Browsing by Author "King'ondu, Cecil"

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    Electrosorption of paraquat pesticide on activated carbon modified by aluminium oxide (Al2O3) with capacitive deionization
    (Elsevier, 2024-03-01) Alfredy, Tusekile; Elisadiki, Joyce; Dahbi, Mouad; King'ondu, Cecil; Jande, Yusufu
    Composite electrode materials for removing paraquat from contaminated water were synthesized by loading aluminium oxide (Al2O3) onto activated carbon (AC) via co-precipitation method. The composite properties were investigated by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy. Capacitive deionization batch experiments compared the electrosorption of paraquat herbicide by the composite electrode and the pristine activated carbon. The performance of the composite electrodes showed that the removal efficiency and adsorption capacity depend on the aluminium oxide loading, applied potential, flow rate, and charging time. At 1.2 V, a flow rate of 15 mL/min, a charging time of 3 h and 20 mg/L PQ initial concentration, the composite electrode (AC/Al2O3-1:1) demonstrated a removal efficiency, electrosorption capacity, and energy consumption of 95.5 %, 1.27 mg/g, and 0.055 kWh/m3, respectively, compared to 62 %, 0.83 mg/g, and 0.11 kWh/m3 for the unmodified AC. The presences of other ions/pollutants were found to have negligible interference on PQ pesticide removal as the removal efficiency and electrosorption capacity of the AC/Al2O3-1:1 composite in both artificial (95.5 %, 1.27 mg/g) and natural water (87.5 % 1.17 mg/g). The study confirmed that composite electrode can reused several times, as there was no significant decrease in its regeneration efficiency even after multiple cycles.
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    Fish bladder-based activated carbon/Co3O4/TiO2 composite electrodes for supercapacitors
    (Elsevier B.V., 2019-06-15) Sirengo, Keith; Jande, Yusufu; Kibona, Talam; Hilonga, Askwar; Muiva, Cosmas; King'ondu, Cecil
    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.
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    Influence of scoria and pumice on key performance indicators of Portland cement concrete
    (Elsevier Ltd, 2019-02-10) Mboya, Hieronimi; Njau, Karoli; Mrema, Alex; King'ondu, Cecil
    Cement industries have a huge CO2 signature that can be reduced in an effort to mitigate climate change via precise cement substitution with supplementary cementing materials (SCMs). The substituting materials and their amounts ought not to degrade the key performance indicators of concrete such as slump, flow, permeability, shrinkage, modulus of rupture, compressive, and tensile splitting strength. In this study, the influence of natural scoria (SN) and pumice (PN) binders on the key performance indicators of the fresh and hardened Portland cement (PLC) concrete was successfully examined. The performance indicators were tested at PLC substitution (with SN or PN) levels of 10, 20, 30, and 40% and the results compared to the control (CTRL) made of PLC only. The results show that 10% is the optimum substitution level for both SN and PN. The compressive strength, modulus of rupture, shrinkage, permeability, and thermal stability of the concrete were not compromised at this substitution level. The 28 days modulus of rupture, shrinkage, and compressive strength for SN and PN at 10% substitution were 6.0 and 6.4 MPa; 0.02 and 0.01 mm; 44.2 and 43.1 MPa, respectively. These compared remarkably well with 6.3 MPa modulus of rupture, 0.01 mm shrinkage, and 43.1 MPa compressive strength of the control. Moreover, SN and PN delivered higher % residual compressive strength of 59.2 and 57.8%, correspondingly, after subjecting the concrete to high temperatures of 600 °C, compared to 52.6% for the control. Likewise, the coefficient of permeability (K) for SN (5.2526E−08 m/s) was similar to that of PLC (5.35714E−08 m/s). At substitution levels higher than 10%, more than one key performance indicators were negatively affected. These results show the utility of SN and PN in reducing the amount of cement used in construction and thus the CO2 emission associated with cement industries while at the same time preserving the strength, permeability, thermal and volume stability and hence the durability of the concrete