Raspberry‐Like Microspheres of Core–Shell Cr2O3@TiO2 Nanoparticles for CO2 Photoreduction.

To promote the interaction of p–n semiconductors, raspberry‐like microspheres of core–shell Cr2O3@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 Cr2O3 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 Ti4O7 and Cr2Ti6O15 compounds, resulting from inner doping between Cr2O3 and TiO2, is formed. The close interaction of Cr2O3 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. [ABSTRACT FROM AUTHOR]