Visible-to-Near-Infrared Light-Driven Photocatalytic Hydrogen Production Using Dibenzo-BODIPY and Phenothiazine Conjugate as Organic Photosensitizer

• Published in: ACS applied energy materials Vol. 2; no. 1; pp. 448 - 458
• Main Authors: Suryani, Okta, Higashino, Yuta, Sato, Haruka, Kubo, Yuji
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28.01.2019
• Subjects: phenothiazine; panchromatic photosensitizer; hierarchical porous TiO2; BODIPY; photocatalysis; hydrogen generation
• ISSN: 2574-0962; 2574-0962
• DOI: 10.1021/acsaem.8b01474

A novel visible-to-near-infrared (visible-to-NIR) light-driven photocatalyst was prepared by loading a dibenzo-BODIPY-phenothiazine conjugate dye 1 as a panchromatic photosensitizer on hierarchical porous TiO2 (HPT) semiconductor. The sensitizer 1, which absorbed visible light at 638 and 440 nm with molecular extinction coefficients (ε) of 1.23 × 105 and 1.80 × 104 M–1 cm–1, respectively, in THF due to the dibenzo-BODIPY and phenothiazine-based D−π–A systems, respectively, showed panchromatic absorption up to 780 nm when deposited on the Pt/HPT photocatalyst to produce Pt/HPT500/1. The photocatalytic activities were investigated in the presence of ascorbic acid as a sacrificial agent in phosphate buffer solution under irradiation with λ > 400 nm using a 300 W Xe lamp at 100 mW cm–2 light intensity. After 10-h irradiation, the system achieved a remarkable catalytic activity for the production of H2 with a turnover number (TON) value of 11100. The sustained activity was suggestive after two sequences of 10-h illumination-period, whereas we found somewhat decrease in the photoactivity for the third run, although a TON value of 5650 still remained. The apparent quantum yields were evaluated by monitoring H2 production for each monochromatic light irradiation (λ = 420, 530, 600, 670, 700, and 750 nm). They were found to be consistent with the absorption profile, proving the panchromatic hydrogen generation sensitized by 1. The active absorption band of dye 1 in the entire visible-to-NIR spectrum led to production of a dye-sensitized photocatalytic system with a light-to-fuel efficiency of 6.96% in the initial irradiation period. This study provides important information for the development of metal-free organic photosensitizers with a wide spectral response up to the NIR region for photocatalytic water-splitting H2 production.