Anionic donor-acceptor conjugated polymer dots/g-C3N4 nanosheets heterojunction: High efficiency and excellent stability for co-catalyst-free photocatalytic hydrogen evolution

Visible light to the second near-infrared light-harvesting donor-acceptor1-donor-acceptor2-type terpolymers for boosted photocatalytic hydrogen evolution via dual-sulfone-acceptor engineering

Developing visible to near-infrared light-absorbing conjugated polymer photocatalysts is crucial for enhancing solar energy utilization efficiency, as most conjugated organic polymers only absorb light in the visible range. In this work, we firstly developed a novel thiophene S,S-dioxide (TDO) monomer with the stronger electron-withdrawing character, and then prepared a series of donor-acceptor1-donor-acceptor2-type (D-A1-D-A2-type) conjugated terpolymers (THTDB-1-THTDB-5) by statistically adjusting the molar ratio of two sulfone-based acceptor monomers, dibenzothiophene-S,S-dioxide (BTDO, A1) and TDO (A2). These terpolymers demonstrate a gradually expanding absorption range from visible light to the second near-infrared (Vis-to-NIR-II) region with the gradual increase of the TDO contents in the polymer skeleton, showcasing excellent absorption properties and efficient light-capturing capabilities. The optimized D-A1-D-A2 polymer photocatalyst THTDB-4 exhibits a high hydrogen evolution rate of 21.27 mmol g-1 h-1 under visible light without any co-catalyst. The dual-sulfone-acceptor engineering offers a viable approach for developing efficient the longer Vis-to-NIR-II light-harvesting polymer photocatalysts.

Phosphate ester functionalized fluorene-benzothiadiazole alternating copolymer/hydroxylated g-C3N4 heterojunctions for efficient hydrogen evolution under visible-light irradiation

It is highly desirable to explore functionalized polymer semiconductor/g-C3N4 heterojunction photocatalysts with the tight interfacial connection for promoting the photogenerated electron-hole pair separation, improving the hydrophilicity, extending the visible light response and achieving the efficient visible light-driven H2 evolution. Herein, we synthesized novel poly[9,9-bis(3-ethyl phosphate propyl)fluorene-alt-benzothiadiazole] (PPFBT) with a phosphate ester on every repeating unit by the Suzuki polymerization and then fabricated PPFBT/hydroxylated g-C3N4 (PPFBT/CN-OH) heterojunctions via a surface hydroxyl-induced assembly process. The ratio-optimized 5PPFBT/CN-OH shows the hydrogen evolution activity of 2662.4 μmol·g-1·h-1, an 11.1-time enhancement compared to CN-OH. The improved photocatalytic activity is mainly attributed to the enhanced electron-hole pair separation due to the tight interfacial connection by hydrogen bond (P=O…H-O) and N…S interactions between PPFBT and CN-OH. It is verified that abundant phosphate ester groups of PPFBT improve the hydrophilicity and form coordination bonds with platinum (P=O:Pt) as a cocatalyst to facilitate water splitting for H2 evolution. It is also confirmed that the enhanced electron-hole pair separation is mainly dependent on the excited high-energy level electron transfer from CN-OH to PPFBT. This work provides a rational molecular design strategy for constructing efficient functionalized polymer semiconductor/g-C3N4 heterojunctions for sunlight-driven H2 evolution.

Enhanced photocatalytic hydrogen evolution activity of co-catalyst free S-scheme polymer heterojunctions via ultrasonic assisted reorganization in solvent

In this work, two donor-acceptor linear conjugated polymers were designed and synthesized based on thianthrene-5,5,10,10-tetraoxide (TTO) as the acceptor unit, benzo[1,2-b:4,5-b']dithiophene derivative (Py1) and thiophene (Py2) as the donor units, respectively. The Py1/Py2 composite was prepared by physical ball milling of the two polymers in a mixture, which was further treated with a N-methyl-2-pyrrolidone (NMP)-assisted sonication treatment, and the obtained catalyst was named N-Py1/Py2. Compared with the single polymer or Py1/Py2, the FTIR characteristic peaks of O=S=O have a red shift for N-Py1/Py2, accompanied by a profound change in morphology. Furthermore, N-Py1/Py2 has a broader light response and more efficient separation and transport of charge carriers, and as a result it exhibits a higher photocatalytic hydrogen evolution rate (26.5 mmol g^-1 h^-1) without the involvement of any co-catalyst than Py1/Py2 catalyst (3.56 mmol g^-1 h^-1). The underlying mechanism for the enhanced photocatalytic activity by the sonication treatment in NMP is discussed based both on experimental and theoretical calculation data.

Main/side chain asymmetric molecular design enhances charge transfer of two-dimensional conjugated polymer/g-C3N4 heterojunctions for high-efficiency photocatalytic sterilization and degradation

Heterojunctions based on conjugated polymers (PHJs) are of promise as photocatalysts. Here, we fabricate the two-dimensional benzodithiophene (BDT) and thieno[2,3-f]benzofuran (TBF) based conjugated polymers/g-C₃N₄ PHJs creatively using the symmetry-breaking strategy. PD1 and PD3 with the asymmetric backbone TBF have better crystallinity. Moreover, PD3 utilizing fluorinated benzotriazole as the electron acceptor unit possesses more compact π - π stacking and higher charge mobility. The conjugated polymer PD5 with asymmetric side chains in the donor unit BDT guarantees more efficient charge transfer in the corresponding PD5/g-C₃N₄ PHJ while maintaining comparable light utilization rate. Consequently, PD5/g-C₃N₄ shows the champion performance with photocatalytic sterilization rates reaching 99.1% and 97.3% for S. aureus and E. coli. Notably, the reaction rate constant for Rhodamine B degradation of PD5/g-C₃N₄ is 8 times that of g-C₃N₄, a record high among conjugated polymers/g-C₃N₄. This study aims to reveal the structure - property correlation of asymmetric conjugated polymers/g-C₃N₄ for potential photocatalysis applications.

Asymmetric surfaces endow Janus bismuth oxyhalides with enhanced electronic and catalytic properties for the hydrogen evolution reaction

The electronic and catalytic properties of Janus bismuth oxyhalide (Bi₂O₂XY, where X/Y = Cl, Br, or I, and X ≠ Y) for the hydrogen evolution reaction (HER) are evaluated through first-principles calculations. Janus Bi₂O₂XY shows an enhanced separation efficiency of electron-hole pairs and an augmented utilization of solar energy due to Janus asymmetry. The asymmetric halogen surfaces on both sides of Janus Bi₂O₂XY induce an electrostatic potential difference, which leads to a staggered band alignment. The solar-to-hydrogen (STH) efficiencies of Janus Bi₂O₂BrI and Bi₂O₂ClI have greatly improved compared to those of pristine BiOBr and BiOCl. Additionally, Janus Bi₂O₂XY achieves stronger internal electric fields (IEFs) and a more suitable Gibbs free energy of hydrogen adsorption (ΔG_H) than pristine BiOX. Moreover, the halogen layer with a smaller electronegativity in Janus Bi₂O₂XY forms a stronger IEF with the oxygen layer; consequently, the ΔG_H of terminations value is closer to the ideal value for the HER. The localized edge states in the p-orbital density of states (DOS) projected onto O atoms are responsible for the HER activity of terminations. This work provides a comprehensive understanding of Janus Bi₂O₂XY for the HER and provides a strategy for improving photocatalysis.