National Repository :: Browsing by Author "Kibet, Joshua K."

Browsing by Author "Kibet, Joshua K."

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A Review of Toxic Metals and Hazardous Organics in Wood Treatment Sites and Their Etiological Implications
(Journal of Chemical Reviews, 2022-02-07) Miranji, Edwin K.; Kipkemboi, Pius K.; Kibet, Joshua K.
Increased natural and human activities over the last century have led to excess levels of inorganic and organic pollutants into the environment and natural ecosystems. This review critically examines heavy metal and organic pollutants' role in wood treatment sites and their etiological consequences. These pollutants are not only recalcitrant but also tenacious to degradation under ordinary conditions. Although some heavy metals are essential to human health, they are toxic at elevated concentrations. Heavy metals feature carcinogenic properties and cause serious health risks to live systems and the environment because of their bio-accumulative, non-degenerative, and refractory characteristics. On the other hand, organic pollutants are readily introduced into the ecosystem from irresponsible use of detergents, volatile organic compounds, paints, pesticides, and wood preservatives. During the wood treatment process, various chemicals are used to enhance durability. Nevertheless, the use of wood preservatives such as chromated copper arsenate (CCA) and pentachlorophenol (PCP) potentially induces pollutants considered detrimental to human health and the ecological environment. Remediation of wood treatment sites using phytomanagement strategies and nanotechnologies has been presented in this review. Therefore, some challenges and recommendations for further research and applications are herein presented.
Dioxin and dibenzofuran like molecular analogues from the pyrolysis of biomass materials—the emerging challenge in bio-oil production
(BMC Chemistry, 2021-01-15) Kirkok, Samuel K.; Kibet, Joshua K.; Kinyanjui, Thomas; Okanga, Francis I.; Nyamori, Vincent O.
Introduction The aggressive search for renewable energy resources and essential pyrosynthetic compounds has marked an exponential rise in the thermal degradation of biomass materials. Consequently, clean and sustainable transport fuels are increasingly desirable in a highly industrialized economy, for energy security and environmental protection. For this reason, biomass materials have been identified as promising alternatives to fossil fuels despite the challenges resulting from the possible formation of toxic nitrogen-based molecules during biomass degradation. In order to understand the free radical characteristic challenges facing the use of bio-oil, a brief review of the effects of free radicals in bio-oil is presented. Methodology Pyrolysis was conducted in a tubular flow quartz reactor at a residence time of 2 s at 1 atm. pressure, for a total pyrolysis time of 5 min. The thermal degradation of biomass components was investigated over the temperature range of 200 to 700 °C typically in 50 °C increments under two reaction conditions; pyrolysis in N2 and oxidative pyrolysis in 5% O2 in N2. The pyrolysate effluent was analysed using a Gas chromatograph hyphenated to a mass selective detector (MSD). Results The yield of levoglucosan in the pyrolysis of cellulose in the entire pyrolysis temperature range was 68.2 wt % under inert conditions and 28.8 wt % under oxidative conditions. On the other hand, formaldehyde from pyrolysis of cellulose yielded 4 wt % while that from oxidative pyrolysis was 7 wt % translating to ⁓ 1.8 times higher than the yield from pyrolysis. Accordingly, we present for the first time dioxin-like and dibenzofuran-like nitrogenated analogues from an equimassic pyrolysis of cellulose and tyrosine. Levoglucosan and formaldehyde were completely inhibited during the equimassic pyrolysis of cellulose and tyrosine. Conclusion Clearly, any small amounts of N-biomass components such as amino acids in cellulosic biomass materials can inhibit the formation of levoglucosan–a major constituent of bio-oil. Overall, a judicious balance between the production of bio-oil and side products resulting from amino acids present in plant matter should be taken into account to minimize economic losses and mitigate against negative public health concerns.
Free radicals and ultrafine particulate emissions from the co-pyrolysis of Croton megalocarpus biodiesel and fossil diesel
(Springer Nature, 2018-08-07) Kibet, Joshua K.; Mosonik, Bornes C.; Nyamori, Vincent O.; Ngari, Silas M.
