Design and development of low cost materials for water electrolyzers

Abstract: The construction and modifications of highly active, stable and low cost electrocatalysts promoting the oxygen and hydrogen evolution reactions (OER and HER) in water splitting are the key areas of research in energy generation and conversion. Given the significance of the HER and OER electrocatalysts, the objective of this study was to fabricate low-cost materials that are capable of being used as cathode and anode electrocatalysts in water splitting. Thus, nanomaterials and nanostructures provide unique properties that have allowed then to play an essential role in recent developments in energy-related applications. As known, the structural and electronic properties of nanomaterials/nanostructures stimulate their physical and chemical properties, and therefore their catalytic activity. Thus, tailoring the morphology of nanomaterials/nanostructures either during the synthesis or post the synthesis process, have been known to promote their structural and electronic properties, thus leading to enhanced catalytic activity...Ph.D. (Chemistry

Near-Infrared Spectroscopy Combined with Multivariate Tools for Analysis of Trace Metals in Environmental Matrices

Environmental contamination by trace elements is becoming increasingly important problem worldwide. Trace metals such as cadmium, copper, lead, chromium, and mercury are major environmental pollutants that are predominantly found in areas with high anthropogenic activities. Therefore, there is a need for rapid and reliable tools to assess and monitor the concentration of heavy metal in environmental matrices. A nondestructive, cost-effective, and environmentally friendly procedure based on near-infrared reflectance spectroscopy (NIRS) and chemometric tools has been used as alternative technique for the simultaneous estimation of various heavy metal concentrations in environmental sample. The metal content is estimated by assigning the absorption features of metals associated with molecular vibrations of organic and inorganic functional groups in organic matter, silicates, carbonates, and water at 780–2500 nm in the near-infrared region. This chapter, reviewed the application of NIRS combined with chemometric tools such as multiple linear regression (MLR), principal component regression (PCR), and partial least squares (PLS) regression. The disadvantages and advantages of each chemometric tool are discussed briefly

Preparation of modified magnetic nanocomposites and their application for preconcentration and speciation of selected trace elements in river water samples

M.Sc. (Nanoscience)Abstract: Trace elements analysis is globally of interest owing to their influence on the quality of water systems which affects both aquatic and terrestrial organisms. Most, if not all trace element exist naturally within the water systems at low concentrations, however, anthropogenic activities such as industrial, mining and agricultural activities elevates these concentrations which compromise the safety and cleanliness of drinking water. Most of the industries, mines and agricultural farms and lands are located outside the central business district areas towards rural based settlement areas. Thus, the discharges of wastes from industrial, mining and agricultural processes affects mostly people staying in the rural areas since most of these areas lack municipal water and people living in and around these areas depend on river, stream and dam water for survival. This study therefore examines the effects and impacts of some industries located in the outskirts of rural areas around Thohoyandou town in terms of the concentration and speciation of selected trace elements in river water. In this study, the nanometer-sized ferrous-ferric oxide magnetic nanocomposite (Fe3O4@MnO2@Al2O3@Au) was successfully synthesized using co-precipitation and sol gel methods. The structural, morphological and magnetic properties of the nanocomposite material were characterized by Fourier transform infrared spectroscopy (FTIR), Nitrogen adsorption-Brunauer Emmett Teller (BET), X-ray diffraction spectroscopy (XRD), Scanning electron microscopy/Energy dispersive x-ray spectroscopy (SEM/EDS), Transmission electron microscopy (TEM), Vibrating sample magnetometer (VSM) and Zeta-potential measurements. The results from TEM and XRD confirm the rhombohedral shape of the nanocomposite with an average particle size of 15 nm and 17 nm, respectively. The SEM results show a variety of shapes of the nanocomposite; however, rhombohedral shaped particles were more dominant. EDS confirms the formation of a pure Fe3O4@MnO2@Al2O3@Au nanocomposite with no impurities. The FTIR also supported the formation of the nanocomposite structure. The nanocomposite was applied as a sorbent for preconcentration of As via ultrasound assisted magnetic solid phase extraction (UAMSPE). The preconcentrated arsenic was quantified using ICP-MS. A 25-1 fractional factorial design was used as a tool for optimizing the developed analytical methodologies. Under optimized conditions, the limit of detection and quantification were 8.6 and 28.5 ng L-1, respectively. The precision of the developed UA-MSPE method estimated in terms of..

