Spreparation of multifunctional materials for photocatalytic applications

Thesis Type: Doctorate

Institution Of The Thesis: Middle East Technical University, Faculty of Arts and Sciences, Department of Chemistry, Turkey

Approval Date: 2019

Student: Cere Uzun



Due to the increasingly polluted environment and the limited energy reserves, the development of high efficient renewable technologies, green energy sources and ecofriendly methods for environmental remediation and energy production is highly important. Hydrogen (H2), as a clean and carbonless energy source, is of great potential in solving the environmental pollution and energy shortage. Turkey is a country that clued-in textile production. But the widespread discharge of wastewaters from the textile industries, which contain large amounts of dyes, has become a great concern to the environment and ecosystem due to their non-biodegradability, toxicity, and potential carcinogenicity. Therefore, finding effective treatment methods and extending the treatment units which use them is necessary. The need to meet stringent international regulations and standards for wastewater discharge has motivated the development of efficient, non-toxic and low-cost photocatalytic materials for the photodegradation of organic pollutants in wastewater. Besides mild operating conditions photocatalytic process can be powered by sunlight which significantly reducing the energy required and therefore the operating costs. Thus, semiconductor photocatalyst has attracted widespread attention in the scientific vi community due to its potential application in environmental remediation and hydrogen production. Owing to the strong oxidizing property, nontoxicity, and long-term photostability, nanostructured titanium dioxide (nano-TiO2) has many advantages when compared with other photocatalysts. However, there are still some shortcomings, such as the lack of a visible light response, a low quantum yield, and lower photocatalytic activity. To overcome these problems, studies have been focused on some strategies, including noble metal deposition, doping of metal or nonmetal ions, blending with another metal oxide, surface photosensitizing with dye, and compositing with a polymer. In particular, doping of metal and organic/inorganic composite materials, where the organic major component is based on polymers, are fast-growing areas of research. Catalyst recovery and reuse are the two most important features for many catalytic processes. Most heterogeneous systems require a filtration or centrifugation step to recover the catalyst. However, magnetically supported catalysts can be recovered with an external magnet due to the paramagnetic character of the support thus remarkable catalyst recovery can be provided without the need for a filtration step and the catalysts can be subsequently reused in another cycle. In this study, multifunctional organic-inorganic composite materials were prepared to provide environmental remediation with the removal of organic dyes found in wastewater from industry and produce H2 from the water-ethanol mixture with photocatalytic process under ultraviolet and visible light respectively. For this purpose, novel, magnetically recyclable, poly (3, 4-ethylene dioxythiophene)(PEDOT) and noble metal nanoparticles modified TiO2 nanoparticles based (CoFe2O4-PEDOT-TiO2/M, (M=Ag, Au, AgAu)) composite materials with high photocatalytic activity and well-separation property were produced. The enhanced photocatalytic properties of the composites driven by the vii synergetic effects of TiO2 nanoparticles with noble metal nanoparticles, and PEDOT were investigated. Besides, their separation from the liquid phase and reuse process were provided with the addition of magnetic silica coated cobalt ferrite (CoFe2O4@SiO2, MNP) nanoparticles into the composite structure. The composition, morphology, and optical properties of the prepared composites were investigated with TEM, FE-SEM, ICP-OES, BET, particle size distribution (Zeta sizer), vibrating sample magnetometer (VSM) and UV-Vis measurements. The comparative photocatalytic activity of the prepared catalysts was investigated by using methylene blue (MB), a typical pollutant in the textile industry which has the relatively high toxicity and complex structures make them difficult to be treated by physical and biological methods, under UV and Visible light.