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Pyrolytic carbon black (CBp) is a solid by-product of tyre pyrolysis that contains various contaminants from the tyre additives. These contaminants limit the use of CBp as a carbon source for energy storage applications such as supercapacitors. This study aims to improve the physicochemical, morphological, and electrochemical properties of CBp by applying different chemical treatments and activation methods. The chemical treatments include acid (HCl), base (NaOH), acid-base (HCl/NaOH), and desulphurization (NaOH in xylene) processes to remove impurities such as sulphur, zinc, and silicon. The treated CBp samples are then activated by KOH impregnation technique to increase the surface area and porosity. The characterizations of the treated CBp samples are performed using Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDX), X-ray Diffraction (XRD), and Brunner Emmett Teller (BET). The electrochemical performance of the treated CBp samples are evaluated using galvanostatic charge-discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results show that the chemical treatments significantly reduce the impurity levels and enhance the electrochemical performance of CBp. The desulphurized CBp sample exhibits the highest specific capacitance of 218 F/g among the treated CBp samples. The findings of this study suggest that CBp can be effectively utilized as a potential carbon source for supercapacitor electrodes by applying suitable chemical treatments and activation methods. This will create a circular economy to valorize CBp.

ABSTRACTRecent studies have focused on the processing of biowaste to obtain added value and to reduce organic waste in the general stream. This study investigated the synthesis of magnesium oxide (MgO) from magnesium-rich Cucurbita pepo (pumpkin) seeds for a precursor solution as a reducing agent via an eco-friendly method for the first time. The pumpkin seeds were ashed at 550°C for 6 h and subjected to acid-leaching. Mg(OH)2 was then precipitated using an aqueous solution of 2.0 M NaOH. The Mg(OH)2 was then calcined at 550°C for 4 h to obtain MgO. Physicochemical properties (i.e. proximate analysis, elemental composition, electrical conductivity (EC), pH) and selected heavy metals (i.e. Pb, Fe, As, Cd, Cr, Hg, Cu, and Ni) analyses were conducted on the seed samples and as-synthesized MgO. X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared (FTIR), citric acid test (CAT), and acid neutralization capacity (ANC) tests were techniques used to characterize the synthesized MgO. The results revealed the percentage yield of the MgO to be 23%. The pH of the as-synthesized MgO was recorded as 10.63. XRF studies showed that MgO made up 75.1% of the total weight synthesized. XRD results showed the presence of crystalline cubic structures of MgO. FTIR results showed a peak at 584 cm−1 which confirmed the formation of MgO. The produced MgO was highly reactive, with a CAT time of 2 s. The ANC of the MgO was high at 22.77 mol+/kg. Also, metal concentrations such as Fe, Cu, Cd, Ni, Pb, Hg, As, and Cr in MgO were below the WHO stipulated limits of 350, 36, 0.8, 35, 85, 0.03, 40, and 100, respectively. This implies its suitability for soil remediation purposes. Results indicate that the as-synthesized MgO from Cucurbita pepo (C. pepo) seeds could be used for several applications due to its high alkalinity, reactivity, and fast CAT time.

Obtaining carbon materials in a sustainable way and applying them in energy storage systems is attracting more attention. Spent potlining (SPL) which is a carbon-rich waste produced in electrolytic cells of aluminium smelters can be a potential source of carbon for engineering applications. However, SPL is hazardous in nature and needs to undergo chemical treatment for most engineering applications. In this study, a four-step procedure was adopted to remove sodium fluoride (NaF), cryolite (Na3AlF6), alumina (Al2O3), calcium fluoride (CaF2), sodium aluminate (NaAl11O17) and silica (SiO2) from the SPL. The adopted treatment processes proved effective as Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD) results showed no traces of the major impurities after the treatment. The treated carbon-rich SPL was activated using NaOH to obtain activated SPL (ASPL). The ASPL was doped with TiO2 to form ASPL-TiO2 (1:1), ASPL-TiO2 (3:1) and ASPL-TiO2 (2:1) electrodes. The electrode materials were tested using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The ASPL, ASPL-TiO2 (1:1), ASPL-TiO2 (3:1) and ASPL-TiO2 (2:1) demonstrated specific capacitance of 180.2 F/g, 279.1 F/g, 536.7 F/g, and 203.2 F/g at 10 A/g respectively with high stability over 1000 cycles. The present study was designed to determine the suitability of using chemically treated SPL as an alternative source of carbon for supercapacitor applications and this was achieved as the material exhibited an improved charge storage capacity.

