Insights into the crystal size and morphology of photocatalysts

Identification of the role of the specific surface area and surface structure as a key factor for photocatalytic performance remains a controversial topic. In this work, three types of N-doped anatase TiO₂ with different morphologies are newly synthesized by changing the addition order for the reagents. Methyl orange, Rhodamine B and Congo red are selected to showcase the photoactivity of the synthesized N-doped TiO₂. The photocatalytic experimental results show that Congo red can be selectively and rapidly degraded by three different N-doped TiO₂ samples. Interestingly, although a microspiny sphere structure possesses a larger specific surface area compared to a microflower structure, a microflower structure dominated by {1 0 0} and {1 0 1} facets exhibits a higher photocatalytic efficiency compared to a microspiny structure dominated by {1 0 1} facets, as demonstrated by a quicker photodegradation rate for Congo red, higher photocurrent density, smaller semicircle in the electrochemical impedance spectrum, and lower photoluminescence intensity. Thus, the result suggests that the surface structure plays a more important role compared to the surface area. In addition, a hollow microsphere structure with the largest specific surface area exhibits the best performance in terms of photodegradation, charge separation ability and electron-hole recombination efficiency, indicating that the proper surface morphology combined with a large specific surface area is greatly promising for enhancement of photoactivity.