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Author: search.filters.author.Covenant University, DissertationSubject: search.filters.subject.chalcogenide

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    SYNTHESIS OF Cu–Mn–S TERNARY METAL CHALCOGENIDE QUANTUM DOTS AS POTENTIAL HIGH-PERFORMANCE OPTICAL NANOSENSORS
    (Covenant University, Ota, 2026-07) LASISI, Bolatito Lateefat; Covenant University, Dissertation
    The detection of environmentally relevant pollutants and biomedical biomarkers by traditional analytical techniques is often time-consuming, invasive, and insufficiently sensitive, underscoring the need for advanced optical nanosensor materials. In this study, the synthesis and characterisation of ternary metal chalcogenide quantum dots (TMC-QDs) of Cu-Mn-S were carried out as candidate materials for advanced optical nanosensors in environmental and biomedical applications. Eight Cu-Mn-S QDs (TMC-1 to TMC-8) were successfully synthesised via the modified solvothermal method. CuCl2, Mn(CH3COO)2, and thiourea were employed as precursors and sulfur source, respectively, in a 1:1 deionised water/ethylene glycol solvent, with two stoichiometries (CuMn2S2 and CuMn1.7S2), three varied temperatures (180 to 190 °C), and two reaction times (10 and 12 hrs). The synthesised QDs were characterised. The UV-Vis absorption measurements revealed a controllable wavelength range from 205 nm to 556 nm and visible-region excitonic absorption, indicating the optical activity of the CuS sub-phase in the samples at low temperatures. The XRD pattern of the resultant particles showed crystalline QDs with particle sizes ranging from 14.97 to 16.19 nm. The product is found to be of a single hexagonal CuS covellite phase except for TMC-6 and TMC-7, which are binary composites of hexagonal CuS covellite and cubic MnS alabandite. FTIR confirmed the presence of both phases, with CuS and MnS stretching. Thus, this work established, for the first time, the synthesis of ternary metal chalcogenide Cu-Mn-S QDs with controlled structural and optical properties. The ternary system conditions for phase segregation of a dual CuS covellite and α-MnS alabandite composite were also found to depend on reaction temperature and time, rather than just the stoichiometric ratio.