BackgroundThe atmosphere has become a major transport corridor for free radicals and particulate matter from combustion events. The motivation behind this study was to determine the nature of particulate emissions and surface bound radicals formed during the thermal degradation of diesel blends in order to assess the health and environmental hazards of binary transport fuels.MethodologyAccordingly, this contribution explored the interactions that occur when Croton megalocarpus biodiesel and fossil diesel in the ratio of 1:1 by weight were co-pyrolyzed in a quartz reactor at a residence time of 0.5 s under an inert flow of nitrogen at 600 °C. The surface morphology of the thermal char formed were imaged using a Feld emission gun scanning electron microscope (FEG SEM) while Electron paramagnetic resonance spectrometer (EPR) was used to explore the presence of free radicals on the surface of thermal char. Molecular functional groups adsorbed on the surface of thermal char were explored using Fourier transform infrared spectroscopy (FTIR).ResultsFTIR spectrum showed that the major functional groups on the surface of the char were basically aromatic and some methylene groups. The particulate emissions detected in this work were ultrafine (~ 32 nm). The particulates are consistent with the SEM images observed in this study. Electron paramagnetic resonance results gave a g-value of 2.0027 characteristic of carbon-based radicals of aromatic nature. Spectral peak-to-peak width (∆Hp-p) obtained was narrow (4.42 G).ConclusionsThe free radicals identified as carbon-based are medically notorious and may be transported by various sizes of particulate matter on to the surface of the human lung which may trigger cancer and pulmonary diseases. The nanoparticulates determined in this work can precipitate severe biological health problems among humans and other natural ecosystems.
Optimization of Binary Mixtures of Biodiesel and Fossil Diesel for Clean Energy Combustion
(Springer Nature, 2019-05-31) Mosonik, Bornes C.; Kibet, Joshua K.; Ngari, Silas M.
There is an urgent interest initiated to develop clean energy resources with the aim of reducing exposure to environmental pollutants and explore model fuels that can hasten the achievement of clean energy combustion. This work investigates various ratios of biodiesel and commercial diesel in order to propose model binary fuels for clean energy combustion. Accordingly, diesel blends of ratios 1:1, 3:2 and 2:3 were each pyrolyzed at a contact time of 5 s in a quartz reactor at 1 atmosphere pressure. A model temperature of 500 °C was explored in these experiments. The charcoal content for pure fossil diesel was compared with the binary diesel residue. Gas-phase molecular components were determined using Gas chromatography (GC) coupled to a mass selective detector (MSD). Elemental composition of thermal char was determined using Smart Elemental Analyzer. Radical intensities for the three types of char (biochar, bio-fossil char, and fossil char) were measured using an X-band electron paramagnetic resonance spectrometer. It was noted that at a ratio of 2:3 (Biodiesel: Fossil diesel), harmful molecular products reduced significantly, 76–99%. Elemental analysis data indicated that the carbon content from commercial diesel was very high (≈ 70.61%) as compared to approximately 53% for biodiesel-fossil diesel mixture in the same ratio 2:3. Interestingly, the free radical content was reduced by nearly 50% in favour of the biodiesel/fossil diesel mixture. These results are encouraging and suggest that a better optimized fuel mixture has been found for better clean energy combustion.
Optimization of Hole Transport Layer Materials for a Lead-Free Perovskite Solar Cell Based on Formamidinium Tin Iodide
(Energy Technology, 2021-10-31) Rono, Nicholas; Merad, Abdelkrim E.; Kibet, Joshua K.; Martincigh, Bice S.; Nyamori, Vincent O.
Recently, lead-based perovskite solar cells have been mainly studied; however, these cells suffer from two main problems: the toxicity of lead and the instability of the devices, which limit their commercialization. Herein, a theoretical investigation of a lead-free perovskite solar cell based on formamidinium tin iodide (HC(NH2)2SnI3) with the general architecture: glass/FTO/WS2/HC(NH2)2SnI3/HTL/Au is reported. All calculations are performed with the SCAPS-1D solar cell simulator. Two inorganic (CuSCN and Cu2O) and two organic (P3HT and D-PBTTT-14) hole transport layer (HTL) materials are tested in this model. The effect of the external operating temperature and different metal work functions of the back contact of the cell on the overall performance of the devices is also studied. Simulations showed that, with the introduction of CuSCN, Cu2O, and P3HT as HTLs, the device can attain a remarkable efficiency of ≈21%. All the modeled devices showed remarkable performance of above 20% at higher temperatures of 380–420 K but degraded slightly when this range is exceeded. Relatively cheaper Pt, Ni, and Pd metals perform better, thus, can replace gold. These simulation results can provide avenues and directions for future advancement of the performance of lead-free perovskite solar cells.
Polycyclic aromatic hydrocarbons in the bottom sediments of Elburgon River—Kenya: precursors for cancer
(Springer, 2019-09-24) Opuru, Francis E.; Kibet, Joshua K.; Kirkok, Samuel K.; Ngari, Silas M.
