Department of Physics

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Novel technique for simultaneous detecting three naturally occurring radon isotopes (222Rn, 220Rn and 219Rn)
(Elsevier, 2022-11) Ntarisa, Amos Vincent; Kim, HongJoo; Aryal, Pabitra; Nguyen, Duy Quang; Saha, Sudipta
Radon inspection is becoming increasingly prevalent due to its negative effects on human health. After cigarette smoking, radon is the second leading cause of lung cancer due to its internal dosage through respiration. In this study, we employed a novel liquid scintillation technique to simultaneously detect three naturally occurring radon isotopes (222Rn, 220Rn and 219Rn). The detection method utilises the delayed coincidence technique and the pulse shape discrimination implemented by digital charge comparison. Furthermore, a Monte Carlo simulation was performed to obtain the gamma response functions of the detector using standard 22Na, 60Co and 137Cs gamma sources. Additionally, the detector resolution and energy calibration parameters were determined by comparing the measured and simulated light output distributions. For the measurement, radon gas from the atmosphere was infused into 700 mL of Ultima Gold AB for 48 h. We determined that the minimum detectable activities of 222Rn (238U decay chain), 220Rn (232Th decay chain) and 219Rn (235U decay chain) were 1.7, 1.0 and 1.2 mBq/l, respectively. The proposed novel technique offers a potential application for detecting all three naturally occurring radon isotopes in water samples.
Scintillation performance of the Ce3+ -activated lithium phosphate glass
(Elsevier, 2022-10) Saha, Sudipta; Ntarisa, Amos Vincent; Nguyen, Duy Quang; Luan, NT; Vuong, PQ; Kim, HongJoo; Intachai, N; Kothan, Suchart; Kaewkhao, Jakrapong
Ce3+ -doped phosphate glasses with intense luminescence were reported extensively for radiation detection in recent decades. With the same intension, we fabricated glasses of composition 45P2O5:35Li2O:(10-x)GdI3:5Al2O3:5Ca2CO3:xCeBr3 (x = 1, 2, 3, 5) in molar ratio using conventional technique followed by thermal annealing. The luminescence studies confirmed the energy transfer process from Gd3+ to Ce3+ -ions. The scintillation measurements of the optimized sample were performed under the excitation of α -particles and γ-rays. A photopeak was detected under γ-ray excitation at 662 keV energy from 137Cs source. The estimated absolute light yield was 1600 ± 200 Photons/MeV. The shortest component of the decay time under α -particles and γ -ray excitations was found 32.5 ± 0.3 ns and 39.9 ± 0.4 ns, respectively. In the future, the glass configuration can be engineered to improve radiation detection performance.
Synthesis and elemental analysis of gadolinium halides (GdX3) in glass matrix for radiation detection applications
(Elsevier, 2022-07) Saha, Sudipta; Ntarisa, Amos Vincent; Nguyen, Duy Quang; Kim, HongJoo; Kothan, Suchart; Kaewkhao, Jakrapong
Numerous researchers were intrigued to glasses for radiation detection and scintillation applications in nuclear and high-energy physics research. To mitigate the requirements of density and luminescence enhancement, gadolinium (Gd) compounds are widely practiced. Gd halides (GdX3) are hygroscopic salts that can function as excellent sensitizers in a glass network to improve activator (Ce) luminescence. To ensure the elemental abundance of the constituents in glass samples after high temperature combustion, EDX reports at both the intermediate and final phases of the glass samples can be useful. However, EDX analysis was unable to detect halogens in glass substances in their intermediate and final forms. The implications were examined on the basis of prior literature indicating the feasibility of high temperature combustion in an air environment. Nevertheless, it was discovered that transmittance spectra are essential for the performance of radioluminescence and scintillation features. Two samples that were previously enriched with GdI3 had transmittance values more than 55% at the X-ray generated emission peak point. α -peaks with an energy resolution (FWHM) of 29% and 31% were obtained utilizing these samples. The scintillation decay projections from these two samples were fitted with three exponential decay components, with the shortest components being 30.6 ns and 29.5 ns, contributing 38% and 37.4%, respectively.
