Theses and Dissertation

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Betalain-Based Dyes As Photosensitizers For Energy Harvesting Application: A Theoretical Investigation
(NM-AIST, 2025-07) Tsere, Melkizedeck
Betalain dyes are natural pigments that have attracted growing research interest as promising materials for light-harvesting applications. In the present work, the modification of betalain dyes was performed through a computational approach, aimed at screening the wide spread of blended triphenylamine-betalain dyes for dye sensitized solar cell applications. In the first modification approach, betalamic acid was joined to the phenyl ring and further grafted with electron donor groups to enhance light absorption and charge transfer ability. The second approach involved the introduction of new anchoring groups featuring carboxylic acid CH=C(X)COOH for the A1-X dyes and nitro group -CH=C(X)NO2 for the A2-X dyes, where X = CN, CH3, CCl3, CF3. In addition to molecular grafting, the solvent effects on the optoelectronic parameters and dye adsorption to the semiconductor surface were evaluated. The geometrical structures, optoelectronic properties of designed dyes and binding to the semiconductor have been explored. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods coupled with B3LYP and CAM-B3LYP at 6- 31+G(d,p) basis set were used for ground and excited state calculations, respectively. In the UV-Vis spectra, the maximum absorption wavelengths range between 400 ‒ 442 nm based on grafting with an electron donor. However, further modifications by introducing new anchoring units resulted in huge redshifts in wavelengths: 400 ‒ 700 nm for CH=C(X)COOH and between 500 and 1000 nm for the -CH=C(X)NO2. The attachment of the dyes to the semiconductor was modelled via binding to (TiO2)6H3 cluster; A2-X dyes exhibited more stable Dye@TiO2 complexes with binding energies (BEs) ranging between ‒4.08 and ‒2.88 eV compared to A1- X dyes with BEs from ‒1.11 to ‒0.05 eV in water solution. The results evince that the blended triphenyl-betalain dyes with the CH=C(X)NO2 anchoring groups could be promising materials for light harvesting applications. Among the CH=C(X)NO2 dyes, the CH=C(CN)NO2 demonstrated superior optoelectronic properties and binding stability, thus, would be expected the most favourable candidate for light-harvesting applications in dye sensitized solar cells.
Investigation Of Honey-Grapes Blend Efficacy For Reducing Radiation-Induced Oral Mucositis Severity Among Head And Neck Cancer Patients: A Case Study For Ocean Road Cancer Institute And Besta Polyclinic
(NM-AIST, 2025-06) Edward, Magaisha
Radiation-induced oral mucositis is a global challenge in radiotherapy of head and neck cancer whereby nearly all patients develop a certain degree of mucositis and it affects treatment outcomes. Various pharmaceutical and natural remedies are used to reduce radiation-induced oral mucositis. However, the efficacy of available treatment modalities is low and is associated with many side effects. This study assessed the efficacy of honey-grape blend for reducing radiation-induced oral mucositis severity in head and neck cancer patients at Ocean Road Cancer Institute and Besta Polyclinic in Tanzania. First, social demographic and clinical characteristics of head and neck cancer patients were determined. Secondly, mucositis prevalence, and honey-grapes' efficacy were assessed. Sixty head and neck cancer patients were divided into a control, honey, and honey-grapes blend juice. The patients from the intervention groups received 50 mL of the respective solution, while the control group received placebo. It was revealed that, about 10% of total registered patients in the study period were head and neck cancer patients, whereby 62% were males and 38% were females (χ² = 22.174, df =1, P < 0.001). Alcohol consumption among males and females was 54.05% and 34.8% respectively (χ²=7.032, df =1, P < 0.001). The Northern zone had the highest incidence of head and neck cancer (37.5%) compared with other zones (χ² =112, df=7, P <0.001). Average weight loss for the placebo group was 2.65, while weight gain for the honey-grape blend group was 0.45 kg. Honey-grapes blend minimized severity of mucositis in head and neck cancer patients. However, larger studies are needed to strengthen the evidence on effective use of honey-grapes blend in reducing mucositis severity in the head and neck cancer patients.
Investigation Of The Efficiency Of Sleepy Morning Plant (Waltheria Indica L.) As An Anti-Bacterial Agent From Shallow Wells Water In Tanzania
(NM-AIST, 2025-04) Ilunde, Josephat
Waterborne-related diseases, such as diarrhoea, schistosomiasis, typhoid, and intestinal worm infections, are very common and widespread in the Misungwi District, Tanzania. These waterborne diseases, can be linked with water consumption from shallow wells contaminated with Escherichia coli and Total coliforms. The District Medical Officer reported 38 735 hospital admissions due to diseases from 2020 to 2023. This study investigated the efficacy of Waltheria indica in three forms as a bacteria killing agent from shallow wells in water in the Misungwi District, rural Tanzania. First, the physicochemical and bacteriological parameters from shallow well water were investigated. Second, the efficiency of the Waltheria indica root part as bacteria killing agent was evaluated, and lastly, the phytochemical compounds in the W. indica root parts were investigated. Water samples were collected from 27 shallow wells in nine wards in the study area for physicochemical and bacteriological parameters investigation. Laboratory experiments were conducted using dried W. indica roots in powdered, soaked and boiled forms to evaluate the efficacy of this plant in eliminating E. coli and Total coliforms at varying concentrations and contact times. The study highlighted that the physicochemical parameters pH, EC, TDS and Temperature from shallow wells water were within WHO and TBS standards except turbidity showed high (103.43±34.11 NTU) exceeding the permissible limit. Similarly, E. coli and Total coliformnumbers were high in all tested shallow wells with colonies ranging from 100 ±58 CFU/100 mL to 3400±58 CFU/100 mL and 8567±2117 CFU/100 mL to 22333±5840 CFU/100 mL respectively, exceeding the WHO and TBS standards. Therefore, the results verify that the water of the shallow well in the Misungwi District is contaminated with bacteria and not safe for consumption without treatment. Also, the results demonstrated that W. indica significantly reduced E. coli and Total coliforms, achieving a 100% from water in 12 hours using the concentration of 0.5 g/L and 100 ml/L of powder and soaked extracts at room temperature and incubation at 37oC and 44oC. However, only 100 ml/L of boiled method eliminated Total coliforms to zero at 12 hours. The identified phytochemical compounds in W. indica roots which could be involved with antibacterial properties includes vanillin, Phenols, Neophytadiene, 2,2-Dihydroxychalcone, Squalene, Hexadecanamide, Lupeol, and 9-Octadecanamide (Z). Therefore, the W. indica roots showed promising agent in eliminating bacteria in water and can be recommended for development of sustainable bacteria removal agent from shallow wells water.
