Materials, Energy, Water and Environmental Sciences

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Adsorption of phenol and methylene blue contaminants onto high-performance catalytic activated carbon from biomass residues
(Cellpress, 2025-01-15) Bih, Numfor; Rwiza, Mwemezi; Ripanda, Asha; Mahamat, Assia; Machunda, Revocatus; Choi, Joon
Organic contaminants from wastewater toxicity to the environment has increased during the last few decades and, therefore, there is an urgent need to decontaminate wastewater prior to disposal. This study aimed to create a high surface area catalytic activated carbon (AC) under same carbonization conditions for phenol and methylene blue (organic wastewater) decontamination. Moringa oleifera husk (MH), sesame husk (SH), and baobab husk (BH) were used to prepare activated carbon for the removal of methylene blue (MB) and phenol (Ph). After characterization of the adsorbent, the BET surface areas of the M. oleifera husk activated carbon (MHC), sesame husk activated carbon (SHC), and baobab husk activated carbon (BHC) were 1902.30 m2/g, 1115.90 m2/g, and 1412.40 m2/g, respectively. Mono-adsorption and binary-adsorption systems were studied for Ph and MB adsorption. Furthermore, the effect of initial organic waste concentration, contact time, pH, temperature and AC dosage, on adsorption capacity were studied. The mono adsorption system isotherms and kinetics studies used to analyze Phenol and MB adsorption best fitted Langmuir and pseudo-second-order models. The Freundlich isotherm and pseudo-second-order model best fitted the experimental data for the binary-adsorption system. The high maximum adsorption capacities of organic waste for the single and binary systems were 352.25–855.96 mg/g and 348.90–456.39 mg/g, respectively. The results showed that the high surface activated carbon produced had the potential to adsorb high concentrations of MB and Phenol contaminants.
Biogas-slurry derived mesoporous carbon for supercapacitor applications
(Elsevier Ltd., 2017-09) Enock, Talam; King’ondu, Cecil; Pogrebnoi, Alexander; Jande, Yusufu
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.
Column design for groundwater hardness removal using cashew nut shells activated carbon with potential application in low-income communities
(2020-01) Mwakabole, Emmanuel; Rwiza, Mwemezi; Njau, Karoli
tigated. Water hardness has a significant impact on groundwater, especially in arid and semi-arid regions, leading to wasted investments in borehole drilling and worsening accessibility to potable water. In many developing countries, groundwater is the main source of drinking water. In this study, low cost and readily available cashew nut shells activated carbons (CNSAC) were used to remove hardness from groundwater in a column setting. The recommended design parameters for the packed-bed column were as follows: area (A) of 265.0 cm2 and diameter (d) of 18.4 cm, at a flow rate (Q) of 75.0 cm3 min–1. For the field hard water at a flow rate of 2.0 mL min–1, the recommended empty bed contact time was 70.7 min whereas the breakthrough time was about 430.0 min. Also for field hard water, the results showed that competing ions in the groundwater lowered the materials adsorption capacity. Results from this study indicated that CNSAC may be used to adequately remove groundwater hardness. Using these results, a filter was designed. The designed water hardness filter, which will be scaled up for point-of-use applications, may provide the much-needed solution to many people in most developing countries where similar field conditions prevail.
Enhanced electrosorption capacity of activated carbon electrodes for deionized water production through capacitive deionization
(Elsevier B.V., 2020-09-15) Sufiani, Omari; Tanaka, Hideki; Teshima, Katsuya; Machunda, Revocatus; Jande, Yusufu
The deionized water (DI) of high purity standards is used in several industrial processes to manufacture products and technologies for high end applications. Currently, DI water is produced by either reverse osmosis or continuous electrodeionization systems, however; both of them are facing several limitations. Therefore there is an urgent need for the alternative technologies for DI water production. This study investigated suitability of producing DI water by using capacitive deionization (CDI) with nitric acid treated activated carbon electrodes (NTAC). Activated carbon (AC) was etched in nitric acid solution to introduce various oxygen functional groups on its surface. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to confirm the increased surface oxygen containing groups on AC after nitric acid treatment that enhanced its salt adsorption capacity. CDI experiments were conducted using water solution of 12.0 μS/cm as a result DI water with the conductivity of 1.6 μS/cm (DI water grade III, according to International Organization of Standards) was produced. Also, electrochemical tests revealed good capacitive behavior due to improved conductivity with NTAC having highest specific capacitance of 381.7 F/g compared to 106.6 F/g of AC electrode. This study provides an insight of the electrosorption performance of materials in desalination of solutions of low ionic strength.