Fabrication and investigation of the effects of various gadolinium compounds on Ce3+-activated phosphate glasses for scintillation applications
(Elsevier, 2022-07) Ntarisa, Amos Vincent; Saha, Sudipta; Nguyen, Duy Quang; Kim, HongJoo; Wantana, N; Pandey, Indra Raj; Aryal, Pabitra; Kothan, Suchart; Kaewkhao, Jakrapong
Ce3+-activated phosphate-based glasses were fabricated for scintillation purposes following melt-quenching technique. Chemical compositions of the glasses were designed in mol. % ratio with formula (62P2O5:20Li2CO3:10X:5Al2O3:3CeBr3 where X Gd2O3/GdF3/GdCl3/GdBr3/GdI3). The amorphous structure of the glasses was verified by the powder X-ray diffraction measurements. Fourier-transform infrared (FTIR) measurements were carried out to study the structural properties of the fabricated glass samples. X-ray-induced luminescence and photoluminescence (PL) spectra were used to investigate the luminescence properties of the glasses. A broad PL excitation band was found for all prepared glasses that refers to Gd3+ and Ce3+ characteristic transitions. GdI3 containing glass sample provided the optimum emission under X-ray and UV (308 nm) excitations peaking at 347 and 341 nm, respectively. The scintillation property of the GdI3 containing glass was studied under 5.5 MeV α-particle from 241Am radiation source and a clear alpha peak was observed with energy resolution of 35.3%. The shortest decay component of the glass sample was observed to be 27.9 ns, 30.7 ns and 29.12 ns under the α-particles, γ-ray, and 266 nm pulsed laser excitations, respectively. In conclusion, the GdI3 prepared glass sample can be used for α -particles detection.
Mn2+ doping inside glass substrate utilizing metal ion beam implantation technique
(Elsevier, 2022-07) Hwang, YongSeok; Aryal, Pabitra; Kim, HongJoo; Ntarisa, Amos Vincent; Saha, Sudipta; Kim, Chorong; Kothan, Suchart; Kaewkhao, Jakrapong
The Korea multi-purpose accelerator complex (KOMAC) has been providing metal ion beam services such as Cr+, Fe+, Co+, Cu+, Mg+ and Ni+ using a modified Bernas ion source for diverse users. In this study, metal ion implantation facilitated by KOMAC has been utilized to implant Mn+ ions into a glass substrate. First, phosphate glass substrate doped with CeBr3 was fabricated following melt-quenching technique and then Mn+ ion beam was irradiated with flounces of 5 × 1016 ions/cm2. The irradiated sample was heat-treated at 400 °C, and characterized by absorption, excitation, and emission spectra. The presence of Mn2+ and the existence of energy transfer from Ce3+ to Mn2+ were explored by characteristic emission and excitation spectra. The emission intensity of Mn2+ was significantly higher when excited by Ce3+ excitation than Mn2+.
Synthesis and luminescence studies of Dy3+ doped Li3Sc(BO3)2 polycrystalline powder for warm white light
(Elsevier, 2022-04-15) Saha, Sudipta; Kim, HongJoo; Khan, Arshad; Cho, Jaeyoung; Kang, Sinchul; Ntarisa, Amos Vincent
Li3Sc(BO3)2, an orthoborate polycrystalline compound, was synthesised using the solid-state synthesis method as a pure and Dy2O3-doped material. Dy3+ ions were used in various concentrations (from 1 to 6 mol. %). The experimental powder X-ray diffraction data and calculated Rietveld refined data are found to be in good agreement, verifying the effectiveness of the synthesis procedure. The luminescence studies were performed under the excitations of X-ray, proton beam, and UV light. The success of radioluminescence studies verifies the prospects of the Dy3+-doped compound for its application as a radiation scintillator in imaging. The experimental study of cross-relaxation processes confirms the lack of potential evidence of the quenching of the emission peak at 765 nm through the absorption via 6H15/2 → 6F3/2 electronic transition cross-relaxation channel−1. The CIE 1931 colour coordinates and correlated colour temperatures were determined for all doped samples under X-ray, proton beam, and photoluminescence excitations. The obtained combined emission colour appeared in the warm white region, unlike many other Dy3+-doped phosphors that suffer suppression of luminescence through the cross-relaxation process.