Investigation Of Radionuclides In Minjingu Phosphate Rock Beneficiation, Their Uptake By Spinacia Oleracea Upon Fertilizer Application, And Associated Radiological Indices
(NM-AIST, 2025-08) Mankala, James
Phosphate rock processing, vital for phosphorus pentoxide in blended fertilizers, raises radiological concerns due to natural radionuclides. The study investigated natural radionuclides 232Th, 226Ra and 40K in phosphate rock and greenhouse-potted Spinacia oleracea in amended soil with five phosphate fertilizers. The phosphate rock, amended soil and Spinacia oleracea were dried, grounded, sieved and sealed for over twenty-one days. Activity concentrations measured with a germanium detector showed: Phosphate rock had 232Th from 239.83 ± 23. 65 to 856. 96 ± 77.79 Bq/kg, 226Ra from 908.48 ± 84.75 to 4 525.9 ± 406.81 Bq/kg and 40K from 349.7 ± 47.34 to 1384.5 ± 129. 61 Bq/kg. Amended soil showed 232Th from 1.97 ± 0.001 to 114.30 ± 10.79 Bq/kg, 226Ra from 24.89 ± 4.77 to 114.24 ± 9.26 Bq/kg, and 40K from 546.76 ± 51.24 to 2 152.78 ± 182.34 Bq/kg. Spinacia oleracea had 232Th from 1.44 ± 0.001 to 18.21 ± 3.84 Bq/kg, 226Ra from 6.91 ± 3.29 to 110. 12 ± 11. 58 Bq/kg and 40K from 418.45 ± 51.15 to 1 880.1 ± 190.32 Bq/kg. Mean annual doses were 33. 05 msv/y for phosphate rock and 0.849 mSv/y for Spinacia oleracea. The hazard indices for phosphate rock were 8.90 (external) and 15.72 (internal); Spinacia oleracea had 0.504. The radium equivalent was 3 293.73 with a gamma index of 22.31. Results show that activity concentrations of 232Th and 226Ra are below recommended values but exceed control samples. Therefore, regular monitoring of phosphate fertilizer in soil is advised
Development of nano-size doped polyaniline composites for enhanced photocatalytic degradation of selected industrial azo dyes
(NM-AIST, 2025-06) Oyetade,Joshua
The toxic impacts of dye-polluted industrial effluent and the limitations of conventional treatments drive the need for innovative photocatalytic techniques. The study carried out a preliminary evaluation of the current efficiency of treatment plants from selected textile industries. It also fabricated, characterized and tested the performance of the photocatalysts for the remediation of dye-polluted effluent while mediating the process with a Fenton-like reagent (FeCl3 and H2O2). The preliminary treatment plant performance reported that the corresponding effluent consists of a high amount of NH3, phosphorus and NH3-N, Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD) above the set limits. The first industry (Morogoro) examined, revealed a colour value of 4042.67 ± 1.76 which was reduced to 1800 ± 0.00 after the filtration treatment technique. Likewise, an initial colour value of 2051.00 ± 0.58 was reported in another industry (Arusha) which later was quantified as 237.33 ± 0.67 after treatment with the activated carbon system. The instrumental characterization of the acid and alkali-treated TiO2 and the fabricatednanocomposite photocatalysts indicated that their respective adsorption-desorption isotherms are of type IV. This illustrates mesoporous materials similar to all the nanocomposites having an amorphous diffraction pattern while the metal oxide (TiO2) exhibited a crystalline diffraction pattern. The surface functionality revealed the functional group features of Ti-O-Ti bonding for the metal oxides. Thereafter, the nanocomposites exhibited the features of polyaniline blended with TiO2 (P-AKT) and polyaniline blended with graphene oxide, magnetite and silver nanoparticle from the in situ reduction of silver nitrate (PANI-GFA), respectively. The study revealed that TiO2 treated with 3 M NaOH showed the highest degradation efficiency of 89.15% after 90 minutes using 18 W UV light-emitting diode photon irradiation. The first fabricated nanocomposite (PAKT) had 94% efficiency and significant reusability up to the 4th cycle while the second fabricated nanocomposite (PANI-GFA) had 95% and high reusability potential up to the 6th run. This value was established optimal conditions of 20 mg dosage, pH of 5 and at 90 mins irradiation time using 100 mL dye polluted effluent. The optimization studies suggested a quadratic model with good correlation and reliability and the variables were statistically significant (p-values < 0.0001). Also, the PANI-GFA test demonstrated high efficiency in treating four real industrial effluents with azo dyes.
