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

Abstract

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.

A Time-Resolved Spectroscopic Investigation of a Novel BODIPY Copolymer and Its Potential Use as a Photosensitiser for Hydrogen Evolution

“…However, using ascorbic acid as the SA, hydrogen evolution (ca. 108 µ mol h −1 g −1 ) was observed under visible light irradiation (λ > 420 nm) (Suryani et al, 2019;Xie et al, 2019).…”

“…Changing the solvent system from a 1:1 CH 3 CN/H 2 O (v/v) 0.1 M ascorbic acid solution to a 1:1 THF/H 2 O (v/v) 0.1 M ascorbic acid solution resulted in an increase in hydrogen generation from 108 µ mol h −1 g −1 after 24 h of irradiation to 152 µmol h −1 g −1 (Figure 9). Solvent effects are well-known to affect hydrogen generation and THF has been previously reported to be the solvent of choice for photocatalytic systems utilising BODIPY chromophores (Artero et al, 2011;Suryani et al, 2019). Furthermore, upon increasing the concentration of the polymer from 0.06 to 0.25 mg/mL (Figure 10), the amount of H 2 evolved increased from 3,645 to 7,664 µmol g −1 , with a corresponding increase in hydrogen turnover frequency of 152-319 µmol h −1 g −1 after 24 h.…”

“…BODIPY monomers and iodinated BODIPY monomers have been used in homogeneous photocatalytic hydrogen evolution, including both intermolecular (Luo et al, 2015b;Sabatini et al, 2016;Dura et al, 2017;Xie et al, 2019) and intramolecular systems (Lazarides et al, 2011;Bartelmess et al, 2014;Luo et al, 2015a;Zheng et al, 2015). Some heterogeneous systems incorporating BODIPY a chromophore onto TiO 2 surfaces have been shown to lead to H 2 evolution (Sabatini et al, 2011;Suryani et al, 2019). BODIPY dyes have been immobilised onto photocathodes including NiO (Summers et al, 2015;Black et al, 2017).…”

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…Phenothiazine-based dyes, featuring thiophene-based spacers and different anchoring groups, have been extensively studied [19], determining an improvement of visible light H 2 generation of Pt/TiO 2 by the effect of the spacer structure [58] and the insertion of a peripheral glucose unit as co-adsorbent ( Figure 5) [59]. Other phenothiazine-and carbazole-based dyes were designed for the same application [60], including a D-π-A-π-A photosensitizer, with benzothiadiazole as auxiliary electron withdrawing unit [61], and, in particular, a dibenzopyrromethene (BODIPY)-conjugated phenothiazine, which gave Pt/TiO 2 high activity up to near-infrared (NIR) region [62]. Different types of photoactive compounds can be included in the design of a dye with specific structure: some D-A-π-A perylene dyes, featuring cyanoacrylic acid and dicyanomethylene rhodamine as the acceptor/anchoring group, combined with a N-annulated perylene donor and a quinoxaline auxiliary acceptor [63]; two triphenylamine-benzimidazole-based dyes bound on TiO 2 , with Cu 2 WS 4 nanocubes as an alternative water splitting co-catalyst to Pt [64]; a particular composite dye, consisting of π-conjugated indoline-rhodanine with a chlorophyll derivative, which induced panchromatic absorption in the visible range, efficient electron transfer, and prolonged stability [65]; a series of dyes with triphenylamine donor, vinyltiophene bridge, and a cationic pyridinium acceptor (cationic D-π-A photosensitizers) [66].…”

Synthetic Organic Design for Solar Fuel Systems

“…Attachment of 8 on platinized hierarchical porous TiO 2 resulted in aDSP system toward H 2 evolution, with aTON PS of 11 100 after 10 hofirradiation (l > 400 nm, 100 mW cm À2 )i nt he presence of AA as SED.A n apparent quantum yield (QY) of 1.0 %a t7 50 nm was recorded. [25] Overcoming the parasitic,f ast electron recombination in PS-catalyst systems as well as suppressing the need for aSED are current challenges in colloidal and homogeneous schemes. Anchoring ad ye and catalyst onto ap -type SC (p-SC) electrode to produce ad ye-sensitized photocathode (DSPC, Figure 5b)isapromising strategy inspired by p-type DSCs to address these limitations.…”