Organic blue-colored D-A-π-A dye-sensitized TiO2 for efficient and stable photocatalytic hydrogen evolution under visible/near-infrared-light irradiation

Photocatalytic splitting of water by titanium dioxide (TiO2) is considered as the most promising approach for the production of hydrogen fuel. However, a low utilization of the solar light spectrum still limits its photoconversion efficiency. Herein, two indeno[1,2-b]thiophene-based organic sensitizers (S5 and S6) are used to sensitize TiO2 to significantly enhance photocatalytic hydrogen production by broadening the spectral response to near-infrared-light region. The results revealed that the average H2 evolution rates of S5@Pt/TiO2 and S6@Pt/TiO2 were 21.5 mmol g−1 h−1 and 7.2 mmol g−1 h−1, which were 11.3 and 3.9 fold than that of the Pt/TiO2 (1.85 mmol g−1 h−1), respectively. Compared with donor-π-acceptor (D−π−A) dye S6, donor−acceptor−π−acceptor (D-A-π-A) blue-colored dye S5 possesses evident dominant in sensitizing TiO2, in which the auxiliary acceptor 2, 3-diphenylquinoxaline (QT) of S5 can effectively disperse donor electron distribution to improve the photo-stability and weak the deprotonation effect to enhance light-harvesting. More importantly, a highly apparent quantum efficiency (AQY) of 2.8% for S5@Pt/TiO2 was obtained at λ = 700 nm monochromatic light, which is, to the best of our knowledge, a recorded value among the pure organic dye-sensitized TiO2 systems. This study offers important insights into the rational design of D-A-π-A organic dye to sensitize TiO2 for highly efficient and stable photocatalytic hydrogen evolution.