Natural Antioxidants For Biodiesel Stability: Predictive Modeling, Kinetics, And Economic Feasibility Of Uapaca Kirkiana Extracts
(NM-AIST, 2025-07) Kahimbi, Henry
Biodiesel, a renewable alternative fuel, is susceptible to oxidative degradation, impacting its performance, stability and shelf life. Traditional methods for optimizing antioxidant dosage have relied heavily on trial and error, leading to inconsistent results and increased costs. This study addresses these challenges by integrating experimental analysis with predictive modeling to evaluate and optimize the use of natural antioxidants extracted from Uapaca kirkiana fruit peels, pulp, stem barks, leaves and root bark. The research primarily focuses on enhancing oxidative stability during storage, where degradation is most likely to begin. Antioxidant potential was assessed through total phenolic content using the Folin–Ciocalteu method and antioxidant activity via 2,2-Diphenyl-1-picrylhydrazyl radical scavenging assays. A predictive model was developed in R software to estimate the optimal antioxidant dosage, using biodiesel's physical-chemical properties as predictors. Storage conditions such as temperature, light and oxygen exposure were standardized to isolate the effects of antioxidant concentration and biodiesel composition. Reaction kinetics were studied to understand antioxidant behavior and degradation pathways. Techno-economic analysis using Aspen Plus® V10 compared the cost-effectiveness of natural and synthetic antioxidants. Results showed that natural antioxidants particularly from fruit peels significantly improved biodiesel stability. Induction periods achieved were 23.9 hours for palm kernel, 21.6 for waste cooking oil, 14.6 for croton, 14.4 for jatropha, and 13.8 for neem seed, all exceeding the 8-hour minimum required by both EN 14112 and ASTM D6751 standards. Predictive model validation with seven biodiesel samples showed close agreement between theoretical and experimental induction periods, with mean absolute percentage errors between 1.69% and 2.44%. Kinetic analysis confirmed that natural antioxidants reduced oxidation rates, with activation energies of 81.39 kJ/mol (fruit peels), 77.73 kJ/mol (pulp), and 63.85 kJ/mol (root bark). The techno-economic analysis demonstrated that natural antioxidants especially from Uapaca kirkiana were not only more effective but also more economically viable, offering shorter payback periods (3.8–12 years) and higher internal rate of returns. In contrast, synthetic antioxidants like BHT and BHA showed negative net present values and longer payback times (11.7–17.8 years). These findings support the use of natural antioxidants as practical, eco-friendly alternatives to synthetic ones in enhancing fuel stability
Synthesis of High-Strength and Durable Metakaolin-Based Geopolymer Cured at Ambient Temperature
(NM-AIST, 2025-08) Hamisi, Hashimu
This study aimed to synthesize high-strength and durable metakaolin-based geopolymers cured at ambient temperature, with a focus on enhancing the pozzolanic reactivity of metakaolin. It employed Taguchi design methods to optimize the compressive strength. The growing need for environmentally friendly building materials has sparked interest in geopolymers, which offer a viable substitute for conventional cement-based systems. Metakaolin, a pozzolanic material that results from kaolin clay, significantly enhances the mechanical properties and durability of geopolymers, making it an ideal candidate for this application. Using The Response Surface Methodology under the Box-Behnken Design, the study systematically examined the effects of several key parameters, including calcination temperature (650-850°C), heating rate (1-19°C/min), and soaking time (1-12 h), revealing that a temperature of 765°C at a rate 10°C/min and soaking time of 6.46 h yields the most reactive Metakaolin, characterized by high pozzolanic reactivity and optimized particle morphology both critical factors for effective polymerization. In achieving maximum compressive strength, the Taguchi method was applied, facilitating a structured approach to assess the influence of multiple variables: The concentration of sodium hydroxide solution (NaOH: 8-12M), the ratio of the Na2SiO3 to NaOH (SS/SH-1.5-2.5), and the solution to binder ratio (S/B-0, 6-1.0) on the mechanical-properties of the resultant geopolymers. The findings indicate that the optimal formulation achieved compressive strengths exceeding 70 MPa at 12M NaOH, 2.5 SS/SH, and a solution-to-binder ratio of 0.80. This significant improvement is attributed to the synergistic effects of the highly reactive Metakaolin and the strategic optimization of mixing ingredients. The strategic incorporation of RHA enhances compressive strength and improves durability, as evidenced by the geopolymers’ strong resistance to rapid chloride permeability and acidic environments. Experimental results demonstrated minimal degradation in aggressive environments, underscoring the materials’ suitability for diverse construction applications. A dense, homogenous matrix necessary for the geopolymers' mechanical integrity was proven by microstructural investigation using methods including X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The development of extra binding phases through pozzolanic interactions between Rice Husk Ash and Metakaolin enhanced the composite material's overall performance.
