Abstarct: In this thesis, CoSe2, MnSe2, doped nanostructures, and their nanocomposites with multi-walled carbon nanotubes were investigated using a hydrothermal-solvothermal method. The aim was to enhance charge transport properties and improve photocatalytic, antibacterial, and optoelectronic sensing performance. XRD results confirmed the formation of the orthorhombic phase of CoSe2 and the cubic phase of MnSe2. FESEM images revealed flower-like morphology for CoSe2 nanoparticles and cubic microcrystals for MnSe2 within the nanocomposite structures. Optical studies indicated an indirect bandgap in all di-selenide samples. The addition of MWCNT and Mn doping in CoSe2 led to improved optical absorption in the visible region and a shift of the absorption edge towards longer wavelengths. Electrical characterization demonstrated the ohmic behavior of the samples and a significant increase in photocurrent compared to dark current, suggesting effective charge carrier separation and reduced recombination. Rhodamine B dye degradation experiments showed that the CoSe2/CNT nanocomposite with 66.8 wt% carbon nanotubes exhibited the highest dye degradation efficiency (nearly 100%) and antibacterial activity against Escherichia coli (inactivation rate of 97.5%) under visible light irradiation. The results indicate that the optimal amount of MWCNT plays a key role in forming conductive pathways and preventing charge carrier recombination, while excessive addition of the conductive phase can lead to discontinuity in the charge transport network and reduced conductivity. This research demonstrates that engineering the structure of cobalt di-selenide nanostructures through doping and forming nanocomposites with MWCNT is an effective strategy for enhancing their electrical, optical, photocatalytic, and antibacterial properties. Furthermore, these materials show significant potential for application in photodetectors.