Doping strategy for enhanced photocatalytic hydrogen production on tantalum layered perovskite nanosheets

Rise in greenhouse gas levels due to human activity, such as burning fossil fuels, causes global warming and environmental problems. Thus, industries and researchers are investigating alternative energy sources to find solutions to environmental problems and slow down global warming. Hydrogen is one of the solutions to these problems. Semiconductor photocatalysis has been researched for hydrogen production as a sustainable energy source since the 18th century. Many photocatalysis materials, such as metal oxide, metal sulfide, and metal nitride, have been studied and used as photocatalysts. In addition to these materials, layered perovskite oxides have gained significant interest in the photocatalytic field over the last 20 years—the heightened interest results from its tunable band structure, flexible interlayer structure, and tunable morphology. Furthermore, exfoliating layered materials gives 2D building blocks of bulk materials. Resulting nanosheets with few atomic layers offer a high surface area, low migration distance, and high charge separation to improve photocatalytic activity. Although there is a vast interest for efficient H2 production with photocatalytic water splitting, research on H2 production activities needs a long way to go to achieve solar hydrogen efficiencies above 10%, raising questions about strategies to achieve effective photocatalytic activity. The common approach to achieve a high productivity from a photocatalyst is to use co-catalysts, which improves charge separation in photocatalysts. In general, noble metals like Pt are used as cocatalysts in nanoparticle form on the surface of photocatalyst. In this case, the inner atoms of the catalysts are inactive since only surface atoms play a role in catalytic activity. In this study, the effects of introducing Pd, Sn, and N into the structure were conducted for photocatalytic hydrogen production in an aqueous 10 vol.% methanol solution as a sacrificial agent without cocatalyst. After exfoliation of tantalum based perovskite oxide, PdO6 and SnO6 octahedra were formed when Ta was substituted iv with Pd or Sn, which acted as a single-atom catalyst site (SACs). These obtained octahedra structures reduce the original phase's electrical structure and serve as sites for trapping electrons, thereby reducing the recombination rate of photo-induced carriers. Furthermore, exfoliated materials have high surface areas, making them ideal platforms to disperse SACs uniformly. This allows for the use of all metal atoms added to the structure with nearly 100% photocatalytic activity. On the other hand, nitrogen, which is partly substituted for oxygen, has a great potential to minimize electronic band energies due to the formation of isolated electronic states positioned above the top of the oxygen (O) 2p valence band. Various structural, spectroscopic, and electrochemical characterization techniques were used to analyze materials' properties in detail. According to the results, all target materials were successfully synthesized, their bandgap changes were determined, and their hydrogen production rates increased after the doping and proton exchange processes