Tailored doping strategies for photocatalytic CO2 reduction and water splitting on KCa2Nb3O10 layered perovskite

Global warming is defined as the long-term heating of the Earth's surface that has been observed since the pre-industrial period. This phenomenon is primarily driven by human activities, especially the use of fossil fuels, and is accompanied by various consequences such as the increasing global population and industrialization, leading to elevated greenhouse gas levels in the atmosphere and a reduction in green areas. The negative effects of global warming and related climate change, the world's most critical problem, are becoming more serious day by the day. Researchers and industries are pursuing two main approaches to address the challenge of reducing CO2 emissions. The primary approach is to tackle CO2 emissions at the production level by reducing reliance on fossil fuels and exploring alternative energy sources such as hydrogen energy. The second way is clearly to convert CO2 into useful products. Recently, photocatalytic reactions have gained popularity in converting CO2 to useful chemicals and producing H2 from water due to their features such as being environmentally friendly, simpler to set-up, more cost-effective, and more scalable. Yet, there is more to investigate about photocatalyst systems. The use of hole-scavengers to improve photocatalytic activity has been widely used, but the behavior of hole-scavengers on 2D nanosheets of perovskite photocatalysts has yet to be discovered. Another way to improve the photocatalytic activity is the utilization of co-catalyst particles on the surface of the photocatalyst. Given that only the surface atoms of particles actively participate in photocatalytic reactions while the inner atoms remain inactive, the sustainability of using co-catalyst particles, especially those incorporating noble metals, becomes a concern. Thus, it is crucial to disperse single-atom co-catalysts in a photocatalytic system. Hole scavenger study as a first chapter, aims to mechanistically investigate the photocatalytic performance of hole scavengers on nanosheets of 2D layered KCa2Nb3O10 perovskite oxide. A range of hole scavengers were added to the photocatalytic system to observe how they influence the charge carrier dynamics and overall photocatalytic efficiency. To analyze the behavior of hole scavengers on a [Ca2Nb3O10]- perovskite nanosheet, photoelectrochemical and photocatalytic experiments were utilized. Investigation of single site noble atom doped 2D layered perovskite for photocatalytic hydrogen evolution reactions is a second chapter. Pd noble metal was chosen for single-site atom doping. The incorporation of Pd as a single-site atom dopant altered the electrical band structure of the photocatalyst. Depending on the doping concentration, this caused the narrowing or shifting of the bandgap to visible spectrum. Also, it can serve as an active site for photocatalytic reactions, facilitating the transfer of charge carriers. Pd doping reduced the recombination rate of electron-hole pairs by providing additional reaction pathways, leading to more efficient charge utilization. In the last chapter, the photocatalytic CO2 reduction performances and photocatalytic activities were investigated by using ultrathin 2D layered Dion-Jacobson type perovskite oxide KCa2Nb3O10 with single-site ruthenium doping. To investigate the impact of ruthenium doping, a study on CO2 reduction was carried out using photoelectrochemical and photocatalytic methods. The nanosheets exhibited higher photocatalytic CO2 reduction activity. The main products obtained were methanol and ethanol. The findings presented in this study will shed light on the tremendous potential of ultrathin 2D layered Dion-Jacobson type perovskite oxide KCa2Nb3O10 with single-site ruthenium doping as a promising photocatalyst for CO2 reduction. This thesis holds significant implications for developing sustainable strategies to combat CO2 emissions and foster a greener future.