Příprava polovodičových nanomateriálů a jejich využití pro fotokatalýzu

Abstract

This Ph.D. thesis deals with the study of the preparation of semiconductor nanoparticles and their photocatalytic properties. In addition, their basic physicochemical properties and the effect of these properties on photocatalytic activity during various photocatalytic reactions were investigated. Three different types of nanomaterials were prepared on the basis of sulphide, oxide and nitride. First, ZnS, CdS and ZnxCd1-xS quantum dots in the range x = 0 – 1 were prepared and characterized. These quantum dots were stabilized with a cationic surfactant. UV-Vis absorption spectroscopy was used to determine the transition energy of electrons in quantum dots, and from these data, their sizes were calculated. The size of quantum dots was depended on the composition x in ZnxCd1-xS. As the Zn increased, the size of the quantum dots decreased. These nanoparticles were tested on degradation of aqueous solution of methylene blue under UVA radiation with an emission peak at 365 nm (3.4 eV). Three areas with different photocatalytic activity, which depended on Zn content, were determined. The highest photocatalytic activity was found for quantum dots with composition x = 0.6, when the transition energy corresponded to the energy of the photons from the UVA lamp. Photocatalytic activity depended on the surface area and quantum states that varied due to the quantum confinement effect. The next part of this Ph.D. thesis deals with the preparation and properties of zinc oxide nanoparticles and their activity in the photocatalytic production of hydrogen from aqueous amonia solution. ZnO nanoparticles were prepared by thermal decomposition of zinc acetate and by precipitation reaction between zinc acetate and sodium hydroxide in the presence of UV radiation and subsequently annealed. Various methods of preparation had an effect on the formation of various defects in the ZnO crystal lattice and these defects were an important factor for photocatalytic hydrogen production. These defects were thoroughly investigated by positron annihilation of spectroscopy andphotoluminescence of spectroscopy. It was found that oxygen vacancies significantly reduced the photocatalytic activity. In addition to a standard preparation methods such as zinc acetate calcination and precipitation reaction, a new method for the preparation of ZnO nanolayer on the surface of an inert SiO2 nanoparticles by using an indium plate as source of electrons was discovered. The photocatalytic activity of these core-shell SiO2-ZnO nanoparticles was tested on degradation of aqueous solution of methylene blue to confirm the formation of the photocatalytic active layer on an inert SiO2 carrier. The last part of Ph.D. thesis was focused on preparation and properties of organic semiconductor material, graphitized carbon nitride (g-C3N4) and testing its photocatalytic activity on phenol decomposition by using different sources of radiation at the University of Porto. For the study of photocatalytic activity, various reactors were used at the IET VŠB-TUO workplace, at the University of Porto and at the workplace of CNT VŠB-TUO.