The exponential growth in the rate of industrialization is a serious precursor for contamination and deterioration of the environment. Water pollution, for instance, is expected to reach disturbing levels in the years to come. Polycyclic aromatic hydrocarbons (PAHs) in water systems are persistent contaminants not only in aquatic systems but also in soil, air and plant materials and are well-known initiators for cancer and gene mutation. Numerous human-dependent activities such as agriculture and suspected wood treatment works in Elburgon may lead to an increased PAH contamination of water in River Elburgon, especially when the internationally set limits are exceeded. The sediment samples were collected in May 2019 during the wet season and treated for analysis of PAHs using a gas chromatograph hyphenated to a mass selective detector. A total of 25 PAHs were quantified in this study out of which pyrene was the most abundant, contributing $$\approx \,17\%$$of the total concentrations of PAHs identified. The total concentration of the PAHs analyzed in this study was found to be $$\mathop \sum \nolimits_{25} {\text{PAH}} = 73.19 \pm 3.67\;\upmu{\text{g}}\;{\text{g}}^{ - 1}$$dry weight (dw) with pyrene contributing a total concentration $$\mathop \sum \nolimits_{\text{pyrene}} = 12.44 \pm 0.54\;\upmu{\text{g}}\;{\text{g}}^{ - 1 }$$ dw. On the other hand, benzo[a]pyrene (BaP)—a well-known carcinogen—was significantly high $$\mathop \sum \nolimits_{\text{BaP}} = 10.67 \pm 0.43\;\upmu{\text{g}}\;{\text{g}}^{ - 1 }$$. Other major PAHs detected included acenaphthene and 5,6-dihydrobenzo[de]anthracene, $$14.57\%$$and $$\approx \,11\%$$, respectively. The low concentration PAHs included 1-ethenylnaphthalene and 1,4,5-trimethylnaphthalene each at $$0.08\%$$. The presence of benzo[a]pyrene in significant amounts is of serious concern on the public health of the residents of Elburgon and its environs. Considering the high levels of PAHs in the sediments of River Elburgon, it is important to note with concern that the water in the river under study is not only be unsuitable for drinking but also unsuitable for other domestic purposes such as irrigation and laundry.
Simulated performance of a novel solid-state dye-sensitized solar cell based on phenyl-C61-butyric acid methyl ester (PC61BM) electron transport layer
(Springer, 2021) Korir, Benjamin K.; Kibet, Joshua K.; Ngari, Silas M.
Climate change has approached a major crisis limit worldwide due to exhaust emissions arising from the use of traditional transport fuels. Solar energy, therefore, appears to be the most promising alternative energy that can mitigate air quality and environmental degradation. Herein, we report numerical simulation of a novel model solid-state dye-sensitized solar cell consisting of solid-state layers with the configuration FTO/PC61BM/N719/CuSCN/Au using 1-dimensional solar cell capacitance simulator software (SCAPS-1D). The motivation underpinning the numerical simulation of the solar cell architecture proposed in this study was to optimize phenyl-C61-butyric acid methyl ester (PC61BM) performance as the electron transport layer. In this model, the effects of varying several parameters—temperature, absorber thickness, defect density, and metallic back contact on the overall solar cell performance have been critically examined. After optimizing the input parameters, the optimal conversion efficiency was 5.38% while the optimized open-circuit voltage was 0.885 V. Besides, 70.94% was the optimum fill factor and the peak short-circuit current of 8.563 mA cm−2 was achieved. Built-in voltage of ~ 1.0 V was estimated from the Mott–Schottky curve and the cell band diagram. The power conversion efficiency obtained in this study is robust for this cell configuration, and is toxic-free compared to the lead-based perovskite solar cells. These findings are therefore useful in the advancement and fabrication of high-performance dye-based photovoltaic devices for large-scale industrial production.
Simulated performance of a novel solid-state dye-sensitized solar cell based on phenyl-C61-butyric acid methyl ester (PC61BM) electron transport layer
(Optical and Quantum Electronics, 2021-07-01) Korir, Benjamin K.; Kibet, Joshua K.; Ngari, Silas M.
Climate change has approached a major crisis limit worldwide due to exhaust emissions arising from the use of traditional transport fuels. Solar energy, therefore, appears to be the most promising alternative energy that can mitigate air quality and environmental degradation. Herein, we report numerical simulation of a novel model solid-state dye-sensitized solar cell consisting of solid-state layers with the configuration FTO/PC61BM/N719/CuSCN/Au using 1-dimensional solar cell capacitance simulator software (SCAPS-1D). The motivation underpinning the numerical simulation of the solar cell architecture proposed in this study was to optimize phenyl-C61-butyric acid methyl ester (PC61BM) performance as the electron transport layer. In this model, the effects of varying several parameters—temperature, absorber thickness, defect density, and metallic back contact on the overall solar cell performance have been critically examined. After optimizing the input parameters, the optimal conversion efficiency was 5.38% while the optimized open-circuit voltage was 0.885 V. Besides, 70.94% was the optimum fill factor and the peak short-circuit current of 8.563 mA cm−2 was achieved. Built-in voltage of ~ 1.0 V was estimated from the Mott–Schottky curve and the cell band diagram. The power conversion efficiency obtained in this study is robust for this cell configuration, and is toxic-free compared to the lead-based perovskite solar cells. These findings are therefore useful in the advancement and fabrication of high-performance dye-based photovoltaic devices for large-scale industrial production.