Thermal Performance and Techno-Economic Analysis of Solar-Biogas Hybrid Dryer for Drying Agricultural Products
(NM-AIST, 2025-07) Mgaya, Gelion
Traditional drying methods, such as solar and fossil fuel-based mechanical drying, are widely used for agricultural products. However, these methods often yield low-quality dried products, which negatively impact market value and consumer satisfaction. Hybrid solar drying technology offers an alternative by enhancing drying efficiency and improving product quality. Despite growing interest in Hybrid solar drying technology, Sub-Saharan Africa lacks experimental studies on biogas-supplemented solar dryers. In addition, while a considerable body of literature addresses the use of biogas for heating in drying applications, only a few studies have explored its potential as a supplemental energy source for solar drying systems.Therefore, this study evaluates the thermal performance and techno-economic feasibility of a solar-biogas hybrid dryer designed to maintain stable drying conditions by supplementing solar energy with biogas during low solar irradiance. Drying experiments using 100 grams of lemongrass were conducted to compare the hybrid dryer with traditional open sun drying. After four hours, the tray samples in the hybrid dryer had lost 75% of their initial moisture, resulting in a 28% reduction in drying time compared to open sun drying. The hybrid dryer showed an average drying rate of 0.31% min⁻¹, compared to 0.27% min⁻¹ for open sun. Ambient conditions averaged a temperature of 31.04°C and a relative humidity of 47.36%. Inlet temperatures for trays 1, 2 and 3 were 53.7°C, 55.96°C and 55.73°C, respectively. The system achieved a thermal efficiency of 34.2% and an average exergy of 0.26 kJ/kg. Quality analysis revealed improved nutrient content, with hybrid-dried lemongrass containing 42.2% carbohydrates, compared to 40.5% in open-sun samples and 10.3% in fresh samples. Potassium and phosphorus were well retained, while copper levels were 1.63 mg/100 g and 1.13 mg/100 g for hybrid and open sun samples, respectively. A techno-economic analysis revealed a 2.3-g year payback period and a 43% return on investment, highlighting the viability of biogas assisted hybrid systems for sustainable agricultural drying
Development and Performance Evaluation of a Solar Dryer Integrated with Thermal Energy Storage Materials for Drying Agricultural Products
(NM-AIST, 2025-03) Rulazi, Evordius
Passive solar dryers are essential in reducing post-harvest losses of vegetable and fruits particularly in developing countries in Africa. Most simple passive solar dryers are being developed in developing countries, but the challenge is the sporadic nature of solar energy, resulting in reduced performance and rendering them ineffective during periods without sunlight. In addition, Techno-economic analysis (TEA) and Life cycle assessment (LCA) have been neglected in most of the studies on solar dryers (SD). In this study, a novel solar dryer incorporating soapstone as a thermal energy storage (TES) system to prolong the drying time was designed, constructed, and evaluated for its performance in terms of TEA and LCA. Experiments were carried out to compare the performance of the developed dryer in two configurations: With and without thermal energy storage (TES) materials. The results were evaluated alongside open-sun drying (OSD) with 50 kg of fresh carrots as well as fresh pineapples on separate occasions. The drying durations were recorded as 12 hours for the dryer with TES, 23 hours for the dryer without TES, and 50 hours for OSD. Notably, the TES integrated dryer could provide energy for approximately 3–4 hours after sunset. The dryer was found to have a thermal efficiency of 45%, a collector efficiency of 43%, and a storage efficiency of 74.5%. The dryer combined with TES materials proved to be more efficient in retaining nutrients in the dried products compared to the dryer without TES materials and OSD based on proximate study. The economic analysis showed that the annual savings for the dryer's 20 years of operation are $ 9814.5 for pineapple and $ 9121.2 for carrots. The cumulative present worth was $ 62 232.7 for pineapples and $ 57 836.3 for carrots. It was found that the pineapples payback period was 1.5 years, whereas for carrots payback was 1.6 years. The LCA revealed that steel materials had higher environmental impact items in material extraction and fabrication compared to aluminum materials for both the midpoint and endpoint categories. Based on techno-economic TEA and LCA assessments, the fabricated solar dryer is economically feasible and environmentally friendly. Solar dryers incorporating soapstone have demonstrated potential as efficient technology for minimizing post-harvest losses especially in developing countries in Africa.
Mesoporous Carbon Derived from Hermetia illucens Pupae Casings and Biogas Slurry for Cadmium Removal from Water by Capacitive Deionization Method
(NM-AIST, 2025-06) Panja, Eva
This study examined capacitive deionization’s effectiveness for recovering Cd2+ from water using novel carbon-based electrodes derived from Hermetia illucens pupae casings (PC) and biogas slurry (BG). Activated carbon (AC) was produced through carbonization at 500°C and chemical activation (KOH) at 700°C. The Brunauer-Emmett-Teller method, Scanning Electron Microscope, X-ray diffractometer, Fourier transform infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, and contact angle measurements were performed on AC. Electrochemical impedance spectroscopy and cyclic voltammetry were used to test the electrochemical properties of carbons. The PC-derived carbon (PC-2-700) had a specific surface area of 640 m²/g, while the BG-derived carbon (BG-2-700) showed a higher 927 m²/g. PC-2-700 exhibited a higher specific capacitance (271.9 Fg⁻¹) compared to BG-2-700 (105.8 Fg⁻¹), indicating better charge storage performance. The CDI cell containing the working electrodes in 5 and 10 mg/L Cd2+ solution was used for Cd2+ removal. The PC-2-700 electrode achieved 91 % removal efficiency (10.9 mg/g capacity) in 5 mg/L Cd²⁺ solutions, outperforming BG-3-700 electrode (60% efficiency, 2.3 mg/g). Moreover, PC-2-700 also demonstrated better charge and energy efficiency, consuming only 0.65 and 0.07 kWhm-3versus BG-2-700’s 0.24 and 0.93 kWhm-3at 5 mg/L concentration, respectively. The enhanced performance of PC-2-700 was due to its better capacitance, specific surface area, and porous structure on the surface. This study showed potential electrodes can be designed from pupae casings to remove heavy metals from water.
