Rational Design of Conjugated Microporous Polymer Photocatalysts with Definite D−π–A Structures for Ultrahigh Photocatalytic Hydrogen Evolution Activity under Natural Sunlight

Abstract

Organic polymers with conjugated architectures have been widely exploited as photocatalyst materials for hydrogen generation. However, it is still an enormous challenge to develop photocatalysts with high hydrogen generation activity under natural sunlight, which is pretty significant for practical applications. Herein, two conjugated microporous polymer photocatalysts with definite D−π–A structures are designed and prepared using dibenzo­[g,p]­chrysene or pyrene with planar conjugated architecture as electron donors, thiophene as a π-spacer, and dibenzo­[b,d]­thiophene-S,S-dioxide as an electron acceptor. Benefiting from the efficient separation of light-generated electrons/holes due to the definite D−π–A structure and the broad light absorption range, the bare polymer Py-TP-BTDO could deliver a high photocatalytic hydrogen evolution rate (HER) of 115.03 mmol h–1 g–1 upon exposure to visible light (λ > 420 nm). Impressively, the outdoor photocatalytic experiment reveals that abundant and continuous hydrogen bubbles could be produced fast and visually observed under natural sunlight by the Py-TP-BTDO polymer film with a large active area of 120 cm2. A water-drainage experiment further demonstrates that 1224 mL of hydrogen gas could be produced by 25 mg of a polymer photocatalyst with 3 wt % Pt cocatalyst under natural sunlight in 7 h, corresponding to a high HER of 312.24 mmol h–1 g–1, which represents the state of the art of organic photocatalyst materials to date. The high photocatalytic activity under natural sunlight suggests the potential of the developed Py-TP-BTDO polymer photocatalyst in the practical applications for photocatalytic hydrogen production.

Simultaneously Achieving Fast Intramolecular Charge Transfer and Mass Transport in Holey D−π–A Organic Conjugated Polymers for Highly Efficient Photocatalytic Pollutant Degradation

“…To date, various strategies have been developed to tackle the issues of PCN in photocatalytic reactions, such as defect engineering, − construction of heterojunctions, − and elemental doping. − Besides, designing organic conjugated polymers (OCPs), such as donor–acceptor (D–A), A–D–A, D–A–A, D–A–D, etc., is becoming a promising strategy, and OCPs display tunable optical and electrical properties . For instance, the band structure of D–A OCPs could be regulated by pushing/pulling the energy of the highest occupied molecular orbital (HOMO)/the lowest unoccupied molecular orbital (LUMO) via the D-units/A-units. , Furthermore, the D–A OCPs could effectively induce intramolecular charge transfer from D to A and thus accelerate the transport/migration of photogenerated electrons. − Although PCN-based D–A OCPs are conducive to improving charge separation, the electron delocalization in this structure is still limited, which restrains the migration of photoexcited electrons. To achieve more effective and faster intramolecular charge transfer, it is essentially necessary to induce an intrinsic driving force in the D–A for the delocalization of charge carriers around the photoexcitation sites.…”

Molecular Engineering in D-π-A-A-Type Conjugated Microporous Polymers for Boosting Photocatalytic Hydrogen Evolution

“…To uncover the impact of the BTDO acceptor content on the light-driven H 2 generation performance, we synthesized four polymers via adjusting the feed ratio of the two bromine-functionalized comonomers. The results demonstrated that the D-π-A-A structure indeed conduces to enhancing the photocatalytic activity, and the bare polymer PyT-BTDO-2 with an optimized BTDO acceptor content shows a high HER of 177.82 mmol h –1 g –1 under the irradiation of visible light, which surpasses its counterpart Py-TP-BTDO with a precise D-π-A structure (115.03 mmol h –1 g –1 ) under the identical photocatalytic reaction conditions …”

“…34 Very recently, we showed that designing a CMP photocatalyst with a precise D-π-A molecular structure could boost the reduction activity of H + , and an HER of 182.78 mmol h −1 g −1 under visible light was obtained by the polymer with a 3 wt % Pt cocatalyst, while the bare polymer shows a lower HER of 115.03 mmol h −1 g −1 under visible light. 26 The precise D-π-A structure is conducive to the separation between lightgenerated carriers, while it is difficult to regulate the component of donor and acceptor, which impinges the photocatalytic hydrogen production activity. With this in mind, we developed here a series of D-π-A-Atype CMPs via ternary statistical copolymerization using pyrene, thiophene, and BTDO as the electron donor, π-bridge, and electron acceptor, respectively.…”

“…The results demonstrated that the D-π-A-A structure indeed conduces to enhancing the photocatalytic activity, and the bare polymer PyT-BTDO-2 with an optimized BTDO acceptor content shows a high HER of 177.82 mmol h −1 g −1 under the irradiation of visible light, which surpasses its counterpart Py-TP-BTDO with a precise D-π-A structure (115.03 mmol h −1 g −1 ) under the identical photocatalytic reaction conditions. 26 ■ MATERIALS AND METHODS Chemicals and Materials. The monomers of 1,3,6,8-tetrakis(5bromothiophen-2-yl)pyrene (M1), 3,7-dibromodibenzo[b,d]thiophene-S,S-dioxide (M2), and 3,7-bis(4,4,5,5-tetramethyl-1,3,2dioxaborolan-2-yl)dibenzo[b,d]thiophene-S,S-dioxide (M3) were prepared according to the reported methods.…”

Enhanced Reducibility via Altering Exciton Binding Energy of Conjugated Microporous Polymers for Photocatalytic Reduction

“…In addition, the open cavity of CMPs is well suited for the binding of small organic molecules, allowing them to access the exposed inner surface, where the transformations occur. Recently, the D–A molecular engineering strategy has been utilized for constructing CMP-based photocatalysts with highly efficient charge separation. − For example, Bojdys et al found that the CMP photocatalyst incorporated stronger D–A interactions with shorter D–A pathways and featured efficient charge separation for water splitting . Despite the extensive research efforts on D–A type CMPs, works dealing with the engineering of D–A interactions and unveiling their influence on exciton binding energy for photocatalytic activity are still rare.…”