Exploitation of the synergistic effect between surface and bulk defects in ultra-small N-doped titanium suboxides for enhancing photocatalytic hydrogen evolution

Fabrication of ultra-small N-doped titanium suboxides (ca. 10 nm) with abundant surface bonds is realized via a hydrothermal-calcination route. The design concept takes advantage of the double-faced roles of surface and bulk defects in engineering the band gap and charge carrier transfer-separation rate. During the preparation process, ascorbic acid functioned as an electron-donating bidentate ligand and reducing agent, and promoted the formation of ultra-small nanocrystalline structure with specific Ti-O-C surface bonds. Urea was utilized as a facet stabilizer and nitrogen source, introducing interstitial nitrogen defects. Comprehensive characterization of the physiochemical properties clearly showed that abundant Ti-O-C bonds, proper nitrogen doping and well-defined bulk crystalline structure contribute to band gap narrowing and fast carrier separation rate. The defective titanium suboxide with optimal crystal and electronic structure exhibited much higher activity for photocatalytic hydrogen evolution compared to commercial P25 and anatase products under identical conditions. It is also noteworthy that the obtained products could still yield photocatalytic activity for H-2 evolution without using any noble metal co-catalyst.