Raspberry‐Like Microspheres of Core–Shell Cr 2 O 3 @TiO 2 Nanoparticles for CO 2 Photoreduction

To promote the interaction of p–n semiconductors, raspberry‐like microspheres of core–shell Cr 2 O 3 @TiO 2 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 Cr 2 O 3 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 TiO 2 in the fourth step, but these monoclinic TiO 2 nanocrystals undergo a phase transition when the applied calcination temperature is above 550 °C. As a result, TiO 2 (B), a magnéli phase of Ti 4 O 7 and Cr 2 Ti 6 O 15 compounds, resulting from inner doping between Cr 2 O 3 and TiO 2 , is formed. The close interaction of Cr 2 O 3 and TiO 2 forms a p–n junction that decreases the recombination of photogenerated electron–hole pairs, leading to enhanced production of CH 4 by photocatalytic reduction of CO 2 .