Activities of artisanal mining pose ecological as well as health challenges through the release of heavy metals into the environment. This study assessed the potential risk of heavy metals in some selected vegetables at an artisanal gold mining site at Moseaso in the Wassa-Amenfi West District of Ghana. A total of 40 soil samples were collected from the study area at depth of 20 cm using a soil auger. At each site two each of the selected vegetables (tomatoes, spring onion, and lettuce) were sampled from the farms. Also, 9 water samples were also taken at sections of the stream (upstream, midstream, and downstream) for the analysis of As, Cd, Pb, and Hg using Atomic Absorption Spectroscopy. The results of the study revealed that the mean concentration of As (22.92 mg/kg), Cd (5.41 mg/kg), Pb (98.01 mg/kg), and Hg (0.81 mg/kg) in soils from the artisanal gold mining sites were all above the stipulated limits. The mean values of As, Cd, Pb, and Hg in the stream water were beyond the stipulated limit of 0.01, 0.03, 0.01, and 0.03 mg/l, respectively. Also, all the examined heavy metals in the selected food crops were above the reference limit. The bioaccumulation factor in the food crops was less than 1 except for cadmium which had a BF>1 in tomatoes, spring onion, and lettuce. The cancer risk assessment also revealed that, with the exception of Pb, all the heavy metals considered were above the USEPA-safe prescriptions of 1.0 × 10−6 to 1.0 × 10−4 for both adults and children. Based on the results, it can be recommended that the dietary intake of vegetables grown from the study site is not safe and poses severe health and environmental threats.

Contamination of the environmental receptors with heavy metals due to mining is a major topical environmental issue in Ghana. This research investigates the possible ecological and human health risks of heavy metal impacts due to mining in the Amansie West District in Ghana. A total of 18 soil samples were taken from the Bontesso illegal mining site in the district and analyzed for the levels of arsenic (As), cadmium (Cd), copper (Cu), nickel (Ni), and lead (Pb) using atomic absorption spectrometry (AAS). From principal component analysis, cluster analysis, and correlation coefficient analysis, the metals are derived from multiple sources, with substantial levels of correlations. Using geo-accumulation index (Igeo), contamination factor (CF), degree of contamination (Cd), pollution load index (PLI), ecological risk index (Er), and noncarcinogenic and carcinogenic risks, respectively, the impacts of As (12.2 mg/kg) and Cd (1.3 mg/kg) are above the WHO stipulated limit. Findings for pollution indices indicate moderate contamination, while HQ 1. Based on the USEPA standard, the carcinogenic risk of the pollutants for humans is higher than the range of 1 × 10−6 to 1 × 10−4. Furthermore, the ingestion route represents the highest contributor to cancer risk with arsenic posing the greatest risk. The results so far suggest that chemical components gradually accumulate and thus emphasize the importance of implementing the necessary mitigation methods to minimize the impacts of illegal mining activities in the study area.

