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CVD Grown Sub 10 nm Size g-C3N4 Particle-Decorated TiO2 Nanotube Array Composites for Enhanced Photocatalytic H2
Kosei Ito1, Sho Yoneyama1, Shusuke Yoneyama1
1Keio University, Department of Electronics and Electrical Engineering, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama 223-8522 Japan.
Abstract:
TiO2 nanotube arrays (NTA) have attracted much attention among photocatalysts because of their large specific surface area and easy surface transfer of excited electrons, and in recent years, attempts have been made to further improve their properties by forming Z-schemes when they are composited with other photocatalysts. However, as the spacing within and between nanotubes is only a few nanometers, the formation of heterojunctions is extremely difficult when TiO2-NTA is composited with other photocatalytic materials with larger grain sizes. Creating nanoparticle photocatalysts with dimensions smaller than those of the nanotube system is thus required to effectively form heterojunctions. We have constructed an original vacuum chemical vapor deposition (CVD) system with fine temperature control, an attribute that we believe is necessary for the preparation of small nanoparticles. Using this system, it is possible to greatly reduce the polymerization rate of melamine, the precursor of the carbon nitride (g-C3N4) photocatalyst, which offers the benefits of increased reduction power and a metal-free composition. As a result, g-C3N4 small nanoparticles with particle sizes of about 10 nm were successfully prepared, and heterojunctions could be formed even inside TiO2-NTA. The fabricated TiO2-NTA/g-C3N4 composite structure exhibited significantly improved redox power and photocatalytic hydrogen production compared to TiO2-NTA and g-C3N4 alone. In addition, while the hydrogen production rates for TiO2-NTA and g-C3N4 were almost constant, TiO2-NTA/g-C3N4 showed a rapid increase in the hydrogen production rate after a certain period of light irradiation, which was presumably caused by oxygen desorption from g-C3N4. The results of this study provide a method for supporting small nanoparticle materials on nanotube substrates and their importance in improving photocatalytic properties, and will also make a significant contribution not only to the field of photocatalysis but also to other fields requiring small nanoparticle materials.
