Carbonation of brine impacted fractionated coal fly ash: Implications for CO2 sequestration

Coal combustion by-products such as fly ash (FA), brine and CO2 from coal fired power plants have the potential to impact negatively on the environment. FA and brine can contaminate the soil, surface and ground water through leaching of toxic elements present in their matrices while CO2 has been identified as a green house gas that contributes significantly towards the global warming effect. Reaction of CO2 with FA/brine slurry can potentially provide a viable route for CO2 sequestration via formation of mineral carbonates. Fractionated FA has varying amounts of CaO which not only increases the brine pH but can also be converted into an environmentally benign calcite. Carbonation efficiency of fractionated and brine impacted FA was investigated in this study. Controlled carbonation reactions were carried out in a reactor set-up to evaluate the effect of fractionation on the carbonation efficiency of FA. Chemical and mineralogical characteristics of fresh and carbonated ash were evaluated using XRF, SEM, and XRD. Brine effluents were characterized using ICP-MS and IC. A factorial experimental approach was employed in testing the variables. The 20–150 μm size fraction was observed to have the highest CO2 sequestration potential of 71.84 kg of CO2 per ton of FA while the >150 μm particles had the lowest potential of 36.47 kg of CO2 per ton of FA. Carbonation using brine resulted in higher degree of calcite formation compared to the ultra-pure water carbonated residues.Web of Scienc

Evaluation of persistent organochlorine pesticides and polychlorinated biphenyls in Umgeni River bank soil, KwaZuluNatal, South Africa

is study investigated the presence and distribution of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in soil collected along the banks of the Umgeni River, one of the largest rivers in the province of KwaZulu-Natal, South Africa. e analysis was performed using gas chromatography-mass spectrometry (GC-MS). e results showed that the levels of OCPs ranged from 3.58±0.09 ng/g for hexachlorobenzene (HCB) to 82.65±2.82 ng/g for HCH, with an individual mean concentration of 24.33±2.00 ng/g dry weight (dw). e levels of PCBs ranged from 10.46 ng/g for PCB105 to 89.46 ng/g for PCB180, with an average PCB value of 25.47±1.26 ng/g, dw. e highest levels of OCPs and PCBs were found at Northern Wastewater Treatment Plant (mean OCP: 32.39±3.97 ng/g and PCB: 67.87±1.67 ng/g). e two most abundant contaminants in the river were endrin and PCB180.Keywords: Umgeni River, bank soil, OCPs, PCBs, gas chromatography mass spectrometr

Use of bipolar electrochemistry in nanoscience: contact free methods for the site selective modification of nanostructured carbon materials (The)

Bipolar electrochemistry occurs when an isolated conductive substrate inside an electric field supports both oxidation and reduction reactions. The method requires no direct contact between the power supply and the substrate. In the following thesis bipolar electrochemistry has been used to deposit palladium onto isolated graphite platelets, carbon nanofibers (CNF), and carbon nanotubes (CNT), as well as, various metals, a semiconductor, and an electropolymer on CNTs. Initial work used pulsed DC electric fields to deposit palladium onto isolated graphite platelets. Transmission electronmicroscopy (TEM) studies on the platelets found palladium metal on one area, indicative of a bipolar mechanism, and palladium deposits that varied from surface bound to highly ramified deposits. No correlation was found betweenthe frequency used to prepare the deposits and the palladium metal dispersion. The same field intensities and frequencies used on the graphiteplatelets were used to produce CNFs with palladium on one tip. The amount of palladium deposited on one tip of a CNF was controlled by adjusting how long the electric field was applied. Preliminary experiments to produce bulkquantities of CNFs with palladium bipolar electrodeposits used CNFs ball milled with silica, and CNFs suspended in tetrahydrofuran or methylene chloride. The palladium content, measured by atomic absorption spectroscopy,of the functionalized CNFs in silica showed no difference with increased CNF loading; however, TEM studies found a small number of functionalized CNFs with palladium on one tip. Work on CNFs suspended in THF and methylenechloride used suspensions with high loadings of CNFs which led to small percentages of CNFs with bipolar electrodeposited palladium. Finally CNTsobtained commercially and CNTs grown using chemical vapor deposition were successfully functionalized using bipolar electrodeposition. These experiments demonstrate a reliable and controlled method to modify nanostructured materials.Ph.D., Chemistry -- Drexel University, 200

Hall measurements on carbon nanotube paper modified with electroless deposited platinum