The release of harmful particles from industries is one of the important sources of environmental pollution worldwide. The goal of this study was to determine the amounts of dust deposition and heavy metal pollution in the soils surrounding a cement mill in Konongo, Ghana. Topsoils (0-10 cm) were sampled at the four geographical axes of the factory within a radius of 400 m, while at the same time, about 500 g of cement was sampled with a hand trowel. A Frisbee dust sampler was used to examine the levels of dust depositions at the various geographical axes of the factory. The heavy metals such as cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), and lead (Pb) were measured in a total of 20 soil samples using atomic absorption spectroscopy (AAS). The results obtained for climatic elements such as wind speed and direction, temperature, and relative humidity were 2.25, 25.7, and 49.5 m3/s, respectively. The average deposition of dust within the study period using the geographical axis indicated that the southern axis recorded the highest dust accumulation with a mean of 60.2 g/m2 per month. The mean concentrations of metals at the various axes were 1.04 mg/kg, 4.78 mg/kg, 8.95 mg/kg, 9.30 mg/kg, and 18.4 mg/kg for Cd, Cr, Cu, Zn, and Pb, respectively. The concentration of chemical components investigated in the soil was below the WHO/FAO standard, except for Cd. The spatial distribution pattern of the examined heavy metals showed that Cd, Cr, and Cu represent possible sources of soil contaminants. According to the conclusions of this research, this paper suggests an approach to investigate the areas contaminated with heavy metals to call out the attention of local authorities to take action.

The levels of heavy metals pollution in water and soil around landfill sites are increasing due to the indiscriminate dumping of domestic and industrial wastes at these sites. This research was conducted to study the characterisation and stabilisation of heavy metals in soils and leachate at the Dompoase landfill site, Kumasi-Ghana. Nine surface composite soil samples (< 40 cm deep) were collected at Dompoase landfill site from the middle (hotspot) of the landfill site through a 15 m radius away from the landfill cell where there were no dumping activities. Untreated leachate sample was also collected from a dugout around the landfill cell at a 4 m distance. This untreated leachate sample is estimated to be over 10 years and has a pH of 7.5. Physicochemical properties (i.e., electrical conductivity, pH, temperature, moisture and clay contents) and heavy metals (i.e., Cu, Cd, Fe, Ni and Zn) analyses were conducted on the collected samples. The results showed that the mean concentrations of all the heavy metals in soil studied were all above the Ghana Environmental Protection Agency (EPA) and WHO guidelines with the exception of Ni. All the psychochemical parameters were also within the EPA guidelines. Concentrations of Ni and Cd in the leachate sample were low and could not be detected. Cu and Zn recorded concentrations below the EPA and WHO guidelines while Fe recorded concentrations above the EPA and WHO limits. The contamination factor revealed that Cu (CF = 0.00) can be classified as exhibiting low contamination with Fe (CF = 1.50), Cd (CF = 1.80) and Zn (CF = 2.35) showing moderate contaminations. Low-grade CaO in varying quantities was utilised as stabilising agent to stabilise the heavy metals within various samples for a 21-day period. The physicochemical properties were monitored within the 21-day period during the heavy metal stabilisation. The results showed a percentage reduction in concentrations of metals within the period. The work shows that low-grade CaO can effectively be used in the remediation of contaminated sites as a result of anthropogenic activities.

The growing need to preserve our natural resources and protect the environment has resulted in a continuous effort to develop clean, renewable, and sustainable materials for energy storage and conversion. Supercapacitors (SCs) are electrochemical storage devices that have attracted the attention of the scientific community owing to their high power density, high charge/discharge efficiency, and relatively infinite cycle-life. Recent efforts have been devoted to the development of hybrid materials for supercapacitor electrodes by combining the properties of electric double-layer (EDL) and pseudocapacitive materials to improve energy density, capacitance, rate capability, and cycle-life. In this work, the electrochemical properties of a hybrid electrode made of activated carbon (AC) and titanium dioxide nanotubes (TNT) were assessed and compared to a pristine AC electrode. The AC/TNT and the 100% AC electrodes were prepared by electrophoretic deposition (EPD) using a reticulated vitreous carbon (RVC) substrate. The electrochemical behavior of the as-prepared electrodes was analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). Generally, the TNTs facilitated the EPD and enhanced the electrochemical performance of the as-prepared AC/TNT electrodes. The specific capacitances of the hybrid and pristine electrodes were 128.4 Fg−1 and 41.73 Fg−1 at 0.5 Ag−1, respectively.