Browsing by Author "Cox, Meleskow"

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    Cathodically-activated boron-doped diamond electrode reactor for sensing and analysis of environmental tenofovir and emtricitabine from combination antiretroviral therapy drugs
    (Elsevier Ltd, 2025) Mokwebo, Kefilwe; Sanga, Nelia; Mini, Sixolile; Cox, Meleskow; Ross, Natasha; Iwuoha, Emmanuel
    Tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC), sold under the brand name Truvada®, are amongst the highly prescribed combination antiretroviral therapy (c-ART) for the treatment and prevention of HIV/AIDS. Herein, for the first time, a simple, selective and rapid electroanalytical approach for the simultaneous co-determination of TDF and FTC on a non-chemically modified boron-doped diamond electrode (BDD) is described. The surface chemistry of the electrode was modified by cathodic pretreatment (CPT) in H2SO4 to generate a CPT-BDD. On a CPT-BDD, TDF and FTC exhibit irreversible oxidation peaks at higher potentials of +1.4 V and +1.65 V, respectively. Comparatively, the voltammetric signal of FTC was not visible on a glassy carbon electrode (GCE). Differential pulse voltammetry (DPV) was able to spatially separate the oxidation peaks of both analytes, and the limit of detection (LOD) of 0.0218 µM and 0.0886 µM were obtained for TDF and FTC, respectively, in the concentration range of 0.1 – 50 µM. The electrochemistry of TDF is pH-dependent, while that of FTC is not at pH>2. Moreover, the signals of TDF and FTC were not affected by the presence of interfering compounds, except for mercury (Hg2+) and lamivudine (3TC). The practicability of this electroanalytical approach was demonstrated by analyzing TDF and FTC in synthetic urine, pharmaceutical formulation and wastewater samples without prior sample pretreatment. The achieved recovery percentages of 93.6 % to 105.7 % demonstrate the practicability of this analytical method in simultaneously monitoring TDF and FTC in real samples
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    Ccu2pdsnse4 and cu2pdsn(s,se)4 palladium-substituted kesterite nanomaterials for thin-film solar cells
    (American Chemical Society, 2025) Nwambaekwe, Kelechi; Yussuf, Sodiq; Tshobeni, Ziyanda; Ikpo, Chinwe; January, Jaymi; Cox, Meleskow; Ekwere, Precious; Iwuoha, Emmanuel
    Kesterites are being studied intensively as sustainable absorber materials for solar cell development. However, elements such as Zn and Cu exhibit antisite defects that function as charge traps and recombination centers that affect the light absorption and carrier transport efficiencies of kesterite solar cells. The substitution of Zn or Cu with other metals is one of the strategies used to improve the photovoltaic performance of kesterites. This study focuses on the preparation and photovoltaics of Cu2PdSnSe4 (CPTSe) and Cu2PdSn(S,Se)4 (CPTSSe) kesterite nanoparticles (containing Pd instead of Zn) by a modified solvothermal (polyol) microwave synthesis method. The nanomaterials exhibited a tetragonal kesterite crystal structure with polydispersed morphology and average crystallite sizes of 22 and 17 nm for CPTSe and CPTSSe, respectively. DAMMIF ab initio analysis of the small-angle X-ray scattering data determined the shape of CPTSe and CPTSSe nanomaterials to be ellipsoidal. Ultraviolet-visible (UV-vis) spectroscopy revealed red-shift absorption properties, with bandgap energy values of 1.13 eV (CPTSe) and 1.20 eV (CPTSSe), thereby making them suitable light absorber materials for photovoltaic applications. Photoluminescence spectroscopy characterization confirmed the attenuation of defect concentrations in CPTSe and CPTSSe compared to the Zn analogue, which positively impacts the charge-carrier transport and recombination properties. A preliminary test of the materials in superstrate photovoltaic cell devices yielded power conversion efficiency values of 1.32% (CPTSe) and 3.5% (CPTSSe). The CPTSe- and CPTSSe-based photovoltaic devices maintained ∼70% mean open-circuit voltage (Voc), which is a significant improvement over the ∼20% Voc retained by Zn-based kesterites after 24 days.