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. 2022 Nov 9;7(46):42283-42291.
doi: 10.1021/acsomega.2c05185. eCollection 2022 Nov 22.

Tetrathiafulvalene-Benzothiadiazole: A Metal-Free Photocatalyst for Hydrogen Production

Hajar Mahmoudi  1 , Abdel El Kharbachi  2 , Hassan Safari  1 , Abbas Ali Jafari  3
Affiliations

Tetrathiafulvalene-Benzothiadiazole: A Metal-Free Photocatalyst for Hydrogen Production

Hajar Mahmoudi et al. ACS Omega. .

Abstract

In this work, a series of hybrid tetrathiafulvalene-benzothiadiazole (TTF-BTD) are designed and applied as a metal-free photocatalyst for hydrogen production, particularly under visible light irradiation. Density functional theory calculations are used to shed light on the photophysical properties observed in the various TTF-BTD derivatives and investigated by the obtained data. Because band gap engineering has normally been used as an effective approach, we studied the effect of the various functional groups on the band gap to set a favorable band alignment with photocatalysts. An increase in highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels is observed in the order CH3 < Br < CF3 < COOMe < CN. The results discover that COOMe-TTF-CN-BTD can have a clear photocatalytic potential in the hydrogen production for specific applications. Our experimental and theoretical studies reveal that the CN-withdrawing group increases the reduction potential of the conduction band; meanwhile, COOMe decreases the reduction potential of the valance band. Moreover, we demonstrate that H2O reduction and oxidation reaction energies are both located inside the COOMe-TTF-CN-BTD band gap that enables an enhanced photocatalytic hydrogen evolution rate of 122 μmol h-1 g-1 under visible light. The efficiency of the COOMe-TTF-CN-BTD photocatalyst is also described in terms of medium pH and the nature of the sacrificial agent, where the maximum hydrogen production efficiency is observed at high pH. The findings point to a means of efficient production of hydrogen that can be directly achieved under visible light irradiation without any modifications.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Synthesis Process and Functionalization of TTF–BTD-Based Photocatalysts
Figure 1
Figure 1
Energy diagram of the TTF–BTD derivatives. NHE, normal hydrogen electrode.
Figure 2
Figure 2
Illustration of the molecular orbitals of CN-TTF-BTD.
Figure 3
Figure 3
Cyclic voltammograms of COOMe-TTF-CN-BTD, COOMe-TTF-Br-BTD, and TTF–BTD derivatives.
Figure 4
Figure 4
Ultraviolet–visible diffuse reflectance spectrum of the COOMe-TTF-CN-BTD and COOMe-TTF-Br-BTD.
Figure 5
Figure 5
Photocatalytic hydrogen evolution of the COOMe-TTF-CN-BTD, COOMe-TTF-Br-BTD, and TTF–BTD derivatives.
Figure 6
Figure 6
Effect of the medium pH on the photocatalytic hydrogen evolution in the presence of the COOMe-TTF-CN-BTD photocatalyst.
Scheme 2
Scheme 2. Photo-electro-chemical Mechanism of Hydrogen Generation and Oxygen Evolution on the COOMe-TTF-CN-BTD Photocatalyst in Alkaline Media
Scheme 3
Scheme 3. COOMe-TTF-CN-BTD Variations in Acidic Media
Figure 7
Figure 7
Photocatalytic H2 production efficiency of COOMe-TTF-CN-BTD using various sacrificial agents.
Figure 8
Figure 8
Reusability and stability of COOMe-TTF-CN-BTD after five consecutive runs.
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