Synthesis and characterization of CeF3‒doped (74.5-x)P2O5:20Li2O:5Al2O3:x(GdF3, LaF3 and YF3) glasses
(Elsevier, 2021-12) Aryal, Pabitra; Saha, Sudipta; Kim, HongJoo; Kang, SJ; Ntarisa, Amos Vincent; Angnanon, A; Kaewkhao, Jakrapong
Glasses have a wide variety of applications in different types of devices, including solid-state lasers, fiber-optic amplifiers, medical imaging, radiation dosimeter, solar cells, neutron imaging, and scintillators. Among several rare-earth (RE) ions, Ce3+ exhibits short decay time and offers promising scintillation when it is doped in a transparent glass matrix. The objective of this study was to investigate the energy transfer from Gd3+, La3+, and Y3+ ions to Ce3+ ion in 64.5P2O5:20Li2O:5Al2O3 glass matrix while considering an enhancement in its scintillation efficiency. Four glass samples doped with CeF3 alone and co-doped with GdF3, LaF3, and YF3 were fabricated. Broad photoluminescence and radio-luminescence emissions peaking near to 340 and 350 nm were found when excited by 310 nm and X-ray, respectively, for all the glasses. A photoluminescence emission quenching was found in LaF3 co-doped glass. A strong energy transfer from Gd3+ to Ce3+ was noticed while the GdF3 co-doped glass was excited by X-ray, 275 nm (from Gd3+), and 310 nm (from Ce3+) excitations. The Gd3+ co-doped glass consisted of a 37 ns decay constant under the 266 nm laser excitation. The thermoluminescence analysis showed two glow curves centered at 210 °C and 345 °C, respectively, after X-ray irradiation. Considering the efficient energy transfer from Gd3+ to Ce3+ ions and short lifetime of Ce3+ emission, the glass composition of the above formula having Gd3+ and Li+ with Ce3+ ions appeared to be a promising candidate in the search of good promising scintillating glasses with fast fluorescence decay time.
Luminescence and scintillation properties of Ce3+-doped P2O5-Li2CO3-GdBr3-Al2O3 glasses
(Elsevier, 2021-09-01) Ntarisa, Amos Vincent; Saha, Sudipta; Aryal, Pabitra; Kim, HongJoo; Khan, Arshad; Nguyen, Duy Quang; Pandey, Indra Raj; Kaewkhao, Jakrapong; Kothan, Suchart
A series of glass samples were fabricated with the composition of (65-x)P2O5:20Li2CO3:10GdBr3:5Al2O3:xCeBr3 (where, x = 0.5,1,2,3,4). The powder X-ray diffraction measurements were performed to verify the amorphous structure of the prepared glass samples. Energy-dispersive X-ray spectroscopy showed an interesting phenomenon of oxygen bridging eliminating Br (Bromine) from the initial compounds. The luminescence characteristics of the samples were studied using X-rays and UV–Vis excitations. Characteristics Ce3+ emission was observed at 350 nm including energy transfer from 4f energy state of Gd3+ to 5d energy band of Ce3+. The fast decay component was observed as 37 ns, 42 ns, and 44 ns for the UV, α-particles, and γ-ray excitations, respectively. The intermediate and slow components were observed for α-particles, and γ-rays excitations indicating Gd3+ to Ce3+ energy transfer and 4f-4f transitions of Gd3+ -ions accordingly. The scintillation property was studied with α-particles using a 241Am source.