Investigation of the Potential of Wild Lettuce for the Biosynthesis of Silver-Zinc Oxide Nanocomposites as Antimicrobial Agents for Water Treatment
(NM-AIST, 2025-05) Makauki, Elizabeth
Silver-zinc oxide nanocomposites (Ag-ZnO NCs) are highly effective antimicrobial agents for point-of-use water treatment. However, chemically synthesized Ag-ZnO NCs pose potential health risks due to the use of toxic and carcinogenic chemicals as reducing and stabilizing agents raising a concern for the use of safe, non-toxic, readily available, and non-carcinogenic biochemicals. This study explored the potential of wild lettuce as a natural source of biochemicals that can serve as safe and eco-friendly reducing and stabilizing agents for the biosynthesis of Ag-ZnO NCs. The study further investigated the use of water hyacinth activated carbon (AC) as a potential impregnation precursor for the biosynthesized Ag-ZnO NCs and evaluated their antimicrobial efficacy. The biochemicals were extracted using 0, 50 and 100% ethanolic solvents (EtOH) in different extraction circles and volumes. The wild lettuce leaf extracts were used to biosynthesize Ag-ZnO NCs and eventually were impregnated in the AC. The antimicrobial activity was performed using ager plate and the water treatment was analysed using synthetic and natural water in a batch reaction. The FTIR results confirmed the presence of alkaloids, flavonoids, tannins, saponins, and proteins which are essential for the biosynthesis process. Phytochemical analysis confirmed the presence of high amounts of biochemicals in wild lettuce leaves. Total phenolic and antioxidant contents of the leaf extract followed the trend 100<0<50% EtOH with the highest yield of about 11 044 ± 63 and 44 112 ± 894 µg/g, respectively (p<0.05). The XRD analysis of Ag-ZnO NCs confirmed their crystalline nature with an average particle size of 21.51 nm. The SEM and TEM images confirmed formation of spherical shaped nanocomposites with a successful doping of Ag into ZnO. It further confirmed a successful impregnation of Ag-ZnO into AC. The BET results of Ag-ZnO-AC indicated an increase of surface area with activation creating more surface for the Ag-ZnO attachment. The antibacterial activity of Ag-ZnO NCs indicated high microbial inhibition on E. coli (21 ± 1.08 mm) and S. aureus (19.67 ± 0.47 mm). The Ag-ZnO-AC had significant antimicrobial activities against E. coli (14.00 ± 0.37 mm) and S. aureus (17.33 ± 0.36 mm). The water treatment analysis of Ag-ZnO-AC indicated complete microbial elimination on synthetic (2 h) and natural water (1 h). These results confirm wild lettuce as a potential natural source of biochemicals for the biosynthesis of Ag-ZnO NCs and water hyacinth as a potential impregnation material due to its high porosity and high surface area
Ammonium removal from water using flow capacitive deionization with MgO-modified biochar derived from orange peels
(Elsevier B.V., 2025-08-14) Mwalusambo, Gabriel ; Jande, Yusufu ; Elisadiki, Joyce ; Son,Moon ; Alfredy, Tusekile
Ammonium (NH+4 ) in water presents substantial environmental challenges, such as eutrophication and toxicity that necessitate effective removal strategies. This study developed flow electrodes using biochar obtained from orange peels for the removal of NH+4 from water through flow capacitive deionization (FCDI). The biochar was prepared through carbonization and modification with MgO at varying ratios using the co-precipitation method. The modified biochar exhibited highhydrophilicity and demonstrated a specific capacitance of 238 F g− 1.The FCDI process was optimized at an applied voltage of 1.2 V, an electrode flow rate of 10 mL min− 1 and a 2.5 wt% carbon content in the flow electrode. The modified flow electrodes showed effective performance, attaining an average NH+4 removal rate of 17.3 mg m− 2 min− 1, removal efficiency of 86.7 % and retention of 91.3 % after 30 cycles. Notably, the modified MgO flow electrode resulted in approximately 62 % reduction in energy con sumption during electrosorption compared to pristine biochar, indicating advantages emanating from reduced solution and charge transfer resistances. Experiments with simulated municipal wastewater confirmed the modified electrode's superior ability, consistent stability over multiple cycles, and selectivity in NH+4 removal. This study highlights the efficacy of the developed flow electrodes for FCDI systems, offering a straightforward electrode synthesis method and effective NH+4 removal
Evaluation of rectal radiation dose during intracavitary brachytherapy for uterine cervical cancer using in vivo dosimetry.
