Mangan Oksit Bazlı Monodispers-Gözenekli Mikroküre Formunda Katalizörlerin Sentezi ve Su Kirleticilerinin Gideriminde Kullanımı

Abstract

Within the scope of this thesis, Mn5O8 monodisperse-porous microspheres and MagSiO2@PDA@MnOx core/shell composite magnetic microspheres were synthesized, characterization studies were conducted, and catalytic activity results were investigated by using PMS, which is an oxidizing agent in advanced oxidation processes based on the formation of sulfate radicals, as a heterogeneous catalyst in organic pollutants degradation system. In the first stage, manganese oxide-based monodisperse-porous microsphere-form catalysts were synthesized by sol-gel technique and methacrylate-based polymeric microspheres used as a template material obtained by multistage microsuspension polymerization of poly (glycidyl methacrylate) microspheres. Multiple oxidation states of Mn5O8 monodisperse-porous microspheres have been used as a highly efficient heterogeneous catalyst for the degradation of model organic pollutants methylene blue (MB) and tetracycline (TC) via peroxymonosulfate (PMS) activation. The removal process consists of two stages: adsorption and chemical degradation of pollutants. Using the Mn5O8-PMS system, all of the MB and 70% of the TC were degraded in a 5-minute time interval. Mn5O8 microspheres with a specific surface area of 58.3 m2/g allowed the removal of pollutants in a very short time. No significant change was observed in the degradation studies carried out in the pH range of 3.3-9. The highest values of first order rate constants of MB and TC were calculated as 0.961 min-1 and 0.570 min-1, respectively. It can be said that these values are approximately 24 times higher when compared to similar degradation systems. Radical quenching experiments were performed to confirm the radical species formed during the catalytic degradation reactions of the Mn5O8-PMS system. Degradation studies in the presence of radical scavengers showed that singlet oxygen (1O2) and superoxide (O2*-) radicals were produced in the Mn5O8-PMS system. After five consecutive degradation studies, the degradation efficiency of MB and TC decreased to 99.3% and 89.3%. For determination of the leaching Mn concentration from Mn5O8, final Mn concentrations lower than 0.14 ppm were used for instant degradation of organic pollutants in aqueous media. Mn5O8 microspheres showed that it is an excellent and highly stable oxidation catalyst. In the second form, MagSiO2@PDA@MnOx core/shell composite magnetic microspheres were synthesized. First of all, the silica microspheres selected for the core part were synthesized by sol-gel technique. The core materials was covered with polydopamine thanks to the ability of active surface groups such as –NH2, –OH of PDA to form metal-ligand complexes with metal ions without the need for extra functionality of the surface and then MnO2 depositing onto the surface of core particles. Synthesized catalyst was used for degradation of methyl orange (MO), methylene blue (MB) and rhodamine-B (RB) in aqueous medium. The average pore size and pore volume of the MagSiO2@PDA@MnOx analyzed by nitrogen adsorption method according to the BET model were determined as 6.36 µm and 0.59 cm3/g, respectively. By using MagSiO2@PDA@MnOx composite microspheres as catalyst, complete removal of MB and RB and 90% of MT removal was achieved after 60 minutes. The MagSiO2@PDA@MnOx-PMS system indicated that the degradation reaction proceeds predominantly through the generation of singlet oxygen (1O2) and superoxide anion (O2*-) radicals. At the end of five consecutive reusability studies of MO and RB, the MagSiO2@PDA@MnOx-PMS system has been successfully used as a stable and durable catalyst for the removal of organic pollutants, although there was an about 10% decrease in degradation efficiency. The magnetic properties of MagSiO2@PDA@MnOx composite microspheres, which is a promising catalyst, allowed it to be easily isolated from the reaction medium with the help of magnetic bar.