reaction time, growth temperature and varying concentration of host matrix composition (Sr:Al). The band gap energies of the SrAl2O4:Eu2+, Dy3+ nanoparticles were adjusted within the range of approximately 5.62 to 5.4 eV by increasing the temperature of the furnace. The band gaps of SrAl2O4:Eu2+, Dy3+ exhibited a range of 6.5 to 5.5 eV as the concentration of Dy3+ during growth increased. The sample of SrAl2O4:Eu2+, Dy3+ NPs, synthesized with a doping of 0.4 mol% Dy3+, grown in a growth medium with a ratio of 2 Al/Sr, and prepared at 700 ºC, exhibited optimal crystallinity, minimal lattice stress, and favorable optical characteristic
Solid-Liquid Extraction of Heavy Metals in Aqueous Solutions using Chelating Ligands Anchored on Solid Supports
(Ian Tharau Kabogo, 2024-08)
The rapid surge of population growth has translated to an unprecedented increase in heavy metal pollution in the environment resulting from various anthropogenic activities. Their non-biodegradable nature, toxicity and persistence in the environment raise a lot of concern. There are various methods for heavy metal removal that have been applied as a means of remediation such as adsorption, chelation, chemical precipitation, and ion exchange among others. These methods, however, pose several disadvantages such as difficulty in treatment of toxic sludge generated and high cost of operation. However, solid-phase chelation removal technique despite not being as widely documented as other methods has been found to be very promising in the effort of remediating polluted environmental components as it averts demerits such as waste generation and poor selectivity. In the effort of designing novel compounds which will be instrumental in the remediation of heavy metal polluted environmental components, Schiff base chelating ligands (E)-2-(3,3-dimethoxy-2-oxa-7,10-diaza-3-silaundec-10-en-11-yl)phenol (L1), (E)-N-(2-((pyridine-2ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L2) and (E)-N-(2-((thiophen-2-ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L3) were immobilized onto SBA-15 mesoporous silica and Fe₃O₄ magnetic nanoparticles to yield their corresponding adsorbents. The synthesized materials were characterized by a wide array of techniques that included NMR, FT-IR, BET/BHJ, TEM, and SEM. The adsorbents were then used for the solid-liquid removal of Cr(VI), Cd(II) and Pb(II) from aqueous solutions. Various physicochemical parameters were varied during the removal studies where the adsorbents recorded relatively high removal efficiencies of the metal cations ranging from 20-68% for Cr(VI), 48-90% for Cd(II) and 62-99% for Pb(II) which varied significantly (p<0.05) between the two adsorbents. Additionally, the nature of adsorption was evaluated using several adsorption isotherms and kinetic models where the Langmuir isotherm model and pseudo-second-order kinetic model yielded the highest correlation coefficients (R²>0.98) that confirmed the role of chemisorption and monolayer adsorption in the removal experiments. The Hard Soft Acid Base (HSAB) theory of metal-ligand interaction was also observed to influence the removal capability of the Schiff bases immobilized adsorbents. Therefore, the Schiff base chelating ligands immobilized onto SBA-15 and Fe₃O₄ magnetic nanoparticles can be synthesized as potential adsorbents for heavy metal removal from aqueous solutions and they can be used as potential sequestering agents for heavy metal cations in wastewater.

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