(NM-AIST, 2025-04) Moses,Omega
High-dose-rate intracavitary brachytherapy is a crucial part of cervical cancer treatment, delivering high doses to the tumor while minimizing exposure to normal tissues. However, improper administration can lead to radiation-induced damage. In vivo dosimetry is essential for verifying that the planned treatment dose matches the radiation delivered doses. This study utilized Thermoluminescent dosimeters (TLDs) to measure the radiation dose delivered to the rectum in two patient groups: one with first fraction-based planning (FFP) and the other with each fraction planned individually (EFP). Applicator and probe positions from the treatment planning system (TPS) were used to assess the shift between treatment fractions. The median dose measured by TLDs (3.85 Gy, IQR = 2.23) exceeded the planned dose by TPS (3.37 Gy, IQR = 1.54), with a p-value < 0.001. The interquartile range (IQR) of dose difference was higher in the second fraction, 1.92 Gy, in the FFP group, and the dose differences between the first and second fractions were not statistically significantly different for either group. The applicator position shows a minimal shift between the first and second fraction compared to a rectal probe. Generally, it is best practice to plan each fraction independently to minimize potential risks. In scenarios such as when patients are transferred from a brachytherapy couch to a stretcher, separate imaging and planning each fraction is not necessary.
Performance evaluation of sodium super ionic conductors for enhanced brackish water desalination by capacitive deionization.
(NM-AIST, 2025-07) Sufiani,Omari
This study reports on the synthesis, characterization and application of sodium superionic conductors for water desalination by Capacitive deionization (CDI).The Sodium super ionic conductors (NASICONs) outperform carbon-based adsorbents and most battery electrodes due to their 3D bulk ion storage, exceptional ionic conductivity and strong structural stability.Variable synthesis conditions were applied namely the number of sulphate ions substituted for phosphates in Na3Fe2(PO4)3 (NFP) and mass ratios of activated carbon (AC)/NFP to prepare NaFe2PO4(SO4)2/C (NFPS/C) and AC/NFP composites respectively. Several characterization techniques such as X-ray diffraction, scanning electron microscopy, Transmission electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption-desorption measurements and X-ray photoelectron spectroscope confirmed the synthesized materials. Characterization results show that the N2 adsorption-desorption isotherms of AC/NFP composite is of type III, suggesting slit shaped pores due to accumulation of flake shaped particles. The X-ray diffraction analysis revealed NFPS/C to exhibit orthorhombic structure while AC/NFP had monoclinic crystal system. The scanning electron micrographs revealed the particles of both NFPS/C and AC/NFP composite less aggregated. Due to less aggregated particles of NFPS/C observed in SEM micrographs it was used in CDI wherein, the salt removal capacity increases with the solution concentration, desalination duration and applied potential. Further, experiments involved desalination of Indian Ocean water solutions diluted several times to achieve the concentration of solution resembling permeates produced by seawater reverse osmosis (SWRO) which is attained by water samples diluted one hundred times (487 µS/cm). The salt removal capacity for desalination of Indian Ocean water samples not diluted and diluted hundred times was about 27.3 and 10.6 mg/g, respectively. Further CDI tests involved comparing the salt removal capacity of the AC and AC/NFP composites wherein, much higher performance of around 22.0 was attained by AC/NFP 1:2 against 18.65 mg/g of AC. The improved performance of AC/NFP 1:2 composite might be due to its high specific surface area and the enhanced interfacial contact between the composite and the salt solution. These results demonstrate that NASICONs present a viable strategy for improving desalination efficiency of a CDI system.
Theoretical study of the complex molecules derived from natural dyes for dye-sensitized solar cells applications
(NM-AIST, 2025-07) Malashi,Nyanda
Dye-sensitized solar cells (DSSCs) are promising third-generation photovoltaic cell technology due to their easy fabrication and environmental friendliness. In DSSCs, a photosensitizer is crucial for photon absorption, and electron transfer. Natural pigments are investigated as photosensitizers in DSSCs due to their abundance and environmental friendliness. However, their narrow solar spectrum absorption and weak bonding with the semiconductor limit their wide application, necessitating the design of novel photosensitizers. This work focuses on the theoretical design of Braz-Bd-ether, Braze-Bd-ether, Aliz-Bd-ether, Braz-Bd-oxane, Aliz-Bdoxane, Quinaliz-Bd- oxane molecules via etherification and bi-etherification reactions. Moreover, Braz 01, Braz 01b, Braz 01t, Braz 01tb, Braz 02, Braz 02b, Braz 02t and Braz 02tb molecules were obtained from the chemical structure modification of brazilin dye. The photoelectrical, optoelectronic and structural properties of the isolated dye, dye@(TiO2)9H4 and dye@I2, were examined using DFT and TD-DFT methods. The DSSCs’ performance was simulated using TiberCAD software. The results reveal that Braz-Bd-oxane, Braze-Bd-ether, Aliz-Bd-ether, Aliz-Bd-oxane and Quinaliz-Bd-oxane complexes exhibited improved nonlinear optical properties (NLO), reduced energy gap, lower exciton binding energy (Eb), lower total reorganization energy (λt), and red-shifted absorption spectra by 10.29 nm ‒ 54.83 nm regarding betanidin dye. The frontier molecular orbital (FMO) plots, ∆Ginj (-0.248 ‒ -0.453 eV), ΔGreg, and energy level alignment plots indicate that all designed complex dyes inject electrons into TiO2 and are regenerated by I‒/I3‒ redox electrolyte, satisfying the photosensitizer requirement. For Braz 01-Braz 02tb, are predicted to have improved charge transfer due to reduced λtotal (0.951 eV ‒ 0.528 eV), increased EA (1.021 ‒ 3.472 eV), and decreased IP (5.5915.252 eV). Additionally, the designed dyes (Braz01‒Braz02 tb) exhibited high current density and minimal charge recombination compared to the brazilin dye, attributed to their redshifted absorption spectra, reduced Eg (5.074‒2.46 eV) and Eb (0.591‒0.137 eV).Negative Eads for the dyes@(TiO2)9H4 and dye@I2 were noticed for all dyes, signifying spontaneous chemisorption adsorption. Moreover, the 1D-DSSCs sensitized with designed complex dyes exhibit greater power conversion efficiency (PCE) than natural dyes forming these complexes. Aliz-Bd-oxane and Braz-Bd-oxane exhibited higher PCEs of 14.78% and 14.74% among the designed complexes. Also, Braz 01-Braz 02tb demonstrated higher PCE than brazilin dye. The 1D DSSC-Braz 01tb dye has the highest PCE of 13.44%. Therefore, the designed molecules BrazBd-oxane, Aliz-Bd-oxane, Braze-Bd-ether, and Braz 01tb are better photosensitizers in DSSC.
