In this work, the reducing power of three reductants: hydrazine (chemical), ascorbic acid (mild) and the extract of Amaranthus hybridus (green) were investigated. Graphene oxide (GO) was synthesized by modified Hummer's method and was reduced by hydrazine (RGO-HZ), ascorbic acid (RGO-AA) and the extract of Amaranthus hybridus (RGO-AH). GO, RGO-HZ, RGO-AA and RGO-AH were characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy and ultraviolet visible spectrometry. The FTIR spectra showed the presence of oxygen functionality groups in GO which were reduced in all RGOs. The morphological properties showed that RGOs sheets were exfoliated forming clusters with roughened surfaces while the optical energy band gaps of 2.19, 3.90, 3.60, and 3.20 eV were estimated for GO, RGO-HZ, RGO-AA and RGO-AH respectively. It can be concluded that the three reductants demonstrated good reducing capacities. The ascorbic acid and the extract of Amaranthus hybridus, apart from being environmentally friendly, can also be good substitutes for the dangerous chemical hydrazine.

Banana peels, a common fruit waste was adopted as a material precursor in this study to synthesize highly porous activated carbon from banana peels (ABP) which serves as an electrode material for a symmetric supercapacitor device. The activation was done using KOH pellets at different carbonization temperatures ranging from 750 °C to 950 °C. The ABP sample obtained from the 900 °C carbonization temperature (ABP900) exhibited unique material properties such as hierarchical porous nano-architecture containing micropores, and mesopores with the highest specific surface area (1362 m 2 g-1). Electrochemical performance investigation in different neutral aqueous electrolytes showed that the best response was obtained in NaNO 3 for the ABP900 electrode. The symmetric device subsequently assembled using 1M NaNO 3 operated in a potential window of 1.8 V, exhibited a specific capacitance of 165 F g-1 with a corresponding energy density of 18.6 W h kg-1 at 0.5 A g-1. A 100% capacitance retention and columbic efficiency were obtained after 10000 continuous charge-discharge cycles at 5 A g-1. Remarkably, after subjecting the symmetric device to a voltage holding test for 60 hours, the specific capacitance was observed to increase from 165 F g-1 to 328 F g-1 with a corresponding increased energy density to about 36.9 W h kg-1 at 0.5 A g-1 , suggesting a 98% increase in device energy density from its initial value after voltage holding. Thus, the results reported showcase the ABP900 material as a potential nanostructured porous material useful in the design of high-performance electrodes for stable electrochemical capacitors.

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Graphene Oxide (GO) was chemically synthesized from Natural Flake Graphite (NFG). The GO was chemically reduced to Reduced Graphene Oxide (RGO) using hydrazine monohydrate. Thin films of GO and RGO were also deposited on sodalime glass substrate using spray pyrolysis technique (SPT). The samples were characterized using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDS) facility attached to it, UV-Visible Spectrometry and Four-Point probe. The FTIR spectra showed the addition of oxygen functionality groups in GO while such groups was drastically reduced in RGO. SEM micrograph of GO thin film showed a porous sponge-like structure while the micrograph of RGO thin film showed evenly distributed and well connected graphene structure. The EDX spectrum of RGO showed that there was decrease in oxygen content and increase in carbon content of RGO when compared to GO. The optical analysis of the GO and RGO thin films gave a direct energy bandgap of 2.7 eV and 2.2 eV respectively. The value of sheet resistance of GO and RGO films was determined to be 22.9 × 10 6 Ω/sq and 4.95 × 10 6 Ω/sq respectively.

Growth conditions, structural, and optical properties of MgO nanostructure have been investigated. Surface composition and shift in binding energy of Mg at 50.8 eV due to oxidation were examined by core-level spectroscopy. The SEM showed that the film is dense, and grain growth and crystallinity are enhanced by post-deposition annealing. Grain distribution was appraised within the confinement of 24.51 μm 2 from the selected scan areas. X-ray diffraction studies indicated prominent peaks, which are attributed to (111), (200), and (220) reflections from fairly crystallized and randomly oriented MgO thin film. Plane (111) is found to be the preferred orientation of the film. The film transmitted well across the visible spectrum and the estimated energy band gap is 5.41 eV. Absence of catalyst in the electrolyte solution aided the purity of the sample.