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.

Photocatalytic Water-Splitting by Organic Conjugated Polymers: Opportunities and Challenges

The future challenges associated with the shortage of fossil fuels and their current environmental impacts intrigued the researchers to look for alternative ways of generating green energy. Solar-driven water splitting into oxygen and hydrogen is one of those advanced strategies. Researchers have studied various semiconductor materials to achieve potential results. However, it encountered multiple challenges such as high cost, low photostability and efficiency, and required multistep modifications. The conjugated polymers (CPs) have emerged as promising alternatives for conventional inorganic semiconductors. The CPs offer low cost, sufficient light absorption efficiency, excellent photo and chemical stability, and molecular optoelectronic tunable characteristics. Furthermore, organic CPs also present higher flexibility to tune the basic framework of the backbone of the polymers, amendments in the sidechain to incorporate desired functionalities, and much-needed porosity to serve better for photocatalytic applications. This review article summarizes the recent advancements made in visible-light-driven water splitting covering the aspects of synthetic strategies and experimental parameters employed for water splitting reactions with special emphasis on conjugated polymers such as linear CPs, planarized CPs, graphitic carbon nitride (g-C₃ N₄ ), conjugated microporous polymers (CMPs), covalent organic frameworks (COFs), and conjugated polymer-based nanocomposites (CPNCs). The current challenges and future prospects have also been described briefly.

Effect of the cross-linker length of thiophene units on photocatalytic hydrogen production of triazine-based conjugated microporous polymers

Conjugated microporous polymers (CMPs) have been investigated in the field of photocatalytic hydrogen production because of their extended π-conjugation, tunable chemical structure and excellent thermal stability. Herein, we construct three CMPs based on thiophenes and triazine, and prove the effect of cross-linker length on photocatalytic activity of CMPs. BTPT-CMP1 exhibits blue-shifted optical absorption compared to BTPT-CMP2 and BTPT-CMP3 with long cross-linkers, however, possesses higher photocurrent because of the large specific surface area and small interface charge transfer resistance of BTPT-CMP1. It was found that BTPT-CMP1 (5561.87 μmol g-1 h-1) with short cross-linkers exhibits better photocatalytic performance compared to BTPT-CMP2 (1840.86 μmol g-1 h-1) and BTPT-CMP3 (1600.48 μmol g-1 h-1). Also, BTPT-CMP1 possesses a higher hydrogen evolution rate than most reported 1,3,5-triazine based conjugated polymers. These results demonstrate that the cross-linker length has great influence on the photocatalytic properties of conjugated microporous polymers, which offers theoretical direction for designing high-performance CMPs.

Promoting charge separation in donor–acceptor conjugated microporous polymers via cyanation for the photocatalytic reductive dehalogenation of chlorides

Conjugated microporous polymers (CMPs) have emerged as promising heterogeneous photocatalysts for organic transformations owing to their structural designability and functional versatility.