A novel blue-emitting phosphors (CsBaYB6O12:Ce3+): Potential applications in w-LEDs and X-ray phosphors
(Elsevier, 2021-08-25) Ntarisa, Amos Vincent; D Joseph, Daniel; D, Balaji; Raja, Arumugam; Kim, HongJoo; Nguyen, Duy Quang
We have synthesized powder samples of pure and Ce3+ doped cesium barium yttrium hexaborate (CsBaYB6O12) using a standard solid-state reaction technique. The prepared samples were characterized by different techniques. Powder X-ray diffraction (PXRD) was used to identify the phase purity of the prepared phosphors. The field emission scanning electron microscopy (FE-SEM) technique was used to examine the size and shape of the synthesized powder samples. The energy-dispersive spectral analysis (EDS) was used to identify the elements present in the synthesized compounds. X-ray-induced luminescence spectra, photoluminescence (PL), and thermoluminescence (TL) analysis were used to investigate the luminescence properties of the prepared compound. The rare earth ion of Ce3+ improves the intrinsic luminescence of CsBaYB6O12 and 4 mol% was found to be the optimal concentration. The dopants found to have two different excitation PL bands at 340 nm and 360 nm which yields the same emission bands of 385 and 417 nm which are well-matched with that found in the X-ray emission bands. The kinetic parameters of the measured experimental TL glow curve has been studied by various standard methods such as deconvolution, Variable heating rate and initial rise method. In this manuscript we report the luminescence properties of the prepared phosphors in a detailed manner for the first time.
Rapid and convenient crystallization of quantum dot CsPbBr3 inside a phosphate glass matrix
(Elsevier, 2022-06-15) Aryal, Pabitra; Kim, HongJoo; Saha, Sudipta; Cho, Jaeyoung; Ntarisa, Amos Vincent; Kothan, Suchart; Kaewkhao, Jakrapong
Although inorganic halide perovskite quantum dots (QDs) have promising photophysical properties and a wide range of applications, they suffer from some issues such as poor water and thermal stabilities. Here, we developed a simple strategy to embedded CsPbBr3 QDs in a glass matrix by adopting conventional melt-quenching technique. We systematically presented the modified glass melting and quenching technique for the direct crystallization of CsPbBr3 QDs inside a glass matrix. Crystallization of the QDs took place during the cooling of the quenched hot glass melt. The effect of the concentration of Cs2CO3, PbBr2 and NaBr on the formation of CsPbBr3 QDs size was also identified. The glasses containing CsPbBr3-embedded QDs showed photoluminescence emission stability without any alteration in their emission peaks and full-width at half-maximum for at least six months under ambient conditions. Our results provide new insights into rapid and convenient crystallization of QDs inside the protective glass matrix. The technique can be utilized to fabricate several rare earth ions co-doped QDs glasses for various color tunable lighting optical devices application.
Synthesis of NiCo2O4/mesoporous carbon composites for supercapacitor electrodes
(Springer, 2020) Kibona, Talam Enock
In this study, nickel cobaltite/mesoporous carbon composites are synthesized by reacting CoCl2, Ni (NO3)2 and nitric acid-treated biogas slurry mesoporous carbon using urea as hydrolyzing agent and hexadecyltrimethylammonium bromide (CTAB) as surfactant. The presence of Ni, Co, C and O peaks in the EDX results confirm that the composites are successfully synthesized. Interestingly at 350 °C, the composite surface morphology switched to cross-linked nanoflake structures interconnected with mesoporous carbon. The X-ray diffraction analysis of the NiCo2O4/mesoporous carbon composites reveals that the spinel structure of the NiCo2O4 is maintained in the composites. The nitrogen uptake increases with increasing annealing temperature to 300 °C then decreases at higher temperature (400 °C). The type IV isotherms are exhibited by all the composites. The contribution of mesopores increases with increasing annealing temperature: 32% for BC-NCo-200, 41% for BC-NCo-250, 56% for BC-NCo-300, 66% for BC-NCo-350 and 86% for BC-NCo-400. The NiCo2O4/mesoporous carbon composites exhibit high specific capacitance of 835 F g−1 at scan rate of 5 mV s−1 for sample annealed at 350 °C. The cyclic stabilities of the electrodes are above 90% after 50,000 cycles indicating that the synthesized composites are suitable candidates for supercapacitors.
