Asymmetric supercapacitor based on novel coal fly ash derived metal–organic frameworks as positive electrode and its derived carbon as negative electrode

Journal of Applied Electrochemistry - The paper presents a comparative study between aluminum fumarate metal–organic framework (Al-FumMOF) and a novel coal fly ash derived aluminum MOF...     

Chemical adsorption of NiO nanostructures on nickel foam-graphene for supercapacitor applications

Few-layer graphene was synthesized on a nickel foam template by chemical vapor deposition. The resulting three-dimensional (3D) graphene was loaded with nickel oxide nanostructures using the successive ionic layer adsorption and reaction technique. The composites were characterized and investigated as electrode material for supercapacitors. Raman spectroscopy measurements on the sample revealed that the 3D graphene consisted of mostly few layers, while X-ray diffractometry and scanning electron microscopy revealed the presence of nickel oxide. The electrochemical properties were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and potentiostatic charge–discharge in aqueous KOH electrolyte. The novelty of this study is the use of the 3D porous cell structure of the nickel foam which allows for the growth of highly conductive graphene and subsequently provides support for uniform adsorption of the NiO onto the graphene. The NF-G/NiO electrode material showed excellent properties as a pseudocapacitive device with a high-specific capacitance value of 783 F g^?1 at a scan rate of 2 mV s^?1. The device also exhibited excellent cycle stability, with 84 % retention of the initial capacitance after 1000 cycles. The results demonstrate that composites made using 3D graphene are versatile and show considerable promise as electrode materials for supercapacitor applications.     

Gas sensing study of hydrothermal reflux synthesized NiO/graphene foam electrode for CO sensing

Nickel oxide nanosheets have been successfully synthesized on the graphene foam (GF) using hydrothermal reflux process for their application as carbon monoxide (CO) gas sensor. X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, energy dispersive spectroscopy, and gas sorption analysis were used to characterize the structure and morphology of the samples. The morphology (SEM), crystal structure (XRD and Raman), and elemental composition (EDS) analysis of NiO/GF composite confirmed the cubic crystal structure of NiO and elemental composition (i.e., Ni, O, and C) of NiO/GF composite. The results reveal that the incorporation of graphene into NiO nanosheets not only improved the surface area of NiO/GF composite, but also enhanced the performance of the composite on CO sensing by improving its conductivity. These results indicate that NiO/GF has potential as electrode material for CO gas sensor.     

Shifts in the food of Nile perch (Lates niloticus) in Lake Victoria

The study investigated diet of Nile perch in Lake Victoria and compared results with past data from the same lake in order to analyse diet shifts over time. Fish samples (2020) were collected by seining and trawling from 2012 to 2016. In overall, Caridina nilotica (59%) was the dominant food item in the diet, while Rastrineobola argentea (5%) contributed the least. The diet of Nile perch of 1 cm was copepods, cladocerans and rotifers. The diet changed to only copepods and cladocerans at 2 cm. The proportion of the relatively large calanoids increased with Nile perch size in 1988/89, comprising between 35 and 80% of the diet of fishes of 3–4 cm. Nile perch of 6–25 cm TL fed more on C. nilotica in 2012/2016, compared to 1988/1989 and 2006/08. Haplochromines were fed on more in 2006/2008 than in 2012/2016 by Nile perch of 6–30 cm TL as fish size increased. The frequencies of occurrence of R. argentea in the diet were highest in 1988/1989, and lowest in 2006/2008, for fish size of up to 30 cm TL. The proportion of Odonata in the diet of size class 16–20 and 21–30 cm TL were highest in 2012/2016 and 1988/1989, respectively. Thus, shifts in Nile perch diet was observed from zooplankton to C. nilotica, then to haplochromines and finally to fish prey as size increased. Nile perch preferred haplochromines with C. nilotica as the substitute food. Cannibalism was observed to have decreased, only being evidenced in Nile perch above 35 cm TL, which could actually have a positive impact on the Nile perch fishery. The information on shifts in diet of Nile perch in Lake Victoria is of considerable ecological importance.     

Some aspects of reproduction and feeding habits of Nile tilapia (Oreochromis niloticus) in three dams in Uasin Gishu County,Kenya

Knowledge of the fisheries status of dams within Uasin Gishu County was needed prior to the government's plan to introduce fish and fisheries in the area. The dams were constructed in the 1950s and stocked with tilapia for local consumption, recreation and control of macrophytes. The Nile tilapia (Oreochromis niloticus) was selected for the present study due to its establishment success and popularity in the Kenyan market. Water samples were collected at subsurface levels for phytoplankton analysis and compared with the phytoplankton found in the stomachs of O. niloticus, revealing the food preference of the fish in a natural environment. Fish samples were collected with gillnets and beach seines. The results of the present study identified the most important food items for the fish were Chlorophyceae (green algae), Bacillariophyceae (diatoms) and Cyanophyceae (blue‐green algae). The fish exhibited a relative condition factor of about 1.00, indicating their robustness or well‐being in the dams. The LM₅₀was reached at 18–20 cm class interval, which coincides with the most critical breeding biomass needing some kind of protection for sustainable management of the fishery.     