Techno-economic analysis and life cycle assessment of locally made solar-powered cooler for storage of vaccine and perishable food stuff
(NM-AIST, 2025-06) Mbugano, Milton
Storage of vaccines and perishable food in regions without access to the national grid electricity presents ongoing challenges, especially in remote regions. Solar-powered system offers a reliable and sustainable alternative. This study presents a techno-economic analysis (TEA) and life cycle assessment (LCA) of a locally developed solar-powered cooler designed for such conditions. The cooler serves as a lower-cost alternative to conventional electric-powered refrigeration units, especially where grid access is unreliable or unavailable. The analysis was performed using ReCiPe2016 midpoint indicators with SimaPro software and Microsoft Excel 2019 to assess both environmental and economic factors. Results from the LCA show that battery production contributes the most toenvironmental impacts, followed by solar panel. Terrestrial ecotoxicity was the highest environmental concern, with human non-carcinogenic toxicity also notable. The TEA indicates strong economic performance, with an initial investment of USD 2682, a payback period of one year, and a return on investment of 98.8%. These results support the cooler’s potential for use in off-grid health and food supply chains. These quantitative analyses provide valuable insights for decision-makers, aiding in understanding both economic aspects and environmental impacts throughout the life cycle of locally manufactured solar-powered coolers, thereby enhancing their sustainability.
Betalain-based dyes as photosensitizers for energy harvesting application: a theoretical investigation
(NM-AIST, 2025-07) Tsere,Melkizedeck
Betalain dyes are natural pigments that have attracted growing research interest as promising materials for light-harvesting applications. In the present work, the modification of betalain dyes was performed through a computational approach, aimed at screening the wide spread of blended triphenylamine-betalain dyes for dye sensitized solar cell applications. In the first modification approach, betalamic acid was joined to the phenyl ring and further grafted with electron donor groups to enhance light absorption and charge transfer ability. The second approach involved the introduction of new anchoring groups featuring carboxylic acid CH=C(X)COOH for the A1-X dyes and nitro group -CH=C(X)NO2 for the A2-X dyes, where X = CN, CH3, CCl3, CF3. In addition to molecular grafting, the solvent effects on the optoelectronic parameters and dye adsorption to the semiconductor surface were evaluated. The geometrical structures, optoelectronic properties of designed dyes and binding to the semiconductor have been explored. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods coupled with B3LYP and CAM-B3LYP at 631+G(d,p) basis set were used for ground and excited state calculations, respectively. In the UV-Vis spectra, the maximum absorption wavelengths range between 400 ‒ 442 nm based on grafting with an electron donor. However, further modifications by introducing new anchoring units resulted in huge redshifts in wavelengths: 400 ‒ 700 nm for CH=C(X)COOH and between 500 and 1000 nm for the -CH=C(X)NO2. The attachment of the dyes to the semiconductor was modelled via binding to (TiO2)6H3 cluster; A2-X dyes exhibited more stable Dye@TiO2 complexes with binding energies (BEs) ranging between ‒4.08 and ‒2.88 eV compared to A1X dyes with BEs from ‒1.11 to ‒0.05 eV in water solution. The results evince that the blended triphenyl-betalain dyes with the CH=C(X)NO2 anchoring groups could be promising materials for light harvesting applications. Among the CH=C(X)NO2 dyes, the CH=C(CN)NO2 demonstrated superior optoelectronic properties and binding stability, thus, would be expected the most favourable candidate for light-harvesting applications in dye sensitized solar cells.