Highly mesoporous Parinari Curatellifolia carbon nanomaterials for supercapacitors
(Elsevier, 2020-04-01) Kibona, Talam Enock; Achola, Laura; Kerns, Peter; Macharia, John; King'ondu, Cecil K; Suib, Steven
High surface area nanostructured electrodes are essential for understanding charge storage mechanisms in high capacitance supercapacitors. Additionally, a growing number of studies provide credible evidence that the highest capacitance in carbon nanomaterials is attainable only when the pore size is in micropore range. In this study therefore, micropore-dominatedcarbon materials derived from Parinari curatellifolia (PC) waste seeds are prepared via pyrolysis and subsequent chemical activation with KOH. SEM, EDAX, TEM, Raman, and XRD studies show that the microstructure and composition of the as-prepared microporous carbon materials are influenced by adjusting the KOH to carbon mass ratio. Sorption studies demonstrate a very high BET surface area of 1898 m2 g−1, type I isotherm, and 99% micropore content in all the samples. The BET surface area, S, V, and total volume increased with increasing KOH content during activation. The fabricated electrodes exhibit high specific capacitances of 423 F g−1 at 5 mV s−1 and cyclic stability of 98% after 50000 cycles both of which are indicative of our carbon materials huge potential in making high performance supercapacitors. The specific capacitance increased with the micropore content in the samples signifying that the pores enhanced diffusion and hence the charge storage. The PC carbon materials deliver high specific capacitance due to the enhancement of diffusion and charge storage stemming from the synergetic interplay of the aforementioned textural parameters. The PC carbon materials therefore provide good prospects for supercapacitor applications.
Application of WRF Mesoscale Model for Prediction of Wind Energy Resources in Tanzania
(Elsevier, 2020-01-30) Kibona, Talam Enock
This study gives an overview of the wind energy resource distribution within and of the coast of Tanzania. Wind speed predictions using WRF model at 60 m a.g.l, which is typically the height of turbine hub, are compared with the wind speed values obtained by extrapolating Final Analysis (FNL) wind speed data at 10m a.g.l using power law. The WRF Model is used for 72-hours wind speed and direction forecasting where the initial boundary of the model is provided by Final Analysis data (FNL) available at UCAR with resolution of 1 × 1 degree. The WRF model has good results in comparison to power law because the variation is very small. At 1200 and 1800 hours over the areas near the land WRF predicts low wind speed than power law. WRF model predicts more offshore wind strength in the night than the noon. At 1300 to 1400 hrs the wind speed in the offshore part of Tanzania is mostly below 9 m/s as predicted by WRF model. Based on the limited studies, it has been observed that the wind energy potential exists in the offshore zones of Tanzania. This study encourage exploring the possibilities of harnessing the offshore wind energy potentials available in Tanzania. The approach adopted could be configuring WRF models with high horizontal resolution and many domains and carrying out detailed theoretical assessment of the wind energy resources, supplemented by actual measurements of the wind pattern using met-masts at different locations across and offshore of Tanzania.
Mesoporous Electrodes for Supercapacitors
(CRC Press (Taylor & Francis Group), 2019-12) Shao, Godlisten N.; Kibona, Talam Enock
Mesoporous electrodes with desirable properties for supercapacitors are very fascinating and their ubiquitous attraction to scientists and engineers is indisputably incessant. Conversely, supercapacitors are highly researched energy storage materials due to their promising potentials to solve the energy storage demands for high-performance energy applications. Investigation of materials with suitable properties for mesoporous electrodes for supercapacitors is mainly carried out to improve their power density and energy density. This chapter highlights the recent investigations and advances toward the development of mesoporous electrodes for supercapacitors.