An investigation on the potential interactions between colophospermum mopane and its neighbouring understory vegetation

MSc (Botany)Department of Botan

Nanocomposites for Electrochemical Sensors and Their Applications on the Detection of Trace Metals in Environmental Water Samples

The elevated concentrations of various trace metals beyond existing guideline recommendations in water bodies have promoted research on the development of various electrochemical nanosensors for the trace metals’ early detection. Inspired by the exciting physical and chemical properties of nanomaterials, advanced functional nanocomposites with improved sensitivity, sensitivity and stability, amongst other performance parameters, have been synthesized, characterized, and applied on the detection of various trace metals in water matrices. Nanocomposites have been perceived as a solution to address a critical challenge of distinct nanomaterials that are limited by agglomerations, structure stacking leading to aggregations, low conductivity, and limited porous structure for electrolyte access, amongst others. In the past few years, much effort has been dedicated to the development of various nanocomposites such as; electrochemical nanosensors for the detection of trace metals in water matrices. Herein, the recent progress on the development of nanocomposites classified according to their structure as carbon nanocomposites, metallic nanocomposites, and metal oxide/hydroxide nanocomposites is summarized, alongside their application as electrochemical nanosensors for trace metals detection in water matrices. Some perspectives on the development of smart electrochemical nanosensors are also introduced

Removal of methylene blue using MnO2@rGO nanocomposite from textile wastewater: Isotherms, kinetics and thermodynamics studies

In this study, the adsorptive removal of methylene blue dye, which is commonly used in textile industries, was investigated using the MnO2@reduced graphene oxide (rGO) adsorbent. The sonication-assisted synthesis from rGO nanosheets and MnO2 nanoparticles resulted to the MnO2@rGO nanocomposite with improved physicochemical properties. The characterization results showed the improved surface area, porous structure and adsorption sites from the nitrogen adsorption-desorption studies, improved morphology from the Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) and the improved crystal structure from X-ray powder diffraction (XRD). The improved physicochemical properties on the MnO2@rGO nanocomposite played a significant role in enhancing the dye removal in textile wastewater. The equilibrium experimental data was best described by the Langmuir isotherm model with a maximum adsorption capacity of 156 mg g−1, suggesting a monolayer adsorption. The kinetic data best fitted the pseudo-second order kinetic model, suggesting a chemisorption adsorption process. The thermodynamic data (ΔG°, ΔH° and ΔS°) confirmed the feasibility, randomness and spontaneous nature of the adsorption process. The mechanism of adsorption involved the hydrogen bonding, π-π interactions and electrostatic interactions. The removal of methylene blue using MnO2@rGO nanocomposite in spiked textile wastewater yielded a 98–99% removal. The method demonstrated competitiveness when compared with literature reported results, paving way for further investigations towards industrial scale applications

A green approach for enhancing the electrocatalytic activity and stability of NiFe2O4/CB nanospheres towards hydrogen production

Among the exfoliation processes applied on layered materials, it is the first time to explore the ultrasonic exfoliation in water for improving the catalytic properties of NiFe2O4/CB (CB = carbon black) nanospheres towards the electrocatalytic hydrogen evolution reaction (HER) in acidic media. It is found that after exfoliation, the overpotential of HER on NiFe2O4/CB nanospheres is improved by about 90 mV at a current density of 10 mA cm−2. Moreover, the exfoliated NiFe2O4/CB nanospheres are not only more stable than the commercial Pt/C catalyst, but also they exhibit an overpotential improvement of about 100 mV at 50 mA cm−2, after 6000 CV cycles. It is also found that the ultrasonic process causes uniformed NiFe2O4/CB particles, an increase of the electrochemical active sites, enriched Fe2+ ion and Fe3+ occupied on tetrahedral sites on the surface layer of the NiFe2O4/CB nanospheres, as resulted from the analysis with XPS, FTIR etc., leading to a higher activity and excellent durability. Furthermore, the approach also provides new insights on processing of materials in a green route. © 2020 Elsevier Lt