Carbon nanotube paper, sometimes referred to as bucky paper, is a random arrangement of carbon nanotubes meshed into a single robust structure, which can be manipulated with relative ease. Multi-walled carbon nanotubes were used to make the nanotube paper, and were subsequently modified with platinum using an electroless deposition method based on substrate enhanced electroless deposition. This involves the use of a sacrificial metal substrate that undergoes electro-dissolution while the platinum metal deposits out of solution onto the nanotube paper via a galvanic displacement reaction. The samples were characterized using SEM/EDS, and Hall-effect measurements. The SEM/EDS analysis clearly revealed deposits of platinum (Pt) distributed over the nanotube paper surface, and the qualitative elemental analysis revealed co-deposition of other elements from the metal substrates used

Rainfall and Temperature Trends and Variability in Arid and Semi-arid Lands of Kitui County, Kenya

A study was carried out to analyse rainfall and temperature trends and variability in selected agro-ecological zones in Kitui County. Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) rainfall dataset was used while temperature data was obtained from the Climatic Research Unit gridded Time Series (CRU TS) dataset. The results indicated that there was a non-significant decreasing trend (p<0.05) in average annual rainfall in all the four agro-ecological zones (p<0.05) for a 30-years period (1988-2018) in the study area. A decreasing trend in March-April-May (MAM) seasonal rainfall trend was reported in the arid and semi-arid agro-ecological zones while an increasing trend was recorded in the transitional and semi-humid zones. For the October-November-December (OND) seasonal rainfall, a non-significant decreasing trend was reported in all the four agro-ecological zones. Additionally, a higher annual rainfall variability was recorded in the drier (arid) and wetter (semi-humid) zones compared to that in semi-arid and transitional zones. Moreover, the study established that there was a spatial variation in both MAM and OND seasonal rainfall variability and that rainfall variability was higher in the OND seasonal rainfall than that of the MAM seasonal rainfall in all the agro-ecological zones. With reference to temperature trends, a statistically significant increasing trend in annual and OND seasonal average maximum and minimum temperatures was reported in all the four agro-ecological zones. Further, the study noted a non-significant increasing trend in maximum and minimum temperatures for the MAM season in all the agro-ecological zones. In regard to temperature variability, the study deduced that there was low temperature variability compared to rainfall variability in all the four agro-ecological zones. The study recommends that location-specific rainfall and temperature analysis should guide planning and implementation of adaptation strategies for effective response to climate variability. Keywords: Agro-ecological Zones, Mann-Kendall Test, Coefficient of Variation, CHIRPS, CRU TS DOI: 10.7176/JEES/12-12-05 Publication date: December 31st 202

Low temperature synthesis of multiwalled carbon nanotubes and incorporation into an organic solar cell

Abstract: Metal nanoparticle (MNP) catalysts used for the synthesis of multiwalled carbon nanotubes (MWCNTs) consisted of single metals (Fe, Ni or Co) and bimetallic mixture (CoFe, NiFe or NiCo). MWCNTs were successfully synthesised at 200 _C in 10 min using liquefied petroleum gas as carbon source with non-equilibrium plasma enhanced chemical vapour deposition (PECVD) method. The nanostructures and the morphology of the MNPs and the MWCNTs film were characterised using relevant microscopic and spectroscopic methods. The synthesised MWCNTs were used as part of the electrode material in organic solar cell (OSC) set-up. Poly (3,4- ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) was used as an electron transporter and poly-3-hexyl thiophene (P3HT) as an electron donor. The performance of OSC devices was tested using standard electrical measurements and solar simulator operating at 100 mW/cm2. The measured power conversion efficiencies was found to be dependent on the metal catalyst used during synthesis. Among all the catalysts employed in this investigation, the best device performance was found from the synthesis of MWCNTs using Fe as a catalyst followed by Co and then Ni, respectively

Chemical, mineralogical and morphological investigation of coal fly ash obtained from Mpumalanga Province, South Africa

Abstract: Background and Objective: Coal fly ash generated from the combustion of coal by thermal power plant stations are enormous and the disposal there of is a big problem. In the present study, the chemical, mineralogical and morphological characterization of coal fly ash samples (CFAs) obtained from Mpumalanga province, South Africa were investigated. Materials and Methods: The CFAs were characterised by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), high resolution transmission electron spectroscopy (HRTEM) and the selected area electron diffraction (SAED) analytical technique. Result: Experimental results showed that the CFAs contain hematite, magnetite, calcite, lime, mullite and quartz. The CFAs are polycrystalline, could be categorized as class F fly ash and the particles are spherical in shape. Conclusion: The phase characterization suggested that CFA could be used for the synthesis of nanoparticles, as well as extraction of valuable metals, more so, the elemental composition of the CFAs suggested that the storage and disposal of CFAs could lead to the release of salts and toxic elements into the environment, thereby, contaminating surface and ground waters