Growth,mortality and recruitment of silver cyprinid (Rastrineobola argentea) in the open waters of Lake Victoria,Kenya

This study investigated the growth, mortality and recruitment of Rastrineobola argentea in Lake Victoria on the basis of length–frequency data collected during the period 2014–2015. The asymptotic length (L _∞ ) had a mean (±SE ) value of 53.50 ± 0.50 mm SL , growth curvature (K ) of 0.81 ± 0.06 year^?1, total mortality (Z ) of 2.96 ± 0.12 year^?1, a natural mortality (M ) of 1.23 ± 0.06 year^?1, a fishing mortality (F ) of 1.74 ± 0.07 year^?1, an exploitation rate (E ) of 0.59 ± 0.01, a growth performance index (?′ ) of 3.36 ± 0.02 and a length at 50% capture (L ₅₀) of 28.25 ± 0.43 mm SL . The fish exhibited a peak breeding during the months of May and August. The Beverton and Holt relative yield‐per‐recruit model indicated mean (±SE ) indices as 0.37 ± 0.01 for optimum sustainable yield (E _0.5), 0.76 ± 0.01 for maximum sustainable yield (E _max) and 0.66 ± 0.01 for economic yield (E _0.1). Compared with previous studies, there is a great decline in the sizes of R. argentea stocks in Lake Victoria. Thus, management measures should include restriction on illegal seine nets <10 mm mesh size and re‐enforcement of a fishing ban or a closed season.     

Application of phytoplankton community structure for ranking the major riverine catchments influencing the pollution status of a lake basin

The present study demonstrates the application of a multi‐metric Phytoplankton Index of Biotic Integrity (PIBI) approach for ranking of major river catchments in the Kenyan part of Lake Victoria on the basis of their pollution status. The index utilizes water quality and zooplankton data, phytoplankton diversity, abundance and attributes, as well as literature information. The rivers were sampled from 2016 to 2018 during the wet season (March) and dry season (July). The separation power of the Mann–Whitney U test (p < .05) qualified eight discriminant metrics for phytoplankton samples into a scoring system of 1, 3 and 5, based on high, fair and slight deviation from the best site, respectively, in development of the final PIBI. The Kuja and Sondu‐Miriu rivers had the highest PIBI, signifying least pollution influence on the lake. In contrast, the Yala and Nzoia rivers exhibited the lowest PIBI, representing the catchments with a higher pollution influence on the lake. The fair to poor integrity classes for the major river catchments in the region signified a deteriorating lakescape. The present study presents the preliminary results of using phytoplankton metrics for development of the Index of Biotic Integrity (IBI) approach in the region as a decision‐making support tool for the effective management and sustainable use of water resources in the lake basin.     

A comparative study of Labeo victorianus (Bouelenger, 1901) and Oreochromis niloticus (Linnaeus, 1758) grown in polyculture systems

A polyculture experiment with African carp (Labeo victorianus) and Nile tilapia (Oreochromis niloticus) was conducted for 24 weeks in 12 earthen ponds measuring 150 m² to assess their compatibility. Monoculture treatments T1 and T4 for L. victorianus and O. niloticus, respectively, were the controls for the two species, while treatments T2 and T3 were a polyculture of L. victorianus and O. niloticus at a ratio of 1:2 and 2:1, respectively. All treatments were carried out in triplicate, with feedings performed twice daily at 09:00 hr and 16:00 hr at 10%, 5% and 3% body weight distributed evenly over the 24‐week growth period. Fish sampling was conducted monthly, while water quality was measured biweekly. Treatment T3 (1L: 2T) had a significantly (p < .05) higher survival (L = 49% and T = 87%), compared to T2 (L = 31% and T = 69%, 2L: 1T). O. niloticus monoculture treatment (T4) exhibited a significantly higher survival (p < .05) and higher growth (80%; 79 ± 20.04 g) than L. victorianus monoculture (T1) (50%; 13.12 ± 4.49 g). Dawn and afternoon temperatures ranged between 20.16–24.49°C and 23.76–31.07°C, respectively. The lowest temperatures were recorded in the months of June, July and August. The NH₃ concentration was zero at 14:00 hr for all treatments throughout the growth period, but significantly higher (p < .05) in T1 at 06:00 hr. The pH and DO levels at 06:00 hr and 14:00 hr were significantly different in all the treatments (p < .05). The slow growth of L. victorianus can be associated with the low temperatures and DO levels. However, there is need to identify other factors that may have contributed to the poor growth of L. victorianus. Accordingly, this study recommends L. victorianus growth trials in other culture systems, coupled with different feed formulations, to identify optimal culture conditions.     

Assessment of catfish (Clarias gariepinus) stock in Lake Baringo,Kenya

The management measures used for sustainable utilization of Clarias gariepinus in Lake Baringo do not have a stock assessment reference, attributable mainly to a lack of information on biological limits and target reference points. Assessment of Clarias gariepinus stock in Lake Baringo was carried out between August 2013 and July 2014. A total of 2772 fish were sampled from 25 boats (40%) for 5 days each week for length and weight measurements. Fish Stock Assessment Tools and yield model were used to estimate population parameters, exploitation rate and optimal fishing scenarios. Annual C. gariepinus standing biomass was estimated at 21 383 kg, L_∞ = 114.30, K = 0.37 year^?1, W = 0.0147L^2.81, Z = 1.14 year^?1, M = 0.61 year^?1, F = 0.53 year^?1, and exploitation rate = 0.46 year^?1. The relative yield‐per‐recruit (Y′/R) and biomass‐per‐recruit (B′/R) resulted in E_max = 0.44 and F_MSY = 0.50 year^?1. The yield‐per‐recruit ratio at maximum sustainable yield was 29.12%, and the SSB_MSY per recruit ratio = 56.10%. The steady‐state biomass, exploitation rate and optimal fishing scenario indicated a pristine fishery for the lake, suggesting the current fishing efforts should not be exceeded to enable sustainable economic utilization of C. gariepinus.