Highly porous biomass-based capacitive deionization electrodes for water defluoridation
(2019-12-09) Elisadiki, Joyce; Jande, Yusufu; Kibona, Talam Enock; Machunda, Revocatus
The high concentration of fluoride (F−) in water sources is the main challenge in major fluoride belts. Though capacitive deionization (CDI) with porous carbon electrodes is the promising alternative in removing charged species from aqueous solution, little has been presented on the usefulness of CDI with biomass-based electrodes in removing F− from natural water existing together with other ions such as Ca2+ and Mg2+. This study investigated the feasibility of using biomass-based electrodes for natural water defluoridation application. Porous carbon was synthesized from jackfruit peels (JFAC) through potassium hydroxide (KOH) activation. Surface morphology, pore structure, and electrochemical properties of the JFAC were investigated. The textural properties of the synthesized carbon and electrochemical characteristics of the fabricated electrodes were found to be influenced by activation temperature. Brunauer-Emmett-Teller (BET) surface area, pore diameter, pore volume, and pore surface area increased with an increase in activation temperature and KOH to carbon ratio. It was further confirmed that as the applied voltage increased from 1.2 to 2 V, the amount of adsorbed anions increased without significantly affecting the pH of the water. At 2.0 V, the electrodes showed a maximum F− adsorption efficiency and electrosorption capacity of 62% and 0.13 mg/g respectively. The electrosorption capacity depends on the initial concentration of the ion in the feed water. It was further observed that natural organic substances contained in the natural water might inhibit JFAC electrode surface and decrease its adsorption efficiency. This study provides cost-effective CDI electrode material prepared from biomass for water defluoridation.
Highly microstructured porous carbon derived from vitex mombassae for high specific capacitance supercapacitors
(Spinger, 2019-08-26) Kibona, Talam Enock
This study reports on producing highly porous carbon materials by carbonization and activation of biomass (Vitex mombassae) seed wastes. The pore textural properties and microstructures of the synthesized materials are controlled by adjusting the activation temperature from 600 to 800 °C. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, Raman and nitrogen adsorption and desorption are used to study the physical characteristics of the synthesized materials. The Brunauer–Emmet–Teller surface area, micropore surface area and pore volume increase with activation temperature. At activation temperature of 700 °C, the porous carbon acquires high specific area (2044 m2 g−1). The pore volume increases with increase in activation temperature 0.8–1.1 cm3 g−1 with high self-doping oxygen content. As a result of good physical characteristics, the prepared electrodes exhibit excellent performance with the specific capacitance up to 437 F g−1 at 5 mV s−1 in 6 M KOH electrolyte. The good capacitive behavior of the synthesized porous carbon depends on high surface area, micropore pore volume as well as moderate microstructures. The synthesized sample demonstrates high cyclic stability with capacitance retention of over 90% after 50,000 cycles.
Biomass-based carbon electrode materials for capacitive deionization: a review
(Springer, 2019-06-27) Elisadiki, Joyce; Kibona, Talam Enock; Machunda, Revocatus L.; Saleem, Muhammad Wajid; Kim, Woo-Seung; Jande, Yusufu A. C.
Capacitive deionization (CDI) is a promising water purification technology which works by removing salt ions or charged species from aqueous solutions. Currently, most of the research on CDI focuses on the desalination of water with low or moderate salt concentration due to the low salt adsorption capacity of the electrodes. The electrosorption capacity of CDI relies on the structural and textural characteristics of the electrode materials. The cost of electrode materials, the complicated synthesis methods, and the environmental concerns arising from material synthesis steps hinder the development of large-scale CDI units. By considering the good electrical conductivity, high specific surface area (SSA), porous structure, availability, mass production, and cost, porous carbon derived from biomass materials may be a promising CDI electrode material. This review presents an update on carbon nanomaterials derived from various biomasses for CDI electrodes. It covers different synthesis methods and the electrosorption performance of each material and discusses the impact of the SSA and porous structure of the materials on desalination. This review shows that a variety of biomass materials can be used to synthesize cost-effective CDI electrode materials with different structures and good desalination performance. It also shows that diverse precursors and synthesis routes have significant influences on the properties and performance of the resulting carbon electrodes. Additionally, the performance of CDI does not depend only on BET surface area and pore structure but also on the applied voltage, initial concentration of the feed solution, and mass, as well as the capacitance of the electrodes.
