Highly ordered TiO₂ nanotube arrays (NTAs) have attracted much attention because of their high surface-to-volume ratio, environmental benignity, and chemical stability. NTAs are therefore promising candidates for diverse applications. However, their performance is limited because of the large band gap of TiO₂, resulting in small absorption of solar light and fast recombination of photo-generated charges. To solve such problems, various attempts have been made to enhance the photocatalytic activity of TiO₂ NTAs by suppressing recombination of photogenerated electron-hole pairs and improving the transport of photocarriers during photoelectrocatalysis. Among them, coupling semiconductors with appropriated band positions is effective to improve the photocatalytic activity of TiO₂ N...[ Read more ]

Highly ordered TiO₂ nanotube arrays (NTAs) have attracted much attention because of their high surface-to-volume ratio, environmental benignity, and chemical stability. NTAs are therefore promising candidates for diverse applications. However, their performance is limited because of the large band gap of TiO₂, resulting in small absorption of solar light and fast recombination of photo-generated charges. To solve such problems, various attempts have been made to enhance the photocatalytic activity of TiO₂ NTAs by suppressing recombination of photogenerated electron-hole pairs and improving the transport of photocarriers during photoelectrocatalysis. Among them, coupling semiconductors with appropriated band positions is effective to improve the photocatalytic activity of TiO₂ NTAs, since it can enhance visible light absorption and also facilitate charges separation.

In this work, graphitic carbon nitride quantum dots modified TiO₂ NTAs (g-CNQDs/TiO₂ NTAs) were fabricated and their enhanced photoelectrochemical degradation capability were displayed. TiO₂ NTAs were first fabricated by two-step electrochemical anodization technique for morphology optimization and then the as-prepared TiO₂ NTAs were modified by graphitic carbon nitride quantum dots (g-CNQDs) with two methods, namely the hydrothermal method and the molecules linking method involving 3-Mercaptopropionic acid (3-MPA) and thioglycolic acid (TGA), respectively. The optimum fabrication conditions for both methods were investigated.

It was found that g-CNQDs/TiO₂ NTAs exhibited improved photoelectrochemical capability under full solar spectrum irradiation. Compared with pristine TiO₂ NTAs, nearly 3-fold enhancement in photocurrent response was achieved using the g-CNQDs/TiO₂ NTAs by both methods. The photoelectrochemical activities of g-CNQDs/TiO₂ NTAs were evaluated by photodegradation of rhodamine B (RhB) aqueous solution. The efficiency of the process using g-CNQDs/TiO₂ NTAs prepared by hydrothermal method was 2 times higher than that of the pristine TiO₂ NTAs. The degradation performance of g-CNQDs modified TiO₂ NTAs in 10 mg L^-1 RhB is enhanced by 8.3 times with 3-MPA linking, and 2.9 times enhanced with TGA linking, compared with unmodified TiO₂ NTAs.