Copper chalcogenide nanoparticles as photocatalysts for the removal of pharmaceuticals from water

Abstract

In recent years, the development of efficient catalytic materials to degrade emerging contaminants in water has become a major research topic. This is due to an increased release of these types of contaminants into the environment and the inability of conventional technologies to remove them. Advanced oxidation processes (AOPs), which utilize generated reactive radicals to effect the degradation of molecules, have gained significant attention, not only because they can completely degrade emerging contaminants, but because they are environmentally friendly, cost-effective, and they have the potential mineralization of pollutants without generation of secondary waste. More attention is specifically focused on the use of semiconductor nanoparticles as catalysts for the generation of radical species in AOPs. Copper chalcogenides CuE (E = O, S) are promising semiconductor materials with various stoichiometric phases that influence their optical and structural properties. These stoichiometric phases are dependent on the methods of preparation, which, when meticulously manipulated, could be used to obtain a wide array of materials with varying properties. This dissertation demonstrated control over stoichiometric phases of Cu2-xS using copper(II)dithiocarbamate complex as a single- source precursor by varying reaction parameters such as type of capping agent used and reaction temperature. While for CuO nanoparticles, copper(II)acetate monohydrate was used as the single- source precursor at different calcination temperatures. Solvothermal decomposition of copper(II) dithiocarbamate complex in dodecanthiol(DDT) was used to prepare pure phase djuleite(Cu31S16) at 120 and 150 °C and roxbyite (Cu7S4) at 220 and 250 °C, while oleylamine was employed in the synthesis of pure phase CuS (covellite) at 120 °C and Cu9S5(degenite) at 220 °C. In between these two temperature extremes, mixed phases were obtained that were not subjected to further characterization. Copper oxide nanoparticles were prepared via the thermal decomposition of copper(II)acetate monohydrate at three different temperatures, which were informed by the decomposition profile of the complex when analyzed by thermogravimetric analysis. The as- prepared pure phase copper chalcogenide nanoparticles were further characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), and UV-visible absorption spectroscopy. The morphologies of the copper sulfides varied from pseudo spherical to spherical, and it was interesting to observe the digenite displayed rod shape morphology despite being prepared from

the same precursor compound. The copper sulfide samples were used as photocatalysts to degrade tetracycline (TC) as model antibiotics under visible light irradiation. The results of the study showed varying degradation efficiencies with Cu7S4 (250 °C) exhibiting the best activity in the reaction system of up to 99% within 120 min of light exposure, compared to CuS, Cu9S5, Cu31S16 (120 °C), Cu31S16 (150 °C) and (Cu7S4 (220 °C) which degraded 88, 98.5, 46.5, 85 and 90 % respectively under the same conditions. The copper oxides of pure phases, obtained at 350 and 400 °C, labeled as CuO (350°C) and CuO (400 °C), respectively, were used to degrade acyclovir (ACV) as model antiviral. Both samples (CuO at 350°C and CuO at 400 °C) demonstrated high and comparable removal efficiency of 96.61 and 99.55 %, respectively, after 120 min. The results of this study confirm the potential of copper chalcogenides as semiconductor catalysts for the degradation of pharmaceuticals from an aqueous solution. In addition, the results showed that the phase of the chalcogenide affects the degradation efficiency.