Green adsorbent from maize biomass for mercury capture: insights from sorption modeling and thermodynamic analysis
(Applied Water Science, 2025-07-05) Bayuo, Jonas; Mwemezi, Rwiza; Oyelude, Emmanuel; Mtei, Kelvin; Joon Weon Choi
Adsorption isotherms and kinetics modeling, as well as thermodynamic analysis, are useful in providing insight into the nature and mechanisms of the adsorption process. The present study investigated the interactive behavior and mechanisms of mercury ions removal using activated carbon produced from maize biomass (bio-adsorbent). To determine the mechanism of mercury removal from the aqueous system using the activated carbon, the equilibrium adsorption isotherm, kinetics, and thermodynamic studies were performed using the batch technique. Among all the isotherm models analyzed, the Langmuir isotherm model best correlated with the equilibrium sorption data of Hg(II) attained by the bio-adsorbent with a high correlation coefficient of 0.9998. The Langmuir maximum monolayer sorption capacity attained by the bio-adsorbent was 112.46 mg/g, and the dimensionless separation factor ( RL) was in the range of 0.00 < RL > 1.00 indicating favorable biosorption. The pseudo-second-order model well fitted the experimental data of Hg(II) better than the other kinetic models with a high correlation coefficient of 0.9712, which is close to unity with an uptake capacity of 82.10 mg/g. The negative values of ΔG0 obtained from all the temperature ranges of 283–358 K indicate the spontaneous nature of Hg(II) ions removal from the adsorption system by the bio-adsorbent. The positive value of + 24.86 kJ/mol and + 8.13 kJ/mol attained for ΔH0 and ΔS0 , respectively, indicates endothermic adsorption and an upsurge in disorder during the adsorptive removal of Hg(II) ions. Therefore, the study found that the activated carbon not only interacted well with the Hg(II) species in the aqueous solutions but also had a high uptake capacity. Hence, the bio-adsorbent is promising and could efficiently be applied for heavy metal remediation in aquatic environments.
Modification strategies to enhance electrosorption performance of activated carbon electrodes for capacitive deionization applications
(Elsevier, 2019-09-01) Sufiani, Omari; Elisadiki, Joyce; Machunda, Revocatus; Jande, Yusufu
Capacitive deionization (CDI) is the competitive technology for water desalination which appears to become an alternative to conventional methods such as ion exchange resins, reverse osmosis, and electrodeionization. Variety of materials including, carbide-derived carbon, activated carbons, carbon nanotubes, carbon aerogels and mesoporous carbons have been studied for CDI applications most of them being porous carbons. However, materials such as carbon nanotubes are highly expensive and hinder applications at large industrial scale. Activated carbon is a cheap and commercially available electrode material for CDI though its desalination capacity is limited by factors such as low electrical conductivity, inability to selectively remove specific ions, co-ion expulsion, poor wettability, inappropriate pore size distribution and lack of inter-pore connectivity to enable ion diffusion. These factors have raised a concern to most researchers and try to find a way to modify the surface of porous materials. Some strategies have been used to modify activated carbons including dip-coating in dopamine solution, mixing with quaternized poly (4-vinylpyridine), combining with graphenes and carbon nanotubes, direct fluorination and etching in acid solution to mention few. This review highlight factor(s) that cause low performance of activated carbon and modification strategies used to treat activated carbon to enhance its adsorption performance. Furthermore, characterization methods used to confirm whether the modification was successful and the practical application of modification methods have been discussed. To our view this work will provide an understanding of the contribution offered by modified activated carbon electrodes in the development of CDI technology.
Naturally occurring metal oxides from rocks as capacitive deionization electrode material for antibacterial activities
(Elsevier, 2023-05) Alphonce, Furaha; Alfredy, Tusekile; Hilonga, Askwar; Jande, Yusufu
The present study aimed to investigate the efficacy of activated carbon (AC) electrode embedded with naturally occurring metal oxides (MO) from rocks for antibacterial activities against both gram- negative (Escherichia coli) and gram-positive (Salmonella aureus) bacteria using capacitive deionization technique. The desalination and disinfection performance of the fabricated AC/MO electrode was evaluated through the batch mode experiments conducted at a potential difference of 1.2 V for 240 min (4 h). The results revealed that the AC/MO electrode achieved a complete removal efficiency of 100% for E. coli and 60% for S. aureus in the field water collected from Nduruma stream (natural water). The bacterial removal mechanism was attributed to the capacitive deionization (CDI) process and physical adsorption. The study highlights the potential of AC/MO electrode material as an effective antibacterial agent for the CDI process, which may have significant implications for the development of new technologies for water purification and disinfection.

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Browsing Materials, Energy, Water and Environmental Sciences by Subject "Activated carbon"