Valorization Potential Of Minjingu Tailings For Re Covery Of Phosphate Fertilizer And Their Environmen Tal Impacts
(NM-AIST, 2024-12) Mdachi, Daniel
Sedimentary and igneous rocks are the two principal sources of phosphate that are extracted and processed into fertilizer. Phosphate is lost into the tailings during the beneficiation process. The extraction and processing of phosphate rock generate substantial waste, including overbur den or mining waste and phosphate tailings (PTs) from the beneficiation process. The extraction and processing of phosphate rock may release radionuclides and heavy metals into the environ ment, which are harmful to living organisms. In order to accomplish this study, first was to evaluate the amount of phosphate in the tailings for possible recovery of the phosphate fertilizer. Second was to determine the concentration of the selected heavy metals and radioactive ele ments in the tailings. Energy-dispersive X-ray fluorescence spectrometry (ED XRF) was used to quantify the concentrations of the chemical composition of tailings for phosphate fertilizer and heavy metals while radionuclide concentrations were determined using a High Pure Garmin Energy detector (HPGe). It was found that the phosphate content in PTs varied from 12.91% of P2O5 (Tailings Dump 2) to 19.61% of P2O5 (Tailings Dump 1). The heavy metal concentrations that were examined were as follows: Cu (12.9 – 27.3) mg.kg-1, Fe (7944.2 – 19052.2) mg.kg-1, Mn (410.9 – 474) mg.kg-1, Ni (1.9 – 13.2) mg.kg-1, Al (3597 – 13129.2) mg.kg-1, Zn (195.2 – 281.7) mg.kg-1, Pb (0.7 –4.5) mg.kg-1, and As (2.7 – 11.3) mg.kg-1. However, the concen tration of radionuclides 226Ra, 232Th, and 40K ranged from 311 to 7606 Bqkg-1, 207 to 654 Bqkg-1, and 131 to 762 Bqkg-1, respectively. This study revealed that Minjingu PTs contain an amount of phosphate that may be recovered for commercial applications. The concentration of heavy metals (Cu, Fe, Ni, As, and Pb) are below the World Health Organization (WHO) permissible levels except for Zn which were above the permissible limit. The concentrations of radionu clides were found to be higher compared to the recommended world value. From the results obtained in this study, further research is recommended at the Minjingu mines to identify the optimal beneficiation methods for the recovery of phosphate from tailings.
Water Desalination By Capacitive Deionization Using Electrospun Micro-Mesoporous Ultrafine Carbon Fibres
(NM-AIST, 2024-08) Tarus, Bethwel
Capacitive deionization is a promising method for desalination of low-to-moderate salinity water. Electrode pore structure is an important factor influencing performance in this technology. For the majority of carbon materials including ultrafine carbon fibres used as electrodes for capacitive deionization, excessive microporosity has hampered optimal performance. In this study, mesoporous ultrafine carbon fibres (277–700 nm diameters) were fabricated from polyacrylonitrile blended with cellulose acetate or terephthalic acid through electrospinning and carbonization for use as capacitive deionization electrodes. Fibre surface and pore attributes were adjusted by varying the proportions of the blended polymers while ensuring no adverse change in their tangible attributes. Fibre structure was further modified by embedding or hydrothermally coating MoS2 nanoparticles to enhance desalination performance through faradaic means. The produced blend-based fibres attained a specific surface area of 925.47 m2/g and a pore volume of 0.7884 cm3/g. Electrochemical tests revealed increasing specific capacitance and reducing charge transfer resistance with increase in surface area and mesopore volume. For MoS2-loaded fibres, hydrothermally-grown MoS2 yielded enhanced charge transfer and higher diffusion-controlled capacitance than the embedded MoS2. Desalination performance was evaluated under various configurations including conventional setup, single and multi-channel asymmetric cells, and multi-channel battery deionization setups. A specific adsorption capacity of 8.03 mg/g was achieved in the plainltrafine carbon fibres using 20 mM NaCl in batch mode at 1.2 V. The highest specific adsorption capacity attained was 32.11 mg/g using 20 mM NaCl in a four-channel battery deionization cell at ±0.8 V. In energy utilization, the MoS2-coated ultrafine carbon fibres when used in a battery deionization cell demonstrated over 3.7 times higher thermodynamic energy efficiency than in the asymmetric setups and 50 times higher than in conventional setups, while maintaining consistent desalination performance. The electrodes in the battery deionizationcells benefited from the coupled effects of electrosorption/intercalation and ion exchange membranes in symmetric conformation to effectively utilize charge. These findings promote the use of cellulose acetate and terephthalic acid as excellent pore templates in mesoporous ultrafine carbon fibre fabrication for capacitive deionization and provide insight into process engineering for improved electrochemical desalination and enhancement in ion intercalation based desalination configurations.
Impacts Of Land Use And Land Cover Change On Urban Heat Islands: A Case Study Of Babati Municipality - Tanzania
(NM-AIST, 2025-06) Majula, Atugonza
To improve living conditions, human development alters natural landscapes, impacting Land Surface Temperature (LST) and contributing to global climate change. Investigating how Land Use Land Cover (LULC) changes influence the Urban Heat Island (UHI) effect is crucial as cities expand and LULC transformations intensify.With urban populations projected to double by 2050, cities are expected to contribute to global warming, trap pollutants, and consume vast energy for cooling. This study assessed LULC changes in Babati from 2002 to 2022 and analyzed their impact on LST using remote sensing techniques. The LULC classification was performed using a maximum likelihood algorithm, while LST retrieval applied computational formulas based on Red (R), Near Infrared (NIR), and Thermal Infrared (TIR) bands. Results showed a rise in built-up areas from 1.2% to 3.8% over 20 years, leading to suburbanization at the expense of farmland and bare land. The conversion of natural areas into urban and agricultural land increased average LST by 0.7°C, with some agricultural hotspots reaching up to 20°C higher than vegetated areas due to exposed dark loam soils during the dry season. While vegetation and water bodies played a crucial role in cooling, agricultural lands emerged as significant contributors to UHI. Given the positive correlation between agricultural lands and UHI, there is a need to adopt sustainable farming practices and improve urban planning strategies. These insights can guide the sustainable development of Babati Municipality and other rapidly growing towns with similar environmental settings.

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