The fate of model organic pollutants; 3,5-dimethylphenol and N-phenyl-1-naphthaleneamine in Lake Naivasha wetland, Kenya
(Elsevier, 2020-07-01) Magollo, Laurence; Kibet, Joshua K.; Ngari, Silas M.
Wetland ecosystems are sinks for organic carbon and greenhouse gases thus faciliating their biotransformation into less harmful compounds through anaerobic degradation. The aim is to protect aquatic ecosystems from ecotoxicological harm. This paper studies model pollutants; N-phenyl-1-naphthaleneamine and 3,5-diethylphenol in Lake Naivasha wetland. N-phenyl-1-naphthaleneamine is a suspected carcinogen which can metabolize into the well-known human carcinogen 2-naphthylamine whereas phenol derivatives scuh as 3,5-diethyl phenols are well-established carcinogens and mutagens. Soil sediments were collected from the wetland at intervals of 3 hours starting from 6.00 am to 6.00 pm three times during the dry season of December, 2018. Extraction of organics from sediments was carried out in a mixture of methanol and dichloromethane. Purified extracts were analyzed using a Gas Chromatograph coupled to a mass selective detector (MSD). The maximum concentration of N-phenyl-1-naphthaleneamine was 2.71 μg/L at 6 am and decreased to ~ 34% at 6 pm. 3,5-dimethylphenol had a maximum concentration of 0.51 μg/L and decreased to ~ 25% at 6 pm. The diminishing concentration of these model organic pollutants is an indication that wetlands play a remarkable role in water purification and environmental management. Degradation pathways of N-phenyl-1-naphthaleneamine and 3,5-dimethylphenol to H2O CH4, and CO2 by microbial action has been suggested in this work. Furthermore, computational simulation on the stability behaviour of the model compounds under study has been performed to support their degradation characteristics.
Theoretical analysis of the electrical characteristics of lead-free formamidinium tin iodide solar cell
(Wiley, 2023-09-14) Katunge, Elizabeth K.; Njema, George G.; Kibet, Joshua K.
Green energy transition and climate change have gathered significant momentum in the world because of the rising population and increased clean energy demands. For this reason, renewable energy alternatives such as inexhaustible photo energy from the sun appear to be the ultimate solution to the world's energy needs. Formamidinium tin tri-iodide (HC(NH2)2SnI3)-based perovskites are found to be more efficient and stable than their methylammonium tin tri-iodide (MASnI3) counterparts because of its wider bandgap and better temperature stability. A device simulation of FASnI3-based solar cell is numerically performed using solar cell capacitance simulator (SCAPS-1D). The focus is to investigate the effect of changing working temperature, metal back contact, absorber thickness, defect density, and doping concentration on the performance of the proposed solar cell device. The optimised solar cell parameters of the proposed solar cell were: short-circuit current density (Jsc) of 28.45 mAcm−2, open-circuit voltage (Voc) of 1.0042 V, fill factor of 63.73%, and power conversion efficiency of 18.21% at 300 K, thus, paving the way for novel perovskite solar cells which are environmentally benign because they are lead-free, have better absorption efficiency, and can be injected into the production work flow for commercial applications.
Theoretical analysis of the electrical characteristics of lead‐free formamidinium tin iodide solar cell
(The Institution of Engineering and Technology (IET), 2023) Katunge, Elizabeth K.; Njema, George G.; Kibet, Joshua K.
Abstract Green energy transition and climate change have gathered significant momentum in the world because of the rising population and increased clean energy demands. For this reason, renewable energy alternatives such as inexhaustible photo energy from the sun appear to be the ultimate solution to the world's energy needs. Formamidinium tin tri‐iodide (HC(NH 2 ) 2 SnI 3 )‐based perovskites are found to be more efficient and stable than their methylammonium tin tri‐iodide (MASnI 3 ) counterparts because of its wider bandgap and better temperature stability. A device simulation of FASnI 3 ‐based solar cell is numerically performed using solar cell capacitance simulator (SCAPS‐1D). The focus is to investigate the effect of changing working temperature, metal back contact, absorber thickness, defect density, and doping concentration on the performance of the proposed solar cell device. The optimised solar cell parameters of the proposed solar cell were: short‐circuit current density (Jsc) of 28.45 mAcm −2 , open‐circuit voltage (Voc) of 1.0042 V, fill factor of 63.73%, and power conversion efficiency of 18.21% at 300 K, thus, paving the way for novel perovskite solar cells which are environmentally benign because they are lead‐free, have better absorption efficiency, and can be injected into the production work flow for commercial applications.

Browsing by Author "Kibet, Joshua K."

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