TiO₂ has been widely used as a photocatalyst for water splitting due to its high activity, low cost, abundance, safety, and stability. However, the further utilization of TiO₂ is still limited to the wide band gap and fast electron recombination speed, so it can only utilize 4% of the energy in the ultraviolet spectral region of the solar spectrum. Therefore, expanding its light absorption range is of great significance.

Carbon is a suitable dopant with metallic conductivity and large electron storage capacity, and the isolated C 2p states can excite high photocatalytic activity under visible light. 

In a study published in Appl. Surf. Sci, the research group led by Prof. LU Canzhong from Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, reported the visible light absorption of ultrathin carbon-modified TiO₂ nanotube arrays (UTC-doped TiO₂@TNT). 

The researchers prepared TiO₂ nanotube arrays by electrochemical anodic oxidation method, using a trace amount of ethylene glycol in the electrolyte as the carbon source. They prepared the ultra-thin carbon-modified TiO2 nanotube arrays by an ultra-thin ethylene glycol adsorption and vacuum annealing treatment, which is simple and efficient and requires no additional carbon source.
The linear sweep voltammetry (LSV) curves showed that there is a peak photocurrent density (0.6 mA×cm^-2) with a max photoelectric-conversion efficiency (η=0.4%) for the UTC-doped TiO₂@TNT under visible light irradiation, which is significantly improved compared to ordinary TiO₂ materials in the visible region. 

They also evaluated the light absorption range of UTC-doped TiO₂@TNT using an incident photo-to-current efficiency (IPCE) test. The results show that UTC-doped TiO₂@TNT still has photocurrent at a wavelength of 600 nm, indicating that its photoabsorption range extends to 600 nm.  

Thanks to the induced doping energy level of ultrathin carbon, the UTC-doped TiO₂@TNT photocatalyst can absorb both ultraviolet(UV) and visible light. In addition, carbon has metallic conductivity and a large electron storage capacity. Therefore, carbon atoms can trap photo-generated electrons on the surface of TNT, effectively enhancing the separation of photo-generated charge carriers. 

This study shows that introducing ultrathin carbon can effectively reduce the band gap of TiO₂ and extend the TiO₂ light absorption to the visible region. 

Illustration of the Research (Image by Prof. LU’s group)  

Contact: 

Prof. LU Canzhong 

Fujian Institute of Research on the Structure of Matter 

Chinese Academy of Sciences 

Email: czlu@fjirsm.ac.cn