Raspberry-Like Microspheres of Core-Shell Cr₂ O₃ @TiO₂ Nanoparticles for CO₂ Photoreduction

To promote the interaction of p-n semiconductors, raspberry-like microspheres of core-shell Cr₂ O₃ @TiO₂ nanoparticles have been fabricated through a five-step process. Raman spectroscopy of products calcined at various temperatures reveal that the titania shell causes crystal distortion of the Cr₂ O₃ core, without changing the microstructures of the fabricated core-shell microspheres. In situ and time-resolved synchrotron-based powder XRD reveals the formation of monoclinic TiO₂ in the fourth step, but these monoclinic TiO₂ nanocrystals undergo a phase transition when the applied calcination temperature is above 550 °C. As a result, TiO₂ (B), a magnéli phase of Ti₄ O₇ and Cr₂ Ti₆ O₁₅ compounds, resulting from inner doping between Cr₂ O₃ and TiO₂ , is formed. The close interaction of Cr₂ O₃ and TiO₂ forms a p-n junction that decreases the recombination of photogenerated electron-hole pairs, leading to enhanced production of CH₄ by photocatalytic reduction of CO₂ .