Fish bladder-based activated carbon/Co3O4/TiO2 composite electrodes for supercapacitors
(Elsevier, 2019) Sirengo, Keith; Jande, Yusufu Abeid Chande; Kibona, Talam Enock; Hilonga, Askwar; Muiva, Cosmas; King'ondu, Cecil K
Cobalt oxide/titanium dioxide/activated carbon (Co3O4/TiO2/Ac) composite was synthesized using simple sol-gel method before annealing at 300 °C. Fish bladder derived porous carbon used for the composite was synthesized by pyrolysis followed by chemical activation. Both scanning electron microscopy (SEM) and X-ray diffraction displayed Co3O4 and TiO2 phases well embedded onto the carbon matrices. Cyclic voltammetry in 6 M KOH electrolyte demonstrated that the composite has an excellent specific capacity of 946 Fg-1 for Co3O4/TiO2/Ac as compared to Co3O4/Ac, TiO2/Ac, and Ac with specific capacitances of 845, 340, and 308 F g−1, respectively at 5 mVs−1. Impedance spectroscopy reveals that the composite has good capacitive behavior with a series resistance of 0.6 Ω. Besides, Co3O4/TiO2/Ac maintains 89.7% of the initial capacitance after 2000 cycles. This study shows that the synergistic effect of the metal oxides and the carbon in the composite can enhance capacitance for practical supercapacitor applications.
Porous carbon derived from Artocarpus heterophyllus peels for capacitive deionization electrodes
(Elsevier, 2019) Elisadiki, Joyce; Jande, Yusufu Abeid Chande; Machunda, Revocatus Lazaro; Kibona, Talam Enock
Sustainable clean water for human use can be attained through cost effective water purification technologies where by capacitive deionization (CDI) technology is among them. To attain high CDI performance porous carbon materials with good electrical conductivity, high surface area, specific capacitance and good chemical stability are essential. In this study high surface area porous carbon has been synthesized through carbonization of agricultural waste jackfruit peels (Artocarpus heterophyllus) followed by KOH activation at 600, 700, and 800 °C for 1 h. It was found that, the activation temperature significantly increased the BET surface area of the synthesized carbon from 607 m2/g to 1955 m2/g. Desalination experiments were carried out with 30–500 mg/L NaCl solution in batch mode at a flow rate of 2.5 ml/min while applying voltage of 1.2, 1.4 and 2.0 V to the cell. The electrosorption capacity and salt-removal efficiency increased with increasing BET Surface area and applied potential. Specifically, ACJF1:1-700 exhibited highest specific capacitance of 307 F/g, high salt removal efficiency and electrosorption capacity of 5.74 mg/g when voltage of 2 V was applied. These results indicated that the Artocarpus heterophyllus can be promising CDI electrode materials for low salinity water desalination.
Specific capacitance–pore texture relationship of biogas slurry mesoporous carbon/MnO2 composite electrodes for supercapacitors
(Elsevier, 2019-02) Kibona, Talam Enock; Shao, Godlisten N.; Kim, Hee Taik; King’ondu, Cecil K.
Here, we report synthesis of biogas slurry mesoporous carbon/MnO2 composites by simple co-precipitation route followed by thermal treatment at 250 °C for 6 h. The texture, morphology, crystal structure, and microstructure of the composites are investigated by nitrogen sorption studies, FESEM, HRTEM, X-ray diffraction, and Raman spectroscopy. All samples exhibit type IV isotherms. The BET surface area decreased from 514 to 110 m2 g−1 while total pore volume decreased from 0.52 to 0.17 cm3 g−1 for samples loaded with 2×10−5 and 2×10−3 moles of Mn. The electrodes fabricated exhibit high specific capacitance of 709 F g−1 at scan rate of 5 mV s−1. The specific capacitance at scan rate of 5 mV s−1 increases with increasing MnO2 content. However, at 50 mV s−1, specific capacitance decreases with increasing MnO2 content. Varying the MnO2 content and hence the textural parameters, strongly influences the specific capacitances of the composite electrodes.

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