Browsing by Author "Pogrebnoi, Alexander"

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    Biogas-slurry derived mesoporous carbon for supercapacitor applications
    (Elsevier, 2017) Enock, Talam Kibona; King’ondu, Cecil K.; Pogrebnoi, Alexander; Jande, Yusufu Abeid Chande
    This study reports on the transformation of biogas slurry into mesoporous carbon for supercapacitor electrodes. Pore structures have been modified by altering activation time, temperature and KOH/carbon mass ratio. The mesoporous carbons are successively developed as evidenced by type IV isotherms obtained in nitrogen sorption studies. BET, micropore and mesopore surface area of 515, 350, and 165 m2 g−1, respectively as well as a narrow pore width distribution of 3–4.5 nm are obtained. X-ray photoelectron results have confirmed the presence of functional groups of oxygen and nitrogen in the samples which facilitates the pseudocapacitance. The electrochemical measurements in 6 M KOH using a three electrode cell with Ag/AgCl as reference electrode and platinum as counter electrode has been performed. The materials activated at 700 °C, 3:1 KOH to carbon mass ratio, and for 120 min exhibit high specific capacitance of 289 F g−1 at a scan rate of 5 mV s−1. Shortening activation time to 30 and 60 min reduces specific capacitance to 163 and 182 F g−1, in that order. Additionally, at 3:1 KOH to carbon mass ratio and 60 min activation time, specific capacitances of 170 and 210 F g−1 at 600 and 800 °C, respectively are obtained. Moreover, specific capacitance increases with increasing the KOH to carbon mass ratio from 148 F g−1 for 1:1–163 F g−1 for 3:1 at 700 °C. Electrochemical impedance spectroscopy studies demonstrate that material has high conductivity. In addition; capacity retention of 96% after 20,000 cycles is shown at scan rate of 30 mV s−1. The study shows that high performance electrodes can be designed from biogas slurry derived porous carbon.
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    Dynamics of Kaolinite-Urea Nanocomposites via Coupled DMSO-Hydroxyaluminum Oligomeric Intermediates
    (Hindawi Publishing Corporation, 2015) Ibahati, Sempeho S.; Kim, Hee T.; Mubofu, Egid B.; Pogrebnoi, Alexander; Shao, Godlisten N.; Hilonga, Askwar
    Kaolinite-urea nanocomposites were prepared via intercalation reactions in an attempt to investigate the dynamic nature of kaolinite morphology for advanced applications in controlled release systems (CRS). Characterization was done using SEM-EDX, XRF, ATR-FTIR, XRD, and DT/DTG; Andreasen pipette sedimentation technique was used to determine the grain size distribution of the raw kaolinite. The X-ray diffraction pattern revealed the existence of an FCC Bravais lattice where the intercalation ratios attained were 51.2%, 32.4%, 7.0%, and 38.4% for hydroxyaluminum oligomeric intercalated kaolinite, substituted urea intercalated kaolinite, calcined DMSO intercalated kaolinite, and hydroxyaluminum reintercalated kaolinite, respectively, along with their respective crystallite sizes of 33.51–31.73 nm, 41.92–39.69 nm, 22.31–21.13 nm, and 41.86–39.63 nm. The outcomes demonstrated that the employed intercalation routes require improvements as the intercalation reactions were in average only ≈32.3%. The observations unveiled that it is possible to manipulate kaolinite structure into various morphologies including dense-tightly packed overlapping euhedral pseudo hexagonal platelets, stacked vermiform morphologies, postulated forms, and unique patterns exhibiting self-assembled curled glomeruli-like morphologies. Such a diversity of kaolinite morphologies expedites its advanced applications in the controlled release systems (CRS) such as drug delivery systems and controlled release fertilizers (CRFs).
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    Effect of biogas-slurry pyrolysis temperature on specific capacitance
    (Elsevier, 2018) Kibona, Talam Enock; King’ondu, Cecil K.; Pogrebnoi, Alexander
    The purpose of this study was to investigate the effect of carbonization temperature of biogas slurry on specific capacitance. The biogas derived mesoporous carbon materials were synthesized through carbonization of biogas slurry at 450, 550, and 650 °C followed by activation using KOH at 700 °C for 1 h. The physical characterization done by nitrogen adsorption and desorption, scanning electron microscope, transmission electron microscope and X-ray diffraction shows that pyrolysis temperature has influence on the textural and structural properties of the biogas slurry derived carbon. BET specific surface area of 567, 521 and 499 m2 g-1 were obtained for samples carbonized at 450, 550, and 650 °C, respectively. The electrochemical performance of the samples in 6 M KOH electrolyte exhibited high gravimetric capacitance of 262, 272, and 238 F g-1 for samples carbonized at 450, 550 and 650 °C, correspondingly at scan rate of 5 mV s-1. Moderate carbonization temperature of 550 °C therefore afforded the highest capacitance.
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    Encapsulated Urea-Kaolinite Nanocomposite for Controlled Release Fertilizer Formulations
    (Hindawi Publishing Corporation,, 2015-05-20) Sempeho, SI; Kim, HT; Mubofu, Egid; Pogrebnoi, Alexander; Shao, Godlisten N.; Hilonga, Askwar
    Urea controlled release fertilizer (CRF) was prepared via kaolinite intercalation followed by gum arabic encapsulation in an attempt to reduce its severe losses associated with dissolution, hydrolysis, and diffusion. Following the beneficiation, the nonkaolinite fraction decreased from 39.58% to 0.36% whereas the kaolinite fraction increased from 60.42% to 99.64%. The X-ray diffractions showed that kaolinite was a major phase with FCC Bravais crystal lattice with particle sizes ranging between 14.6nm and 92.5 nm. Theparticle size varied with intercalation ratioswithmethanol intercalated kaolinite >DMSO-kaolinite > urea-kaolinite (KPDMU). Following intercalation, SEM analysis revealed a change of order from thick compact overlapping euhedral pseudohexagonal platelets to irregular booklets which later transformed to vermiform morphology and dispersed euhedral pseudohexagonal platelets. Besides, dispersed euhedral pseudohexagonal platelets were seen to coexist with blocky-vermicular booklets. In addition, a unique brain-form agglomeration which transformed into roundish particles mart was observed after encapsulation. The nanocomposites decomposed between 48 and 600∘C. Release profiles showed that 100% of urea was released in 97 hours from KPDMU while 87% was released in 150 hours from the encapsulated nanocomposite.The findings established that it is possible to use Pugu kaolinite and gum arabic biopolymer to prepare urea CRF formulations.
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    Status of biomass derived carbon materials for supercapacitor application
    (Hindawi, 2017) Enock, Talam Kibona; King’ondu, Cecil K; Pogrebnoi, Alexander; Jande, Yusufu Abeid Chande
    Environmental concerns and energy security uncertainties associated with fossil fuels have driven the world to shift to renewable energy sources. However, most renewable energy sources with exception of hydropower are intermittent in nature and thus need storage systems. Amongst various storage systems, supercapacitors are the promising candidates for energy storage not only in renewable energies but also in hybrid vehicles and portable devices due to their high power density. Supercapacitor electrodes are almost invariably made of carbon derived from biomass. Several reviews had been focused on general carbon materials for supercapacitor electrode. This review is focused on understanding the extent to which different types of biomasses have been used as porous carbon materials for supercapacitor electrodes. It also details hydrothermal microwave assisted, ionothermal, and molten salts carbonization as techniques of synthesizing activated carbon from biomasses as well as their characteristics and their impacts on electrochemical performance.