Design of multi-layer graphene membrane with descending pore size for 100% water desalination by simulation using ReaxFF

DATA AVAILABILITY STATMENT : Data are available upon request from the corresponding author and based on university rules.The performance of a desalination membrane depends on a specific pore size suitable for both water permeability and salt rejection. To increase membrane permeability, the applied pressure should be increased, which creates the need to improve membrane stability. In this research article, a molecular dynamics (MD) simulation was performed using ReaxFF module from Amsterdam Modeling suite (AMS) software to simulate water desalination efficiency using a single and multi-layer graphene membrane. The graphene membrane with different pore sizes and a multi-layer graphene membrane with descending pore size in each layer were designed and studied under different pressures. The stability of the membrane was checked using Material Studio 2019 by studying the dynamics summary. The single-layer graphene membrane was evaluated under pressures ranging from 100 to 500 MPa, with the salt rejection ranging from 95% to 82% with a water permeability of 0.347 109 to 2.94 109 (mm.g.cm2s1.bar1), respectively. Almost 100% salt rejection was achieved for the multi-layer graphene membrane. This study successfully demonstrated the design and optimization of graphene membrane performance without functionalization.The Faculty of Sciences at the University of Johannesburg, South Africa,https://www.mdpi.com/journal/membranesam2023Chemistr

An in-situ FTIR-LCR meter technique to study the sensing mechanism of MnO2@ZIF-8/CNPs and a direct relationship between the sensitivity of the sensors and the rate of surface reaction

DATA AVAILABITY STATEMENT: Data will be made available on request.SUPPORTING INFORMATION: FILE S1: Appendix ADiethylamine vapor is harmful to people if inhaled or swallowed, as it results in the oxidation of hemoglobin in the body into unwanted methemoglobin, which is unable to transport oxygen in the blood, resulting in reduced blood oxygenation. Lack of blood oxygenation leads to hypoxemia. MnO2 nanorods, carbon soot, and MnO2@ZIF-8 are sensing materials used to prepare solid-state gas sensors that operate at room temperature. The prepared sensing materials were characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The performance of the MnO2@ZIF-8 based sensor improved significantly when the carbon soot was introduced into the composite. The effect of the amount of CNPs in the composite on the performance of the sensors was studied. The MnO2@ZIF-8/CNPs-based sensor with a 3:1 mass ratio was highly selective towards diethylamine vapor over acetone, methanol, ethanol, and 3-pentanone vapors. An in situ FTIR coupled with LCR meter was used to understand the sensing mechanism of diethylamine vapor and it was found that the sensing mechanism was by deep oxidation of diethylamine to CO2, H2O, and other molecules. The sensing mechanism was studied by monitored by CO2 band intensity which was produced from the reaction between the sensing materials and the analyte vapor. As the sensor’s exposure time increased the intensity of the CO2 IR band increased. We observed the direct relationship between the surface reaction rate and the sensor’s sensitivity.The University of Johannesburg.https://www.elsevier.com/locate/rinpChemistrySDG-09: Industry, innovation and infrastructur

Zeolitic imidazolate framework as humidity-resistant solid state-chemiresistive gas sensors : a review

DATA AVAILABILITY : Data will be made available on request.With significant technological advances, solid-state gas sensors have been extensively applied to detect toxic gases and volatile organic compounds (VOCs) in confined areas such as indoor environments and industries and to identify gas leakage. Semiconductor metal oxides are the primary sensing materials, although their major drawbacks include a lack of sensitivity, poor performance at high humidity, and operating at high temperatures ranging between 140 and 400 ◦C. Recently, the use of zeolitic imidazolate frameworks (ZIFs) in gas sensors has received considerable attention as a promising material to overcome the drawbacks possessed by semiconductor metal oxide-based gas sensors. Because of their unique properties, including size tunability, high surface area, and stability in humidity, ZIF becomes a preferred candidate for sensing materials. The use of ZIF materials in gas sensors is limited because of their high-temperature operation and low gas responses. This review outlines the strategies and developments in the utilization of ZIF-based materials in gas sensing. The significant influence of the addition of carbon additives in ZIF materials for temperature operation sensors is discussed. Finally, ZIF-carbon additives and SMO@ZIFs/carbon additives are the proposed materials to be studied for future prospects for the detection of VOCs at low temperatures and exhibiting good selectivity towards the gas of interest.http://www.cell.com/heliyonam2024ChemistrySDG-09: Industry, innovation and infrastructur