Mangan Oksit Bazlı Monodispers-Gözenekli Mikrokürelerin Sentezi ve Enerji Bazlı Uygulamaları
Özet
In this thesis, monodisperse-porous manganese oxide (MnOx) microspheres were synthesized for the first time using a multistep template-assisted reduction method. Monodisperse-porous poly(methacrylic acid-co-ethylene dimethacrylate) microspheres were used as the template material. The polymer/MnOx composite structure was calcined over a wide temperature range (380-560 °C). With increasing calcination temperature, the obtained MnOx microspheres exhibited a transition from mesoporous to macroporous morphology and a crystal structure transformation from monoclinic Mn5O8 to α-MnO2. The MnOx microspheres obtained by this method have sizes ranging of 3-5 µm, with an average pore size ranging from 15-59 nm and a specific surface area of 17-71 m2/g. The suitable size and porosity properties of the MnOx microspheres enable their potential use as a stationary phase in a continuous microcolumn separation.
The synthesized monodisperse-porous MnOx microspheres were derivatized with amine groups and decorated with iridium oxide nanoparticles (IrO2 NPs) for their utilization as heterogeneous catalysts in chemical water oxidation studies. The catalytic activities of both plain forms and forms decoratde with IrO2 NPs of Mn5O8, MnO2 and Mn2O3 microspheres were measured. The MnOx microspheres exhibited high catalytic activity due to their unique multiple oxidation states and interaction with active sites. IrO2@Mn5O8 microspheres achieved the formation of 244 µmol oxygen 30 min. TON (turnover number) and TOF (turnover frequency) values of 298 and 557 h-1, respectively.
MnOx microspheres derivatized with amine groups were synthesized by immobilizing 3 nm sized palladium nanoparticles (Pd NPs) for their use as heterogeneous catalysts in the selective oxidation of benzyl alcohol (BzOH). Mn5O8 and MnO2 microspheres were used as supports. As references, titanium dioxide and silicon dioxide microspheres (Pd@TiO2, Pd@SiO2) with similar pore size characteristics were synthesized. Pd@Mn5O8 microspheres exhibited the highest BzOH conversion (92.2%) and benzaldehyde (BzCHO) selectivity (96.3%). The synergistic interaction between active sites and Mn5O8, as well as the the multivalent structure of Mn5O8 [Mn(II), Mn(III), Mn(IV)], contributed to the formation of oxygen vacancies, leading to its high catalytic activity. Pd@Mn5O8 microspheres maintained high catalytic activity even after 5 cycles, indicating their stable structure.
Using monodisperse-porous poly(glycerol dimethacrylate) (poly(GDMA)) microspheres as template material, hollow MnOx (h-MnOx) microspheres with a size of 1 µm were synthesized. These h-MnOx microspheres were utilized as cathode material in supercapacitors (SCs). Furthermore, composites (rGO/h-MnOx) with reduced graphene oxide (rGO) structures were synthesized at different doping ratios (%w/w). The rGO/h-MnOx composites were tested using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analysis with a two-electrode cell configuration. The GCD measurements resulted in a specific capacitance of 56.8 F g-1.
